No abstract

Using fiber-reinforced polymer (FRP) bars instead of steel bars to reinforce concrete columns in harsh environments has become an important method for solving corrosion problems. The brittleness of FRP bars significantly reduces the ductility of columns. It has been proposed that columns can be reinforced with hybrid FRP and steel bars to improve ductility, but related research is very limited. In this research, the axial compression behaviour of seawater sea sand concrete (SSC) columns reinforced with hybrid FRP bars and stainless steel (SS) bars was studied. In total, 84 SSC columns were designed, including 15 SS reinforced SSC (SS-SSC) columns, 15 glass-FRP (GFRP) reinforced SSC (GFRP-SSC) columns, 45 hybrid FRP-SS reinforced SSC (FRP-SS-SSC) columns and nine plain SSC columns. The failure modes, load-axial displacement curves, bearing capacity, and ductility were analyzed with consideration of the effects of the reinforcement types, reinforcement ratios, and concrete strength. The results showed that ductility could be significantly improved by hybrid reinforcements, and the ductility indexes of the FRP-SS-SSC columns were close to those of the SS-SSC columns. The proposed equation could accurately predict the bearing capacity of SSC columns Furthermore, the theoretical stress-strain relationship for the studied axial compression SSC columns was proposed.

The deterioration of steel rebar in reinforced concrete is a major issue that reduces RC structures’ durability and structural integrity. Significant efforts have been devoted to developing high-performance coatings to provide efficient protection of the rebar, and one promising approach is to utilize nanofiller as additives to improve the performance of polymer resins. This study aimed to improve the corrosion resistance of steel rebar by applying an epoxy coating with graphene nanoplatelets (GNPs) and silica nanopowders (NSs) as additives. The corrosion behavior of nanocomposite-coated rebars was characterized via an electrochemical impedance spectroscopy (EIS) test, and salt spray exposure was utilized to evaluate the durability of the coated rebars. Investigation of abrasion resistance and mechanical properties of the coatings was conducted using the falling sand test and tensile coupon test. In addition, the nanocomposites were scanned by micro-CT to explore the effect of binary nanofillers on the intactness of the polymeric matrix. The GNP-NS hybrid filler reduced the void fraction to 0.002%, whereas the void fraction in pure epoxy was 0.07%. Significant reinforcement was found in the mechanical properties; the addition of GNP-NS hybrid filler increased the tensile strength to 37.1 MPa, a 56% increase compared to the pure epoxy. Additionally, the GNP-NS hybrid fillers have led to an improvement of 16% in the Young’s modulus. In terms of corrosion resistance, the Rc value of rebar coated with GNP-NS coating was about three times greater than the ones coated with a single-filler epoxy coating during the initial test, and this value remained undegraded after 200 hr of exposure. In contrast, the group containing hybrid fillers displayed the lowest thickness loss following abrasion testing, with a 74% reduction in thickness loss, showing the coating’s high abrasion resistance. Hence, the results reveal that GNP-NS hybrid fillers have superior wear resistance, mechanical capabilities, anticorrosion properties, and durability. This research provides valuable insights into developing and implementing high-performance polymeric material to protect steel rebars in concrete structures, therefore significantly increasing the sustainability of concrete structures.