Creep Compliance Tests Research Articles

Improved Research on Two-Step Thermal Stress Calculation Method for Asphalt Mixture: Extended Creep Compliance Test.

The two-step thermal stress calculation method (TTSCM) is commonly used to predict the cracking temperature of asphalt mixture. The aim of this study is to improve TTSCM's mathematical model so as to enhance its prediction accuracy. First, this study evaluated the errors of predicted cracking temperatures of original TTSCM for AC-16 and AC-25 asphalt mixtures by thermal stress-restrained specimen test (TSRST). Then, an improved method called the extended creep compliance test (ECCT) was developed to modify the TTSCM. The test results show that the cracking predictions of the original TTSCM are not always accurate. Particularly for AC-16 asphalt mixture, the predicted cracking temperature is 2.9 °C (-10.6%) higher than the measured value by the TSRST. The ECCT method has been proven to be an effective way to enhance the prediction accuracy of the TTSCM. The predicted cracking temperatures modified by the ECCT method for both asphalt mixtures are relatively accurate, having an error within ±2%. The ECCT method changed the calculated thermal stress values at different temperatures of the TTSCM; however, they still conformed to a basic changing trend with respect to the initial temperature and cooling rate. Finally, a recommendation regarding the ECCT method was presented.

Assessing the effects of copolymer modifier addition on asphalt attributes: Towards achieving performance optimization

The use of polymers to modify asphalt binders has become a widely accepted practice in modern pavement construction, offering a promising solution to address key factors contributing to asphalt pavement deficiencies. These factors include issues such as rutting, moisture-induced deterioration, and fatigue-related wear. The copolymer referred to as PGXpand was utilized as the modifying additive for the virgin binder in this study. It demonstrates exceptional performance in terms of high-temperature resilience and resistance to rutting. The impact of incorporating the PGXpand on asphalt properties was investigated. A comprehensive series of tests were conducted, covering storage stability, penetration, softening point, ductility, viscosity, and elastic recovery. Further analyses involved calculations of stiffness modulus, complex modulus, and phase angle. Mechanical and performance evaluations were also carried out, including Marshall properties, moisture susceptibility, creep compliance, and Kim tests. The results demonstrate the effectiveness of the PGXpand in enhancing asphalt performance, with modified mixtures exhibiting significant improvements compared to their unmodified counterparts. Consequently, integrating the PGXpand into asphalt technology emerges as a highly promising approach for optimizing road infrastructure, especially in regions with high-temperature conditions. Ultimately, such integration contributes substantially to the development of sustainable and resilient transportation networks.

Evaluation of Mechanical Performance of Asphalt Emulsion Stabilized Base Course Composed of Reclaimed Asphalt Pavement and Asphaltenes

Abstract Reclaimed asphalt pavement (RAP) is a material that is produced by milling old asphalt pavement that can be mixed with virgin asphalt binder and aggregates to fabricate a recycled asphalt mixture. Using RAP in pavement structure can promote sustainability and reduce construction costs. In this study, asphaltenes, which is a waste material derived from oil sands deasphalting operation, was added as a modifier to recycled mixtures composed of different contents of RAP. A proctor test was conducted to determine the optimum fluid contents. Mix designs were performed for mixtures with 50 %, 75 %, and 100 % RAP with asphalt emulsion and different asphaltenes contents. Mechanical properties of the modified mixtures were evaluated by conducting the indirect tensile strength (ITS) test, creep compliance and strength test, indirect tensile asphalt cracking test (IDEAL-CT), and Hamburg wheel tracking test. The optimum emulsion content was determined to be 1.5 % based on sample performance using the ITS test. The results indicate that asphaltenes improves the strength up to the design-specified limits. The asphaltenes-modified samples show lower creep compliance and fracture energy (FE) values than the unmodified sample, indicating these samples are potentially more prone to cracking. Further, statistical analysis shows the difference in FE is significant at the lowest testing temperatures (−20°C). Asphaltenes-modified mixtures have greater cracking resistance at the intermediate temperature (25°C) and rutting performance at high temperature (40°C) than the unmodified mixture. However, based on FE and rutting resistance index, the improvements are not significant. Overall, the 100 % RAP mix with 1 % asphaltenes had the best tensile strength, cracking resistance, rutting resistance, and low temperature properties compared to other modified mixes.

Effects of asphalt binder type, aggregate type, and gradation characteristics on fracture properties and performance of asphalt mixtures at intermediate temperatures

This study aimed to design and evaluate asphalt mixtures by considering various factors including different binders, aggregate types, and gradation characteristics of the fine portion of mixtures, referred to as the interstitial component (IC). The mixtures were compacted to 93% of maximum theoretical density to prepare specimens for Superpave IDT tests, which included resilient modulus, creep compliance, and fracture tests. Parameters such as failure limit (fracture energy), damage rate (dissipated creep strain energy per cycle), and the relative cracking performance indicator (number of cycles to failure) were assessed for test specimens subjected to the long-term oven aging and the cyclic pore pressure conditioning. The results showed that mixtures with styrene–butadiene–styrene modified binders exhibited slightly higher failure limits but significantly lower damage rates compared to mixtures with unmodified binders, indicating improved cracking performance. Similarly, the limestone mixtures demonstrated equivalent failure limit but much lower damage rate to the granite mixtures, attributed to the porous surface morphology and inherent weakness of limestone aggregates. Notably, even small changes in the IC characteristics of the mixtures yielded substantial differences in fracture properties and performance, a phenomenon believed to be linked to the distribution of asphalt binder and the structure of air voids within the mixture. In conclusion, a thorough examination confirmed the impact of polymer modification and aggregate type on fracture properties and, notably, highlighted the pivotal role of the fine portion's characteristics in determining mixture cracking performance.

Use of the Iron Chloride Type of Lewis Acid Catalyst in High Reclaimed Asphalt Pavement Content Asphalt Mixtures

The use of reclaimed asphalt pavement (RAP) as a partial replacement for virgin aggregates and asphalt binders has received considerable attention recently. This approach is one of many promising methods for improving sustainability. However, many state Departments of Transportation are cautious in adopting high RAP content into their designs because of cracking and durability issues resulting from the aged RAP binder. A Lewis acid catalyst has been used to modify the asphalt binder’s chemical composition and disrupt the associated molecules formed in the aged RAP binder. The objective of this study is to assess the effectiveness of the use of a Lewis acid catalyst in improving the cracking resistance of an asphalt mixture containing high RAP contents. A suite of laboratory mechanical tests was performed, namely, the dynamic modulus test for linear viscoelastic properties; the semi-circular bend, Illinois flexible index, ideal cracking tolerance, and simplified viscoelastic continuum damage tests for fracture and fatigue resistance; the loaded wheel tracking test for rutting resistance and moisture susceptibility; indirect tensile creep compliance and strength tests for low-temperature cracking resistance; and the Cantabro abrasion test for durability. Further, AASHTOWare Pavement ME software was used to predict the long-term performance of asphalt pavements containing mixtures with high RAP contents and a Lewis acid catalyst. Results showed that the use of the Lewis acid catalyst can disrupt associated molecules formed in the aged RAP binder. Thus, asphalt mixtures containing high RAP contents (recycled binder ratio > 0.20) and a Lewis acid catalyst exhibited similar performances to conventional mixtures. Further, Pavement ME predicted fatigue cracking was lower for a structure containing a FeCl3-modified mixture as compared to a similar one with no FeCl3, illustrating the effectiveness of FeCl3.

Viscoelastic parametric conversions and mechanical response analysis of asphalt mixtures

In this study, dynamic modulus, dynamic resilience modulus, and creep compliance tests were conducted to characterize and quantify the effects of viscoelastic parameters of asphalt mixtures on the mechanical response of pavement structures. From the laboratory testing under different loading waveforms, master curves were generated to computed the viscoelastic parameters that were used as input for ANSYS modeling. In general, the corresponding results indicated that the stress magnitude had a significant influence on the evolution of master curves for the viscoelastic parametric conversions from creep compliance and that all the mechanical responses (namely stress, strains, and deformations) tended to increase with temperature. For the asphalt mixtures evaluated, the relaxation modulus transformed from the creep compliance was largely indifferent whilst those converted from the dynamic modulus did not exceed 15% from the actual values. In terms of the loading mode, the highest fitting accuracy for the viscoelastic parameters and master curves was obtained for the half-sine waveform. Overall, the study results indicated that ensuring good interlayer bonding is imperative for minimizing the compressive/shear stresses and strains in pavement structures to mitigate shear failure, debonding, delamination, etc. Additionally, the study also demonstrated that use of modified asphalt mixtures was critical to mitigate high compressive and shear strains arising for heavy traffic loading in high temperature climatic conditions.

The effect of waste low-density polyethylene on the mechanical properties of thin asphalt overlay

In recent years, there has been a huge demand for innovative methods to upcycle waste materials. This study aims to explore and evaluate the effect of using waste low-density polyethylene (w-LDPE), collected from waste plastic bags for domestic purposes, on the mechanical properties of dense Thin Asphalt Overlay (TAO). Waste materials have been deemed appropriate in the development of asphalt pavement mixtures, due to the expected enhancement in mixture properties further to the reduction in cost and saving natural resources. Three dosages of w-LDPE were incorporated with asphalt binder: 2%, 4%, and 6%. Marshall stability and flow test, indirect tensile strength, creep compliance, skid resistance, wheel track, Cantabro abrasion loss and tensile strength ratio tests were carried out on both control and modified asphalt mixes to achieve the aim of the study. The results show a substantial enhancement in the performance of TAO modified with w-LDPE when compared to the control mix. The pre-eminent improvement was obtained in the creep compliance test, in which the creep compliance value decreased by 83% compared to the control mixture when using 6% of w-LDPE. This study indicated that using waste material is an effective method of asphalt modification that also contributes to promoting environmental sustainability.

Oscillatory Microrheology, Creep Compliance and Stress Relaxation of Biological Cells Reveal Strong Correlations as Probed by Atomic Force Microscopy

The mechanical properties of cells are important for many biological processes, including wound healing, cancers, and embryogenesis. Currently, our understanding of cell mechanical properties remains incomplete. Different techniques have been used to probe different aspects of the mechanical properties of cells, among them microplate rheology, optical tweezers, micropipette aspiration, and magnetic twisting cytometry. These techniques have given rise to different theoretical descriptions, reaching from simple Kelvin-Voigt or Maxwell models to fractional such as power law models, and their combinations. Atomic force microscopy (AFM) is a flexible technique that enables global and local probing of adherent cells. Here, using an AFM, we indented single retinal pigmented epithelium cells adhering to the bottom of a culture dish. The indentation was performed at two locations: above the nucleus, and towards the periphery of the cell. We applied creep compliance, stress relaxation, and oscillatory rheological tests to wild type and drug modified cells. Considering known fractional and semi-fractional descriptions, we found the extracted parameters to correlate. Moreover, the Young’s modulus as obtained from the initial indentation strongly correlated with all of the parameters from the applied power-law descriptions. Our study shows that the results from different rheological tests are directly comparable. This can be used in the future, for example, to reduce the number of measurements in planned experiments. Apparently, under these experimental conditions, the cells possess a limited number of degrees of freedom as their rheological properties change.

Assessment of performance of hot mix asphalt contained various types of mineral fillers and newly polymer modified bitumen

This research aims to test various types of fillers such as (limestone dust, rice husk ash and ordinary Portland cement) and examine their influence on the performance of the asphalt mixture containing Polymer Modified Bitumen (PMB) binder. The research includes designing a regular reference mix for the purposes of comparison and designing several asphalt mixtures with various percentage (25, 50, 75 and 100) % RHA & OPC as mineral filler and PMB. Several tests were conducted to evaluated the mechanical characteristics and performance of Hot Mix Asphalt (HMA) such as Marshall stability, Indirect Tensile Strength (ITS), creep compliance and wheel track test. The results of investigation revealed that, the using of PMB significantly improved the mechanical characteristics and performance of HMA. The results of creep compliance demonstrated that the replacement of conventional MF with 50% RHA or 50 % OPC leads to decrease creep compliance values of HMA contained PMB by 68% and 64 % respectively compared with control mix. Also, for the same percentages of replacement and PMB, the rut depth values decreased by 64% and 48 % respectively compared with the reference mixture.

Evaluation of performance of hot mix asphalt contained various sizes of Reclaim asphalt pavement and polymer modified Bitumen

The present investigation intends to investigate the performance of Hot Mix Asphalt (HMA) included Reclaim Asphalt Pavement (RAP) and Polymer Modified Bitumen (PMB) binder prepared with Novolac (phenol–formaldehyde solid resin)polymer. In order to assess the mechanical properties and performance of HMA with various RAP contents, several laboratory tests such as Marshall tests, indirect tensile strength testing, moisture damage evaluation, creep compliance test, and wheel track test was performed. The substitution was conducted in two stages: the first stage includes replacing the coarse aggregate with RAP up to 40percent with an increment of 10percent and the second stage includes the substitution of fine aggregate with the same percentages. The PMB binder was prepared by testing several mixes with various percentages of Novolac and its cross-linking agent (Hexamine). The findings of experimental work showed that the use of PMB binder significantly improves the mechanical properties and performance of HMA. Also, it shows that the substitution of coarse aggregate with RAP produces a substantial improvement in mechanical properties and performance of HMA compared with the substitution of fine aggregate or with control mix.

Investigation the effect of newly used polymer modified bitumen on the performance of hot mix asphalt containing reclaimed asphalt pavement

The current research focuses on investigating the effect of using reclaimed asphalt pavement (RAP) on performance of hot mix asphalt (HMA) prepared with polymer modified bitumen (PMB) binder. This PMB used for the first time with HMA contained RAP. The mechanical properties and performance of HMA were assessed using several standard tests including Marshall, indirect tensile strength, creep compliance, and wheel track test. The RAP replacement was conducted up to 70% of total aggregate in HMA with an increment of 10%. The results of investigation showed, that the use of PMB binder prepared by addition novolac (phenol formaldehyde solid resin) and hexamine to conventional bitumen, significantly improved the performance of HMA contained RAP. Also, the optimum percentage of RAP replacement was found to be 50% of total aggregate in HMA. For this level of replacement, the rut depth reduced up to 38% of its original value.

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.

Evaluating the mechanical properties of thin asphalt overlay incorporating reed ash

Thin Asphalt Overlay (TAO) is a preservation maintenance technique that has been shown to overcome shortcomings in the functional properties of surface pavement layers. Although TAO is not a structural layer, its application sustains the pavement’s structural strength and increases its lifespan, which is a valuable effect for the paving industry. Due to recent realisation of the limits of natural resources and the high cost of raw materials, the paving industry has also developed a secondary target of incorporating waste materials as an alternative to conventional raw materials, both to reduce environmental pollution and minimise costs, in such applications. This study focuses on evaluating the effect of using reed ash (RA) in this manner on the mechanical properties of TAO. The control TAO mixture was densely graded, with a 9.5 mm nominal maximum aggregate size (NMAS) utilising a 40/50 asphalt binder grade. Three percentages of RA were incorporated, 6%, 12% and 18%, to produce modified asphalt binder. To verify the effect of this material on cracking behaviours, resistance to permanent deformation of TAO, indirect tensile strength, creep compliance, and wheel track tests were carried out on both control and modified asphalt mixtures. The results showed a significant enhancement in the performance of TAO modified with 6% RA as compared to the control mixture, although the very high dosage of 18% reduced the performance of the relevant TAO mixtures. This study thus indicates that using this waste material can offer an alternative solution for asphalt cement modification, increasing sustainability, if dosages are carefully controlled.

Environmental impact evaluation and long-term rutting resistance performance of warm mix asphalt technologies

The adoption of warm mix asphalt (WMA) technologies is well accepted due to its promising environmental benefits, however, their long-term field performance is not well understood. This study focused on the long-term rutting resistance of WMA and their companion hot mix asphalt (HMA) based on 83 field samples collected from 28 field projects across the United States covering four climate zones, and quantified environmental impacts for various WMA technologies as compared to HMA. Field cores were evaluated by dynamic modulus, creep compliance, and Hamburg wheel-tracking device tests. Asphalt binders extracted from field cores were evaluated by continuous performance grading (PG), multiple stress creep recovery (MSCR), and monotonic shear tests. The results showed that WMA binders exhibited similar rutting resistance compared with the HMA binders after long-term field aging. Existence of polymer in the asphalt binder was displayed through the plot of non-recoverable creep compliance and percent recovery. The long-term field aged polymer modified asphalt binders for WMA and HMA were comparable. The results also showed that the CO2 reduction by using WMA ranged from 89.09% to 42.79% depending on WMA type. On average, the CO2 emission was reduced to 66.89% by using WMA technologies. Overall, environmental impact analysis and long-term field performance results validated the confident use of WMA technologies.

Physical and Tribological Properties Degradation of Silicone Rubber Using Jatropha Biolubricant

ABSTRACT This article aims to investigate the degradation of physical and tribological properties (friction coefficients and wear resistance) of a dynamic sealing material (silicone rubber [VMQ]) exposed to Jatropha oil (JO), engine mineral oil (EMO), and a blend (B20; 80% EMO–20% JO), separately. JO has demonstrated better lubricating properties than EMO in various mechanical applications; however, the degradation of elastomers by using this oil has not been studied yet, nor have its effect on their tribological properties. The physical degradation was evaluated by conducting static immersion tests (670 h at 25 °C) based on ASTM-D471 and ASTM-D7216 methods. Hence, the changes in mass, volume, tensile and tear strengths, and hardness of VMQ were measured. In addition, creep compliance tests were conducted to determine the changes in viscoelastic properties and the changes in morphology and topography were measured by scanning electron microscopy (SEM) and optical profilometry, respectively. In addition, the compositional changes were determined by Fourier transform infrared (FTIR) analyses to complement the degradation examination. Changes in the friction coefficients were determined by ball-on-disk tests and changes in wear resistance were obtained by accelerated wear tests (microabrasion tests). Finally, VMQ exhibited no significant physical and compositional degradation due to immersion in the three lubricants. However, considerable changes in the friction coefficients and wear resistance were observed; the change in the friction coefficients was minimal using JO. In addition, the coefficients using JO were 50% lower than those for EMO and the changes in wear resistance were lowest after immersion in JO.

Influence of material heterogeneity in the fracture of asphalt mixtures

ABSTRACTThis work numerically evaluates the role of material heterogeneity in the variability of fracture processes in Hot Mix Asphalt (HMA) materials. Specifically, the paper focuses on the heterogeneity induced by the spatial air void distribution within HMA specimens, and it uses a fracture test configuration to assess the differences produced by these distributions in the fracture response of the mixtures. The work initiated with an experimental stage that provided fracture, creep compliance and indirect tensile strength (IDT) test results and data on the heterogeneous distribution of air voids (AV) in HMA specimens. The outcome from this phase revealed that the air void content in HMA specimens significantly impacted the viscoelastic, tensile resistance and fracture response of the material. This stage also provided information on the typical internal distribution of AV within cylindrical HMA testing specimens. These experimental results were used in the development of computational Finite Element (FE) models that used the geometrical configuration of the semi-circular bending (SCB) test, and that incorporated cohesive surface contacts and stochastic Random Fields (RF) techniques. The cohesive contacts were used to simulate fracture within the computational specimens, while RF theory was used to indirectly account for the non-uniform spatial distributions of the air void phase and of the mechanical- and fracture-related material properties within the specimens. The numerical results suggest that HMA heterogeneity due to non-uniform air void distributions accounts for an important portion of the variability associated with fracture processes in HMA materials.

Testing protocol to obtain failure properties of asphalt binders at low temperature using creep compliance and stress-controlled strength test

Good fracture properties are an essential requirement for asphalt materials used in the construction of pavements in cold regions. For asphalt binder, two instruments were developed during SHRP research effort to investigate the low-temperature behaviour of these materials: bending beam rheometer (BBR) and direct tension tester (DTT). These two devices are used to obtain the performance grade (PG) of asphalt binders in the US. The DTT is expensive and the results are less repeatable due to a complex sample preparation and difficult-to-achieve strain-controlled loading. For these reasons, many agencies do not use DTT when selecting asphalt binders, and rely entirely on the creep properties obtained with the BBR testing method. In this paper, a modified BBR is used to perform three-point bending strength tests on asphalt binder beams at low temperature, with the final goal of developing a specification for binder selection, similar to the current PG specification. BBR strength and DTT tests are first performed on a common set of binders, and the results are compared using size effect theory. Then, additional tests are performed and a simple and practical strength test procedure based on BBR creep data and on BBR strength data obtained under constant loading rate is proposed.

Smart viscoelastic and self-healing characteristics of graphene nano-gels

Readily synthesizable nano-graphene and poly ethylene glycol based stable gels have been synthesized employing an easy refluxing method, and exhaustive rheological and viscoelastic characterizations have been performed to understand the nature of such complex gel systems. The gels exhibit shear thinning response with pronounced yield stress values which is indicative of a microstructure, where the graphene nanoflakes intercalate (possible due to the refluxing) with the polymer chains and form a pseudo spring damper network. Experimentations on the thixotropic behavior of the gels indicate that the presence of the G nanoflakes leads to immensely augmented structural stability capable of withstanding severe impact shears. Further information about the localized interactions of the G nanoflakes with the polymer chains is revealed from the amplitude and frequency sweep analyses in both linear and non-linear viscoelastic regimes. Massively enhanced cross over amplitude values are recorded and several smart effects such as enhanced elastic behavior at increasing forcing frequencies are registered. Structural resonance induced disruption of the elastic behavior is observed for the gels for a given range of frequency and the proposition of resonance has been justified mathematically. It is observed that, post this resonance bandwidth, the gels are able to self-heal and regain their original elastic behavior back without any external intervention. More detailed information on the viscoelastic nature of the gels has been obtained from creep and recovery compliance tests and justifications for the spring damper microstructure has been obtained. Smart features such as enhanced stress relaxation behavior with increasing strain have been observed and the same explained, based on the proposed microstructure. The viscoelastic response of the gels has been mathematically modeled and it has been revealed that such complex gels can be accommodated as modified Burger's viscoelastic systems with predominant elastic/plastic behavior. The present gels show promise in microscale actuators, vibration isolation, and damping in devices and prosthetics, as active fluids in automotive suspensions, controlled motion arrestors, and so on.

Influence of the Volume Fraction, Size and Surface Coating of Hard Spheres on the Microstructure and Rheological Properties of Model Mozzarella Cheese

This study investigated the influence of model filler particles (glass beads) on the microstructure and rheological properties of Mozzarella cheese. Model Mozzarella cheese composites with increasing volume fractions of glass beads of various sizes and surface properties were processed in a Rapid Visco Analyser (RVA). Confocal laser scanning microscope images showed that all the hard spheres were dispersed in the protein phase, rather than in the fat phase. Dynamic oscillatory rheology revealed that the volume fraction of the glass beads had a major influence on the complex modulus (G*) of the cheese composites, whereas the size and the coating of the glass beads had no influence. However, the zero shear viscosity (η 0), measured using the creep-compliance test, was affected by both the size and the volume fraction of the glass beads. This indicated that there were some interactions between the glass beads and the cheese matrix. Filler–matrix interactions played a major role in the fracture properties of the cheese composites. The fracture stress (σ f ) was highly dependent on the coating and the size of the glass beads. Simple equations for filled gels from the literature fitted well with the experimental results and could be successfully applied for future predictions. According to this study, the transfer of knowledge from filled polymer composites to model cheese appears relevant. This can provide a good basis for designing new dairy product structures.

Comparison of laboratory performance of asphalt mixes containing different proportions of RAS and RAP

Despite environmental and economic advantages associated with incorporating recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) in hot-mix asphalt (HMA), concerns focus on fatigue and low-temperature cracking potential of pavements containing RAS and RAP. This study was undertaken to identify the areas in need for research through conducting a national survey among departments of transportation and to evaluate the effects of RAS and RAP on fatigue, low-temperature cracking and stiffness of HMA. National survey results indicated that while the fatigue cracking is the major concern when RAS and/or RAP are used in mixes, no specific test is recommended for fatigue evaluation of these mixes at the mix design stage. It was found that, fatigue life of mixes with a non-polymer-modified binder containing a blend of 5% RAS and 5% RAP led to the maximum increase in fatigue life. However, incorporation of 6% RAS decreased the fatigue life of mixes, when compared with virgin mix. Also, it was found that addition of RAS and/or RAP to asphalt mixes increased their dynamic moduli which may result in a better rutting performance. From creep compliance test results it was concluded that use of RAS and/or RAP may lead to a higher low-temperature cracking potential when compared with the virgin mixes. Findings of this study can be used to develop/update guidelines/special provisions for design of HMA containing RAS and RAP.