Experimental investigation on the restrained shrinkage of internally cured concrete with combined use of superabsorbent polymers, nanosilica and basalt fibers

Superabsorbent polymers (SAP) are widely used in concrete to mitigate autogenous shrinkage by absorbing and releasing water when internal humidity drops. However, SAP can negatively affect concrete's mechanical properties, particularly compressive strength, due to pore formation after water release. To address this issue, this study systematically investigates the effects of superabsorbent polymers (SAP), nanosilica (NS), and basalt fibers (BF) on the mechanical properties, shrinkage behavior, and cracking resistance of concrete. The addition of NS mitigates the pore formation caused by SAP by enhancing hydration and filling voids, while BF improves tensile strength and crack resistance by bridging microcracks, especially under shrinkage restraint conditions. The experimental program focused on analyzing the performance of concrete mixtures with SAP, NS, and BF, specifically addressing restrained shrinkage and its impact on early-age cracking. The results reveal that SAP significantly reduces shrinkage and delays cracking by providing internal curing, thereby mitigating moisture loss during the early curing phase. However, the addition of SAP was found to decrease compressive strength and modulus of elasticity due to pore formation within the matrix. In contrast, the inclusion of NS and BF compensated for the strength reduction, improving both compressive strength and tensile resistance, as well as providing limiting crack propagation under restraint. The combined incorporation of 0.3% SAP, 0.9% NS, and 1.2% BF (NSBF-ICC mix) demonstrated the best overall performance, offering improved shrinkage resistance and cracking behavior while maintaining mechanical integrity. Specifically, the NSBF-ICC mix exhibited an 11.2% increase in compressive strength and a 16.8% improvement in tensile strength compared to the control mix, while also showing a 30% reduction in shrinkage strain relative to the control mix and a 25% reduction in shrinkage strain compared to the SAP-only mixture. The synergy between SAP, NS, and BF significantly mitigated the negative effects of SAP alone, providing a balanced solution for internally cured concrete. These findings highlight the potential for optimizing the use of hybrid additive systems to improve concrete durability without compromising strength, offering valuable insights for future research into hybrid cementitious mixtures in applications like concrete pavements and bridge decks that require enhanced durability.