Search Results (56)

This paper presents the possibilities of using steel cord from car tires as a structural concrete reinforcement obtained after initial mechanical treatment. The steel wire constituting tire reinforcement after mechanical separation from rubber is not further processed and, in the form partially contaminated with rubber, is stored in landfills. Further processing is usually not economically justified. The purpose of the work is to determine the physical properties of fiber concrete, made of ordinary concrete with the addition of steel fibers recovered from tires, obtained in the process of relatively easy recycling. The work is mainly experimental. The literature review presents the basics of the current state of knowledge regarding the methods of making and testing elements made of fiber-reinforced concrete. In the next part, the authors’ own research and results of testing fiber-reinforced concrete with wires after pre-cleaning are shown. Chapter five summarizes the results of research and juxtaposes the most important observations that can be used for the practical use of fibers obtained in a simple recycling technology. The utilitarian value of the work is to show the practical possibilities of recovery (recycling) of used tires, in particular for the fiber-reinforcement of concrete. Among other things, it was shown that the addition of steel fibers (contaminated with rubber) to approximately 1.3% reduces the shrinkage of concrete with these fibers by 7–10% compared to a fiber-free concrete matrix cured under the same conditions. Full article

Rubber aggregate concrete (RAC) offers excellent frost resistance and impact toughness, but the incorporation of rubber particles substantially reduces its compressive strength, limiting structural applications. Existing improvement strategies have mainly relied on a single modification route, whereas the dynamic compressive response of RAC containing both ceramic balls and steel fibers remains insufficiently clarified. Here, a ceramic ball–steel fiber rubber aggregate concrete (CBSFRC) was investigated using quasi-static compression, a Φ120 mm split Hopkinson pressure bar system, and high-speed photography. Three steel-fiber volume fractions (1.0%, 1.5%, and 2.0%) were tested. The CBSFRC waveform displayed a characteristic ‘low-first, high-second’ double-peak pattern, in contrast to the ‘high-first, low-second’ pattern of the reference rubber aggregate concrete (CRC). At the common interpolated strain rates of 40, 45, and 50 s⁻¹, the dynamic compressive strengths of CBSFRC were 35.9–53.6% higher than those of CRC; no extrapolation was used. The largest quasi-static strength increase among the tested mixtures was 51.7%. The observed CBSFRC ultimate strains and strain energy densities ranged from 11.1–17.5 × 10⁻³ to 8.1–14.1 × 10⁵ J/m³, respectively. Matched-rate analysis showed that the largest DIF increment was 18.8% for SF-1CBRC at 40 s⁻¹, whereas the largest strain-energy-density increment was 70.2% for SF-1.5CBRC at 50 s⁻¹. These results describe the tested range and do not establish a universal optimum steel-fiber content. Full article

This study investigates the blast-protective performance of RC slab strengthened on the blast face with various concrete protective layers under contact-detonation loading. The research focuses on analyzing shock wave propagation characteristics, peak pressures at measurement points, energy absorption capacities of the protective layers, the development of damage, and the governing failure mechanisms of the RC slab. The protective layers used for structural reinforcement include Steel Fiber-Reinforced Cellular Concrete (SFR-CC), Asphalt Concrete (AC), Rubberized Concrete (RBC), and Foamed Concrete (FC). Among these, the maximum support rotation angle of the structure strengthened with the SFR-CC concrete layer (T-1) is 0.20°, indicating significantly less damage and deformation compared to other protective schemes. Based on the damage coefficient calculated from the remaining sectional moment of inertia of the protected RC slabs, the destruction grades of the structures at different concrete protective schemes were classified. Among these, the SFR-CC layer exhibits the most effective attenuation of shock wave peak pressure. Additionally, the maximum support rotation angle of the structure strengthened with the SFR-CC concrete layer is 0.20°, indicating significantly less damage and deformation compared to other protective schemes. Damage grades were assigned according to a coefficient derived from the residual sectional moment of inertia of the protected RC slabs. The SFR-CC configuration (T-1) gives the lowest damage index, 0.178, approximately 64.5% below that of the NC scheme, and is classified as slight damage. In contrast to the severe damage sustained by the protected RC slabs strengthened with the NC concrete scheme, those strengthened with the AC, RBC, and FC protective layer schemes exhibit only a moderate damage grade. Empirical formulas predicting the damage index of protected structures under the combined effects of varying blast charges and concrete layer thicknesses were further developed for rapid damage assessment. Full article

Semi-circular bending tests were conducted on high-elasticity asphalt concrete under different aging conditions to investigate the effects of rubber particles and polyester fiber contents on its fracture properties. Results showed that the incorporation of approximately 3% rubber particles increased the fracture energy by 15%, whereas the addition of 1.2% polyester fibers increased the fracture toughness and fracture energy by 4% and 19%, respectively. Aging-induced oxidative hardening enhanced the overall elastic modulus and interfacial constraint effect of the asphalt mixture, thereby improving the stress transfer efficiency among the rubber particles, polyester fibers, and the surrounding matrix. As a result, both the peak load and fracture toughness increased. However, compared with the unaged state, aged asphalt concrete became more susceptible to brittle fracture, with a decrease in fracture energy and a change in the crack propagation path from a curved to a straight trajectory. Full article

This research aims to study the compressive behavior of concrete with partial replacement of fine aggregate by recycled rubber. In addition, the mechanical capacity of these concretes will be analyzed when reinforced by carbon fibers (CFRP) and basalt (BFRP) confinement. To carry out the work, 48 cylindrical test specimens were made, corresponding to 4 mixes, with different percentages of recycled rubber by volume (0%, 10%, 20%, and 30%). The compressive behavior of unreinforced concrete with and without recycled rubber, reinforced concrete made from concrete with and without recycled rubber previously taken to failure, and reinforced concrete with and without recycled rubber without prior failure were evaluated in order to assess the influence of concrete quality before placing the reinforcement. The results show that replacing fine aggregate with recycled rubber in concrete reduces its strength and stiffness, increasing its ductility, with the optimum replacement percentage being 10%. On the other hand, confining concrete with FRP (BFRP and CFRP) improves its strength and ductility compared to unconfined concrete, obtaining similar values regardless of the initial strength of the reinforcing concrete. Confining concrete with CFRP achieves strength improvements of 26% compared to reinforcement with BFRP. Full article

To investigate the deterioration law of the mechanical properties of PVA-fiber-reinforced rubber concrete under the combined action of high-temperature and salt erosion, physical index tests, dynamic mechanical property experiments, and microstructural morphology observations were carried out on specimens subjected to different temperatures (ambient temperature, 100 °C, 300 °C) and various solution attacks (water, 5% NaCl, 5% Na₂SO₄, and 5% NaCl + 5% Na₂SO₄ mixture). The results show that, after exposure to 300 °C, the PVA fibers melt and the rubber pyrolyzes, since this temperature exceeds their melting points. A residual pore network is formed inside the matrix, and the damage degree of ultrasonic pulse velocity is about 2.3 times that of the 100 °C group. Although salt solution and its crystallization products can physically fill the pores and cause a partial recovery of pulse velocity, this change is mainly due to the alteration of the pore medium and does not represent a substantial restoration of the microstructure. The effects of different salt solutions on dynamic mechanical properties vary significantly: Sulfate erosion improves the dynamic performance significantly at ambient temperature by forming gypsum and ettringite to fill pores, but this strengthening effect disappears after 300 °C. Sodium chloride attack generates Friedel’s salt and consumes C₃A, leading to general strength deterioration. In composite salt erosion, the competitive and synergistic effects of Cl⁻ and SO₄²⁻ destabilize erosion products and weaken interfacial bonding, resulting in consistent decreases in dynamic compressive strength and elastic modulus under all temperatures and impact pressures. The strength reduction reaches 66.2% after 300 °C. Microscopic analysis confirms that composite salt erosion leads to the dissolution of ettringite and loose structure, which verifies the synergistic deterioration law of macroscopic properties. This study systematically reveals the damage evolution mechanism of PVA-fiber-reinforced rubber concrete under the coupled action of high-temperature and salt erosion, and provides a theoretical basis for the dynamic bearing capacity evaluation and durability design of concrete structures in such coupled environments. Full article

This study examines the impact of recovered steel fibers (WTSFs) and waste tire aggregates of varying sizes—fine (FWTR), small coarse (SCWTR), and large coarse (LCWTR)—on the compressive strength of concrete subjected to elevated temperatures. Forty mixes were formulated utilizing four distinct WTR replacement ratios (0%, 5%, 10%, 20%) and four WTSF doses (0%, 0.5%, 1%, 2%), and evaluated at temperatures of 24 °C, 100 °C, 200 °C, and 300 °C. The findings indicate that elevated temperatures consistently diminish compressive strength, although the reference concrete saw around 18% loss at 300 °C, with WTR-containing mixes demonstrating losses ranging from 25% to 45%, contingent upon rubber size and dose. The type of WTR was critical—LCWTR mixes exhibited superior residual strength retention due to enhanced particle–matrix interlocking, whereas FWTR mixtures saw the most significant decline. The inclusion of WTSF increased strength by 2–10% at 0.5–1.0% fiber content through crack bridging, but excessive fiber addition (2.0%) decreased workability and caused clustering, leading to up to 40% strength loss. The ideal combination was 5LCWTR–1WTSF, which sustained 36.97 MPa at 24 °C and 29.65 MPa at 300 °C, indicating superior performance across all temperature ranges. Predictive modeling utilizing machine learning techniques (SVR, KRR, 1D-CNN, and DRL) corroborated the experimental results, with the CNN attaining the maximum generalization accuracy (R² = 0.9374) and the KRR exhibiting the most consistent performance (R² = 0.9305). The models indicated that WTR and temperature were the primary variables diminishing strength, although modest WTSF ratios enhanced overall thermal resilience. SHAP and ALE analysis further validated that WTR content exhibited the most significant negative feature contribution (~−6 MPa), succeeded by temperature, although modest fiber inclusion demonstrated a positive SHAP effect (+2–4 MPa), corroborating the experimentally observed non-linear reinforcement threshold. The combined experimental–computational framework demonstrates that the combination of coarse rubber aggregates (5–10%) with appropriate WTSF content (0.5–1.0%) improves sustainability and high-temperature durability. The integration of physical testing and interpretable AI modeling creates a hybrid approach that can anticipate and enhance thermo-mechanical performance in sustainable concrete systems. Full article

To enhance the damage resistance of protective engineering materials under extreme loads such as explosions and impacts, this study, building upon the improvement in impact resistance of concrete achieved by rubber modification, further incorporates steel fibers and glass fibers to synergistically enhance impact resistance and to investigate the underlying mechanisms. Using split Hopkinson pressure bar (SHPB) testing, a comparative investigation was conducted on the dynamic mechanical responses of four specimen groups, namely plain rubberized concrete, single steel fiber-reinforced, single glass fiber-reinforced, and hybrid steel–glass fiber-reinforced rubberized concrete, over a strain-rate range of 30–185 s⁻¹. The results demonstrate that the incorporation of hybrid fibers significantly enhances the dynamic compressive performance of plain rubber concrete. Specifically, the dynamic compressive strength increases from 40.73–61.29 MPa to 60.25–101.86 MPa, accompanied by a 59.5% increase in strain-rate sensitivity. Meanwhile, the fragment fineness modulus after failure rises from 3.20–3.33 to 3.73–4.20, indicating improved post-impact integrity. In addition, the hybrid fiber-reinforced specimens exhibit the highest energy dissipation capacity at identical strain rates. Their dynamic stress–strain responses are characterized by higher stiffness, improved ductility, and more pronounced progressive failure behavior. These findings provide experimental evidence for the design of high-impact-resistant protective engineering materials. Full article

This study investigates the synergistic effects of steel fibers and waste rubber powder on the properties of ultra-high-performance concrete (UHPC) to advance its sustainable development. A comprehensive experimental program was conducted, incorporating three types of steel fibers (8 mm straight, and 14 mm and 20 mm hook-end) at volumes up to 2.5%, and rubber powder as quartz sand replacement at levels from 5% to 30%. The flowability, compressive strength, splitting tensile strength, abrasion resistance, and chloride ion penetration resistance of the mixtures were evaluated. The results indicate that steel fiber reinforcement significantly enhances the mechanical and durability properties. Specifically, a 2.5% steel fiber content increased the compressive strength, splitting tensile strength, and abrasion resistance by 28.9%, 55.3%, and 72.4%, respectively. Conversely, the incorporation of rubber powder improved flowability (optimal at 10% replacement) and abrasion resistance (increased by 41.1% at 30% content) but at the expense of reduced mechanical strength and increased chloride ion permeability. The primary novelty of this work lies in systematically quantifying the trade-offs and synergistic interactions between a wide range of steel fiber geometries and high-volume rubber powder content, providing a practical basis for designing UHPC with balanced performance and enhanced sustainability. Full article

This study examines the use of electronic waste (e-waste) as an alternative material in concrete for sustainability and natural resource conservation. Various e-wastes, such as Polyvinyl Chloride (PVC), Glass-Reinforced Plastic (GRP), Glass Fiber-Reinforced Polymer (GFRP), cross-linked polyethylene (XLPE), polyethylene (PE), electronic cable waste (ECW), Waste Electrical Cable Rubber (WECR), copper fiber (Cu Fib.), aluminum Fibers (Al fib.), steel fibers, basalt fibers, glass fibers, aramid−carbon fibers, Kevlar fibers, jute fibers, and optical fibers, were tested for influence on compressive, flexural, tensile strength, modulus of elasticity, and water absorption. Outcomes show that fine particle waste at low levels (0.2–1.5%) can improve mechanical performance, while higher levels of replacement or coarse particles generally reduce performance. Mechanical and physical properties are highly sensitive to material type, particle size, and dose. Life cycle assessment (LCA) and predictive modeling are recommended as validation for sustainability benefits. Full article

This study investigates the effects of different proportions of waste rubber fiber aggregates on the flexural behavior of reinforced concrete beams. Beam specimens were prepared with different proportions (5%, 10%, and 15%) of waste rubber fiber aggregates, and composite beams formed with pultruded GFRP profiles were tested under vertical load. According to the results of this study, cube compressive strength, cylinder tensile strength, and beam flexural strength decreased by 27.5%, 50%, and 47.6%, respectively, with the use of a 15% waste rubber aggregate. As a result of the four-point bending tests performed on reinforced concrete beams, the maximum load-carrying capacity of the beams decreased significantly after increasing the waste rubber aggregate ratio to 10% and 15%. However, a general improvement in the ductility of the beams was observed. One of the main results of this study is that when the waste rubber aggregate content is 5%, the best balance between strength and ductility is achieved, and the performance closest to the reference beams is obtained. The tests also revealed that the Ø10-5% specimen exhibited higher performance in terms of both load-carrying capacity and yield stiffness. On the other hand, although the 15% waste rubber aggregate ratio caused a decrease in the maximum load-carrying capacity. along with an increase in the diameter of the tensile reinforcement, this decrease was quite low. Finally, an overall decrease in energy consumption capacity was observed with increasing waste rubber aggregate content in all test beams. This can be attributed to the acceleration of shear damage in the beam and the shrinkage of the area under the load–displacement curve as the amount of waste increases. Additionally, SEM analyses were conducted in order to investigate the microstructural behavior of the rubberized concrete. This study has shown that the use of waste rubber aggregates can be environmentally and economically beneficial, especially at the 5% level. Full article

This study evaluates low-strength concrete incorporating recycled rubber aggregates from waste tires and polymer fiber for use as “forgiving” safety barriers that enhance road safety while promoting environmental sustainability. Incorporating the rubber and fiber enables recycling the tires close to the source where they were originally used—the road. These barriers are designed to absorb collision energy, reduce vehicle deceleration, and minimize the severity of accidents. The key requirements for such concrete are low strength, low elastic modulus, high ductility, high toughness, and minimal dispersion of large fragments upon failure. The study investigated various concretes containing different percentages of recycled rubber (0–20% by volume) and polymer fibers (0–1.2% by volume). We conducted compression, flexural, and dynamic impact tests to assess the effects of these additions on the properties of the concrete. Dynamic tests were carried out in a cantilever loading scheme with strain rates of 2.5–3 s⁻¹, to emulate barrier loading during car crush. Key findings include indications that recycled rubber decreases concrete strength, while its contribution to energy absorption is limited. In contrast, polymer fibers enhance the concrete’s elongation and toughness, increasing energy absorption. The quantity of fibers present in the fracture area is critical for energy absorption. Notably, energy absorption under dynamic loads is more significant than that under quasi-static loads; however, the difference between these results diminishes as the fiber percentage increases. Furthermore, quasi-static tests on fiber-reinforced concrete can effectively evaluate its response to impact loads. In conclusion, the combined use of recycled rubber and polymer fibers in low-strength concrete offers a sustainable solution for developing safer and more environmentally responsible roadside infrastructure by repurposing waste materials and reducing the ecological footprint of construction. Careful attention should be paid to the distribution of fibers within the concrete, as this significantly influences energy absorption. Full article

Recycling rubber and steel fibers from end-of-life tires for use in structural concrete presents a sustainable pathway to improve resource efficiency and reduce environmental impact. This study assesses the shear performance of reinforced concrete beams in which shredded tire rubber substitutes 20 vol.% of both fine and coarse natural aggregates. The effect of including recycled tire steel fibers (RSF) and industrial steel fibers (ISF), each at a dosage of 20 kg/m³, is also examined. The experimental program involved testing twenty-four cylindrical specimens and seven reinforced concrete beams to evaluate the mechanical and structural behavior of the proposed mixtures. A novel layered concrete configuration is also evaluated, in which rubberized (RU) concrete or steel fiber reinforced rubberized (RUSF) concrete is placed in the tensile zone, and plain (P) concrete is placed in the compressive zone. The results indicate that rubber incorporation alone reduces shear strength by 30.9% compared to P concrete. However, the inclusion of steel fibers not only compensates for this reduction but significantly improves strength and ductility. Beams fully cast with RUSF concrete exhibit a 31.9% increase in shear strength compared to P concrete. In contrast, layered beams with RUSF concrete in the bottom and P concrete in the top show a comparable performance. These findings highlight the potential of integrating steel fiber reinforced rubberized concrete and functional layering to enable the use of substantial quantities of recycled tire materials without compromising structural performance, offering a promising solution for eco-efficient construction. Full article

In the saline soil area of western China, the concrete is simultaneously subjected to cyclic loading and sulfate attack. To reveal the effect of sulfate attack on fatigue performance of normal concrete (NC) and hybrid fiber-reinforced rubber concrete (HFRRC), the uniaxial compression test and cyclic loading test were carried out on the specimens after sulfate erosion. The loading strain, plastic strain, and elastic strain of the concrete were compared and analyzed. The compressive strength, fatigue resistance, and strain energy of the concrete were compared and analyzed. Ultrasonic Pulse Velocity (UPV) measurements were also used to quantify the damage in sulfate attack tests. The results indicate that the fatigue failure stress of concrete is lower than its uniaxial compressive strength. The fatigue resistance coefficient of HFRRC is always higher than that of NC. Under the cyclic loading with the same level, the stress–strain curve of HFRRC is denser than that of NC, exhibiting good elasticity. The energy evolution is independent of whether or not sulfate attacks, but its growth rate is affected by sulfate erosion time. It can provide an experimental and theoretical foundation for the application of HFRRC in engineering structures subjected to repeated loads in sulfate environments. Full article

To address challenges posed by waste tires and greenhouse gas emissions associated with ordinary Portland cement, exploring eco-friendly construction materials is critical for sustainability. This study examines the workability and mechanical properties of straight steel fiber-reinforced rubberized geopolymer concrete (SFRRGC), where rubber powder is derived from recycled waste tires. The experimental variables included rubber powder (RP) content (0%, 6%, 12%, and 20% by volume of fine aggregate) and steel fiber (SF) content (0%, 0.5%, 1.0%, and 1.5% by volume). The results show that incorporating RP and SFs reduced the workability of SFRRGC but increased its peak strain. Specifically, RP addition decreased the elastic modulus, compressive strength, and toughness; increasing the SF content enhanced energy dissipation, while the effects of SF and RP contents on Poisson’s ratio were negligible. The specimens showed that a higher RP content would weaken the crack-bridging effect of SF. For example, specimens with 1.0% SF and 6% RP achieved 49.56 MPa compressive strength and 4.04 × 10⁻³ maximum peak strain; those with 0.5% SF and 20% RP had 118.40 J compressive toughness, which was 5.53% lower than that of the reference specimens (125.33 J). Furthermore, a constitutive model for SFRRGC was proposed, and its theoretical curves aligned well with the experimental results. This proposed model can reliably predict the stress–strain curves of geopolymer concrete with different SF and RP mixture proportions. Full article