Control of Thermal Cracking in Mass Concrete

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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