Assessment and mechanism study of bleeding process in cement paste by 1H low-field NMR

Based on detection technology of H-1 low-field nuclear magnetic resonance (NMR), this study developed a novel method for assessment and mechanism study of bleeding. This method is sensitive to bleeding water as well as water in cement paste and diluted grout, gives a vivid scenario of microstructure variation and provides important insights into mechanism of bleeding. In this study, influence of parameters such as cement type, water/cement ratio, chemical additives and environmental temperature on bleeding process was investigated. Results show that bleeding property of cements can be rapidly and precisely evaluated by the proposed method. It is found that peaks of T-2 distribution correlate with separated layers of fresh cement paste with bleeding, and the bleeding process generally consists of a significant growth, a relative stable period and a water-sucking stage. Results also demonstrate that retarder significantly increases bleeding, however, bleeding, to a certain extent, can be reduced by the addition of air-entraining agent. Furthermore, bleeding results of the cement paste under different temperatures (15.5 and 22.5 degrees C) suggest that higher temperature leads to a smaller T-2 value (around 10 ms) and a lower bleeding rate. The high precision of H-1 low-field NMR and linear correlation (R >= 0.921) between R-t(B) and bleeding rate both evidenced the superiority and feasibility of the proposed method on study of bleeding. (C) 2015 Elsevier Ltd. All rights reserved.