Properties of Cement-Based Materials with Low Water–Binder Ratios and Evaluation Mechanism under Further Hydration Effect

Unhydrated cementitious materials in high-performance concrete (HPC) and ultra-high-performance concrete (UHPC) undergo further hydration when they are further supplied with water. A further hydration experiment on cement pastes was conducted to study the effects of temperature and humidity on their macroscopic properties. A rapid evaluation mechanism for further hydration was eventually presented. The results obtained under the four analysed humidity conditions indicated that the compressive strength and flexural strength increased by 22.6% and 75.2%, respectively, after further hydration for 180 d at a relative humidity (RH) of 95%. Considering water soaking under three analysed temperature conditions, water soaking at 60 °C had the largest impact on macroscopic properties, such as compressive strength and flexural strength, which showed an increase of 31.4% and a decrease of 13.8%, respectively, after further hydration for 180 d. Moreover, the expansion strain at 60 °C was 1.1 times higher than the strain determined under water soaking at 40 °C. Considering the stability of the evaluation indices, the combined water content for further hydration, expansion strain, and compressive strength were used to evaluate further hydration effect. Considering the acceleration and damaging effects, water soaking at 60 °C was an effective method to accelerate further hydration.