Coupled effect of the freeze-thaw cycles and salt erosion on the performance of concretes modified with nanoparticles

Abstract

In cold and saline soil regions, freeze-thaw (F-T) cycles and salt erosion are two major factors determining the durability of concrete structures. This paper aims to investigate the influential mechanism and deterioration of the mechanical and microstructural properties for the concretes modified with nano-TiO2 (NT) and nano-SiO2 (NS) exposed to the coupled environment conditions of the F-T cycles and salt erosion. 180 F-T cycles were conducted on the concretes immersed in five kinds of environment media, namely, water (WF), air (AF), solution with a concentration of 5% Na2SO4 (SSF), solution with a concentration of 5% NaCl (SCF), and a mixture solution with the concentration of 5% Na2SO4 and 5% NaCl (HSF). The results indicate that the added nanoparticles and media significantly influence the overall performance of concrete samples. The SCF has the greatest influence on the degradation of concretes, following by the HSF, SSF, WF, and AF. Meanwhile, the compressive strength of concretes modified with NT is lower than that modified with NS. There is an optimal nanoparticles ratio for the nano-concrete samples to resist coupled effect of the F-T actions and salt erosion, and the optimal nanoparticles ratios for the concretes modified with NS and NT are 1% and 2%, respectively. Moreover, the filling effect on pore structure for the concretes modified with NS is better than that with NT, more hydration products and corrosion products occur on the concrete surfaces, and the crystals on the surface of concretes modified with NS are larger than that modified with NT. Furthermore, for the concretes modified with nanoparticles in the first 90 F-T actions, the gel micro-pores (<10 nm) increase, while the macro-pores (>5000 nm) decrease. However, the gel micro-pores decrease and the macro-pores increase within the 90–150 F-T cycles. This research would provide significant instructions on the exploration of the anti-erosion and frost-resistance of nano-concretes in marine and cold region engineering.