Water absorption characteristics in autoclaved aerated concrete, diatomite, and calcium silicate board

Water absorption into cementitious materials has been discussed to be anomalous because of the nonlinearity of cumulative water absorbed with the square root of time. In this study, the water absorption characteristics in porous materials such as autoclaved aerated concrete (AAC), diatomite, and calcium silicate board were examined focusing on the different pore structures and the gravity effect. The one‐dimensional water absorption into diatomite and calcium silicate board both from top and bottom surface can be explained by water flow under its own capillary pressure based on the Washburn equation. On the other hand, the cumulative water volume absorbed into AAC was not proportional to the square root of time. The effect of gravity affected the absorption rate but was small for the ultimate cumulative water volume absorbed in AAC. The moisture content near the top drying surface was only half of that near the bottom wetting surface. It was hypothesized that the capillary pores in AAC can be dried while the fine pores at nano meter scale can be saturated under the pore humidity near the drying surface. It is concluded that the anomaly of water absorption in AAC may be affected by complicated pore structures with fine pores as well as drying conditions opposite to wetting surfaces.