Control of Thermal Cracking in Mass Concrete

本年度对水泥水化引起的绝热温升进行了预测。此外，还研究了混凝土的拉伸徐变和早期钢筋混凝土构件的粘结徐变特性。本研究的总结如下。(1)为了预测水泥水化热引起的绝热温升，建立了水泥水化热率随养护温度变化的实验方程。因此，在任何时刻和任何固化温度下产生的热量的热率可以用上面的公式计算出来。绝热条件下的水泥水化热也可由上述方程积分计算。然后由上述水泥水化热计算绝热温度。最后将所得结果与相应的实验结果进行比较。实验结果表明，实验精度对实验结果有显著的影响。在本文提出的方法中考虑了这一影响，可以准确地预测绝热温度。(2)为了解热应力产生的机理，研究了混凝土在压应力作用下的拉伸徐变特性。结果表明：经受压应力历史作用的混凝土的拉伸徐变大于未经受压应力历史作用的混凝土；此外，通过声发射测量发现，这种拉伸蠕变部分是由混凝土微裂纹引起的变形引起的。(3)为建立一种有效的热裂缝宽度预测方法，对干缩条件下早期钢筋混凝土构件粘结蠕变进行了分析。分析结果与实验结果吻合较好。该方法可以定量预测粘结强度、粘结蠕变和粘结滑移。(4)采用有限元方法对考虑钢筋位置的热裂纹发展进行了分析，结果表明可以计算出裂纹尖端附近的诱发位移和热应力。因此，利用上述方法可以相当准确地监测热裂的发展。少

In this year, prediction of adiabatic temperature rise as a result of cement hydration was attempted. In addition, properties of tensile creep in concrete and bond creep in reinforced concrete member at early age were also studied. The summary of this study is as follow.(1) To predict adiabatic temperature rise induced by heat of cement hydration,an experimental equation based on the rate of heat induced by cement hydration is obtained as a function of curing temperature. The rate of heat of heat generated at any instant and at any curing temperature can thus be calculated by using the above equation. Heat of cement hydration under adiabatic condition can also be calculated by integrating the above equation. The adiabatic temperature is then calculated from the above heat of cement hyfration. The results obtained from the above is then finally compared with its corresponding experimental results. It is found that the accuracy of the experiment has a signfificant effect on thesee result … More s. By taking the consideration of this effect into the proposed method, the adiabatic temperature can be accurately predicted.(2) To understand the mechanism of thermal stress, tensile creep property of concrete subjected to compressive stress history is studied. The redults show that the tensile creep of concrete subjected to compressive stress history is greater than that of concrete without subjected to compressive stress history. In addition, based on the acoustic emission measurement, part of this tensile creep is found to be induced by the deformation of concrete due to the micro crack.(3) To establish an effective way of predicting the thermal crack width, the bond creep of reinforced concrete members at the early age under drying shrinkage condition was analyzed. The analytical results showed good agreement with the experimental results. The bond strength and the bond creep as well as the bond slip can be quantitatively predicted by the proposed method.(4) A finite element approach was used to analyze the development of thermal crack by taking the consideration of the position of reinforcement, Results show that it is possible to calculate the induced displacement and thermal stress near cracking tip. Thus, the development of thermal cracking can be rather accurately monitored by using the above approach. Less