Crumb Rubber Modified Asphalt Mixtures Research Articles

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.

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.

Reconstruction of Asphalt Pavements with Crumb Rubber Modified Asphalt Mixture in Cold Region: Material Characterization, Construction, and Performance

Dry-processed rubberized asphalt mixture has recently attracted a lot of attention as an alternative to conventional asphalt mixtures. Dry-processed rubberized asphalt pavement has improved the overall performance characteristics compared to the conventional asphalt road. The objective of this research is to demonstrate the reconstruction of rubberized asphalt pavement and evaluate the pavement performance of dry-processed rubberized asphalt mixture based on laboratory and field tests. The noise mitigation effect of dry-processed rubberized asphalt pavement was evaluated at the field construction sites. A prediction of pavement distresses and long-term performance was also conducted using mechanistic-empirical pavement design. In terms of experimental evaluation, the dynamic modulus was estimated using materials test system (MTS) equipment, the low-temperature crack resistance was characterized by the fracture energy from the indirect tensile strength test (IDT), and the asphalt aging was assessed with the rolling thin-film oven (RTFO) test and the pressure aging vessel (PAV) test. The rheology properties of asphalt were estimated by a dynamic shear rheometer (DSR). Based on the test results: (1) The dry-processed rubberized asphalt mixture presented better resistance to cracking, as the fracture energy was enhanced by 29-50% compared to that of conventional hot mix asphalt (HMA); and (2) the high-temperature anti-rutting performance of the rubberized pavement increased. The dynamic modulus increased up to 19%. The findings of the noise test showed that at different vehicle speeds, the rubberized asphalt pavement greatly reduced the noise level by 2-3 dB. The pavement M-E (mechanistic-empirical) design-predicted distress illustrated that the rubberized asphalt pavement could reduce the IRI, rutting, and bottom-up fatigue-cracking distress based on a comparison of prediction results. To sum up, the dry-processed rubber-modified asphalt pavement has better pavement performance compared to the conventional asphalt pavement.

Sustainable crumb rubber modified asphalt mixtures based on low-temperature crack propagation characteristics using the response surface methodology

Fracture regime of asphalt concrete is of utmost importance in the sustainable design of optimized mixtures against low-temperature cracking. The energy dissipated in blunting the crack tip, stable crack growth, as well as post-peak resistance of the mixtures to the propagating crack comprise the overall fracture performance of the mixtures. In this research, employing the fracture resistance curve (R-curve) concept, three energy parameters: cohesive energy, fracture energy, and energy rate, are extracted to quantify the crack propagation regime of the mixtures incorporating ground recycled waste tire. A temperature range of 0 °C to −20 °C with 0 %, 10 %, and 20 % crumb rubber contents (CRC) were considered and the experiments were carried out in Single Edge notched Beam (SE(B)) fracture testing protocol. An environmental index comprising CO2 and CH4 emissions, as well as the energy consumption, was developed and the production cost of AC samples were also determined. A design of experiments based on the Central Composite Design (CCD) is applied. The Response Surface Methodology (RSM) is used to develop the best model between the fracture response, environmental factor, cost, and the input mixture properties. Multi-objective optimization scenarios were assessed by the RSM and a 4.74 % binder content with 19.5 % crumb rubber incorporation was resulted as the optimal mix design for maximum fracture response and minimized cost and environmental concerns in low temperatures. The environmental effects and costs were by average reduced by 15 % and 1 %, respectively and fracture responses have been improved compared to the reference optimum mix design (CRC = 0).

Mechanical properties of coarse asphalt Mixture-Paved trackbed under High-Speed moving train loads

The long-term stability of the substructure is a critical guarantee for the safety and ride comfort of high-speed railway (HSR) operations. The asphalt mixture-paved trackbed (APT) can not only play a favorable role in preventing and draining water on the top of the subgrade but also be beneficial to the gradual change of vertical stiffness between layers. This paper determines a coarse but dense-graded asphalt mixture suitable for the APT and numerically analyzes the mechanical properties of APT under high-speed moving train loads. The results indicate that the SBS-modified asphalt mixture (SBS-25) with the optimum asphalt content (OAC) of 4.2 % is more appropriate than the crumb rubber-modified asphalt mixture (CRMA-25) for the APT. The dynamic stress in the subgrade of APT is significantly determined by the conditions of the AC layer. Meanwhile, the vibration attenuation of APT is directly related to temperature change. Compared with the traditional ballastless track, the vibration acceleration of APT with trackbed thickness of 300 mm reduces by 20.1 % at 20 ℃ while only reducing by 1.7 % at 40℃. Moreover, the greater the structural stiffness of the APT, the stronger the control on dynamic deformation of each layer in the subgrade, and the influence on the formation is weaker than that on the bottom layer of the subgrade. The findings hopefully contribute to the APT substructure design; however, further verification of real engineering still needs to be conducted by field or full-scale tests.

Effect of Freeze–Thaw cycles on the pavement performance of SBS modified and composite crumb rubber modified asphalt mixtures

The effect of freeze–thaw cycles on the pavement performance of SBS modified asphalt mixture (SBSMA) and SBS/crumb rubber composite modified asphalt mixture (CCRMA) was studied using a triaxial repeated creep test, semicircular bending fatigue test based on digital image correlation (DIC), and thermal stress restrained specimen test. The mechanical model of the residual strain (RS) of the asphalt mixtures is established, and the residual viscous flow strain (εRvf,N) and residual viscoelastic strain (εRve,N) are separated. Based on the horizontal strain (Exx) of DIC, a new mesofatigue damage variable (D) is proposed. According to the characteristic curve of D, the antifatigue damage parameter (AFDP) is established and the correlation between AFDP and fatigue life (Nf) is analyzed. Simultaneously, a calculation model of the relaxation temperature stress (σRts(T)) of the asphalt mixture at different cooling rates (v) is established based on the finite element method. Results showed that the growth rates of RS, εRvf,N, and D of both asphalt mixtures accelerate, AFDP decreases, and freeze–break temperature (TD) rises with increasing freeze–thaw cycles. However, the growth rates of RS, εRvf,N, and D of CCRMA are always slower than SBSMA, the AFDP is larger than SBSMA, TD is lower than SBSMA, εRve,N is a fixed value under specific conditions, and a good correlation exists between the AFDP and Nf. The pavement performance of the asphalt mixtures worsens after the freeze–thaw cycles, and the influence of a salt freeze–thaw cycles is greater than that of a water freeze–thaw cycles. Moreover, CCRMA has better high-temperature deformation resistance, fatigue damage resistance, and low-temperature cracking resistance than SBSMA. The conversion point temperature (TZ) increases with the acceleration of v, and the σRts(T) calculation model can accurately reflect the σRts(T) of the asphalt mixture at different v.

Research on fatigue performance of composite crumb rubber modified asphalt mixture under freeze thaw cycles

To study the effect of freeze thaw cycles on the fatigue damage characteristics of composite crumb rubber modified asphalt mixture (CCRMA), the semicircle bending fatigue test and the digital speckle correlation method (DSCM) were combined and the fatigue damage characteristics of CCRMA and styrene–butadienestyrene-modified asphalt mixture (SBSMA) under freeze thaw cycles were analyzed. The plateau valve (PV) of the stiffness modulus degradation ratio curve of the asphalt mixture is proposed as the analysis index to evaluate the macroscopic fatigue damage evolution of the asphalt mixture. The horizontal strain density (DE value) obtained through analyzing the horizontal strain characteristic cloud map of the main crack zone is identified as an index to evaluate the mesoscopic fatigue damage evolution of the asphalt mixture. The results show that after a freeze thaw cycle, the PV increases, DE decreases, fatigue damage rate accelerates, and fatigue resistance decreases. CCRMA has better freeze thaw resistance and fatigue resistance than SBSMA. The fatigue damage model established has high fitting accuracy and can effectively reflect the fatigue damage evolution degree of an asphalt mixture. A correlation analysis of PV and DE values reveals that there is a good linear correlation between them, indicating that applying the DSCM method to semicircle bending fatigue tests for studying the fatigue damage characteristics of asphalt mixtures is reliable.

Effect of Temperature Segregation on Crumb Rubber-Modified Asphalt Mixture of Pavement Compaction Degree

Effect of Temperature Segregation on Crumb Rubber-Modified Asphalt Mixture of Pavement Compaction Degree

R-Curve Characterization of Crumb Rubber Modified Asphalt Mixtures Incorporating Warm Mix Additive at Low Temperatures

In a previous research by authors, a methodology was developed to derive J-R curves for Hot Mix Asphalt (HMA) mixtures using an elastic-plastic approach where a comprehensive understanding of crack propagation regime could be achieved. In this research, the effect of crumb rubber modification of HMA binder is studied in terms of R-curves and crack propagation at low temperatures. Mode I Single edge notched beam (SE(B)) fracture tests were conducted in temperature levels of 0 °C, -10 °C, and -20 °C. PG58-22 and PG64-22 binders were used in the fabrication of HMA samples. Modified specimens consist of 20% crumb rubber along with the incorporation of 3% warm mix admixture. Crack growth resistance curves were obtained in SE(B) tests by means of image processing and recording of the progressive crack length. Elastic-plastic J-R curves revealed that crumb rubber modified mixtures exhibit higher crack growth resistance for each bitumen performance grade. As well, increased ductility and cohesive energy can be observed according to the R-curves as the mixtures are modified by crumb rubber.

Predict the Phase Angle Master Curve and Study the Viscoelastic Properties of Warm Mix Crumb Rubber-Modified Asphalt Mixture.

To identify the most accurate approach for constructing of the dynamic modulus master curves for warm mix crumb rubber modified asphalt mixtures and assess the feasibility of predicting the phase angle master curves from the dynamic modulus ones. The SM (Sigmoidal model) and GSM (generalized sigmoidal model) were utilized to construct the dynamic modulus master curve, respectively. Subsequently, the master curve of phase angle could be predicted from the master curve of dynamic modulus in term of the K-K (Kramers–Kronig) relations. The results show that both SM and GSM can predict the dynamic modulus very well, except that the GSM shows a slightly higher correlation coefficient than SM. Therefore, it is recommended to construct the dynamic modulus master curve using GSM and obtain the corresponding phase angle master curve in term of the K-K relations. The Black space diagram and Wicket diagram were utilized to verify the predictions were consistent with the LVE (linear viscoelastic) theory. Then the master curve of storage modulus and loss modulus were also obtained. Finally, the creep compliance and relaxation modulus can be used to represent the creep and relaxation properties of warm-mix crumb rubber-modified asphalt mixtures.

Workability, compactibility and engineering properties of rubber-modified asphalt mixtures prepared via wet process

The purpose of this study is to compare the performance of rubber-modified asphalt mixtures prepared with incorporation of latex and crumb rubber. The service characteristics of the rubber-modified asphalt mixtures were evaluated using workability index and compaction energy index to determine the ease of placing, handling, and compacting of the asphalt mixture. The engineering properties of the asphalt mixtures were also evaluated in terms of indirect tensile strength (ITS), resilient modulus, permanent deformation, moisture susceptibility, and the Leutner shear test. Crumb rubber and latex were separately used as modifiers in this study. The percentage of crumb rubber and latex used were 5% and 10%, while organo silane additive was added at a rate of 0.1%, all by the weight of asphalt binder. Through the evaluation, the modified asphalt mixture required comparable energy for compaction through the assessment of compaction energy index (CEI) as compared to the control asphalt mixture. Based on the results of performance test, it can be concluded that the crumb rubber-modified asphalt mixture showed a better performance than the latex-modified asphalt mixture in terms of fracture resistance, permanent deformation, resilient modulus, shear resistance, and moisture resistance. Overall, the rubberised asphalt mixture has better engineering performance properties that can prolong the lifespan of the flexible pavement compared to the conventional asphalt mixture.

Laboratory and field performance investigation of pre-swollen crumb rubber modified asphalt mixtures

The pre-swollen crumb rubber (PSCR) is a pelletized rubber produced by the reaction of scrap tire rubber particles with bitumen-compatible oil at elevated temperatures. It does not require a prior blending with bitumen, and it can be added directly at an asphalt plant. A laboratory investigation was carried out to evaluate the performance of plant-produced PSCR modified mixtures for surface and intermediate courses and analyze their suitability for low-traffic volume road in cold environment applications. Linear viscoelastic properties, rutting and thermal cracking performance were investigated in the laboratory. The presence of pre-swollen rubber particles and, in particular, the bitumen-compatible oil softened the mixtures as indicated by the dynamic modulus master curves. The different mechanical responses led to an enhancement of thermal cracking resistance but increased the rutting susceptibility of the PSCR mixtures. Despite the laboratory findings, no rutting was observed after five years of service life based on visual inspection of the field test sections constructed in Michigan with PSCR-modified Hot-Mix Asphalt (HMA). A few transverse cracks were generated in the lanes where the control mix with neat bitumen was used. Those cracks did not propagate into the PSCR modified material, in agreement with the laboratory findings.

The Discrete and Continuous Retardation and Relaxation Spectrum Method for Viscoelastic Characterization of Warm Mix Crumb Rubber-Modified Asphalt Mixtures.

To study the linear viscoelastic (LVE) of crumb rubber-modified asphalt mixtures before and after the warm mix additive was added methods of obtaining the discrete and continuous spectrum are presented. Besides, the relaxation modulus and creep compliance are constructed from the discrete and continuous spectrum, respectively. The discrete spectrum of asphalt mixtures can be obtained from dynamic modulus test results according to the generalized Maxwell model (GMM) and the generalized Kelvin model (GKM). Similarly, the continuous spectrum of asphalt mixtures can be obtained from the dynamic modulus test data via the inverse integral transformation. In this paper, the test procedure for all specimens was ensured to be completed in the LVE range. The results show that the discrete spectrum and the continuous spectrum have similar shapes, but the magnitude and position of the spectrum peaks is different. The continuous spectrum can be considered as the limiting case of the discrete spectrum. The relaxation modulus and creep compliance constructed by the discrete and continuous spectrum are almost indistinguishable in the reduced time range of 10−5 s–103 s. However, there are more significant errors outside the time range, and the maximum error is up to 55%.

Decision support for selecting optimal method of recycling waste tire rubber into wax-based warm mix asphalt based on fuzzy comprehensive evaluation

Recycling crumb rubber (CR) derived from waste vehicle tire as asphalt modifier is an effective waste management approach with both engineering and environmental merits. However, the high viscous asphalt rubber (AR) brings higher energy consumption and hazardous construction emission. Wax-based warm mix asphalt (WMA) additive has proven to be able to alleviate these concerns. Application of WMA additives enriches the methods of recycling CR into asphalt. Preliminary investigations documented the effects of CR recycling methods on the service performance of warm crumb rubber modified asphalt mixture (WCRMA). Therefore, making a decision on the optimal recycling method considering the overall service performance is necessary. Nevertheless, there are limited studies focusing on the recycling method assessment and decision-making approach. To fill this gap, WCRMAs with different crumb rubber recycling methods were prepared and tested in laboratory. The effect of the recycling method on the overall service performance of WCRMAs was characterized. A fuzzy comprehensive evaluation (FCE) method was employed to quantify the performance grade of asphalt mixtures according to fuzzy logic. The weight matrix of all the service properties was developed based on the Analytic Hierarchy Process (AHP) under the considering of the circumstance of southern China. The experimental work revealed the significant influence of the recycling method on the service performance of WCRMAs. By means of the FCE method, this study suggested that for southern China with hot and humid climate, the optimal method of recycling CR into wax-based WCRMA is mixing AR and Sasobit first followed by incorporating them into aggregate. In rainy regions, asphalt mixture produced by directly mixing AR, Sasobit, and aggregate at 160 °C may perform better because it showed the best moisture damage resistance and good overall performance.

Experimental Study on the Phase Transition Characteristics of Asphalt Mixture for Stress Absorbing Membrane Interlayer

Asphalt mixtures used in stress absorbing membrane interlayers (SAMIs) play a significant role in improving the performance of asphalt pavement. To investigate the rheological properties and phase transition characteristics of asphalt mixtures used in SAMI with temperature changes, twenty-seven candidate mixtures with different binders, gradation types and binder contents were selected in this research. During the study, dynamic mechanical analysis method was employed to evaluate their temperature-dependent properties and a series of wide-range temperature sweep tests were conducted under a sinusoidal loading. Some critical points and key indexes from the testing curves such as glass transition temperature (Tg) can be obtained. Test results show that phase transition characteristics can better reflect the rheological properties of asphalt mixtures at different temperatures. Crumb rubber modified asphalt mixtures (AR) provide a better performance at both high and low temperatures. Additionally, the range of AR asphalt mixtures’ effective functioning temperature ΔT is wider, and the slope K value is greater than the others, which indicates that AR asphalt mixtures are less sensitive to temperature changes. Additionally, gradation type and asphalt content also influence the properties: finer gradation and more asphalt content have a good effect on the low-temperature performance of the asphalt mixtures; while mixtures with a coarser gradation and less asphalt content perform better at high temperature and they are less sensitive to temperature changes. Finally, AR asphalt mixture is more suitable to be applied in the SAMI due to its phase transition characteristics from this method.

Rheological and environmental characteristics of crumb rubber asphalt binders containing non-foaming warm mix asphalt additives

Introducing crumb rubber (CR) into asphalt binder can both provide environmental benefits such as conservation of natural resources and conservation of landfill space and significantly improve rheological and mechanical performance characteristics of asphalt binders. Incorporation of CR into asphalt binder demands some amount of kinematic energy to make modified asphalt binder sufficiently fluid for mixing and compaction purposes that liberates some greenhouse and fume emissions. By taking advantage of warm mix additives (WMA), it is possible to effectively reduce the production temperature of hot-mix asphalt mixtures to mitigate such environmental concerns. This study, Firstly, aims to investigate the CR dosage effect on the properties of asphalt binder containing different non-foaming warm mix additives: Sasobit and Evotherm M1. Secondly, the environmental concerns regarding CR inclusion into asphalt binder are evaluated by implementing gas chromatography-mass spectrometry (GC–MS) test. Rheological and mechanical tests have provided deep insight into the effects of such combinations of WMA and CR in asphalt binders and results indicated that a crumb rubber modified (CRM) asphalt binder with 15–20% CR yielded optimum performance concerning rutting, fatigue, and cracking performance. Furthermore, while both WMA additives can significantly improve the workability and enhance the rutting performance of CRM asphalt binders, they have a slightly negative effect concerning fatigue and cracking performance of CRM asphalt binders. From the environmental aspect, application of WMA additives also could potentially result in a 63–75% reduction in total emission of CRM asphalt mixtures containing 10–25% CR. Relationship between temperature and the total emission of CRM binders is not linear and it is more than likely a second-order polynomial relationship. Moreover, the results of emission analysis showed that CRM binders deliberate some hazardous fumes due to high temperature, which can be alleviated by incorporating WMA additives into the modified blend.

Effect of mixing sequence on asphalt mixtures containing waste tire rubber and warm mix surfactants

Abstract Crumb rubber modified asphalt mixture (CRMA) has gained rapid-growing interest as a sustainable paving material, because it allows value-added recycling of waste tire into durable and low-noise asphalt pavements. However, the poor workability of CRMA leads to higher construction temperature, which results in more energy consumption and hazardous emission. Surfactant, a typical warm mix asphalt additive, has been proven to be effective in alleviating the workability concern of CRMA without obviously deteriorating its mechanical properties. Nevertheless, performance of CRMA with surfactant may be influenced by the mixing sequence of different components (raw asphalt, crumb rubber, surfactant and aggregates), which unfortunately has not been well investigated yet. This study aims to address this issue by characterizing the engineering performance of warm CRMA prepared by six different mixing sequences. Properties including Marshall stability and flow value, workability, rheological property, rutting resistance, moisture sensitivity and fatigue resistance of prepared mixtures were measured and compared. Analytic hierarchy process (AHP) was employed to determine the optimal mixing sequence of warm CRMA considering the overall engineering performance. Test results showed that the effect of warm CRMA’s mixing procedure on its engineering performance is noticeable. Earlier incorporation of surfactant additive had limited negative influence on mechanical properties of warm CRMA but allows for more energy saving during the production of rubberized asphalt binder. The AHP analysis results indicated that among the six mixing sequences, the optimal option is to make rubber absorb surfactant first, then incorporating the rubber-surfactant compound to raw asphalt and finally blending the modified binder to aggregates.

Study on the Performances of Waste Crumb Rubber Modified Asphalt Mixture with Eco-Friendly Diatomite and Basalt Fiber

A sustainable and environmentally friendly society is developing rapidly, in which pavement engineering is an essential part. Therefore, more attention has been paid toward waste utilization and urban noise pollution in road construction. The object of this study was not only to investigate the mix proportion of waste crumb modified asphalt mixtures with diatomite and basalt fiber but also to evaluate the comprehensive performances including sound and vibration absorption of modified asphalt mixtures. Firstly, the mix proportion scheme was designed based on Marshall indices and sound and vibration absorption properties according to the orthogonal experimental method. Considering the specification requirements, as well as better performances, the optimal mix proportion was determined as follows: diatomite content at 7.5%, basalt fiber content at 0.3%, and asphalt-aggregate ratio at 5.5%. The range and variance analysis results indicated that asphalt-aggregate ratio has the most significant influence on volumetric parameters, diatomite has the most significant influence on sound absorption, and basalt fiber has the most significant influence on vibration reduction. Furthermore, the conventional pavement performances and sustainable sound and vibration absorption performances of modified asphalt mixtures were also analyzed. The results showed that the performances of modified asphalt mixtures were improved to different extents compared to the base asphalt mixture. This may be attributed to the microporous structure property of diatomite and the spatial network structure formed by basalt fibers. The pavement as well as sound and vibration absorption performances of the waste crumb modified asphalt mixture with diatomite and basalt fiber would be a good guidance for asphalt pavement design.

Effect of liquid anti-stripping agents on moisture sensitivity of crumb rubber modified asphalt binders and mixtures

Influence of three liquid anti-stripping agents (ASAs) (named as M1, T9 and LOF-6500) with three dosages (0.25%, 0.50%, and 0.75%) on laboratory performance of crumb rubber modified asphalt (CRMA) mixture was investigated. The performance included aggregate–CRMA binder adhesion bond, water stability, high-temperature stability and low-temperature anti-cracking property, which were evaluated by surface free energy (SFE), freeze-thaw indirect tensile strength (ITS), Marshall stability and low-temperature ITS tests, respectively. The results manifest that the addition of ASAs can improve effectively the adhesion bond between aggregate and CRMA binder under dry or wet condition. Compared with three ASAs, the CRMA containing LOF-6500 has the highest wet adhesion energy. With regard to M1 and LOF-6500, the CRMA incorporating 0.75% dosage shows the highest dry and wet adhesion energy. Additionally, the water resistance and high-temperature stability of CRMA mixture are improved obviously by incorporating ASAs despite of the types and dosages. However, the ASAs can lower the low-temperature anti-cracking property of CRMA mixture in certain degree, and the influence of T9 is less than that of M1 or LOF-6500.