Etude de la consolidation de la latérite par le biais d’acides organique et inorganique

International audienc

Metakaolin-based inorganic polymer synthesis using cotton shell ash as sole alkaline activator

Inorganic polymers were synthesised using metakaolin and cotton shell ash as activator. In this way, the negative environmental impact of sodium or potassium silicate solutions as alkaline activators can be eliminated. Phase transformations investigated using FTIR suggested the formation of inorganic polymers through the shift of the most intense band from 1031 cm−1 in metakaolin to around 973 cm−1 in the final product and the absence of the band at 789 cm−1 in the latter. XRD results revealed the presence of kalsilite and zeolite K-F, which appear as hexagonal and elongated crystals in SEM. A maximum compressive strength of 36.7 MPa was obtained. Compressive strength values increased with increasing K/Al ratios and with the reduction of pore densities due to the formation of the amorphous inorganic polymer matrix as observed on the SEM micrographs. Cotton shell ash can thus be used as an alternative activator

Effect of solution type and temperature on the strengthening of laterite (Cameroon) based geomaterials: Rheological and micro calorimetry analyses

International audienc

Metakaolin-based inorganic polymer synthesis using cotton shell ash as sole alkaline activator

Inorganic polymers were synthesised using metakaolin and cotton shell ash as activator. In this way, the negative environmental impact of sodium or potassium silicate solutions as alkaline activators can be eliminated. Phase transformations investigated using FTIR suggested the formation of inorganic polymers through the shift of the most intense band from 1031 cm−1 in metakaolin to around 973 cm−1 in the final product and the absence of the band at 789 cm−1 in the latter. XRD results revealed the presence of kalsilite and zeolite K-F, which appear as hexagonal and elongated crystals in SEM. A maximum compressive strength of 36.7 MPa was obtained. Compressive strength values increased with increasing K/Al ratios and with the reduction of pore densities due to the formation of the amorphous inorganic polymer matrix as observed on the SEM micrographs. Cotton shell ash can thus be used as an alternative activator. © 2018 Elsevier LtdCaracterisation et valorisation des argiles de Foumban (Ouest Cameroun

Substitution of sodium silicate with rice husk ash-NaOH solution in metakaolin based geopolymer cement concerning reduction in global warming

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

The corrosion of kaolinite by iron minerals and the effects on geopolymerization

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

Mechanical and microstructural properties of geopolymer mortars from meta-halloysite: effect of titanium dioxide TiO2 (anatase and rutile) content

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.]

Effect of slag on the improvement of setting time and compressive strength of low reactive volcanic ash geopolymers synthetized at room temperature

Abstract This paper presents an investigation on the effect of ground granulated blast furnace slag on the geopolymerization of low reactive volcanic ash. Volcanic ash was blended up to 50 wt% with slag at 10% intervals. The fresh geopolymer samples were cured at 25 and 60 °C for 3, 7 and 28 days. XRD, FTIR, TG and SEM were used for phases analysis. The results outlined that only 10 wt% of slag was enough to reduce the initial setting time of the geopolymer from more than 7 days to couple of hours (6.7 h). At 25 °C, the 28 days compressive strength increased with the addition of slag in the system until an optimum value of about 85 MPA. This strength development was suggested to arise from a synergetic formation of C-A-S-H/N-A-S-H gel. At 60 °C, curing for periods longer than 7 days was not beneficial for strength development. These results are of interest for the valorization of low reactive volcanic ashes in the development of structural geopolymers, with related environmental and socioeconomic benefits

Occurrences of kaolin in Koutaba (west Cameroon): Mineralogical and physicochemical characterization for use in ceramic products

Thirty clay samples collected from three hills in Koutaba (west Cameroon) were characterized in order to evaluate their potential use as raw materials for ceramics. After preliminary mineralogical identification by X-ray diffraction, three representative samples from the three different hills, referred to hereafter as K1M, K2M and K3M, were selected for further investigation by X-ray fluorescence, plasticity, granularity and thermogravimetric analysis. The main clay minerals are kaolinite (32-51%) and illite (up to 12%). Additional major phases are quartz (32-52%), goethite (6-7%) and feldspars (0-4%). The chemical composition showed variable amounts of SiO2 (60-72%), Al2O3 (15-20%) and Fe2O3 (1-9%), in accordance with the quartz abundance in all of the samples studied. The particle-size distribution showed a large proportion of silty fraction (64-88%) with moderate sandy (9-19%) and clayey fractions ( < 5% for K2M, 12% for K1M and 20% for K3M). All of the clays showed moderate plasticity-index values (8-11%). Because of these characteristics, K1M and K3M may be suitable for use in common bricks and hollow ceramic products. Sieving or the addition of ball clays is recommended to increase the plasticity of sample K2M for use in common bricks. © 2016 by Walter de Gruyter Berlin/Boston 2016