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

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

Characterization and performance evaluation of laterite based geopolymer binder cured at different temperatures

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