Effect of adding mineral additives to alkali-activated natural pozzolan paste

Natural pozzolans are raw materials from geological deposits with a range of chemical compositions that when combined with suitable alkali activators can be converted to geopolymer cement for concrete production. In this paper the concept of adding mineral additives to enhance the properties of geopolymer cement is introduced. Taftan andesite, a natural Iranian pozzolan, was used to study the effect of adding mineral additives such as kaolinite, lime and other calcined pozzolans on the compressive strength of geopolymer cement under both normal and autoclave curing. Scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) was used to determine the composition of the gel phase in both alkali-activated Taftan pozzolan with and without mineral additions. The work has shown that deficiencies in SiO2, Al2O3 and CaO content in the raw natural pozzolan can be compensated for by adding mineral additives for enhanced properties.

Use of Gypsum and CKD to enhance early age strength of High Volume Fly Ash (HVFA) pastes

Use of higher proportions of fly ash as a cement replacement in concrete has obvious environmental and performance benefits but high volumes of fly ash are not commonly used due to perceived lower early age strengths. In this investigation, addition of cement kiln dust (CKD) and gypsum to activate the fly ash was studied and the proportions used in the paste mixes were designed to optimize the mixture ingredients to achieve the highest early age compressive strength. Change of mineral phase composition and micro structure of the composites was analyzed. It was found that CKD was much more effective in activating the fly ash than gypsum. Appreciable early age compressive strengths were achieved for fly ash contents up to 60% of the binder and these observations were supported by analysis of the mineral phases.