Search Results (907)

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

The current study examines the innovative use of rubber–concrete composites as structural solutions that provide significantly higher noise absorption properties compared to traditional concrete. Focusing on their potential for sound insulation in challenging environments such as wind energy infrastructure, the study examines the effect of varying contents of ground tyre rubber (GTR) content (20%, 40%, and 60% by volume) and acetone treatment duration (0, 1, 6, and 24 h) on the characteristics of the composite. The results demonstrate that these rubber–concrete composites significantly improve both sound absorption and sound insulation. An increase in sound absorption coefficients to approximately 0.18 was observed, representing an average improvement of 43.4% compared to the average coefficient of the reference mixture, 0.043. This improvement is particularly effective in the 100–1250 Hz frequency range and maintains stable properties from 50 to 1600 Hz. Sound transmission losses also showed a clear improvement in the mid-frequency ranges. Despite their excellent acoustic characteristics, these structural composites demonstrate a compromise in mechanical properties. Compressive strength decreased from approximately 43–46 MPa (control) to 25–38 MPa at 60% rubber content after 28 days, representing a 40–46% reduction. The reduction in flexural strength was even more pronounced, decreasing by approximately 60% at a rubber content of 35%. However, treatment of GTR with acetone significantly improved interfacial bonding, increasing mechanical integrity at moderate rubber doses (20–40%). The optimal range of rubber content, providing a balance between acoustic benefits and structural integrity, appears to be 15–25%. Full article

Epoxy asphalt, as a thermosetting material, has received increasing attention due to its outstanding mechanical properties and durability. However, its insufficient low-temperature resistance, limited toughness, and relatively high material cost still restrict its large-scale application in pavement engineering. To improve its low-temperature performance and reduce construction costs, this study investigates the low-temperature behavior of epoxy asphalt modified with desulfurized crumb rubber. In this study, a functional additive, hereafter referred to as WJFL (a laboratory-designated organic disulfide-based rubber plasticizer), was incorporated during the preparation of the desulfurized rubber–asphalt binder to enhance the curing rate of the modified epoxy asphalt. The addition of WJFL promotes the devulcanization and activation of rubber powder, enhancing the overall performance of the modified epoxy asphalt. When the desulfurized rubber content is 20%, WJFL additive dosage is 2%, and asphalt content is 300% of epoxy resin mass, the modified epoxy asphalt not only meets the specification requirements but also exhibits excellent low-temperature crack resistance and improved economic efficiency. The addition of crumb rubber increased tensile strength by 15.38% and elongation at break by 17.24%. Furthermore, WJFL additive increased tensile strength by 80% and elongation at break by 25% when WJFL content was increased from 0% to 2%. Additionally, optimizing the asphalt-to-epoxy ratio, with asphalt content increased from 100% to 300%, resulted in an 80% increase in tensile strength and a 28.57% improvement in elongation at break. Moreover, desulfurized crumb rubber modification enhanced the low-temperature stiffness modulus, highlighting better performance in cold regions. Relaxation tests conducted at −10 °C, −15 °C, −20 °C, and −25 °C show that the modified epoxy asphalt has significant potential for use in pavement surfacing, particularly in cold climates. Full article

This study addresses the need for flexible and high-toughness materials for transmission tower pile foundations subjected to typhoons and earthquakes by investigating the static and dynamic mechanical behavior of rubberized concrete prepared using vibratory mixing. The objectives are to assess how vibratory mixing influences strength evolution, failure modes, strain rate sensitivity, and energy absorption of rubberized concrete compared with conventional mixing at 0%, 20%, and 30% rubber contents. Quasi-static compression tests and Split Hopkinson Pressure Bar (SHPB) dynamic compression tests were conducted to quantify these effects. The results show that vibratory mixing significantly improves the paste–aggregate–rubber interfacial structure. It increases the compressive strength by 8.4–30% compared with conventional mixing and reduces the strength loss at the 30% rubber content from 51.12% to 38.98%. Under high-speed impact loading, vibratory mixed rubber concrete exhibits higher peak strength, stronger energy absorption capacity, and a more stable strain rate response. The mixture with 20% rubber content shows the best comprehensive performance and is suitable for impact-resistant design of transmission tower foundations. Future research should extend this work by considering different rubber particle sizes and vibratory mixing frequencies to identify optimal combinations, and by incorporating quantitative fragment size distribution analysis under impact loading to further clarify the fracture mechanisms and enhance the application of rubberized concrete. Full article

One of the main obstacles to producing natural rubber-modified asphalt is the difficulty of mixing Technical Specification Natural Rubber (TSNR) or its compounds with asphalt, leading to long mixing times and high costs. This study aims to evaluate the use of 60/70 penetration asphalt as a plasticizer to accelerate the mixing process and improve the rheological properties of modified asphalt using Technical Specification Natural Rubber (TSNR). The production process for technical specification natural rubber-modified asphalt involves two stages: the production of the technical specification natural rubber compound (CTSNR) and the production of CTSNR-based modified asphalt (CTSNRMA). The CTSNR production process begins with mastication of technical specification natural rubber (TSNR), followed by the addition of activators (zinc oxide, stearic acid), accelerators (Mercaptobenzothiazole sulfenamide (MBTS)), antioxidants (2,2,4-Trimethyl-1,2-dihydroquinoline (TMQ)), and 60/70 penetration asphalt as a plasticizer (at concentrations of 30%, 40%, and 50%). After homogeneous mixing for 30–60 min, the CTSNR is diluted 5–10 mm for the next mixing stage with hot asphalt at 160–170 °C. The best results of this study showed that CTSNR-modified asphalt with 4% rubber content and 50% plasticizer (CTSNRM-450) successfully reduced the mixing time to 16 min, making it more efficient than the traditional method, which takes up to 180 min. The addition of asphalt plasticizer decreased penetration to 35.6 dmm and increased the softening point to 55.4 °C. The CTSNRMA-440 formula, with 4% rubber content and 40% plasticizer, produced the best results in terms of storage stability, meeting the ASTM D5892 standard with a softening-point difference of 0.95 °C, which is well below the threshold of 2.2 °C. The CTSNRMA-440 sample achieved a Performance Grade (PG) of 76, suitable for hot-climate conditions, with a significant reduction in mixing time, greater stability, and increased resistance to high temperatures. Full article

To address the impact-induced damage to concrete pile foundations of transmission structures caused by nearby blasting vibrations, this study investigates the dynamic splitting tensile behavior of an environmentally friendly lightweight rubberized concrete—Rubber-Toughened Ceramsite Concrete (RTCC)—under impact loading. Quasi-static tests show that the static splitting tensile strength increases first and then decreases with increasing rubber content, reaching a maximum value of 2.01 MPa at a 20% replacement ratio. Drop-weight impact tests indicate that RTCC20 exhibits the highest peak impact force (42.48 kN) and maximum absorbed energy (43.23 J) within the medium strain-rate range. Split Hopkinson Pressure Bar (SHPB) tests further demonstrate that RTCC20 shows the highest strain-rate sensitivity. Overall, RTCC with 20% rubber content provides the best comprehensive performance, achieving a favorable balance between strength and toughness across the entire strain-rate range. These findings offer experimental support for applying RTCC to blast-vibration-resistant transmission structure foundations. Full article

Traffic noise is one of the main sources of environmental problems and a growing challenge for national traffic authorities. It is widely accepted that tire-pavement interaction is the main cause of traffic noise at speeds between 40 and 90 km/h. Typically, noise attenuation strategies include earthworks, tree belts, or noise barriers. However, a solution that is almost always viable is the use of low-noise pavements, which are characterized by their porous macrotexture, such as Stone Mastic Asphalt (SMA) mixtures. These mixtures are increasingly used for heavy traffic volumes because of their many advantages, including drainage properties and mechanical strength. Based on the experimental results obtained on different roads in southern Spain, this paper compares noise reduction in an SMA standard mixture due to the incorporation of different additives, such as crumb rubber and polymeric additives. According to the analysis, increasing the additives content by 1% reduces CPX by 1.18 decibels, approximately, and none of the analyzed sections shows increases greater than 3 dB within 24 months. Additionally, the paper proposes design recommendations regarding macrotexture and the percentage of voids for zones with warm, dry climates, such as Mediterranean Spain. Full article

The use of waste rubbers and polyurethane has a significant impact on the abrasion resistance of the porous elastic road surface (PERS) mixture. The purpose of this work is to study the anti-abrasion performance of the PERS mixture under different contents of waste rubbers. First, features of the surface of the PERS mixture were collected by image processing technology. Then, the abrasion performance of the mixture was studied by image processing and wear tests. The correlation between the surface texture parameters and the anti-abrasion performance of the mixture was analyzed by the gray entropy correlation method. It is found that the change of convex particle area in the equivalent diameter range of 2–5 mm had the greatest correlation with the abrasion resistance of the PERS mixture. The effect of the waste rubber content of the mixture on the anti-abrasion performance was investigated, and a waste rubber content of 10% showed the best anti-abrasion performance. It is expected that this work can provide a new method for analyzing the anti-abrasion performance of functional pavement. Full article

Utilizing waste tire crumb rubber to modify asphalt enhances the damping and noise reduction performance of pavements. This study employs a multi-scale approach to investigate the effect of crumb rubber content (5–25%) on the damping performance of crumb rubber-modified asphalt (CRMA). The results show that damping performance improves initially with increasing crumb rubber content, peaking at 20%, and then declines. At this optimal content, the loss modulus increases by 110% and 440% at 46 °C and 82 °C, respectively, compared to base asphalt, with enhanced damping efficiency and damping temperature stability. Fluorescence microscopy (FM) images and quantitative analysis reveal that, at 20%, the crumb rubber forms a moderately connected three-dimensional network. Molecular dynamics (MD) simulations indicate that, at this content, the solubility parameter of the CRMA system is closest to that of the base asphalt, and interfacial binding energy increases, suggesting optimal compatibility. Ridge regression models, with R² values of 0.903 and 0.876 for the FM and MD scales, respectively, confirm that crumb rubber dispersion is the dominant factor governing damping performance, with moderate phase separation further enhancing performance. This study establishes a quantitative structure–property relationship, providing a framework for understanding the damping performance of rubber-modified asphalt pavements. Full article

The growing demand for sustainable pavement materials has driven increased interest in asphalt mixtures incorporating recycled crumb rubber (CR). While CR modification enhances mechanical performance and durability, its often increases initial production costs and energy demand. This study develops an integrated framework that combines machine learning (ML) and economic analysis to identify the optimal balance between performance and cost in CR-modified asphalt overlay mixtures. An experimental dataset of conventional and CR-modified mixtures was used to train and validate multiple ML algorithms, including Random Forest (RF), Gradient Boosting (GB), Artificial Neural Networks (ANNs), and Support Vector Regression (SVR). The RF and ANN models exhibited superior predictive accuracy (R² > 0.98) for key performance indicators such as Marshall stability, tensile strength ratio, rutting resistance, and resilient modulus. A Cost–Performance Index (CPI) integrating life-cycle cost analysis was developed to quantify trade-offs between performance and economic efficiency. Environmental life-cycle assessment indicated net greenhouse gas reductions of approximately 96 kg CO₂-eq per ton of mixture despite higher production-phase emissions. Optimization results indicated that a CR content of approximately 15% and an asphalt binder content of 4.8–5.0% achieve the best performance–cost balance. The study demonstrates that ML-driven optimization provides a powerful, data-based approach for guiding sustainable pavement design and promoting the circular economy in road construction. Full article

The stability of physical and mechanical properties of highly filled swelling rubbers in polar and nonpolar liquids (oil, mineralized water) was studied. Nitrile butadiene rubber of BNKS-28 AMN grade served as the elastomer matrix, with sodium salt of carboxymethylcellulose (NaCMC) as the swelling filler. Oxal T-92, a mixture of dioxane alcohols (10–50 phr, step 10 phr), was used as a plasticizer due to its good thermodynamic miscibility with rubber (confirmed by Scatchard–Hildebrand calculations). Adding Oxal T-92 to NaCMC-filled compounds markedly reduced Mooney viscosity, improving processing through increased macromolecule mobility, without significantly affecting vulcanization kinetics—indicating chemical inertness toward crosslinking centers. Increasing Oxal T-92 from 10 to 50 phr reduced tensile strength from 4.1 MPa to 2.9 MPa. Swelling in aqueous solutions of varying mineralization was evaluated via volume and mass change. The optimal plasticizer content for high swelling with acceptable strength is 20–30 phr. After 3 days in oil and formation water, NaCMC-filled rubbers retained stable physical and mechanical properties. Full article

This study investigates the influence of synthetic fibers and rubber powder derived from end-of-life tires (ELTs) on the rheological behavior of asphalt mastics composed of paving-grade bitumen and mineral filler. Nine asphalt mastic formulations were prepared with varying fiber and rubber contents, reflecting the composition of stone mastic asphalt mixtures. Dynamic shear rheometer tests were conducted to assess dynamic stiffness modulus, phase angle, non-recoverable creep compliance, and elastic recovery. The results demonstrated that ELT-derived additives significantly enhanced high-temperature stiffness and elasticity, while maintaining satisfactory viscoelastic balance at lower temperatures. Synergistic effects between fibers and rubber were observed, improving both non-recoverable compliance and percent recovery, particularly at elevated shear stresses. Prolonged exposure to production temperatures (175 °C) confirmed the thermal stability of the modified mastics, with the most notable performance gains occurring during the first hour of heating. Based on the findings, it was concluded that ELT-based fiber–rubber additives can improve high-temperature performance of asphalt mastics without negative effects in intermediate and, possibly, also low service temperatures. This permits expanding the use cases for these kinds of additives beyond the role of inert stabilizers in stone mastic asphalt to an active modifier for extending asphalt mix performance. Full article

To address the challenges of decarbonization in the global transportation sector and disposal of waste tires, warm asphalt rubber (WAR) with low viscosity and high performance was prepared. In particular, the preparation and rheological behavior of WAR incorporating composite warm mix systems at relatively high crumb rubber contents have not been thoroughly documented. In this study, WAR prepared under such conditions was systematically examined. A five-factor, three-level segmented orthogonal experimental design (OED) was employed to investigate the effects of preparation parameters on hot mix asphalt rubber (AR) properties. Based on the optimized AR formulation, a composite warm mix system combining Ultra-Warm Mix additive (UWM) and Sasobit was developed, and control groups containing 5% UWM only and 1.5% Sasobit only were prepared for comparison. Conventional physical tests together with rheological characterization, including Dynamic Shear Rheometer (DSR), Multiple Stress Creep Recovery (MSCR), and Bending Beam Rheometer (BBR) tests, were conducted to evaluate the high- and low-temperature performance of WAR. Results show that the optimal preparation process consisted of aromatic oil content 5%, crumb rubber content 30%, shear temperature 220 °C, shear time 120 min, and reaction time 90 min. The composite warm mix system notably enhanced WAR performance, with the WAR-5U1.5S group exhibiting the most balanced properties. A marked reduction in rotational viscosity was achieved while maintaining a stable softening point, and satisfactory ductility and elastic recovery were also retained. DSR and MSCR tests confirmed improved high-temperature deformation resistance, an increase in percent recovery R, and a decrease in non-recoverable creep compliance J_nr. BBR test further verified that the composite system maintained good low-temperature cracking resistance, meeting all specification requirements. Overall, these results indicate that, compared with the optimized AR, WAR can reduce mixing viscosity without sacrificing rutting or cracking performance, while alleviating the limitations observed for single warm mix additives. This study provides essential technical support for promoting WAR that integrates low-carbon construction with superior pavement performance. Full article

This study evaluates the performance of ethylene propylene diene monomer (EPDM) composites for rubber sealing applications in a cable-based tsunami system. Rubber composites were prepared using EPDM rubber with varying monomer and filler content to determine the most suitable composite. Mechanical characterization reveals that the composition of EPDM and the amount of filler loading influence the mechanical properties. Dynamic mechanical analysis shows that ethylene and 5-ethylene-2-norbornene (ENB) content influence the glass transition and viscoelastic behavior of the composite. Thermal analysis of rubber composites using EPDM containing 70% ethylene and 5% ENB indicates no change in thermal stability due to prolonged immersion in seawater. Visual inspection using a microscope reveals no cracks on the surface of the rubber seal after the pressure chamber test for rubber composites utilizing EPDM with 70% ethylene and 5% ENB. It was shown that EPDM containing 70% ethylene and 5% ENB, with optimal reinforcement with 80 phr carbon black, exhibits the best performance for rubber sealing applications in subsea environments. Full article

Although rubber waste devulcanization has been widely studied, its industrial-scale implementation remains limited due to challenges in process scalability. This study examines the feasibility of devulcanizing off-spec latex waste through a two-phase approach involving laboratory and pilot-scale trials. The latex waste was sourced from off-spec condom products composed of natural rubber latex. Laboratory-scale experiments were initially conducted to establish process parameters and generate baseline data, including gel content before and after the devulcanization process. Thermogravimetric analysis (TGA), gel permeation chromatography (GPC), and dynamic mechanical analysis (DMA) were employed. The laboratory findings have been used to design and operate the subsequent pilot-scale devulcanization process, using a retrofitted waste rubber machine. Samples from the pilot trials underwent the same analytical tests to assess consistency and process performance at scale. Results from the pilot scale experiments suggest that comparable levels of devulcanization were achieved, with gel contents of 52.5% and 55.2% achieved at the laboratory scale and pilot scale. GPC analysis confirmed a uniform distribution, with an increase in the number average molecular weight, indicating the scission of crosslinks in the sample. GPC analysis also revealed a decrease in dispersity index (Ð) value of 2.27 in lab scale conditions and 1.76 for pilot scale conditions, suggesting a more uniform molecular weight distribution and improved devulcanization efficiency, which enhances the possibility of recycling. The successful translation from lab-scale to the pilot setup highlights the process’s potential for industrial rubber recycling using retrofitted equipment. Full article