The reinforcing bar cages in concrete-encased steel (CES) structures are replaced with steel fibers to form the steel fiber-reinforced concrete-encased steel (SFRCES) structures, which can avoid common difficulties in the construction of a traditional CES structure. To study the bonding properties and interfacial damage between shaped steel and steel fiber-reinforced concrete (SFRC), the pushout tests of 16 specimens were conducted. Main parameters including steel fiber ratio (ρsf) (0, 1, 2, and 3%), thickness of concrete cover (Css), and effective bonding length (Le) of specimens were considered. In this paper, some important performance indicators are obtained, such as P-S curves, bonding strength, interfacial energy dissipation, and interfacial damage variables. The experimental results show that the P-S curves at the loading end and free end have the greatest difference under the peak load. A higher ρsf has a stronger constraint effect on concrete cracks, which leads to better post-peak bonding behavior. A bigger Css can delay the interfacial damage in the middle and late stages of the test. A larger Le means more elastic deformation energy can be stored at the interface, so the damage variable increases at a slower pace.

The structural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) is mainly affected by the fiber volume fraction, the fiber distribution, and the fiber orientation. Fiber orientation especially may vary (locally) in structural members depending on their geometry, the consistency of the fresh concrete, and the way of placing and compacting the concrete. As a result, UHPFRC may behave anisotropically in both tension and compression. To quantify the effect of fiber orientation on the behavior of UHPFRC in compression, tests on cylinders and differently fabricated cubes made of fine- and coarse-grained UHPFRC mixtures were performed. Especially for high fiber volume fraction, specimens with predominantly unidirectional fiber orientation perpendicular to the loading direction showed significantly higher compressive strengths than specimens with predominantly unidirectional alignment of the fibers parallel to the loading direction. Unlike for ultra-high-performance concrete without fibers, a noticeable difference between cylinder and cube compressive strength could be observed in case of UHPFRC.

It is well known that creep can affect the serviceability of concrete structures, including tunnel linings made using fiber-reinforced shotcrete (FRS). However, the possible effect of creep on the strength of structures is seldom explicitly considered in design. For cracked FRS loaded in tension or flexure, creep rupture of the fiber-concrete composite, either by pullout or rupture of fibers, can lead to structural collapse, at least when no alternative load path exists. In the present investigation, the influence of fiber geometry and surface roughness on creep rupture (expressed as the time-to- collapse) of FRS panel specimens subjected to a sustained flexural-tensile load has been assessed. The results suggest that geometric aspects of fiber design influence the propensity of the fiber composite to suffer creep rupture at a crack, and that collapse primarily occurs as a result of fiber pullout rather than tertiary creep of individual fibers. For the fibers presently investigated, geometric aspects of fiber design appear to exert a greater influence on creep rupture of the fiber composite than the properties of the material comprising the fibers.

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.