Volume changes and acoustic emission study of alkali-activated slag pastes in free and sealed conditions

Alkali-activated materials have become of interest as potential solution to reduce CO2 emissions of the construction sector. Because these materials are prone to shrinkage and cracking, this study investigates the volume changes and acoustic emission of slag activated by sodium hydroxide. At early-age, investigations revealed higher shrinkage and acoustic emission with high-intensity periods, as the solution concentration was increased for a 0.5 solution-to-binder. The E-modulus was calculated based on the ultrasonic pulse velocity (UPV) measurements and the cracking potential was evaluated. The more the composition was prone to cracking, the higher the accumulated acoustic emission. The strains might result in localized stress buildup higher than the material’s tensile strength, potentially resulting in micro-cracking. Long-term autogenous strain results revealed a separation into groups based on the solution concentration. Later-age thermal expansion coefficient (CTE) revealed significantly decreased results compared to early-age, indicating the importance of early-age CTE determination for the cracking risk assessment.