![]() These unhydrated cementitious materials have been shown to be capable of undergoing a rehydration reaction when subsequently encountering water, which was defined as a ‘rehydration reaction’, and could occur not only in UHPC, but also in HPC and even in ordinary concrete. established that the unhydrated cement content of cement paste with water/binder ratios of 0.30 and 0.50 was 7.9% and 32.4%, respectively, after 1 year. studied the content of unhydrated cement particles in cement-based materials with different water/binder ratios using nano-indentation technology and found that in the cement paste specimens with water/binder ratios of 0.15 and 0.20, the content of the unhydrated cement particles was 41% and 30%, respectively. According to Powers’ theory, cement can only be completely hydrated when the water/cement ratio is greater than 0.42, which means that a considerable amount of unhydrated cementitious materials remains inside the cement-based material after curing. First, the influence of temperature on the rehydration rate was more noticeable when the water/binder ratio was below 0.3 second, whereas adding large amounts of fly ash and silica fume did not prove to be conducive to repairing and enhancing cement-based materials undergoing rehydration, adding slag and small quantities of silica fume, or alternatively compounding small amounts of silica fume and fly ash could improve the repair and enhancement effects of rehydration.Ī lower water/binder ratio and a larger amount of cement-based materials are required to manufacture high performance concrete (HPC) and ultra-high performance concrete (UHPC) compared to standard concrete, and the emergence of superplasticizers has enabled the water/binder ratio of cement-based materials to be reduced to 0.2 or even lower. As the water/binder ratio rose, the rehydration rate first increased and then decreased. ![]() The capillary water absorption coefficient decreased continuously over a rehydration period of 120 days. During rehydration, the compressive strength and porosity of the specimens were found to first increase and then decrease. The key study findings included that rehydration could still occur in cement-based materials after one year of hydration, and that the capacity for rehydration-induced repair or damage to cement-based materials depended on whether their internal pores could accommodate rehydration products. This study aimed to explore how rehydration influences the macroscopic and microscopic properties of cement-based materials. Cement-based materials with a low water/binder ratio contain a high number of unhydrated cement particles, which implies that a rehydration reaction occurs when they encounter water again.
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