Combined Impact of Nano-SiO2 and Superabsorbent Polymers on Early-Age Concrete Engineering Properties for Water-Related Structures

High-performance concrete (HPC) is currently widely used in water-related structures. The incorporation of nano-silica (nano-SiO2, NS) can further refine its pore structure, thereby enhancing the compressive strength and durability of HPC without necessitating a reduction in the water-to-binder (w/b) ratio. However, the addition of nano-materials significantly increases the autogenous shrinkage (AS) of concrete, leading to elevated tensile stresses and making the concrete more susceptible to early-age cracking. To mitigate AS, superabsorbent polymers (SAPs) can be introduced to internally cure the concrete, thereby improving the internal relative humidity (IRH) and reducing the AS in NS-reinforced concrete. In this study, we experimentally investigate the setting behavior, pore structure, compressive strength, IRH, and AS properties of concrete with a w/b of 0.3, incorporating both NS and SAP. The results demonstrate that the addition of NS advances setting time, significantly densifies the pore structure, markedly enhances compressive strength, accelerates the decline in IRH, and increases AS strain. Conversely, the incorporation of SAP exhibits opposite effects on these properties, particularly in substantially mitigating AS strain. The combined incorporation of 1.5% NS and 0.15% (or 0.30%) SAP achieves both higher compressive strength and lower AS strain compared to plain concrete at 28 days. These findings suggest that the simultaneous introduction of NS and SAPs into concrete formulations is recommended to achieve an optimal balance between shrinkage and strength properties. Such advancements are particularly beneficial for applications in hydraulic and water-related structures, where enhanced durability and reduced cracking are critical for maintaining structural integrity and ensuring longevity.

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