Characterization, reactivity and rheological behaviour of metakaolin and Meta-halloysite based geopolymer binders

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

Industrial potentiality of alluvial clays deposits from Cameroon: influence of lateritic clayey admixture for fired bricks production.

peer reviewe

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

International audienc

Polysialate matrixes from Al-rich and Si-rich metakaolins: Polycondensation and physico-chemical properties

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

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

International audienc

Characterisation of porcelain compositions using two china clays from Cameroon

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

Alternative geomaterials using laterites: reactivity and properties of use

International audienc

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