Properties of alkali-activated fly ash/slag repair mortars

The study presented herein evaluates fresh, strength and transport properties of alkali-activated fly ash/slag mortars, and compares their performances with those of control mixtures. To this aim, four mixtures were made including two alkali-activated and two control mortars. Alkali-activated mortars contained 50% fly ash and 50% slag as binders, with two different combinations of sodium hydroxide and sodium silicate solutions as alkaline activators. The control mixtures included a similar mixture of slag and fly ash without alkali, and a standard Portland cement mortar. The experimental program used in this study included various evaluation methodologies to determine flow, setting times, compressive strength, modulus of elasticity, absorption, void content, and chloride migration and penetration. Slump flow and setting times were tested immediately after batching. The produced samples were de-molded after one day and cured in a moist room until time of testing. Compressive strengthwas measured at the ages of 3, 7, 14, 21 and 28 days. Modulus of elasticity, water absorption, rapid chloride migration (RMT) and rapid chloride penetration (RCPT) tests were done on 28-day cured samples. The results of study revealed higher strength of alkali-activated mortars than those of the control mortars. Their 3-days strengths were 34 and 41 MPa, being in a suitable range for repair applications. The alkali-activated mixtures showed superior performance in RCPT, RMT, water absorption, and void content results compared to those of the control mixtures. However, their setting times were shorter than those of the control mixtures.