Rubber Modified Asphalt Research Articles

Experimental Study on the Influence of Crumb Rubber on Temperature Susceptibility of Asphalt for Railway Application in the Tropics

The granular sub-ballast in conventional ballasted trackbed structure, though cheap and easy to construct, requires frequent maintenance, and cannot protect the subgrade against water infiltration. However, asphaltic sub-ballast in asphalt-ballast trackbed can reduce stress on the subgrade and provide a waterproofing layer against water infiltration. Asphalt binder is however, susceptible to temperature fluctuations. The aim of this study therefore is to investigate whether the addition of crumb rubber to asphalt binder could reduce the susceptibility of asphalt to temperature, and thus, improve its performance. The main objective of this research is the addition of four different ratios of crumb rubber; 1, 2, 3, and 4%, of size 0.3 mm to bitumen or asphalt 60/70 grade. The results showed that penetration of the asphalt binder reduced from 66.70 to 59.20 mm at 4% rubber content, implying that the modified asphalt became harder with addition of crumb rubber and thus, can withstand temperatures variations in asphaltic pavements. Softening point, used to test temperature susceptibility of bitumen, increased from 49.10°C to 52.80°C at 4% crumb rubber content, implying that crumb rubber modified asphalt can withstand elevated temperatures in asphaltic pavements, in the tropics. Flashpoint increased from 295.20 to 296.12°C, fire point also increased from 306.50°C to 308.28°C, Specific gravity of the unmodified and crumb rubber-modified asphalt did not change significantly because crumb rubber is not very flammable, Viscosity at 135°C increased from 338.00 to 360.00 cSt at crumb rubber content of 4%, Ductility at 25°C reduced from 122.40 cm to 79.40 cm at 4% crumb rubber content, implying that crumb rubber made asphalt stiffer. This study concludes that crumb rubber can reduce the susceptibility of asphalt to temperature changes.

Emission Risk and Inhibition Technology of Asphalt Fume from Crumb Rubber Modified Asphalt

Crumb rubber-modified asphalt mixtures have been proven to have extensive utilization value in road engineering. However, the rubber releases more fumes during the construction period, which causes severe harm to human health and the environment. This research focused on the emission risk of asphalt fume from crumb rubber-modified asphalt, and then the inhibition technology was also optimized. Firstly, the emission behavior and the hazardous evaluation of the asphalt fume from crumb rubber-modified asphalt were investigated. Then, the characteristics of the inhibition materials were evaluated. Finally, the reduction in the emission of inhibited crumb rubber-modified asphalt fume was identified, and the optimized formula was determined based on the inhibition effect, rheological properties, and cost. The results indicate that crumb rubber-modified asphalts release more fume components with an increment in the temperature and crumb rubber content. Desulfurized rubber reduces the release of H2S and NO. Benzene compounds, including paraxylene, toluene, and benzene, are the most released pollutants that harm human health, especially DS CRA 20% and CRA 50%. Kaolin powder and expanded graphite have a sufficient pore structure and volume, the addition of which reduces the release of pollutants while possibly promoting the release of NO and H2S. Their addition also has a significant control effect on the release of particulate matter at 170 °C and 185 °C. With the consideration of emissions, rheological properties, and cost, CRA 40%-EG2%-KL2% was determined as the optimization formula. This research is helpful to the application of crumb rubber-modified asphalt in road construction and maintenance.

Performance evaluation of bio-oil and high rubber content modified asphalt: More effective waste utilization

In this study, the bio-oil was used to reduce the viscosity and preparation temperature of high content of rubber-modified asphalt. The high rubber content modified bio-asphalt (RMBA) was prepared, the rubber and bio-oil contents were 20 %-30 % and 5 %-15 % (mass ratio of neat asphalt), respectively. The viscosity, temperature sweep (TS), frequency sweep (FS), multi-stress creep recovery (MSCR), and bending beam rheometer (BBR) tests were performed to assess the properties of RMBA. The Fourier Transform infrared spectroscopy (FTIR), Fluorescence microscopy (FM), and Scanning electron microscope (SEM) tests were conducted to explore the microscopic morphology of RMBA. Besides, the economic analysis and life cycle assessment (LCA) were assessed. Bio-oil contributed to the viscosity-reduction of the RMBA. When the rubber content was 30 %, the viscosity decreased by 48.16 % with a bio-oil content of 15 %. The temperature and frequency sensitivity of RMBA were lower than neat asphalt. Rubber improved the creep recovery and anti-rutting deformation behavior for bio-asphalt. The absorption peaks appeared at 1010 and 1038 cm−1, which represented the SO function group. The rubber did not absorb enough bio-oil for solubilization. This resulted in the functional group of SO appeared in 30 %+B-10 % and R-30 %+B-15 %. FM and SEM test results indicated that the rubber in RMBA exists in different states: undissolved rubber and dissolved rubber. The high content rubber could be partially dissolved in bio-asphalt and retained its elastic properties. The dissolved rubber particles exhibited a large crosslinked network structure. The raw material cost of RMBA decreased significantly with the rise of rubber and bio-oil contents. The reasonable application of waste rubber is beneficial to the alleviation of black pollution. The efficient application of rubber and bio-oil could contribute to the development of waste utilization and green transportation.

Effect of salt erosion on interfacial adhesion of waste tire crumb rubber-modified asphalt mixtures: A molecular dynamics study

In this study, a wetting and migration model was established using the molecular dynamics simulation method. Through in-depth analysis of parameters such as contact angle, mean square displacement, and work of adhesion, the dynamic wetting and migration characteristics of salt solution were explored, and the damage mechanism of waste tire crumb rubber-modified asphalt mixtures under salt erosion was revealed. The results showed that compared with an aqueous solution, the salt solution was more likely to be adsorbed and dispersed on the asphalt surface. This exacerbated its damage. However, the presence of salt ions reduced the wetting effect of the solution on the aggregate surface and reduced the migration rate of the solution at the asphalt-aggregate interface. Significant diffusion of Na+ and Cl- ions occurs during salt solution migration, while SO42- ions mainly accumulate near the aggregate surface. In addition, salt solution migration alters the distribution of asphalt components. This further affects the interface adhesion effect. The inclusion of crumb rubber can effectively reduce the sensitivity of asphalt to salt solutions and enhance its hydrophobicity. Simultaneously, it enhances the adhesion strength and stability of the asphalt. This effectively obstructs the intrusion of water molecules and salt ions.

Performance of rubber modified asphalt mixture with tire-derived aggregate subgrade

The objective of this research is to investigate the long-term performance of rubber-modified asphalt mixture (RMA) on Tire-Derived Aggregate (TDA)-replaced saturated subgrade as a drainage material. In lab testing setup, the mixtures were subjected to a 5-day conditioning at 85°C to ensure complete long-term aging. A series of laboratory and field tests were conducted. The study found that the surface course rubber mix had the best-cracking resistance than the leveling course control mix and surface layer control mix. Additionally, the fracture energy of the surface layer rubber mix was 17.4–21.9 % higher than that of the surface layer control mix. After the long-term aging condition, all three types of hot mix asphalt (HMA) exhibited exceptional resistance to deformation. Rubber-modified asphalt improved fatigue properties and crack performance. In summary, implementing RMA in pavement construction improved the pavement's thermal cracking and fatigue properties and significantly reduced pavement noise. TDA has potential as a fill material in subgrade applications, and rubber-modified asphalt shows promising performance for asphalt pavement.

Influence of field aging on viscoelastoplastic performance of rubberized asphalt mixtures incorporating reclaimed asphalt pavement in arid urban climate

This study investigates the effects of reclaimed asphalt pavement (RAP) and crumb rubber-modified asphalt (CRMA) on the viscoelastoplastic properties of asphalt mixtures under a range of aging conditions. Six asphalt mixtures, with varying RAP contents (0 %, 30 %, and 50 %) and CRMA modifications, were evaluated through dynamic modulus (|E*|) and flow number (FN) analyses. The specimens were subjected to authentic field-aging conditions for periods of 0, 3, 6, and 9 months. The results reveal that increasing RAP content enhances volumetric properties, Marshall stability, and rutting resistance. CRMA significantly improves fatigue performance and further bolsters rutting resistance, although some detrimental effects are observed at lower temperatures. Aging has a pronounced impact on the mixtures’ performance, particularly on |E*|, Prony series coefficients, viscoelastic strain (εve), and viscoplastic strain (εvp). Newly proposed aging indices, the dynamic modulus aging index (DMAI) and viscoplastic aging index (VPAI), effectively capture the changes in viscoelastoplastic behavior under different aging durations. These findings underscore the potential of RAP and CRMA to enhance pavement durability, prolong service life, and contribute to the development of sustainable and resilient infrastructure. The research offers valuable insights into the performance of asphalt mixtures incorporating RAP and CRMA under real-world conditions.

Mechanism of reinforced interfacial adhesion between steel slag and highly devulcanized waste rubber modified asphalt and its influence on the volume stability in steel slag asphalt mixture

The volume expansion risk of steel slag is a predominant challenge hindering its usage as an alternative aggregate in road pavements. In this study, the interfacial adhesion properties of base asphalt-basalt, base asphalt-steel slag, rubber modified asphalt (RMA) -basalt and RMA-steel slag were compared employing both experiment and molecular dynamics simulation. The volume stability and road performance of the asphalt mixture was also explored. The results showed that the residue rate of the RMA asphalt mixed with steel slag aggregates showed an increase from 87.5 % to 95.7 % compared to base asphalt after 100°C boiling water test. The interfacial adhesion between steel slag and asphalt surpasses that of basalt and asphalt, with the use of rubber modified asphalt further enhancing the adhesion with steel slag aggregates, as investigated through quantitative evaluation of interface adhesive work. The enhanced interaction between steel slag and RMA was primarily due to the integration of acidic functional groups from rubber chain with the alkaline active constituents (f-CaO) of steel slag aggregates, as confirmed by molecular dynamics simulations and accurate density functional theory calculations. Furthermore, the volume stability and road performance of the steel slag stone mastic asphalt were also greatly improved compared with basalt asphalt mixture. The dynamic average stability of RMA steel slag mixture was 9218 cycles/mm and the expansion rate of steel slag asphalt mixture under did not exceed 1.2 % after 216 hours water immersion. Therefore, this study provides an alternative aggregate for road pavement and a sustainable recycling strategy for the steel slag waste.

Rheological behavior and microscopic characteristic of electromagnetic thermal activated crumb rubber and SBS modified asphalt

Rubber activation provides a feasible approach for the preparation of high-content rubber modified asphalt without increasing the complexity of the production process. The electromagnetic thermal activation method was used for crumb rubber. The high dosage (30 % mass ratio of neat asphalt) activated crumb rubber and SBS (1.2 % mass ratio of neat asphalt) modified asphalt (ARMA) was prepared. The neat asphalt (NA) and 20 % non-activated crumb rubber modified asphalt (RMA) constituted the control group. Storage stability, rheological behavior, and microscopic properties tests were conducted to evaluate the performance differences of them. The rheological behavior of RMA and ARMA was superior to NA. The electromagnetic thermal activation method fragmented rubber particles into numerous disordered small particles, thereby expanded the contact area with asphalt. This resulted in the storage stability of ARMA significantly better than that of RMA. The cross-linked wrinkles were generated by the combined effect of SBS modifier and activated crumb rubber, which enhanced the rheological, anti-fatigue, and elastic behavior. Both RMA and ARMA exhibited high-temperature PG grades of 82˚C. At 70°C, ARMA retained the capability to endure Extremely Heavy Traffic Grade conditions. At a strain level of 2.5 %, ARMA exhibited a 178 % increase in fatigue life compared to RMA. The crumb rubber was dispersed within the RMA and ARMA. Both ARMA and RMA did not exhibit the obviously bee-structure. However, ARMA exhibited a stronger polymer network. Moreover, both the carbonyl index and sulfoxide index of ARMA were lower than those of RMA and NA. The activation process improved the compatibility between rubber and asphalt, and realized the high value utilization of waste rubber.

Characterization of emissions from rubber modified asphalt and their impact on environmental burden: Insights into composition variability and hazard assessment

Rubber modified asphalt (RMA) is a promising avenue for recycling waste tires but faces concerns over hazardous fumes emission during production and construction. This study employs a specialized apparatus to analyze RMA's emission behavior, focusing on crumb rubber size variations under thermal conditions. Ozone Formation Potential (OFP) and Secondary Organic Aerosol Formation Potential (SOAFP) were quantified to evaluate the environmental burden. Results indicate distinct periods of emission behavior for different pollutants, with H2S emissions primarily occurring within the initial 150 min while volatile organic compounds (VOCs) dominate within the first 270 min. The size of rubber particles and thermal exposure duration influence the VOCs microscopic emission characteristics and environmental burdens. Polycyclic aromatic hydrocarbons (PAHs) emerge as the primary contributors to OFP and SOAFP, accounting for nearly 65 % and 25 %−60 %, respectively. High molecular weight aliphatic hydrocarbons (ALHs) also significantly contribute to SOAFP, with PAHs dominating throughout, while ALHs peak during the middle stage. H2S emissions likely stem from rubber, while early VOC emissions originate from rubber, transitioning to petroleum asphalt during the middle and late stages. Asphalt fractions influence emission behavior and property evolution. These findings inform emission suppression strategies and highlight the need for tailored approaches to mitigate emissions effectively.

Resurface of rubber modified asphalt mixture with stress absorbing membrane interlayer: From laboratory to field application

The increasing concern over tire pollution, exacerbated by the improper disposal of waste tires, serves as the backdrop for this research, which aims to explore the efficacy of incorporating ground tire rubber (GTR) into asphalt mixtures enhanced with a stress-absorbing membrane interlayer (SAMI). In this study, three variations of Hot Mix Asphalt (HMA) were evaluated: a conventional mix, a rubber-modified asphalt mixture (RMA), and a trans-polyoctenamer rubber (TOR) modified asphalt mixture in the laboratory. The assessment focused on the high and low-temperature performance of the asphalt mix and binder. Key findings from the laboratory tests indicate that the integration of a SAMI layer and GTR as additives markedly boosts the crack resistance of the asphalt mixture. Despite a reduction in fracture energy across all three HMA types following long-term aging, the GTR-modified HMA maintained superior fracture energy relative to the conventional mix. Initially, the inclusion of GTR adversely affected the mixture's rutting resistance. However, after undergoing long-term aging, both the conventional and GTR-modified HMAs exhibited exceptional rutting and moisture damage resistance. Field noise assessments further demonstrated that GTR-enhanced pavements produced noise levels approximately 2 dB lower than those of standard asphalt pavements. Additionally, pavements lacking a SAMI layer manifested low-severity cracking, with an average cracking frequency occurring every 2 ∼ 6 m, whereas pavements equipped with a SAMI layer exhibited no cracking following two winter seasons. The rubber asphalt overlay may increase the leaching of 6PPD-quinone, but the SAMI layer helps reduce tire wear particle generation by preventing road cracking. Rubber asphalt overlay leaching tests resulted in 6PPD-quinone concentrations lower than currently available toxicity data (LC50 for Coho Salmon, 0.095 ug/L). In conclusion, the utilization of dry-processed rubber asphalt mixes alongside a SAMI layer in pavement construction not only has the potential to extend the service life of pavements but also contributes to the production of quieter road surfaces. This study underscores the environmental and functional benefits of incorporating rubber modifications into asphalt pavements, presenting a viable strategy for mitigating tire pollution through the reuse of waste tires in infrastructure.

Study on the Performance of Asphalt Modified with Bio-Oil, SBS and the Crumb Rubber Particle Size Ratio.

To enhance the properties of SBS and crumb rubber-modified asphalts, four different amounts (5%, 10%, 15%, and 20%) of castor oil were added to crumb rubber-modified asphalts to mitigate the adverse effects of high levels of fine crumb rubber particles on the aging resistance of SBS and crumb rubber-modified asphalt. Initially, a conventional test was conducted to assess the preliminary effects of bio-oil on the high-temperature and anti-aging properties of SBS and crumb rubber-modified asphalt. Subsequently, dynamic shear rheometer and bending beam rheometer tests were employed to evaluate the impact of bio-oil on the high- and low-temperature and anti-fatigue properties of SBS and crumb rubber-modified asphalt. Finally, fluorescence microscopy and Fourier transform infrared spectroscopy were used to examine the micro-dispersion state of the modifier and functional groups in bio-oil, SBS and crumb rubber composite-modified asphalts. The experimental results indicated that bio-oil increased the penetration of SBS and crumb rubber-modified asphalt, decreased the softening point and viscosity, and significantly improved its aging resistance. The addition of bio-oil enhanced the anti-fatigue properties of SBS and crumb rubber-modified asphalt. The optimal amount of added bio-oil was identified. Bio-oil also positively influenced the low-temperature properties of SBS and crumb rubber-modified asphalt. Although the addition of bio-oil had some adverse effects on the asphalt's high-temperature properties, the asphalt mixture modified with bio-oil, SBS, and crumb rubber still exhibited superior high-temperature properties compared to unmodified asphalt. Furthermore, fluorescence microscopy and Fourier transform infrared spectroscopy results demonstrated that bio-oil can be uniformly dispersed in asphalt, forming a more uniform cross-linked structure and thereby enhancing the aging resistance of SBS and crumb rubber-modified asphalt. The modification process involved the physical blending of bio-oil, SBS, and crumb rubber within the asphalt. Comprehensive research confirmed that the addition of bio-oil has a significant and positive role in enhancing the properties of SBS and crumb rubber-modified asphalt with different composite crumb rubber particle size ratios.

Effects of Silicone Rubber on Rheological Properties and Aging Characteristics of Asphalt Binder.

Silicone rubber (SR) is a kind of polymer insulation material with excellent performance. With the service life of silicone rubber products reaching the limit, how to dispose of waste silicone rubber is an urgent problem to be solved. In this paper, silicone rubber-modified asphalt binder (SRMA) was prepared by SR and 90# base asphalt binder. The simulated short-term aging and long-term aging tests of SRMA were carried out using the thin film oven aging test (TFOT) and pressure aging vessel test (PAV). The rotary viscosity test and dynamic shear rheological test (DSR) were applied to the rheological properties of SRMA before and after aging. The degradation degree and chemical composition changes of SR were explored by the toluene insoluble matter test, Fourier transform infrared spectroscopy (FTIR), and a Fluorescence microscope (FM). The results demonstrate that SR can significantly affect the aging resistance, fatigue life, and high-temperature stability of SRMA. As the content of SR rose, the elastic component in SRMA increased, leading to a nice performance in stability at high temperatures and fatigue resistance. However, excessive content (14%wt and 16%wt) had a negative influence on the performance of SRMA. So, the optimal content was speculated to be between 12% and 14%. Furthermore, SR and asphalt binder would be aged and degraded together in the aging process, and this phenomenon was more obvious during long-term aging.

Interface Interaction of Waste Rubber–Asphalt System

Asphalt pavement construction is a large-volume project, with the ability to recycle the industrial waste and reduce carbon emissions. Rubber-modified asphalt is a carbon-neutralized asphalt-based material, facilitating the recycling of waste rubber materials and improving the road performance of the asphalt mixture. To evaluate the interface interaction of the rubber–asphalt system and its effect on the viscosity characteristics of rubber-modified asphalt, the contact properties of rubber particles in asphalt were analyzed on a microscopic level. Rubber swelling tests and solvent elution tests were conducted on the rubber–asphalt system under different preparation conditions. The swelling ratio, degradation ratio, and swelling–degradation ratio were proposed to evaluate the interface interaction. The results show that the interface interaction of the rubber–asphalt system can be divided into the following three stages: swelling, effective degradation, and over-degradation. The degree of swelling is mainly affected by the content and size of the rubber particles and it is physically condensed, while the degradation is mainly affected by the preparation temperature and preparation time. The effective interface interaction greatly affects the viscosity with the building of the stable three-dimensional network structure. The stronger the interface interaction, the greater the viscosity of the rubber-modified asphalt, except for the 25% content of rubber particles. The gel film will be generated on the surface of the rubber particles throughout the swelling and effective degradation, increasing the viscosity of the rubber-modified asphalt.

Compositional analysis and quantitative evaluation of organic emissions from asphalt materials: Improvements and refinements

The organic emissions resulting from the use and application of asphalt materials can pose significant risks to plant, animal life and human health, consequently, it is crucial to conduct compositional analysis and quantitative evaluation of organic emissions from asphalt materials. In this study, the qualitative and quantitative analysis method of organic emissions from asphalt materials was developed based on headspace gas chromatography-mass spectrometry (HS-GC-MS), selected ion monitoring (SIM) mode, internal standard method and calibration curve. The spiked recovery and surrogate standard recovery were employed to validate the method. The results show the excellent accuracy, precision, and reliability of the HS-GC-MS quantitative analysis method. And the results provide confirmation that total volatile organic compounds (TVOCs), polycyclic aromatic hydrocarbons (PAHs), and n-alkanes can indeed be identified as typical organic emissions originating from asphalt materials. Furthermore, the study successfully identifies benzothiazole, cyclohexyl disulfide, and N-(1,3-dimethylbutyl)-N′-phenyl-1,4-phenylenediamine as characteristic emissions in crumb rubber-modified asphalt (CRMA). The inclusion of the styrene-butadiene-styrene (SBS) modifier results in a significant reduction in n-alkane emissions by 41.11%, PAHs emissions by 25.22%, and TVOCs emissions by 47.21% in comparison to the base asphalt, demonstrating the effective inhibitory effect of the SBS modifier on organic emissions. When compared to the base asphalt, the addition of crumb rubber results in increased emissions of n-alkanes by 12.68% and PAHs by 50.60%, as well as the introduction of the emissions associated with CRMA characteristic compounds, indicating that the emission issue of CRMA is particularly prominent.

Effect of waste engine oil and warm mix additive on the physical, rheological, and short-term aging attributes of Styrene–Butadiene Rubber-modified asphalt binders

Styrene-butadiene rubber (SBR) latex is used widely to increase the low-temperature resistance of asphalt binders. However, the high content of butadiene copolymer in SBR-treated asphalt causes oxidation and aging. Furthermore, following the SBR modification, the compatibility and thermal storage stability of SBR-modified asphalt is not satisfactory. Therefore, the best approach to improve the quality of short-term aged SBR-modified asphalt is to lower the manufacturing temperatures of the SBR-modified asphalt mixture. In this study, to reduce the preparation temperatures of SBR-modified asphalt mixes and improve their performance after short-term aging, several additives i.e., waste engine oil (WEO), warm mix agent i.e., ZycoTherm, and WEO/ZycoTherm combination (WEO+ ZycoTherm) were selected. The rheological properties and aging performance of binder samples were evaluated through the rational viscosity, dynamic shear rheometer, bending beam rheometer and Fourier transform infrared spectroscopy tests. The results showed that adding WEO together with ZycoTherm into an SBR-modified binder contributed to reducing the compaction and mixing temperatures. The chemical analysis showed that the three additives i.e., WEO, ZycoTherm, and ZycoTherm/WEO declined the aromaticity and chemical aging indicators of aged SBR-modified binders. Furthermore, it was demonstrated that both the ZycoTherm and WEO/ZycoTherm improved the asphalt resistance to rutting at elevated temperatures in both conditions i.e., before and after short-term aging. In addition, the findings revealed ZycoTherm /WEO compound yielded the best performance to improve the minimal-temperature cracking resistance of the SBR-modified binder, resulting in lower short-term aging temperatures. In summary, this study highlights the necessity of lowering preparation temperatures in asphalt mixes containing SBR to enhance binder resistance to rutting and cracking and reduce susceptibility to oxidation during short-term aging.

Effects of Aging on Rheological Properties and Microstructural Evolution of SBS Modified Asphalt and Crumb Rubber Modified Asphalt Binders

Focusing on the comparison of aging resistance between styrene-butadiene-styrene (SBS) modified asphalt (SBSMA) and crumb rubber modified asphalt binders (CRMA), the influences of aging on rheological properties and microstructural characteristics of different modified asphalts were investigated in this work. Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) tests were carried out, and the variations in rheological properties for different modified asphalts after the rotating thin film oven test (RTFOT) were analyzed with the rutting factor aging index (RAI) and creep rate aging index (CAI). By using Fluorescence microscopy (FM) and Fourier transform infrared (FTIR) spectroscopy, the evolutions of microstructure and chemical composition for two modified asphalts were analyzed with carbonyl index growth rate (CIR) and sulfoxide index growth rate (SIR). Then, The relationships between CIR/SIR and RAI/CAI were established to show the correlation between the deterioration of macroscopic performance and the evolution of micro-structure. The results indicated that the aging degree of asphalt increases with elevated temperatures, leading to decreasing low-temperature performance while improving high-temperature performance. Nevertheless, SBSMA exhibited strong sensitivity to aging temperature. Under thermo-oxidative aging, the RAI and CAI of SBSMA were lower than those of CRMA, whereas the regularities of CIR and SIR were opposite, indicating that CRMA was superior to SBSMA in terms of anti-aging properties due to the rupture of the cross-linked network structure of SBSMA. However, CRMA experienced aging accompanied by full swelling, and thus, relatively minor performance declined. The CIR and SIR exhibited a better correlation with the RAI and CAI, illustrating that both CIR and SIR could characterize the aging degree of modified asphalts well.

Mechanisms associated with sulfidation gas release, desulphurisation and degradation of rubber powder in crumb rubber modified asphalt

ABSTRACT Odorous sulphidation gases are released during the construction of crumb rubber-modified asphalt (CRMA), causing pollution to the environment. To study the associated mechanism of sulfidation gas (H2S, CH4S, COS and CS2) release and the desulphurisation and degradation of CR in asphalt, the release law of sulphidation gas of CRMA was studied by a gas detector. Gel permeation chromatography (GPC), fluorescence microscope, toluene insoluble (TI) and potentiometric titration tests were used to study the desulphurisation and degradation of CR. The results showed that vulcanised CR in CRMA led to the generation of sulphidation gas with the increase in temperature, time and stirring speed. The average molecular weight of CRMA increased, while the TI and unsaturation (A) decreased after the desulphurisation and degradation of CR. Under the influence of temperature, heating time and stirring speed, the A was reduced by 0.72%∼8.87%, 1.18%∼10.69% and 0.75%∼8.12%, respectively. There was a strong correlation between the concentration of sulphidation gas and the desulphurisation and degradation parameters of CRMA. The reaction of ·H, –CH3, CO with the –SxH generated by the C–S, S–S, C=C fracture during the desulphurisation and degradation of CR was the main reason for the generation of sulphidation gas.

Interaction of composite fume suppression and odor elimination agents with crumb rubber modified asphalt: Inhibition behavior of volatile organic compounds (VOCs) and inorganic fume

The production and construction of crumb rubber modified asphalt (RMA) at high temperatures can produce a large amount of toxic fume, which is detrimental to human health and environment. In this study, a series of composite fume suppression and odor elimination agents (CSEAs) with both physical adsorption and chemical capture functions were adopted to reduce the emissions of volatile organic compounds (VOCs) and hydrogen sulfide (H2S). The material composition, microstructure, and specific surface area of CSEA were analyzed by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and N2 adsorption-desorption isotherm (BET). The inhibitory effects of adding CSEA on toxic fume emissions from RMA at high temperatures were investigated through a combination of fume emission tests, H2S gas detection, gel permeation chromatography (GPC), and gas chromatography–mass spectrometry technology (GC–MS). The adsorption behavior of CSEA on H2S was analyzed through adsorption dynamics. Results showed that the physical and chemical properties of CSEA are stable while chemical adsorption dominates the CSEA's effect on H2S. ZnO and Ca(OH)2 exhibit good crystallization effects on the surface of the carrier by forming mesoporous structures mostly above 3.4 nm in size. The incorporation of CSEA significantly reduced the total emissions of RMA fume and the main components of VOCs in which the average inhibition rate of H2S can reach 44 % at an initial 30 mins.

Effect of the reclaiming degree of catalytic pre-desulfurization recycled crumb rubber on the properties of modified asphalt

The application of crumb rubber (CR) as an asphalt modifier in flexible pavements is an effective way to achieve sustainable utilisation. The performance of crumb rubber modified asphalt (CRMA) can be improved by pretreatment of CR to make it desulfurized to a certain extent. This study aims to determine the optimal regeneration degree of CR to obtain CRMA with better performance. Recycled crumb rubber (RCR) was prepared by catalytic regeneration at low temperatures and used to prepare recycled crumb rubber-modified asphalt (RCRMA). Furthermore, the characteristics of RCR with different regeneration degree and the performance of RCRMA were investigated to determine the reasonable range of regeneration degree. The results showed that solubility was a reliable indicator of the degree of regeneration of RCR and that the solubility of RCR was positively correlated with its regeneration degree. The higher the degree of RCR regeneration, the lower the molecular weight, the more uniform the distribution, and the larger the surface structure. The low-temperature performance, fatigue resistance, and construction workability of the RCRMA were better than those of the CRMA. When the solubility of RCR was greater than 30%, the compatibility and storage stability of RCRMA were significantly improved. As the solubility of RCR increases, the high-temperature performance of RCRMA decreases; however, as long as the solubility of RCR does not exceed 60%, the decrease in the high-temperature performance of RCRMA is very small. According to a comprehensive analysis, the solubility of RCR should be maintained at 30–60%.

Effect of vulcanisation on the properties of natural rubber-modified asphalt

Natural rubber (NR), a bio-based polymer, has significant potential for economic and environmental sustainability when used as an asphalt modifier in flexible pavements. In this study, natural rubber-modified asphalt (NRMA) was produced and the effects of vulcanisation on NRMA were investigated. The results showed that vulcanisation can improve the stiffness and elasticity of NRMA, thereby strengthening its resistance to deformation at high loads and temperatures. Specifically, vulcanisation increased the rutting factor of NRMA by 1.5, increased the elastic recovery by 60%, and decreased the temperature-sensitivity factor by 6.75%. In addition, the softening-point difference (SPD) of vulcanised natural rubber-modified asphalt (VNRMA) was significantly reduced by 36.8%, and the thermal-storage stability was improved. The micromorphology and changes in chemical bonds that occurred in VNRMA revealed that vulcanisation not only deepened the level of crosslinking between NR and asphalt, but also refined the NR particles, making NR more uniformly dispersed within the asphalt phase. By creating new chemical bonds, vulcanisation reinforced the NR network structure and change the main modification method for asphalt using NR from physical to chemical modification. This improved the rheological and mechanical properties of NRMA. The results of this study provide new solutions for NRMA applications and help improve its performance and application scope.