2022 Volume 76 Issue 1 Pages 290-298
The previous studies have reported that the water absorption amount with time can be proportional to the fourth root of absorption time. In this study, the water uptake characteristics of hardened cement paste was studied from a viewpoint of fourth root of uptake time. The one bottom surface of cement paste specimen was exposed to liquid water after drying equilibrium at 20, 40 and 105℃. The amount of water absorption was proportional to the fourth root of time as reported in the previous studies. In the case of drying at 105℃, the relationship was bilinear, which suggests that the water can penetrate into relatively large capillary pores and then fine gel pores as two processes. The model to apply different diffusion equations to the assumed capillary and gel pores can reproduce the water uptake behavior of cement paste dried at 105℃ when the constant diffusivities are used for each pore. The diffusion equations were applied to divided pore diameters, respectively when the simple pore distribution was assumed. It was found that the model to use constant large and small diffusivities according to threshold of pore diameter can represent the bilinear relationship between the water absorption amount and fourth root of time rather than the model to use the decreasing diffusivity with decreasing pore diameter.
