When it comes to sustainability, steel rebar corrosion has always been a big issue, especially when they are exposed to harsh environmental conditions, such as marine and coastal environments. Moreover, the steel industry is to blame for being one of the largest producers of carbon in the world. To supplant this material, utilizing fiber-reinforced polymer (FRP) and hybrid FRP bars as a reinforcement in concrete elements is proposed because of their appropriate mechanical behavior, such as their durability, high tensile strength, high-temperature resistance, and lightweight-to-strength ratio. This method not only improves the long performance of reinforced concrete (RC) elements but also plays an important role in achieving sustainability, thus reducing the maintenance costs of concrete structures. On the other hand, FRP bars do not show ductility under tensile force. This negative aspect of FRP bars causes a sudden failure in RC structures, acting as a stumbling block to the widespread use of these bars in RC elements. This research, at first, discusses the effects of different environmental solutions, such as alkaline, seawater, acid, salt, and tap water on the tensile and bonding behavior of different fiber-reinforced polymer (FRP) bars, ranging from glass fiber-reinforced polymer (GFRP) bars, and basalt fiber-reinforced polymer (BFRP) bars, to carbon fiber-reinforced polymer (CFRP) bars, and aramid fiber-reinforced polymer (AFRP) bars. Furthermore, the influence of the hybridization process on the ductility, tensile, and elastic modulus of FRP bars is explored. The study showed that the hybridization process improves the tensile strength of FRP bars by up to 224% and decreases their elastic modulus by up to 73%. Finally, future directions on FRP and hybrid FRP bars are recommended.

One of the main disadvantages of steel bars is rebar corrosion, especially when they are exposed to aggressive environmental conditions such as marine environments. One of the suggested ways to solve this problem is to use composite bars. However, the use of these bars is ambiguous due to some weaknesses, such as low modulus of elasticity and linear behavior in the tensile tests. In this research, the effect of the hybridization process on mechanical behavior, including tensile strength, elastic modulus, and energy absorbed of composite bars, was evaluated. In addition, using basalt fibers because of their appropriate mechanical behavior, such as elastic modulus, tensile strength, durability, and high-temperature resistance, compared to glass fibers, as the main fibers in all types of composite hybrid bars, was investigated. A total of 12 hybrid composite bars were made in four different groups. Basalt and carbon T300 composite fibers, steel bars with a diameter of 6 mm, and steel wires with a diameter of 1.5 mm were used to fabricate hybrid composite bars, and vinyl ester 901 was used as the resin. The results show that, depending on composite fibers used for fabrication of hybrid composite bars, the modulus of elasticity and the tensile strength increased compared to glass-fiber-reinforced-polymer (GFRP) bars by 83% to 120% and 6% to 26%, respectively. Moreover, hybrid composite bars with basalt and steel wires witnessed higher absorbed energy compared to other types of hybrid composite bars.

Using steel bars in corrosive conditions imposes a high cost on concrete elements. This is due to corrosion of steel bars. In order to eliminate this issue, the use of composite materials in civil engineering practices has become an area of focus because of their acceptable mechanical behavior, such as high strength, suitable durability in corrosive environmental conditions, and low weight. However, composite bars show low ductility and brittle fracture in tensile tests. These weaknesses act as a stumbling block to the widespread use of such bars in concrete elements. Therefore, a new generation of hybrid composite bars, fabricated by a combination of two or more composite fibers, has been proposed to eliminate these downsides. In this research project, six reinforced concrete beams in three groups, including beams reinforced with basalt‐wire hybrid composite bars, carbon‐basalt hybrid composite bars, and steel bars, have been evaluated in statistical 4‐point flexural tests. The test results showed that the energy absorption rate for beams reinforced with basalt‐wire hybrid bars compared to beams reinforced with steel bars was up to 93% in the statistical 4‐point flexural test.

The application of FRP composites in recent years has attracted much attention. Lightweight, high strength, and corrosion resistance are among the properties that make this material available in various forms in construction engineering. The present study analyzed the performance of carbon fiber‐reinforced accelerated corrosion‐proof box. Nine columns without corrosion and cross‐corrosion reinforcement were tested in laboratory and software. Syntax reinforcement was applied locally to the damaged area with respect to a transverse and longitudinal layer. The results of the axial test showed that, due to corrosion, the damaged site was weakened by the loading and severe resistance decreased, and the range of damage points due to the axial load was highly deformed compared to the initial state. The damage caused on both sides of the steel column had a significant effect on reducing the hardness and deformation of the steel columns; it is worth noting that the corrosion on both sides of the steel column had the most variations among the samples. Application of CFRP with 2 layers in the damaged steel columns resulted in increased bearing capacity and hardness in the affected area due to corrosion so that reinforcement of these columns by carbon fibers improved the axial strength.