Experimental study on interior relative humidity development in early-age concrete mixed with shrinkage-reducing and expansive admixtures

Abstract Early age concrete may crack due to volumetric shrinkage caused by a decrease in the interior relative humidity (RH) in the self-desiccation process. Shrinkage-reducing admixtures (SRAs) and expansive admixtures (EAs) are utilized to mitigate the volumetric shrinkage. Using a self-developed wireless and automatic relative-humidity monitoring system, a series of experiments for the measurement of the RH within concrete specimens was conducted. A systematic analysis was conducted in the aspects of the setting time, critical time and interior RH development in early-age concrete with different dosages of the polymer-type SRA and CaO-type EA. On the basis, a critical time model and a two-stage RH development model considering the effects of the water to binder ratio, SRA and EA dosages were established. Both of the models are in good agreement with the experimental data.