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Foam concrete is a porous cement-based material that could accommodate a high-volume particle addition at the mid- to high-density range (0.8 to 1.6 g/cm3). However, with low-density foam concrete (0.4 to 0.8 g/cm3), conventional particle inclusion (e.g., sand) tends to degrade the cellular microstructure and mechanical performance. Therefore, to improve low-density foam concrete, the novel use of crumb rubber (the rubber particles recycled from waste tires) in foam concrete is studied, as its unique attributes can potentially allow for the retention of structure and improved performance in foam concrete. The influence of no inclusion, sand, and crumb rubber on the microstructure and mechanical performance in foam concrete with the density of cellularized cement paste as 0.40 and 0.60 g/cm3 was studied. Computed tomography indicates that the inclusion of crumb rubber can mitigate the foam degradation concern associated with particle inclusion in low-density mixtures. A notable improvement was also observed in the mechanical properties of 0.40 g/cm3 rubberized foam concrete mixtures—compressive strength, plateau strength, and impact resistance—when referenced to the sand inclusion counterpart. [ABSTRACT FROM AUTHOR]

Composite modification of an asphalt binder forms an interesting approach to enhance the properties over diverse performance regimes. Aging of asphalt binders during the production, construction, and service life of the asphalt mixtures in pavement increases its stiffness and may have a negative impact on their resistance toward fatigue and low-temperature cracking, thus generating the need to evaluate the aging behavior of a composite-modified asphalt binder. This study analyzed the aging characteristics of individual and composite asphalt binders produced with waste ethylene-propylene-diene-monomer (EPDM) rubber, derived from manufacturing units dealing with nontire automotive rubber products, and the tire pyrolysis oil (TPO) derived from the pyrolysis of scrap tires. Three different pathways were used to formulate composite-modified binders, namely, without pretreatment and with pretreatment through heat and microwave irradiation. The study focused on the evaluation of physical, rheological, chemical, and microstructural characteristics of the composite-modified binders produced in different manners after being subjected to both short-term and long-term aging. Results showed that the effect of aging was adverse on the base binder and the binder prepared with TPO alone. In contrast, the addition of EPDM rubber alone improved the binder's aging resistance. The composite-modified binder through the pretreatment yielded significantly improved performance against aging; thus, composite modification with pretreatment can be a useful approach to yield aging-resistant binders prepared by EPDM and TPO. [ABSTRACT FROM AUTHOR]

The application of waste tire rubber in the concrete industry is one of the most effective and environmentally friendly ways to solve the problem of so-called black pollution. However, the application of rubber particles (RP) in the concrete industry is hindered by their low stiffness and poor bonding performance with the cement matrix. In this paper, a novel modification method of polydopamine (PDA) modification was used to enhance the hydrophilicity of the RP surface. The surface morphology, element content, and hydrophilicity of RP treated with PDA and KMnO4 were analyzed through scanning electron microscope and energy dispersive spectrometer (SEM-EDS) and sedimentation methods. The unit weight, ultrasonic pulse velocity (UPV), compressive strength, compressive toughness, toughness index, and flexural strength were taken to determine the mechanical properties of ultrahigh-performance rubber concrete (RUHPC). The results showed that the adhesion between paste and RP and the sedimentation rate of RP with PDA or KMnO4 treatment methods exhibited a remarkable improvement. Compared with unmodified RUHPC, the basic mechanical properties of KMnO4 -modified RUHPC were improved slightly, and its toughness index was improved greatly. SEM and EDS results confirmed that PDA was deposited on the surface of RP, eliminating the gap of interface transition zone and significantly enhancing UPV, compressive strength, and flexural strength of RUHPC by 4.1%–5.8%, 17%–20%, and 6.1%–9.8%, respectively. In addition, the compressive toughness of unmodified and KMnO4 -modified RUHPC decreased, whereas that of PDA-modified RUHPC increased significantly. It can be concluded that the mechanical properties of RUHPC with treated RP have improved significantly and the application of RP in ultrahigh-performance composites (UHPC) offers more opportunities for recycling RP. [ABSTRACT FROM AUTHOR]

Rubber-coated ballast (RCB) is a new innovative ballast aggregate obtained by coating natural aggregates with recycled crumb rubber by using polyurethane binder. The objective of RCB is to reduce the ballast degradation, thereby reducing the deterioration of rail track geometry and also maintenance costs. Natural ballast; crumb rubber of sizes 0.4, 0.8, and 2 mm; Elastan polyurethane; and geogrid (triangular, 69 mm aperture size) were used in this study. The results of abrasion, impact value, and soundness tests show that RCB has a higher resistance to abrasion, impact, and weathering compared to natural ballast. Subsequently, the shear behavior and particle breakage of natural ballast, RCB, unreinforced, and geogrid-reinforced RCB–natural ballast mix was explored using the large-scale direct shear apparatus at different normal stresses and shearing rates (Sr). The test results indicate that due to rubber coating the peak friction angle (φ) of RCB samples reduces as compared to natural ballast. The reduction in φ of RCB samples is attributed to a change in surface texture. Moreover, 0.4-RCB (RCB made with rubber crumbs of size 0.4 mm) shows the least reduction in φ compared to 0.8-RCB and 2-RCB (RCB made with rubber crumbs of size 0.8 and 2 mm). It was further observed that with the increase in proportion of 0.4-RCB in geogrid-reinforced natural ballast both the peak friction angle and particle breakage (Bg) of ballast decreased significantly. The current study established the optimum content of 0.4-RCB to be mixed with geogrid-reinforced natural ballast to be in the range of 44%–53%. The problem of excessive degradation of ballast particles and the associated changes in the track geometry owing to the repeated application of heavy axle loads is addressed by coating the natural ballast with crumb rubber generated from waste tires. The rubber-coated ballast (RCB) is found to offer better abrasion, impact, and weathering resistance when compared to natural ballast. Moreover, it undergoes negligible particle breakage under direct shear conditions. The decrease in the extent of particle breakage helps in reducing the frequency of ballast replacement operations and hence tracks maintenance costs. Furthermore, RCB, when reinforced with geogrid, offers better shear strength than that of natural ballast alone. These observations imply that the tracks with geogrid-reinforced RCB can effectively reduce the risk of track instability. [ABSTRACT FROM AUTHOR]

High-performance concrete (HPC) is known as a material of high strength and high durability. This investigation is focused on the influence of the use of rubber waste tires on the physical, mechanical, and durability characteristics of HPC. Tire-rubber residues were used in the contents of concrete at 7.5%, 15%, and 30% in relation to the sand mass. Eleven mixtures were tested in the experimental program. To improve the mechanical strength of rubberized concrete, superficial treatment of the rubber was carried out with calcium carbonate and silica fume. From the results obtained, the following are notable: reduction of the area between the rubber and the cement paste, increased resistance to compression and traction of the concrete with treated rubber, and lower water absorption value and void index, evidencing the benefit of this type of surface treatment. Regarding the durability, electrical resistivity, chloride ion penetration, and carbonation tests, high-strength rubberized concrete shows the potential to be used in aggressive environments. [ABSTRACT FROM AUTHOR]

The crumb rubber (CR) derived from waste tires has been used widely to prepare rubberized asphalt for paving applications. However, rubberized asphalt severely suffers from poor compatibility and consequent storage instability. Therefore, a solution soaking pretreatment was used to activate the CR surface to improve the compatibility of rubberized asphalt in this study. Three different solutions—water, sodium hydroxide, and sulfuric acid—were employed. The Fourier-transform infrared spectroscopy (FTIR) spectra indicated the removal of zinc stearate from the CR surface after solution soaking. Consequent improvement of the surface hydrophilicity of CR was found from the promoted sedimentation in water and the reduced water contact angle. Dynamic dhear rheometer (DSR) test results showed that the effect of solution soaking on the rheology of rubberized asphalt was slight. However, according to the results of the segregation test and a novel drainage-based method, the solution soaking pretreatments significantly improved the compatibility of rubberized asphalt. This was reflected directly in the reduced segregation degree and promoted CR/asphalt interactions. The solution soaking pretreatment of CR had no adverse effect on the moisture susceptibility of rubberized asphalt according to the modified binder bonding strength (BBS) test results. Of the three pretreatments, sodium hydroxide performed best, followed by sulfuric acid and water. [ABSTRACT FROM AUTHOR]

The safe disposal of waste tires has been seen as having a negative impact on the environment. To mitigate this impact, the components of waste tires can be used in the production of green concrete. This study explores the effects of the curing and drying regime on the mechanical properties and permeation characteristics of concrete containing both crumbed rubber and steel fibers that are removed from waste tires. Five concrete mixes were designed, and concrete cubes, cylinders, and prisms were cast using waste tires extracts. Crumb rubber was treated by submersion in sodium hydroxide and then used to partially replace 10% and 30% of fine aggregates in the concrete mix. Extracted steel fibers were added at the rate of 1% and 2% per volume of each mix. Compressive and indirect splitting tensile as well as flexural strengths were conducted after normal curing while observing several drying conditions. Additionally, air permeability was assessed using a portable apparatus that was developed to assess permeability easily. For the concrete test specimens containing 10% partial replacement of fine aggregate by crumb rubber and 1% steel fibers, it was discovered that the splitting tensile strength and flexural strength were higher than that of the control mix by 21% and 22.6%, respectively. For specimens that included the 10% crumb rubber and 1% steel fibers, when exposed to oven drying at 105°C for 12 h, the compressive strength results increased by 17% compared with the control specimens exposed to the same conditions. Unlike the compressive strength results, the splitting tensile and flexural strength results decreased after exposing the specimens to elevated temperature. The addition of crumb rubber and steel fibers as a partial fine-aggregate replacement resulted in increasing the air permeability of the concrete to different degrees depending on the percentages used. The oven-drying curing regime improved the permeability by reducing it in specimens containing the 10% crumb rubber and 1% steel fibers as indicated by increasing their permeability time index by 15% when compared with air-dried specimens. Using waste tire extracts as a partial replacement of concrete fine aggregate can be recommended for both indoor and outdoor applications. This study showed that this was a viable, economic, and environmentally friendly method for reducing carbon footprint. [ABSTRACT FROM AUTHOR]

The effect of ethylene vinyl acetate (EVA) on the aging properties and rheological properties of rubberized asphalt was measured in this paper to identify the optimum proportion of EVA combined with waste tire rubber (WTR) modified asphalt. Aging methods of thin-film oven test (TFOT) and pressure aging vessel test (PAV) were conducted to imitate the different degrees of the aging process. At first, frequency sweep at different temperatures was carried out to construct the construction of G* master curves, following the time-temperature superposition principle, to evaluate the aging sensitivity. The black diagram was depicted to compare the rheological behavior of different asphalt binders. The calculation of the WLF equation based on the shift factor of master curves was conducted to calculate the values and aging index of 15°C DSRFn to assess the resistance to fatigue cracking at the intermediate temperature. Then, zero shear viscosity (ZSV) and rutting factor (G*/sinδ) at 60°C were also used to calculate the aging index, because these both are measurements of resistance to rutting deformation at high temperature. Finally, the microstructure of unaged and aged asphalt binder was studied by Fourier transform infrared spectroscopy (FTIR). The relationship between rheological and chemical indexes was studied. The results show that 15%WTR+4%EVA has the best antiaging performance, and EVA can reduce the aging sensitivity of different parameters, especially in the high-temperature area. [ABSTRACT FROM AUTHOR]

Waste tire rubber constitute a serious worldwide problem due to the lack of landfills and the health hazards associated with these landfills. In addition to the environmental motivation for providing a means of recycling large quantities of waste tire rubbers, the use of tire rubber particles provides a new type of concrete that has unique mechanical and fracture criteria. This paper presents the results of recent experimental investigations on rubber concrete. Chipped and crumbed tire rubber particles were used to replace coarse and fine aggregate with different volume replacement levels. The mechanical and fracture properties of rubber concrete were examined. Quasi-brittle fracture mechanics models are used to determine the effect of incorporating tire rubber particles on the fracture performance of rubber concrete. Finally, some microstructural features of rubber concrete are also reported. It is concluded that the choice of the optimal replacement ratio of the tire rubber particles can yield concretes with desirable strength and fracture toughness criteria for different applications. [ABSTRACT FROM AUTHOR]