大坝混凝土早龄期变温条件下拉伸徐变研究

为解决大坝混凝土早龄期拉伸徐变确定困难的问题，本文综合考虑大坝混凝土早龄期水化发展进程和约束状态，采用温度-应力试验技术，测试获得粉煤灰掺量分别为35%和80%掺量的两种大坝混凝土在两种不同温度养护模式下约束试件和自由试件的温度、变形和应力的发展曲线，由此确定两种大坝混凝土的早龄期拉徐变及其发展规律。结合温度-应力试验和绝热温升试验数据，提出变温条件下的改进开尔文模型的大坝混凝土早龄期拉徐变模型，并对模型进行验证。结果表明：粉煤灰掺量为80%的大坝混凝土早龄期拉伸徐变度较大，可减小约束应力的发展，对混凝土早龄期抗裂有利。基于水化发展进程的改进开尔文模型可较好地预测约束状态下大坝混凝土的早龄期拉伸徐变，从而用于其早龄期开裂风险评估。

Tensile creep of dam concrete at early age under variable temperature history

To determine the tensile creep of dam concrete at early age, this study conducts an experiment on the development of temperature, deformation, and restraint stress of fly ash dam concrete, using temperature-stress test technology and considering comprehensively its hydration process and restraint state at early age. We test restrained specimens and free specimens of concrete materials with fly ash contents of 35% and 80% under different temperature curing conditions, and obtain their early age tensile creep and developing trends. By the measurements of temperature-stress tests and adiabatic temperature rise tests, we develop and verify a tensile creep model of the concrete materials at early age under variable temperature history based on an improved Kelvin model. The results show the concrete with 80% fly ash has a larger specific tensile creep and slower development of restraint stress, a condition favorable to its crack resistance. The improved Kelvin model, based on a better consideration of the hydration process, can predict the tensile creep of dam concrete at early age under the restraint condition, and is useful to the assessment of early age cracking risk.