The corrosion resistance of engineered cementitious composite (ECC) containing high-volume fly ash and low-volume bentonite against the combined action of sulfate attack and dry-wet cycles

This study aims to investigate the corrosion resistance of engineered cementitious composite (ECC) containing high-volume fly ash and low-volume bentonite against the combined action of sulfate attack and dry-wet cycles. The fly ash/cement ratios (FA/C) were 1.2, 1.8, and 2.4. The amounts of bentonite blended in the ECCs of each FA/C were 0%, 3%, and 6% by mass. The specimens were immersed in 10% sodium sulfate solutions (S), 10% magnesium sulfate solutions (M), and water (W) for 150 dry-wet cycles. The pore fluid distribution and threedimensional pore distribution of the specimens were observed with nuclear magnetic resonance (NMR) and industrial computed tomography (CT); the compressive strength and relative dynamic modulus of elasticity (RDME) of the specimens were measured every 25 dry-wet cycles; The microstructures of the ECC were observed with a scanning electron microscope (SEM) after 150 dry-wet cycles. The results showed that the corrosion resistance of the ECC decreased with the increase of FA/C. In contrast, adding bentonite improved the pore structure and the performance of the ECC. Analysis of the interactions between fly ash and bentonite revealed that the ECC with a FA/C of 1.8 and a bentonite content of 3% is highly corrosion resistant. Moreover, the corrosion resistance of ECC is related to the coupling effects of sulfate corrosion and dry-wet cycles. Sulfate exerted has negative and positive effects on the ECC before and after the 75th dry-wet cycle. After 150 dry-wet cycles, the corrosion resistance of ECC from highest to lowest is the ones immersed in W>in M>in S.