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The constitutive compressive stress–strain response of hybrid high-performance, fiber-reinforced concrete (HyHP-FRC) containing steel and polyvinyl alcohol (PVA) fibers is scarcely reported. In this study, the compressive stress–strain behavior of plain high-performance concrete and 18 HyHP-FRC mixtures containing steel-PVA fiber systems were experimentally measured and analyzed. The incorporation of steel-PVA fibers significantly enhanced the postcracking stress–strain response of HyHP-FRC, including its compressive strength. Additionally, physical measurements revealed that the dosage and geometry of the steel fibers significantly affected the postcracking toughness of the concrete. Using the least-squares fitting approach and additional independent data, the volumetric reinforcing index of the fibers (RIv) and the predictive equations for the properties of the HyHP-FRC under uniaxial compression were established in terms of RIv. These equations indicated that the compressive strength of HyHP-FRC was linearly proportional to RIv ; however, nonlinear correlations were observed for the elastic modulus and strain at the peak stress of HyHP-FRC. Finally, straightforward and more refined models for the full-scale constitutive compressive stress–strain curve of HyHP-FRC were developed and validated against the test and other data. The proposed models can be used to accurately predict the entire stress–strain response of cement-based composites containing hybrid combinations of metallic and synthetic fibers. [ABSTRACT FROM AUTHOR]

The main purpose of this research is to assess the influence of different design parameters on the mechanical performance of high-performance fiber-reinforced concrete (HPFRC) mixtures. Special attention is also paid to achieving deflection-hardening behavior in the presence of a large amount of coarse aggregates. Different mixture design parameters were the initial curing ages (3, 7, 28, and 90 days), ratios of Class F fly ash (FA) to portland cement (PC) (0.0, 0.2, and 0.4), addition/type of nanomaterials [nanosilica (NS), nanoalumina (NA), and nanocalcite (NC)], and combinations of fibers [polyvinyl-alcohol + steel (P, S) or brass-coated microsteel + steel (B, S)]. The experimental program included the evaluation of compressive strength, flexural strength, and midspan deflection results in addition to test parameters recorded under biaxial flexural loading via a series of square panel tests, including peak load and energy absorption capacities. Test results revealed that deflection-hardening response coupled with multiple microcracks can be obtained when large amounts of coarse aggregates are available for all HPFRC mixtures. As expected, experimental results change depending on the different curing ages and FA/PC ratios. The most distinctive parameters affecting the results are addition/type of nanomaterials and the presence of different fiber combinations. In the presence of nanomaterials, all results from the different tests improved, especially for NA and NS inclusions. With slight concessions in flexural deflection results, B fiber is shown to be a successful candidate to fully replace costly P fibers because most properties of B, S fiber-reinforced HPFRC mixtures outperformed those with P, S fibers, both under four-point bending and biaxial flexural loading. [ABSTRACT FROM AUTHOR]

This paper presents the results of extensive experimental tests on the fresh and hardened properties of self-compacting concrete reinforced with hybrid polypropylene (PP) fiber and recycled steel fiber (RSF) in different fiber volume fractions. In the present paper, RSFs were recovered from waste tires. The mix compositions were reinforced with different combinations of hybrid recycled-steel fiber (0.35, 0.7, and 1.05%) and PP fiber (0.35 and 0.7%). The fresh state of the mix compositions were assessed by using slump flow diameter, T500, and Tv. Moreover, the hardened properties of specimens were characterized by using compressive strength, flexural strength, and impact resistance. Regression analysis was executed on the relatively large amount of gathered experimental data to correlate properties of fresh and hardened states of self-compacting concrete reinforced with hybrid recycled steel–PP fibers. The results showed that adding hybrid recycled steel–PP fiber improves the impact resistance and mechanical properties. Adding recycled steel fiber led to higher improvement in the compressive strength compared to PP fiber. Moreover, increasing the content of PP fiber reduces the effect of recycled steel fiber in improvement of flexural strength. [ABSTRACT FROM AUTHOR]

This study investigated the effects of hybrid steel fiber of different sizes (6 and 13 mm) on the uniaxial compression performance of ultra-high performance concrete (UHPC). The failure pattern, stress–strain relationship, and toughness under the uniaxial compression of a reference UHPC mixture with no fiber and five UHPC mixtures with mono or hybrid fiber content of 2%, by volume of concrete, were studied. The results indicated that the incorporation of hybrid fiber significantly improved compression properties, with increased strength and toughness. An UHPC mixture with 1.5% long and 0.5% short fiber showed the best compressive behavior, whereas those with 2% short fiber showed the worst properties. Based on the obtained peak stress, strain at peak stress, elastic modulus, and compression toughness index, an analytical model was proposed to generate the complete stress–strain relationship. The proposed model agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

The multiscale nature and multiscale cracking behavior of cementitious composite determine its micro-, meso-, and macroperformance. A new kind of fiber hybridization containing steel fiber, polyvinyl alcohol (PVA) fiber, and cheap calcium carbonate () whisker (approximately $230 per ton) was designed to increase the multiscale cracking resistance for cementitious composites. Mechanical properties, microstructures, reinforcing mechanisms, and economic efficiency of this designed hybrid fiber-reinforced composite were presented. The results indicated that both the flexural strength and flexural toughness are significantly improved. Scanning electron microscopy images and fracture tests confirmed that the interaction of different fibers and multiscale cracks contributes to enhancing the mechanical properties of cementitious composite, which is also reflected in its deflection hardening performance and multiple cracking behavior. Moreover, it seems possible that the steel fibers and PVA fibers can be partly replaced with whiskers, which is very beneficial in decreasing the production cost of fiber-reinforced cementitious composites for large-scale construction project applications. [ABSTRACT FROM AUTHOR]