International Concrete Abstracts Portal

Slender columns are highly susceptible to buckling, which induces additional bending moments and reduces their axial load capacity compared to short columns, potentially leading to stability failure. This study presents the results of 10 full-scale glass fiber-reinforced polymer-reinforced concrete columns with a slenderness ratio of 45, exploring the influence of longitudinal reinforcement ratio (1.21 or 3.44%) and eccentricity-to-diameter ratio (e/D = 0, 8.5, 17, or 34%). Reference specimens with slenderness ratios of 20 and 28 were included for comparison. Results revealed that the e/D ratio had the most significant influence, markedly reducing axial capacity and magnifying secondary moments. A threshold ofe/D = 17% was identified beyond which stability failure occurred. The contribution of reinforcement ratio became more apparent as the e/D ratio increased. Increasing the slenderness ratio from 20 to 28 reduced the axial capacity, while a further increase to 45 primarily increased secondary moments without a noticeable additional reduction in axial capacity.

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 through 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 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 approximately 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 to 0.01 mol/L (pH ≈ 13.0 to 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.

Geopolymer concrete offers a lower-carbon alternative to ordinary portland cement (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 approximately 20% (GPC80C20) to 30% (GPC90C10). In alkaline solution, losses were approximately 5% (GPC100C0), 20% (GPC90C10), and 33% (GPC80C20). In acidic solution, GPC80C20 showed the lowest loss (approximately 8%), whereas GPC90C10 showed the highest loss (approximately 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 mixture selection and UPV-based in-service condition assessment.

This study investigated the flexural behavior of innovative precast self-consolidating concrete stadium bleacher units with an L-shaped cross section and reinforced with glass fiber-reinforced polymer (GFRP) bars. Six full-size reinforced concrete stadium bleacher specimens with a width, height, and thickness of 950, 390, and 150 mm (37.4, 15.35, and 5.9 in.), respectively, and with a total length of 4200 mm (165.4 in.) were tested under four-point bending load up to failure. Six specimens were fabricated: three with normal concrete and sand-coated GFRP reinforcement with three different reinforcement ratios, and three with fiber-reinforced concrete (FRC) and sand-coated GFRP reinforcement. The test parameters included GFRP reinforcement ratio and concrete type. The test results were analyzed based on the cracking and ultimate moment specified in the existing FRP design codes. The comparison shows that the experimental moment capacities of the bleachers were generally conservative in the design standards. Moreover, the reinforcement ratio had a substantial impact on the serviceability performance of the bleacher specimens. Increasing the ratio of flexural reinforcement led to reduced crack widths and decreased deflections. Changing the concrete type from normal to fiber with the same bar size showed improved serviceability and moment capacity results. This research enhances the understanding of precast self-consolidating concrete stadium bleacher units with an L-shaped cross section reinforced with GFRP bars subjected to flexural load and supports their use in infrastructure.

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 placement; and four unconditioned beams serving 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.