Assessment of the Extended Fatigue Life for Rubber and Polymer Modified Asphalt Mixtures Using Flexural Bending Beam Fatigue Test

Load associated fatigue cracking is one of the major distress types occurring in flexible pavement systems. Flexural bending beam fatigue laboratory test has been used for several decades and is considered to be an integral part of the new superpave advanced characterization procedure. One of the most significant solutions to prolong the fatigue life for an asphaltic mixture is to utilize flexible materials as rubber or polymer fibers. A laboratory testing program was performed at Arizona State University (ASU) on a reference, Asphalt Rubber (AR) and polymer modified gap graded mixtures. Strain controlled fatigue tests were conducted according to American Association of State Highway and Transportation Officials (AASHTO) procedures. Using COANOVA statistical analysis approach, the results from the beam fatigue tests indicated that the AR and polymer modified gap graded mixtures would have much longer fatigue life compared with the reference (conventional) mixtures

Effects of Short-Term Aging on Asphalt Binders and Hot Mix Asphalt at Elevated Temperatures and Extended Aging Time

The production process of Hot Mix Asphalt (HMA) causes a short term aging (STA) to asphalt binder due to the heating of both asphalt binder and aggregates before mixing together. Laboratory protocols are followed to simulate the STA conditions for both asphalt binders and asphalt mixtures. STA protocols expose asphalt binders or asphalt mixtures to specific aging temperature for a specific period of time to produce stiffening that is similar to that of actual production conditions. Successful construction of HMA in cold season/regions may require elevating the production temperature of HAM to achieve proper compaction of HMA layers. Producing HMA mixtures at elevated temperatures may cause further increase in the binder stiffness and negatively affect the future field performance of asphalt pavements. This negative affect can be even worse especially if it is coupled with extended exposer time increase. This study aims to investigate effect of elevated production (mixing and STA) temperatures and exposure time on the stiffening of binders and asphalt mixtures. The binder experiment involved aging of two Performance Graded (PG) binders (PG 76-16 and PG 64-22) at two different temperatures and aging durations. The asphalt mixture experiment involved the STA of asphalt mixtures produced in the laboratory at mixing and STA temperatures 25°F above standard practice and aging time 2 and 4 hours longer than standard practices. The effect of different aging times and temperatures was investigated by running viscosity tests on binders and dynamic modulus |E*| and Indirect Diametrical Strength (IDT) tests on asphalt mixtures. The results showed that increasing the mixing and STA temperatures by 25°F seems to have no significant effect on the asphalt mixture properties while doubling the standard STA time seems to have a significant effect on binder and asphalt mixture properties

Cracking Characteristic of Asphalt Rubber Mixtures

The Arizona Department of Transportation (ADOT) has used Asphalt Rubber (AR) modified binders since the early 1970’s. The primary purpose for using AR is to reduce reflective cracking in Hot Mix Asphalt (HMA) rehabilitation overlays. The AR mixtures have also performed well in cold climate conditions. This research study had the primary objective of conducting a laboratory experimental program to obtain typical cracking properties for asphalt rubber mixtures used in Arizona and comparing the performance of these AR mixtures to other conventional asphalt mixtures. Gap and open graded mixtures were subjected to fatigue and indirect tensile cracking tests. All test specimens in this study were prepared using hot mix AR mixtures that were collected during construction. Fatigue testing of AR specimens was conducted at different test temperatures using the beam fatigue apparatus proposed by the Strategic Highway Research Program (SHRP). The indirect tensile strength and creep tests were carried out at three temperatures according to the procedures described in the draft indirect tensile test protocol developed for the new 2002 Design Guide. The results from the fatigue tests indicated that the AR mixtures would have longer fatigue life compared with the ADOT conventional dense graded mixtures. For the indirect tensile strength tests, the analysis for strains measured at failure showed that the AR mixtures have higher values than the conventional mixes. AR mixtures exhibiting higher strains at failure would have higher resistance to thermal cracking. The fracture energy results indicated that the AR mixtures are not as greatly affected by the decrease in temperature as compared to the conventional mixes. This relative insensitivity for changes in temperature makes the AR mixtures better resisting to thermal cracking in the field

Fatigue properties of nano-reinforced bituminous mixtures: A viscoelastic continuum damage approach

The experimental investigation described in this paper focused on the effects of nanoclays on the fatigue behaviour of bituminous mixtures. Damage characteristics of a bituminous mixture produced by making use of a nano-reinforced binder were compared to those of a reference mixture obtained by employing the same neat bitumen used as a base in the preparation of the nanoclay–bitumen blend. Dynamic modulus tests and direct tension cyclic fatigue tests were carried out to determine the linear viscoelastic properties and the damage evolution characteristics of materials. Corresponding results were modelled by means of a viscoelastic continuum damage approach and by making use of a more empirical evaluation based on the classical Wöhler representation. It was found that the use of nanoclays produced a reinforcement of bituminous mixtures, the benefits of which were observed both in the progression of damage and in the occurrence of ultimate failure condition

Laboratory Performance Evaluation of a Gap-Graded Asphalt-Rubber Mixture in Puerto Rico

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Rejuvenation Mechanism of Asphalt Mixtures Modified with Crumb Rubber

Asphalt aging is one of the main factors causing asphalt pavements deterioration. Previous studies reported on some aging benefits of asphalt rubber mixtures through laboratory evaluation. A field observation of various pavement sections of crumb rubber modified asphalt friction courses (ARFC) in the Phoenix, Arizona area indicated an interesting pattern of transverse/reflective cracking. These ARFC courses were placed several years ago on existing jointed plain concrete pavements for highway noise mitigation. Over the years, the shoulders had very noticeable and extensive cracking over the joints; however, the driving lanes of the pavement showed less cracking formation in severity and extent. The issue with this phenomenon is that widely adopted theories that stem from continuum mechanics of materials and layered mechanics of pavement systems cannot directly explain this phenomenon. One hypothesis could be that traffic loads continually manipulate the pavement over time, which causes some maltenes (oils and resins) compounds absorbed in the crumb rubber particles to migrate out leading to rejuvenation of the mastic in the asphalt mixture. To investigate the validity of such a hypothesis, an experimental laboratory testing was undertaken to condition samples with and without dynamic loads at high temperatures. This was followed by creep compliance and indirect tensile strength testing. The results showed the higher creep for samples aged with dynamic loading compared to those aged without loading. Higher creep compliance was attributed to higher flexibility of samples due to the rejuvenation of the maltenes. This was also supported by the higher fracture energy results obtained for samples conditioned with dynamic loading from indirect tensile strength testing

Effects of Short-Term Aging on Asphalt Binders and Hot Mix Asphalt at Elevated Temperatures and Extended Aging Time

The production process of Hot Mix Asphalt (HMA) causes a short term aging (STA) to asphalt binder due to the heating of both asphalt binder and aggregates before mixing together. Laboratory protocols are followed to simulate the STA conditions for both asphalt binders and asphalt mixtures. STA protocols expose asphalt binders or asphalt mixtures to specific aging temperature for a specific period of time to produce stiffening that is similar to that of actual production conditions. Successful construction of HMA in cold season/regions may require elevating the production temperature of HAM to achieve proper compaction of HMA layers. Producing HMA mixtures at elevated temperatures may cause further increase in the binder stiffness and negatively affect the future field performance of asphalt pavements. This negative affect can be even worse especially if it is coupled with extended exposer time increase. This study aims to investigate effect of elevated production (mixing and STA) temperatures and exposure time on the stiffening of binders and asphalt mixtures. The binder experiment involved aging of two Performance Graded (PG) binders (PG 76-16 and PG 64-22) at two different temperatures and aging durations. The asphalt mixture experiment involved the STA of asphalt mixtures produced in the laboratory at mixing and STA temperatures 25°F above standard practice and aging time 2 and 4 hours longer than standard practices. The effect of different aging times and temperatures was investigated by running viscosity tests on binders and dynamic modulus |E*| and Indirect Diametrical Strength (IDT) tests on asphalt mixtures. The results showed that increasing the mixing and STA temperatures by 25°F seems to have no significant effect on the asphalt mixture properties while doubling the standard STA time seems to have a significant effect on binder and asphalt mixture properties

Effects of Short-Term Aging on Asphalt Binders and Hot Mix Asphalt at Elevated Temperatures and Extended Aging Time

The production process of Hot Mix Asphalt (HMA) causes a short term aging (STA) to asphalt binder due to the heating of both asphalt binder and aggregates before mixing together. Laboratory protocols are followed to simulate the STA conditions for both asphalt binders and asphalt mixtures. STA protocols expose asphalt binders or asphalt mixtures to specific aging temperature for a specific period of time to produce stiffening that is similar to that of actual production conditions. Successful construction of HMA in cold season/regions may require elevating the production temperature of HAM to achieve proper compaction of HMA layers. Producing HMA mixtures at elevated temperatures may cause further increase in the binder stiffness and negatively affect the future field performance of asphalt pavements. This negative affect can be even worse especially if it is coupled with extended exposer time increase. This study aims to investigate effect of elevated production (mixing and STA) temperatures and exposure time on the stiffening of binders and asphalt mixtures. The binder experiment involved aging of two Performance Graded (PG) binders (PG 76-16 and PG 64-22) at two different temperatures and aging durations. The asphalt mixture experiment involved the STA of asphalt mixtures produced in the laboratory at mixing and STA temperatures 25°F above standard practice and aging time 2 and 4 hours longer than standard practices. The effect of different aging times and temperatures was investigated by running viscosity tests on binders and dynamic modulus |E*| and Indirect Diametrical Strength (IDT) tests on asphalt mixtures. The results showed that increasing the mixing and STA temperatures by 25°F seems to have no significant effect on the asphalt mixture properties while doubling the standard STA time seems to have a significant effect on binder and asphalt mixture properties

Impact of Asphalt Rubber Friction Course Overlays on Tire Wear Emissions and Air Quality Models for Phoenix, Arizona, Airshed

Tire wear contributes to atmospheric particulate matter (PM) and is regulated by the U.S. Environmental Protection Agency because PM has been shown to affect human health. Vehicle emissions are a significant source of both PM2.5 and PM10. Vehicle fleet emissions per mile traveled have been reduced significantly in the past 30 years as a result of improved engine operation and tailpipe controls. However, “zero emission” vehicles will continue to generate PM from tire wear, road wear, brake wear, and resuspended road dust. In this study, aerosol measurement techniques at Arizona State University were applied to evaluate tire wear emissions from the vehicle fleet by using the Deck Park Tunnel in Phoenix, Arizona. The Deck Park Tunnel highway surface was portland cement concrete (PCC) and was resurfaced with an asphalt rubber friction course (ARFC) layer as part of the Arizona Department of Transportation Quiet Pavements Program. This study took advantage of a rare opportunity to sample tire wear emissions at the tunnel before and after the ARFC overlay. The hypothesis was that an ARFC surface results in less tire wear than the existing PCC road surface. This paper reports on the measured PM emissions from the on-road vehicle traffic during typical highway driving conditions for the two different roadway surfaces. It presents the analysis of representative tire tread samples for tire wear marker compounds and a comparison of roughness and frictional surface characteristics as measured before and after the ARFC overlay. The study found that emission rates of tire wear per kilometer driven on PCC road surfaces were 1.4 to 2 times higher than emission rates of tire wear on ARFC road surfaces

Effect of Aramid Fibers on Balanced Mix Design of Asphalt Concrete

Fiber-reinforced asphalt concrete (FRAC) was tested using limestone, PG 64-22 binder, and 20% reclaimed asphalt pavement (RAP). After mixing fibers with different lengths and dosages, they were extracted and recovered to evaluate their dispersion in the FRAC. The uniaxial fatigue test, IDEAL CT test, and flow number test were performed on FRAC with different fiber lengths and asphalt contents. The balanced mix design (BMD) approach was then used to analyze the uniaxial and flow number test results in order to evaluate the effect of aramid fibers on fatigue and rutting resistance of the pavement. The dispersion test showed that the 19 mm and 10 mm aramid fibers at a dosage rate of 0.5 g/kg provided the best dispersion. The 19 mm fibers showed better performance test results than the 10 mm and 38 mm fibers. The BMD approach provided ranges of asphalt contents to produce mixes with certain resistances to fatigue and rutting. The BMD approach also demonstrated the effect of fibers with different lengths on increasing the resistance to fatigue and rutting. The study concluded that the 19 mm fibers with a dosage of 0.5 g/kg produce best results. The BMD approach is a good tool that can be used to refine the mix ingredients, including additives such as fibers, in order to optimize pavement resistance to various distresses such as fatigue cracking and rutting