Nuova ricerca

ELIE KAMSEU

LAUREATO FREQUENTATORE
Dipartimento di Ingegneria "Enzo Ferrari"


Home |


Pubblicazioni

2022 - A Low Thermal Conductivity of Lightweight Laterite-cement Composites with Cotton Wastes Fibres [Articolo su rivista]
Kamg, a. Samen V. E. L.; Nemaleu, J. G. D.; Kaze, R. C.; Kammogne, F. D.; Meukam, P.; Kamseu, E.; Leonelli, C.
abstract

The development of eco- friendly environmental and sustainable building materials having low thermal conductivity and optimal physic-chemical abilities ensuring passive thermal comfort is imperative in the global quest for the minimization of greenhouse-gases (GHG) emission and energy needs in homes. To attend this objective, the present work underlines the feasibility of using waste cotton fibres for the design of the lightweight laterite-cement composites with low thermal conductivity for structural applications. The final products were obtained by replacing laterite cement composite with cotton wastes fibres (0.3-0.6 wt%) and then uniaxial pressing around 14 MPa. The thermo-engineering and structural properties were performed using several techniques: X-Ray Diffraction (XRD), Environmental Scanning Electron Microscope (ESEM), Fourier Transform Infrared Spectroscopy (FTIR), mechanical properties as well as thermal conductivity. This process accounts for the optimum (0.78 W.m−1. K−1) structural material made with 6 wt% cement, 0.6 wt% cotton fibres and better packing density of laterites particles (50/50). Regardless of the particle size distribution of aggregates (laterite), the increase of cotton fibres content resulted in lowering mechanical performances. This is due to the creation of pores and the weakness adhesion between the cellulosic fibres and laterites particles within the matrix. In addition, the presence of cellulose within a matrix enhanced the crystallinity of cementitious phases (CASFH and CASH) of the end-products. The formulated samples with the reduction around 29% of embodied energy compared to the conventional materials, appears as a promising eco-friendly composite with good thermal comfort, small-embodied energy and low environmental impact through sustainable process.


2022 - Alkali-silica reactions in granite-based aggregates: The role of biotite and pyrite [Articolo su rivista]
Venyite, P.; Giogetti Deutou Nemaleu, J.; Cyriaque Kaze, R.; Bruno Tchamba, A.; Kamseu, E.; Chinje Melo, U.; Leonelli, C.
abstract

Concrete structures built in granite-based aggregate develop and proliferate contour-like cracks as they aged. Such cracks are often associated to alkali-aggregate reactions (AAR). Though, in most cases, the alkali-silica reaction (ASR) involving these aggregates has shown to be non-destructive to concretes, their contents of iron-contained minerals, including biotite and pyrite predict novel chemical route for AAR. This study aims to investigate the alkali reactivity of granite-based aggregates, and the rule of biotite and pyrite as potential contributors to AAR. Aggregate samples were collected from three different deposits in tropical Africa, denoted: Deposit I, Deposit II and Deposit III. Mineralogical and microstructural characteristics of the aggregates, by XRD, optical microscopy and ESEM-EDX, indicated micaceous, felspathic, garnet and sulphide mineral groups. XRF shows quite significant levels of FeO + Fe2O3, ranging from 6.38 wt% to 9.86 wt%. Optical microscopy and ESEM analysis of NaOH-leached residues showed quite elevated fractions of Fe Sulphur was quantified in the leached residues of most corroded aggregate samples from deposit III, pointing to the dissociation of pyrite. The absence of S and the presence of ample amounts of Fe in the less degraded aggregates leached residues of deposits I and II points to the release of Fe by other iron containing minerals, including biotite. Findings of this study is a reference point for the development of control and mitigation of AAR involving pyrite and biotite – rich aggregates.


2022 - Design of porous Geopolymers for hygrothermal applications: role of nano and meso porosity [Articolo su rivista]
Ngouloure, Z. N. M.; Kamseu, E.; Moungam, L. M. B. A.; Tchakoute, H. K.; Valentini, L.; Leonelli, C.
abstract

Soluble silica content and the concentration of hydrogen peroxide were used to achieve porous geopolymers with nano, meso and milliporosity. The use of rice husk ash as a partial replacement for metakaolin allows to maintain the SiO2/Al2O3 ratio between 1.93 and 2.71 and achieve layered bulks with the desired moisture buffering capacity. Stereo Optical Microscopy, Environmental Ecanning Electron Microscopy, Mercury Intrusion Porosimetry, and Microtomography were used with the aim of correlating the intrinsic characteristics of the porous network to the moisture buffering capacity. A detailed analysis of the results permitted to link the moisture buffering capacity to the SiO2/Al2O3 ratio and the gel pores/large pores ratio. The saturation regime of these layered porous systems was found between 20 and 27%, while the daily moisture buffering capacity varied from 0.37 to 4.82% considering cycles of desorption and absorption. It was revealed that specimens with a high volume of gel pores (nano and meso) and optimal aeration with millipores are ideal matrices for hygroscopic applications. The porous matrices were found promising for the design of building systems with passive thermal comfort.


2022 - Pore network and microstructure in the prediction of heat flux transport in sponge-like geopolymers for thermal insulation [Articolo su rivista]
Kamseu, E.; Ngouloure, Z. N. M.; Nait-Ali, B.; Valentini, L.; Zekeng, S.; Rossignol, S.; Leonelli, C.
abstract


2022 - Valorization of marble powder wastes using rice husk ash to yield enhanced-performance inorganic polymer cements: Phase evolution, microstructure, and micromechanics analyses [Articolo su rivista]
Kamseu, E.; Akono, A. -T.; Rosa, R.; Mariani, A.; Leonelli, C.
abstract

The challenge for sustainable development is now constraining scientists, and policymakers to consider alternative materials and processes requiring low energy consumption and low emissions while prioritizing local materials and industrial waste recycling. This study investigates ways to valorize marble waste powders to design a new class of inorganic polymer cement. These powders are among the most important solid wastes globally, and in the Italian island of Sardinia they create a disposal problem. When these powders, which are rich in calcium silicate hydrate (C–S–H) phases, are incorporated into the geopolymer synthesis, this gives rise to a mix between C–S–H and alkali metal aluminosilicate hydrate (M-A-S-H) systems that are the focus of this study. In detail, C–S–H systems are prepared with various Ca/Si ratios, including CS, C2S, and C3S. The microstructure and mechanical properties are investigated using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy, along with density methods (mercury intrusion porosimetry), macroscopy mechanical testing methods (flexural strength tests) and nanoscale mechanical testing methods (indentation testing and scratch testing). The resulting inorganic polymer cements exhibit both an amorphous and a crystalline phase containing sodium-calcium-aluminum-silicate hydrate N–C-A-S-H. The fraction of the crystalline phase increases when the silica content decreases, from CS to C3S, and when the C–S–H fraction increases. In turn, the crystalline phase dictates the pore structure and mechanical properties. Specifically, a homogeneous and compact microstructure with low porosity is observed. The flexural strength ranges from 5.8 to 8.7 MPa, the elastic modulus ranges from 10 to 17 GPa, and the fracture toughness ranges from 0.23 to 0.48 MPa m1/2. In general, the lower the silica percentage of the calcium-silicate hydrates and the higher the fraction of calcium silicate hydrate are, the higher the flexural strength, elastic modulus, and fracture toughness. The underlying mechanism for the observed stiffening, strengthening, and toughening is the insertion of aluminum in the C–S–H defect sites to yield C-A-S-H, along with the formation of sodium silicate gel from excess colloidal silica, which contributes to the reduction in gel pores and matrix densification. The values of porosity, density, and mechanical properties suggest that inorganic polymer cements derived from marble wastes are promising candidates for innovative low-temperature and low-density binders with low carbon footprint satisfying both the requirements of sustainability and the local material concept.


2021 - Characterization, reactivity and rheological behaviour of metakaolin and Meta-halloysite based geopolymer binders [Articolo su rivista]
Rodrigue Kaze, C.; Adesina, A.; Alomayri, T.; Assaedi, H.; Kamseu, E.; Chinje Melo, U.; Leonelli, C.
abstract

The type of aluminosilicate precursor used in the synthesis of geopolymer binders plays a huge role in the resulting performance. Thus, it is critical to understand the properties of precursors and how they influence the corresponding performance of geopolymer binders. In this study, metakaolin and meta halloysite are used as the aluminosilicate precursor in the synthesis of geopolymer binders. These precursors are obtained locally in order to propel the sustainable development and application of geopolymers. The precursors were characterized and the corresponding influence on the reactivity, rheology and setting times of geopolymers was investigated. In addition to the influence of precursor type on the properties of the geopolymers, the effect of two silica moduli (i.e. 1.3 and 1.5) was also evaluated. The results from this study indicated that increasing the activator silica modulus from 1.3 to 1.5 extended the setting times and increased the stress strain of the geopolymer binders. Characterization of the precursors indicated that metakaolin has a higher amorphous content compared to that of meta halloysite. However, the finer particles of meta halloysite embodied it with the ability to participate in a faster geopolymerization and result in more formation of activation products.


2021 - Dependence of the insulating behavior of some common woods to the pore network and packing density of their fibers: a microstructural approach [Articolo su rivista]
Nouemsi, E. S.; Ngouloure, Z. N. M.; Bidoung, J. C.; Kamseu, E.; Rossignol, S.; Leonelli, C.
abstract

Thermophysical and microstructural behavior of eleven tropical woods widely available and commonly used was investigated. Experimental measurements of thermal conductivity and thermal diffusivity of wood were performed using the heat flow meter and transient plane source technique. The results show values in the range of 0.2–0.37 mm2/s for thermal diffusivity and 0.12–0.34 W m−1 K−1 for thermal conductivity. The correlation between the thermal conductivity and parameters as porosity, pore size distribution, intensity ratio of lignin and microstructure was drawn. The thermal conductivity of wood decreases with the increase in pores volume (vp). For vp > 70%, the values are between 0.1 and 0.15 W m−1 K−1 and reach 0.23 W m−1 K−1 for vp between 40 and 60%. For dense woods with the vp less than 40%, the values are between 0.24 and 0.35 W m−1 K−1. The results show experimental values of the effective thermal conductivity of wood species closer to the values of parallel model. The presence of ray and parenchyma which appear perpendicular to the axis of the fibers in the structure of the wood species makes it difficult to have straight correlation. This suggests that heat flux which travels through the matrix of wood follows a very complex road linked to the microstructural features of each class of wood. These results appear as significant contribution for the future development of sustainable energy technologies in relation to the prediction of energy saving and building energy metering.


2021 - Effect of Combined Metakaolin and Basalt Powder Additions to Laterite-Based Geopolymers Activated by Rice Husk Ash (RHA)/NaOH Solution [Articolo su rivista]
Venyite, P.; Makone, E. C.; Kaze, R. C.; Nana, A.; Nemaleu, J. G. D.; Kamseu, E.; Melo, U. C.; Leonelli, C.
abstract

The present study deals with the use of locally prepared rice husk ash (RHA)-based sodium silicate for alkaline activation of laterites (uncalcined (LNW) and calcined (LCA)). RHA-based activator (SSR) was prepared by adding as-collected RHA to 6 M NaOH at a solid/liquid mass ratio of 0.56. The various proportions of metakaolin (MK) and basalt powder (BA) influenced the final properties of the geopolymer products. After 28 days of curing at room temperature, XRD, SEM and FT-IR analyses were used to study the evolution phases. Uncalcined laterite-based formulations showed their highest compressive strength at 29.86 MPa with 20 wt.% of MK, whereas calcined ones showed the most elevated strength at 47.02 MPa, with the addition of 25 wt.% MK. Further additions above these thresholds tend to reduce strength and increase setting time. Substitution of calcined laterite with basalt powder permitted to control the porosity of samples at low values with the consequent reduction of strength. In general, the water absorption and apparent porosity decrease with addition of metakaolin in raw laterite-based formulations and relatively decrease with addition of basalt powder in calcined laterite-based formulations, while bulk density remains relatively constant. The locally produced RHA-based alkaline activator is efficient for laterite geopolymerization, resulting in products with robust mechanical and physical properties capable of fostering application in quality housing.


2021 - Effects of curing cycles on developing strength and microstructure of goethite-rich aluminosilicate (corroded laterite) based geopolymer composites [Articolo su rivista]
Nouping Fekoua, J. N.; Kaze, C. R.; Duna, L. L.; Ghazouni, A.; Ndassa, I. M.; Kamseu, E.; Rossignol, S.; Leonelli, C.
abstract

The present work carried out the influence of curing cycles on the performance of laterite-based geopolymer composites. To do so, the end products were obtained by altering laterite with 15, 20, and 25 wt% of rice husk ash (RHA). Alkaline solution in a constant solid/liquid ratio of 0.35 was added together with fine and coarse aggregates (representing equal and double weight of laterite, respectively). The different obtained matrices were treated in the following three curing cycles before characterization: room temperature curing (RTC), oven curing at 80 °C (OTC) and controlled humidity steam curing at 80 °C (STC). The mechanical tests carried out at 28 days give the following maximum values for each curing mode: 16.40, 28.82 and 56.41 MPa for RTC, OTC, and STC modes respectively. This means that when the samples, submitted in a moisture-controlled environment, the end products are more stable, less porous and resistant. Regarding the physical properties, the results show that the maximum value of open porosity is 11.62% corresponding to a matrix that was cured at room temperature without rice husk ash added, while the minimum value of 7% corresponds to a matrix that was cured under controlled humidity and containing 20% rice husk ash. The optimum and minimum absorption values are 2.70 and 4.60% respectively for the OTC and RTC curing modes. As for bulk densities, the optimum value is 2.64 g cm−3 for the matrix having 15% rice husk ash and the minimum value is 2.33 g cm−3 for a matrix having 20% rice husk ash, for OTC and STC curing modes respectively. The appropriate curing type for laterite-based geopolymer is when the humidity is controlled.


2021 - Engineering properties, phase evolution and microstructure of the iron-rich aluminosilicates-cement based composites: Cleaner production of energy efficient and sustainable materials [Articolo su rivista]
Samen, V. E. L. K.; Kaze, R. C.; Deutou Nemaleu, J. G.; Tchakoute, H. K.; Meukam, P.; Kamseu, E.; Leonelli, C.
abstract

This paper investigates the direct transformation of laterites (natural iron-rich aluminosilicates) to cementitious composites with principal mineral phases being Gismondine and Stratlingite. The effects of particles size distribution and cement content (2 to 8 wt%) on the mechanical properties and microstructure of laterite-cement composites are assessed. Four grades of granulometry with various percentages of fine and coarse particles were considered. The Environment Scanning Electron Microscopy (ESEM), Mercury Intrusion Porosimetry (MIP), Fourier Transformed Infrared Spectroscopy (FT-IR) and X-ray Powder Diffractometry (XRD) were performed after 1, 90 and 365 days, to assess the phase's evolution, mechanical performance and the microstructure of the laterite-cement composites. It is found that fines particles, essentially pozzolanic and amorphous, are responsible for the bonding strength while coarse particles improve the compressive strength. Dense and compact microstructure, water absorption under 18% and flexural strength above 6 MPa (compressive strength > 30 MPa) could be achieved as from 4 wt% of cement making the laterite-cement composite appropriate as building and construction materials. The choice of a highly corroded class of laterite and the selection of the particle size distribution allows the production of optimum composite that is presented as energy-efficient and sustainable. Thus, corroded or indurated laterites are considered as “green metakaolins” which do not require any energy for their transformation unlike clayey materials.


2021 - Influence of the synthetic calcium aluminate hydrate and the mixture of calcium aluminate and silicate hydrates on the compressive strengths and the microstructure of metakaolin-based geopolymer cements [Articolo su rivista]
Moudio, A. M. N.; Tchakoute, H. K.; Ngnintedem, D. L. V.; Andreola, F.; Kamseu, E.; Nanseu-Njiki, C. P.; Leonelli, C.; Ruscher, C. H.
abstract

The main goal of this study is to investigate the effects of the calcium aluminate hydrate (CA04) and the mixture of calcium aluminate and silicate hydrates (CA04 + CS04) on the compressive strengths and the microstructure of metakaolin-based geopolymer cements. Bauxite, rice husk and eggshells were calcined and mixed in proper amounts to prepare CA04 and CS04. Metakaolin has been substituted by 0, 5, 10, 15 and 20 wt% of CA04, 10 and 20 wt% of (CA04 + CS04) in the formulation of geopolymer cements. The clay-like solid materials were characterized by measuring their compressive strengths, the crystalline and amorphous phases were monitored using the X-ray diffractometry analysis, their microstructures were investigated using the scanning electron microscope and mercury intrusion porosimetry and the functional groups were studied using the infrared spectroscopy. The compressive strengths of geopolymer cements containing 0, 5, 10, 15 and 20 wt% of CA04 are 49.50, 57.17, 63.59, 38.79 and 35.05 MPa, respectively. Those containing 10 and 20 wt% of (CA04 + CS04) are 40.59 and 51.19 MPa, respectively. The average pore diameters of geopolymer cements containing 0, 10 and 20 wt% of CA04 are 11.80, 10.10, 12.20 nm, respectively. Whereas the one containing 20 wt% of (CA04 + CS04) is 10.80 nm. It appears that geopolymer cement with 10 wt% of CA04 and 20 wt% of (CA04 + CS04) have higher compressive strengths and lower average pore diameters. It was found that 10 and 20 wt% of CA04 and (CA04 + CS04), respectively, could be used as additives for the preparation of geopolymer cements with higher strength development.


2021 - Innovative porous ceramic matrices from inorganic polymer composites (IPCs): Microstructure and mechanical properties [Articolo su rivista]
Nana, A.; Cyriaque Kaze, R.; Salman Alomayri, T.; Suliman Assaedi, H.; Nemaleu Deutou, J. G.; Ngoune, J.; Kouamo Tchakoute, H.; Kamseu, E.; Leonelli, C.
abstract

The thermal performance of pegmatite-based geopolymer composites is investigated. Dense and compact matrix was prepared replacing metakaolin with pegmatite in the range of 70–85 wt% and activate with sodium hydroxide/sodium silicate solution in 1:1 vol ratio. The products of geopolymerization, cured at room temperature for 28 days, were heated at 100, 200, 400, 600, 800, 900, 1000 and 1100 °C with 2 h soaking time. The high values of flexural strength (46–51 MPa) were observed at 1000 °C as the consequences of low porosity (173 mm3/g) and water absorption (4.50–5.62%). The increase of the vitrification at 1100 °C enhanced the liquid phase and develop porosities responsible for reduction of strength. The mechanical properties, microstructural evolution and pore size distribution were found to be influenced by the amount of fine powder of pegmatite (solid solution).


2021 - Marble wastes recycling: Design and synthesis of low-temperature calcium silicate hydrate under various CaO:SiO2 ratio and alkalinity [Articolo su rivista]
Kamseu, E.; Alzari, V.; Rosa, R.; Nuvoli, D.; Sanna, D.; Mariani, A.; Leonelli, C.
abstract

Marble sludge wastes (MSW) are investigated as solid precursors for the production of low-temperature calcium silicate hydrate (CSH). Calcined powder of MSW is ball-milled with rice husk ash (RHA) and the slurries are treated in the oven at 100°C for 24 h in a context where water evaporation is minimized. The initial CaO:SiO2 molar ratio varies from 1 to 3 (CS, C2S and C3S) and the solution used for the preparation of the calcium silicate hydrate presents NaOH with concentration of 0, 1, 2 and 3 N. FTIR, XRD, Particle size distribution, BET surface area and Environmental Scanning Electron Microscope (ESEM) permitted to confirm the formation of CSH(I) at 100°C through pozzolanic reactions. The increase of the alkalinity of the solution improves the silica dissolution and enhances the formation of CxS and CSH up to 2N. Further increase of the alkalinity affected the silica polymerization, the particle size and the concentration of CSH into the final matrix. The precursor with CaO:SiO2 = 1 seems to promote C-S-H(I) with more monomers while 2CaO:SiO2 and 3CaO:SiO2 resulted in orthosilicate chains and interlayer respectively. The high reactivity and fine particles (diametre < 32 nm) of CSH obtained appeared promising for the design of low-cost, environmentally-friendly and sustainable binders as well as others engineering applications including binder and concrete seed, refractory precursors, hydroceramics, insulating matrices, filtration and catalysis.


2021 - Mechanical Performance, Phase Evolution and Microstructure of Natural Feldspathic Solid Solutions Consolidated Via Alkali Activation: Effect of NaOH Concentration [Articolo su rivista]
Nana, A.; Tome, S.; Anensong, S. C. D.; Venyite, P.; Djobo, J. N. Y.; Ngoune, J.; Kamseu, E.; Bignozzi, M. C.; Leonelli, C.
abstract

Five different alkali activators were prepared by mixing sodium hydroxide with molar concentrations of 8, 10, 12, 14 and 16 M and sodium silicate, Na2SiO3 in volume ratio 1:1. The obtained alkaline activators were used for producing metakaolin/feldspathic rock-based geopolymer composites. These geopolymer composites were obtained by mixing different solid precursors of natural solid solutions (trachyte, pegmatite and granite) in the range of 70 to 85 wt% with metakaolin and adding each alkaline solution at a liquid/solid mass ratio of 0.37. The pastes were cured at room temperature for 28 days before testing. The influence of NaOH concentration on structural modifications was investigated using Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). Water absorption for open porosity, Environment Scanning Electron Microscope (ESEM) and compression tests were adopted to observe the morphology and mechanical properties. The results indicate that the NaOH concentration of 12 M was optimum for solid solution of trachyte with 98–106 MPa due to content of higher amorphous phases compared to solid solutions of pegmatite (94–105 MPa) or granite (101–108 MPa) where the better results were achieved at 10 M.


2021 - Mechanical strength and microstructure of metakaolin/volcanic ash-based geopolymer composites reinforced with reactive silica from rice husk ash (RHA) [Articolo su rivista]
Nana, A.; Epey, N.; Rodrique, K. C.; Deutou, J. G. N.; Djobo, J. N. Y.; Tome, S.; Alomayri, T. S.; Ngoune, J.; Kamseu, E.; Leonelli, C.
abstract

The physical, mechanical and microstructural properties of metakaolin/volcanic ash-based geopolymer composites were investigated, as well as the influence of the incorporation of a reactive silica from rice husk ash (RHA) in their performance. The geopolymer composites were designed by replacing metakaolin with volcanic ash, VA (10–30 wt%) and RHA (0–20 wt%). Physical and mechanical testing, FTIR, XRD, optical microscopic and SEM were used to characterize the geopolymer composites. The results showed that the mechanical strengths and physical properties were mostly affected by the VA content as well as RHA content where the optimal mechanical strengths (19.3 and 60.73 MPa for flexural and compressive strength, respectively) were obtained with the composite sample containing 20 wt% of VA and 10 wt% of RHA. This was due to the additive that enhances the compactness and microstructure of geopolymer matrices obtained and also the increase of SiO2/Al2O3 ratio with the addition of RHA. Synergistic use of metakaolin, volcanic ash, and rice husk ash for construction materials through alkaline activation looks like the upcoming trend to valorize these materials.


2021 - Organic-inorganic materials through first simultaneous frontal polymerization and frontal geopolymerization [Articolo su rivista]
Alzari, V.; Kamseu, E.; Leonelli, C.; Spinella, A.; Malucelli, G.; Bianco, G.; Nuvoli, D.; Sanna, D.; Armetta, F.; Rassu, M.; Mariani, A.
abstract

The first frontal geopolymerization (FGP) took place in the same reaction medium in which the frontal polymerization (FP) of 1,6-hexanediol diacrylate (HDDA) was occurring, thus giving rise to an organic-inorganic hybrid in one step in just a few minutes. Because of their exothermicity, the two reactions support each other and sustain propagating fronts. By contrast, using the classical techniques (prolonged heating) instead of FP, due to large gas formation, the reaction is explosive or, if carried out at room temperature, phase separation occurred.


2021 - Particles size and distribution on the improvement of the mechanical performance of high strength solid solution based inorganic polymer composites: A microstructural approach [Articolo su rivista]
Nana, A.; Kamseu, E.; Akono, A. -T.; Ngoune, J.; Yankwa Djobo, J. N.; Tchakoute, H. K.; Bognozzi, M. C.; Leonelli, C.
abstract

This research reports on the influence of particle size and distribution on the physical, mechanical and microstructural features of solid solutions (feldspathic materials) based inorganic polymer composites (IPCs). Both granite and pegmatite were ground to different degree of finess making four different granulometry with particles of 63, 80, 125 and 200 μm. The respective mixes receive 15 wt% of metakaolin and were activated with a well designed alkaline solution. Matrices obtained showed high compressive and flexural strengths in the range 101.2–131.3 MPa, and 29–35.5 MPa, respectively. It was observed that the optimum mechanical performance of these matrices can be achieved through a mix-design of different grades of granulometry. This was suggested by mechanism combining reactivity and particles packing. In fact, although it can be expected that the finess of the combination of the particles size under 63 μm might present the better reactivity, it is showing that the combination of fine, medium and coarse particles is efficient in achieving denser and tougher microstructure. Lower cumulative pore volume (17 mL g−1) of the composites based on pegmatite, value not far from that of natural stones, resulted in a higher impact resistance of 3.03 J. It was concluded that designing the feldspathic rock-based composites with high strengths appear as sustainable, low energy consumption and environmentally-friendly materials for the structural construction.


2021 - Performance of geopolymer composites made with feldspathic solid solutions: Micromechanics and microstructure [Articolo su rivista]
Kamseu, E.; Akono, A. -T.; Nana, A.; Kaze, R. C.; Leonelli, C.
abstract

This study investigates the high performance of feldspathic solid solution-based geopolymer composites. The results show that a feldspathic solid solution with incongruent dissolution in an alkaline medium produces a differential amount of N-A-S-H+ polysialate geopolymer, depending on the mineral nature of the raw solid precursor. In turn, the presence of both N-A-S-H and polysialate geopolymer reduced the cumulative pore volume to a nanometric size, leading to flexural and compressive strengths in the range of 26–36 MPa and 86–100 MPa, respectively. The limited dissolution in the alkaline medium of the feldspathic powders allowed for a direct correlation among the Young modulus, the hardness, and the N-A-S-H + polysialate geopolymer. The findings show that when the amount of N-A-S-H and polysialate geopolymer is sufficient to cover the incongruent dissolved grains of solid solutions with no excess of geopolymer gel, the bonding strength developed exhibits high mechanical performance in the final composite The results confirm the possibility of reproducing dimensioned stones by geopolymerizing the feldspathic solid solutions.


2021 - Thermal behaviour and microstructural evolution of metakaolin and meta-halloysite-based geopolymer binders: a comparative study [Articolo su rivista]
Kaze, C. R.; Nana, A.; Lecomte-Nana, G. L.; Deutou, J. G. N.; Kamseu, E.; Melo, U. C.; Andreola, F.; Leonelli, C.
abstract

Two calcined clays (halloysite and kaolinite clays at 700 °C) were used as solid precursors for geopolymer synthesis. This study compares the physicochemical properties of the both resulting geopolymer series heated at 200, 400, 600 and 800 °C. The end specimens were characterized using Optical Dilatometer, XRD, FTIR, MIP and SEM analyses. Results revealed that the flexural strengths were 18.10 and 21.74 MPa for meta-halloysite- and metakaolin-based geopolymers, respectively. After subjected to high temperatures, the flexural strength drastically decreased from 18.10 ± 1.06 to 6.7 ± 0.23 MPa and 21.74 ± 1.20 to 4.63 ± 0.24 MPa, respectively. The maximum shrinkage recorded on metakaolin and meta-halloysite-based geopolymers was 14 and 16% around 950 °C, respectively. The thermal conductivities decreased with increase in heating temperature from 0.78 to 0.19 Wm−1 K−1 and 0.96 to 0.26 Wm−1 K−1, respectively. This reduction is linked to the additional voids and microcracks that occurred within the geopolymer network. The cumulative intrusion in both geopolymers increased with increase in heating temperature up to 600 °C, leading to the degradation of geopolymer network that affected the mechanical strength evolution. Both synthesized geopolymer series are potential candidates for insulation materials or refractory applications.


2020 - Characterization and performance evaluation of laterite based geopolymer binder cured at different temperatures [Articolo su rivista]
Rodrigue Kaze, C.; Ninla Lemougna, P.; Alomayri, T.; Assaedi, H.; Adesina, A.; Kumar Das, S.; Lecomte-Nana, G. -L.; Kamseu, E.; Chinje Melo, U.; Leonelli, C.
abstract

This paper presents the results of experimental evaluation of curing conditions on the microstructure and performance of geopolymer binders developed from iron-rich laterite soils. Two calcined iron-rich laterites namely LB600 and LY600 were used as solid precursors in the preparation of geopolymer binders. The geopolymer samples were cured at 20, 60 and 80 °C. FTIR, XRD, EDS and DTA/TG were used to evaluate the microstructural properties of the prepared products. The performance of the binder was evaluated in terms of the compressive strengths, water absorption, porosity, bulk density and thermal conductivity. The findings from this study showed that the dissolution of the calcined laterites in 8 M NaOH increased the dissolution of Al, Si and Fe elements with increasing temperature from 20 to 80 °C. This higher dissolution of the monomers further resulted to an increase in the compressive strength of the binders at 7 and 28 days. It was also found out that curing the geopolymer in the dry state resulted in higher compressive strength at all ages compared to those cured in the wet and wet-dry state. Drying shrinkage evaluation of the geopolymer samples cured between 60 and 80 °C exhibited a lower linear shrinkage due to a high degree of geopolymerization. Microstructural investigation of the geopolymer samples cured at 80 °C showed a heterogeneous compact and dense structure resulting from high polycondensation. This densified microstructure also induced an increase in the thermal conductivity from 0.65 to 0.90 W/mK and 0.75 to 0.91 W/mK for LB600 and LY600, respectively. Nonetheless, both geopolymer binders made of LB600 and LY600 laterite powders performed well in dry, wet and wet-dry conditions, and can be used for various construction applications especially in the precast industry.


2020 - Dependence of the geopolymerization process and end-products to the nature of solid precursors: Challenge of the sustainability [Articolo su rivista]
Kamseu, Elie; Alzari, Valeria; Nuvoli, Daniele; Sanna, Davide; Lancellotti, Isabella; Mariani, Alberto; Leonelli, Cristina
abstract

This review retrieves the determinant role of the solid precursor on the definition, chemistry, processing and applications of geopolymers. It is demonstrated that the process, the alkaline solution, the curing conditions as well as the orientation of the end-products in term of performance and potential application are governed by the intrinsic nature and characteristics of the aluminosilicate precursors. In particular, the amorphous fraction and the available Al and Si cations governs the geopolymerization. Solid precursors with relatively large amount of amorphous phase are easily activated with standard alkaline solution (6–8 M) leading to the formation of a gel, designated as cement or binder. Al-rich gels are efficient for the design of high strength concretes or composites. Solid precursors with low amorphous fraction need relatively high concentrated alkaline solution (>8 M), particularly aluminosilicates with crystalline habitus such as fly ash, volcanic ash, feldspars, granites, nepheline, etc. In these cases, both the dissolution and the curing steps require temperature above ambient. The pastes produced are dominated by non-reacted or incongruently dissolved particles more addressed for mortars and precast. When high concentrated alkaline solution is used, some additions of Si-rich or Al-rich reactive materials are needed to stabilize the extra alkali present within the matrix: steam or long-term curing are, therefore, required. Regarding the curing conditions, the temperature and relative humidity to be applied are directly linked to the nature of the solid precursor. This paper should be viewed as a significant contribution for the understanding and classification of geopolymer cement and composites as well as the science and technology of the geopolymers.


2020 - Ferrisilicates formation during the geopolymerization of natural Fe-rich aluminosilicate precursors [Articolo su rivista]
Kamseu, E.; Kaze, C. R.; Fekoua, J. N. N.; Melo, U. C.; Rossignol, S.; Leonelli, C.
abstract

The progressive addition of the reactive silica from rice husk ash (10–50 wt%) changes the phases evolution and the microstructure of the laterites based geopolymer composites. It was found that the presence of soluble silica enhanced the formation of Si–(A)-OH–Fe bonds and changed considerably the FTIR and XRD patterns of the products: polysialates, ferrosialates and ferrisilicates were present into the matrices. The solid/liquid ratio and the curing cycle influenced the pore network, the bulk density, the total pore areas, and the final microstructure. The relative low viscous paste that is maintained at ambient temperature for 1–2 h before curing at 90 °C gave better cohesion and low porosity resulting to the high concentration of strongest (Fe–O–Si) bonds compared to pastes cured directly after preparation or those with high viscosity. While polysialates and ferrosilicates are hindered in the case of quite treatment at 80 °C due to the rapid evaporation of water, polysialates, ferrosialates and polynuclear ferrisilicates complexes are formed at room temperature and polynuclear complexes can growth to more crystalline phases with the increase of the temperature. Ferrisilicates integrated the interlayers of the matrix improving the geopolymerization with significant modification of the microstructure. Those newly formed phases are promising components for the development of eco-friendly and sustainable high strength composites, porous matrices for filtration, heavy metal removal/immobilization, membranes for catalysis and template for new carbone replicate.


2020 - Mechanical Properties and Microstructure of a Metakaolin-Based Inorganic Polymer Mortar Reinforced with Quartz Sand [Articolo su rivista]
Nana, A.; Alomayri, T. S.; Venyite, P.; Kaze, R. C.; Assaedi, H. S.; Nobouassia, C. B.; Sontia, J. V. M.; Ngoune, J.; Kamseu, E.; Leonelli, C.
abstract

The synthesis, mechanical behaviour, and microstructure of metakaolin-based geopolymer mortar reinforced with quartz sand are presented in this investigation. Fine sand (quartz sand) aggregate were added in different proportions of 50, 60, 70 or 80 wt.% to prepare the fresh metakaolin-based geopolymer paste. The geopolymer mortar was achieved by a mixture of geopolymer paste and river sand in the ratio 2:5 by mass. The mixture of sodium hydroxide solution (10 M) and sodium silicate solution (Na2SiO3) in a volume ratio of 2:3 was used as an alkaline activator. All the specimens were cured at room temperature and tested after 28 days of curing. The investigations on microstructure and physical properties indicated a significant reduction of the open pores and interconnection of micro and meso cracks in the structure network with increase in the amount of quartz sand. As a consequence, the samples show a good mechanical strength principally with the addition of 60 wt.% of quartz sand to binder with values of 8 and 66 MPa for flexural strength and compressive strength, respectively.


2020 - Mechanical and microstructural properties of geopolymer mortars from meta-halloysite: effect of titanium dioxide TiO2 (anatase and rutile) content [Articolo su rivista]
Mohamed, H.; Deutou, J. G. N.; Kaze, C. R.; Beleuk a Moungam, L. M.; Kamseu, E.; Chinje Melo, U.; Leonelli, C.
abstract

Abstract: This study aimed to investigate the effect of Titanium Dioxide TiO2 (anatase and rutile) on mechanical and microstructural properties of meta-halloysite based geopolymer mortars namely GMHA and GMHR series. Meta-halloysite received 2.5, 5.0, 7.5 and 10 wt% of anatase or rutile as addition before calcination and geopolymerization. The raw materials and the end products were characterized using XRD, FTIR, ESEM and MIP analyses. The flexural strength increases from 6.90 to 9.13 MPa and from 6.90 to 12.33 MPa for GMHA and GMHR series respectively. The cumulative pore volume decreases from 102.2 to 84.2 mm3 g−1 and from 102.2 to 51.3 mm3 g−1 for GMHA and GMHR products respectively. Both matrices present micrographs with very low capillaries pores and fractured surfaces that confirmed the enhancement of the mechanical properties. It was concluded that TiO2 in both forms is beneficial for the reduction of porosity and densification of geopolymer matrices. Rutile enabled more compact and denser geopolymer structure compared to anatase. The aforementioned results showed the efficiency of both fine TiO2 particles to improve the geopolymer network significant for its durability. Graphic abstract: [Figure not available: see fulltext.].


2020 - Meta-halloysite to improve compactness in iron-rich laterite-based alkali activated materials [Articolo su rivista]
Kaze, C. R.; Venyite, P.; Nana, A.; Juvenal, D. N.; Tchakoute, H. K.; Rahier, H.; Kamseu, E.; Melo, U. C.; Leonelli, C.
abstract

In this paper, the results of the experimental investigation were used to understand the effect of fine meta-halloysite on the reactivity, mechanical and microstructural properties of laterite-based geopolymers. Laterite was replaced by 0, 20, 30 and 50 wt% of meta-halloysite in order to improve the physico-chemical performance. Meta-halloysite was prepared by calcination of natural halloysite at 600 °C. The moduli (molar ratio SiO2/Na2O) of the activating solutions were 1.04, 0.92, and 0.75 with H2O/Na2O = 9.78, 10.45 and 12.04, respectively. The results indicated that calcined laterite has a high specific surface area (43.00 ± 0.12 m2/g), notwithstanding a high average particle size (d50 = 45.20 μm) compared to meta-halloysite with a smaller average particle size (d50 = 8.40 μm) and a specific surface (29.80 ± 0.16 m2/g). The compressive strength of geopolymers increased upon the addition of meta-halloysite from 12 MPa to 45 MPa at 28 days. While the setting time and water absorption decrease with increase in the of meta-halloysite content as well as with increase in Si/Al, Si/Fe, Al/Fe and Na/Al molar ratios used in the synthesis of geopolymers. The use of fine meta-halloysite resulted in better efficiency and improved mechanical performance of synthesized products.


2020 - Microstructural and mechanical properties of poly(sialate-siloxo) networks obtained using metakaolins from kaolin and halloysite as aluminosilicate sources: A comparative study [Articolo su rivista]
Tchakoute, H. K.; Melele, S. J. K.; Djamen, A. T.; Kaze, C. R.; Kamseu, E.; Nanseu, C. N. P.; Leonelli, C.; Ruscher, C. H.
abstract

This work focuses on the comparison between the mechanical and microstructural properties of poly(sialate-siloxo) networks based on metakaolins from halloysite and kaolin. Poly(sialate-siloxo) networks were prepared using three metakaolins as aluminosilicate sources. Sodium waterglass from rice husk ash and commercial sodium waterglass were used as chemical reagents. The obtained results showed that metakaolins from kaolins have plate shapes with coarse particle sizes whereas the one from halloysite has a spherical morphology and smaller particle sizes. The IR spectra of poly(sialate-siloxo) networks from calcined halloysite indicate the higher value of the wavenumber of the main band. The XRD patterns of all poly(sialate-siloxo) networks show the broad hump structure with higher intensity between 18 and 40°(2θ). The XRD patterns of poly(sialate-siloxo) networks show the band of the unreacted metakaolin at about 20.45°(2θ). This band is more pronounced on the XRD patterns of geopolymer cements from calcined halloysite. The obtained poly(sialate-siloxo) networks based on metakaolins from halloysite and kaolin have a compact, homogenous and denser microstructures. The compressive strength values of the poly(sialate-siloxo) networks using calcined kaolin are ranging from 58.43 to 66.52 MPa whereas those using calcined halloysite are between 72.29 and 88.50 MPa. The compressive strength values of poly(sialate-siloxo) networks using calcined halloysite are higher compared to those from calcined kaolin. The higher compressive strength values of the geopolymer cements from calcined halloysite could be attributed to the fine and spherical particle sizes of calcined halloysite. This implies that the shape and the fine particle sizes of the raw materials influence the properties of the poly(sialate-siloxo) networks. Metakaolin from halloysite can be used as an aluminosilicate source for producing poly(sialate-siloxo) network with higher mechanical properties.


2020 - Microstructure and physico-chemical transformation of some common woods from Cameroon during drying [Articolo su rivista]
Nouemsi Soubgui, E.; Tene Fongang, R. T.; Kamseu, E.; Oum Lissouck, R.; Andreola, F.; Boubakar, L.; Rossignol, S.; Leonelli, C.
abstract

The influence of drying on the microstructure, physical and chemical properties of some tropical wood species has been investigated using thermogravimetric analysis, differential scanning calorimetric (DSC), FTIR-ATR spectroscopy, mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM) analysis. Eleven tropical species were used in this study. Results showed that the common Cameroonian wood species can be grouped into three classes: Ga (lightwood) with cross-linking fibers having high volume of macropores, density in the range 0.2–0.4 g cm−3 and high lignin content; Gb (medium dense) with unidirectional fibers packing, density around 0.6 g cm−3 and Gc group showing high densification of unidirectional fibers and low porosity justifying the density > 0.8 g cm−3. Both the Gb an Gc groups have less significant lignin content. A relatively high rate of drying for Ga with respect to low drying rate for Gc was observed in direct relation with their porosity of ~ 72 Vol% and ~ 36 Vol%, respectively. LTF and WG showed similar cumulative pore volume (0.44 mL g−1) with different pore size distribution: 28% and 22% of macropores, 39% and 60% of mesopores and 33% and 18% micropores, respectively. Thermal analysis revealed that lightwoods have the highest amounts of residues and lower thermal stability of chemical components than dense woods. It has been found that the degradation process of hemicellulose, cellulose and lignin occurs mainly at about 200–300 °C, 300–350 °C and 350–500 °C, respectively. The group Ga with low drying rate, a low cycle of reproduction, a high volume of porosity together with large pore sizes appeared promising candidates for the design of ecological, environmental and sustainable management policy of wood transformation in developing countries and even worldwide.


2020 - Preparation of low-cost nano and microcomposites from chicken eggshell, nano-silica and rice husk ash and their utilisations as additives for producing geopolymer cements [Articolo su rivista]
Tchakoute, H. K.; Tchinda Mabah, D. E.; Henning Ruscher, C.; Kamseu, E.; Andreola, F.; Bignozzi, M. C.; Leonelli, C.
abstract

This work aims to prepare low-cost nanocomposite and microcomposite with lower molar ratio CaO/SiO2 (0.4). Nano-silica, rice husk ash and calcined chicken eggshell have been used as silica and calcium sources. Metakaolin has been separately replaced by 0, 10 and 20 wt% of each composite in order to study their behavior on the properties of geopolymers. The hardener used is sodium waterglass from rice husk ash. The surface area of nano-silica and rice husk ash was 54.40 and 4.08 m2/g, respectively. The cumulative volumes of the control geopolymer, the ones containing 10 wt% of microcomposite and nanocomposite are 119.71, 89.92 and 110.49 mm3/g, respectively. The compressive strength of the control specimen is around 64.02 MPa. The one using 10 wt% of microcomposite was 68.97 MPa. It drops to 42.88 MPa when metakaolin was replaced by 20 wt % of microcomposite. Whereas the one using 10 wt% of nanocomposite was 30.03 MPa and it decreases to 26.05 MPa when metakaolin was substituted by 20 wt% of nanocomposite. It can be concluded that 10 wt% of microcomposite could be mixed to metakaolin for strength development and nanocomposite does not recommend to use as an additive for producing high strength of geopolymer cements.


2020 - Production of Porous Poly(phospho-siloxo) Networks for Thermal Insulations Using Low-Value Calcium-Rich Wastes as Pore-Forming Agents [Articolo su rivista]
Tchakoute, H. K.; Bewa, C. N.; Kesseng, N. A.; Ruscher, C. H.; Kamseu, E.; Andreola, F.; Ali, B. N.; Leonelli, C.
abstract

Abstract: This study focuses on the preparation of porous poly(phospho-siloxo) networks for thermal insulation applications using commercial calcium carbonate and calcium-rich wastes such as oyster shell, snail shell and eggshell powders as pore-forming agents. The control and porous poly(phospho-siloxo) networks were prepared by adding phosphoric acid (4 M) as a chemical ingredient to metakaolin containing 0 and 15 wt% of each foaming agents. The final products were monitored using the X-ray diffractometry, infrared spectroscopy, apparent density, absolute density, thermal conductivity, optical microscopy, scanning electron microscopy and mercury intrusion porosimetry. The results show that the thermal conductivity of the control and porous poly(phospho-siloxo) network from commercial calcium carbonate are 0.35 and 0.20 W/mK, respectively. They were higher compared to those from snail shell (0.17 W/mK), eggshell (0.15 W/mK) and oyster shell (0.14 W/mK). The cumulative pore volumes are 211.4, 365.5, 380.6, 389.7 and 393.3 mm3/g for the control and porous specimens from chicken eggshell, commercial calcium carbonate, snail shell and oyster shell powders, respectively. Their total porosity measured by mercury intrusion porosimeter are 30.9, 45.5, 46.0, 45.9 and 45.4%, respectively, whereas those calculated with apparent and true density measured by pycnometer are 34.48, 45.25, 52.74, 50.84 and 52.60%, respectively. The concentrated pore size diameter of the porous sample from eggshell is highest compared to the others. It can be seen that the total porosities measured by mercury intrusion porosimeter of porous specimens are nearly the same trend as well as the thermal conductivity. It was found that the low-value calcium-rich wastes could be used for producing porous poly(phospho-siloxos) networks which could be utilized for thermal insulation applications. Graphic Abstract: [Figure not available: see fulltext.].


2019 - Design of low cost semi-crystalline calcium silicate from biomass for the improvement of the mechanical and microstructural properties of metakaolin-based geopolymer cements [Articolo su rivista]
Tchinda Mabah, D. E.; Tchakoute, H. K.; Ruscher, C. H.; Kamseu, E.; Elimbi, A.; Leonelli, C.
abstract

The main objective of this work is to use low-value SiO2 and CaO-rich wastes like rice husk ash and chicken eggshell powders, respectively for producing semi-crystalline calcium silicate with molar ratio CaO/SiO2 equal to 0.4. The prepared valuable semi-crystalline calcium silicate was used as an additive for a replacement level of metakaolin (0, 1, 3, 5, 7 and 10% by mass). The resulting powders were used to synthesize geopolymer cements using hardener obtained by mixing commercial sodium silicate, sodium hydroxide and distilled water. The final products were characterized by compressive strengths, apparent density, X-ray diffractometry, infrared spectroscopy, scanning electron and optical microscope observations. The results show that the compressive strengths of geopolymer cements were between 33.25 and 51.38 MPa. They increase when metakaolin was replaced by 5, 7 and 10% of semi-crystalline calcium silicate, but no significant change was observed on the strengths of geopolymer cements content 0, 1, 3 and 5% of semi-crystalline calcium silicate. The micrograph images of the selected geopolymer cements were homogeneous and compact and the one from 10% of semi-crystalline calcium silicate shows a coarse microstructure. It was found that the low-value silica and calcium-rich wastes such as rice husk ash and eggshell can be used to prepare semi-crystalline calcium silicate. The obtained product could be used as a low-cost additive to enhance the microstructural and mechanical properties of poly(sialate-siloxo) network.


2019 - Improving insulation in metakaolin based geopolymer: Effects of metabauxite and metatalc [Articolo su rivista]
Zenabou, Ngouloure N. M.; Benoit-Ali, Nait; Zekeng, S.; Rossignol, S.; Melo, U. C.; Tchamba, A. B.; Kamseu, E.; Leonelli, C.
abstract

To improve the thermal stability of porous geopolymers, metabauxite and metatalc were used as partial replacement of metakaolin. The results of optical microscopy, Scanning Electron Microscopy (SEM), thermal sintering, mercury intrusion porosimetry (MIP) and hot disk investigations, were used to establish the effective stability of the porous composites up to 800 °C. At 1000 °C, the metabauxite based composites showed microcracks into the larger pores and small microcracks into the matrix as the results of residual poorly bounded Alumina oligomers. Metatalc based porous composites showed microcracks only inside larger pores. Those microcracks can be eliminated with the optimization of the mix-design. Despite those microcracks, the specimens maintained their integrity and stability. Above 800 °C it can be seem that the thermal conductivity of the matrices with only metakaolin increases more rapidly compared to matrices containing metatalc or metabauxite. The combination of high volume of porosity (60–65%), low thermal conductivity (̴ 0.30 W/m/K) and good thermal stability gives to porous refractory geopolymers a large scale of intrinsic properties that can be positively exploited in the field of incinerators, anti flames, kilns and building constructions.


2019 - In vitro surface reaction in SBF of a non-crystalline aluminosilicate (geopolymer) material [Articolo su rivista]
Tippayasam, C.; Sutikulsombat, S.; Kamseu, E.; Rosa, R.; Thavorniti, P.; Chindaprasirt, P.; Leonelli, C.; Heness, G.; Chaysuwan, D.
abstract

Geopolymer is a non-crystalline material based on aluminosilicate reaction exhibiting ceramic-like properties. It showed the possibility to use geopolymer as biomaterials by soaking in SBF solution to induct carbonate apatite onto the surface of samples. Carbonate apatite possesses good biocompatibility and bioactivity. The aims of this research were to study the geopolymer synthesis as a biomaterial to replace bones and the effects of Ca/P ratio on bioactivity properties of metakaolin-based geopolymers. For in vitro bioactivity test, the samples were soaked in SBF to study the influence of Ca(OH) 2 contents on the surface reaction. The 14, 28, and 90 day-soaked sample surfaces were investigated using SEM, XRD, and FTIR characterization. The compressive strength of samples was also tested. The SEM micrographs revealed that the increase of Ca/P ratio resulted in the increase of the carbonate apatite on sample surfaces. FTIR results confirmed that the formation of Ca 10 (PO 4 ) 3 (CO 3 ) 3 (OH) 2 was investigated.


2019 - Influence of the molar ratios CaO/SiO2 contained in the sustainable microcomposites on the mechanical and microstructural properties of (Ca, Na)-poly(sialate-siloxo) networks [Articolo su rivista]
T. Mabah D., E.; K. Tchakoute, H.; Fotio, D.; Ruscher, C. H.; Kamseu, E.; Bignozzi, M. C.; Leonelli, C.
abstract

The sustainable microcomposites with different molar ratios CaO/SiO2 such as 0, 0.4, 0.6, 0.8, 1.0 and 1.2 were prepared using calcined brown chicken eggshell, rice husk ash and distilled water. 10 wt% of each microcomposite was used to substitute metakaolin and the obtained calcium aluminosilicate materials were used for investigating the effects of the molar ratios CaO/SiO2 in the microcomposites on the physical, mechanical and microstructural properties of (Ca, Na)-poly (sialate-siloxo) networks. Commercial sodium waterglass and sodium waterglass from rice husk ash with a molar ratio SiO2/Na2O kept constant at 1.6 were used as chemical ingredients. Each (Ca, Na)-poly (sialate-siloxo) network was obtained by mixing each calcium aluminosilicate material with each hardener. The final products were characterized by infrared spectroscopy and X-ray diffractometry. The determination of the apparent density, compressive strength and scanning electron microscopy analysis were done. The results show that the compressive strength values of geopolymer cements using hardener from rice husk ash and microcomposites containing the molar ratios CaO/SiO2 equal to 0, 0.4, 0.6, 0.8, 1.0 and 1.2 are 64.01, 67.97, 66.15, 65.09, 60.73 and 49.40 MPa, respectively. Whereas, those from commercial sodium waterglass are 64.75, 69.03, 64.64, 56.73, 36.47 and 28.30 MPa, respectively. It was found that the most convenient molar ratio CaO/SiO2 in the structure of microcomposite required for producing (Ca, Na)-poly (sialate-siloxo) networks with higher mechanical properties is around 0.4.


2019 - Microstructural and mechanical properties of (Ca, Na)-poly(sialate-siloxo) from metakaolin as aluminosilicate and calcium silicate from precipitated silica and calcined chicken eggshell [Articolo su rivista]
Tchuente, F. M.; Tchakoute, H. K.; Banenzoue, C.; Ruscher, C. H.; Kamseu, E.; Andreola, F.; Leonelli, C.
abstract

The aim of this work is to investigate the influence of the amorphous calcium silicate on the microstructural, physical and mechanical properties of (Ca, Na)-poly(sialate-siloxo) networks. The calcium silicate with molar ratio CaO/SiO 2 equal to 1.0 was prepared from the precipitated silica and calcined chicken eggshell. The X-ray patterns and infrared spectra of the synthesized calcium silicate indicate that it mainly constitutes of the amorphous calcium silicate hydrate. The X-ray patterns of geopolymer cements indicate that the prepared amorphous calcium silicate hydrate does not include in the network. The compressive strengths of the geopolymer mortars decrease from 28.92 to 12.03 MPa with increasing the replacement level of metakaolin (from 0 to 25% by mass). Whereas, the values of the apparent densities increase with increasing the replacement level of metakaolin. It seems that the amorphous calcium silicate hydrate in the structure of calcium silicate affects negatively the mechanical properties of the (Ca, Na)-poly(sialate-siloxo) network. The heterogeneous structure of geopolymer mortars containing 25% of calcium silicate could be related to the higher calcium content and the amorphous structure of calcium silicate hydrate. It was typically found that in the absence of significant levels of dissolved calcium, the precursors such as silicate and aluminate condense to form (Ca, Na)-poly(sialate-siloxo) networks. This implies the homogenous structure and the higher values of the compressive strengths of geopolymer mortars containing 0, 5, 10 and 15% of calcium silicate. Whereas those from the replacement level of metakaolin by 20 or 25% of calcium silicate contain significant levels of dissolved calcium and amorphous calcium silicate hydrate in their structure which hinder the formation of the precursors and therefore impede the formation of the (Ca, Na)-poly(sialate-siloxo) networks.


2019 - Microstructure and mechanical, physical and structural properties of sustainable lightweight metakaolin-based geopolymer cements and mortars employing rice husk [Articolo su rivista]
Riyap, H. I.; Bewa, C. N.; Banenzoue, C.; Tchakoute, H. K.; Ruscher, C. H.; Kamseu, E.; Bignozzi, M. C.; Leonelli, C.
abstract

This work focuses on an in-depth investigation of the formation of pores in the structure of lightweight geopolymer cements and mortars using rice husk as a foaming agent. The hardener used in this study was sodium waterglass. Metakaolin was replaced by 0, 10, 20, 30 and 40 % by mass of husk and the obtained powders were used to produce lightweight geopolymer cements and mortars. The formation of pores in the lightweight geopolymer cements was monitored using X-ray diffractometry and infrared spectroscopy while those in the mortars were assessed using apparent density and compressive strength measurements, mercury intrusion porosimetry and optical and scanning electron microscopy. The values for the compressive strength and apparent density were in the ranges of 28.92–0.75 MPa and 1.88–1.70 g/cm 3 , respectively. The results indicated that the values for the compressive strength and apparent density of geopolymer mortars decreased while those of the cumulative pore volume increased with increases in the metakaolin replacement level. Stereomicroscopic and scanning electron microscopic images showed the presence of rice husk and fibres of rice husk, respectively, in the networks. It was found that rice husk can be used as a foaming agent for producing sustainable lightweight geopolymer mortars.


2019 - Room-temperature alkaline activation of feldspathic solid solutions: Development of high strength geopolymers [Articolo su rivista]
Nana, A.; Ngoune, J.; Kaze, R. C.; Boubakar, L.; Tchounang, S. K.; Tchakoute, H. K.; Kamseu, E.; Leonelli, C.
abstract

Amorphous fraction, grains defects and the incongruent dissolution of solid solutions (pegmatite, trachyte, and granite) were used to design high strength geopolymer composites with crystalline content in the range of ∼70–85%. The geochemical history of the natural solid solutions affects the dissolution and polycondensation/geopolymerization. These solid solutions were altered with 15, 20, 25 and 30% of metakaolin and activated with alkaline solution. Experimental results (phase evolution, three-point flexural strength, microstructure, mercury intrusion porosimetry and water absorption) indicated that polycondensation/polymerization is enhanced in trachyte, granite and pegmatite based specimens, compared to sand, due to the increase in N-A-S-H secondary phases. The amorphous/crystalline ratio of the solid precursors were used to understand the role of dissolved and undissolved fraction into the strength development of geopolymer composites. It was concluded that high strength geopolymer composites of chemico-mechanical equilibrium can be achieved with solid solutions having reduced fraction of pores volume and pore-size.


2018 - Effect of silicate modulus on the setting, mechanical strength and microstructure of iron-rich aluminosilicate (laterite) based-geopolymer cured at room temperature [Articolo su rivista]
Kaze, C. R.; Djobo, J. N. Y.; Nana, A.; Tchakoute, H. K.; Kamseu, E.; Melo, U. C.; Leonelli, C.; Rahier, H.
abstract

This paper studies the alkali activation of iron-rich aluminosilicates (laterites). Three activating alkaline solutions were prepared from sodium hydroxide solution (8, 10 and 12 M) with sodium silicate (Na2SiO3) in order to obtain the sodium silicate solutions with moduli of SiO2/Na2O equal to 0.75, 0.92 and 1.04; H2O/Na2O = 9.78, 10.45 and 12.04. The effects of above-defined solutions on the setting time, physical and microstructural properties of geopolymer binders from calcined laterite (600 °C), containing metakaolinite, as the sole binder at room temperature are reported and discussed. A laterite from Eloumden and one from Odza were used. The synthesized products were labelled GPEL(i=1.04, 0.92 and 0.75) and GPOD(i=1.04, 0.92 and 0.75) series. The dry compressive strength measured after 7 and 28 days were 4–10 and 10–18 MPa, respectively. It was typically found that the geopolymer paste from sodium hydroxide with molar concentration 12 M and the molar ratio SiO2/Na2O of the silicate solution equal to 0.75 produced the highest compressive strength (~ 18 MPa). These samples also have a denser matrix. The dry bulk densities of both series increased with the decrease of silica moduli and were in the range 2.31–2.43 and 2.32–2.52 g/cm3 and the water absorptions were in the range of 8.21–11.40% and 7.23–13.03% for geopolymers GPEL and GPOD series, respectively. The setting time decreased with increasing molarity of NaOH solutions. The physicochemical properties and the mineralogy of both iron-rich aluminosilicates were influenced by the silicate modulus of activating solutions and the best compositions were achieved with characteristic SiO2/Na2O = 0.75 and H2O/Na2O = 9.78.


2018 - Investigation of the relationship between the condensed structure and the chemically bonded water content in the poly(sialate-siloxo) network [Articolo su rivista]
Melele, Sorelle J. K.; Tchakouté, Hervé K.; Banenzoué, Charles; Kamseu, Elie; Rüscher, Claus H.; Andreola, Fernanda; Leonelli, Cristina
abstract

The main objective of this work was to investigate the relationship between the condensed structure and the chemically bonded water content in the metakaolin-based geopolymer network. The kaolin used in this work as an aluminosilicate source was transformed to metakaolin by calcination at 700 °C. The powder of the waste glass and the silica fume were used as silica sources for the synthesis of the hardeners, dissolving with caustic soda solution. The obtained hardeners were characterized by infrared spectroscopy and MAS-NMR 29Si. The metakaolin and the hardeners were used for producing geopolymers cements. The synthesized products were characterized by X-ray diffractometry, infrared spectroscopy, mercury intrusion porosimetry, scanning electron microscopy, MAS-NMR 29Si and 27Al, thermal analyses (TG and DSC) and compressive strength. The results show that the compressive strength of geopolymer cements using hardener from silica fume and the one from waste glass are 61.93 and 25.51 MPa, respectively. The microstructure (SEM observations) of geopolymer cements obtained using hardener from silica fume is homogeneous, compact and dense with an average pore diameter around 13 nm. Whereas, the one obtained using hardener from waste glass are heterogeneous and contains larger pores (with average pore diameter around 168 nm). MAS-NMR 29Si and 27Al results show that the specimen obtained using hardener from the silica fume contains more aluminum in four-fold coordination in its network than the ones using hardener from waste glass. This indicates a higher degree of crosslinking of poly(sialate-siloxo) chains which could lead to a smaller pore sizes and a higher water uptake in the structure of the sample. The amount of chemically bonded water contained in the network of geopolymer cements using hardeners from waste glass and silica fume were 6.82 and 11.23%, respectively, as determined from weight loss in the range 100–300 °C. All these results indicate that the higher content of chemically bonded water in the network of geopolymer cement obtained using hardener from silica fume is related to the much smaller average pore size diameter and the hydrophilic character of aluminum, which reveals obviously better mechanical and microstructural properties of the specimen. This could indicate here a higher degree of condensation using silica fume based hardener for geopolymerization.


2018 - Microstructure and engineering properties of Fe2O3(FeO)-Al2O3-SiO2 based geopolymer composites [Articolo su rivista]
Kaze, R. C.; Beleuk a Moungam, L. M.; Cannio, M.; Rosa, R.; Kamseu, E.; Melo, U. C.; Leonelli, C.
abstract

The objective of this study is to develop low cost, eco-friendly and sustainable building materials by applying the technology of mineral polymerization (geopolymerization) process on naturally abundant iron-rich aluminosilicate (laterite) materials. Iron-rich aluminosilicates based-geopolymer composites containing 10 to 40 wt% of rice husk ash (RHA) were cured at room temperature and at 90 °C. This paper examines the phase transformation, microstructural and mechanical changes that occur in the geopolymer composites when fine aggregates of quartz sand are added. Experimental results indicate good polycondensation and more cohesion resulting in high strength due to the better dissolution of RHA that provides soluble reactive silica to equilibrate the Si/Al and Si/Fe molar ratios. Ferro-sialates, Fe(Al)–S–H, were identified at the room temperature in addition to polysialates, S–A-N–H, phases. The flexural strength of resultant composites increases from 10 to 12 MPa for room temperature curing to ∼40 MPa when the composites were cured at about 90 °C as from the intensive formation of ferrisilicates. The formation of ferri-silicates that changed the flexural strength and microstructure seem to play significant role in the engineering properties of laterites based geopolymer composites making them promising candidates for applications as pavements, roads and building construction.


2018 - Moisture Control Capacity of Geopolymer Composites: Correlation of the Bulk Composition–Pore Network with the Absorption–Desorption Behavior [Articolo su rivista]
Kamseu, E.; Mohamed, H.; Sofack, J. C.; Chaysuwan, Duangrudee; Tchakoute, H. K.; Djobo, J. N. Y.; Rossignol, S.; Leonelli, C.
abstract

Abstract: Porous composites with the principal class of porosity in the range of those presented in the literature as ideal for the moisture control capacity of building environment are described. In the course of the design of the matrices, micrometric pores are introduced to give to the pore systems a bi- or multimodal characters with the aim of improving the phases percolation during the course of desorption and make the moisture accumulation–desorption behavior of the porous composites essentially function of weather and environment. The porous composites present size of pores in the range 0.001-1μm for the gel pores and peak centered at 10μm for the micrometric pores which insure the matrices efficiency in moisture control capacity and durability. The results of cycles of moisture absorption–desorption in the course of various seasons of the year permit to identify the activities of gel pores meanly efficient in the extreme environment: absorption when the temperature is under 11∘C; relative humidity is >60% and desorption when the temperature is above 18∘C. At ambient conditions, the pores more active are micrometric pores, while gel pores enter in activity only in the extreme environment conditions. The proposed porous geopolymer composites appeared promising candidates for the management of the moisture while improving the thermal insulation of residential building particularly in the regions with important fluctuation of weather. The use of geopolymerization process for the production of those porous composites, the choice of recycling industrial and municipal inorganic wastes appears ideal solution, environmentally friendly, eco-efficient and sustainable for the design of newly materials for the moisture control capacity in building environment. Graphical Abstract: [Figure not available: see fulltext.].


2018 - Role of ɣ-Al2O3 on the mechanical and microstructural properties of metakaolin-based geopolymer cements [Articolo su rivista]
Tchakouté, Hervé K.; Kamseu, Elie; Banenzoué, Charles; Rüscher, Claus H.; Andreola, Fernanda; Tchamo, Claudia C. L.; Leonelli, Cristina
abstract

The main target of this work is to investigate the influence of ɣ-Al2O3 on the properties of metakaolin-based geopolymer cements. The kaolin used as starting material for producing geopolymer cements contains approximately 28 and 64% of gibbsite and kaolinite, respectively. This kaolin was transformed to metakaolins by calcination at 500, 550, 600, 650, and 700 °C for 1 h. Gibbsite contained in kaolin was transformed to γ-Al2O3 during the calcination process. The hardener was obtained by mixing commercial sodium silicate and sodium hydroxide solution (10 M) with a mass ratio sodium silicate/sodium hydroxide equal to 1.6:1. Geopolymer cements, GMK-500, GMK-550, GMK-600, GMK-650, and GMK-700, were obtained using the prepared hardener with a mass ratio hardener/metakaolin equal to 0.87:1. It could be seen that the specific surface area of metakaolins decreases with increasing the calcination temperature of kaolin owing to the formation of the particles of γ-Al2O3. The compressive strengths 18.21/29.14/36.61/36.51 increase in the course GMK-550/GMK-600/GMK-650/GMK-700. The X-ray patterns and micrograph images of geopolymer cements, GMK-600, GMK-650, and GMK-700, indicate the presence of γ-Al2O3 in their structure. It was typically found that γ-Al2O3 remains largely unaffected during the geopolymerisation, and therefore could act as an inert filler and reinforce the structure of geopolymer cements. [Figure not available: see fulltext.].


2018 - Synthesis and properties of inorganic polymers (geopolymers) derived from Cameroon-meta-halloysite [Articolo su rivista]
Kaze, C. R.; Tchakoute, H. K.; Mbakop, T. T.; Mache, J. R.; Kamseu, E.; Melo, U. C.; Leonelli, C.; Rahier, H.
abstract

Cameroonian Balengou clay has been characterized as precursor for inorganic polymer (geopolymer) binder. The lowest possible calcination temperature for this halloysite type clay was found to be 600 °C to convert it into meta-halloysite (MH), which is reactive enough for geopolymerization. This implies an energy saving compared to the 800 °C, previously reported in literature. The inorganic polymer has been produced using sodium hydroxide or sodium silicate solutions. A maximum dry compressive strength of 27.5 MPa after 28 days was obtained with a sodium silicate solution [Na2O·1.25SiO2·9.76H2O] resulting in a material with composition: Na2O·3.78SiO2·7.22Al2O3·9.76H2O. This inorganic polymer was amorphous according to XRD, showed a compact microstructure (scanning electron microscopy), with lower values of water absorption, porosity, and higher density. In addition the same composition showed better resistance to 5% sulfuric/hydrochloric solution than the ones made with higher and lower ratio of Na/Al. Meta-halloysite based geopolymers had a 20–30% reduction in strength after immersion in 5% sulfuric/hydrochloric acids for 7 days and even up to 62.5% after 28 days, due to the depolymerisation process of the geopolymer network. The results obtained demonstrated the suitability of Cameroonian meta-halloysite for geopolymer synthesis at room temperature.


2018 - The effects of synthesized calcium phosphate compounds on the mechanical and microstructural properties of metakaolin-based geopolymer cements [Articolo su rivista]
Tchakouté, Hervé K.; Fotio, Daniel; Rüscher, Claus H.; Kamseu, Elie; Djobo, Jean N. Y.; Bignozzi, Maria C.; Leonelli, Cristina
abstract

Dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HAP) were prepared from oyster shell powder and phosphoric acid solution as raw materials using sol-gel process in order to study the influence of calcium phosphate compounds on the mechanical and microstructural properties of metakaolin-based geopolymer cements. The synthesized DCPD and HAP with molar ratio Ca/P equal to 1.00 and 1.65, respectively, were used as additives for replacement of metakaolin (0, 2, 4, 6, 8 and 10 wt%) and the resulting powders were used for producing geopolymer cements. The compressive strengths of geopolymer cements containing DCPD were in the range 40–48 MPa with increasing DCPD content, but when 10 wt% was used, the strength fell to 26 MPa. Similar results were obtained for HAP addition with a decrease of the compressive strength at 8 wt%. The ESEM images of geopolymers containing 4–10 wt% of HAP showed some non-reacted or partially reacted particles that do not well connect to the matrix. Samples of geopolymer with 4–8 wt% of DCPD present a lower number of unreacted particles and the matrix appeared denser than that of the control geopolymer cements. The use of calcium phosphate compounds such as brushite and hydroxyapatite led to the overall improvement in compressive strength and contribute to the densification of the structure of geopolymer cements. On the other hand, the addition of 4% of HAP and 10% of DCPD resulted in a large amount of hydroxyapatite and brushite, respectively in the systems. The matrix appear less dense indicating that a fraction of calcium phosphate addition at the aforementioned level was excessive.


2018 - Water resistance and thermal behavior of metakaolin-phosphate-based geopolymer cements [Articolo su rivista]
Nobouassia Bewa, C.; Tchakoute, H. K.; Fotio, D.; Ruscher, C. H.; Kamseu, E.; Leonelli, C.
abstract

The main target of this work was to investigate the thermal behavior and water resistance of geopolymer cement made from metakaolin as an aluminosilicate source using phosphoric acid solution (10 M) as a hardener. The obtained geopolymer cements were cured at room temperature for 28 days, the one part was treated at 200°C, 400°C, 600°C, 800°C and 1000°C, and the others were soaked in water for 28 days. The geopolymer cements were characterized by microstructural properties using X-ray diffractometry, infrared spectroscopy, microstructure, physical property based on water resistance and thermo-mechanical properties (thermal analysis, compressive strength). The results show that the compressive strength of the unheated geopolymer cement was 87.96 MPa. The ones soaked in water revealed a strength of 40.71 MPa. This indicates that the specimens soaked in water lose about 54% of their strengths. The X-ray patterns of heated geopolymer cements showed the formation of crystalline phases even at relatively low temperatures. It was typically found that the compressive strength of metakaolin-phosphate-based geopolymer cements decreases due to the hydrolysis of Si-O-P bonds in the presence of water.


2017 - Design of ceramic filters using Clay/Sawdust composites: Effect of pore network on the hydraulic permeability [Articolo su rivista]
Youmoue, Martine; Fongang, R. T. Téné; Sofack, J. C.; Kamseu, Elie; Melo, U. Chinje; Tonle, Ignas K.; Leonelli, Cristina; Rossignol, Sylvie
abstract

Clay based ceramic composite materials with hydraulic permeability were elaborated using sawdust as porogent agent. Their mechanical, morphological, microstructural and pore network properties were investigated. Mixtures in various ratios of two kaolinite clay minerals, Ba (highly plastic) and Va (sand-rich) constitute the five ceramic matrixes studied (CM1, CM2, CM3, CM4 and CM5). Due to their high flexural strength, CM3 and CM4 received 0%, 5%, 10% and 15% sawdust before firing, to improve the porosity of the final matrixes. Results revealed that 900–1000 °C is the range of temperature necessary to get good sintering and flexural strength (≥2 MPa). A typical clay-sawdust based materials (parallepipedic bricks) present porosity ≥40 vol% and 1.5 g/cm3 density. Characterizations such as FTIR, SEM, MIP and flow permeability of ceramic candles were performed. A Hydraulic permeability of ~10 mDarcy was obtained and the mean pore diameter varies from 0.05 to 0.1 µm, in agreement with the microstructure exhibited by the ceramic candles. In the presence of sawdust, pores with size up to 10 µm were observed, justifying the increase of flowing permeability. The elaborated matrixes are promising candidates for microfiltration.


2017 - Geopolymerization as cold-consolidation techniques for hazardous and non-hazardous wastes [Relazione in Atti di Convegno]
Leonelli, Cristina; Kamseu, Elie; Lancellotti, Isabella; Barbieri, Luisa
abstract

Many interesting studies on the utilization of wastes produced in different human activities (urban, agricultural and industrial) have been carried out with the goals to reduce, to recycle, to reuse or to recovery: the R4 strategy. Many of these waste contains high amount of silicoaluminates, making them suitable for alkali activation to become one of the most promising binders for the future. Other type of wastes, even if hazardous, such as incinerator fly ash, electric arc furnace dust, lead smelting slag, etc. can be easily added as minor components to the geopolymer matrix for being immobilized as either cations or anions or both.


2017 - Influence of the molar concentration of phosphoric acid solution on the properties of metakaolin-phosphate-based geopolymer cements [Articolo su rivista]
Tchakoute, H. K.; Ruscher, C. H.; Kamseu, E.; Andreola, F.; Leonelli, C.
abstract

Six different phosphoric acid solutions with molar concentrations 4, 6, 8, 10, 12 and 14 M were prepared by dilution of commercial phosphoric acid in distilled water. The obtained phosphoric acid solutions were used for producing metakaolin-phosphate-based geopolymer cements. These geopolymer cements were obtained by adding each fresh prepared phosphoric acid solution to metakaolin with a mass ratio phosphoric acid solution/metakaolin = 0.80. It was observed in the infrared spectra of phosphoric acid solutions 8, 10, 12 and 14 M, the absorption bands at 875–879 and 949–972 cm− 1 which are assigned to H2PO4−. The SEM images of geopolymer cements exhibit the presence of berlinite (AlPO4) which is dispersed in the matrix and contributes to enhancing the strength, whereas the geopolymer cements from phosphoric acid solution with 14 M are heterogeneous microstructures. The compressive strength of phosphate-based geopolymer cements was between 36.4 and 93.8 MPa; it increased with increasing the concentration of phosphoric acid solutions up to 10 M. It can be concluded that the most convenient concentration of phosphoric acid solution required for producing phosphate-based geopolymer cements with good mechanical properties is around 10 M.


2017 - Substitution of sodium silicate with rice husk ash-NaOH solution in metakaolin based geopolymer cement concerning reduction in global warming [Articolo su rivista]
Kamseu, Elie; Beleuk à. Moungam, L. M.; Cannio, Maria; Billong, Ndigui; Chaysuwan, Duangrudee; Melo, U. Chinje; Leonelli, Cristina
abstract

Rice husk ash (RHA), a by-product from the rice industry, was used as principal source of amorphous silica for the production of sodium silicate solution (MR ∼ 3) used for the replacement of standard commercial sodium silicate in the mix-design of metakaolin based geopolymer composites. Three initial concentrations of NaOH were considered (8, 10 and 12 M) with the aim to investigate on the optimum dissolution and formation of silica oligomers capable to act as binder during the geopolymerization. Results (FT-IR and XRD) showed that RHA-NaOH sodium silicate solutions have characteristics similar to that of standard commercial sodium silicate and the residual carbonates present in the viscous pastes can be monitored during the preparation of geopolymers using the mix-design. Combined 25 vol% standard sodium silicate solution with ∼75 vol% of RHA-NaOH based sodium silicate solution conducted to good polycondensation, densification, high flexural strength (∼8 MPa) and low porosity similar to that of the standard matrix of metakaolin based composites. The new approach is found promising for the significant reduction of the Global Warming Potential of Geopolymers.


2017 - The corrosion of kaolinite by iron minerals and the effects on geopolymerization [Articolo su rivista]
Kaze, R. C; Beleuk à. Moungam, L. M.; Fonkwe Djouka, M. L.; Nana, A.; Kamseu, Elie; Chinje Melo, U. F.; Leonelli, Cristina
abstract

Iron-rich aluminosilicates with disordered structure (laterites) due to the corrosion of kaolinite by iron minerals were investigated as solid precursors for geopolymerization. The particle size distribution, B.E.T surface area, thermal activation, and chemical and mineralogical compositions were used to evaluate the reactivity of iron-rich laterites (35 wt.% of Fe2O3-FeO). The raw materials in the temperature range between 25 and 500 °C showed geopolymerization behaviour similar to that of metakaolin. At temperatures higher than 500 °C, the coarsening of particles and the decrease of B.E.T surface area correspond to an initial sintering of laterites explaining the poor polycondensation/geopolymerization and the decrease of strength of the final products. The increase of the temperature of calcination of raw laterites between 25 and 500 °C corresponds to a reduction of the setting time of geopolymer products. However, this variation of temperature did not significantly affect the flexural strength that remained between ~ 4 and ~ 6 MPa, confirming the possibility to produce sustainable matrices, with more energy saving, using highly corroded laterites.


2017 - The influence of gibbsite in kaolin and the formation of berlinite on the properties of metakaolin-phosphate-based geopolymer cements [Articolo su rivista]
Tchakoute, H. K.; Ruscher, C. H.; Kamseu, E.; Djobo, J. N. Y.; Leonelli, C.
abstract

Two different kaolins (Kao1, Kao2) containing about 11 and 28% of gibbsite were applied for producing metakaolin-phosphate-based geopolymer cements. These kaolins were transformed to metakaolins by calcination them at 700 °C. Gibbsite contained in these kaolins were transformed to γ-Al2O3 during the calcination. The hardener used in this work was a phosphoric acid solution with molar concentration 10 M. It could be observed that the compressive strength of metakaolin-phosphate-based geopolymer cements (54.41/36.01 MPa) decreases in the course GMK1/GMK2. The both geopolymer cements indicate the formation of berlinite which is well dispersed in GMK1 and therefore reinforced the structure of the specimen. The micrograph images of phosphate-based geopolymer cements GMK2 is heterogeneous while the one of the GMK1 is homogeneous and more compact microstructure. The higher content of gibbsite in Kao2 affects negatively the mechanical and microstructural properties of metakaolin-phosphate-based geopolymer cements.


2017 - Thermal Behavior of Metakaolin-Based Geopolymer Cements Using Sodium Waterglass from Rice Husk Ash and Waste Glass as Alternative Activators [Articolo su rivista]
Tchakouté, Hervé K.; Rüscher, Claus H.; Kong, Sakeo; Kamseu, Elie; Leonelli, Cristina
abstract

The aim of this work was to study the thermal behavior of metakaolin-based geopolymer cements using sodium waterglass (NWG) from rice husk ash and waste glass as alternative alkaline activators. Metakaolin-based geopolymer cements were obtained by adding freshly prepared NWG and metakaolin. The geopolymer cements obtained using sodium waterglass from rice husk ash and the one obtained with sodium waterglass from the waste glass were treated at room temperature for 28 days and then heated at 200, 400, 600 and 800 °C. The results show that the metakaolin-based geopolymer cements lose their compressive strength from room temperature to 400 °C. At 600 °C, the compressive strength of geopolymer cements increases relative up to 200 and 400 °C. At 800 °C, the reduction of compressive strength of geopolymer cements is assigned to the total evaporation of the rest of structural water. However, it is higher than that measured at ambient temperature for geopolymer cement obtained using the sodium waterglass from waste glass but lower for the sample obtained with sodium waterglass from rice husk ash. The total mass loss of geopolymer cements obtained with sodium waterglass from rice husk ash and one obtained with sodium waterglass from waste glass are about 12.57 and 15.04 %, respectively. This suggests that geopolymer cement obtained using sodium waterglass from waste glass are more condensed geopolymer structure indicating that it could a very suitable material for fire resistant application. The results indicate that NWG from rice husk ash and waste glass could be served as suitable alternative activators for producing metakaolin-based geopolymer cements with high-temperature performance.


2017 - Utilization of sodium waterglass from sugar cane bagasse ash as a new alternative hardener for producing metakaolin-based geopolymer cement [Articolo su rivista]
Tchakoute, H. K.; Ruscher, C. H.; Hinsch, M.; Djobo, J. N. Y.; Kamseu, E.; Leonelli, C.
abstract

Sugar cane bagasse ash from SOSUCAM company in Cameroon was used to synthesize sodium waterglass as a new alternative hardener. The new hardener was used to prepare metakaolin-based geopolymer cements. The compressive strength of the resulting geopolymer cement cured at room temperature for 28 days was 32.9 MPa. Samples soaked for 28 days in water in parallel experiments revealed a strength of 31.4 MPa. This shows that exposure of water does not lead to any weakening. The value of water absorption was 7.1% in the water-soaked cements, indicating the presence of fewer pores and voids than in the dry cements. However, in SEM micrographs, the microstructure of geopolymer cement appears rather homogeneous and compact without any change by water soaking. It can thus be concluded that sodium waterglass from sugar cane bagasse ash can be used as an alternative hardener or reactive ingredient for producing geopolymer cement with a high degree of cross-linking geopolymer framework. The use of this low-value silica-rich waste for producing sodium waterglass results in environmental benefits including a significant reduction of CO2 emission and energy consumption compared to the production of commercial sodium waterglass.


2016 - Comparison of metakaolin-based geopolymer cements from commercial sodium waterglass and sodium waterglass from rice husk ash [Articolo su rivista]
Tchakouté, Hervé K.; Rüscher, Claus H.; Kong, Sakeo; Kamseu, Elie; Leonelli, Cristina
abstract

Abstract: Three sodium waterglass (NWG) such as commercial NWG (S1), NWG from pure rice husk ash (S2) and NWG from raw rice husk ash (S3) were applied for producing geopolymer cements using metakaolin (MK) as aluminosilicate source. Geopolymers (Geo1, Geo2 and Geo3) were prepared using each NWG with the molar ratios SiO2/Na2O and H2O/Na2O kept constant at 1.5 and 12, respectively. It could be observed that the water absorption of Geo1, Geo2 and Geo3 is 7, 9 and 13.2 % and the mass loss is 15.8, 14.7 and 12.4 %, respectively. Their compressive strength at 20 days (37.5/34.3/29.6 MPa) and 28 days (43.3/40.3/33.2 MPa) increases with increasing the aging and decreases in the course Geo1/Geo2/Geo3. Their average pore radius (6/8/20 nm) and cumulative pore volumes (155/205/245 mm3/g) increase in the course Geo1/Geo2/Geo3. It is discussed that the presence of phosphate known as corrosion inhibitors in raw rice husk ash hinders the dissolution of SiO2. It entails the formation of NaH2PO4 in S3 which reduces the soluble Si atoms. Therefore, less amount of metakaolin could be dissolved leaving thus a higher amount of unreacted metakaolin particles in Geo3. The reacted volumes and compositions of the geopolymers are different in the three cases, too. A content of approximately 20, 25 and 35 % of unreacted metakaolin was proved for Geo1, Geo2 and Geo3, respectively. Graphical Abstract: [Figure not available: see fulltext.]


2016 - Design of inorganic polymer mortar from ferricalsialic and calsialic slags for indoor humidity control [Articolo su rivista]
Kamseu, Elie; Lancellotti, Isabella; Sglavo, Vincenzo M.; Modolo, Luca; Leonelli, Cristina
abstract

Amorphous silica and alumina of metakaolin are used to adjust the bulk composition of black (BSS) and white (WSS) steel slag to prepare alkali-activated (AAS) mortars consolidated at room temperature. The mix-design also includes also the addition of semi-crystalline matrix of river sand to the metakaolin/steel powders. The results showed that high strength of the steel slag/metakaolin mortars can be achieved with the geopolymerization process which was particularly affected by the metallic iron present into the steel slag. The corrosion of the Fe particles was found to be responsible for porosity in the range between 0.1 and 10 μm. This class of porosity dominated (~31 vol %) the pore network of B compared to W samples (~16 vol %). However, W series remained with the higher cumulative pore volume (0.18 mL/g) compared to B series, with 0.12 mL/g. The maximum flexural strength was 6.89 and 8.51 MPa for the W and B series, respectively. The fracture surface ESEM observations of AAS showed large grains covered with the matrix assuming the good adhesion bonds between the gel-like geopolymer structure mixed with alkali activated steel slag and the residual unreacted portion. The correlation between the metallic iron/Fe oxides content, the pore network development, the strength and microstructure suggested the steel slag's significant action into the strengthening mechanism of consolidated products. These products also showed an interesting adsorption/desorption behavior that suggested their use as coating material to maintain the stability of the indoor relative humidity.


2016 - Potassium alkali concentration and heat treatment affected metakaolin-based geopolymer [Articolo su rivista]
Tippayasam, Chayanee; Balyore, Pongpob; Thavorniti, Parjaree; Kamseu, Elie; Leonelli, Cristina; Chindaprasirt, Prinya; Chaysuwan, Duangrudee
abstract

Geopolymers prepared using KOH and K2SiO3 alkali solution instead of the more common NaOH and Na2SiO3 are reported. The influence of KOH concentration, curing temperature and heat treatment on the properties of metakaolin-based geopolymers were studied. The KOH concentrations were varied at 6, 8, 10, 20, 30 and 40 M, the K2SiO3/KOH ratios used were 1 and 1.5 and curing temperatures of 40 °C and 60 °C for 24 h were applied. Results showed that geopolymer with 10 M KOH, cured at 40 °C, 24 h and heat treated at 550 °C gave the highest compressive strength at 28 days. The heat treatment process caused the porosity of geopolymer increased because water was eliminated from the geopolymer structure by the applied heat, therefore, the density decreased whereas the water absorption and the porosity of geopolymer specimens increased. The microstructure of heat-treated specimens showed more mature geopolymer matrix than that of non heat-treated ones leading to higher compressive strength in the former geopolymers and had ceramic-like property.


2016 - Self-compacting geopolymer concretes: Effects of addition of aluminosilicate-rich fines [Articolo su rivista]
Kamseu, Elie; Ponzoni, Chiara; Tippayasam, Chayanee; Taurino, Rosa; Chaysuwan, Duangrudee; Sglavo, Vincenzo M.; Thavorniti, Parjaree; Leonelli, Cristina
abstract

The presence of alunimosilicate based fine aggregates (2.5 to 7.5 wt%) effectively acted to densify the microstructure of the interfacial zone with a reduction of pore threshold and mean pore size jointly with change on the fracture mode of the Self-Compacting (SC) geopolymer concretes. From the results, pumice and recycled glass with amorphous structure improved the bi-axial four-point flexural strength from 5 to 8 MPa while semi-crystalline feldspar sludge (nepheline syenite) reached 11 MPa. The formation of additional geopolymer gels were responsible for the strengthening mechanism. The specimens with amorphous fines showed the tendency to delay the desorption in the laboratory conditions indicating the need for a very long curing time for the final consolidation. The semi-crystalline fines -nepheline syenite- appeared appropriate for the design of self-compacting geopolymer concretes due to their bulk composition, capacity to enhance densification and strength with low deformation rate, in a short range of curing together with a high rate of desorption, all important parameters for the prediction of the durability of concretes.


2015 - Cleaner production of the lightweight insulating composites: Microstructure, pore network and thermal conductivity [Articolo su rivista]
Fongang, R. T. Tene; Pemndje, J.; Lemougna, P. N.; Melo, U. Chinje; Nanseu, C. P.; Nait Ali, B.; Kamseu, Elie; Leonelli, Cristina
abstract

Inorganic polymer cement paste was used as cleaner binder for the design of lightweight matrices as insulating envelopes and panels in building and construction industries. Sponge-like structure with a homogeneously distributed pore network, low density and low thermal conductivity permitted to classify the geopolymer-wood fiber composites promising clean insulating materials. Matrices with the density ∼0.79 g/cm<sup>3</sup>, bi-axial four-point flexural strength of ∼4 MPa presented thermal conductivity between 0.2 and 0.3 W/(m K). The possibility of substituting the sodium silicate with rice ash-NaOH system and the efficiency of the matrices to constitute an effective tortuous road for the thermal gradient improved the sustainability and quality of this new class of products. The pores network and the microstructure approximated by a spatial periodic geometry suggested a "macro transport" mechanism to explain the movement of heat across the matrix of light geopolymer composite.


2015 - Cold-setting refractory composites from cordierite and mullite-cordierite design with geopolymer paste as binder: Thermal behavior and phase evolution [Articolo su rivista]
Djangang, Chantale N; Tealdi, Cristina; Cattaneo, Alice S.; Mustarelli, Piercarlo; Kamseu, Elie; Leonelli, Cristina
abstract

Cordierite and mullite-cordierite based geopolymer binders were prepared as refractory bonds to embed coarse kyanite aggregates. Alkali activation was used to consolidate the refractory at room temperature and generate a reactive interface between the matrix and the aggregates. The flexural strength at room temperature of consolidated materials was 11 MPa without kyanite addition, whilst it reached 28 MPa when kyanite was added. The latter showed thermal expansion near to zero up to 500 °C, followed by an expansion of ∼0.5% up to 1000 °C, then a decrease between 1000 and 1050 °C, concluding with a constant value of expansion <0.5% up to 1250 °C. The increase in expansion was found to be linked to the transformation of the geopolymer into ceramic bond with the formation of crystalline phases, while the decrease was apparently related to the liquid phase sintering. The stability of mullite, cordierite and leucite formed up to 1250 °C was responsible for the constant expansion observed up to this temperature. The mechanical properties, the phase evolution and the thermal behavior of the K2O-MgO-Al2O3-SiO2 bonds, together with the refractory behavior of kyanite aggregates, were found suitable for the design of sustainable cold-setting refractory composites.


2015 - Cumulative pore volume, pore size distribution and phases percolation in porous inorganic polymer composites: Relation microstructure and effective thermal conductivity [Articolo su rivista]
Kamseu, Elie; Ngouloure, Zénabou N. M.; Ali, Benoît Nait; Zekeng, S.; Melo, U. C.; Rossignol, S.; Leonelli, Cristina
abstract

Rice hush (R) and volcanic (P) ashes, two recycled natural wastes were used for their high amorphous silica to improve the homogeneity and structure composition of inorganic polymer pastes before the expansion with aluminum powder. The fine powders were found to be appropriate in enhancing the geopolymerization and expansion conducting to lightweight structure with pore size and pore distribution linked to the viscosity, the concentration of blowing agent, and the crystalline nature of the waste. From the Stereo optical microscope, environmental scanning microscope and the mercury intrusion porosimetry used for the characterization, it appeared that in the interval of complete percolation of the skeleton, there exists correlation between the viscosity, expansion, roundness of pores, pores size distribution. The interpretation of the microstructure of porous geopolymer in this interval allows the description of their effective thermal conductivity with the Maxwell-Eucken model and the novel effective medium theory proposed recently.


2015 - Influence of fine aggregates on the microstructure, porosity and chemico-mechanical stability of inorganic polymer concretes [Articolo su rivista]
Kamseu, Elie; Ponzoni, Chiara; Tippayasam, Chayanee; Taurino, Rosa; Chaysuwan, Duangrudee; Bignozzi, Maria Chiara; Barbieri, Luisa; Leonelli, Cristina
abstract

This work investigates the effects of the structure, the bulk chemical composition and amount of the aluminosilicate fines on the strength development, pore refinement, water permeability, moisture control capacity and the microstructure of inorganic polymer concretes (IPC). The amorphous fines, one from pumice and another from recycled glass, presented sponge-like microstructure with tortuous pore network that maintained the presence of fine capillary pores while semi-crystalline feldspar sludge, the third type of fine aggregates used for this study, showed more dense and compact microstructure that explain the higher strength enhancement. Both amorphous and semicrystalline fines contributed to decrease the porosity, improve the strength and microstructure. However, based on the moisture control capacity and the durability indicators, the fine aggregate derived from semicrystalline feldspar was found to be more appropriate and efficient for the development of IPC at short time scale of curing. Pumice fine aggregate was found to be effective only with a long term curing.


2015 - Recycled natural wastes in metakaolin based porous geopolymers for insulating applications [Articolo su rivista]
Ngouloure, Zénabou N. M.; Nait Ali, Benoît; Zekeng, S.; Kamseu, Elie; Melo, U. C.; Smith, D.; Leonelli, Cristina
abstract

The effectiveness of two amorphous silica based wastes, rice husk ash and volcanic ash powders, used to act as structural reinforcement and partial replacement of metakaolin in porous matrices for thermal isolation was assessed. Both wastes produced colloidal phase that contributed to improve the reactivity and homogeneity of the matrices enhancing the mechanical strength. Rounded pores were obtained in relation with significant reduction of the interpore partitions under controlled addition of the blowing agent. The bulk thermal conductivity decreased from 0.6 to less than 0.15 W m-1 K-1 with the increase of the concentration of blowing agent. The final matrix presented pore size distribution and pore connectivity that allows analytical description and prediction of their effective thermal conductivity.Results demonstrated that clear relations can be established among the viscosity of the pastes, chemical composition, amount of blowing agent and the volume expansion/pore size distribution.


2015 - Transformation of the geopolymer gels to crystalline bonds in cold-setting refractory concretes: Pore evolution, mechanical strength and microstructure [Articolo su rivista]
Kamseu, Elie; Djangang, Chantale; Veronesi, Paolo; Andreola, Nora Maria; Melo, Uphie Chinje; Sglavo, Vincenzo Mario; Leonelli, Cristina
abstract

Two K2O-MgO-Al2O3-SiO2 based geopolymer gels with bulk chemical composition corresponding to cordierite (Co) and 1:1 mullite-cordierite (MuCo) were successfully transformed to crystalline bonds in high temperature service of cold-setting made refractory concretes. Kyanite aggregates changed the flexural strength of the gels from11 to 28 MPa due to the development of good adhesive bonds. Under thermal cycles, up to 1250 °C, the cumulative pore volume remained at 0.09 mL/g, as fromthe absence of important densification/shrinkage. However, the behavior of the cumulative pore volume curves changed from that of a matrix with a wide range of distribution of pore sizes to that, of matrix, consisting of relatively coarse grains. The latter exhibits a rise at 10 μm as void spaces created around the contact points among the coarse kyanite grains and that at 0.054 μm as poreswithin the crystalline phases (cordierite, kalsilite, leucite,mullite, enstatite) formed. Themicrostructural observations confirmed the transformation of gel pores (size around 0.01 μm) to interparticle and intergranular pores due to the crystallization. The flexural strength of refractory concretes increased from28MPa to 40MPa in agreement with the increase in the elastic modulus from 9 to 30 GPa. The crystallization was enhanced by the MgO content (being important in Co compared to MuCo) and the kyanite concentration as particles of kyanite effectively acted as phase separation and nucleation sites


2014 - A sustainable approach for the geopolymerization of natural iron-rich aluminosilicate materials [Articolo su rivista]
Obonyo, Esther A.; Kamseu, Elie; Lemougna, Patrick N.; Tchamba, Arlin B.; Melo, Uphie C.; Leonelli, Cristina
abstract

Two iron-rich clayey materials (L1 and L2, with the main difference being the level of iron accumulation) have been studied for their suitability as solid precursors for inorganic polymer composites. L1, with the lower iron content, was calcined at 700°C for 4 h and used as replacement, in the range of 15-35 wt%, for both raw laterites in the formulations of geopolymeric composites. The different mixtures were activated with a highly concentrated alkaline solution containing sodium hydroxide and sodium silicate. River sand with semi-crystalline structure was added to form semi-dry pastes which were pressed to appropriate shape. X-ray diffraction, Infrared spectroscopy, Scanning Electron Microscopy and Mercury Intrusion Porosimetry results demonstrated the effectiveness of the calcined fraction of L1 to act as nucleation sites and extend the geopolymerization to the matrix composites. A highly compact matrix with low porosity and good stability in water, together with a strength comparable to that of standard concretes was obtained allowing for conclusions to be made on the quality of laterites as promising solid precursor for sustainable, environmentally-friendly, and cost-efficient structural materials. © 2014 by the authors.


2014 - Binder chemistry – Low-calcium alkali-activated materials [Capitolo/Saggio]
Provis, John L.; Fernández Jiménez, Ana; Kamseu, Elie; Leonelli, Cristina; Palomo, Angel
abstract

Early developments in the developments of low-calcium (including calcium-free) alkali-activated binders were led by the work of Davidovits in France, as noted in Chap. 2. These materials were initially envisaged as a fire-resistant replacement for organic polymeric materials, with identification of potential applications as a possible binder for concrete production following relatively soon afterwards [1]. However, developments in the area of concrete production soon led back to more calcium-rich systems, including the hybrid Pyrament binders, leaving work based on the use of low-calcium systems predominantly aimed at high-temperature applications and other scenarios where the ceramic-like nature of clay-derived alkali-activated pastes was beneficial. Early work in this area was conducted with an almost solely commercial focus, meaning that little scientific information was made available with the exception of a conference proceedings volume [2], several scattered publications in other conferences, and an initial journal publication [3]. Academic research into the alkaline activation of metakaolin to form a binder material led to initial publications in the early 1990s [4, 5], and the first description of the formation of a strong and durable binder by alkaline activation of fly ash was published by Wastiels et al. [6-8]. With ongoing developments in fly ash activation, which offers more favourable rheology than is observed in clay-based binders, interest in low-calcium AAM concrete production was reignited, and work since that time in industry and academia has led to the development of a number of different approaches to this problem. A review of the binder chemistry of low-calcium AAM binder systems published in 2007 [9] has since received more than 350 citations in the scientific literature, indicating the high current level of interest in understanding and utilisation of these types of gels.


2014 - Metakaolin-based inorganic polymer composite: Effects of fine aggregate composition and structure on porosity evolution, microstructure and mechanical properties [Articolo su rivista]
Kamseu, E.; Cannio, M.; Obonyo, E. A.; Tobias, F.; Bignozzi, M. C.; Sglavo, V. M.; Leonelli, C.
abstract

This paper examines the phase transformation, pore evolution, microstructural and mechanical changes that occur in inorganic polymer cement (IPC) in the presence of three different grade of fine aggregates (φ &lt; 100 μm) of ladle slag, nepheline syenite and quartz sand. Experimental results indicate that polycondensation was enhanced in nepheline syenite based specimens, compared to quartz sand, due to the increase in HMAS phases in relation to the dissolution and interaction of amorphous/disordered fraction of aggregates. HCS and HCAS with HMAS phases were identified in the ladle slag based specimens. The formation of these new phases reduced both the cumulative pore volume and pores size. The apparent increase in volume of capillary pores in ladle slag based specimens was explained by the residual bubbles from the carbonates included in raw slag. The flexural strength of the inorganic polymer cement increases from 4 MPa to 4.2, 4.8 and 6.8 MPa with the addition of 20 wt% of quartz sand, nepheline syenite and ladle slag respectively. These values increase significantly between 28 and 180 days of curing (9.1 MPa for ladle slag and 10.0 MPa for nepheline syenite). It was concluded that fines can be used to remove the HM and poorly bounded alumina oligomers in metakaolin based inorganic polymer matrices and improve the interfacial zone for the design of an optimum grade and high-performance composites. © 2014 Elsevier Ltd. All rights reserved.


2014 - Reaction sintering and microstructural evolution in metakaolin-metastable alumina composites [Articolo su rivista]
Djangang, Chantale Njiomou; Tchamba, Arlin Bruno; Kamseu, Elie; Melo, Uphie Chinje; Elimbi, Antoine; Ferrari, Anna Maria; Leonelli, Cristina
abstract

Fine needles of mullite grains were obtained successfully in a compact and low porous matrix using solid state sintering. We treated high-grade kaolin and sand-rich kaolin at 750 °C to amorphous metakaolins, and bauxite at 1,000 °C to metastable alumina. By designing a stochiometric composition of mullite, each amorphous metakaolin was added to metastable alumina. Fine grains of mullite with almost complete crystallization were obtained from 1,350 °C in a case of amorphous metakaolin from high-grade kaolin and at 1,550 °C in the other case where amorphous metakaolin is from sand-rich kaolin. The difference in the temperatures of mullitization was linked to the late dissolution of silica from the cristobalite and quartz phases which were still present in the sand-rich metakaolin sample at 1,350 °C. The use of metastable alumina and metakaolin instead of kaolin to design the mullite matrix allows the increase in number of mullite nucleation sites. This results to high densification and crystallization, fine grain size, and high mechanical properties of the final matrix. © 2014 Akadémiai Kiadó, Budapest, Hungary.


2013 - Induration of laterites in tropical areas: Assessment for potential structural applications [Articolo su rivista]
Kamseu, E.; Nzeukou, A.; Lemougna, P.; Billong, N.; Melo, U. C.; Leonelli, C.
abstract

Indurated lateritic blocks (yellow-brown and red) were collected from two deposits in Yaounde, Cameroon for investigation as structural building and construction materials. Dimensioned blocks were characterized using XRD, DTA/TGA, mechanical compression, water absorption and porosity tests, and examination by optical and electron microscope. Water absorption values, pore size distribution and cumulative pore volume were used to compare indurated laterites with fired day-based bricks. Atmospheric exposure of the test specimens resulted in progressive strengthening of the matrix and transformation of yellow areas to a browner colour. This confirms other observations in the literature which describe induration as the transformation of goethite to hematite with red matrix as the end step and most stable laterite form. Presence of larger size pores and significant pore-to-surface area ratio negatively affect the material's compressive strength. However, due to stability in water, blocks with significant phase distribution and amorphous interlinking are suitable as structural building and construction materials.


2013 - Mix-design and characterization of alkali activated materials based on metakaolin and ladle slag [Articolo su rivista]
Maria Chiara, Bignozzi; Stefania, Manzi; Lancellotti, Isabella; Kamseu, Elie; Barbieri, Luisa; Leonelli, Cristina
abstract

Recycling industrial waste to produce newmaterials is a driving path to promote a sustainable development. Alkali activation can be a very effective tool to reach this goal especially when the starting material can be carbon fly ash and blast furnace slag instead of calcined natural clays such as metakaolin. With the aim to further increase the type ofwaste to be used as precursor and to promote a new recycling route, alkali activated materials based on partial substitution of metakaolin with ladle slag, deriving from the refining process of steel produced by arc electric furnace technology, are reported. In particular, being ladle slag rich in Ca-containing crystalline phases, its effect on the consolidation process has been investigated by means ofmicrostructure analysis carried out with XRD, SEM and MIP techniques. The results show that ladle slag are activated by alkaline solutions and participate in gels formation. Indeed, an optimization in terms of ladle slag content (60–80 wt.%) and the coexistence of different types of gels (3D aluminosilicate, C-S-H and Ca-rich aluminosilicate) have been envisaged.


2013 - Porcelain stoneware with pegmatite and nepheline syenite solid solutions: Pore size distribution and descriptive microstructure [Articolo su rivista]
Kamseu, E.; Bakop, T.; Djangang, C.; Melo, U. C.; Hanuskova, M.; Leonelli, C.
abstract

Investigations correlating the pore size distribution-cumulative pore volume to the microstructure are used to compare the efficiency of two solid solutions of pegmatite and nepheline syenite as fluxing agents for the design of porcelainized stoneware. Particularly the fusibility of the two solid solutions was modified by adjusting the CaO content of the bodies. As results, the pegmatite based flux produced an extended viscous phase capable on embedding the crystalline phases and close open porosity as from 1175°C. Conversely, the bodies with nepheline syenite remained relatively porous up to 1225°C although the similar results of the mechanical strength at this temperature. The investigations on microstructure, pores size distribution and cumulative pore volume indicated almost complete reduction of the open pores in the pegmatite based bodies and the development of a band of closed pores ranged between 0.080 and 0.9μm showing P series as a more compact structure. For the nepheline syenite based bodies, the incomplete reduction of the open pores and the relative absence of the band of pores between 0.080 and 0.9μm were ascribed to the difference in fusibility and the viscosity of the glassy phases. These differences were interpreted in term of the differential action of CaO in Na2O-Al2O3-SiO2 and K2O-Al2O3-SiO2 on the amount and viscosity of the liquid phase formed already described in the literature. © 2013 Elsevier Ltd.


2013 - Sintering behaviors of two porcelainized stoneware compositions using pegmatite and nepheline syenite minerals [Articolo su rivista]
Tchakounte Bakop, T.; Tene Fongang, R. T.; Melo, U. C.; Kamseu, E.; Miselli, P.; Leonelli, C.
abstract

Semi-vitreous bodies, with flexural strength of ~78 MPa and water absorption of ~0.4 % for the optimal maturated specimens, were successfully prepared with solid solutions of pegmatite and nepheline syenite, respectively, for the full dense (P) and relatively porous composition (G). Despite the similarity on the bulk chemical composition of the two formulations, it was found that their thermal behaviors were significantly affected by the action of CaO on the flux system considered leading to earlier vitrification of P specimens with high flexural strength as from 1,175 C. Conversely, the flexural strength of G specimens increases progressively with soaking time and temperature development up to 1,225 C. The positive action of 5 mass% of CaO in the vitrification range of pegmatite solution, the relative low temperature of maturation of the semi-vitreous matrices, and the results of water absorption allow us to describe the formulations studied to offer promising potential in the production of sustainable and low-cost porcelainized stoneware. The high strength of P at relatively low temperature could be explained by the matrix-strengthening theory, while the extent of crystallization of G could be ascribed to the mullite theory. © 2013 Akadémiai Kiadó, Budapest, Hungary.


2012 - Bulk composition and microstructure dependence of effective thermal conductivity of porous inorganic polymer cements [Articolo su rivista]
Kamseu, Elie; B., Nait Ali; M. C., Bignozzi; Leonelli, Cristina; S., Rossignol; D. S., Smith
abstract

Experimental results and theoretical models are used to assess the effective thermal conductivity of porous inorganic polymer cements, often indicated as geopolymers, with porosity between 30 and 70 vol.%. It is shown that the bulk chemical composition affects the microstructure (grains size, pores size, spatial arrangement of pores, homogeneity, micro cracks, bleeding channels) with consequently the heat flow behaviour through the porous matrix. In particular, introduction of controlled fine pores in a homogeneous matrix of inorganic polymer cements results in an increase of pore volume and improvement of the thermal insulation. The variation of the effective thermal conductivity with the total porosity was found to be consistent with analytical models described by Maxwell–Eucken and Landauer.


2012 - Correlation between microstructural evolution and mechanical properties of a-quartz and alumina reinforced K-geopolymers during high temperature treatments [Articolo su rivista]
Kamseu, E.; Catania, V.; Djangang, C.; Sglavo, V. M.; Leonelli, C.
abstract

Geopolymer material based K 2O-Al 2O 3-SiO 2 systems were investigated for high temperature applications. High viscous geopolymer paste was prepared using standard grade metakaolin dissolved in potassium hydroxide/potassium silicate solution (volume ratio, 1 : 1). The alkalinity of the solution was predetermined to optimise the dissolution of amorphous aluminosilicate. Quartz sand and alumina (25, 50 and 75 wt-%) were successively introduced as filler to form refractory concretes. RGPS4, RGPS2 and RGPS34 for sand and RGPA4, RGPA2 and RGPA34 for alumina were produced. The samples obtained were cured in sealed plastic containers for 7 days at room temperature before sintering at 200, 800, 1000, 1100 and 1200°C. The heating rate was 5°C min -1, and the dwelling time at peak temperature completes the sintering time to 4 h. Unvaried mechanical strength, up to 800°C, was observed: ~25 MPa for biaxial and ~20 MPa for uniaxial four-point bending strengths. This behaviour was ascribed to the maintenance of the structure of the geopolymer materials within the temperature interval considered. Above this temperature, all the samples presented significant densification; the most important increase in mechanical strength was ~65 and ~60 MPa respectively for biaxial and uniaxial four-point bending strengths. This was accompanied by a decrease in porosity. The dense structures observed at 1000-1100°C were affected by a further increase in temperature. Microcracks, vitrification and deformation appeared at 1200°C, which can be considered as detrimental to the mechanical properties. The mechanical properties and the microstructural evolution were found to be influenced by the amount of fillers added. Si and Al rich geopolymer concretes were found promising for the development of potential thermoresistant materials through the cold process. © 2012 Institute of Materials, Minerals and Mining.


2012 - Insulating behavior of metakaolin-based geopolymer materials assess with heat flux meter and laser flash techniques [Articolo su rivista]
Kamseu, Elie; B., Ceron; H., Tobias; Leonelli, Cristina; M. C., Bignozzi; Muscio, Alberto; Libbra, Antonio
abstract

Thermo physical behavior of metakaolin-based geopolymer materials was investigated. Five compositions of geopolymers were prepared with Si/Al from 1.23 to 2.42 using mix of sodium and potassium hydroxide (~7.5 M) as well as sodium silicate as activator. The products obtained were characterized after complete curing to constant weight at room temperature. The thermal diffusivity (2.5-4.5 × 10-7m2/s) and thermal conductivity (0.30-0.59 W/m K) were compared to that of existing insulating structural materials. The correlation between the thermal conductivity and parameters as porosity, pore size distribution, matrix strengthening, and microstructure was complex to define. However, the structure of the geopolymer matrix, typical porous amorphous network force conduction heat flux to travel through very tortuous routes consisting of a multiple of neighboring polysialate particles.


2012 - Mechanical and biological characterization of geopolymers for potential application as biomaterials [Articolo su rivista]
M., Catauro; F., Bollino; I., Kansal; Kamseu, Elie; Lancellotti, Isabella; Leonelli, Cristina
abstract

In this study three different geopolymer compositions have been investigated and characterized as potential biomaterials. Two geopolymer formulations are mainly composed of metakaolin, with some silica additions so that to reach Si/Al = 2.10 molar ratio, the third one contains a reduced amount of metakaolin and it is constitutes mainly of silica gel with composition: H24AlK7Si31O79 with Si/Al = 31. While in the first two formulations the powders were added of NaOH and sodium silicate in different percentages as activator and ligand, respectively, in the third one two different KOH addition methods (separately or jointly with potassium silicate solution) were performed. Room temperature consolidation was followed by thermal activation of composition Si/Al=31 at 60°C for 150 min and at 500°C for 180 min. The work presents exhaustive microstructural characterization (FT-IR, SEM/EDS, XRD) jointly with compression resistance tests and bioactivity studies on pressed powders of the two geopolymers. The materials were composed of amorphous aluminosilicates and a limited amount of zeolitic phases, found on the top surface. The compressive strength of the first two compositions was higher than 15 MPa and flexural strength around 2 MPa after 2 days of curing at room temperature. Compressive strength tests were carried out on Si/Al = 31 geopolymer on both activated sample series and demonstrated that when added separately the activator leads to more fragile specimens (0.90 MPa vs 1.95 MPa). To authors knowledge the effect of geopolymer preparation on mechanical properties of thermally activated Si/Al = 31 formulation has never been proved before. The bioactivity was successfully tested with the soaking of the samples in a simulated body fluid (SBF) for 3 weeks. The formation of a layer of hydroxyapatite on the surface of the materials was shown both by SEM micrograph and EDS analysis.


2012 - Procedimento per l'inertizzazione di rifiuti liquidi [Brevetto]
Leonelli, Cristina; Barbieri, Luisa; Lancellotti, Isabella; Kamseu, Elie; Ponzoni, Chiara
abstract

Un procedimento per l’inertizzazione di rifiuti liquidi che comprende le fasi di: - selezionare un rifiuto liquido contenente ioni di metalli pesanti in soluzione, sali solubili e sostanza organica; - aggiungere a detto rifiuto liquido una polvere alluminosilicatica atta a geopolimerizzare; - mescolare fino all’ottenimento di un impasto omogeneo; e - essiccare l’impasto ottenuto.


2011 - Advancing the use of secondary inputs in geopolymer binders for sustainable cementitious composites: A review [Articolo su rivista]
Obonyo, E.; Kamseu, E.; Melo, U. C.; Leonelli, C.
abstract

Because of concerns over the construction industry's heavy use of cement and the general dissatisfaction with the performance of building envelopes with respect to durability, there is a growing demand for a novel class of "green" binders. Geopolymer binders have re-emerged as binders that can be used as a replacement for Portland cement given their numerous advantages over the latter including lower carbon dioxide emissions, greater chemical and thermal resistance, combined with enhanced mechanical properties at both normal and extreme exposure conditions. The paper focuses on the use of geopolymer binders in building applications. It discusses the various options for starting materials and describes key engineering properties associated with geopolymer compositions that are ideal for structural applications. Specific properties, such as compressive strength, density, pore size distribution, cumulative water absorption, and acid resistance, are comparable to the specifications for structures incorporating conventional binders. This paper presents geopolymer binders, with their three dimensional microstructure, as material for structural elements that can be used to advance the realization of sustainable building systems. © 2011 by the authors.


2011 - Evolution of fired clay products: From origin to sustainable building ceramics [Articolo su rivista]
Kamseu, E.; Leonelli, C.; Obonyo, E.
abstract

Nowadays, the design of building and construction materials should be straightly linked to the environmental context of industrial development and the many regulations and constraints linked to energy, ecosystems, geography and communities. In one word, building materials today have to be sustainable. In this paper, the authors turn back to the history of structural clay products and described their evolution and the factors that have affected the evolution of their products.


2011 - Polysialate matrixes from Al-rich and Si-rich metakaolins: Polycondensation and physico-chemical properties [Articolo su rivista]
Kamseu, E.; Leonelli, C.; Chinje Melo, U. F.; Perera, D.; Lemougna, P. N.
abstract

Two metakaolins from Al-rich and Si-rich kaolinitic clays were used to design polysialate matrices with different Si/Al and NaK/Al ratios. The aim was to investigate the influence of oligomers formed during dissolution and hydrolysis on the polycondensation and transformation to hard and stable matrices. Products of geopolymerization of the different matrices were subjected to mechanical testing considering various loading configurations. The geopolymer matrices showed compressive strength from 51 ± 5 MPa (Si/Al=1.23) to 61 ± 2 MPa (Si/Al = 2.42) and bi-axial four-point strength from 11 ± 2 MPa to 16 ± 1.1 MPa respectively. These results were consistent with density, leaching ability and microstructure. It is proposed that the mechanical properties and the stability of the products of reactions can be discussed as the important parameters for the evaluation of the quality of geopolymer matrices. Moreover, polycondensation and the final performance of the product are greatly influenced by the unreacted crystalline or semi-crystalline phases that act as fillers and contribute to increased stability and mechanical properties. A good geopolymer material resulting from our study will be defined as an amorphous matrix of polysialates in which various unreacted or partly reacted crystalline phases are embedded. It is suggested that Si-rich metakaolin will present the more hardening and stable matrix with shorter setting time leading to small pores and an enhanced interlocked microstructure.


2010 - Alkali-silica glassy matrixes (AGM ) as replacement for feldspar in conventional porcelain compositions [Articolo su rivista]
Kamseu, Elie; Leonelli, Cristina; Boccaccini, Dino Norberto; Veronesi, Paolo; V. M., Sglavo; U. C., Melo; D., Njopwouo
abstract

The effect of alkali-silica glassy matrixes (AGM), as replacement for feldspar, on the microstructure, physical properties and mechanical strength of conventional porcelain has been studied. AGM with chemical composition similar to feldspars has been prepared to introduced alkali-ions (Na+ and K+) in porcelain compositions. It has been found that the replacement of feldspar by AGM ameliorates the mechanical properties of the material. The improvements are attributed to sharp changes in the microstructure as result of a reduction of glassy phase and increase in crystalline mullite amount. AGM were found to be promising candidates as substitutes for feldspar in conventional porcelain.


2010 - Chemical and biological characterization of geopolymers for potential application as hard tissue prostheses [Relazione in Atti di Convegno]
Michelina, Catauro; Flavia, Bollino; Lancellotti, Isabella; Kamseu, Elie; Leonelli, Cristina
abstract

In this study different geopolymers have been investigated and characterized as potential biomaterials. The work presents exhaustive FT-IR, SEM/EDS and X-ray diffraction studies of twogeopolymer formulations, where water content, water to solid content and curing conditions have been varied during mixing stage, maintaining constant the ratios among Na-Al-Si. The amorphous matrix is typical of sodium aluminosilicates, as shown by the FT-IR spectra. The presence of zeolitic phases has been observed by XRD at the surface of the material while the main matrix was characterized by amorphous aluminosilicate phases. The compressive strength of all the compositions was higher than 50 MPa. In order to study their bioactivity, samples of the studied materials were soaked in a simulated body fluid (SBF). The bioactivity of the synthesized geopolymers was shown by the formation of a layer of hydroxyapatite on the surface of thematerials by using the SEM.


2010 - Chemical stability of geopolymers containing municipal solid waste incinerator fly ash [Articolo su rivista]
Lancellotti, Isabella; Kamseu, Elie; Michelazzi, Marco; Barbieri, Luisa; Corradi, Anna; Leonelli, Cristina
abstract

Municipal solid waste incinerators every year produce tons of fly ashes which, differently from coal fly ashes, contain large amounts of toxic substances (heavy metals, dioxins, furans). The stabilization/solidification (S/S) technology known as geopolymerization is proposed with the purpose to bond physicallyand chemically incinerator fly ashes (IFA) in a solid matrix, in order to reduce pollutant mobility. The chemical stability of geopolymers with Si/Al ratio of 1.8–1.9 and Na/Al ratio of 1.0, synthesized by alkali activation of metakaolin and the addition of 20 wt% of two different kinds of IFA, is presented. The concentration of the alkaline solution, water to solid ratio and curing process have been optimized. The room temperature consolidation of IFA containing geopolymers has been tested for leachability in water for 1 day, accordingly to EN 12457 regulation and extended to 7 days to increase the water attack on solid granules. Leachable metals in the test solution, determined by ICP_AES, fall within limit values set by regulation for non-dangerous waste landfill disposal. Geopolymeric matrix evolution with leaching time has been also evaluated in terms of pH and electrical conductivity increase in solution.


2010 - Geopolymers sintering by optical dilatometry [Relazione in Atti di Convegno]
Kamseu, E.; Leonelli, C.; Perera, D. S.
abstract


2010 - Materie prime di origine naturale nel processo di geopolimerizzazione [Articolo su rivista]
Leonelli, Cristina; Kamseu, Elie; Valentina, Medri; Samanta, Fabbri
abstract

Geopolymers are inorganic materials prepared via a room temperature treatment (25-120°C) with alkali activation. The main applications of these materials is in the field of building materials, recycle and inertization of waste, restoration. The production and final product is optimised by a careful selection of starting materials, i.e. aluminosilicate powders. In this paper are presented aluminosilicates from natural source, as an example kaolin, clays or volcanic ash. Metakaolin is the most reactive due to its amorphous structure and aluminium coordination; its reactivity is also influenced by its mineralogical origin, morphology of grains, and calcinations method. Volcanic ash present lower reactivity and the better consolidation temperature to obtain mechanically strong materials appears to be around 400°C.


2010 - Transformation of polysialate matrixes from Al-rich and Si-rich metakaolins: Polycondensation and physico-chemical properties [Relazione in Atti di Convegno]
Kamseu, E.; Leonelli, C.
abstract

Two metakaolins from Al-rich and Si-rich kaolinitic clays were used to design polysialate matrices with different Si/Al and NaK/Al ratios. The aim was to investigate the influence of oligomers formed during dissolution and hydrolysis on the polycondensation and transformation to hard and stable matrices. Products of geopolymerization of the different matrices were subjected to mechanical testing considering various loading configurations. The geopolymer matrices showed compressive strength from 51 ± 5 MPa (Si/Al = 1.23) to 61 ± 2 MPa (Si/Al = 2.42) and bi-axial four-point strength from 11 ± 2 MPa to 16 ± 1.1 MPa respectively. These results obtained were consistent with density, leaching ability, and microstructure. It is proposed that the mechanical properties and the stability of the products of reactions can be discussed as the important parameters for the evaluation of geopolymer matrices. Moreover, polycondensation and the final performance of the product are greatly influenced by the unreacted crystalline or semi-crystalline phases that act as fillers and contribute to increase the stability and mechanical properties.


2009 - Alkali-ions diffusion, mullite formation, and crystals dissolution during sintering of porcelain bodies: Microstructural approach [Articolo su rivista]
Leonelli, C.; Kamseu, E.; Boccaccini, D. N.; Sglavo, V. M.; Pellacani, G. C.
abstract

The effect of alkali-silicate glassy matrix as replacement for feldspar in soft and hard porcelain compositions was studied. SEM and X-ray diffraction analysis were used to evidence phase evolution. For each composition, the influence of soaking time was evaluated. The difference in chemical composition (amount of alkali and alumina) between the two types of porcelain studied influenced the final microstructure: density, pore size and shape, and mullite content. Quartz dissolution was more important in soft porcelain where the mullitization was limited by the low amount of alumina compared to hard porcelain. Replacing the feldspar by alkali-silicate glassy matrices with similar chemical composition, the amount of secondary mullite and mechanical properties increased in both soft and hard compositions.


2009 - Bi-axial four points flexural and compressive strength of geopolymer materials based Na2O-K2O-Al2O 3-SiO2 systems [Relazione in Atti di Convegno]
Leonelli, C.; Kamseu, E.; Sglavo, V. M.
abstract

Bi-axial four point flexural and compressive strength tests were used for the assessment of mechanical properties of geopolymer material-based, calcined kaolin and kaolinitic clays. Various activating solutions which consist in the mixture of potassium and sodium hydroxide, water and sodium silicate were designed and tested. Six specimens, over a wide number of investigated compositions, were selected with SiO2/Al2O3 varying from 1:1 to 3:1, The compositions 1:1 and 2:1 were obtained by using two different grades of kaolin as raw materials (standard and sand-rich), while the 3:1 was obtained by adding required amounts of silica to either kaolin or kaolinitic clay, All the samples were prepared by slip casting, using density (≈1,5 g/cm3) as indicator of the optimum viscosity for shaping geopolymer pastes, and cured at room temperature for different periods. The bi-axial four points flexural strength values vary from 13 to 21 MPa while the compressive strength vary from 45 to 67 MPa, being essentially influenced by curing time, SiO2/Al2O3 and K 2O/Na2O/H2O ratios, Increasing the SiO 2/Al2O3 ratio from 1:1 to 3:1, the mechanical properties increase but longer setting and curing times were required, Low SiO2/Al2O3 ratio results the appearance of micro cracks and deformations during curing. The flexural and compressive behaviour of the specimens studied were directly correlated to the porosity, density and the final product microstructure. The chemical behaviour of the six compositions is discussed with respect to basic dissolution-hydrolysis- polycondensation processes that occur in Na2O-K2O-Al 2O3-SiO2 systems.


2009 - Dehydration, dehydroxylation, densification and deformation during sintering of geopolymers based on the K2O-Al2O3-SiO2 system [Capitolo/Saggio]
Kamseu, E.; Rizzuti, A.; Leonelli, C.; Perera, D.
abstract

Based on the principle of stability of geopolymer gel as refractory binder, a geopolymeric paste in the K2O-Al2O3-SiO2 system was developed and used to produce refractory concretes by adding various amount of α-quartz sand (grain size in the range 0.1μm-1mm) and fine powder alumina (grain size in the range 0.1-100 μm). The consolidated samples were characterized before and after sintering using optical dilatometer, DSC, XRD and SEM. The total shrinkage in the range of 25-900°C was less than 3%, reduced with respect to the most diffused potassium or sodium based systems, which generally records a &gt;5% shrinkage. The maximum shrinkage of the base geopolymer was recorded at 1000°C with a 17% shrinkage which is reduced to 12% by alumina addition. The maximum densification temperature was shifted from 1000°C to 1150°C or 1200°C by adding 75wt% α-quartz sand or fine powder alumina respectively. The sequences of sintering of geopolymer concretes could be resumed as dehydration, dehydroxylation, densification and finally plastic deformation due to liquid phase appearance. The geopolymer formulations developed in this study appeared as promising candidates for high temperature applications. © 2009 Copyright


2009 - Descriptive microstructure and fracture surface observations of fired volcanic ash [Abstract in Atti di Convegno]
Leonelli, C.; Kamseu, E.; Melo, U. C.; Corradi, A.; Pellacani, G. C.
abstract

Crystals of the pyroxene group (diopside, augite and enstatite, hedenbergite), series of crystals with the general formula: (MgxFe1-x)2SiO4 having various geometry, identified as spinel (and olivine), and plagioclase crystals from anorthite to anorthoclase that grow together in mass having thin parallel groves embedded in a complex matrix together with calcium alumina silicate grains were found to be the descriptive microstructure of fired volcanic ash. Quartz grains were rarely present as confirmed by dilatometry analysis, XRD, SEM and DTA. The presence of dendrites continuously growing to pyroxene crystals indicated the precipitation/crystallization of these crystals from matrix and regions of glass concentration enhance by ions diffusion. Rings of Ti-rich iron micro-crystals observed around spinel (and olivine) suggested the probable nucleating role of these micro-crystals for the precipitation/crystallization phenomenon. The various type of crystals formed, the difference in their geometry and size and their interlocking mechanism results in a contiguous and dense structure with relevant characteristics at relative low temperature (1125-1150°C) confirm volcanic ash as promising alternative raw materials for vitrified ceramic products. It was concluded that controlled precipitation/crystallization of raw volcanic ash results on microstructure similar to that of glass-ceramic materials. The observation of fracture surface allowed comparison of fracture mechanics of volcanic ash ceramic to that of conventional vitrified ceramics. © 2009 Woodhead Publishing Limited.


2009 - Descriptive microstructure and fracture surface observations of fired volcanic ash [Articolo su rivista]
Leonelli, C.; Kamseu, E.; Melo, U. C.; Corradi, A.; Pellacani, G. C.
abstract

Crystals of the pyroxene group (diopside, augite and enstatite, hedenbergite), series of crystals with the general formula (Mg x Fe1-x )2SiO4 having various geometry, identified as spinel (and olivine), and plagioclase crystals from anorthite to anorthoclase that grow together in mass having thin parallel groves embedded in a complex matrix together with calcium alumina silicate grains were found to be the descriptive microstructure of fired volcanic ash. Quartz grains were rarely present as confirmed by dilatometry analysis, XRD, SEM and DTA. The presence of dendrites continuously growing to pyroxene crystals indicated the precipitation/crystallization of these crystals from matrix and regions of glass concentration enhance by ions diffusion. Rings of Ti-rich iron micro-crystals observed around spinel (and olivine) suggested the probable nucleating role of these micro-crystals for the precipitation/crystallization phenomenon. The various types of crystals formed, the difference in their geometry and size and their interlocking mechanism result in a contiguous and dense structure with relevant characteristics at relative low temperature (1125-1150 °C) confirming volcanic ash as a promising alternative raw material for vitrified ceramic products. It was concluded that controlled precipitation/crystallization of raw volcanic ash results on microstructure similar to that of glass-ceramic materials. The observation of fracture surface allowed comparison of fracture mechanics of volcanic ash ceramic to that of conventional vitrified ceramics. © 2009 Springer Science+Business Media, LLC.


2009 - Investigation of volcanic ash based geopolymers as potential building materials [Articolo su rivista]
Kamseu, Elie; Leonelli, Cristina; Perera, D. S.; Melo, U. C.; Lemougna, P. N.
abstract

Volcanic ash powders from Etna (Italy) and Cameroon were used as the principal source of aluminosilicate to produce geopolymers with the potential for making building products. The volcanic ash was ball milled and reacted with concentrated alkaline solutions for polymerisation and subsequent curing at 75-400 °C for 12-48 h. It was found that the gel was more viscous than a similar gel formed from metakaolin. Geopolymers made from both ashes had bulk densities of 1.7-2.0 g/cm3 and water absorption values of 20-25 %. Their compressive strength values were 25-35 MPa and the bi-axial four-point flexura! strength values ranged from 14-20 MPa. These values increased by 20 % when cured for 21 d after 90 d storage. It was also found that by curing at 200-400 °C the mechanical properties increased. Scanning electron micrographs showed that with thermal curing microcrystalline phases were present along with undissolved crystalline phases. These phases remained bound to the matrix and acted as a filler for strengthening the materials. The Ca, Mg and Fe present as impurities in the volcanic ash formed some of these crystalline phases and did not form any deleterious hydroxide or carbonate phases.


2009 - Microstuctural evolution during thermal treatment of three kaolinitic clays from Cameroon [Articolo su rivista]
Kamseu, E.; Braccini, S.; Corradi, A.; Leonelli, C.
abstract

The paper examines the influence of Al2O3/SiO 2 ratio, bulk chemical composition and temperature in mullite nucleation and growth from kaolinitic clays. Samples from NTAMUKA (TAN), Mayouom (MAY) and Wabane (WAB), region of high hills of West-Cameroon, undergo series of phase changes during sintering between 1000 and 1500°C. Phases transformation included: amorphous SiO2 and Al2O 3 as result of breakdown of kaolin above 700°C, nuclei of mullite that growth with temperature development to fine and then large grains at high temperature. The microstructure of the sintered products consisted on the elongated secondary mullite (types II and III) interlocking with primary (type I) mullite in a compact matrix with relative amount of liquid film for MAY and WAB. The morphology of mullite grains in TAN was more different being larger cuboid grains aggregated to form together with cristobalite a compact microstructure. The formation of TiO2 crystals and then Ti-Al (tialite: Al2TiO5) crystals influenced the microstructure of MAY and WAB. The microstructure at high temperature of the three kaolinitic clays indicated their suitability for dense refractory and fine ceramic applications. © 2009 Institute of Materials, Minerals and Mining.


2009 - Use of noncontact dilatometry for the assessment of the sintering kinetics during mullitization of three kaolinitic clays from Cameroon [Articolo su rivista]
Kamseu, Elie; Rizzuti, Antonino; Miselli, Paola; Veronesi, Paolo; Leonelli, Cristina
abstract

Noncontact dilatometry, compared to differential scanning calorimetry (DSC), was used together with scanning electron microscopy and densification behavior studies to investigate the parameters that govern the kinetics of transformation of kaolin to mullite during sintering.Three kaolinitc clays from Cameroon, with different SiO2/Al2O3 molar ratio, were examined. The temperatures of mullite nucleation were 973, 979, and 984 deg C at 5 deg C/min heating rate, respectively, for values of SiO2/Al2O3 molar ratio equal to 4.22, 2.22, and 2.08. At 20 deg C/min heating rate, the temperatures are shifted to higher values, 992, 997, and 1,001 deg C. The mullitization phenomenon, which includes a first step of nucleation and a second one of crystal growth, presented activation energy in the range of 650–730 kJ/mol, depending on the nature of the sample investigated. These values, obtained by noncontact dilatometer measurements, were comparable to those obtained by means of DSC and are in agreement with literature values. The difference in sintering kinetics for the three kaolinitic clays could explain the different morphologies obtained for the mullite grains.


2008 - Mullitization behaviour during thermal treatment of three kaolinitic clays from Cameroon: Densificaron, sintering kinetics and microstructure [Articolo su rivista]
Leonelli, C.; Kamseu, E.; Melo, U. C.; Corradi, A.; Pellacani, G. C.
abstract

Three kaolinitic clays from Cameroon were studied for their mullitization behaviour. The three clayey materials were from Ntamuka (TAN), Mayouom (MAY) and Wabane (WAB), all situated in the hills of western Cameroon. X-ray diffraction and thermal, dilatometric and SEM-EDS analyses were used to follow up the phase evolution, sintering kinetics and microstructure of the three materials as a function of temperature (1000-1500°C). Fine powders of each sample were pressed and treated in the above temperature range with the goal to correlate the phase evolution with densificaron parameters (shrinkage, porosity, density and mechanical strength). The nucleation of mullite and the increase of peak intensities were directly correlated to continuous densification and reduction of open porosity as observed under the SEM, The mullitization peak temperatures at 5°C/min were 973°C, 979.1°C, and 983.6°C respectively for TAN, MAY and WAB and - in the same order but at 20°C/min 992.1°C, 997.4°C and 1001.2°C. The mullitization phenomenon, which includes a first step of nucleation and a second of crystal growth, shows an activation energy that varies depending on the nature of sample investigated: the values ranged from 650 to 730 kJ/mol. The microstructure of the sintered products consisted on the elongated secondary mullite (types II and III) interlocking with primary (type I) mullite in a compact matrix with relative amount of glassy phase for MAY and WAB. The morphology of mullite grains in TAN was more different being laiger cuboid grains aggregated with cristobalite to form a compact microstructure. The formation of TiO2 crystals and then Ti-Al (tialite: Al2TiO5) crystals influenced the microstructure of MAY and WAB.


2008 - Prediction of service life of cordierite-mullite refractory materials by non-destructive methods [Relazione in Atti di Convegno]
Boccaccini, Dino Norberto; Kamseu, Elie; Volkov Husoviæ, T. D.; Cannio, Maria; Romagnoli, Marcello; Veronesi, Paolo; Dlouhy, I.; Boccaccini, A. R.; Leonelli, Cristina
abstract

Ultrasonic pulse velocity testing was used to perform non-destructive quality control of refractory plates used as substrates in fast firing of porcelain whitewares. The measurement of the ultrasonic velocity was used to asses the presence of internal voids or cracks originated from the manufacturing procedure. Image analysis was used to predict thermal stability of the refractory materials. Two cordierite-mullite compositions were investigated that are characterized by different microstructure morphologies and crack propagation behaviour. A brief discussion about the correlation between microstructure, crack propagation behaviour and thermal shock resistance is presented. Moreover, empirical models were developed to predict the service life of refractory plates from measured values of ultrasonic velocities in plates in the as-received state.


2008 - Sintering behaviour, microstructure and mechanical properties of low-quartz content vitrified ceramics using volcanic ash [Articolo su rivista]
Kamseu, Elie; Boccaccini, Dino Norberto; Sola, Antonella; Rizzuti, Antonino; Leonelli, Cristina; U., CHINJE MELO; N., Billong
abstract

-


2008 - Thermal behaviour of geopolymer materials: Influence of temperature on mineralogical composition and microstructure of sodium-potassium polysialates [Relazione in Atti di Convegno]
Kamseu, E.; Leonelli, C.; Sglavo, V. M.
abstract

DSC, TGA, XRD, SEM and mechanical tests were used to characterize geopolymer materials based on Na2O-K2O-Al 2O3-SiO2 system up to 1300°C. For all compositions, sodium silicate was used as binder. The samples of geopolymer which were cured at room temperature demonstrated dimensional stability up to 1200°C, with exception of samples with K which was stable up to 1300°C, retaining their predominant x-ray-amorphous tetrahedral Al and Si network (polysialates). The four point flexural and compressive strengths test demonstrated a slight decrease of mechanical properties up to 700°C followed by an exponential increase up to the melting temperature.


2007 - Bending Strength and Elastic Modulus of Porcelain Compositions under Various Specimen Loading Configurations [Articolo su rivista]
Kamseu, Elie; Leonelli, Cristina; V. M., Sglavo; Boccaccini, Dino Norberto; Veronesi, Paolo; Pellacani, Gian Carlo; D., Njopwouoc
abstract

-


2007 - Characterisation of porcelain compositions using two china clays from Cameroon [Articolo su rivista]
Kamseu, Elie; Leonelli, Cristina; Boccaccini, Dino Norberto; Veronesi, Paolo; Miselli, Paola; Pellacani, Gian Carlo; U., CHINJE MELO
abstract

Mayouom and Ntamuka china clays, from Cameroon were used to produce porcelain bodies. Two soft porcelain formulations: PSI (withMayouom) and PSII (with Ntamuka) and one hard porcelain, PH (with both Mayouom and Ntamuka) were prepared.The maximum density and flexural resistance for these formulations were obtained at 1200 8C for PSI, 1225 8C for PSII and 1350 8C for PH.Their properties and values were, respectively, density (2.42, 2.58 and 2.59 g/cm3), water absorption (0.15, 0.15 and 0.02%), porosity (4.3, 5.3 and4.2%) and flexural strength (148, 148 and 160 MPa). In addition to varying amounts of liquid phase, the soft porcelain formulations containedmullite and quartz crystals while the hard porcelains contained quartz and more intense mullite peaks. At 1250 8C PSI and PSII presented a selfglazingphenomenon which gave significant brightness and high aesthetic quality. PH with lower alkali (especially Na+) did not self-glaze even at1400 8C. Considering the soft porcelain formulations, the higher amounts of TiO2 (0.83%) and Fe2O3 (0.31%) in PSI (with Mayoum clay) resultedin a higher sintering effect at lower temperatures, giving lower water absorption and higher resistance. Both Mayouom and Ntamuka china clayswere found to be suitable raw materials for the production of porcelain stoneware tiles. Ntamuka could also be used for the manufacture of optimalquality whitewares.


2007 - Non-contact dilatometry of hard and soft porcelain compositions [Articolo su rivista]
Kamseu, Elie; Leonelli, Cristina; Boccaccini, Dino Norberto
abstract

Two different porcelain compositions were studied: a soft and a hard one. DTA, optical non-contact dilatometry and DSC were used to evaluate the thermal behaviour of the porcelain compositions with the aim to master the suitable thermal cycle for each. Results were interpreted on the basis of mineralogy and microstructure: the amorphous phase, abundant in soft porcelain, plays an important role on thermal expansion (8·10–6 K–1 for soft and 6·10–6 K–1 for hard at 1000°C). Thermal expansion behaviour as function of firing time was also studied. Non-contact dilatometry characterisation of porcelain bodies enable to master the suitable thermal cycle for the sintering.


2007 - Volcanic ash as alternative raw materials for traditional vitrified ceramic products [Articolo su rivista]
Leonelli, Cristina; Kamseu, Elie; Boccaccini, Dino Norberto; Melo, U. C.; Rizzuti, Antonino; Billong, N.; Misselli, P.
abstract

Investigation on the use of volcanic ash as 100% raw materials for traditional vitrified ceramic products is reported. X-ray diffraction (XRD), thermogravimetric-thermal differential analyses (DTA-TGA) and chemical analysis were used to characterise raw samples. Fired specimens were used to evaluate their ceramic properties. Volcanic ash contains essentially classical traditional ceramic oxides, plagioclase, pyroxene and olivine as principal minerals. In the temperature range 1100-1150°C, they present dense structure, low open porosity, without isolated quartz grains. The fired materials properties were found to be in agreement with those of stoneware class BI referring to standard ISO 13006 (i.e. the water absorption values were <1.5%). The presence of a sufficiently extended glassy phase capable of embedding crystalline phases developed during sintering allows comparison of the microstructure of fired volcanic ash with that of traditional porcelain or stoneware. © 2007 Institute of Materials, Minerals and Mining.


2006 - Evaluation of thermal shock damage in refractory materials by ultrasonic pulse velocity testing [Relazione in Atti di Convegno]
Leonelli, Cristina; Romagnoli, Marcello; Kamseu, Elie; Boccaccini, Dino Norberto; Veronesi, Paolo
abstract

-