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

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

Thermal behaviour of metakaolin–bauxite blends geopolymer: microstructure and mechanical properties

This paper investigates the use of bauxite widely available in northern Cameroon as an additive in the optimization of some properties of metakaolin-based geopolymer. To do this, several geopolymer mixtures were prepared by substituting metakaolin (MK) by bauxite (BA) (from 0 to 50%) and partially kept at room temperature (28 °C), while others were sintered at 200, 800 and 1200 °C. The raw materials and resulting products were characterized using X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), densification parameters, mechanical properties as well as microstructural morphologies. The results revealed that the setting time of the geopolymer pastes increased with the bauxite content due to its low dissolution in alkaline medium at room temperature. The mechanical strength of samples decreased from 35.20 to 11.10 MPa at room temperature. At 1200 °C, the higher strengths (50, 98 and 70 MPa) were achieved in MKBA10, MKBA20 and MKBA30, respectively. These samples also exhibited dense and compact microstructure partially due to packing particles effect and the nature of bauxite known as refractory material. Thermal shrinkage and relatively high mass losses reflected the decomposition of chemical compounds within the system. Thus, the synthesized materials heated at 1200 °C could be used as a potential candidate for refractory applications

Semi-vitrified porous kyanite mullite ceramics: Young modulus, microstructure and pore size evolution

Microporous porcelain formulations are successfully carried out through sintering processing. During the thermal treatment of ceramic products, it was found that the addition of kyanite together with ϕ- and γ-Al2O3 allowed to enhance interconnected pores network with micrometric size from 0.1 to 9 µm in a semi-vitrified composite. Between 1200 and 1350 °C, the mullitization of kyanite hindered the extension of vitrification and the growth of acicular mullite from the transformation of metakaolin. The main pores size decreased from 4.33 to 1.54 µm for the formulation containing 32 wt% of kyanite. In this interval the specific pore area increased from 0.64 to 8.75 m2 g−1 due to the total conversion of the kyanite to fibrous and acicular mullite that reduced the voids provided by the earlier mullitization. The improvement in the mullitization without extensive vitrification and grain growth and the reduction of the pores size with the increase in the specific pore area contributed to the formation of a microporous matrix with the Young's modulus increased from 7 to > 20 GPa. The microstructure of the microporous porcelain, their specific pore area and pores size as well as the interconnection of pores was found innovative for the applications in the field of engineering filtration where high mechanical strength, strain, stiffness and pressure resistance are required

Alkali-activated laterite binders: Influence of silica modulus on setting time, Rheological behaviour and strength development

This paper present the results from a comprehensive study undertaken to investigate and develop alkali-activated binders (AABs) with laterite soil as the aluminosilicate precursor. In this study, the effect of the silica modulus (SiO2/Na2O) of the activator on the setting time, rheological properties and strength development were investigated. Iron-rich laterite sourced from West Africa was used as the aluminosilicate precursor alongside sodium silicate and sodium hydroxide for the production of the activator. The activators were prepared to have varying silica modulus of 1.3, 1.5, 1.7 and 2. The findings from this study showed that the silica modulus of the activator used in the synthesis of the laterite-based AABs has a significant influence on the resulting properties of the binders. It was found out the optimum silica modulus is 1.3 and increasing the silica modulus of the activator results in detrimental effects on the hardened properties of the AABs. In the same context, increasing the silica modulus of the activator from 1.3 to 2.0 extended the final setting of the binder time by 56.1% while the compressive strength at 56 days reduced by 57%. Microstructural investigation on the binders showed that the main products of alkali activation of the calcined laterite are quartz, ilmenite, hematite and maghemite. It was concluded that laterite-based AABs with good performance can be produced with a silica modulus of 1.3 and used as a possible alternative for Portland cement as a binder

Ferrisilicates formation during the geopolymerization of natural Fe-rich aluminosilicate precursors

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Production, characteristics, and utilization of rice husk ash in alkali activated materials:an overview of fresh and hardened state properties

Abstract Vast amounts of rice husk ash (RHA) are generated annually, with most of them unutilized or disposed to landfills, resulting in serious environmental degradation. To avoid this, the use of RHA as precursors or co-binder in the development of alkali activated materials (AAMs) is viewed as a viable alternative to avert this significant problem. In this paper, the generation, properties, and utilization of RHA in AAMs are systematically and comprehensively reviewed. Furthermore, the physical, chemical, and mineralogical composition of several RHA were critically examined, and their impact on fresh and hardened state properties of AAMs and blended formulations are presented. Generally, the properties of RHA are influenced by the source material and the production process (pre-treatment, burning time, burning temperature, cooling rate, coolingduration and milling) which in turn affect their pozzolanic reactivity. Due to its high pozzolanic nature, low energy requirement and greenhouse gas emission during production, RHA is an environmentally friendly and cost-effective alternative cementitious material to produce AAMs. Various studies have reported the beneficial role of RHA on the mechanical, microstructural and durability properties of AAMs, especially when used at an optimal level. Overall, this review will provide valuable insight, direction, and recommendations for researchers and industrial sectors on the generation, recycling, characteristics, and utilization of RHA in the development of AAMs for potential construction applications

Effects of curing cycles on developing strength and microstructure of goethite-rich aluminosilicate (corroded laterite) based geopolymer composites

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Mechanical and physical properties of inorganic polymer cement made of iron-rich laterite and lateritic clay: A comparative study

International audienceIn this work, two different laterites (iron contents of 13.07 and 49.34 wt%, respectively, for lateritic clay, LAC, and iron-rich laterite, LAI) were selected and calcined at 600 °C. The obtained calcined laterites, namely LAI600 and LAC600, were separately mixed with an alkaline solution (silicate modulus of 1.35) or an acidic solution (phosphoric acid solution at pH ≤ 2) for the synthesis of inorganic polymer products. The fabricated products were cured at 20 °C (ambient) and 40 °C (oven). The obtained results showed that the compressive strength of each series of alkaline-based inorganic polymer binder increased with ageing time (7 and 28 days) for room temperature curing, while the reverse trend was noted for oven-cured specimens. The best mechanical performance was obtained when using a phosphoric acid solution, 38 and 52 ± 1 MPa; 62 and 65 ± 1 MPa at 28 days for LAC and LAI respectively. It appeared that a higher iron content within the laterite contributed to an increase in the compressive strength under acidic conditions (LAI (59 MPa) > LAC (48 MPa)) compared to the behavior obtained under alkaline conditions (LAI (6 MPa) < LAC (29 MPa)). Accordingly, the acidic products exhibited a dense structure (with lower porosity) and contained amorphous iron/aluminium phosphate phases such as berlinite (FePO4), iron hydrogen phosphate hydrate (Fe3H15(PO4)8·4H2O), ferrowyllieite (AlFe2Na2(PO4)3) and sodium iron phosphate (Na3Fe2(PO4)3) arising from the alteration of iron minerals in an acidic medium, confirmed by Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy

Effect of silica and lignocellulosic additives on the formation and the distribution of meso and macropores in foam metakaolin-based geopolymer filters for dyes and wastewater filtration

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