Curing Conditions of Alkali-Activated Fly Ash and Slag Mortar

Abstract

This study compared the effect of seven common curing conditions on the compressive strength, pore alkalinity, efflorescence, and shrinkage of five alkali-activated fly ash and slag (AAFS) mortars and one cement mix. The fly ash to slag ratio and the activator content were altered in the AAFS mortars, which were then placed in the fog room, the carbonation chamber, the outside environment, bottom contact with water, and surface contact with 0%, 3.5%, and 10% sodium chloride solutions. It was found that the shrinkage was primarily a function of the dryness of the environment. The submerged curing conditions increased the extent of leaching but reduced shrinkage. For mixes with a high activator content, the effect of leaching was small. Therefore the compressive strength improved as a result of the reduced shrinkage, with the highest achieving 129.5 MPa at 56 days. The alkalinity of the curing solutions decreased as their salinity increased after 56 days of submergence. The rate of diffusion decreased as the concentration difference of the sodium cations decreased; therefore, the extent of leaching was lowered. This could incentivize the use of AAFS instead of cement, especially in highly saline underground environments.