Effect of Rehydration of Unhydrated Cement on Ultra-High Performance Concrete After Heat Curing

Abstract

Mechanical performance testing, X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were used to study the effect of rehydration of unhydrated cement on ultra-high performance concrete (UHPC) under contact moisture and to isolate the moisture environments after different curing temperatures. The results indicated that the unhydrated cement particles can continuously hydrate when in contact with moisture and reduce the porosity, especially the 10 ~ 100 nm pores, and continuously improve the late strength of UHPC at 20 ℃ and 90 ℃ under a contact moisture environment. Contact with moisture will significantly increase the porosity and the 10 ~ 100 nm pores of the specimen, thereby leading to severe strength shrinkage and causing moisture susceptibility problems to the UHPC, while the isolated moisture also causes a slight reduction in the strength after curing at 250 ℃. Contact with moisture can cause more severe strength shrinkage when the curing temperature is 250 ℃.

Strength development and hydration products of alkali-activated Pisha sandstone geopolymer cement

“…The cylindrical samples were formed by pressure (50 kN), with a size of Φ50 mm × 50 mm. After removal from the mold, 15 samples of each formulation were covered with a plastic bag (preventing evaporation) and cured in an 80 °C (Fu et al, 2021;Luo et al, 2022;Snellings et al, 2022;Wu et al, 2022) air box for 12 h. The samples were then set at room temperature and further solidified and hardened at 20 °C for 1, 3, 7, 28, and 90 days. In the last step, the compressive strength of the three samples of each formulation was measured at 1, 3, 7, 28, and 90 days.…”