Autogenous shrinkage and cracking of ultra-high-performance concrete with soda residue as an internal curing agent

Autogenous shrinkage and shrinkage-induced cracking present significant challenges in ultra-high-performance concrete (UHPC). To address this issue, this study explores the feasibility of using soda residue (SR), an industrial waste product, as a sustainable internal curing agent for UHPC. Experimental results demonstrate that the inclusion of SR substantially mitigates shrinkage and cracking in UHPC, while also enhancing compressive strength. The use of SR with additional water showed comparable or superior performance in reducing shrinkage and cracking compared to higher dosages of SR. Through internal humidity measurements, thermogravimetric analysis, and scanning electron microscopy, two primary mechanisms for the improvement were identified: (1) SR increases internal humidity by releasing additional water, thus preventing shrinkage; and (2) the ettringite formation induced by SR expands the solid phase volume, compensating for shrinkage. Furthermore, utilizing SR as a recycled material not only improves the early-age properties of UHPC but also contributes to sustainable construction practices.