International Concrete Abstracts Portal

This study investigates the feasibility of utilizing a hybrid combination of recycled steel fibers (RSF) obtained from scrap tires and manufactured steel fibers (MSF) in concrete developed for pavement overlay applications. A total of five concrete mixtures with different combinations of MSF and RSF, along with a reference concrete mixture, were studied to evaluate fresh and mechanical properties. The experimental findings demonstrate that the concretes incorporating a hybrid combination of RSF with hooked-end MSF exhibit comparable or higher splitting tensile strength, flexural strength, and residual flexural strength to that of concretes containing only hooked-end MSF, straight MSF, and RSF. This enhanced mechanical performance can be ascribed to the multiscale fiber reinforcement effect that controls different scales (micro to macro) of cracking, thereby providing higher resistance to crack propagation. The concretes containing only RSF show lower splitting tensile strength, flexural strength, and residual flexural strength compared to concrete solely reinforced with straight MSF or other steel fiber-reinforced concrete (SFRC) mixtures due to the presence of various impurities in the RSF, such as thick steel wires, residual rubber, and tire textiles. Interestingly, blending RSF with hooked-end MSF overcomes these limitations, enhancing tensile strength, flexural strength, and residual flexural strength, while significantly reducing costs and promoting sustainability. Lastly, the findings from the pavement overlay design suggest that utilizing a hybrid combination of RSF with hooked-end MSF can reduce the design thickness of bonded concrete overlays by 50% compared to plain concrete without fiber reinforcement, making it a practical and efficient solution.

In this study, fabric formwork is used to cast I-shaped and non-prismatic tapered reinforced concrete (RC) beams that have up to a 40% reduction in concrete volume, resulting in lower embodied CO₂, compared to a rectangular prismatic beam. The primary aim of this research is to use distributed sensing to characterize the behavior of these shape-modified beams to an extent that was not previously possible and compare their behavior to that of a conventional rectilinear beam. Four RC beams (a rectangular control and three fabric-formed sections) were tested in three-point bending. Distributed fiber optic strain sensors were used to measure strains along the full length of the longitudinal reinforcement, and digital image correlation was used to acquire crack patterns and widths. The results indicate that fabric-formed RC beams can achieve the same load carrying capacity as conventional rectilinear prismatic beams and meet serviceability requirements in terms of crack widths and deflections. The longitudinal reinforcement strains along the full length of the specimens were captured by Canadian concrete design equations as they account for the effects of both flexure and shear on reinforcement demand.

The weakness of concrete in tension can be mitigated by developing fiber-reinforced concrete (FRC) to induce pseudoductility. However, enhancing the intrinsic tensile strength of the matrix in FRC has received little attention. In this regard, nanofibers, which can improve the intrinsic tensile properties of the matrix, were used in conjunction with microfibers to enhance intrinsic tensile strength. Different volumes of nanofibers (0.0 to 0.6%) and microfibers (0.0 to 2.0%) were tested, and various fresh and hardened properties were analyzed. Test results show that the high-range water-reducing admixture dosage increased with both nanofiber and microfiber volume and that strength increased with microfiber volume, reaching an optimum point at a certain nanofiber dosage. Moreover, incorporating nanofibers and microfibers to develop multiscale FRC (MSFRC) significantly improved direct tensile strength and energy absorption. The synergy between nanofibers and microfibers was revealed both qualitatively and quantitatively, contributing to the advancement of FRC.

This investigation attempted to analyze the environmental impact of fibers, including their effect on the cost and durability of concrete mixtures, especially given the variety of fibers that are available in the market. Five types of fibers (polypropylene [PP], glass, basalt, polyvinyl alcohol [PVA], and steel) possessing different aspect ratios were considered in this study. The concrete mechanical properties—including the resistance to sorptivity, heat, and freezing- and-thawing cycles—were evaluated. Test results showed that the best environmental/cost/durability indicator was achieved for concrete prepared with 0.25% PVA or PP fibers by volume. This indicator gradually degraded with the use of basalt, glass, and steel fibers because of higher cost and greenhouse gas emissions generated during the fiber manufacturing. The use of PVA fibers significantly enhanced the resistance to heat and freezing-and-thawing cycles, while the least-performing concrete contained basalt fibers with relatively reduced flexural properties and increased sorptivity.

Reinforced concrete walls are commonly used in low- and mid-rise construction because they provide high strength, stiffness, and durability. In regions of low and moderate seismicity, ACI 318 Code requirements for minimum reinforcement ratio and maximum reinforcement spacing typically control over strength-based requirements. However, these requirements are not well-supported by research. The current study investigates requirements for the amount and spacing of reinforcement using experimentally validated nonlinear finite element modeling. For lightly reinforced concrete walls subjected to out-of-plane loading: 1) peak strength is controlled by concrete cracking; and 2) residual strength depends on the number of curtains of steel. Walls with very low steel-fiber dosages were also studied. Results show that fiber, rather than discrete bars, provides the most benefit to wall strength, with fiber-reinforced concrete walls achieving peak strengths more than twice that of identically reinforced concrete walls.