Experimental investigation on the fracture properties of concrete under different exposure conditions.

• Under different exposure conditions, the initial fracture toughness of concrete increases but the unstable fracture toughness of concrete decreases with the increase of exposure duration. • The stress-free crack opening displacement decreases largely under exposure conditions, indicating the brittleness of the concrete becomes stronger. • The sulphate ion contents under dry-wet cycling are obviously higher than those under the other exposure conditions, demonstrating that dry-wet cycling has the most serious sulphate attack. The fracture properties of concrete subjected to sulphate attack are investigated. First, concrete beams were subjected to different exposure conditions, i.e., full immersion, partial immersion and dry-wet cycling, for 90, 180 and 270 days, and a subsequent three-point bending test was conducted. A softening constitutive relationship of concrete was then derived and a simplified bilinear model was proposed for different exposure conditions. Finally, a chemical titration test was conducted to obtain the profiles of sulphate ion contents along the depth of concrete. The results indicate that, when concrete is subjected to different exposure conditions, the initial fracture toughness increases but the unstable fracture toughness decreases with the exposure duration. The stress-free crack opening displacement in the simplified bilinear model decreases significantly, indicating that concrete attacked by sulphate becomes more brittle. In addition, the sulphate ion content decreases rapidly along the depth and the sulphate ion content in concrete under dry-wet cycling is obviously higher than those under the other exposure conditions, demonstrating that dry-wet cycling results in the most serious sulphate attack on concrete. [ABSTRACT FROM AUTHOR]