Nanocellulose-regulated volumetric stability of UHPC under high-temperature curing: Coupled effects of sulfate behavior and ettringite evolution

High-temperature curing is commonly used for precast ultra-high performance concrete (UHPC) production to shorten manufacturing cycles and accelerate early strength development, yet the associated non-isothermal temperature path often exacerbates autogenous shrinkage and thermally induced deformation, increasing deformation-induced early-age cracking risk in precast components. This study investigates the effects of two types of nanocellulose on hydration behavior, volumetric stability, and mechanical performance of UHPC under curing temperatures of 40°C and 60°C. Results show that nanocellulose significantly enhances volumetric stability, with a pronounced stage-dependent and temperature-amplified effect. Compared with 40°C curing, UHPC at 60°C exhibits stronger transient expansion during heating and greater shrinkage during constant-temperature curing, while Type B nanocellulose effectively suppresses thermal expansion and reduces cumulative autogenous shrinkage. Simultaneously, nanocellulose-modified UHPC maintains superior strength development under high-temperature curing. Mechanistic analyses reveal that nanocellulose regulates UHPC behavior not only through internal curing, but also via coupled control of moisture migration, sulfate-ion dynamics, and AFt-related phase evolution under elevated temperatures. This multi-process regulation mitigates volumetric incompatibility induced by accelerated hydration and temperature-sensitive sulfate-related phase evolution. The findings provide mechanistic insight into nanocellulose-enhanced volumetric stability and offer a practical material-based strategy for potentially reducing deformation-induced early-age cracking risk in precast UHPC components.