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In this paper, a series of shear specimens with or without groove were manufactured to mainly analyze the effects of grooves (or shear section height) and steel fibers on the shear properties of concrete with recycled coarse aggregate through double-side direct shear test. In addition, the relationship between the shear strength and the compressive strength and splitting tensile strength of steel fiber reinforced concrete with recycled coarse aggregate (SFRCAC) was also discussed. The experimental results showed that the peak load, deformation corresponding to the peak load and calculated shear strength of the specimens with grooves were lower than those of the specimens without grooves. The steel fiber and recycled coarse aggregate (RCA) had a significant effect on the shear properties of SFRCAC. As the volume content of steel fibers increased, the shear strength of SFRCAC and the corresponding deformation increased gradually. With the replacement ratio of RCA increasing, the shear strength of SFRCAC decreased but the corresponding deformation increased gradually. Finally, the formula for calculating the shear strength of SFRCAC was proposed by analyzing and fitting the test results and the data of related literature. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mechanical properties of SFRC exposed to sulfuric acid for 36 months were monitored. • The mechanism was also analyzed by the evolution of alkalinity and mineral phases. • The SFRC showed good mechanical properties in the sulfuric acid environment. Steel fiber reinforced concrete (SFRC) has significant advantages for preparing pipes, however, concrete sewer pipes are susceptible to deterioration caused by biological acids (i.e., sulfuric acid). In this study, the mechanical properties—including cube compressive strength, axial compressive and flexural properties, and relative dynamic elastic modulus—of SFRC exposed to sulfuric acid for 36 months were monitored. Further, the evolution of the morphology, alkalinity, and mineral phases was also monitored. According to the morphology and pH evolution, SFRC showed rapid corrosion after 12 months of exposure, and the thicknesses of damaged and transition layers reached approximately 2 and 8 mm, respectively, after 36 months. Further, gypsum was formed and deposited on the specimen surface after exposure to sulfuric acid. Although the SFRC did not deteriorate after 12 months of exposure and still showed good mechanical properties, the cube compressive strength of SFRC showed a slight decrease after 36 months of exposure; however, the axial compressive load and flexural load capacities improved, and the flexural toughness also increased as a result of the exposure to sulfuric acid. This study provides valuable evidence for the potential application of SFRC in sewage environments. [ABSTRACT FROM AUTHOR]

The waste fiber reinforced polymer (FRP) bars are difficult to degrade naturally, and inevitably pose a significant challenge to environmental protection, resulting in the recycling of waste FRP bars is of great significance. Compared to chemical recycling and thermal recycling, mechanical recycling processes are more economical and environmental. In this study, the waste Hybrid FRP (HFRP) bars were mechanically recycled into fiber clusters for reinforcing concrete, and the influences of the fiber clusters on the mechanical properties of concrete were studied through compression test, splitting tensile test and four-point bending test. Meanwhile, Fourier transform infrared (FT-IR) spectroscopy and Scanning electron microscopy (SEM) were used to observe the interaction between the fiber clusters and the concrete, and acoustic emission (AE) technique was utilized to monitor the fracture characteristics inside the concrete. Results showed that the performance of mechanically recycled fiber clusters was retained to a certain extent and the alkaline environment of concrete produced slight damage to the fiber clusters. The addition of fiber clusters could obviously improve the mechanical properties of concrete, especially its energy absorption capacity under the splitting tensile and flexural loads. The absorbed energy E H/50 and peak flexural toughness of concrete with 2% fiber clusters were 97.24% and 126.47% higher than those of conventional concrete, respectively, and its flexural toughness index T P,150 was 163.16% higher than that of concrete containing 0.5% fiber clusters. As the volume fraction of fiber clusters increased, the number of AE event localization points and shear cracks mainly caused by fiber clusters pull-out and sliding increased. This study can bring enlightenment for the mechanical recycling of FRP bars into fiber clusters for concrete. • Mechanical recycling of waste HFRP bars for being used as short fiber clusters. • Prepare a kind of concrete with short fiber clusters. • The effect of fiber clusters content on the mechanical properties of concrete is investigated. • FT-IR and SEM are used to observe the interaction between fiber clusters and concrete. • AE technique is used to monitor the internal fracture characteristics of concrete containing fiber clusters. [ABSTRACT FROM AUTHOR]

• An analytical DAM for the tensile stress-crack width constitutive was proposed. • Effects of initial and residual embedded lengths of fiber on DAM were analyzed. • The integral region of the pullout force was divided by using the polar coordinate. • The DAM proposed was applicable to SFRC members with 3D, 4D, and 5D steel fibers. The most important characteristic of steel fiber reinforced concrete (SFRC) is its excellent post-cracking behavior. An analytical diverse angle-length-width model (DAM) was proposed to calculate the tensile stress-crack width (σ-w) constitutive behavior of SFRC members subjected to tension and to evaluate its post-cracking behavior. In the proposed model, the tensile stress in SFRC members with end-hooked steel fibers was generated from the straight fiber part, the end-hooked fiber part, and the concrete part. The effects of straight and end-hooked parts were separately considered, and three cases for different crack width ranges were analyzed for each part. The model was derived by considering all of the possible fiber inclination angles, fiber embedded lengths, and crack widths. It was found that SFRC members with new types of 4D and 5D steel fibers possessed a higher tensile stress than those with 3D steel fibers, and the tensile stress intensity increased with the increasing fiber volume fraction. Finally, the accuracy of the model was verified by comparing the values by DAM with the experimental results based on the sectional analysis. [ABSTRACT FROM AUTHOR]