International Concrete Abstracts Portal

Glass fiber-reinforced polymer (GFRP) bars have emerged as a promising alternative to traditional steel reinforcement in concrete structures due to their superior corrosion resistance and light weight. These advantages make GFRP particularly suitable for use in saline environments, such as for marine infrastructure, where exposure to chloride ions and harsh conditions accelerates the degradation of conventional steel reinforcement. This study investigated the durability and flexural behavior of concrete beams reinforced with GFRP bars preconditioned in simulated marine environments. Ten beams were prepared: six beams reinforced with GFRP bars conditioned in a saline solution at 60°C for 3, 6, and 12 months prior to concrete pouring; four unconditioned beams served as controls. The experimental results revealed that the GFRP-reinforced beams exhibited negligible reductions in flexural capacity and stiffness after exposure to marine conditions, confirming their suitability for marine structural applications. In addition, theoretical calculations using the Arrhenius model were conducted to predict the long-term performance of GFRP bars over a 100-year period in tropical regions and a 150-year period in northern regions. This research enhances the understanding of GFRP’s long-term durability in aggressive environments and supports its use in infrastructure subjected to marine conditions.

To promote the application of fiber-reinforced polymer (FRP) bar-reinforced ultra-high-performance seawater sea-sand concrete (FRP-UHPSSC) structures in marine construction, four-point static bending tests were carried out on 16 FRP-UHPSSC beams with different reinforcement ratios, cross-section heights, and types of FRP bars to investigate the ultimate load-carrying capacity, the midspan deflection, and the failure modes of the beams. The experimental results show that all the test beams had brittle failure, and the failure mode of the beams is shear failure when the ratio of the actual reinforcement ratio to the balanced one is higher than 2.73. Increasing the reinforcement ratio and the beam section height improve both bending moment at ultimate load and flexural stiffness at the service limit state. The steel-FRP composite bar (SFCB)-reinforced UHPSSC beams have the maximal bending moment at ultimate load, and the basalt fiber-reinforced polymer (BFRP) bar-reinforced UHPSSC beams have the optimal ductility. The deviation of ultimate bending moment and midspan deflection obtained by proposed calculation method is reduced from 7.5 to 2.8%, and from 15 to 3%, respectively, compared with current specifications for FRP-reinforced concrete structures.

The alkali resistance of glass fiber-reinforced polymer (GFRP) bars is a key property that must be evaluated before they can be used as an alternative to steel reinforcement in marine concrete structures. To clarify the effect of alkalinity on GFRP bars, their durability was investigated via accelerated aging in simulated seawater sea-sand concrete environments with different alkalinity levels. The physical and mechanical properties, including moisture uptake, interlaminar shear strength, transverse shear strength, and tensile strength of GFRP bars, were measured after exposure to solutions with pH values of 10.1, 12.3, and 13.2. Furthermore, microstructural deterioration was analyzed using Fourier transform infrared spectroscopy and scanning electron microscopy. A refined predictive model based on reaction kinetics and Arrhenius theory was proposed to quantify the role of alkalinity. The results indicated that the degradation of GFRP bars is highly sensitive to alkalinity. When the pH decreased from 13.2 to 12.3, the deterioration in mechanical strength was reduced by more than 60%, accompanied by significantly mitigated glass fiber etching. Below a threshold between high and moderate alkalinity, this sensitivity diminished as alkalinity decreased. The loss of mechanical properties was reduced by only about 10% when the solution pH dropped from 12.3 to 10.1, with clear alleviation of resin disintegration and fiber surface corrosion. Within the typical alkalinity range of ordinary concrete, the degradation rate follows a power function of the hydroxyl ion concentration. The effect on the degradation rate is much greater within the concentration range of 0.1 mol/L to 0.01 mol/L (pH ≈ 13.0-pH ≈ 12.0) than below 0.01 mol/L (pH ≤ 12.0). It is therefore recommended to keep the hydroxyl ion concentration in concrete pore solution below 0.01 mol/L (pH ≈ 12.0) to minimize alkaline attack on embedded GFRP bars.

Hydrostatic pressure has a significant impact on the transportation of chloride ions in concrete, especially in underground structures and marine environments. This paper proposes a new seepage velocity model that considers the combined effects of hydrostatic pressure and initial hydraulic gradient on chloride ion transport. By combining saturated and unsaturated concrete seepage models and convection-diffusion coupled chloride ion transportation analysis, the influence of hydrostatic pressure and seepage velocity on chloride ion transport in concrete is studied. Experimental verification shows that the proposed model can accurately predict the concentration distribution of chloride ions. The analysis results indicate that the seepage velocity under hydrostatic pressure is not only positively correlated with the permeability coefficient of concrete and hydrostatic pressure, but also negatively correlated with the initial hydraulic gradient, and has a significant impact on the transient seepage characteristics of unsaturated concrete. The effect of seepage velocity on the chloride ion transportation process exhibits nonlinear characteristics. Before a critical value, seepage velocity promotes the transportation of chloride ions, while after exceeding this critical value, the influence gradually decreases. Based on this conclusion, it suggests that in the durability design of underground concrete structures, a chloride ion transportation model considering the convection-diffusion coupled effect should be adopted for a more accurate prediction on the service life of the structure.

Geopolymer concrete offers a lower-carbon alternative to OPC concrete, but long-term durability under aggressive exposure remains critical for field adoption. This study evaluated low-calcium fly ash geopolymer concretes with 0%, 10%, and 20% OPC replacement (denoted GPC100C0, GPC90C10, and GPC80C20) after immersion in tap water, seawater (pH ≈ 7.25), an alkaline solution (pH ≈ 12.5), and an acidic solution (pH ≈ 2.5). Compressive strength and ultrasonic pulse velocity (UPV) were measured at 1, 3, 6, 9, and 12 months. Across all conditions, net mass change remained below 3%. In tap water, 12-month reference compressive strengths were approximately 22 MPa (GPC100C0), 40 MPa (GPC90C10), and 43 MPa (GPC80C20). After 12 months, compressive-strength loss was clearly dependent on the exposure medium. In seawater, losses ranged from about 20% (GPC80C20) to 30% (GPC90C10). In alkaline solution, losses were about 5% (GPC100C0), 20% (GPC90C10), and 33% (GPC80C20). In acidic solution, GPC80C20 showed the lowest loss (about 8%), whereas GPC90C10 showed the highest loss (about 30%). UPV in tap water was approximately 3.2 to 3.9 km/s, and UPV–strength relationships were mixture- and exposure-specific (best-fit R² ≈ 0.84). These results provide practical guidance for durability-oriented mix selection and UPV-based in-service condition assessment.