Active SAP desorption control in concrete through acoustic emission for optimized curing

Abstract

The quality and durability of concrete strongly depend on the mixing and curing processes. Relative humidity and temperature changes can induce premature drying, resulting in shrinkage cracking. Monitoring and controlling the concrete curing process is essential in preventing undesirable behaviours. Methods such as acoustic emission (AE) have proven promising for monitoring the curing of cementitious materials due to their high sensitivity and simple application. Shrinkage cracking can be mitigated using admixtures such as superabsorbent polymers (SAPs) which provide internal curing to the concrete matrix for several hours after casting. Their action taking place in the microstructure, although beneficial, is difficult to trace or control. However, recently it was shown that the release of SAP water (desorption) into the cementitious matrix is accompanied by high AE recordings, enabling monitoring of the process. This study presents a novel methodology that uses real-time AE data to actively control internal curing, optimizing curing conditions and material properties. By treating the concrete surface with water, at the moments dictated by the increased AE signals, the SAP desorption is delayed, allowing multiple activation cycles, extending internal curing, and enhancing hydration. Results indicate improved mechanical properties, with increased compressive strength and ultrasonic pulse velocity for actively controlled SAP concrete compared to conventional SAP concrete. Finally, scanning electron microscopy (SEM) measurements near the surface, show a 70 % and 81 % reduction of cracking compared to untreated SAP concrete and conventional concrete, respectively, demonstrating the importance of active curing on the shrinkage-prone near-the-surface area.