2 research outputs found
Calcined low-grade multimineral clays as supplementary cementitious materials: a feasibility study
© 2020, © 2020 The Korean Society of Mineral and Energy Resources Engineers (KSMER). The relevance of calcined clays as sources with great potential for low-clinker blended Portland cements has significantly increased in recent decades. This article reports on a study to evaluate the potential of the two low-grade clays containing 9.37% of montmorillonite/chlorite and 12.26% of montmorillonite/kaolinite/chlorite accompanied with 29.73% and 32.79% of calcite, respectively, as supplementary cementitious materials. The clays after thermal treatment at 800°C demonstrated poor pozzolanic activity, slight increase in the C-(S)-H and decline in the CH contents, and decrease in the mechanical properties of the blended Portland cement pastes. The results showed that the investigated clays fall below the range of the clays suitable for pozzolan production
Role of Clay Minerals Content and Calcite in Alkali Activation of Low-Grade Multimineral Clays
© 2020 American Society of Civil Engineers. The increased contribution of science-intensive clean materials and technologies to the total industrial production is one of the essential prerequisites for the future of sustainable industrial development. Chemical activation based on a nonfired or low-temperature approach for the production of cementitious materials from glassy aluminosilicates, including calcined clays, is an intensively developing and promising clean technology. This study investigated the potential of calcined clays as precursors of alkali-activated cements (AACs) by considering three types of low-grade multimineral clays (with a clay mineral content of <20%). The alkali activation of the calcined clays was analyzed based on the type and content of clay minerals, presence of calcite, calcination temperature, type of alkali activator, and curing conditions. The results indicated that clays containing 20% of 21 layer lattice clay minerals are not suitable as precursors of AACs, while those containing 9%-12% of 11 and/or 21 layer lattice minerals combined with 29%-32% calcite lead to hardened pastes displaying compressive strengths of up to 12.4 MPa after 2 days and 20 MPa after 28 days and after steam curing. The reaction products of 6M NaOH-activated systems determined by XRD, TG/DSC, and FTIR spectroscopy analyses were X-ray amorphous binder gel, calcite (CaCO3), clinozoisite (Ca2Al3(SiO4)(Si2O7)(O,OH)), and gaylussite (CaNa2(CO3)(H2O)5)