Study On The Effect Of Void On The Macro-Mechanical Properties Of Concrete

Concrete material is one of the most widely used construction materials, the destruction of concrete material is the result of the damage accumulation, the mesoscopic structure characteristics is one of the most important characteristics of concrete materials, in-depth understanding of void distribution and its evolution or development process of concrete and then find out how pore parameters influence the macroscopic characteristics, further establish the connection between the porosity and the concrete damage, ultimately provide a reasonable basis for improving the mechanical properties of concrete.Concrete is a kind of composite material consisting of cement, coarse aggregate, cracks and pores. The change of microscopic structure parameters affects the macroscopic mechanical behaviors of concrete, such as the elastic modulus, the tensile and compressive strengths.This article mainly uses the model of random aggregate of concrete and then numerical loading tests are carried out, when generate the model, different pore diameter and porosity of were introduced to the cement mortar. Throuth the numerical analysis by finite element analysis software Marc, the influence law of the pore diameter and porosity of concrete to the uniaxial compressive strength and elastic modulus were researched, The test results show that the elastic modulus of concrete is linear decline as the growth of the porosity when in the same aperture and logarithmic decrease as the growth of the aperture when in the same porosity; Tensile or compressive strength of concrete is logarithmic decline no matter as the growth of the porosity or as the growth of aperture.Secondly, the numerical test results compared with empirical formulas and verify the numerical test results and rationality of the formula. Based on strength damage formula the initial damage was calculate, this paper establish the relationship between concrete with initial damage and porosity and pore size. Finally according to the damage calculation formula, the concrete initial damage surface was described.In order to get the failure law of concrete in the process of loading, the element deletion method was adopt to study the stress strain relationship, and through the secondary development program to calculate the failure area variation in the loading process. we can find out that with the increase of porosity, the material damage area is small when reaching the peak stress. Because of the concrete contains a number of aperture, numerical specimen with multi aperture was tested. The results shows that the distribution and porosity of pore has much effect on the elastic modulus and strength. The weight coefficient influence on macroscopic mechanical properties of concrete with different pore sizes are closely related with the percentage of different aperture.