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A tack coat is a thin layer that ensures the bonding between an asphalt overlay and existing pavement. Adequate tack coat bonding is required for the composite pavement structure to behave as a single layer. The adhesion between the layers is significantly reduced at high temperatures, given that tack coat is characterized as a temperature-dependent material. This implies that debonding frequently occurs at elevated temperature during summer season. However, the distresses or failures related to debonding may not be occurred due to the bond strength recovery effects of the tack coat material in the early-age of the composite pavement. This study intended to investigate the bond strength recovery effect of the tack coat at the interface between the asphalt overlay and existing concrete layer based on the pull-off tests. The bond strengths measured between 18 to 20°C were 0.75 MPa and 0.81 MPa for the cationic rapid setting emulsified asphalt and modified rubberized asphalt, respectively. However, the measured bond strengths of all the specimens were 0.08 MPa or less at a high temperature of 38 to 42°C. As a result of testing the possibility of recovering the bond strength to the debonded specimens at high temperature, the bond strength of 75% or more could be recovered at the interface.

This paper evaluates the mechanical properties of rubberized asphalt binder and mix containing 5% and 10% rubber. This rubberized asphalt binder was manufactured in a field-blend process using devulcanized rubber particles, finer than 250 microns, derived from waste tires. Comparison between the rubberized binder and the base binder test results showed that the rubberized binders had higher complex moduli and lower phase angles at the grade temperature. They also had a higher percentage recovery in the multiple stress creep recovery test, and a significant creep stiffness reduction in the bending beam rheometer test. Given the low rubber content and small rubber particle size, this rubberized binder can be used in dense-graded mixes, whereas asphalt rubber binders, with larger rubber particles and higher rubber content (>15%), must be used in gap- or open-graded mixes. This rubberized dense-graded mix met the volumetric design criteria at the same binder content as the control mix prepared with the unmodified base binder. Laboratory tests on the mix included repeated load triaxial, Hamburg wheel track, flexural dynamic modulus, and beam fatigue. The rubberized mixes had slightly lower stiffnesses than the control mix, but better resistance to moisture damage, rutting, and fatigue cracking. A strong linear correlation was found between the carbonyl area index and the rheological properties of the long-term aged binder and fatigue life of the mixes. Based on these findings, these rubber-modified binders can be considered for use in dense-graded mixes to improve overall performance and make use of waste tires.

Warm Mix Asphalt (WMA) is an innovative technology that aims at decreasing the mixing and compaction temperature of asphalt mixtures as compared to the conventional Hot Mix Asphalt (HMA) thereby reducing harmful emissions and fuel consumption. The rubberized asphalt mixtures are found to have better physical and strength properties, but they are compacted at a higher temperature than that of conventional mixes. In this study Cashew Nut Shell Liquid (CNSL), an organic additive, was added from 0.5% to 3 % by weight of the binder at an increment of 0.5 % to modify the bitumen. The optimum content of CNSL to reduce the viscosity was found to be 2% and the viscosity reduction was 44.4 % at 140°C The modified NRMB (Natural Rubber Modified Bitumen) was used to prepare Dense Bituminous Macadam (DBM) and a comparison of volumetric, stability and rutting characteristics of both Natural Rubber modified Hot Mix Asphalt (RHMA) and Natural Rubber modified Warm Mix Asphalt with CNSL additive (RWMA) was made. Storage stability results indicated that there was no phase separation between rubberized bitumen and additive at high temperature and will act as uniform blend at high temperatures. Dynamic Shear Rheometer test results showed that the addition of CNSL to rubberized bitumen increased the values of G*/sinδ and could improve the resistance of asphalt binder against rutting. Stability value of RWMA was 11.5 % higher than that of RHMA and rutting depth was 10.1 % less than that of RHMA. The fatigue strength results obtained from Repeated Load Testing showed that the number of cycles to failure at 20% stress level was 9.04 % more for RWMA than RHMA. All volumetric properties of both RHMA and RWMA were within the limits specified by Ministry of Road Transport and highways (MoRTH) 2013. The statistical analysis authenticates the experimental findings. ANOVA analysis for Marshall Quotient revealed that RWMA had improved compaction characteristics than RHMA and the result for rutting and fatigue strength showed that the additive CSNL and temperature had significant effect on rutting resistance and fatigue life.

The crumb rubber (CR) derived from waste tires has been used widely to prepare rubberized asphalt for paving applications. However, rubberized asphalt severely suffers from poor compatibili...

Terminal blend rubberized asphalt (TBRA) is widely used as binder of asphalt mixtures due to its technical characteristics of storage stability. However, its road performance deteriorates d...

There is a general trend toward improving the terminal blend process of producing rubberized asphalt mixtures. Recently, the addition of nanosized materials to strengthen the performance-re...

In recent years, the significant importance of solid waste management, increase in the cost of bitumen and polymer modifiers have encouraged the pavement engineers to use reusable alternative sources. Ground tire rubber (GTR) and amorphous carbon powder (ACP) are considered as two industrial waste which their using in asphalt mixture prevents their releasing in the environment. This study aims to analyze moisture sensitivity, fatigue performance, and rutting resistance of asphalt mixture influenced by using GTR (8, 12, and 16% of bitumen weight) as the modifier of bitumen properties, and ACP (25, 50, and 75% of filler weight) as filler. The results of this study shows that the ACP increases the resilient modulus and indirect tensile strength of rubberized asphalt concrete (RAC) mixtures. The results revealed that despite the negative effect of GTR on the moisture resistance of asphalt mixture, ACP improves the moisture performance. The results of fracture energy also implies that using ACP decreases the fracture energy, but using the GTR improves the fatigue resistance of asphalt mixture. Furthermore, the results of dynamic creep and wheel track tests indicates that 16GTR + 50ACP has the lowest permanent deformation and highest rutting resistance. The results of ANOVA analysis demonstrates that using GTR and ACP has a considerable effect on the performance properties of asphalt mixture. Finally, the results of this study illustrate the simultaneous use cleaner production and wasted materials decreases the environmental damages in addition to improvement of physical properties of the asphalt mixture.

The aim of this study is to investigate effect of a liquid Nanomaterial antistripping agent, namely Zycotherm, as asphalt mixture (AM) additive on fatigue life and rutting resistance of rubberized asphalt at intermediate and high temperatures, respectively. With regard to fatigue performance, indirect tensile strength (ITS) and four-point beam fatigue tests were performed at 25 °C on unmodified and 15% rubberized mixtures containing Zycotherm at concentrations of 0.08, 0.1 and 0.12% by weight of total bitumen. Moisture susceptibility was also examined using wet/dry ITS and, for rutting performance, dynamic creep and wheel tracking test were employed. Results of fatigue-related tests indicated that 0.1% Zycotherm content improves fatigue performance of warm mix asphalt the most as a result of increasing fatigue life and dissipated energy along with reduction in ITS. Furthermore, results of performing dynamic creep and wheel tracking tests at 50 °C proved the high potential of Zycotherm at preserving the rutting performance of rubberized asphalt mixtures.

Application of rubber particle from the scrap tire through dry-process is a practical and economical efficient way to resolve the recycling problem and environmental concern of the disposed tires. However, the added rubber aggregate reduces both the strength and durability of the rubberized asphalt mixture. This study aims to improve the strength and durability of dry-processed asphalt mixture by using the cement (Portland Type Ⅰ) coating methods and gap-gradation system (Stone Matrix Asphalt (SMA)). The cement coating was applied to enhance the bonding performance between rubber aggregate and asphalt binder, and limits its expansion due to swelling in hot asphalt binder. The SMA mixtures were prepared with different sizes and proportions of mineral aggregates. The samples with conventional aggregate and untreated rubber aggregate both serve as control samples for the sample evaluation. Finally, tests on tensile strength, moisture susceptibility, rutting resistance, anti-stripping resistance, fatigue cracking resistance, and bonding between rubber particles and asphalt binder of SMA mixtures were conducted. The results showed that SMA mixture with pre-coated rubber aggregate owns similar performance comparing to the samples prepared with conventional aggregate and also has higher strength and better performance than that of the mixture with untreated rubber aggregate. Results also clearly indicated that the asphalt mixtures with 50% of No.16 mineral aggregates replaced by pre-coated rubber aggregates performed the best-satisfied performances; while, with a further increase in replaced size or proportion, the satisfied performances of SMA mixtures would be degenerated.

In the production of terminal blend (TB) rubberized asphalt binder, crumb rubber is digested into asphalt matrix, meanwhile polymers might be added to the degraded rubber/asphalt composite to meet the performance grade criteria. The anti-aging property of TB rubberized asphalt binder is not clear yet. The present study aims to evaluate the aging properties of TB rubberized asphalt binder and TB hybrid binder containing polymeric additive. Fourier transform infrared (FTIR) spectroscopy, Gel permeation chromatography (GPC) and rheological master curve were used to capture the evolution of asphalt binders with aging. The results indicate that TB hybrid binder offers better anti-aging properties than polymer modified asphalt (PMA) with respect to asphalt oxidation and polymer degradation. The presence of nano-silica component in TB rubberized asphalt is considered to improve the anti-aging property. The polymer molecular weight retention index retrieved from GPC test and phase angle difference determined from phase angle master curve are connected with each other. These two methods are very promising in evaluating polymer degradation behavior of PMA.

The objective of this study was to develop artificial neural networks to predict the viscosity of rubberized asphalt rejuvenated reclaimed asphalt pavement binders. Eight variables were sel...

Studies show that warm mix asphalt (WMA) technology is a practical solution against the high production temperature of rubberized-asphalt (RA) mixtures. RA mixture containing WMA additive is considered as an eco-friendly technology contributing to noise reduction and performance optimization of asphalt mixtures. This study aims to introduce two organic WMA additives called slack wax (SW) and polypropylene wax (PPW) which are used to lower the production temperatures by reducing the viscosity of RA mixtures. Rotational viscosity (RV) as a common bitumen test (Equiviscous, ZSV, and S-ZSV methods), as well as tests related to mixtures including resilient modulus (Mr) and moisture susceptibility (TSR and MRR methods), were carried out on binder and mixture specimens. According to the results, 6% (by the binder’s weight) of both WMA additives reduced the mixing and compaction temperatures of the RA binder by about 20–25 °C. Also, CRM and both WMA additives improved the stiffness of mixtures by increasing the resilient modulus (Mr). In terms of moisture susceptibility, although nearly all specimens could pass the minimum requirement of SCDOT, both WMA additives and CRM caused a reduction in ITS value of wet mixtures and final TSR value. MRR test results followed a similar trend, though resilient modulus was more sensitive to moisture damage compared to ITS. The results suggest that PPW and SW are suitable and cost-effective warm additives that can be used in combination with CRM in areas with hot climates and low precipitation. Nevertheless, additional experiments should be done to further validate the performance of CRM mixtures with these two warm additives.

The effect of ethylene vinyl acetate (EVA) on the aging properties and rheological properties of rubberized asphalt was measured in this paper to identify the optimum proportion of EVA comb...

High-content rubberized asphalt (HCRA) is a road engineering material with favorable economic and environmental benefits. However, HCRA is still not widely used due to concerns of workability and storage stability. To improve rubber content and maintain rubberized asphalt (RA) performance, five RAs with different activated powder contents were prepared by wet process. Firstly, composite viscosity and softening point difference were used to optimize the preparation process of activated powder and RA. The dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were carried out and the stability index was proposed to evaluate performance of HCRA. Finally, the mixture performances of HCRA, base asphalt and SBS modified asphalt were compared. The results show that the 60-mesh rubber powder with 20% waste oil is beneficial to reduce viscosity and improve compatibility of HCRA when treated by microwave for 2 mins and sheared for 5 h. As the powder content increases, RAs have excellent high and low temperature performances. Overall, the performance of HCRA binder and mixture with 60% content of rubber powder possess optimal comprehensive properties in terms of high temperature rutting resistance, cracking resistance, and moisture resistance. This study helps facilitate the incorporation of high content rubber in RA and promote its potential application in road engineering.

Non-tire rubber products (e.g. hoses, weather strips, vibration insulators, and miscellaneous parts) are progressively increasing as scrapped and repaired vehicles rise, and are abundantly discarded due to various reasons, such as high-cost recycling, complex rubber components, and poor mechanical properties. The non-tire rubber products have similar chemical components as scrap tires that have been widely applied in the field of road engineering, so it is anticipated that waste non-tire rubber products can be pretreated and used in road engineering as scrap tires. Hence, the purpose of this study was to gain a comprehensive understanding of asphalt binders modified with waste non-tire rubber with or without a microwave and/or waste engineering oil (WEO) treatment by using the terminal blend (TB) process as crumb rubber. A variety of laboratory tests were conducted, including scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric coupled with FTIR (TG-FTIR), storage stability, high-temperature performance, fatigue, and other basic rheological properties. It was found that microwave irradiation and WEO treatment can accelerate the pyrolysis and decomposition of waste non-tire rubber particles while there were no obvious differences between the pyrolysis gaseous products of waste non-tire rubber particles with or without the microwave or/and WEO treatment. Additionally, the microwave or/and WEO treatment enhanced the thermal stability and fatigue resistance of TB rubberized asphalt, especially for that with 100% WEO and 40 mesh of non-tire rubber particles. The microwave or/and WEO treatment reduced the viscosities and high-temperature properties of TB rubberized asphalt, especially for TB rubberized asphalt with fine rubber particles. In general, it is feasible to use waste non-tire rubber particles to produce TB asphalt binders and offer a cleaner way of using waste non-tire rubber products. The method of microwave and WEO treatment can be used to prepare TB asphalt with high content of non-tire rubber particles in the future.

Recent studies show that using crumb rubber modifier (CRM) improves the mechanical and rheological properties of asphalt samples. However, the higher viscosity of rubberized binders increases the production temperatures of resulting mixtures. Using Warm Mix Asphalt (WMA) technology in combination with rubberized binders is a practical solution to alleviate this problem. However, mechanical characteristics of rubberized warm mixtures should be further analyzed to determine the effects of warm additives on the performance of asphalt mixtures. This study was performed to investigate the effects of an organic WMA additive, Slack wax (SW) (2%, 4%, and 6% by weight of binder), upon rutting and fatigue resistance of rubberized asphalt mixtures (15% and 20% CRM by binder weight). Further, a statistical analysis was conducted to define the possible relationships between fatigue life and three mechanical factors: toughness index (TI), resilient modulus, and indirect tensile strength (ITS). The results of the dynamic creep test indicated that both CRM and SW increased the flow number of asphalt samples yielding more resistant mixtures against rutting distress. The wheel tracking test results were consistent with the dynamic creep test. According to the indirect tensile fatigue test, the addition of SW was effective in improving the fatigue life of both control and rubberized asphalt specimens under two studied stress levels. TI values derived from the ITS test showed that rubberized warm mixtures can significantly increase the flexibility and energy absorptivity of asphalt mixtures. The results of bivariate correlation analysis indicated a direct relationship between the fatigue life- M r and fatigue life-TI parameters. The significant values of correlation demonstrate that TI value derived from a cheap, easy, and fast ITS test is a practical parameter to predict the fatigue life of rubberized warm mixtures.

With the promotion of sustainable development globally, it is a positive and feasible measure to put waste tires into road engineering, such as rubber asphalt pavement. Therefore, it is very significant to improve the accuracy of fatigue resistance design of rubber asphalt pavement structures. This work aims to truly characterize the fatigue resistance of rubberized asphalt pavement structure, and provides favorable conditions for the efficient utilization of waste rubber powder in asphalt pavement engineering. First, the strength tests under different stress status and loading rates were carried out, which set up the strength yield surface on account of the Miller yield criterion. The fatigue tests of rubberized asphalt mixture in various stress levels and stress state were carried out. Von mises stress was taken as the characteristic parameter of the fatigue equation, and a unified fatigue characteristic equation of rubberized asphalt mixture affected by individual stress states was developed through the routine fatigue test. Finally, combined with Miller yield criterion and fatigue unified equation, the fatigue resistance model of rubberized asphalt pavement structure under the three-dimensional stress state was conducted. The results indicate that: the established Miller strength yield surface can reasonably describe the three-dimensional failure characteristics of rubberized asphalt mixture. Besides, the unified model of fatigue properties of rubberized asphalt mixture only needs to be characterized by single parameter, which is a power function coefficient in the new fatigue equation, and the value is −6.021. Moreover, the fatigue resistance model of the rubberized asphalt pavement structure sufficiently considers the difference between the tension–compression strength and fatigue characteristics of rubberized asphalt mixture and the stress state correlation. This study improves the scientificity and reliability of structural resistance design, and provides help for predicting the fatigue life of rubberized asphalt pavement.

Applying waste tire rubber powder to modify the asphalt binder is a promising protocol to achieve sustainable pavement materials. This study aims to examine the feasibility of using Lucobit type asphalt additive in the rubberized asphalt and further enhance its performance. The 90# asphalt binder and the rubber powder with 30 mesh were selected to prepare the rubberized asphalt. Two Lucobit adding ratios (5% and 10%) were then selected for the modification of three types rubberized base binder (Rubber replacement ratios 15%, 20%, and 25%). The modified asphalt binder was prepared under 180 ± 5 ℃ by using the high-speed shear mixer under 5000 rpm for 2 h. Then the FTIR and TGA tests were conducted for the phase analysis of the asphalt co-modified with rubber powder and Lucobit. The test results indicated the modification mainly belong to the physical blending instead of chemical bonding. Further study with DSR test indicated the added Lucobit can further enhance the high-temperature stability of the rubberized asphalt. Further study based on Multiple Stress Creep Recovery (MSCR) test indicated the anti-rutting performance of the asphalt binder would be enhanced while the sensibility of asphalt binder to shear stress would be reduced with the added Lucobit. Finally, the topography analysis on the original and aged binders were analyzed with Atomic Force Microscopy (AFM) test. The results indicated obviously reduced bee-like structure can be observed in the samples with Lucobit, which is in accordance with the measured complex modulus after aging tests. Overall, this study indicates the added Lucobit can further enhance the high-temperature stability, antiaging performance, and reduce shear stress sensitivity of the asphalt binder.

Thermal oxidation and ultraviolet exposure contribute to major changes in the physicochemical and rheological properties of asphalt binder, leading to the deterioration of pavements. This paper investigates the merits of grafting bio-derived molecules onto particles of crumb rubber to create bio-modified rubberized asphalt binder with enhanced resistance to thermal aging and ultraviolet aging. The bio-modification of the crumb rubber was made via a hybrid process where molecules of waste cooking oil were grafted to rubber with the help of microwave radiation. The evolution of bio-modified rubberized asphalt during thermal aging and ultraviolet aging was then characterized and compared with those of conventional rubberized asphalt. Study results showed bio-modification was effective to delay both thermal aging and ultraviolet aging. However, the effectiveness varied with the type of aging with the resistance to thermal aging being enhanced by 35%-84% and the resistance to ultraviolet aging being enhanced by 34–106%. Overall, the synergy between waste cooking oil, crumb rubber, and asphalt binder led to a significant improvement in the resistance against aging, thereby promoting sustainability in construction while making use of two waste streams including waste cooking oil and crumb rubber from scrap tire.

The compatibility between crumb rubber (CR) and asphalt binder plays a key role in the storage stability and rheological performance of rubberized asphalt binder. This review provides a comprehensive overview of characteristics of rubberized asphalt binder, factors influencing compatibility, compatibility evaluation methods, and improvement approaches. Desired compatibility results from the fact that CR is cross-linked with molecules of asphalt binder and evenly distributed in the asphalt binder, forming a homogeneous system. Rheological methods are the most widely used methods for compatibility evaluation. Additionally, the hybrid processing of surface activation treatment of CR and additives-grafting has shown to be a promising method for improving the compatibility of rubberized asphalt binder.

The degradation of crumb rubber modifier (CRM) was confirmed to affect the rheological properties in the production Terminal Blend (TB) rubberized asphalt binder. However, the quantitative analysis on the components distribution of TB rubberized asphalt binder and correlations to rheological properties were not investigated yet. The present study was to investigate the effect of CRM degradation on components distribution and rheological properties of TB rubberized asphalt binders produced under various curing temperatures and times. The solubility test and the Gel Permeation Chromatography (GPC) test were performed to obtain the distribution of insoluble components, dissolved polymers, apparent asphaltenes and maltenes. Brookfield viscometer and Dynamic Shear Rheometer (DSR) were used to investigate the viscosity properties, rutting resistance and rheological behaviour at wide frequencies. The results indicated that interaction time played a similar role as interaction temperature did in promoting the dissolution of CRM whereas the breaking of backbone of the main chain of rubber was more dependent on interaction temperature. With the gradual degradation of CRM, the workability and storage stability were improved with the sacrifice of rutting resistance. In addition, the enhance effects of CRM on |G∗| values at both lower and higher frequencies and phase angle values at lower frequencies gradually weakened. The evolution of log |G∗| lower asymptote and crossover modulus indicated TB rubberized asphalt binders became softer with the degradation of CRM. The well link between apparent asphaltenes and various rheological parameters indicated that it was the transform of CRM from insoluble components and dissolved polymers to medium size molecules that affected the rheological properties of TB rubberized asphalt binder.

The benefits of applying the crumb rubber modified binders have been widely recognized. The improvements on low temperature properties of asphalt binders have been proven by adding crumb rubber. The article reviews the crack resistance mechanism of crumb rubber modified asphalt. Rubber particles can block the generation of cracks, leading to the improvement of low-temperature properties of the binder. The review finds that the low temperature properties of crumb rubber modified binder (CRMB) are govern by the factors such as asphalt properties, crumb rubber properties, mixing temperature, mixing time, mixing type and admixture. These factors have effects on the interaction between crumb rubber and binder that affect the low temperature performance of CRMB. The bending beam rheometer (BBR) test is the most frequently used method to evaluate the low-temperature properties of CRMB. Meanwhile, the low temperature properties of crumb rubber modified asphalt mixtures are commendably evaluated by the indirect tensile test (IDT), the semi-circular bending (SCB) test and the asphalt concrete cracking device (ACCD). Furthermore, the low temperature anti-cracking properties of CRMB can be improved by the chemical modification and physical treatment methods.

Terminal Blend (TB) rubberized asphalt is a promising technology in producing crumb rubber asphalt as it overcomes the shortcomings such as lack of storage stability and workability. However, the limitation of TB asphalt is that the high temperature property is drastically reduced compared to conventional rubberized asphalt binders due to the degradation of crumb rubber. Currently, the studies regarding to modification to improve its high temperature property is not adequate. The objective of this paper is to investigate the optimum modification formula of asphalt binders using styrene-butadienestyrene (SBS) and polyphosphoric acid (PPA) and explore their mechanism of modification. Firstly, dynamic shear rheometer (DSR) test and bending beam rheometer (BBR) test were conducted to evaluate the rheological properties at both high and low temperatures. Furthermore, Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) test were conducted to detect the chemical changes of TB modified asphalt binders. Finally, the high temperature stability and fatigue property of TB modified asphalt mixtures were applied to verify the performance properties. Results indicates that 20T3S (20 wt% crumb rubber and 3 wt% SBS) used to produce the modified binders was the best modification formula considering both high and low temperature rheological properties. The modification mechanism was that SBS formed 3D cross-linking network structure in TB binder, which played an important role in enhancing high temperature properties of TB binders. Additionally, 20T3S asphalt mixture had better high temperature stability and fatigue performance comparing to 4.5S (4.5 wt% SBS) modified asphalt mixture.

The addition of crumb rubber modifier (CRM) could enhance the low temperature properties of asphalt binder. However, in the production of terminal blend (TB) rubberized asphalt binder, the degradation of CRM results in the change of molecular components of TB rubberized asphalt binder. The effect of components evolution on low temperature rheological behaviour of TB rubberized asphalt binder was not clear yet. The present study aims to investigate the evolution of components distribution and its effect on low temperature properties of TB rubberized asphalt binders produced under various interaction temperatures and interaction times. The solubility test and the Gel Permeation Chromatography (GPC) test were performed to obtain the distribution of insoluble components, dissolved polymers, apparent asphaltenes and maltenes in various TB rubberized asphalt binder. Bending Beam Rheometer (BBR) was conducted to investigate the low temperature properties of TB rubberized asphalt binder before and after aging. Burgers model was used to retrieve the relaxation time at low temperature. The results indicated that interaction time plays a more important role in promoting the dissolution of CRM whereas the interaction temperature is more responsible for the breaking of backbone of the main chain of rubber. Low temperature stiffness of TB rubberized asphalt binder increased with the degradation of CRM, which has a negative effect on low temperature performance. Relaxation property of TB rubberized asphalt binder was improved with the increase in percentage of apparent asphaltenes. However, the loss of relaxation property of TB rubberized asphalt binder after aging is more remarkable with the gradual degradation of CRM. TB rubberized asphalt binder investigated in the present study exhibits better low temperature performance than styrene-butadienestyrene (SBS) modified asphalt binder and base binder. The parameter ΔT c increases linearly with the reduction of insoluble components and dissolved polymers, which indicates that the low temperature property is becoming less m-value controlled with the degradation of CRM.

To evaluate the effect of crumb rubber size on asphalt performance, four crumb rubbers were chosen to prepare the composite modified asphalt via the pretreatment of crumb rubber by bio-oil under microwave heating. After short-term aging, the temperature sweep test, the MSCR test, LAS test and the cigar tube test were performed to evaluate the high-temperature performance, fatigue property and the storage stability of the composited asphalt, respectively. All Jnrs from the composite modified asphalt were less than 2.0 kPa−1 at 3.2 kPa. The crumb rubber size was positively correlated with the fatigue life. The relatively lowest segregation index was observed in the composite modified asphalt containing 40 mesh (0.38 mm) crumb rubber. It is concluded that the rubber size affects the performance of the composite modified asphalt. The pretreatment of bio-oil on crumb rubber facilitated the swelling and depolymerization of crumb rubber in the melt asphalt.

Terminal Blend rubberized asphalt (TBRA) is a novel application of Crumb Rubber (CR) modified asphalt. Compared with traditional CR modified asphalt, TBRA has good storage stability with a lower viscosity. However, TBRA generally has inferior high temperature performance, thereby SBS polymer is usually incorporated for composite modification. This paper evaluates the performances of TB/SBS composite modified asphalt with various modification formulas. Different rubber contents and SBS polymer contents were considered. Low temperature performance grading test, thermal stress master curve and low temperature Semi-Circular Bend (SCB) test were conducted for low-temperature performance evaluation. Multiple Stress Creep and Recovery (MSCR) and Hamburg Wheel Tracking (HWT) test were conducted for high-temperature performance evaluation. The results show that a 2% SBS addition can enhance the rutting resistance and moisture resistance of TBRA mixture without impairing its low-temperature performances. But more SBS introduction is not putting much extra value. Also, it is observed that with the presence of chemically active SBS polymer, rubber molecules from TB process also take part in the polymer crosslinking networking and strengthen the mixture. Based on both performance evaluation and cost analysis, a 10%TB plus 2%SBS formula is recommended in this study.

Asphalt modifications can contribute to the moisture susceptibility and fatigue resistance of asphalt mixtures. This study investigated the effects of various asphalt modifications on the bond and healing properties of modified asphalt binders and the mechanism of changes caused by the modification. Five modified asphalt binders were prepared in the laboratory for this study, including SBS-modified asphalt, crumb rubber-modified asphalt, terminal blend (TB) rubberized asphalt, high-density polyethylene (HDPE)-modified asphalt, and gilsonite-modified asphalt. A modified binder bond strength (BBS) test was applied to evaluate the bond and healing performance of five modified binders at both dry and wet conditions. The surface free energy (SFE) test was conducted on the modified binders to investigate the cohesion/adhesion energy variation due to the binder modification. In addition, the ravelling resistance, moisture susceptibility, and fatigue life of the asphalt mixtures prepared using the modified binders and basalt (which is widely used in China) were measured using the Cantabro test, Hamburg wheel-tracking test, and four-point beam fatigue test, respectively. The performance results of the asphalt mixtures are employed to verify the findings of BBS and SFE tests for the modified binders. It is found that the modified BBS test provides a promising tool for evaluating the bond and healing properties of modified asphalt binders, and the SFE could help to explain the mechanism of binder modification. The testing results indicate that gilsonite enhanced the bond strength and surface energy of asphalt, and high-density polyethylene significantly improve the healing performance.

Previous studies have documented the disconnect between the rotational viscosity of asphalt rubber (AR) and the workability of AR mix. There is a possibility that the particle effect of crumb rubber modifier (CRM) particles within AR causes this phenomenon. This study measured the viscosities of ARs and the corresponding liquid phases at three temperatures. The workability of the corresponding AR mixes was evaluated using the number of gyrations of Superpave Gyratory Compactor (SGC) samples. The changes on AR caused by the CRM contents were measured using Gel permeation chromatography (GPC) test. The experimental results revealed that the rotational viscosity of the AR liquid phase is more suitable to be used as a workability indicator. In addition, thresholds of CRM content were reported. Once the threshold is exceeded, the increase in AR viscosity is only caused by the increase in CRM particle effect and there is no detectable CRM/asphalt interaction.

Under the action of traffic load, the stress and failure state of pavement structure and materials are complex and diverse. Moreover, pavement materials are multi-phase, multi-component, and multi-scale mixtures. Their mechanical properties have significant differences in tension behavior, compression characteristics, and correlations with stress states. In view of the above problems, different testing approaches were carried out in this paper. A suitable yield criterion for rubberized asphalt mixtures was proposed. Then, the strength yield surface was determined under different loading rates. Based on the fatigue test results, the concept of fatigue stress ratio was further proposed. The relationship between the rubberized asphalt mixtures fatigue life and the fatigue stress ratio was established. The results showed that the yield criterion covers the impact of the loading rates and tensile-compression strength difference on the rubberized asphalt mixtures’ mechanical behavior. The strength yield surface's shape is elliptical in the σ m - σ e stress space and expands outward as the loading rate increases. This paper unified the fatigue equations under different testing approaches. The established fatigue equations reflect the viscoelastic characteristics and strength characteristics of materials. The study effectively solves the difficult problem of fatigue equation selection in the structural design of asphalt rubber pavement.

Although rubberized asphalt has more than a 50-year history, it has not been widely adopted due to difficulties with its processability, unstable properties and high initial cost. Chemical approaches, including chemical characterization and the addition of chemical additives to rubberized asphalt, are useful tools to promote the applications of this technology. Chemical characterization techniques such as infrared spectroscopy, thermogravimetric analysis, gel permeation chromatography, and sol-gel analysis are used to analyze the chemical composition of rubberized asphalt. The development of chemical characterization for rubberized asphalt is described in terms of chemical degradation of rubber in asphalt, and stabilization of rubber in asphalt. The evolution of the chemical composition of rubberized asphalt has been evaluated and correlated for dry and wet processing, and indoor and outdoor aging. Following this, high performance rubberized asphalt realized by modification with different chemical additives is also discussed. The additives are categorized into polymers, inorganic filler, plasticizer and others. Finally, methods that combine several types of different additives that can be used to produce rubberized asphalt with stable properties and in an environmentally friendly manner are described.

Rubberized hot-mix asphalt (RHMA) has been widely used in construction projects by the California Department of Transportation (Caltrans) for the environmental benefits of its recycled waste tires and for its improved fatigue and reflective cracking resistance. Currently, Caltrans does not permit the use of reclaimed asphalt pavement (RAP) in any gap- or open-graded rubberized asphalt mixes. However, given the cost and environmental benefits of RAP to replace portions of required virgin binder and aggregates in conventional mixes, interest is growing in the addition of some RAP to RHMA mixes as well. This study investigated concerns about this proposed practice. Three phases of laboratory testing (i.e., asphalt binder testing, fine aggregate matrix mix testing, and full-graded mix testing) were conducted to evaluate the effects of the addition of RAP into new RHMA mixes. The results indicated that the gap-graded aggregate structure of RHMA might limit the amount of RAP that could be used in the mix. Only 10% RAP by binder replacement could be achieved for the mix tested in this study, but the other specified volumetric requirements were still met. Replacement of a portion of asphalt rubber binder with age-hardened RAP binder increased the binder stiffness at low and high temperatures, which indicated enhanced rutting performance but diminished low-temperature cracking performance. Test results from full-graded mixes indicated similar trends, with improved rutting performance with the addition of RAP but also with significantly poorer fatigue and reflective cracking resistance.

In the production of Terminal Blend (TB) rubberized asphalt, degradation of crumb rubber in asphalt matrix can help improve the storage stability and workability of crumb rubber modified asphalt. However, degradation process of crumb rubber modified (CRM) binders was not clear from molecular components to rheological properties. This study investigated chemical and rheological perspectives of the degradation process of CRM asphalt under high interaction temperature (220–280 °C) and extended curing time (2–8 h), namely high-cured CRM asphalt. Attenuated Total Reflection (ATR) Fourier Transform Infrared (FT-IR) Spectroscopy was used to characterize the degradation behaviors of CRM binders at varying curing temperatures and times. Active Polymer Index (API) was defined as the ratio between band areas at 978–918 cm −1 and 850–785 cm −1 of FTIR tests to characterize the released active polymer from vulcanized crumb rubber. Besides, dynamic shear rheometer (DSR) was used to perform elastic recovery (ER) test, dynamic oscillatory test and multiple stress creep recovery (MSCR) test. Test results indicated that the critical degradation temperature was 260 °C in this limited study. Interaction temperature contributed more to the degradation than interaction time. Pearson correlation analysis indicated that API derived from ATR-FTIR test was a good indicator of degradation of CRM binders.

The influence of aging properties of terminal blend rubberized asphalt (TBRA) with styrene-butadiene-styrene (SBS) polymer was investigated. 3% content of SBS was added into TBRA, which was made of base asphalt and crumb rubbers with different contents (0, 5, 10, 15, 20%) to prepare TB hybrid asphalt. The functional groups of TB hybrid asphalt were monitored by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). All the samples of TB hybrid asphalt were tested with rolling thin film oven test (RTFOT) and pressure aging vessel (PAV), respectively. Physical and rheological properties were tested on all samples of TB hybrid asphalt, and chemical structures were analyzed by ATR-FTIR. FTIR test result shows that TB hybrid asphalt can inhibit the degradation of SBS polymer, and degradation of SBS in TB hybrid asphalt may occur mainly in the short-term aging, while the oxidation of bitumen mainly occurs in the long-term aging process. Compared with SBS modified asphalt, TB hybrid asphalt offer better anti-aging performance than SBS modified asphalt, and 3S_5TB (3 wt% SBS and 5 wt% crumb rubber) and 3S_20TB (3 wt% SBS and 20 wt% crumb rubber) exhibit the best short-term anti-aging properties and long-term anti-aging properties respectively. Furthermore, TB hybrid asphalt is softer than SBS modified asphalt, has better low temperature performance, and higher viscosity, but its high temperature performance is reduced. After RTFOT and PAV aging, the temperature sensitivity of TB asphalt is improved. With the increase of the content of crumb rubber, the influence of temperature sensitivity is better, and 3S_20TB (3 wt% SBS and 20 wt% crumb rubber) showed the best temperature sensitivity performance. Moreover, based on correlation analysis, the complex modulus aging index could be used as an index to evaluate the aging degree of TB hybrid asphalt.

Terminal Blend (TB) rubberized asphalt binders exhibit excellent storage stability compared with conventional rubberized asphalt binders, but there is still a phase separation in TB rubberized asphalt binders. Previous studies have developed different assessment methods to examine the phase separation of polymer modified asphalt binders, but it is still unclear whether these methods are suitable for TB rubberized asphalt binders. In this study, current commonly used assessment methods of storage stability were examined with TB rubberized asphalt binders that were prepared with two types of crumb rubber in various particle sizes and contents. After storage stability tests, non-dissolved crumb rubber particles were extracted from TB rubberized asphalt binders. The relationships between non-dissolved crumb rubber particles and different assessment methods were then examined with the help of Spearman’s rank correlation coefficient. It was found that crumb rubber content has a positive effect on the storage stability of TB rubberized asphalt binders and the effect of particle size on the storage stability is highly dependent on rubber source. Additionally, softening point difference, separation index, separation and degradation ratios at intermediate temperatures are not reliable indicators for assessing the storage stability of TB rubberized asphalt binders. Conversely, separation and degradation ratios at high temperatures and low frequencies are better indexes to characterize the storage stability compared with the other indexes, followed by percentage of separation.

Terminal blend (TB) rubberized asphalt binder can be produced through the dissolution of crumb rubber modifier (CRM) in asphalt, meanwhile other modifiers, like styrene–butadienestyrene (SBS) polymer and crosslinking agent sulphur are supplemented to enhance the properties of modified asphalt. The effect of sulphur on asphalt oxidation and polymer degradation is not well documented for TB rubberized asphalt binder. This paper investigates anti-aging potential of sulphur in TB rubberized asphalt binder from chemical and mechanical perspective. Carbonyl index and butadiene/styrene ratio, which are derived from fourier transform infrared (FTIR) spectrums, are applied to analyse carbonyl growth and butadiene reduction. Gel permeation chromatography (GPC) based polymer retention index is used to detect the change of polymer molecular weight. The complex modulus |G*| is used to calculate hardening index and phase angle master curve is used to analyse the elastic contribution of sulphur. Crosslinking agent sulphur does not have definite positive or negative effect on the carbonyl growth of TB rubberized asphalt binders in this laboratory aging study. However, sulphur does help to alleviate the age hardening behavior. For miscible TB rubberized asphalt binders, 0.3% or 0.4% sulphur can improve the resistance to polymer degradation. In addition, sulphur can improve elastic response of TB rubberized asphalt binder even for pressurized aging vessel (PAV) aged asphalt.

The skeleton-stabilized gradation based on discrete element model was used to design a warm mix rich asphalt concrete, and its fatigue and fracture performance were studied. The main findings of this study include that: (1) adding warm mix additive could effectively reduce the viscosity of rubberized asphalt and improve the mixing of rubberized asphalt mixture; (2) the splitting strength and the fatigue life of warm mix rubberized asphalt concrete were better than warm mix raw asphalt concrete; (3) critical stress intensity factor was a suitable index to evaluate anti-crack performance of warm mix rich asphalt concrete.

Improving fatigue cracking resistance of asphalt mixtures is an important issue that concerns roadway agencies, public and industry. There are various, well-established methods for improving the material characteristics, such as polymer modification methods. Recycling/reusing scrap tire rubber in asphalt pavements has also been an interest of engineers. As such, many different methods of scrap tire rubber (herein called crumb rubber) modification alternatives are being developed. This study focused on a comparative evaluation of the fatigue cracking resistance of various base and recycled tire rubber modified asphalt mixtures, including the relatively new and innovative devulcanized rubber (DVR), crumb rubber terminally blend (CRTB), crumb rubber wet process (CRWET), original/base PG58-28 and softer PG58-34 binders, by using Push-Pull Viscoelastic Continuum Damage (PP-VECD) analysis and AASHTOWare Pavement Mechanistic Empirical Design (Pavement ME) software. The results of the study revealed that rubberized asphalt mixtures provided better fatigue lives than the base and softer binders did. Especially, DVR mixtures outperformed at high strain levels, implying they can be used for heavy traffic roads to enhance the fatigue life of asphalt pavements. Both PP-VECD and Pavement ME produced results that showed similar trends.

Construction and building materials 239, 117824 (2020). doi:10.1016/j.conbuildmat.2019.117824, Published by Elsevier Science, Amsterdam [u.a.]

The use of waste tire rubber as asphalt modifier has been a practice-ready technology. However, the interaction among components within asphalt rubber (AR) and warm asphalt rubber (WAR) is still unclear. During the blending process, the swelling rubber releases polymer agents in asphalt and absorbs components from both asphalt and warm mix asphalt (WMA) additive simultaneously. The component interaction significantly influences the final rheological properties. A comprehensive understanding of the selective absorption of crumb rubber during the blending process provides references to optimize the material and procedure design of rubberized asphalt. To this end, one AR and two WARs were prepared with three mixing durations. The liquid phases and crumb rubber particles were separated. The separated swelling rubber particles were then processed by the staged extraction method to divide the asphalt-rubber interacting area from outside to inside into four layers. The absorption preference of swelling rubber and its influence on rheological properties were investigated by chemical and rheological tests. Test results showed that asphalt fractions with smaller molecular weight were absorbed into deeper layers of swelling rubber. By contrast, crumb rubber was found to be reluctant to absorb the fractions with C O bond during the mixing process. In addition, the Fischer Tropsch (FT) wax showed a negligible influence on the absorption preference, while the effect of surfactant on absorption preference was significant. Finally, the relationship between absorption preference and rheological properties was established. It was found that the absorption preference of crumb rubber is beneficial to the rutting resistance of rubberized asphalt.

It is well known that rutting is one of the major distresses for asphalt pavements. To enhance the rutting resistance of asphalt pavements, different approaches have been developed, among which using high-modulus asphalt mixtures (HMAM) has been proved effective. The main objective of this study is to characterize and compare the performances of using hard binders, HMAM additives, and polyester fiber, in producing HMAM. To achieve this objective, the rheological properties of four hard binders, including rubberized bitumen, lake bitumen and SBS collectively modified asphalt binder, rock bitumen and SBS collectively modified asphalt binder, and hard-grade asphalt binder, were first tested. Then, three modulus parameters, namely resilient moduli, dynamic moduli and stiffness moduli, of seven mixtures, including four mixtures prepared with the four hard binders, one SBS modified mixture, one SBS modified mixture with an HMAM additive, PR.M., and one SBS modified mixture with polyester fiber, were measured and compared, followed by comprehensive laboratory performance tests, including rutting resistance, low-temperature cracking resistance, fatigue resistance, and moisture damage resistance tests, and binder-mixture performance correlation analysis. It was found that all the four hard binders can produce mixtures with high modulus as expected. Among different mixtures, rubberized asphalt mixture was provided best overall performance. For the purpose of rutting treatment, rubberized asphalt mixture, the mixture collectively modified by SBS and rock bitumen, and the SBS modified asphalt mixture with PR.M. additive are the better candidates in consideration of their superior rutting resistance and relatively more balanced performance properties.

The use of reclaimed asphalt pavement (RAP) represents an environmentally positive method of recycling besides saving cost. Experience has shown that properly designed hot-mix asphalt (HMA) containing RAP performs as well as HMA produced with virgin materials. Crumb rubber asphalt represents, on the other hand, a promising paving material that recycles waste tires. The combination of the two techniques has promising environmental significance, i.e. recycling asphalt concrete pavement using rubberized asphalt, which remains a virgin research topic. In this paper, microstructure of rubberized asphalt mixture containing RAP was studied to obtain its optimum mixing conditions. Specimens were prepared in the laboratory and scanned by X-ray Computed Tomography (CT) system to identify distribution of the components. An improved Otsu’s algorithm was used to segment the mixture images. The results indicate that the algorithm could effectively solve the uneven brightness problem of scanned images. Statistical indicators were used to analyze uniformity of component distribution. Three mixing time and three mixing temperatures were used in the blending process to evaluate effects of mixing time and mixing temperature on the distribution of mixture component. It was found that distribution of air voids and virgin aggregates are relatively more sensitive to mixing time and mixing temperature. Optimum mixing time is 150 s and it should not be less than 90 s to achieve well distribution of components. Optimum mixing temperature is at least 150 °C.

Asphalt pavement rutting is one of the most commonly observed pavement distresses, and crumb rubber can decrease this distress. This paper uses the two-dimensional (2D) and three-dimensiona...

Asphalt rubber has been commonly used in the United States for modifying asphalt binder. There have been several studies on improving the interaction and adhesion between rubber and asphalt matrix. The modification of asphalt binder with crumb rubber (CR) is mainly controlled by the exchange equilibrium between components of asphalt binder and CR. This phenomenon increases the size of rubber particles (swelling) up to three times their original size and leads to a significant increase in the viscosity of the resulting asphalt. Swelling and increased viscosity not only promote separation of the modified matrix into two distinguishable phases but also increase the difficulty of pumping and application of rubberized asphalt. This study investigated the effectiveness of treating rubber with an amide-enriched biomodifier to facilitate breakage of disulfide bonds in rubber polymer while promoting interactions between free radicals and amide groups of biomodifier. Promoting interactions between rubber polymer and asphalt aromatic compounds by adding a biomodifier could alleviate phase separation while enhancing overall matrix elasticity. This modification enhanced the rheological properties of rubberized asphalt, including high-temperature properties as well as its palpability. The rotational viscometer and dynamic shear rheometer were used to evaluate the effect of biomodifier on the rheological properties of asphalt rubber at high and intermediate temperatures. Fourier transform infrared spectroscopy was used to examine the presence of rubber polymer compounds inside the asphalt matrix. The results showed that introduction of biomodifier facilitated the application of higher CR percentages while improving the overall rheological properties of the asphalt rubber.

Rubberized asphalt has been widely used for extending the service life of pavement. Understanding the weathering mechanism of rubberized asphalt is useful for selecting appropriate rubberiz...

The use of ground rubber from scrap tires has long been supported by environmental and government agencies to reduce the disposal problem associated with waste tires. In 2008, Louisiana turned to the use of crumb rubber in asphalt mixtures to address a shortage in polymer-modified asphalt binder. As a result, the state developed new specifications for rubberized asphalt binder, which was allowed as a substitute to polymer-modified asphalt binder. This study presents the research activities that led to the development of the Louisiana rubberized specifications. A laboratory experimental program was conducted to evaluate the performance of asphalt mixtures prepared with crumb rubber (CR) modified binder as compared to mixtures prepared with polymer-modified asphalt binder with and without reclaimed asphalt pavement. In addition, the field performance of test sections constructed with CR-modified binder was compared to a test section prepared with polymer-modified conventional mixtures under accelerated loading. Based on the results of the laboratory experimental program, it is concluded that the rutting and intermediate temperature fracture performances of CR-modified asphalt mixture were adequate and comparable to mixtures prepared with polymer-modified asphalt binder. Test results from the accelerated loading facility experiment showed that acceptable performance for asphalt mixtures can be achieved using either polymer-modified or CR-modified asphalt binders.

Waste tires pose significant health and environmental concerns if not recycled and/or discarded properly. Over the years, recycling waste tires into civil engineering applications, especially into asphalt paving mixtures and portland cement concrete, has been gaining more and more interests. This review summarizes the recent advances in the use of waste tire rubber in asphalt and portland cement concrete. The use of crumb rubber in asphalt paving mixture has long been proven successful due to good compatibility and interaction between rubber particles and asphalt binder, leading to various improved properties and performance of asphalt mixtures. The rubberized asphalt mixtures also have shown good compatibility with two widely used sustainability technologies in asphalt paving industry – reclaimed asphalt pavement (RAP) and warm-mix asphalt (WMA). In comparison with its use in asphalt paving mixtures, recycling of waste rubber in Portland cement concrete has not been so successful due to two factors: (1) incompatibility in chemical property between rubber and cement paste and (2) the significant difference in stiffness resulting in stress concentrations. Various methods have been proposed to overcome the barriers to improve the performance of rubberized portland cement concrete, some of which have shown to be promising.

Terminal blend rubberized asphalt (TB), a rubber-modified asphalt, exhibits excellent storage stability and compatibility compared with traditional rubber modified asphalt. However, the investigation regarding its performance at high temperatures is not sufficient. In this study, the amorphous-poly-alpha-olefin (APAO) additive was employed as a modifier to improve the performance of the TB asphalt at both high- and low-temperature. Firstly, the general performance and rotational viscosity were tested via conventional tests in the laboratory. Besides, the rheological properties at both high and low temperatures were evaluated by a dynamic shear rheometer (DSR) test and a bending beam rheometer (BBR) test, respectively. Finally, the micromorphology of specimens was detected through an environmental scanning electron microscope (ESEM) test. The experiment results showed that with the increase in APAO content in the TB asphalt, the increasing trend of rotational viscosity and the softening point was noticeable. In addition, the rutting factor (G*/sinδ), recovery percentage (R), and non-recoverable compliance (Jnr) suggested that the APAO modified TB asphalt presented a remarkable rutting resistance at high-temperature. When the content of APAO reached 6% (wt.), the low-temperature crack resistance of asphalt was significantly improved through the results of low-temperature toughness. Meanwhile, the ESEM test results presented that the APAO modifications were evenly distributed in asphalt and formed a dense grid structure, which helped improve the binding force between the components in the polymer modified asphalt.

There are nearly 4,800,000 km (3,000,000 miles) of paved roads and 80,000 km (50,000 miles) of paved highways in the United States, many of which are in poor condition and approaching the end of their design life. To upgrade this valuable infrastructure, state and federal governments have advocated for rubberized asphalt concrete (RAC) technology, which would meet the current needs without compromising the ability of future generations to meet their own demands. This paper presents a cost-estimating system for rubberized asphalt road rehabilitation projects. The proposed system utilizes information collected from 44 projects and applies neural networks to perform its task. This tool is believed to be helpful in many road pavement applications, such as preparing accurate budget estimates and life-cost analyses, as well as managing financial resources in limited budget environments.

In this paper, the fatigue life of rubberized asphalt concrete mixtures containing reclaimed asphalt pavement is investigated through probabilistic analysis. The simple traditional empirical models updated with a reliable database are employed to predict the fatigue lives of various mixtures containing crumb rubber and/or reclaimed asphalt pavement. The effects of model uncertainty and input parameter uncertainty on the fatigue life are interpreted with the probability of fatigue failure, this is defined herein as the probability that the predicted fatigue life fails to satisfy the minimum requirements of fatigue life. The probabilistic analysis of fatigue failure is estimated with a simple reliability-based approach, known as point estimate approach (PEM). Comparison study shows that the probability of fatigue failure obtained with PEM is identical with that obtained with the Monte Carlo simulation (MCS). The results indicated that the probabilistic analysis using PEM and MCS methodologies can be used for exploring the fatigue life probability effectively, requires very limited computational effort, and thus has the potential and ease as a practical tool to employ in pavement engineering.

This paper documents and discusses an investigation of performance-based testing of asphalt cement (AC), AC modified with warm-mix technology additives (warm AC), rubberized asphalt cement (RAC), and warm RAC. A number of control, warm, and RAC binders from Ontario, Canada, construction contracts were investigated for their compliance with conventional Superpave® as well as additional specification criteria. It was found that all samples passed the Superpave requirements but only one satisfied the additional Ontario criteria. One warm AC and two field-blended RAC samples showed high levels of physical hardening, which can lead to early cracking. The warm AC lost 8°C when stored isothermally for 3 days at low temperatures according to Ontario's extended bending beam rheometer protocol (LS-308). The two RAC samples lost 10°C and 12°C following the same conditioning. Many of the investigated samples showed deficient strain tolerance as measured in Ontario's double-edge-notched tension test (LS-299). In an effort to formulate warm RAC with improved properties, a number of compositions were prepared with soft Cold Lake AC and a small quantity of naphthenic oil. These binders showed little chemical and physical hardening and reasonable critical crack tip opening displacements. Strain tolerance was much improved by coblending with a high vinyl-type styrene–butadiene–styrene polymer and a small amount of sulfur. The Ministry of Transportation of Ontario is interested in using the developed formulations in future pavement trials with expected improvements in pavement performance.