Evaluation of the Thermal and Shrinkage Stresses in Restrained High-Performance Concrete

The early age volume deformation is the main course for the cracking of high-performance concrete (HPC). Hence, the shrinkage behavior and the restrained stress development of HPC under different restraints and curing conditions were experimentally studied in this paper. The method to separate the stress components in the total restraint stress was proposed. The total restrained stress was separated into autogenous shrinkage stress, drying shrinkage stress and thermal stress. The results showed that the developments of the free shrinkage (autogenous shrinkage and drying shrinkage) and the restrained stress were accelerated when the drying began; but the age when the drying began did not significantly influence the long-term shrinkage and restrained stress of HPC; the autogenous shrinkage stress continuously contributed to the development of the total restrained stress in HPC; the drying shrinkage stress developed very rapidly soon after the drying began; and the thermal stress was generated when the temperature dropped. The thermal stress was predominant at the early age, but the contributions of the three stresses to the total restrained stress were almost the same at the age of 56 d in this study.

Research of Mechanical Properties of Concretes as Cement-Based Porous Materials

The concrete as a porous cement-based material is widely used in practice. The analysis of the basic reason why the drying shrinkage stress develops in concrete at early age is made by using the principal of the equilibrium between capillary water repulsive force and molecular attracting force. The model for computing the drying shrinkage stress for nonbinding concrete is presented by relating the capillary water pressure to relative humidity. Based on it ,the model for concrete fully restrained is given. The measurement of the drying shrinkage stress and depth of cracks caused by the drying shrinkage stress is made by using translation symmetric theorem and adopting dog-shaped specimens, and the analysis of changes in depth of cracks over time for two kinds of specimens is made. using the method of comparison ,the comparison of the gradient of the drying shrinkage stress for two kinds of specimens is made ,and it comes to the conclusion that the median drying shrinkage stress in the concrete fully restrained is higher in value by 1MPa compared to the drying shrinkage stress in non-restrained concrete