Scouring erosion resistance of nano-marine concrete under simultaneous flexural load and chloride attack

Abstract

To reveal the improving mechanism associated with various types of nanoparticles, an indoor experiment 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 with microscopic tests. Results indicated that the higher the stress levels, the greater the scouring erosion speed and the wear area. Compared to σmax = 0 ft, the scouring erosion speed of PC, NSC20 and NFC20 increased by 70.35 %, 76.56 % and 97.47 % for σmax = 0.7 ft, respectively. Scouring promoted the depth of Cl− attack and exacerbated the expansion of concrete microcracks. Scouring resistance of marine concrete was 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. The wear area and the scouring erosion speed of NSC20 and NFC20 were decreased by 22.23 % and 20.25 %, 23.72 % and 18.11 %, respectively, compared with PC at T = 70 d and σmax = 0.7 ft. The high chemical activity of nano-SiO2 and nano-Fe3O4 promoted the strength development of marine concrete through improved density and homogeneity of chlorinated products and optimizes the structure of the C–S–H and C–F–H gels in ITZ, as indicated by SEM-EDS observation, XRD, and DTG analysis. Size of harmful pores was limited by nano-SiO2 to 10～17 %, and that the PC, NSC20, and NFC20 had the most numerous and widest microcracks at the outer edges of the tensile zones, with maximum microcrack width of 45.4 μm, 13.4 μm, and 18.7 μm, respectively, as indicated by the MIP and CT analysis.