Experimental Study On Biaxial-to-uniaxial Strength Ratio Of Concrete At Early Age

Failure criteria and constitutive relation of concrete are two significant issues in nonlinear analysis of structure. In order to determine a failure criterion of concrete, it is necessary to introduce many material parameters, among which biaxial-to-uniaxial strength ratio, β, as an important material character should be obtained. So far, most of the researches prefer to focus on the strength of biaxial compression than the strength of equally biaxial compression of concrete. Particularly, it is rare for the concrete at early age under equally biaxial compression condition. In line with this, the tests were carried out in this study to investigate the value of β for the concrete with different maximum of aggregate sizes, strength grades, and ages. The research contents are as follows:1. The concrete cubes with different maximum aggregate sizes (10mm,20mm,30mm), strength grades (C30, C40, C50), and ages (6h,12h,1d,3d,7d,14d,28d) were tested subject to axial and equally biaxial compression. The results indicate that, for the cubes after curving12hours, they present columnar and sheet failure models under axial and equally biaxial compression conditions, respectively. The value of β decreases with the increase of age and strength grade of concrete. Also, for concrete with C30and C40strength grades, the value of β increases with the increase of maximum aggregate size. While, for the concrete with C50strength grade, it is not obviously influenced by the maximum aggregate size.2. Based on the experimental data collected from other literatures and tested in this study, the relationship between β and the age of concrete was established by fitting with logarithmic function. Also, the power function was used to fit the relationship between β and the strength grade of concrete. It is shown that the results from two fitting formulas have a good agreement with the experimental data. For concrete with C30and C40grades, the values of β increase with the increase of maximum aggregate size, in which the growth rates are0.067and0.072, respectively.