Hydration kinetics, freeze-thaw resistance, leaching behavior of blended cement containing co-combustion ash of sewage sludge and rice husk

Abstract

The application of co-combustion of sewage sludge together with rice husk is expected to increase in the coming years because of the economic and environmental benefits. Hence, resources of massive residues from co-combustion process deserve particular attention. In this study, cementitious materials that are composed of co-combustion ash, H (co-combustion of 20% sewage sludge+80% rice husk) or W (co-combustion of 30% sewage sludge+70% rice husk), were developed. Hydration characteristics, mechanical properties, freeze-thaw (F-T) durability, and environmental performance were investigated. Results show that the cumulative hydration heat increases along with the increase in the amount of amorphous SiO2 in blended cement. The inclusion of H and W inhibits hydration at the early hydration stage and decreases the diffusion coefficient of paste at the later hydration stage. Moreover, the addition of H or W reduces the unconfined compressive strength (UCS) of sample at an early age. However, the UCS for 7-day and 28-day specimens even exceeds that of the reference. Blended cement containing co-combustion ash possesses leach resistance and poor frost resistance. Meanwhile, a significant increase of leached heavy metals is generated after F-T cycle. This phenomenon is a negative environmental impact of F-T action.