Experimental and numerical investigations on damage evolution of concrete under sulfate attack and freeze-thaw cycles

The macro-microstructure tests of concrete under the alternating action of salt freezing (ASF) were conducted to investigate the macro-mechanical properties and microstructure pore evolution patterns of concrete. Combined with CT scanning and 3D pore model reconstructing technologies, we present the evolution equation of concrete porosity and the quantitative relation between the fractal dimension of concrete pores and the macroscopic strength under the ASF. Then, a macro-microscopic damage evolution model of concrete was proposed to study the structural performance evaluation of an aqueduct. The results show that the compressive strength (fc), splitting tensile strength (ft), and relative dynamic modulus (Erd) of concrete specimens under the ASF show a decreasing trend as a whole, and the mechanical properties of concrete gradually decrease with the increase of sulfate solution concentration. With the increase of the cycles of salt freezing alternation, the pore fractal dimension of the concrete gradually decreases and the porosity gradually increases. After the cycle of 8 times, the pore fractal dimension decreases by 6.06%, and the porosity increases by 7.30% compared with the initial state. The porosity of concrete is negatively correlated with the strength, while the fractal dimension of the pore structure is positively correlated with the strength. When the ASF reaches 8 times, the maximum compressive stress and tensile stress of the groove body are 9.48 MPa and 3.13 MPa, respectively, which appear at the ends of the lower chord. The displacements of the bottom and side wall plates are 0.384 mm and 3.289 mm, respectively. The penetrating cracks appear at the junction, and the structure severely deteriorates.