Modeling constitutive relationship of sulfate-attacked concrete

Abstract

Sulfate attack is one of the most common factors responsible for the performance deterioration of concrete exposed to aggressive environment. The transport of sulfate in concrete is a gradual process causing a gradient sulfate attack in concrete. Nominal stress-strain relationship which is directly based on the whole cross-sectional area is not applicable in practical engineering because of its dependence on geometrical dimensions. In this paper, a method is developed to obtain a real constitutive model for sulfate-attacked concrete. To investigate the transport behavior of sulfate ion in concrete, 16 cubic specimens were immersed in 10% sodium sulfate solution for eight immersion durations. Based on the development of sulfate ion content distribution, a modified diffusion model was developed to simulate the transport of sulfate ion in concrete. To clarify the effects of sulfate attack on mechanical properties of concrete, 24 prism specimens were immersed in 10% sodium sulfate solution, and another 24 specimens were immersed in pure water as control group to compensate the influence of further hydration. Based on the sulfate ion content distribution and nominal stress-strain curve for concrete in different immersion durations, real stress-strain curves of concrete with different sulfate ion contents were obtained by an innovative method. After analyzing the effects of sulfate ion content on the mechanical properties of concrete, a real constitutive model was proposed, which can well predict the structural performance of sulfate-attacked concrete members. With the increase of sulfate immersion duration, the peak stress and elastic modulus increase first and then decrease, while the peak strain decreases first and then increase.