Crumb Rubber Content Research Articles

Experimental and Statistical Investigation to Evaluate Impact Strength Variability and Reliability of Preplaced Aggregate Concrete Containing Crumped Rubber and Fibres.

The proper disposal of used rubber tires has emerged as a primary concern for the environment all over the globe. Millions of tires are thrown away, buried and discarded every year, posing a major environmental concern owing to their slow decomposition. As a result, it is advantageous to use recycled waste rubber aggregates as an additional building resource. Recycling crushed rubber would lead to a long-term solution to the problem of decreasing natural aggregate resources while conserving the environment. This study examines the impact strength variability and reliability of preplaced aggregate concrete containing crumped rubber and fibres. Ten different mixtures were prepared by replacing natural aggregate with crumped rubber (5, 10, 15 and 20%). The crumped rubber was pretreated by the water with sodium hydroxide dilution for 30 min before usage. Hooked-end steel fibres were used at a dosage of 1.5%. The compressive strength, impact strength, impact ductility index and failure pattern were examined and discussed. In addition, a statistical method called Weibull distribution is used to analyze the scattered experimental results. The results showed that when the crumb rubber content was raised, the retained first cracking and failure impact numbers increased. As a result of substituting crumb rubber for 20% of the coarse aggregate in plain and fibrous mixes, the percentage development in first crack and failure was between 33% and 76% and 75% to 129%, respectively.

High-Temperature Rheological Properties of Crumb Rubber Composite Modified Asphalt

As a kind of environmentally friendly material, crumb rubber modified asphalt is widely used in highway engineering to accelerate the consumption of end-life tires. The objective of this study is to investigate the high-temperature rheological properties of crumb rubber composite modified (CRCM) asphalt. In this study, the same content of crumb rubber and different content of composite additives were added to prepare the CRCM asphalt, including CRCM-SBS, CRCM- Sasobit/BRF, and CRCM-RARX. The viscosity, phase angle, rutting factor, critical temperature, storage modulus, non-recoverable creep compliance, percent recovery, stress sensitivity, and the functional groups of all testing specimens were obtained by the rotational viscometer, dynamic shear rheometer, multiple stress creep recovery, and Fourier transform infrared spectroscopy tests to evaluate the high-temperature rheological properties of asphalt. In general, the results were favorable for enhancing the high-temperature performance and reducing the stress sensitivity of asphalt. It showed that the incorporation of crumb rubber and additives increased the viscosity of asphalt under different testing conditions. Additionally, the addition of crumb rubber and additives in the base asphalt could be used to increase elastic components and improve the permanent deformation resistance, and the performances are closely related to the types of additives. Thus, considering the high-temperature performance, the asphalt modified by crumb rubber and RARX additive was recommended to apply to asphalt pavement.

Chronic toxicity of tire crumb rubber particles to mummichog (Fundulus heteroclitus) in episodic exposures

Microrubber (MR) encompasses all tire-related particles in the micro-scale and has recently drawn increased attention as a subclass of the broader group of microplastics. While tire particles entered the environment since the introduction of rubber tires for vehicles, the concern regarding tire wear particles (TWP) as an environmental contaminant is relatively new. Recent studies have examined physical and chemical toxicity of MR particles and leachates to a variety of organisms. However, there is a lack of information on the long-term effects of tire particle exposure under environmentally realistic conditions. The current study examined the chronic toxicity of crumb rubber (CR) particles to the estuarine fish species, mummichog (Fundulus heteroclitus) under episodic exposures at environmentally relevant concentrations. Immunohistochemistry (IHC) of fish gill, intestine, and liver was performed to assess CYP1A induction in these organs. Bile fluorescence was measured as an indicator of exposure to polycyclic aromatic hydrocarbons (PAHs) from CR. DNA damage was measured through the formation of 8-hydroxy-2′-deoxyguanosine (8-OHdG) together with other oxidative stress measures as lipid peroxidation (TBARS assay), free glutathione (GSH), and oxidized glutathione (GSSG) concentrations. Upregulation of CYP1A in gill, intestine, and liver was observed especially in gill filaments and general vasculature. Increased bile fluorescence demonstrated exposure to aromatic compounds, especially pyrene-like PAHs. Data for DNA damage indicated greater plasma 8-OHdG concentrations as a result of increased DNA repair. There was a decrease in malondialdehyde (MDA) production and an increase in total GSH at higher concentrations of CR. It appeared that under long-term repeated dosing, antioxidant systems in mummichog were upregulated to deal with exogenous stressors released by the CR particles. Combined, these data demonstrate that fish exposed to tire crumb rubber particles illicit significant biomarker responses under environmentally relevant CR concentrations, but induced antioxidant and detoxification pathways may prevent mortality and serious physiological effects in F. heteroclitus when exposed to environmentally relevant concentrations of CR.

Alkali-activated slag (AAS) and OPC-based composites containing crumb rubber aggregate: Physico-mechanical properties, durability and oxidation of rubber upon NaOH treatment

Value-added utilization of waste tires in cementitious materials has been studied for decades, whereas the synergy between rubber and alkali-activated cements deserves more investigations. To this end, we compared physico-mechanical and durability properties of alkali-activated slag (AAS) and OPC-based composites containing NaOH-pretreated/as-received crumb rubber (CR). It was found that the incorporation of CR had both positive and negative effects on specimens due to its special attributes. CR reduced electrical conductivity which was associated with the ion transport ability, since it worked as an electrical insulator and increased hydrophobicity of pore walls. The sulfate expansion decreased with CR content because the flow of sulfate ions was demobilized, and the flexibility of CR relieved the internal stress. CR also improved the freeze-thaw durability of composites if the total CR content was less than 30% in specimens. However, the low Young's modulus of CR impaired the compressive strength and failed to effectively control the total shrinkage upon drying. The composites with CR must avoid high temperature exposure which resulted in the pyrolysis of rubber. In addition, the NaOH pretreatment enhanced adhesion between CR and hydrated cement and improved overall performances of composites. The FTIR spectra confirmed the NaOH-induced accelerated oxidation of CR surface and the generation of polar functional groups including carbonyl and carboxyl groups, increasing the total surface energy of rubber. More importantly, the alkali-activation process for AAS could treat the CR aggregate in the meantime, which means the use of CR in alkali-activated cements does not require the pretreatment of CR before blending.

Performance evaluation of bitumen modified with styrene–isoprene-styrene and crumb rubber compound

Modifying bitumen with polymers has become inevitable to achieve resistance to severe traffic and environmental conditions. Researchers have focused on using modifiers with low-cost additives, such as crumb rubber (CR) obtained from waste vehicle tires, to enhance the efficiency of polymer modification. The present study investigated the effects of using styrene–isoprene-styrene (SIS) alone and in combination with CR on conventional and rheological properties of bitumen. To this end, viscosity, softening point, penetration, bending beam rheometer (BBR), and dynamic shear rheometer (DSR) tests were conducted. Elastic properties and performance grading were evaluated by the multi-stress creep recovery (MSCR) test. The use of 3% SIS with 7% CR gave one degree higher high-temperature performance level and 15% lower low-temperature stiffness than 6% SIS modification. It also provided 2.5 times lower non recoverable creep compliance and 1.5 times higher percent recovery than 6% SIS modification at 64 °C. The combined use of SIS and CR provided satisfactory performance under low- and high-temperature conditions and ensured a cost-effective solution when compared to the use of SIS polymer alone. Although SIS and CR modified binders exhibited satisfactory rutting resistance and elastic properties, the percent-difference criterion significantly restricted their high-temperature performance grade. According to this criterion, modification makes the binders suitable for extremely heavy traffic conditions without changing the resistance against temperature. Furthermore, it was determined that the estimated softening point, viscosity and rutting parameter values as a function of SIS and CR contents are highly compatible with the experimental results.

Numerical analysis of dynamic behavior of Bi-block precast asphalt trackbed for High-Speed railway

In this paper, asphalt trackbed, including the dry-wet hybrid rubberized asphalt mixture (D-WHRAM) trackbed and dry-mixed rubberized epoxy asphalt mixture (DREAM) trackbed, has been proposed. The dynamic response and the design parameters of the proposed trackbed were evaluated by numerical analysis. A three-dimensional finite element model of the bi-block precast asphalt trackbed was developed using the ABAQUS software. The thickness and width of the prepared asphalt mixture cuboid (PAMC) were set as 25 – 40 cm and 85 – 100 cm, respectively. Then, the effects of thickness and width on the structure performance were analyzed according to the dynamic response, including vertical dynamic compressive stress, deformation, acceleration collected from the top of the PAMC, the tensile strain collected from the bottom of the PAMC, and the evolution mechanism of the vertical dynamic compressive stress within the whole subgrade. The results showed that the suitably designed parameters of PAMC for two types of asphalt trackbed were 35 cm in thickness and 100 cm in width. Although the material compositions of the two types of the asphalt trackbed are remarkable, the maximum values of compressive stress on the top of PAMCs were about the same. However, the DREAM trackbed shows a larger dynamic deformation than the D-WHRAM trackbed due to the greater crumb rubber content.

Experimental investigation of impact of crumb rubber on modified bitumen

ABSTRACT Population growth and industrialisation have led to the accretion of rubber waste which increased public concern about environmental pollution. The use of crumb rubber (CR) as a bitumen modifier is an effective way to protect the environment from pollution. The study of different properties of crumb rubber modified bitumen (CRMB) is the substance area of today’s research. Base bitumen having penetration grade 60/70 and crumb rubber proportions from 4% to 12% by weight of bitumen content following wet process was used. Physical properties, rheological properties, chemical properties and binding properties of unaged CRMB and aged CRMB were evaluated by using conventional tests, dynamic shear rheometer (DSR), Fourier transform infrared spectroscopy (FTIR) and bitumen bond strength (BBS) test, respectively. Modification index of complex shear modulus (G*) of bitumen increased with an increase in CR content. FTIR spectra of aged CRMB illustrated that rate of change in indices decreased with an increase in CR content which shows ageing resistance of CRMB. Crumb rubber influenced the adhesion phenomenon of bitumen and aged CRMB tends to achieve better adhesion effects. BBS results revealed that in dry conditions, POTS values of samples after peaking tended to decrease with an increase in the concentration of crumb rubber above 8%.

Effects of crumb rubber inclusion on strength, permeability, and acid attack resistance of alkali‐activated concrete incorporating different industrial wastes

AbstractThis study examines the suitability of alternate binders and crumb rubber (CR) to produce light weight alkali‐activated concrete (AAC). For this, strength, and durability performance of AAC incorporating CR by partially replacing fine aggregate was studied. To produce AAC, four different binders, including fly ash, rice husk ash (RHA), metakaolin, and bottom ash were used. Fine aggregates were substituted with CR at 0%, 10%, 20%, and 30% for each AAC mix (with different binders). Furthermore, the mixes were prepared using 12 M sodium hydroxide (NaOH) solution, and the ratio of sodium silicate (Na2SiO3) to NaOH was taken as 2.5. The samples were cured at ambient temperature. Strength and durability properties, including permeability through water absorption and acid attack (hydrochloric acid [HCl] and sulfuric acid [H2SO4]), were also checked. Results of this study revealed that the strength decreased with the increase in CR content. Further, this decrease was high at 30% replacement but strength was satisfactory. AAC showed good relationships among compressive, flexural, and split tensile strengths. Similar footprints were observed for permeability results. However, highest water absorption was observed for bottom ash binder (with 30% substitution of CR). Mixes with fly ash and metakaolin binders outperformed the other mixes while comparing the compressive strength of acid exposed samples. Overall, a sustainable and durable light weight AAC can be prepared using 20% CR.

Mechanical Behaviour of Concrete Containing Crumb Rubber as Partial Fine Aggregates Replacement

Nowadays, the waste tires became a critical issue for many countries as the transportation industries increase around the world. Normally, the worn-out tires will be discarded and become an environmental threat or resourceful end product depending on the waste management of the country. Thus, the aim of this study is to investigate the effect of crumb rubber as partial replacement of fine aggregates in compressive and tensile strength of concrete. Based on the mechanical behaviour, the optimum content of crumb rubber as partial fine aggregates replacement in concrete is determined. The size of crumb rubber used in this study was between 2 mm and 3 mm with 5% to 15% replacements. The targeted strength of concrete at 28th days is 35 MPa with 0.32 water to cement ratio. The slump test was conducted to measure the workability of the mix. 24 concrete cubes with dimension of 150 mm x 150 mm x 150 mm were tested for compressive strength after 7 and 28 days of water curing. In addition, 12 cylinders (100 mm x 200 mm) were prepared for tensile strength test. Based on the results of compressive and tensile strength, generally both strengths decreased as the percentages of replacement increased. However, for 5% and 10% replacement, the targeted strength is still achieved. Hence, it can be concluded that, 10% of rubber crumb is the optimum percentages to be partial replacement of fine aggregates in concrete.

Preparation and properties of integrally hydrophobic self-compacting rubberized concrete

Brittleness and water invasion are critical reasons for the deterioration and failure of ordinary self-compacting concrete (SCC). To enhance the deformability and water repellency of SCC, integrally hydrophobic self-compacting rubberized concrete (HSCRC) was prepared by adding crumb rubber (CR) and a hydrophobic agent (HA) into ordinary SCC. Furthermore, the combined effect of CR and HA on the fresh properties, hydrophobicity and mechanical properties of HSCRC were comprehensively studied. The results showed that the addition of CR resulted in a decline in the flowability, filling ability and passing ability and an enhancement in the viscosity and anti-segregation properties. However, the effect of adding HA on the fresh properties was opposite to that of adding CR. The surfaces of the samples mixed with the HA obtained contact angles greater than 130°, and the 48-hour capillary water absorption and the 48-hour immersion water absorption of these samples were significantly reduced. Moreover, the compressive strength, splitting tensile strength, axial compressive strength and elastic modulus of the concrete samples decreased gradually with the increase of CR and HA content. Multiple regression models between different mechanical properties and CR and HA contents, as well as the conversion formulas between different mechanical properties, were obtained.

Performances of rubber asphalt with middle/high content of waste tire crumb rubber

In order to study the performances of rubber asphalt (RA) with different middle/high waste tire crumb rubber content and preparation conditions, RA samples with 15–35% of rubber content, 170–230 °C of reaction temperature, 8–225 min of reaction time and 0–10% of aromatic oil (AO) content were prepared. The reaction mechanism between crumb rubber and asphalt was studied by micro and macro tests, and the fundamental properties, construction workability, storage stability, high and low temperature performances of RA were explored. The results showed that the crumb rubber in 15–35% RA only swells at 170 °C, while the crumb rubber swells first and then degrades at 190–230 °C. The swelling and degradation rates of crumb rubber increase with the increase of reaction temperature, the decrease of rubber content and the increase of AO content. The higher rubber content means higher softening point, ductility, elastic recovery and lower penetration of RA. Higher reaction temperature means higher penetration, ductility and lower softening point of RA. With the increase of AO content of RA, the penetration and ductility increase while the softening point and the elastic recovery decrease. The construction workability of RA promotes with higher rubber content and lower AO content. The storage stability of RA decreases with the increase of rubber content and the decrease of reaction time as well as the AO content. The complex modulus increases while the phase angle decreases when swelling is dominant, and the complex modulus decreases while the phase angle increases when degradation is dominant. The high temperature rutting resistance of RA increases with the increase of rubber content and the decrease of AO content. The low temperature crack resistance of RA increases with the increase of rubber content and AO content. The results could provide reference for the preparation of RA with middle/high content of waste tire crumb rubber.

Preparation and Temperature Susceptibility Evaluation of Crumb Rubber Modified Asphalt Applied in Alpine Regions

In alpine regions, the durability of asphalt pavement is worse due to the harsh climate. However, crumb rubber modified asphalt has the potential to improve the durability of pavement. Based on matrix asphalt, crumb rubber, Trans-Polyoctenamer Rubber Reactive Modifier (TOR), and an orthogonal test, the preparation scheme of crumb rubber modified asphalt suitable for alpine regions was obtained. The crumb rubber was selected 30 mesh, and the content of crumb rubber was 24% of the quality of matrix asphalt. Shearing time was 60 min, and preparation temperature was 205 °C. Shearing rate was 5000 r/min, and optimum TOR content was set as 4.5% of the quality of crumb rubber. The temperature susceptibility of matrix asphalt (JZ), crumb rubber modified asphalt (AR), crumb rubber modified asphalt mixed with TOR (TAR) was investigated. The high temperature performance indexes, including phase angle, the complex modulus index, and rutting factor, and the low temperature performance indexes including creep rate and stiffness modulus, the ratio of creep rate and stiffness modulus, Burgers model parameters, dissipated energy ratio, and the derivative of creep compliance were analyzed in depth with multiple parameters. Meanwhile, the mechanisms of prepared AR and TAR were explored. The results indicate that the PG grading is PG64-22 of JZ, PG70-34 of AR, and PG82-28 of TAR. The deformation resistance of TAR at high temperature is superior to AR. The addition of crumb rubber not only improves the temperature susceptibility, but also enhances its viscoelasticity at low temperatures. After the crumb rubber swell in the asphalt system, the network structures are crosslinked and the physical and chemical effects are produced, such as cracking and repolymerization in the asphalt system. TOR can further enhance the swelling and network crosslinking effects of rubber-asphalt. The TAR has the strongest weather resistance. The study provides guidance for AR and TAR to be used in alpine regions.

Investigation on the properties of epoxy asphalt mixture containing crumb rubber for bridge expansion joint

The purpose of this research is to propose epoxy asphalt materials for bridge expansion joints. Epoxy asphalt was modified by adding 0%, 20%, 30% and, 40% crumb rubber (CR). The viscosity, tensile properties, adhesion, high-temperature stability, moisture resistance, low-temperature, and stress relaxation properties of rubber-modified epoxy asphalt (REA) were investigated comparing with the commercial BJ200-red. Thermal stress of epoxy asphalt expansion joint was also simulated by the finite element analysis platform. The results indicated that with the increase of CR content, the viscosity and deformation of REA binder increase, while operation time, the tensile strength, and adhesive decreases. CR has a slight negative effect on the high-temperature performance of epoxy asphalt mixture, and has a positive effect on low temperature deformation. When the rubber powder content is 30%, epoxy asphalt mixture has excellent mechanical properties and its high-temperature stability is higher than BJ200 mixture, but the low-temperature performance of the two is equivalent. Thermal stress analysis shows that epoxy asphalt containing 30% CR cannot fracture above −15 ℃, so it can be recommended for bridge expansion joints.

Eco-Friendly Incorporation of Crumb Rubber and Waste Bagasse Ash in Bituminous Concrete Mix.

The consumption of waste materials in the construction sector is a sustainable approach that helps in reducing the environmental pollution and decreases the construction cost. The present research work emphasizes the mechanical properties of bituminous concrete mix prepared with crumb rubber (CR) and waste sugarcane bagasse ash (SCBA). For the preparation of bituminous concrete mix specimens with CR and SCBA, the effective bitumen content was determined using the Marshall Mix design method. A total of 15 bituminous concrete mix specimens with 4%, 4.5%, 5%, 5.5% and 6% of bitumen content were prepared, and the effective bitumen content turned out to be 4.7%. The effect of five different CR samples of 2%, 4%, 6%, 8% and 10% by weight of total mix and SCBA samples of 25%, 50%, 75% and 100% by weight of filler were investigated on the performance of bituminous concrete. A total of 180 samples with different percentages of CR and SCBA were tested for indirect tensile strength (ITS) and Marshall Stability, and the results were compared with conventional bituminous concrete mix. It was observed that the stability values rose with an increase in CR percentage up to 6%, while the flow values rose as the percentage of SCBA increased in the mix. Maximum ITS results were observed at 4% CR and 25% SCBA replacement levels. However, a decrease in stability and ITS result was observed as the percentages of CR and SCBA increased beyond 4% and 25%, respectively. We concluded that the optimum CR and SCBA content of 4% and 25%, respectively, can be effectively used as a sustainable alternative in bituminous concrete mix.

Impact of Crumb Rubber Concentration and Plastic Coated Aggregates on the Rheological Performance of Modified Bitumen Asphalt

The diminution of natural resource exploration, the retrieval of waste, and the structural modification of polymers by additives are the main contributions to sustainable development. The properties of bitumen are enhanced by the crumb rubber through effective bitumen modification techniques, which have environmental and economic advantages. In this study, plastic waste, plastic-coated aggregate (PCA), and bitumen were blended in order to enhance the engineering properties of the flexible pavement. In order to compute the composition of crumb rubber modified bitumen (CRMB), the adopted materials were subjected to the relevant experiments. PCA was a very effective material when compared to the standard bitumen road pavement. The recycling of waste crumb rubber and plastic was tested by adding them into the hot mix asphalt. The Marshall properties of standard (virgin) bituminous mix, CRMB grade 55, and plastic mix asphalt were studied in detail to explore the solutions for a sustainable environment. The comparison was performed between these two materials with the standard bitumen, which resulted in the CRMB and plastics being found as the most effective additions with robust properties such as low-cost material, high strength, long life usage, and un-harmful to nature. The optimal bitumen content was found to be 6.166%, 6.1%, and 5.833% for standard bitumen, crumb rubber modified bitumen, and plastic-coated aggregate, respectively.

Mechanical Properties and Durability Performance of Recycled Aggregate Concrete Containing Crumb Rubber.

Despite extensive research studies, recycled aggregates and worn-out tyres of motor vehicles are still not fully reused and are hence disposed of in ways that are damaging to the environment. Several studies have been carried out on recycled aggregate and rubberized concrete, but very limited studies are conducted on rubber recycled aggregate concrete. This study focuses on the workability, mechanical properties and durability performance of concrete made with 100% recycled aggregates and crumb rubber at different replacement level (5%, 10%, 15% and 20%). The first stage of the study covers the effect of incorporating crumb rubber at different concentration on the workability and mechanical properties of recycled aggregate concrete. The results revealed that the workability and mechanical properties of the recycled aggregate concrete can be used for structural applications when 5% of crumb rubber are used to replace recycled aggregates. The 28-days compressive strength of the rubberized recycled aggregate concrete with 5% crumb rubber concentration is reduced by 21.1% and 32.8% when compared to recycled aggregate concrete and control concrete, respectively. The second stage of the study assesses the durability performance of the recycled aggregate concrete with 5% crumb rubber concentration. The 5% crumb rubber content for durability tests was considered because the ultrasonic pulse velocity tests revealed that the quality of the recycled aggregate concrete is questionable if the concentration of crumb rubber particles is beyond 5%. The durability performance using the surface resistivity test also shows that the chloride ion penetration of recycled aggregates concrete with 5% crumb rubber replacement is moderate using air dried curing technique and high using the water bath curing method. Hence the study suggests the use of rubber recycled aggregate concrete for applications were the exposure condition is not extreme.

Composition Optimization and Damping Performance Evaluation of Porous Asphalt Mixture Containing Recycled Crumb Rubber

Composition optimization of the asphalt mixture of pavement is one effective measures to reduce the harm of traffic noise. To improve the noise reduction effect of porous asphalt mixture (PAM) and promote the recycling of crumb rubber in highway engineering, the preparation parameters of high-viscosity modified asphalt for PAM were optimized in this study, and the mixture gradation was optimized based on the unbalance force and contact force of mixed aggregate. The effects of crumb rubber content and particle size on the damping performance and dynamic shear modulus of the mixture were studied. The effects of different preparation parameters on the performance of the PAM were comprehensively evaluated based on the orthogonal test, and preparation parameters of PAM were recommended. The results show that with the increase of crumb rubber content, the damping ratio of the mixed aggregate increases gradually. The addition of crumb rubber is conducive to improving the damping performance and toughness of the PAM, but it has an adverse impact on the bearing capacity. Under the condition of low strain, the damping ratio of the mixed aggregate containing 2–5 mm crumb rubber is 1.2–5 times that of the mixed aggregate containing 0.6–1 mm crumb rubber. The recommended optimum content of crumb rubber in PAM is 4%, and the optimum particle size of alternative aggregate is 2.36–4.75 mm. The significant factors affecting Marshall stability are rubber particle content, asphalt aggregate ratio, mixing temperature, compaction times, and forming temperature. The rational utilization of crumb rubber in PAM is of positive significance to promoting the green development of highway construction and the harmless treatment of waste resources.

The influence of the mass ratio of crumb rubber and waste cooking oil on the properties of rubberised bio-rejuvenator and rejuvenated asphalt

With the increasing emphasis on RAP recycling technology in recent years, a waste rubber/oil (WRO) asphalt rejuvenator was self-developed by mixing crumb rubber (CR) with waste cooking oil (WCO) at high temperatures. This study was designed to determine the effect of the ratio of rubber to oil (RRO) on the properties of WRO rejuvenators and rejuvenated asphalt binders. Results indicate that the WRO sample with higher CR content exhibited better storage stability and contained more soluble macromolecular polymers. The effect of the RRO on solubility of CR was more significant than that of the reaction time. WCO served the main role in asphalt softening, while CR mainly contributed to the aging resistance of asphalt. Asphalt rejuvenated by WRO with a greater RRO exhibited better elasticity and rutting resistance. In terms of sulfoxide functional group content, increasing the RRO of the WRO was beneficial to the rejuvenation effect.

Performance Characteristics of Cemented Tailings Containing Crumb Rubber as a Filling Material

Increasing amounts of tailings and waste rubber tires have caused threats to the environment. In order to reuse these solid wastes, this study proposed a cemented tailings material containing crumb rubber recovered from waste tires. Unconfined compression tests and thermal conductivity measurements were conducted to evaluate the feasibility and performance of the proposed cemented tailings. Results revealed that the stress-strain behavior of the cemented tailings changed by the inclusion of crumb rubber. The unconfined compressive strength of cemented tailings decreased with increasing crumb rubber content. The inclusion of crumb rubber increased the failure strain and nonlinearity index of the cemented tailings. It was found that the addition of 4% crumb rubber provided the greatest improvement in ductility. The increase of the rubber content further increased the thermal insulation capacity of the cemented tailings. The low stiffness and the dimpled surface of the crumb rubber were responsible for the reduced compressive strength and thermal conductivity of the cemented tailings. In conclusion, the crumb rubber had both positive and negative effects on the cemented tailings. In practical application, the rubber admixture amount should be flexibly adjusted for different use case to make the cemented tailings material show the most suitable performance characteristic.

Thermal and acoustic properties of sustainable structural lightweight aggregate rubberized concrete

This study investigated the effect crumb rubber recycled from wasted tires on properties of structural lightweight aggregate concrete (LWAC). Two types of concrete were tested: control LWAC and rubberized lightweight aggregate concrete (RLWAC). The control LWAC consisted of cement, fine aggregate (river sand), and lightweight coarse aggregate (porous aggregates). For the RLWAC, the fine aggregate was replaced by crumb rubber at the rate of 10, 20, 30, 40, and 50% by volume. The water to cement ratio for both concrete types was set at 0.35. The experiment series consisted of density (ASTM C567), compressive strength (ASTM C39), flexural strength (ASTM C78), thermal conductivity (ASTM C518), and sound absorption coefficient (ISO 10534-2). Results showed the decrease in density of about 10%, compressive strength of 21.4%, and flexural strength of 35.4% with the increasing crumb rubber replacement ratio up to 50%. For thermal and sound properties, the increasing crumb rubber content of up to 50% improved the thermal insulation of concrete, as seen by the decrease in thermal conductivity by about 14.6%. RLWAC also exhibited superior sound insulating properties to LWAC as seen by higher sound absorption coefficient over the working sound frequency range. In order to satisfy the requirements of ASTM C330 and ACI 318, the optimum crumb rubber replacement was recommended at less than 10%.