Tensile strain capacity of concrete under various states of stress

Abstract

The direct-tension-test method and the mechanical properties of concrete in compression, flexure and tension have been investigated. The mould used for preparing the specimens in the direct tension test has been modified to overcome the difficulties in centralizing and aligning the two embedded bars in the specimens. The method adopted improves the weak bond strength between the embedded bar and concrete and reduces the stress concentration at the end of the embedded bar. Concrete is most brittle under tension. The state of stress affects the failure characteristics of concrete. The tensile strain capacity, which is used to evaluate cracking in concrete, should be chosen judiciously depending on the state of stress in the concrete. The tensile strain capacity obtained from the flexure test has a higher standard deviation, indicating wider variability of the results. Relationships between tensile strength and flexural strength and between compressive strength and tensile or flexural strength are also presented in this paper. The modulus of elasticity from the tension test is similar to that obtained from the compression test for low-grade concrete, but the values obtained from the tension test are lower than those from the compression test for concrete of high grade. The values of Poisson's ratio in tension and flexure decrease when the tensile or flexural stress in the concrete is raised. The values of Poisson's ratio in compression vary insignificantly before reaching the discontinuity point, and increase sharply afterwards.