Hydration of ternary blended cements with sewage sludge ash and limestone: Hydration mechanism and phase assemblage

Abstract

The hydration kinetics and phase assemblage of ternary blended cements composed of sewage sludge ash (SSA) and limestone were investigated. Isothermal calorimetry reveals an inhibition effect of SSA on the hydration of C3S within the first day, while the hydration degree of C3S in ternary blended cements exceeds that in PC after 3 days. The reaction between SSA and limestone generates additional carboaluminate phases and inhibits the transformation of AFt to monosulfate, increasing the stability of AFt. This reaction is reflected on the second peak in the deceleration period of heat flow curves. The generation of a large amount of carboaluminate phases has a significant effect on porosity refinement and strength development of ternary blended cements. The pozzolanic reaction of SSA generates C-(A)-S-H with high Si/Ca and Al/Ca atomic ratios. Iron from the dissolution of SSA is captured by C-(A)-S-H, leading to the increase in Fe/Ca atomic ratios of C-(A)-S-H.