Preliminary observations of water movement in cement pastes during curing using X-ray absorption

X-ray absorption and concurrent mass measurements are used in quantifying water movement in 4 to 5 mm thick cement paste specimens with their top surface exposed to drying. Experimental variables examined in this preliminary study include water-to-cement (wic) ratio and open vs. capped samples. Layered specimens (e.g., 0.3 w/c ratio paste over 0.45 wic ratio paste) are also examined to monitor the preferential water movement from less dense (higher wic ratio) paste to denser paste due to capillary forces. For the open samples examined in this study, the initial drying is observed to occur uniformly throughout the thickness of the specimen, as opposed to proceeding as a sharp front progressing inward from the surface exposed to the external environment. In the layered specimens, the higher w/c ratio paste layer is seen to "dry out" first regardless of its location within the composite. The implications of these experimental observations for curing of concrete and application of repair materials are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.