Microstructure and engineering properties of Fe2O3(FeO)-Al2O3-SiO2 based geopolymer composites

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

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.]