Interior Relative Humidity of Normal- and High-Strength Concrete at Early Age

The moisture content in the concrete pores is a critical parameter for most of the degradation processes suffered by concrete, for example concrete shrinkage and related cracking. In the present paper, the development of internal relative humidity of a concrete slab at an early age was investigated by applying the temperature and humidity combined digital sensor. The experimental results show that the internal relative humidity of concrete is reduced with concrete age. The general law of the development of relative humidity inside of concrete can be described by a vapor-saturated stage with 100% relative humidity (Stage I) followed by a stage that the relative humidity gradually reduced (Stage II). The length of Stage I and the magnitude of relative humidity in Stage II are greatly influenced by the strength of concrete and the location in concrete. A humidity gradient along the thickness of the concrete specimen existed at an early age. The humidity gradient in high-strength concrete (C80) is more obvious than that in normal-strength concrete (C40). In addition, for a given age, the reduction in relative humidity in C80 is much higher than that in C40.