Effect of internal curing on shrinkage and cracking potential under autogenous and drying conditions

Autogenous shrinkage is a significant issue in ultra-high-performance concrete (UHPC). Internal curing has been effective in mitigating autogenous shrinkage, but its impact on drying shrinkage and crack-free concrete needs to be considered. This study investigates the controversial phenomenon of the effect of internal curing on shrinkage strains under drying conditions. A very specific steel fiber reinforced cementitious composite (Slurry infiltrated fiber concrete (SIFCON)) was examined to better understand the cumulative effects. Two additional internal curing water contents (36 kg/m3 and 60 kg/m3) and two superabsorbent polymers (SAP) with different particle sizes (D50: 215 mu m and D50: 725 mu m) were utilized. Shrinkage measurements were conducted on the SIFCON matrix for early (up to 7 days) and long-term (up to 90 days), under both autogenous and drying conditions. The SIFCON specimens were cured under autogenous and drying conditions for 90 days, then dried to simulate the field conditions, which was followed by crack mapping. The results indicate that SAP effectively mitigates shrinkage strains under both autogenous and drying conditions, attributed to its ability to reduce plastic shrinkage strains during the initial hours. However, crack mapping studies revealed increased cracked areas in specimens with SAP usage, higher internal curing water content, and larger SAP size. Additionally, specimens cured under autogenous conditions exhibited more cracks compared to those cured under drying conditions. This suggests that although shrinkage measurements demonstrate positive effects of internal curing in both condi-tions, the cumulative effect can vary.