THE STATISTICAL DAMAGE MODEL OF CONCRETE UNDER UNIAXIAL COMPRESSION CONSIDERING FREEZE-THAW DETERIORATION EFFECT

A statistical damage constitutive model of concrete under uniaxial compression is proposed to consider the impact of freeze-thaw. The entire compression process is divided into two stages: uniform damage and local failure, considering two mesoscopic damage modes of yield and fracture. Under the freeze-thaw environment, the internal pore structure and the mechanical characteristics of the microstructure will change significantly, which can be reflected by the initial elastic modulus E. In the process of further bearing the compressive load, the shape, path and quantity of microcracks initiation and propagation in the microstructure will also change due to the influence of the initial freeze-thaw degradation, which could be characterized by damage parameters ε_a, ε_h, ε_b and H. Assuming that under different number of freeze-thaw cycles, the evolution trend of the mechanical properties of the microstructure and the meso-damage process obey a certain regularity, thusly define the above 5 characteristic parameters as functions of the number of freeze-thaw cyclesN. To verify the rationality of the model, the uniaxial compression test was carried out, and the stress-strain full curves of concrete were obtained when the number of freeze-thaw cycles N changed from 0 to 150. Meanwhile, five groups of experimental data in the literature were also analyzed. The results show that: prediction curves are in a good agreement with the test curves, and the characteristic parameters in the model show obvious regularity as the number of freeze-thaw cycles increases. This model provides an effective tool for both the analysis and predicting damage mechanism of concrete in the freeze-thaw environment.