Crumb Rubber Modified Asphalt Research Articles

Secondary degradation of bio-oil degraded crumb rubber and preparation of stable degraded crumb rubber modified asphalt

Using bio-oil to desulfurize and degrade crumb rubber (CR) significantly enhances the compatibility between CR and asphalt, improving the workability of CR-modified asphalt and providing environmental and economic benefits. However, the secondary degradation of bio-oil degraded crumb rubber (ODR) in asphalt hinders the stability of ODR-modified asphalt. To optimize the mechanical performance of ODR-modified asphalt, the secondary degradation behaviors of ODR were investigated. The degree of CR degradation was determined by solubility testing, while the rheological properties and chemical structures of ODR-modified asphalt were characterized through rotational viscometer, dynamic shear rheometer, bending beam rheometer, and Fourier transform infrared spectrometer. The processes for preparing stable ODR modifier and ODR-modified asphalt were proposed to mitigate the damage caused by bio-oil and degraded CR to the high temperature mechanical properties of asphalt. The results show that at lower processing temperatures for ODR-modified asphalt, the volatilization of light components is predominant, while higher processing temperatures prompt secondary degradation of ODR. By stirring at 280°C for 2 hours to acquire moderately degraded CR, and then concentrating it at 220°C for 2 hours, a stable ODR less susceptible to secondary degradation can be obtained. The workability, temperature sensitivity, and low temperature cracking resistance of stable ODR-modified asphalt improve significantly. The reduction of ester group and increase in aromaticity restore the high temperature deformation resistance of ODR-modified asphalt. Further, the inclusion of composite SBS extends the range of rheological properties in ODR-modified asphalt, bolstering the application potential of ODR in asphalt pavement.

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%.

Ultrasound-assisted preparation of crumb rubber modified asphalt: Characterization and molecular dynamics simulation

The traditional method of crumb rubber modified asphalt (CRMA) preparation can improve the stability but is not conducive to cleaner production. From the perspective of process optimization, ultrasound is introduced into the crumb rubber modified asphalt preparation process, and the high temperature, high pressure and high energy accompanied by the cavitation effect are used to generate free radical triggering chemical effects at the two-phase interface between crumb rubber and asphalt. In this paper, the influence of ultrasound on the compatibility and stability of crumb rubber modified asphalt system was evaluated by combining experiment and molecular dynamics simulation. An experimental platform for ultrasound-assisted preparation of crumb rubber modified asphalt was established. The effects of ultrasonic on the physical properties of asphalt and crumb rubber modified asphalt were studied through Brookfield viscosity test, thin film oven aging test and Fourier infrared spectroscopy. The base, aged, and ultrasonically treated asphalt samples were simulated using molecular dynamics, and various parameters such as Cohesive Energy Density (CED), Mean Square Displacement (MSD), and Free Volume Fraction (FFV) of asphalt and its components were calculated and analyzed. The results showed that under the ultrasonic-assisted preparation, the agglomeration phenomenon of rubber particles is weakened, the particle size is reduced, the penetration degree is reduced, and the compatibility between rubber and asphalt is improved. Under the action of ultrasonic, the MSD and diffusion coefficient of crumb rubber modified asphalt are much higher than other kinds of asphalt, the dipole moment is increased, and the molecular motion range is wider. This indicates that the diffusion ability of crumb rubber modified asphalt is significantly enhanced under the external force of ultrasonic simulation. The molecular bonds of crumb rubber modified asphalt changes greatly, the energy decreases obviously, and the system stability increases. In conclusion, ultrasonic action on crumb rubber modified asphalt preparation is a green and effective way to improve system stability and compatibility.

Long-Term Performance of Flexible Pavements Containing Crumb Rubber Modified Asphalt in Louisiana

The use of crumb rubber modifiers (CRMs) in asphalt mixtures plays a significant role in creating a sustainable circular economy. This study aims to evaluate the field performance of CRM asphalt sections with service years greater than eight. Five field projects were evaluated. Each project had one or two CRM sections constructed alongside a companion control section. Five types of CRM products were considered. A 16-mesh proprietary CRM, a Rouse-80 powder (R-80), and a Neste Wright powder were used in the wet blending process. Further, a 16-mesh generic crumb rubber, a PlusRideTM shredded rubber, and R-80 were used in a dry blend. Field performance data, including rutting, roughness, and cracking, were collected and analyzed. Moreover, economic analysis was performed to ascertain the cost-effectiveness (CE) of constructing CRM sections. Furthermore, laboratory performance indicators measured during construction were analyzed to ascertain their ability to rank field performance. Generally, CRM sections exhibited significantly similar or better ride quality, cracking and rutting resistance, and pavement condition index than their corresponding control sections. In some cases, the styrene-butadiene-styrene polymer modifier showed better cracking resistance in the control sections than the CRMs. CRM asphalt sections generally exhibited higher CE than their corresponding control sections because of their high initial unit costs. The Rouse wet CRM asphalt section in field project 4, which had a relatively lower unit cost, was found to be cost-effective compared to its corresponding control section. The limited laboratory mechanical performance parameters considered were ineffective in consistently ranking field performance indicators.

Thermal Oxidative Aging Effect on Chemo-Rheological and Morphological Evolution of Crumb Rubber Modified Asphalt Binders with Wax-Based Warm Mix Additives

Wax-based warm mix additives can decrease the viscosity and improve the workability of crumb rubber (CR)-modified asphalt, but the mechanism of influence on the aging performance of CR-modified asphalt is not clear. To investigate the thermal aging behavior and mechanism of wax-based warm mix CR-modified asphalt, polyethylene wax (PEW) and polyamide wax (PAW) were mixed to prepare warm mix CR-modified asphalt. The effect of thermal aging on the rheological and mechanical properties was characterized by a basic property test, frequency sweep test, and multiple stress creep recovery test. The chemical composition changes during aging were then analyzed by Fourier transform infrared spectroscopy and gel permeation chromatography. Finally, the phase morphology during thermal aging was observed by fluorescence microscopy. The results showed that compared with the degradation of CR, the oxidative aging of the asphalt binder played a dominant role in the process. Not only did PEW and PAW attach to the asphalt surface in the form of crystallization to prevent its reaction with oxygen but they also promoted the dissolution of CR, and released polymerization chains, thereby enhancing the antiaging properties of CR-modified asphalt. Furthermore, the antiaging of PAW/CR-modified asphalt was better than that of PEW/CR-modified asphalt, because the amide group of PAW reacted with CR-modified asphalt to form a polymer structure.

Viscosity Reduction Mechanism and Rheological Properties of Ethylene-Bis-Stearamide and Crumb Rubber Modified Asphalt

This study investigates the effect of ethylene-bis-stearamide (EBS) on viscosity reducing of crumb rubber modified asphalt (CRMA) and explores the interaction mechanism via molecular dynamics simulation (MD), microscope method and rheological experiment. It is confirmed that the EBS play an important role in reducing the viscosity of ethylene-bis-stearamide and crumb rubber modified asphalt (EBS-CRMA), especially when the content is within 3%. The micro morphology and MD results showed that the EBS is coating on rubber and asphaltenes and then forming lubrication film, which is the main reason leading to the viscosity decrease of EBS-CRMA. Additionally, other factors also have significant effect in reducing the viscosity of EBS-CRMA, including the more uniform distribution of asphaltenes, the enhanced diffusion ability of saturates and resins, the reduction of hydrogen bonds and soluble substances within asphalt phase. When EBS content exceeds 3%, the influence on viscosity of EBS-CRMA is not obvious with the EBS content continuously increasing. It can be concluded from Fourier Transform Infrared (FTIR) Spectrometer and MD results that the molecular aggregation, the concentration increase of intermolecular hydrogen bonds and the diffusion ability decrease of EBS-CRMA molecular system are main reasons. Meanwhile, the coating effect of EBS and soluble substances concentration within asphalt phase are limited as the EBS content over 3%.

Laboratory short-term aging of crumb rubber modified asphalt: RTFOT temperature optimization and performance investigation

Improper disposal of substantial scrap tires can result in significant environmental issues, such as air pollution, water resources, and soil contamination. The scrap tires can be turned into valuable materials by preparing tire rubber powder into Crumb rubber modified asphalt (CRMA). This method can effectively reduce environmental pollution and achieve the concept of energy conservation, environmental protection, and low-carbon. However, during the production process of CRMA mixtures, the elevated construction temperature may induce more severe short-term aging of the mixtures. The standard laboratory short-term aging scheme of asphalt binders, the Rolling Thin Film Oven Test (RTFOT), cannot simulate the short-term aging of CRMA due to the increase in construction temperature. Besides, the determination methods and indices of RTFOT aging temperature are still unclear and inconsistent. In this study, three CRMA binders were treated by RTFOT with five temperatures, and the short-term oven aging (STOA) protocol was conducted on CRMA mixtures with three types of gradations. Firstly, the chemical and rheological performance of CRMA binders and mixtures were investigated by conducting Gel permeation chromatography (GPC), Fourier transformation infrared spectroscopy (FTIR), Dynamic shear rheology (DSR) tests, and Bending beam rheometer (BBR) test. Then, the equivalent aging temperatures were determined to optimize RTFOT temperatures by comparing the chemical indicators of binders and mixtures. Finally, the correlations of chemical and rheological indices were established, and the rheological properties of aged asphalt in mixtures were predicted. The analysis results indicate that suitable RTFOT temperature is not only related to the technical routes and viscosity of CRMA binders, but also relevant to the mixture gradations. Binders with higher viscosity need elevated RTFOT temperatures from 173 °C to 193 °C, especially simulating short-term aging of mixtures with higher air voids. The swelling and degradation of crumb rubber contribute to the enhancement of the anti-aging performance. The aging index (AI) can reflect the anti-aging performance of CRMA binders, and the variation of AI can validate the rationality of the optimized RTFOT temperatures.

Presentation of machine learning methods and multi-objective optimization of fracture indices for asphalt rubber mixtures containing wax-based warm mix additives modified by nano calcium carbonate

Warm mix asphalt (WMA) additives have been proposed to overcome the high viscosity problem of crumb rubber modified asphalt (CRMA) binders. Various additives have been used to improve the low-temperature cracking performance of asphalt mixtures, but no study has been conducted to present the optimum additive content in CRMA binders in different loading modes. Therefore, this research aims to present the optimum content of nano calcium carbonate (NCC) to improve the fracture toughness and energy of asphalt rubber mixtures containing WMA additives (slack wax (SW) and polypropylene wax (PPW)). The semi-circular bend (SCB) fracture test was applied under pure mode I, mixed mode I-II, mixed mode II-I and pure mode II loadings at subzero temperature. Machine learning methods, including multivariate regression (MVR) and artificial neural network (ANN) models of group method of data handling (GMDH) and multilayer perceptron (MLP), were used to provide the prediction models of effective stress intensity factor (Keff) and fracture energy (Gf). Finally, the multi-objective optimization of Keff and Gf was performed to obtain optimum NCC content. The results indicated that in MVR model, the outputs had a small correlation with laboratory values, so that R value of MVR was 0.8406 and 0.8011 for Keff and Gf, respectively. Also, it was revealed in MVR that NCC had the highest impact on Keff and Gf significantly. GMDH model results showed that the relationships between predicted and laboratory values of Keff and Gf are appropriately described with R value of 0.9546 and 0.9229 for Keff and Gf models, respectively. In MLP model, different layer structures of the feed-forward neural network were developed to obtain the most accurate structure. It was indicated that MLP with 4–22–1 and 3–19–1 structures had a higher accuracy for Keff and Gf prediction models with R value of 0.9951 and 0.9978, respectively. Finally, by the use of the best model relationships, the results of the multi-objective optimization indicated that 4.91% and 6.37% NCC were the design optimum contents resulting in a maximum of Keff and Gf simultaneously for SW and PPW-modified CRMA mixtures. Moreover, the optimum NCC contents in loading modes of mode mixity Me of 1, 0.8, 0.4 and 0 were 3.62%, 5.12%, 4.08% and 3.42% for SW-modified CRMA mixtures and 4.35%, 6.51%, 7.19% and 2.84% for PPW-modified CRMA mixtures, respectively.

Effect of Fractionation Process and Addition of Composite Crumb Rubber-Modified Asphalt on Road Performance Variability of Recycled Asphalt Mixtures with High Reclaimed Asphalt Pavement (RAP) Content

The application of reclaimed asphalt pavement (RAP) can help reduce resource waste and environmental pollution in road construction. However, so far, only a small percentage of RAP materials can be used in road construction. The key obstacles to the application of a recycled asphalt mixture (RAM) with high RAP content are the variability of RAP materials and the difficulty of fully rejuvenating aged asphalt. However, there is still a lack of research on the effect of the variability of RAP materials and recycled asphalt on the quality control of a RAM. Therefore, this study investigates the effects of sieve pretreatment of RAP material using 4.75 mm sieve mesh and the use of composite crumb rubber-modified asphalt (CCRMA) to reclaim aged asphalt on the road performance and frame variability of reclaimed asphalt mixtures. Therefore, this study investigates the effects of the fractionation process of RAP material using 4.75 mm sieve mesh and the use of CCRMA to reclaim aged asphalt on the road performance of a RAM. The results show that the fractionation process can effectively reduce the mitigation of RAP agglomeration and reduce the variability of gradation, which in turn reduces the variability of road performance. The incorporation of CCRMA can effectively improve the high-temperature stability performance and low-temperature cracking resistance. The dynamic stability and the fracture energy of the CRAM (RAM prepared using CCRMA) were four and one and a half times as large as that of the NAM (RAM prepared using base asphalt), respectively. The fractionation process of RAP material and the utilization of CCRMA could help reduce the variability of the RAM while improving the road performance of the RAM.

Innovative Use of Waste PET-Derived Additive to Enhance Application Potentials of Recycled Concrete Aggregates in Asphalt Rubber.

Polyethylene terephthalate (PET) drinking bottles, rubber tires, and concrete are the very common municipal solid wastes, which are usually disposed of at landfills and stockpiles and cause continuous damage to the environment. Some studies have indicated that waste PET can be chemically converted into an additive for improving the overall properties of asphalt pavement incorporating natural aggregates, especially the moisture-induced damage resistance. However, it is not clear whether this PET additive still works for asphalt rubber containing recycled concrete aggregates (RCA). To well reveal this issue, this study first adopted a similar way to chemically recycle waste PET into the additive for modifying crumb rubber modified asphalt (CRMA) binder and then mixed the binder with the 13 mm maximum aggregate stone matrix asphalt containing 100% coarse RCA for preparing the mixtures. After a series of physicochemical characterizations of the PET additive, the moisture resistance, rutting resistance, low-temperature cracking resistance, and fatigue resistance of the mixture were systematically evaluated. The results showed that the PET additive is capable of improving the resistance to moisture and high-temperature deformation of asphalt rubber and helps greatly reduce the moisture-induced damage to the interfacial bonding layer. To be more detailed, the residual Marshall stability (RMS) value of RCA-CRMAM/1PET after 72 h of immersion is higher than 85% by contrast to that of RCA-CRMAM (77.1%), while the tensile strength ratio (TSR) value of RCA-CRMAM/1PET shows more than 80% compared to that of 65.2%. In addition, only 1% PET additive can enhance the high-temperature resistance of asphalt rubber containing RCA to rut and allow it to maintain higher resistance to rut after moisture-induced damage. 1% PET additive can help improve the bearing capacity of RCA-CRMAM under a low-temperature environment and delay its fatigue life at small stresses. Generally, with the successful introduction of PET additives to asphalt rubber containing RCA, more durable and sustainable highway pavement can be produced and applied in practice to alleviate the negative impacts caused by waste PET, waste tire rubber, and waste concrete.

Evaluating the interfacial properties between crumb rubber modified asphalt and aggregates using molecular dynamics simulation methods

In the present study, the molecular dynamics (MD) simulation methods were used to investigate the interfacial properties of crumb rubber modified asphalt (CRMA)-aggregates considering the effects of crumb rubber (CR) degradation behavior and moisture. The interface models with different CR degradation degrees were then constructed. The interfacial adhesion properties between CRMA and aggregates were discussed by the interaction energy and work of adhesion; the agglomeration characteristics of CRMA on aggregates surface were evaluated by the radial distribution function (RDF); the diffusion behaviors of CRMA on aggregates surfaces were investigated using the mean square displacements (MSD); the asphalt adhesion strength test was performed to further verify the reliability of the simulation results. The results showed that the incorporation of CR into asphalt could significantly improve the adhesion and moisture damage resistance of the asphalt mixtures, while the CR degradation would slightly decrease these properties. The results of asphalt adhesion strength test exhibited similar trends with those of the work of adhesion, indicating that the simulation possessed a certain rationality. The RDF curves showed that the intrusion of water enlarged the distance between the polar components and aggregates, whereas the CR molecules displayed satisfactory agglomeration properties. Furthermore, the addition of CR weakened the mobility of asphalt on aggregates surface. This was mainly attributed to the poor mobility of the CR and its limitation on the mobility of the constituent components of asphalt. However, these problems would be alleviated as the CR degradation.

Rheological properties and viscosity reduction mechanism of aromatic/naphthenic oil pre-swelling crumb rubber modified asphalt

Using light oil to pretreat the crumb rubber (CR) could reduce the viscosity of the modified asphalt, thereby enhancing its compatibility with asphalt binder and improving the workability of CR modified asphalt (CRMA). However, the effects of CR pre-swelling on rheological properties of CRMA and the viscosity reduction mechanism are not well understood, especially for commonly used aromatic and naphthenic oils. In this study, the comparative investigations on rheological properties of CRMA before and after pre-swelling process were performed by frequency sweep, temperature sweep, multiple stress creep and recovery (MSCR) and storage stability tests. Meanwhile, the molecular dynamic (MD) simulation method was applied to simulate the distribution, migration, and aggregation characteristics of aromatic oil, naphthenic oil, and asphalt components in CRMA from natural aggregation state to heating mixing and finally cooling, aiming to reveal the viscosity reduction mechanism. The results showed that aromatic and naphthenic oils can significantly reduce the viscosity of CRMA. In addition, the low-temperature crack resistance and storage stability of CRMA can be improved through pretreatment with aromatic and naphthenic oils, which is correlated with the oil content. However, the effects of aromatic and naphthenic oils pre-swelling processes on the high temperature properties of CRMA are different. The MD simulation results showed that the binding energy between asphalt molecules reduced after mixing with aromatic and naphthenic oils, which is which is the primary reason for the viscosity reduction of CRMA. However, there are differences regarding the distribution characteristics of these two oils within asphalt binder. The CR, aromatics, aromatic oil and resins were uniformly dispersed in CRMA system by aromatic oil, whereas the naphthenic oil was adsorbed onto the surface of CR and asphaltenes.

A Laboratory Investigation Regarding Storage Stability of the CRM-Modified Bitumen—CRM Processing Method (Untreated vs. Treated)

The aim of this study is to analyze the phase separation that occurs between treated and untreated rubber crumb particles produced by wet processes in the laboratory. The percentage of replacement used for both the treated and untreated crumb rubber-modified asphalt (CRMA) was 5%, 10%, 15%, and 20%. Tests to evaluate binder properties were performed using a rotational viscometer and a DSR, and the following properties were determined—viscosity, G*/sinδ, % recovery, and Jnr. The phase separation study was analyzed using the viscosity and G*/sinδ results. In general, the results of the study show the following. (1) The treated CRMA binders had higher viscosity values than untreated CRMA binders, although some values could not be measured due to the high viscosity values. (2) The G*/sinδ, % recovery and Jnr results also had a similar trend with viscosity results. (3) The viscosity and G*/sinδ phase separation values demonstrate that treated CRMA binders perform better than untreated CRMA binders. (4) Different experimental methods have shown variations in the calculated SI value; hence, a more improved approach should be explored to accurately assess the storage stability of asphalt binders containing various additives.

Laboratory evaluation of the performance of reclaimed asphalt mixed with composite crumb rubber-modified asphalt: reconciling relatively high content of RAP and virgin asphalt

ABSTRACT Reclaimed asphalt pavement (RAP) applications are largely limited by the insufficient performance of reclaimed asphalt (RA). To address this challenge, the composite crumb rubber-modified asphalt (CCRMA) with SBS and SBR modifiers was mixed with RA to prepare reconciling and reclaimed modified asphalt (RRMA) and evaluate its performance in laboratory tests. Experimental groups of RRMA included five RA contents (30%, 40%, 50%, 60%, and 70%) and three aging degrees. Results showed that RRMA’s high-temperature and fatigue resistance performances improved by adding CCRMA, while this improvement was weakened with increasing RA content and aging degree. This was because the addition of CCRMA reduced the morphology of ‘bee-like structures’ and improved resistance to deformation. CCRMA slightly reduced moderate-temperature crack resistance but still improved low-temperature crack resistance because adding CCRMA reduced the internal adhesion of asphalt. The moderate-temperature crack resistance was below the threshold. However, it is necessary to consider adding other technical means when RRMA was aged for more than 20 hours with more than 60% RA content. Furthermore, the reliability of excellent performance was 85% for RRMA with 30% RA content under a short-term aging state, which provided a reference for the design of reclaimed asphalt binder.

Conventional properties, rheological properties, and storage stability of crumb rubber modified asphalt with WCO and ABS

To enhance the performance of asphalt and conserve resources, there is growing interest in the use of diverse waste polymer materials to modify asphalt. In this study, waste cooking oil (WCO) was used to activate crumb rubber (CR) and acrylonitrile–butadienestyrene (ABS) to obtain crumb rubber modified asphalt (CRMA) with low temperature sensitivity, excellent storage stability, and improved working performance. The physical properties of the modified asphalt were evaluated by conventional tests and rheological tests. The cohesive properties and compatibility of modified asphalt were investigated by the 60℃ dynamic viscosity, cigar tube test, and fluorescence microscope. The test results showed that WCO activated ABS/CR reduced the penetration of CRMA but increased its softening point and low temperature fracture work. In addition, the WCO activated ABS/CR could reduce the rotational viscosity of CRMA, and the viscosity-temperature curves prove that WCO activation of ABS/CR reduced the mixing and compaction temperature. Besides, the dynamic viscosity value of CRMA at 60℃ was also improved. The addition of ABS has a higher complex modulus and a lower phase angle, thus reducing the temperature sensitivity of asphalt. The zero shear viscosity (ZSV) value of the compound CRMA was six times higher than that of single CRMA. Additionally, proper proportions of ABS and WCO reduced the separation index (SI) of CRMA and enhanced its storage stability. Notably, group “AWCRMA1” exhibits a much higher ZSV than other asphalts while exhibiting lesser temperature sensitivity.

Evaluation of Warm Mix Crumb Rubber Modified Asphalt Mixture (WCRMA) on resisting permanent deformation

Crumb rubber (CR) is generated from the recycling of used or discarded car tires and has long been utilized in the paving industry. Crumb rubber can be used in asphalt mixes in two ways: dry process and wet process. However, compared to standard combinations, crumb rubber modified asphalt (CRMA) requires much higher mixing and compaction temperatures. As a potential substitute, using warm mix asphalt (WMA) technology significantly lower hot-mix asphalt (HMA) production and placement temperatures through viscosity reduction. In accordance, the objectives of the study are to produce warm mix crumb rubberized asphalt mixtures (WCRMA) using a dry process and to evaluate WCRMA’s performance in terms of rutting resistance. WCRMA is produced by adding 1, 3, and 5% Sasobit® of the total weight of the binder. The rutting performance of WCRMA was evaluated by Dynamic Creep test. The result showed that the asphalt mixes with the largest percentages of Sasobit® (5%) showed the lowest lowest accumulated strain and permanent deformation. The modified asphalt mixture performed better and had greater rutting resistance due to the replacement of fine aggregate with crumb rubber and the addition of Sasobit® compared to control sample.

Effect of Crumb Rubber Particles on Antisliding and Noise-Reduction Performance of Asphalt Pavement

Traffic noise has gradually become the primary source of noise in urban areas. The risk of health issues such as cardiovascular diseases and sleep disturbances associated with noise exposure are receiving widespread attention. The skid resistance of asphalt pavements is important for safe driving. However, its antisliding performance deteriorates owing to automobile driving, and the antisliding index cannot satisfy requirements of long-term safe driving. Crumb rubber-modified asphalt (CRMA) has been widely used owing to its characteristics, such as excellent noise reduction, antisliding performance, and durability. This study aims to investigate the effect of crumb rubber (CR) particle content (0%, 2%, 3%, and 4% by weight of fine aggregates in asphalt mixture) on the antisliding and noise reduction characteristics of asphalt pavements. The functional performances of three different types of asphalt mixtures were tested to obtain the best gradation. Then, an accelerated wear tester was used to analyze the deterioration of the antisliding performance under different cumulative load times. A British pendulum number (BPN) tester and 3D laser technology were used to measure friction properties and texture depths of asphalt mixtures with varying CR particle contents after wheel-load repetitions. The tire-drop and standing wave tube methods were employed to evaluate the noise-reduction characteristics and acoustic absorption performance of asphalt mixtures with varying CR particle contents. Finally, the optimal CR particle content was determined using grey-target decision-making based on the entropy weight method. The results indicate that adding rubber particles to asphalt mixtures slows down the attenuation rate of BPN and texture depth, which shows a clear enhancement of the antisliding performance. The addition of rubber particles to asphalt mixtures improves the noise-reduction performance in tire-pavement systems by increasing damping properties and the sound absorption coefficient. The asphalt mixture with 3% rubber particles exhibited the optimal performance.

Preparation and mechanism of rubber-plastic alloy crumb rubber modified asphalt with low viscosity and stabilized performance

Recycled rubber and plastics for asphalt modification are gaining increasing attention for sustainable pavements. However, the high viscosity and low stability of modified asphalt are the primary reasons limiting its widespread application. In this work, the rubber-plastic alloy crumb rubber (ACR) was prepared with the twin-screw extruder using crumb rubber (CR) and polyethylene (PE). The properties influence of the preparation process on ACR modified asphalt (ACRMA) was investigated by fluorescence microscopy, basic properties, and storage stability tests. The viscosity reduction characteristics of asphalt and asphalt mastic were assessed at different temperatures. Differential scanning calorimetry (DSC) and contact angle tests were used for modification mechanism analysis. Results showed that, compared with CR modified asphalt (CRMA), the thermal stability of ACRMA was improved, and its cohesion energy was not significantly reduced. The high-temperature viscosity of asphalt and its mastic was decreased by 35.1% ∼ 69.1%. But it had the same mid-temperature viscosity as CRMA. The rutting factor, high-temperature PG grade of ACRMA increased, and the phase angle decreased. The optimum dosage of PE was 15 wt% in ACR, ACR was 15 ∼ 20 wt% in asphalt, and the stabilizer was 0.05 ∼ 0.1 wt%. Compared with traditional CRMA, ACRMA with low viscosity and stabilized performance. It has good application potential, which can effectively reduce construction temperature and promote factory production.

Preparation of terminal blend/ grafting activated crumb rubber composite modified asphalt based on response surface methodology

Recycling waste tires, crushing them into crumb rubber (CR) and adding them to asphalt can effectively improve the performance and prolong the service life of asphalt pavement. However, the crumb rubber modified asphalt (CRMA) prepared by aforementioned process is prone to segregation during storage and transportation. The terminal blend rubber asphalt (TB) prepared with fine rubber powder by high-speed shearing at high temperature for long time, which effectively improves the storage stability and working performance of crumb rubber modified asphalt, but reduces the high-temperature performance. In this study, grafting activated crumb rubber (GACR) was incorporated into TB to improve its high temperature performance without impairing storage stability. Using shearing temperature, shearing time and grafting activated crumb rubber content as influencing factors, the response surface method (RSM) was carried out to optimize the preparation process. The results indicated that 180°C was a critical temperature, and the swelling of crumb rubber dominated with the temperature below it, but the desulfurization prevailed with the temperature above it. The extension of time favored the swelling of crumb rubber at low temperature but promoted desulfurization at high temperature. With the increase of crumb rubber content, the high temperature performance of modified asphalt improved whereas the storage stability deteriorated. According to the determination of response values and the prediction of optimal values, the suitable preparation conditions and parameters were recommended as shearing temperature of 190°C, shearing time of 90 min, and GACR content of 15%. The composite modified asphalt prepared through the optimized process showed good high temperature stability and storage stability.

Synergistic Effects of Epoxidized Soybean Oil and Polyester Fiber on Crumb Rubber Modified Asphalt Using Response Surface Methodology.

The incorporation of crumb rubber (CR) into asphalt pavement materials can improve the performance of asphalt pavement and generate environmental benefits. However, the storage stability of the crumb rubber asphalt (CRA) remains an issue that needs to be resolved. This study explores the interaction laws among various modified materials based on the response surface methodology. Optimal preparation dosages of each material are determined, and performance predictions and validations are conducted. The storage stability of the CRA compounded with epoxidized soybean oil (ESO) and polyester fiber (PF) is investigated by combining traditional compatibility testing methods with refined characterization methods. The results indicate that the modification of CRA exhibits better rheological properties when the percentages of CR, PF, and ESO are 22%, 0.34%, and 3.21%, respectively. The addition of ESO effectively complements the light components of CRA to improve asphalt compatibility, and the addition of PF alleviates the adverse effects of ESO's softening effect on rheological properties through stabilization and three-dimensional strengthening. The scientifically compounded additions of ESO and PF can effectively enhance the storage stability and rheological properties of CRA, promoting the development of sustainable and durable roads.