Low-carbon blended cement containing wet carbonated municipal solid waste incineration fly ash and mechanically activated coal fly ash

Municipal solid waste incineration fly ash (IFA), after treated by wet carbonation, can be adopted as a supplementary cementitious material. However, the total replacement rate is limited at about 20 %, and a higher replacement may be achieved by introducing additional alumina. In this work, a ternary blended cement was developed by jointly blending wet carbonated IFA and mechanically activated coal fly ash (CFA) into Portland cement, and effects of total replacement rate and mechanical activation on the hydration behavior were investigated. Results showed that the joint incorporation of IFA and CFA delayed early hydration, leading to lower strength at 1 day. The sulfate in the IFA and aluminate in the CFA favored the formation of ettringite. Meanwhile, the calcium carbonate in the IFA stabilized the ettringite by reacting with aluminate phase to form hemicarbonate. Mechanical activation on CFA had physical benefit on the hydration due to improved filler effect, and chemical benefit by enhanced pozzolanic reaction and further promoted formation of ettringite and hemicarbonte. These reactions refined the pore structure, contributing to increased mechanical strength. Based on the compressive strength at 3 and 28 days, a total replacement rate of 45 % was allowable without compromising the strength. Furthermore, lead (Pb) was the only heavy metal in the raw IFA whose leaching concentration exceeded permitted limit, yet the concentration remained below 1/80 of the limit for the produced mortar samples. It was also observed that 42 % of carbon emission can be reduced without sacrificing the overall behavior of cement.