To investigate the detailed deterioration behavior of concrete under sulfate wetting-drying (WD) attack, high-frequency strength detection and 3D digital image reconstruction were implemented. The compressive strength of the concrete was tested every three cycles. X-ray computed tomography (X-CT) scanning (voxel size ≈ 0.25 mm 3 ; 120 kV, 200 mA; 1024 projections per rotation) and digital image processing were conducted on the samples every fifteen cycles. The results indicated that compressive strength decreased initially, reached the peak at the ninth cycle, and declined in a fluctuating trend which cannot be observed in traditional low-frequency detection. 2D digital image processing results indicated the pore number firstly increased and then decreased during WD cycles. More pores were concentrated at the edges of the sample. More cracks were distributed in the interfacial transition zone (ITZ). 3D digital image reconstruction model illustrated that the critical pore size was increased and some pores even penetrated to cracks. Cracks showed a through-cracking trend. The “filling-damage” cycle of expansive crystals resulted in the evolution trends of pore and crack. In addition, the evolution trends of pore and crack drove the fluctuating trend of compressive strength. These were meaningful for further understanding the deterioration mechanism of concrete. • High-frequency WD cycle compressive strength tests were conducted. • Compressive strength initially increases and then exhibits a fluctuating decline. • The 2D and 3D distributions of pore structures were quantitatively analyzed. • Visualization and 3D quantitative analysis of internal cracks were achieved.
Wu et al. (Wed,) studied this question.