A MICRO FRACTURE MODEL FOR CONCRETE CONSIDERING THE INFLUENCE OF TEMPERATURE

A three-phase micro fracture spherical model for concrete considering the influence of temperature is established based on a rule that volumes of each component in the model are the same as those of the real material. The components of concrete is simplified as aggregate, water and cement paste, and each part is modeled as a spherical layer. Cracking of concrete at elevated temperature is considered to be the result of evaporation and escape of the water in the mid-layer. The gas state equation is employed to determine the internal pressure of the model, and the stress states of the aggregate and cement paste layers are studied as well. The releasable elastic energy and the surface energy are investigated for concrete which has a penny-shaped crack. According to the Griffith fracture criterion, the relation between fracture toughness for concrete and temperature is clarified. Numerical calculations are conducted for this present model, and a comparison with the test data is performed. Results indicate the validation of the model in calculating the fracture toughness of concrete at and after elevated temperature. This study addresses a fact that: as the temperature increases, the fracture toughness increases while the initial length of crack where the fracture takes place for concrete decreases.