Recycled Asphalt Pavement Mixtures Research Articles

Investigating the Field Performance of High- Recycled Asphalt Pavement Mixtures with Bio-oil Recycling Agent

The use of recycling agents (RAs), along with recycled asphalt pavement (RAP) modifiers, has been increasing over recent years. However, the field performance of asphalt mixtures containing high-RAP materials modified with RAs has raised some concerns with the long-term performance of RAs. This study evaluated the laboratory and field performance of high-RAP mixtures with and without bio-oil RA. Five sets of plant-produced specimens were collected: 1) plant-produced laboratory-compacted; 2) field-compacted, cored after paving; 3) field-compacted, cored after one year; 4) field-compacted, cored after two years; and 5) field-compacted, cored after three years. The Hamburg wheel tracking test was used to evaluate the specimens’ resistance to rutting and moisture damage, while the semi-circular bending test was performed to examine the cracking resistance of specimens. The laboratory test results showed that using the bio-oil RA increased cracking resistance and decreased rutting and moisture damage resistance of the RAP-blended mixtures. However, after one and two years of exposure to environmental conditions and traffic loads, the specimens modified by RA showed better moisture damage and rutting resistance. The cracking resistance of laboratory and field-aged specimens, estimated by flexibility index, implied that the bio-oil RA used in this study could not provide long-term improvement for the RAP-blended mixtures. Field observations suggest that using bio-oil RA may have resulted in inferior pavement performance compared with the control section. However, drawing conclusions based on just two years of data might yield inconclusive results. Longer field performance monitoring is, therefore, warranted for a more comprehensive analysis.

Sustainable Use of Recycled Asphalt Pavement in Soil Stabilization

This study addresses unused recycled asphalt pavement (RAP) incorporated into sedimentary soil from the Guabirotuba Formation in Curitiba, Southern Brazil. Different percentages of RAP, ranging from 0% to 80% by weight, were mixed with the pure soil, with and without the addition of pozzolanic Portland cement. Tests were conducted to evaluate the mixtures' compaction properties, mechanical strength, and expansion after curing for up to 28 days. The results showed that adding RAP improved the mixtures' unconfined compressive strength (qu) and splitting tensile strength (qt). Up to 60% RAP, the qu increased by 260 kPa, and the qt increased by 340 kPa compared to the pure soil. The California Bearing Ratio (CBR) tests demonstrated an 18.62% improvement when 80% RAP was added to the untreated soil. In addition, the RAP also reduced the expansion of the compacted blends, with values decreasing from 1.19% to 0.88% with 80% RAP replacement. The expansion value was further reduced to 0.86% when the cement was added. The cement-soil-RAP compacted blends showed suitability for subgrade reinforcement, meeting the criteria of expansion <1% and CBR> 2%. Additionally, 3% cement and 40% RAP mixtures were suitable as a sub-base layer, with expansion <1% and CBR > 20%. The results provide valuable insights into utilizing RAP as an alternative material in soil improvement techniques employing the novelty porosity-to-cement index. Doi: 10.28991/CEJ-2023-09-09-016 Full Text: PDF

Feasibility and Sustainable Performance of RAP Mixtures with Low-Viscosity Binder and Castor Wax–Corn Oil Rejuvenators

The utilization of Recycled Asphalt Pavement (RAP) mixtures in pavement construction is an environmentally friendly approach that promotes sustainable development by reducing energy consumption and material waste. However, the high cost of conventional rejuvenators limits the widespread use of RAP mixtures. In this study, a novel approach is proposed to enhance the performance of RAP mixtures by incorporating a combination of high-penetration asphalt binder and rejuvenators, namely Castor wax and Corn oil. The newly developed rejuvenator consists of 8.5% Castor wax oil, 3% Corn oil, 3% fatty acid amine surfactant, 0.2% additive, and 79.8% water. The test results demonstrate that the modified mixture exhibits superior properties compared with conventional RAP mixtures. The Multiple Stress Creep Recovery test results showed a 20% reduction in cumulative strain rate for the RAP mixture with the new rejuvenators compared with that for the conventional ones. Furthermore, the Tensile Strength Ratio test indicated a notable 9.47% improvement in the rejuvenated RAP mixture’s resistance to moisture-induced damage compared with the conventional mixture. Evaluation of viscoelastic behaviors revealed a slight reduction in dynamic modulus for the rejuvenated binder, but a significant improvement in elastic behavior. In terms of rutting resistance, the Hamburg wheel tracking rut depths of the rejuvenated binder were significantly lower, representing reductions of 21.83% for specific binder compositions. Additionally, the absence of the stripping phenomenon further confirmed the superior moisture resistance of the modified mixture. The rejuvenated binder exhibited a remarkable 28.55% increase in fatigue load cycles to failure compared with the reference RAP binder, demonstrating substantial resistance to fatigue cracking. These quantitative comparisons not only confirm the superior performance of the modified mixture over conventional RAP mixtures, but also highlight the potential cost savings achieved through the utilization of Castor wax and Corn oil rejuvenators.

Cracking performance evaluation and modelling of RAP mixtures containing different recycled materials using deep neural network model

This study evaluates the cracking resistance of recycled asphalt pavement (RAP) mixtures including waste engine oil (WEO), crumb rubber (CR), and steel slag aggregates using the Illinois flexibility index test (I-FIT). Performance indices, derived from both this study and another, were predicted by comparing deep neural network (DNN), linear, and polynomial regression models via a k-fold cross-validation process. I-FIT test results demonstrated that WEO, steel slag aggregates, and specific CR proportions enhance cracking resistance while RAP utilisation decreased it. In terms of modelling, it was found that the most appropriate prediction model for the dataset structure of this study is the deep neural network model. The DNN model sensitivity analysis identified WEO as key for high and intermediate temperature (I-FIT) performance. Meanwhile, CR significantly impacted intermediate temperatures (IDEAL-CT), while RAP influenced moisture susceptibility. This model proves reliable and efficient, suggesting its potential for predicting the performance of recycled mixtures.

Potential Use of Recycled Asphalt Pavement (RAP) in Hot MixAsphalt

The objective of the present paper is to examine the effect of Recycled Asphalt Pavement (RAP) on marshall properties and indirect tensile strength of HMA through experimental investigation. A mixture with 0% RAP was used as a control mix to evaluate the properties of mixes with 5%, 10%, and 15% RAP. One type of RAP was brought from Bab Al-moadam’s road in Baghdad for this purpose. The experimental testing program included Marshall and Indirect Tensile Strength tests. The results indicated that the bulk density, flow and VFA increase with the increasing of the percentage of RAP, while increasing in RAP results decreases in VTM and VMA values. Furthermore, the stability is changed from 10.1 kN for the control mix to12, 13.6 and 11.7 kN for mixes with 5%, 10% and 15% RAP respectively. The results reveal that the inclusion of RAP into HMA mixtures increases the indirect tensile strength and decreases the values of ITS with the increasing of the test temperature. The results also indicated that increasing the percentage of RAP produces an increasing in temperature susceptibility value. The results of marshall properties and IDT test indicate that the amount of new binder that needs to be added to the RAP mixture can be reduced without significant effects on the quality of the produced mix

Laboratory and Field Testbed Evaluation of the Performance of Recycled Asphalt Mixture Using High-Penetration Asphalt

The application of recycled asphalt pavement (RAP) on a large scale is highly promoted to meet the current needs of carbon neutrality and sustainable development purposes. However, a majority of RAP mixture productions are currently relying on the restoring effects provided by the rejuvenators. Therefore, the study focuses on the feasibility of using high penetration asphalt binder (HPAB) in RAP mixture as a replacement for conventional rejuvenators. In this study, a recycled asphalt pavement mixture containing HPAB (RAP-H) was developed to resolve the cracking issue of RAP pavement in winter seasons owing to the rigid behavior of aged binders. To verify the applicability of the RAP-H mixture, the results of the quality standard test and mechanical performance test were compared with the reference RAP mixture having rejuvenator (RAP-R). Through the fatigue cracking test, by using Overlay Tester (OT) device, it was found that all specimens did not reach 93% load reduction after 1000 OT cycles, indicating a satisfied stress-bearing capacity. Additionally, the highest dynamic modulus of 27,275 MPa was found in the modified HPAB mixture, and this result is 4.4% higher than that of the reference mix. In the full-scale testbed, the long-term field applicability of the proposed approach was verified through field test construction. The measurement in practice reveals that the elastic modulus of RAP-H back-calculated from the FWD (Falling Weight Deflectometer) test is increased by more than 50% compared to RAP-R, which resulted in excellent performance characteristics of the HPAB pavement layer. In addition to the efficiency in the surface layer, an improved elastic modulus of the sub-base and subgrade layers in the HPAB section was found to be at 28.6% and 19.5%, respectively, compared to the RAP-R mix. In general, the performance of RAP-H satisfied all of the domestic and international quality and performance standards. The field test results confirmed the possibility of field application by showing performance higher than conventional recycled asphalt pavement.

Rice husk ash as an alternative soluble silica source for alkali-activated metakaolin systems applied to recycled asphalt pavement stabilization

Alkali-activated binders have been shown as a viable alternative do ordinary Portland cement. However, the development of lower carbon emission activators for this process is still a research-gap. The goal of this research was to analyze the stabilization of recycled asphalt pavement (RAP) mixtures with a metakaolin-based binder, alkali-activated by rice husk ash synthetized sodium silicate. Compaction, unconfined compressive strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests were conducted in stabilized RAP mixtures, submitted to different curing periods and temperatures. Also, results were correlated with the porosity/binder content index. Compaction results showed a reduction in dry unit weight as the RAP content increased for non-stabilized mixtures and a non-linear behavior for stabilized ones. For the UCS tests, the increase in binder content led to an increase in strength for all mixtures. High curing temperatures prevented the efflorescence phenomenon, however reduced strength due to crack formation. XRD analyzes showed the formation of minerals rich in silica and alumina, indicating the formation of geopolymerization products. Finally, the porosity/binder index was shown to be a viable dosage method to predict the strength of stabilized RAP mixtures.

Evaluating effect of rejuvenators on high RAP mixtures through laboratory performance tests and construction of field test sections

Although thirty-one US states utilize 20% recycled asphalt pavement (RAP) or greater in asphalt pavements, Iowa limits the usage of RAP to 20%, and 30% with a softer binder in the surface layer. Because high RAP mixtures can cause asphalt mixtures to stiffen due to the hardening effect of the aged binder, rejuvenators should be used to improve the cracking resistance of high RAP mixtures. Due to increasing demand for sustainable, and environmentally materials, two bio-based rejuvenators, Invigorate and Tufftreck, were considered for this study. To evaluate effect of rejuvenators on high RAP mixtures, field test sections were constructed in Cerro Gordo County, Iowa, 2020. The field test consists of six different sections with two rejuvenators and three different RAP contents of 22%, 34% and 45%. Performance grading (PG) of asphalt with rejuvenators adopted for the field test sections lowered both high and low temperatures of the virgin asphalt. Based on the eight cores for each test section, all six test sections with or without rejuvenators exhibited field densities between 93.6% and 95.2%, exceeding the minimum requirement of 93%. First, loose field samples were compacted at the laboratory for Hamburg wheel tracking test, semi-circular bending test, and disc-shaped compact tension test. Second, the laboratory test results were analyzed to determine if rejuvenators were effective in mitigating rutting, moisture damage and cracking. Based on the analysis of limited laboratory test results, Tufftrek was effective in lowering rutting and moisture damage whereas, for minimizing cracking, using a soft binder was most effective. Third, a condition survey on test sections was performed in one year after construction. Based on a condition survey of six test sections, no rutting was observed from all test sections, but some low-severity cracks were observed in sections without rejuvenators. Based on the limited condition survey results, it can be concluded that rejuvenators were effective in delaying the initiation of cracking.

Mechanical Properties of Cold Mix Asphalt (CMA) Mixed with Recycled Asphalt Pavement

From the perspective of sustainability and environmental concerns, the use of cold-mix asphalt (CMA) and recycled asphalt pavement (RAP) is more advantageous than the use of hot mix asphalt (HMA) and warm mix asphalt (WMA). Some researchers used a mixture of CMA and RAP to improve the mechanical properties of pavement and made it more economical. However, only a few studies have focused on using a high content of RAP—particularly 100% RAP—as the virgin aggregate. Therefore, this study aims to analyse cold-mix asphalt (CMA) using 100% recycled asphalt pavement (RAP) instead of virgin aggregate raw materials and to determine the best mixture for the production of environmentally friendly asphalt. It is necessary to investigate the performance of CMA mixed with RAP in terms of the resilient modulus, indirect tensile strength, fatigue and rutting resistance. In this study, the percentage of bitumen emulsions added is 2%, 2.5%, 3%, 3.5%, and 4%, along with 100% RAP material. The results indicate that the fatigue life of the RAP mixture increased by 49.34% with the addition of bitumen emulsion (BE) from 2% to 4%, while the wheel tracking test experienced a decrease in rutting depth along with an increase in BE dose of 4%, which was 9 mm. The mixture containing 4% asphalt emulsion has the best performance. The results suggested that increasing the BE dosage increases the resistance against rutting and fatigue.

Effect of glass fibers and waste engine oil on the properties of RAP asphalt concretes

ABSTRACT The increase in the cost of virgin materials and the environmental sustainability have contributed to increasing the incentive to use asphalt mixtures containing high percentages of recycled asphalt pavement (RAP). However, the use of high percentage of RAP into virgin asphalt mixture could negatively affect the performance of some properties of asphalt mixtures. Thus, using an appropriate additive to offset the negative effect of RAP could lead to an increase in the amount of RAP in asphalt mixtures. Therefore, this study aimed to evaluate the effect of using glass fiber (GF) with different contents (0.0%, 0.1%, 0.2%, and 0.3%) as an additive on the performance of asphalt mixtures containing RAP materials (60%, 70%, and 80%) and rejuvenated with waste engine oil (WEO) i.e., 6%, 9%, and 12%. The performance of RAP mixtures incorporating GF was evaluated using the indirect tensile strength test (ITS), resilient modulus test, and moisture susceptibility test. Hamburg wheel track testing was done to evaluate the rutting performance of the 70% RAP mixture. The results showed that the GF modification enhanced the ITS, rutting resistance, moisture susceptibility, and resilient modulus of rejuvenated mixtures. It was also found that the GF content of 0.2% was the optimum.

Investigation on Hamburg Wheel-Tracking Device Stripping Performance Properties of Recycled Hot-Mix Asphalt Mixtures.

Moisture damage in hot mix asphalt pavements is a periodic but persistent problem nowadays, even though laboratory testing is performed to identify different moisture-susceptible mixtures. In this study, a Hamburg Wheel Tracking device (HWTD) was used for rutting tests which were conducted on control and a high percentage of recycled asphalt pavement (RAP), i.e., 30%, 50% and 100% of virgin mixtures, under air dry and water-immersed conditions. Similarly, the extracted bitumen from RAP was tested for binder physical properties. Results showed that the asphalt mixtures containing RAP have less rut depth as compared to the control mix both in air dry and immersion conditions and hence showed better anti-rutting properties and moisture stability. Stripping performance of control and RAP containing mixtures was also checked, concluding that the RAP mixture was greatly dependent on the interaction between the binder (virgin plus aged) and aggregates.

Self-Healing Analysis of Half-Warm Asphalt Mixes Containing Electric Arc Furnace (EAF) Slag and Reclaimed Asphalt Pavement (RAP) using a Novel Thermomechanical Healing Treatment.

Nowadays, the self-healing of asphalt pavements promoted by microwave radiation heating energy is gaining attention and strength in the scientific community. However, most of these studies are only conceptual and, thus, remain shrouded in uncertainty regarding technology development, economy, and application effect. Therefore, there are several efforts underway to offer more effective assisted healing treatments that are capable of overcoming such uncertainties. This paper aims to assess and quantify the healing performance rates (HR) of half-warm recycled asphalt (HWRA) mixtures containing electric arc furnace (EAF) slag and total recycled asphalt pavement (RAP) rates. To this end, a novel assisted thermomechanical healing treatment (i.e., a recompaction-based technique and microwave heating energy) was put forward to promote the potential healing effect of this treatment on the mechanical properties of the asphalt mixtures. In order to do this, three microwave heating temperatures (25 °C, 60 °C, and 80 °C) and three mechanical recompaction levels (0, 25, and 50 gyrations) were selected. After that, the healing performance rates (%, HR) of the asphalt mixtures were calculated by repeated indirect tensile strength (ITS) and indirect tensile stiffness modulus (ITSM). The results indicated that the 8% EAF slag mixture was found to provide significant microwave heating energy savings by up to 69% compared with the benchmark 100% RAP mixture, and, at the same time, it experienced a remarkable stiffness recovery response of 140% of the initial mechanical properties. These findings encourage greater confidence in promoting this innovative thermomechanical-based healing treatment for in-situ surface course asphalt mixtures of road pavements.

Performance Evaluation for Rutting and Moisture damage of Hot Asphalt Mixtures using High Percentage of Recycled Asphalt Pavement Material

Recycled Asphalt Pavement (RAP) usage has increased a lot from the last two decades. World highway agencies are attempting to use higher quantities of RAP to cope up with not only economic and green environment but also to save natural resource and comparable or even better performing hot mix asphalt (HMA) mixtures. Continuous damages of flexible pavements like rutting, moisture damage and thermal cracking reduces the pavement performance as well as riding quality. Studies have shown that high amount of RAP mixtures has impact on the fatigue performance, stiffness and permanent rut deformation characteristics of hot mix asphalt. Therefore, this study was done by using experimental approach to check the rutting and moisture damages of RAP combined with HMA by using Hamburg Wheel-tracking Device (HWTD). The hot mix asphalt designs included a control or having mix with 0% RAP and six samples of HMA with 10%, 20%, 30%, 45%, 60% and 100% recycled asphalt mixture to get an optimum percentage on which performance testing was done, after finding out the corresponding volumetric properties of mixtures stability and flow parameters of RAP mixtures. In this research all tested mixtures with RAP showed better performance than the virgin mixes.

Field performance evaluation of asphalt mixtures containing high percentage of RAP using LTPP data

Recycled asphalt pavement (RAP) has been used in production of new mixtures for many decades and has become a common practice in highway agencies. However, concerns about field performance of RAP mixtures have been lingering on since the beginning of RAP usage. In this study, the field performance of RAP was verified through the Long-Term Pavement Performance (LTPP) program. Particularly, pavement overlays constructed with virgin asphalt and those constructed with a significant RAP percentage were examined and compared regarding their field performance. To achieve this goal, data from the Specific Pavement Study experiment 5 (SPS-5) of LTPP were retrieved and statistically analyzed for comparison. A total of eighteen projects comprised of 162 sections were collected. Various performance measures were incorporated, including alligator cracking, longitudinal cracking (wheel path and non-wheel path), transverse cracking, patching, potholes, rutting, roughness, and pavement surface deflections. In addition to the key variables used in the SPS-5 experiment (thickness, materials and pre-overlay treatment), the impacts of other important factors, including climatic conditions, initial surface condition and subgrade soil classification, were also investigated. Exploratory data analyses and logistic regression were used to compare the performance of RAP and virgin asphalt overlays. Results from the analysis results show that RAP had little effects on longitudinal cracking, transverse cracking, and roughness, but slightly increased the risk of fatigue cracking and weakened pavement structure. As expected, use of RAP was beneficial in reducing the rutting potential of thick overlays. For both RAP and virgin asphalt overlays, thicker overlays performed better than thinner ones in all performance measures except for rutting. Pre-overlay treatment methods and subgrade soil types were found to be critical factors affecting fatigue cracking and roughness. The initial surface condition also showed significant effects on pavement structural capacity and fatigue cracking over the long run.

Blending efficiency evaluation of plant asphalt mixtures using fluorescence microscopy

With the use of high percentage recycled asphalt pavement (RAP), there is an increasing concern over how much of the aged binder in RAP that can be blended into virgin binder. In this study, a laboratory procedure was proposed based on fluorescence microscopy for quantifying the mobilization rate of aged binder in plant-produced RAP mixtures. This procedure was derived from the mean gray value of an asphalt-coated aggregate particle. A linear blending chart was developed and used to relate aged binder content to the mean gray value of binder blend. The mobilization rate of aged binder was calculated on the basis of surface area proportion of aggregates with different size. Three types of asphalt mixtures, including one warm mix with foaming technology, two hot mixes with or without rejuvenator, were used to validate the proposed method. Results indicated that the mobilization rate varied by aggregate type (virgin or RAP). Compared with hot mix, warm mix with foaming technology showed a slightly higher mobilization rate.

Quantitative evaluation of blending and diffusion in high RAP and RAS mixtures

Due to variable aging of recycled asphalt pavement (RAP) and recycled asphalt shingle (RAS), the concerns arise over old-new binder blending during mixture production and subsequent diffusion process. In this study, a modified staged-extraction method was validated and employed to extract binder in approximately equal layers from retrieved virgin and RAP/RAS aggregates after mixing and subsequent diffusion treatment. Quantitative analysis was done on extracted binders in terms of large molecule size percentage LMS (%) from gel permeation chromatography (GPC). The results indicated that a well-blended binder film coated virgin aggregates from 50% RAP mix, while a non-homogeneous binder film was observed on RAP aggregates. The system of binder blend coating the virgin and RAP aggregates with un-mobilized RAP binder was validated. A possible composite binder system was found coating the virgin aggregates in 10% RAS mix. The diffusion study showed that within the mixture silo storage time, binder diffusion could be accomplished in both warm and hot mixes containing 50% RAP, indicating that binder homogeneity may not be an issue in high RAP mix. The binder diffusion in RAS mix was captured in a very slow rate. It was suggested that binder homogeneity can still be critical for high RAS mix.

Characterizing Compactability of High RAP and Warm Mix Asphalt Mixtures in the Superpave Gyratory Compactor.

Abstract Compactability of asphalt concrete mixtures is critical for successful long-term performance in the field. Laboratory samples are necessary for volumetric analysis and performance testing during the design process, so the ability to quantify compactability during specimen production in the lab would be highly beneficial. While there has been significant work in defining compaction characteristics of asphalt concrete, most of this work has revolved around traditional Hot Mix Asphalt (HMA), and little work has been done with Warm Mix Asphalt (WMA) or high percentage Recycled Asphalt Pavement (RAP) mixtures. This research examined HMA without RAP (HMA Virgin), HMA with 35 % RAP (HMA RAP), and two WMA technologies with 35 % RAP (WMA 1 and WMA 2). Four compactability metrics were evaluated, including number of gyrations to 92 % density (N92), Construction Densification Index (CDI), the Construction Force Index (CFI), and the newly introduced Normalized Shear Index (NSI). This research found that the WMA technologies improved the compactability of asphalt concrete, as did the addition of RAP. In general, the WMA 1 showed better compactability than WMA 2, but this could be partially attributed to a softer binder grade, higher asphalt binder content, and the potential for a tender mix, as indicated by the normalized shear curve. The HMA RAP mixture also had a higher asphalt binder content compared to HMA Virgin, which could have contributed to the improved compactability. The NSI metric consistently showed the lowest Coefficient of Variation (COV) values and has the potential to distinguish tender mixtures.

Characterization of Recycled Asphalt Pavement (RAP) for Use in Flexible Pavement

Due to economical reasons and the need for environmental conservatism, there has been an increasing shift towards the use of Recycled Asphalt Pavement (RAP) materials in the pavement construction industry. The majority of HMA mixtures in Egypt are produced only from virgin materials although there are about 4 million tons per year of reclaimed asphalt materials, due to continuous pavement milling or scraping processes, are not used. High durability potential usually implies that the mechanical behavior of the mixture will endure for a long service life. Now, flexible pavement, made of Hot-Mix Asphalt (HMA) with the addition of the reclaimed asphalt pavement granules in the central asphalt mixing plant, is increasingly used. The main objective of this paper is to investigate the use of a homogeneity reclaimed asphalt pavement in the pavement industry evaluating the effects of partial and total replacements of aggregates by RAP on the mechanical and durability performance of dense-graded HMA mixtures. The performance of RAP mixtures was evaluated through a series of laboratory tests including Marshall test, indirect tensile strength test, granule adhesion test and material test systems. A series of binder mixes containing varying percentages of RAP were designed and subjected to different moisture conditioning periods (1, 3 and 7 days) to investigate the moisture damage effect on RAP mixtures. The laboratory results indicated that when properly designed, the asphalt mixes with RAP especially at 50 to 100% replacement ratio provided better performance compared to those of new conventional HMA mixtures where they minimized the environmental impacts through the reduction of energy consumption, improved the mechanical properties, durability performance and also stripping resistance.

Compressibility of Recycled Materials for Use As Highway Embankment Fill

AbstractCompressibility of recycled materials including bottom ash (BA), foundry slag (FSG), foundry sand (FSD), recycled asphalt pavement (RAP), recycled pavement material (RPM), recycled concrete aggregate (RCA), and recycled asphalt shingle (RAS) mixed with glacial outwash sand (GOS) was evaluated using one-dimensional (1D) compression tests. Results showed that except RCA, compressibility of all the compacted recycled materials is higher than that of the compacted GOS. Different compression mechanisms were attributed to each recycled material depending on the type, composition, and morphological characteristics of the particles. Bituminous recycled materials including RAP, RPM, and RAS-GOS mixtures exhibited relatively higher compressibility compared with nonbituminous recycled materials. At a constant vertical effective stress (σv′), compression of the recycled materials increased over time with strain rates that are higher for bituminous recycled materials compared to nonbituminous recycled material...

Strategies for Incorporating Higher Recycled Asphalt Pavement Percentages

Because there is a greater emphasis on promoting sustainable materials within transportation infrastructure, state agencies in the U.S. Northeast are investigating different strategies that will enable the use of higher percentages of recycled asphalt pavement (RAP) while not sacrificing the performance of the asphalt pavement. In particular, most state agencies in the Northeast are concerned with the fatigue and thermal cracking performance, as well as the general workability and handling of the higher-RAP-content asphalt mixtures when greater percentages are used. In conjunction with the Transportation Pooled Fund study TPF 5(230), Evaluation of Plant-Produced High-Percentage RAP Mixtures in the Northeast, three potential strategies were evaluated for incorporating higher RAP contents: using a softer asphalt binder grade to offset the stiff RAP asphalt binder, limiting the amount of RAP binder credited to the total asphalt content of the asphalt mixture, and using a performance-based specification that the high-RAP content mixture must meet for acceptance. The findings of the strategies through plant-produced mixtures, as well as case studies evaluated in detail through laboratory test procedures and analysis, are summarized. The project trials and results shown will, it is hoped, provide guidance to other agencies looking to increase the percentage of RAP used in their asphalt mixtures.