Synergistic Effects of Pre-wetted Recycled Sand as an Internal Curing Agent on Concrete Performance: The Role of Replacement Ratio and Saturation Degree

This study investigates the synergistic effects of recycled sand (RS) replacement ratio and pre-wetting degree on low water-to-binder ratio concrete. Experiments characterized the moisture absorption-desorption behavior of RS and measured the workability, compressive strength, internal relative humidity, autogenous shrinkage, and drying shrinkage of twelve concrete mixes. Results indicate that finer RS particles exhibit higher absorption-desorption capacity. Increasing the replacement ratio impaired workability, compressive strength, and shrinkage resistance, while a higher pre-wetting degree improved workability retention, enhanced compressive strength, and significantly reduced both autogenous and drying shrinkage. A synergistic optimum was achieved at 50% replacement with 100% pre-wetting, minimizing strength loss while effectively mitigating shrinkage. These improvements are attributed to the internal curing effect of pre-wetted RS, which sustains moisture release, delays internal humidity reduction, and promotes continued hydration. The findings support the use of pre-wetted RS as an efficient internal curing material in sustainable concrete.

本研究探究了再生砂（Recycled Sand，RS）替代率与预湿润程度对低水胶比混凝土的协同作用效应。试验表征了RS的吸脱湿行为，并测试了12组混凝土配合比的工作性、抗压强度、内部相对湿度、自收缩（Autogenous Shrinkage）以及干燥收缩性能。结果表明，粒径更细的RS颗粒具备更高的吸脱湿容量。提高RS替代率会降低混凝土的工作性、抗压强度与抗收缩性能；而更高的预湿润程度则可改善工作性保持能力、提升抗压强度，并显著降低自收缩与干燥收缩。当RS替代率为50%且预湿润程度为100%时，可实现协同最优效果，在有效缓解收缩的同时将强度损失降至最低。上述性能改善可归因于预湿润RS的内部养护效应：其能够持续释放水分、延缓内部湿度下降，并促进混凝土的持续水化反应。本研究结果证实，预湿润RS可作为高效内部养护材料应用于可持续混凝土中。