Assessing the influence of external curing on the early drying shrinkage of ultra-high-performance concrete

Early drying shrinkage significantly impacts UHPC's cracking risks and structural stability in practical applications. This study uses a simulated curing system to explore how different external curing durations affect UHPC's early drying shrinkage, as well as its hydration degree and pore structures. The objective is to correlate pore sizes with shrinkage behaviors of UHPC under varying curing durations. Initial findings show intense evaporation within the first 4 h leads to noticeable drying shrinkage. However, external curing slows down the decline rate of critical pore sizes, leading to significantly reduced early drying shrinkage. Meanwhile, pores in UHPC larger than 50 nm exhibit low volume, underscoring the importance of critical pore diameters over their volumes in shrinkage assessment during curing. Ultimately, a pore diameter of 150 nm in UHPC is identified as the threshold for effectively minimizing initial drying shrinkage.