This study aims at assessing the long-term bond behavior of headed-end glass fiber-reinforced polymer (GFRP) bars to basalt fiber-reinforced cementitious composite (BFRCC) exposed to 300 consecutive freezing-and-thawing cycles, followed by 75 cycles of wetting and drying, mimicking successive winter and summer seasons. A total of 85 pullout specimens reinforced with recently developed basalt fiber pellets and steel fibers were tested. The durability of the specimens was quantified in terms of visual analysis, residual compressive strength, relative dynamic modulus of elasticity, as well as the residual pullout capacity. The addition of fibers was capable of retaining approximately 90% of the pullout capacity for specimens exposed to harsh conditions owing to the restriction of cracks in the fiber-reinforced cementitious composites. Therefore, the results confirmed the suitability of steel-free reinforcement systems for long-term application under severe freezing-and-thawing and wetting-and-drying environments.

This paper presents the derivation as well as empirical verification of a compressive stress-strain model of concrete confined with fiber-reinforced concrete (FRC) jackets made using steel fibers. Both conventional (that is, strain-softening) FRC and high-performance (that is, strain-hardening) FRC (HPFRC) were considered. The model accounts for the tensile response of the jacket as a function of the fiber properties, fiber volume fraction, orientation, and the effects of fiber debonding, fiber pullout, and multiple cracking. Specific FRC and HPFRC materials used in this study include fiber-reinforced mortar (FRM), FRC, and slurry-infiltrated fiber-reinforced concrete (SIFCON), all made using steel fibers. Experimental behavior of model columns jacketed with FRC and HPFRC was compared to that of columns confined with conventional fiber-reinforced polymer (FRP) jackets. HPFRC jackets made with continuous aligned fibers exhibited fiber debonding and multiple cracking leading to the post-peak softening response. Varying the orientation of fibers in FRC and FRM jackets produces radial tensile stresses on the concrete core, thus reducing the strength of confined concrete. Concrete confined with FRC jackets exhibited post-peak softening response with lower ductilities than concrete confined with HPFRC jackets due to the random orientation and lower volume fraction of fibers within FRC jackets. HPFRC jackets with steel fibers are expected to sustain large rupture strains in the longitudinal and transverse directions, which translates into an improved ductility and energy absorption, making it a suitable retrofit option for existing columns.

Concrete infrastructure is deteriorating at a fast pace because of corrosion issues inherent to traditional black steel reinforcing bars. Alternative non-corrosive reinforcement materials for concrete structures have been developed and reinforcing bars made from fiber-reinforced polymers (FRP) are one of the most predominantly used non-corrosive materials for internal reinforcement. This research focused on basalt FRP reinforcing bars as this technology is still in development for the U.S. market and no standard specifications are available yet. In an effort to develop basalt specific acceptance criteria, two commonly available BFRP reinforcing bar sizes from five different sources and two different production lots were tested to quantify the tensile strength and stress-strain behavior of this emerging reinforcing bar technology. The obtained results were used to evaluate the performance of each reinforcing bar type in a relativistic comparison to existing benchmark values for glass FRP reinforcing bars given in AC454. The tensile strengths were consistent for all reinforcing bar types and the recorded values surpassed the strength measurements generally reported for comparable GFRP reinforcing bars. It was found that No. 3 reinforcing bars measured guaranteed tensile strengths between 760 and 1266 MPa (110 and 184 ksi), while No. 5 reinforcing bars ranged between 836 Pa and 1074 MPa (129 and 131 ksi). Though the fiber-to-resin ratio of all tested reinforcing bar types was similar, the tensile strength of these reinforcing bars varied due to differences in the raw materials and production. The elastic moduli were calculated according to AC454 and it was noted that this property varied significantly between the different reinforcing bar types because of irregular cross-sectional dimensions and the various proprietary (not standardized) manufacturing processes. It was determined that acceptance criteria for BFRP reinforcing bars can be conservatively defined according to the currently available GFRP values, but more specific criteria can be developed through further research to take advantage of the additional load capacity and potential improved stiffness of BFRP reinforcing bars.

This paper presents the infiltration of sulfuric acid (H2SO4) through concrete confined with carbon fiber-reinforced polymer (CFRP) sheets. Despite the popularity of such a rehabilitation method in upgrading the strength and ductility of existing reinforced concrete columns, scarce information is available when these members are exposed to H2SO4 as a result of changes in service environments after strengthening. In an experimental comparative study alongside plain concrete, the efficacy of CFRP confinement is elaborated in the context of durability. Concrete specimens with and without CFRP confinement are immersed in a 5% solution for up to 6 weeks and are used to examine their physical and chemical responses. In the concrete subjected to the acid, H2SO4 dissolves the cement binder, alters surface-level pH values, and lowers the electrical resistivity of the plain concrete. Although the resin of the CFRP allows the ingress of H2SO4, the influence was not as significant as that of its plain counterpart. The CFRP system impedes the progression of chlorides through the conditioned concrete, which is beneficial in mitigating the potential corrosion damage of strengthened concrete members, preserves the integrity of the conditioned concrete, and lessens the absorption and effective diffusivity of H2SO4.

The influence of factors such as cementitious matrix characteristics, fiber inclination, and temperature on the interfacial bond between fiber-reinforced polymer (FRP) fibers and cementitious matrix are studied herein. It was noticed that use of glass fibers in the form of glass FRP (GFRP) composite fiber greatly improved the bonding mechanism over using just constituent glass fibers. With matrix maturity, a steady increase in bond was observed with over 60% bond strength achieved within a day. Densification of the cementitious matrix with the addition of silica fume was found to greatly increase the interfacial bond and changed the failure mode from fiber pullout to fiber rupture and delamination. At inclined loading as well, a different failure mode in the form of fiber rupture after partial pullout was noticed. This change in failure mode from fiber pullout to fiber rupture was also accompanied by a lower apparent tensile strength at large inclination. At lower temperature of –20°C, the bond between FRP fibers and the cement matrix was found to improve, but increased brittleness in fibers was also noted. At higher temperatures, FRP fibers performed satisfactorily up to 80°C, after which a gradual degradation in bond was observed.