Experimental study on water absorption of unsaturated concrete: w/c ratio, coarse aggregate and saturation degree

•Effect of saturation degree on water absorption of concrete was investigated.•Effect of volume fraction and particle size of coarse aggregates on water absorption were studied.•A model for predicting the rate of water absorption of concrete was established. Better understanding of water transport in concrete is of great significance to assess the durability and predict service life. In this study, effects of water to cement ratio (W/C), volume fraction of coarse aggregate (Va) and particle size of coarse aggregate on water absorption of concrete were investigated. Besides, more attention was paid to the effect of saturation degree (θ) on water absorption of concrete. The results showed that the process of water absorption can be divided into two stages: rapid absorption and steady absorption. The rate of water absorption increases with the increasing W/C of concrete. An increase of Va reduces the water absorption of concrete; however, the particle size of coarse aggregate has no effect on the water absorption of unsaturated concrete. The initial rate of water absorption decreases with the saturation degree of concrete increasing. According to experiment results, a model for predicting the initial rate of water absorption of concrete with any saturation degree is established. From that, the initial rate of water absorption of concrete with any saturation degree can be calculated.