Mitigating plastic shrinkage cracking in alkali-activated slag systems by internal curing with superabsorbent polymers

In this study, superabsorbent polymers (SAPs) are studied to mitigate the plastic shrinkage in three alkali -activated slag (AAS) systems. Plastic shrinkage cracking tests were performed on fresh AAS pastes, while monitoring the capillary pressure, the internal relative humidity, the setting time, and the compressive strength. The setting time of the water glass-activated slag (WG-AAS) system was extremely short, no cracks occurred before its final setting time, and no capillary pressure break-through was observed within 24 h. In the NaOH-activated slag (SH-AAS) system and the Na2CO3-activated slag (SC-AAS) system, the use of SAPs effectively delayed the occurrence of plastic shrinkage cracking and reduced the crack width, and the time of capillary pressure break-through was also observed to be delayed. SAPs also slowed the drop in internal relative humidity by releasing water into the hardening paste. Therefore, the use of SAPs appears to be an effective strategy for mitigating plastic shrinkage cracking in AAS systems, although SAPs also caused a reduction in compressive strength. However, adding additional water without SAPs is not an effective strategy to mitigate plastic shrinkage cracking as plastic shrinkage cracking still occurs.