Liu Wei-Jia, Niu Xu-Jing, Yang Ning, Tan Yao-Shen, Qiao Yu, Liu Chun-Feng, Wu Kun, Li Qing-Bin, Hu Yu
State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China.
China Three Gorges Projects Development Co., Ltd., Chengdu 610017, China.
Materials (Basel). 2021 Jun 10;14(12):3201. doi: 10.3390/ma14123201.
Mass concrete is usually poured in layers. To ensure the interlayer bonding quality of concrete, the lower layer should be kept in a plastic state before the upper layer is added. Ultimately, it will lead to the prediction of concrete setting time as a critical task in concrete pouring. In this experiment, the setting time of concrete in laboratory and field environments was investigated. The equivalent age of concrete at the initial setting was also analyzed based on the maturity theory. Meanwhile, factors affecting the setting time in the field environment were studied by means of multiple stepwise regression analysis. Besides, the interlayer splitting tensile strength of concrete subjected to different temperatures and wind speeds was determined. The results of laboratory tests show that both setting time and interlayer splitting tensile strength of concrete decrease significantly with the increase of air temperature and wind speed. In addition, the equivalent age of concrete at initial setting remains the same when subjected to different temperatures, while it decreases obviously with the increase of wind speed. In the field environment, the equivalent age of concrete at initial setting is greatly different, which is related to the variability of relative humidity and wind speed. The average air temperature and maximum wind speed are the main factors affecting the initial setting time of concrete. Furthermore, a prediction model is established based on the stepwise regression analysis results, which can predict the actual setting state in real-time, and hence controlling the interlayer bonding quality of dam concrete.
大体积混凝土通常分层浇筑。为确保混凝土层间粘结质量，在浇筑上层混凝土之前，下层混凝土应保持塑性状态。最终，这使得预测混凝土凝结时间成为混凝土浇筑中的一项关键任务。在本试验中，研究了实验室环境和现场环境下混凝土的凝结时间。还基于成熟度理论分析了混凝土初凝时的等效龄期。同时，通过多元逐步回归分析研究了现场环境中影响凝结时间的因素。此外，测定了不同温度和风速下混凝土的层间劈拉强度。实验室试验结果表明，随着气温和风速的增加，混凝土的凝结时间和层间劈拉强度均显著降低。此外，不同温度下混凝土初凝时的等效龄期保持不变，而随着风速的增加明显减小。在现场环境中，混凝土初凝时的等效龄期差异很大，这与相对湿度和风速的变异性有关。平均气温和最大风速是影响混凝土初凝时间的主要因素。此外，基于逐步回归分析结果建立了预测模型，该模型可实时预测实际凝结状态，从而控制大坝混凝土的层间粘结质量。
