Compressive strength and hydration characteristics of high-volume fly ash concrete prepared from fly ash

Abstract

This paper investigated the feasibility of replacing cement with fly ash (FA) mass ratios ranging from 40 to 70% to produce high-volume FA (HVFA) concrete. A suite of mechanical tests were conducted over a 180-day time frame. The hydration properties were systematically evaluated using isothermal calorimetry test, X-ray diffraction analysis, thermogravimetric analysis and selective dissolution method. Specially, a thermodynamic modeling was also used to predict phase assemblage and compare the experimental results in terms of the HVFA blended cement system. Experimental results showed that HVFA concrete exhibited lower early-age compressive strengths. However, beyond 28 days, the compressive strength of HVFA concrete developed faster than that of control concrete and the HVFA concrete with FA replacement of 40% showed comparable 180-day compressive strength to the control concrete. Hydration tests showed that the dilution and the pozzolanic effects of FA on cement hydration can be the critical reasons for the compressive strength development of HVFA concrete at early and later ages, respectively. Additionally, a good agreement between the experimental and modeling results can also be observed. These findings help to provide a sustainable and environmentally friendly solution to local FA disposal.