Effect of Portland cement addition on initial dissolution of coal gangue based alkali-activated cement

Release of silicon and alumina from aluminosilicate occurs at early stages of alkaline reaction. Alkalinity and different aluminosilicate could influence dissolution of particles and modify microstructure of alkali-activated systems. However, there is a lack of study regarding the effects of Portland cement (OPC) addition on alkali-activated systems. This paper investigates alkaline dissolution of aluminosilicate by leaching experiments, varying Portland cement content. Chemical stability of AA-hybrid pastes was determined by water immersion and compressive strength at 28 days. Hybrid alkali-activated cement was produced with coal sludge (CS) and coal gangue (CG). Portland cement was added in 10 wt% and 20 wt% of precursor, and the water to binder ratio was of 0.75. Compressive strength increased in hybrid alkali-activated materials after chemical stability test, and leached solutions have a peak of pH and electrical conductivity at seven days. Chemical analysis of leached solutions detected contents of SiO2, SO3, K2O, Fe2O3 and CaO. Portland cement addition increased alkaline dissolution of Si and Al from aluminosilicate at initial stages of chemical reaction with a synchronized behaviour. Dissolution efficiency was according to the material reactivity, following CST>CG>CS.