Experimental Study on the Internal Relative Humidity in Concrete under Dry-Wet Cycles

Using clean water and sulfate solution as the wetting medium,the internal relative humidity in concrete under dry-wet cycles was measured.The test results show that at the beginning of concrete placement,the variation law of the internal relative humidity in concrete with age can be described by a water-vapor saturated stage with 100% relative humidity followed by a stage that relative humidity gradually decreases and significant humidity gradient along the height can be found.Under dry-wet cycles,the changes of the relative humidity occur just within a certain depth from the concrete surface.This depth is commonly known as the influencing depth.Under the same dry-wet cycles,different influencing depths were observed for concretes with different strength.The lower the water to cement ratio and/or the higher the concrete strength,the shorter the influencing depth.The influencing depth is larger when sulfate solution is used as the wetting medium than that when the clean water is used.