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The service environment of concrete in the marine environment is harsh, and demands regarding the durability of marine concrete have increased. Marine concrete in harbor and wharf areas suffers from the combined effect of fatigue load, dry–wet cycles, and Cl− erosion, which can result in spalling of the concrete surface, corrosion of the internal reinforcement, and even concrete damage. This paper reviews recent research results on the durability of concrete and reinforced concrete (RC) under the combined effect of fatigue load, dry–wet cycles, and Cl− erosion. We further assess the variation in Cl− transport properties with fatigue load, the causes behind the reduction in the carrying capacity of RC products under fatigue load, the methods of Cl− erosion on concrete under the pressures imposed by dry–wet cycles, and the damage of the protective layer of concrete due to accelerated Cl− erosion caused by the action of dry–wet cycles. Further studies are needed on the durability of concrete under the action of fatigue load, wet and dry cycles, and Cl− erosion, in addition to the testing of the durability of concrete under the combined effects of the afore-mentioned various factors. [ABSTRACT FROM AUTHOR]

In order to study the influence of nanomaterials on the carbonation resistance of marine concrete under bending loads, an appropriate amount of nano-SiO2 was added to plain concrete, and a self-developed carbonation box and bending loading device were used to conduct a coupling test. Four different stress levels were set to measure the carbonation depth of nano-concrete at different ages. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the concrete interfacial transition zone. The carbonation depth was used as the test index to evaluate the durability of nano-SiO2-based concrete under the combined action of bending load and carbonation. The test results showed that the compressive and flexural strengths of concrete remarkably improved when the nano-SiO2 concentration was 2%. Compared with regular concrete, the compressive and flexural strengths of nano-SiO2 based concrete improved by 15.5% and 15.3%, respectively. When the stress level was 0.15 and 0.6, the carbonation depths of NS20 were 20.5 and 18.4% lower than those of PC in the tensile zone and 18.9 and 23.7% lower than those of PC in the compression zone. The carbonation depth of the NS20 tensile zone was lower by 31 and 18.4% at 3 and 28 days than that of PC. Compared with PC, the carbonation depth in the compression zone of NS20 decreased by 50 and 23.7%, and the carbonation depth of nano-concrete was significantly lower than that of conventional concrete under the same stress level and age. When the stress level is constant, the carbonation depth of the tension zone and compression zone increases gradually with the increase in age, and the carbonation depth of the concrete in the first 7 d was 50% that at 28 days. Under the same age, the carbonation depth in the tension zone increased with increasing stress levels, while the carbonation depth in the compression zone decreased with increasing stress levels. When the stress level was 0.3–0.45, the slope of the carbonation depth curve significantly increased. SEM and XRD analysis results revealed that nano-SiO2 significantly improved the internal structure of concrete by reducing the width of the microcracks, the number of pores, and the number of microcracks. The number of C3S/C2S and CaCO3 crystals in nano-SiO2 based concrete was significantly less than that in plain concrete, and the amount of C-S-H gel was more than that in plain concrete. Under bending loads, the nano-SiO2 significantly improved the carbonation resistance of concrete. When the dosage of nano-SiO2 was 2%, its improvement effect was the most significant. [ABSTRACT FROM AUTHOR]