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

Microstructure and properties of hybrid coal gangue-based alkali-activated cement

Addition of Portland cement in low-calcium aluminosilicate-based alkali-activated materials can provide rapid hardening at room temperature, thus modifying microstructure and mechanical properties. In the present study, the effect of Portland cement addition on alkali-activated materials, cured at room temperature, was analysed by mechanical strength test, FT-IR and electrochemical impedance spectroscopy. The results showed samples hardening at room temperature after 24 hours and compressive strength of 26 MPa (7 days) for 5% of OPC addition. Hybrid alkali-activated cements presented higher sorptivity and lower electrical resistance than alkali-activated cement without OPC addition which can be related to more connected pores. The analysis of EIS spectrum highlights continued formation of microstructure over the ages of alkali-activated cement and can be related to mechanical properties and sorptivity