Low cost and sustainable repair material made from alkali-activated high-calcium fly ash with calcium carbide residue

Abstract

In this work, a study on a low cost and sustainable repair material made from alkali-activated high-calcium fly ash (FA) incorporated with calcium carbide residue (CCR) is reported. The FA was partially replaced with CCR (additional calcium source) at the dosages of 0%, 10%, 20%, and 30% by weight of binder. The alkaline activators were sodium silicate (SS) and sodium hydroxide (SH) solutions with SS-to-SH ratios of 1.0, 1.5, 2.0 and 2.5 by weight. The alkali activator liquid/solid binder (FA + CCR) ratio of 0.60 and curing at 25 °C (ambient temperature) were used for all mixes. Experimental results showed that the setting time of mortar decreased with increases of CCR replacement level and SS-to-SH ratio, whereas the strength development increased. XRD and SEM results demonstrated that an optimum level of CCR replacement and SS-to-SH ratio resulted in the additional formation of C-S-H (calcium silicate hydrate) that coexisted with N-A-S-H (sodium aluminosilicate hydrate). The bond strength of the alkali-activated mortar with concrete substrate was also improved. The setting time and strengths complied with the requirement of the ASTM standards for repair materials and thus indicated its suitable as an alternative repair material in terms of environmentally friendly and low cost.