Study on autogenous shrinkage of carbon nanotubes modified rockfill dam face slab concrete at early age under different temperature

Abstract

Autogenous shrinkage is one of the important factors affecting early-age cracking of concrete face slabs in rockfill dams. Carbon nanotubes (CNTs) possess excellent potential to enhance the performance of face slab concrete. The autogenous shrinkage behavior of CNTs-modified face slab concrete urgently requires investigation. Currently, studies on the effect of temperature on autogenous shrinkage often focus on a single temperature condition. To address this limitation, this study investigates the effects of different curing temperatures (20°C, 30°C, and 40°C) and CNT dosages (0%, 0.03%, 0.06%, 0.10%, and 0.15%) using cement paste. The results showed that an increase in curing temperature significantly accelerates the early-age autogenous shrinkage rate, particularly within the first 24 h, and also intensifies the ultimate shrinkage magnitude. Similarly, a higher CNT content was found to enhance both the development speed and the final value of early-age autogenous shrinkage. Furthermore, a multiscale model for early-age autogenous shrinkage of cement paste was established by integrating continuum micromechanics with capillary pressure theory, which provided good agreement with the experimental data. The results showed that chemical shrinkage in the unsaturated humidity stage is driven by capillary pressure. Moreover, the model indicates that chemical shrinkage accounts for the majority of autogenous shrinkage, approximately over 70% of the total. It also reveals that the effects of temperature and CNTs on autogenous shrinkage primarily manifest through accelerated early-age cement hydration, increased chemical shrinkage during the humidity-saturated phase, and the prolonged duration of this phase.