Rational Constitutive Laws to Describe Creep and Shrinkage of Concrete at Elevated Temperatures

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Since the late of 1950's, the development of prestressed concrete nuclear reactor containment vessels has demanded the knowledge of mechanical behavior of concrete at high temperatures. Mathematical models for creep and shrinkage of concrete at temperatures over. 100^ﾟC have been asked particularly for finite element analysis of the safety in nuclear reactor structures. For this purpose, numerous experimental studied have been tried and various mathematical models have been proposed as the constitutive laws for the finite element analysis. Most of them, however, have failed to simulate the experimental results. The influence of moisture content and movement on the mechanical properties such as Young's modulus, shrinkage and creep behavior is significant even under 100^ﾟC as well as over 100^ﾟC. Therefore, it is very important to study the moisture migration in concrete for understanding the mechanical properties of concrete at elevated temperatures.In this project, the following result … More s are obtained:(1). Cylindrical specimens of mortar and concrete were tested under several temperature atmosphere to study the moisture migration process and changes of mechanical properties such as modulus of elasticity, compressive strength, tensile strength and so on. Moreover, these results of moisture migration were analyzed by a finite element method as a nonlinear diffusion process and the obtained material parameters were discussed.(2). By means of thin wall cylinder specimens, the moisture migration process and shrinkage of hardened cement paste at elevated temperatures were studied. It was shown that the the relationship between shrinkage and water loss had some changing points and this tendency became more clear as the temperature increased.(3). Coefficients of the double power law for creep of concrete are influenced by the moisture content in the concrete. In order to develop a generic constitutive law to describe rationally the creep of concrete, these coefficients should be given as functions of the moisture content. Less