Study On The Effect Of Moisture On The Mechanical Performance Of Concrete Based On Mesoscopic Level

Concrete structures are often erected in the ambient water, the water will seep into the microcracks and pores, making its static and dynamic mechanical properties changing, and then the strength and durability of concrete structures will be affected. Concrete buildings that work in the water will inevitably bear seismic loads, wave loads, impact loads or explosion loads and other power loads, the dynamic mechanical properties of concrete is different from its static mechanical properties.Therefore, to ensure the safe running of the concrete structures in water, it is necessary to carry out the research on the changing law of strength、elastic modulus and other mechanical properties of concrete and its failure mechanism in the water environment. The model based on macroscopic phenomena can not reveal the complex microscopic characteristics and the damage and failure mechanism of concrete, accordingly, this paper was based on mesomechanics, taking static and dynamic mechanical properties of concrete under different moistur as the main object, analyzed C20 and C30 two kinds of concrete’s compressive strength’s variation with moistur and loading rate, main works and results are as follows:(1)In the mesoscopic level, concrete was treated as a three-phase composite material consisting of aggregate, mortar, and the bonding interface between them. A two-dimensional random aggregate model that was similar to the real concrete was generated using Monte Carlo method and Walraven formulas. Numerical simulation of fracture process of concrete specimens under uniaxial compression are performed with explicit integration finite element analysis software platform ANSYS / LS-DYNA, the elastic-brittle meso-damage constitutive relations was introduced to analyze the failure mechanism concrete.(2)On the basis of random aggregate three-phase composite model, six different moisture mesoscopic concrete models were generated by randomly changing element mechanical parameters, the uniaxial compressive failure process of concrete with different moisture contents was simulated, the influence of moisture on the static mechanical properties of concrete was studied. The results show that static compressive strength of concrete decreases with the increase of moisture, and the initial elastic modulus increase with the increase of moisture.(3) Dynamic numerical experimental programs of concrete with different moisture were designed, the influence of intensity level, moisture and loading rate on the compressive strength of concrete was analyzed comprehensively. The results show that moisture is an important factor affecting the dynamic compressive strength of concrete, rate sensitivity of concrete with high moisture is more significant than that of dry and low moisture content concrete; rate effect of high-strength grade concrete is smaller than that of the low-strength grade concrete.