Scouring erosion resistance of nano-marine concrete under the coupled effect of chloride attack and dry - wet cycles

Abstract

In order to reveal the improving mechanism associated with different types of nanoparticles under the three-factor coupled effects (scour, dry-wet cycles, and Cl- attack), a laboratory investigation was undertaken to evaluate and compare the influence of nano-SiO2 and nano-Fe3O4 with different content on scouring erosion resistance properties of marine concrete. The micro-structure of the interface transition zone (ITZ) in marine-concrete, as well as the features of hydration products, were characterized using advanced techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), differential thermal gravimetric (DTG-DSC) analysis, and mercury intrusion porosimetry (MIP). The test results showed that compressive and flexural strength, as well as scouring erosion resistance of marine-concrete were enhanced with the increasing content of nano-SiO2 and nano-Fe3O4 until the threshold limit of 2%, and performance of NSC20 was better than that of NFC20. Under the three-factor coupling, the strength corrosion resistance coefficient of nano-marine concrete was negatively correlated with the scouring erosion rate and the change rate of scouring erosion area, and positively correlated with the resistivity and the Cl- diffusion coefficient with the increase of corrosion age. When the corrosion age reached 70 days, the average scouring erosion rates of NSC20 and NFC20 were decreased 19.86% and 14.43%, respectively, compared with PC. The convective depth of concrete steadily decreased while its diffusive depth increased relative to concrete without scouring. Cl- binding was increased by 28.5%, 27.2%, and 21.4% for PC, NSC20, and NFC20, respectively. The high chemical activity of nano-SiO2 and nano-Fe3O4 promoted the mechanical performance and durability of concrete through improved density and homogeneity of chlorinated products and optimized the structure of the C-S-H/C-F-H gels in ITZ, as indicated by SEM-EDS observation, XRD, and DTG-DSC analysis. The coupling effects resulted in increasing volume of air voids and micro-cracks, as well as weak ITZ due to SA, which hindered scouring resistance development, as indicated by the MIP analysis.