Deterioration of concrete fracture toughness and elastic modulus under simulated acid-sulfate environment

In order to investigate the deterioration of the elastic modulus and fracture toughness of corroded concrete, three-point bending (TPB) tests were conducted by using corroded concrete specimens. The initiation load, the maximum load, the P-CMOD (loads versus crack mouth opening displacements) curves and the stress-strain curves were measured. Meanwhile, the deterioration near crack tips of the corroded specimens was observed with the aid of scanning electronic microscopy (SEM). Under the simulated acid solutions, the corrosion depth near crack tips gradually grows with the increase of corrosion time, and finally the concrete microstructures are porous and loose and microcracks are developed, which will deteriorate concrete material parameters, such as elastic modulus and fracture toughness. The test results show that subcritical propagation occurs during the loading progress from the initiation load to the maximum load, and the initiation toughness is about 80%-85% of the fracture toughness of the corroded concrete. For the specimens immersed in pH 2.5 and 3.5 solutions, both the fracture toughness and the elastic modulus increase in the early stage and then decrease with the increase of corrosion time, whereas for the specimens immersed in pH 1.5 solutions, both the elastic modulus and fracture toughness decrease almost linearly with immersion time. H+ and SO42- are two main factors in the deterioration of concrete in the simulated acid solutions.