In this study, the performance degradation law and mechanism of glass fiber reinforced polymer (GFRP) bars were investigated by being immersed in natural seawater (denoted as SW), saline-alkali solution (SA), or wrapped with concrete, and then submerged in natural seawater (SWC). A series of short-beam shear tests were conducted to investigate the effects of aging temperature and time on the interlaminar shear strength (ILSS) of GFRP bars. Microstructure changes, glass transition temperature (T_g) difference, and hydrolysis degree of GFRP bars after aging in three environments for 183 days were analyzed using scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and Fourier transform infrared spectroscopy (FTIR). Test results demonstrated that the temperature could accelerate the strength degradation of GFRP bars significantly. After 183-day aging treatment at 60 °C, the ILSS retention rates of GFRP bars in the three environments of SW, SWC, and SA were 66.41%, 53.10%, and 45.36%, respectively; and T_g was 1.7%, 7.0%, 7.8% lower than that of unconditioned sample, respectively. Meanwhile different degrees of damage, such as separation between fiber and resin and few holes in the resin, were observed on the GFRP bars in the SWC and SA environments. It was also found that irreversible hydrolysis took place in some resins. The durability prediction model of GFRP bars serving in the Yellow Sea of China was established by using Arrhenius equation, and the correlation coefficient with the test data was not less than 0.94.

Fiber‐reinforced polymer (FRP) bar‐reinforced unsaturated polyester resin concrete (UPC) can solve the problem of rebar corrosion in ordinary reinforced concrete members. However, it has not been widely used in engineering practice because there have been few studies conducted on the bond behaviors of FRP bar and UPC, and the interaction mechanisms between FRP bar and UPC have not been well understood. A series of pull‐out tests are conducted on FRP bar‐UPC specimens to study the bond behaviors between these two materials. Parametric studies are also carried out to investigate the effects of FRP bar diameter, fiber type, type of surface treatment, concrete cover thickness, and interfacial bond length between the two. Three failure modes of the specimens are observed from pull‐out tests, i.e., FRP bar pull‐out, tensile failure of FRP bar, and UPC split. A new constitutive model is, therefore, proposed to predict the bond stress of FRP bar and UPC in the residual stage, and the proposed model is finally verified by test data reported in this study.

Currently, resin polymer anchoring agents are widely used for bolting support in coal mine roadways to anchor the bolts to the surrounding rock mass. However, due to the relatively low strength of the resin anchoring agent itself, the required anchoring length tends to be excessively long. Based on this, this paper proposes the use of resin concrete as a replacement for resin. Compared to resin anchoring agents, resin concrete offers greater mechanical interlocking force with anchor rods, which can reduce the theoretical anchoring length. To systematically investigate the influence of factors such as the diameter and anchorage length of Glass Fiber-Reinforced Polymer (GFRP) bolt on the bond behavior between GFRP bolts and resin concrete, 33 standard pull-out tests were designed and conducted in accordance with the CSA S807-19 standard. Taking the 18 mm-diameter bolt as an example, when the bond lengths were 2D, 3D, 4D, and 5D, the average bond strengths were 41.32 MPa, 39.18 MPa, 38.84 MPa, and 37.44 MPa, respectively. This represents a decrease of 5.18%, 6.00%, and 9.39% for each subsequent increase in bond length. The results indicate that the bond strength between GFRP anchors and resin decreases as the anchorage length increases. Due to the shear lag effect, the average bond strength also decreases with increasing anchor diameter. Taking a 5D (where D is the anchor diameter) anchorage length as a reference, the average bond strengths for anchor diameters of 18 mm, 20 mm, 22 mm, and 24 mm were 37.44 MPa, 33.97 MPa, 32.18 MPa, and 31.50 MPa, respectively. The corresponding reductions compared to the 18 mm diameter case were 9.27%, 14.05%, and 15.87%. Based on the experimental results, this paper proposes a bond–slip constitutive model between the bolt and resin concrete, which consists of a rising branch, a descending branch, and a residual branch. A differential equation relating shear stress to displacement was established, and the functions describing the variation in displacement, normal stress, and shear stress along the position were solved for the ascending branch. Although an analytical solution for the differential equation of the descending branch was not obtained, it will not affect the subsequent derivation of the theoretical anchorage length for the GFRP bolt–resin concrete system, as structural components in practical engineering are not permitted to undergo excessive bond-slip.

Unsaturated polyester resin concrete (UPC) exhibits high strength and corrosion resistance, and it has been widely used in hydraulic engineering structures. However, the diffusion of water molecules inevitably induces matrix plasticization and debonding at the aggregate–resin interface, which leads to progressive degradation of mechanical performance under long-term aqueous service conditions. To elucidate the water-induced mechanical deterioration mechanism of UPC and to develop a temperature-adaptive model for long-term compressive strength prediction, we prepared UPC specimens using graded quartz sand aggregate, an unsaturated polyester binder, V388 curing agent, and KH570 coupling agent at a fixed mass mixing ratio, followed by 7 days of natural curing after demolding. Accelerated water aging tests were conducted at three temperature levels (25 °C, 40 °C, 60 °C) and four immersion durations (15 d, 30 d, 45 d, 60 d), including water absorption, compressive, splitting tensile, and flexural tests. Based on Fick’s second diffusion law and the Arrhenius equation, we quantitatively analyzed moisture diffusion behavior and the evolution of mechanical degradation. The results indicate that the water absorption of UPC strictly follows Fickian diffusion, and that elevated temperature increases both the water absorption rate and the saturated water absorption capacity. The saturated water absorption ratios reached 0.15%, 0.16%, and 0.22% at 25 °C, 40 °C, and 60 °C, respectively, corresponding to apparent diffusion coefficients of 1.13 × 10⁻⁶, 1.67 × 10⁻⁶, and 4.52 × 10⁻⁶ mm/s. Long-term water aging progressively degrades the mechanical properties of UPC; after 60 d of immersion at 60 °C, the retention rates of compressive, splitting tensile, and flexural strength decreased to 88%, 85%, and 78%, respectively. We developed a physically coupled compressive strength prediction model based on moisture erosion depth and the associated reduction in effective bearing area. The ratio of model predictions to experimental data ranged from 0.93 to 0.98, indicating favorable conservative accuracy for engineering applications. When further combined with the Arrhenius relationship, the model enables extrapolation of the long-term mechanical properties of UPC under arbitrary service temperatures. This work provides theoretical support and a quantitative calculation framework for assessing the durability and predicting the service life of UPC hydraulic structures.

To derive a calculation formula for the fundamental development length of glass fiber-reinforced polymer (GFRP) bars in unsaturated polyester resin concrete (UPC), a series of forty pull-out tests were conducted on GFRP bar-UPC specimens. Analyses were performed on failure modes, bond strength, and bond-slip curves, and the differential equation governing the GFRP bar-UPC bond-slip curve was then proposed and solved. Based on existing criteria and the differential equation solution of the bond-slip curve, two formulas for calculating the basic development length of GFRP bars in UPC were derived. The results indicate that the extraction of reinforcement bar is the predominant failure mode in the GFRP bar-UPC pull-out tests. Bond strength and bond length show a negative correlation relationship. When the bond length increases from 3 to 7 times the bar diameter (with a bar diameter of 10 mm), the bond strength decreases from 35.71 MPa to 26.61 MPa, representing a reduction of 25.48%. The bonding strength is positively correlated with the thickness of concrete cover. When the concrete cover thickness is 2.5, 3, and 3.5 times the bar diameter, bond strength is 29.14 MPa, 29.71 MPa, and 30.25 MPa, respectively. The bond-slip curve of GFRP bars in UPC consists of three sections: rising stage, decreasing stage, and residual stage. The rising section of the curve fits well with the MBPE model curve.