Recycled Asphalt Pavement Mixtures Research Articles

Microstructural analysis of asphalt mixtures using digital image processing techniques

In this paper, the internal microstructure of asphalt mixture is analyzed through digital image processing (DIP) of two-dimensional asphalt mixture images. A set of 12 mixtures prepared with two binders, two air voids percentages, and different recycled asphalt pavement (RAP) contents is used. First, small asphalt mixture beams of the same size of bending beam rheometer specimens are prepared for the images acquisition. Then, based on mixture volumetric properties, a three-phase material model is obtained. Finally, 2- and 3-point correlation functions of the material phases are numerically evaluated. No significant differences were observed in the microstructure and spatial distributions of aggregates, asphalt mastic, and air voids for asphalt mixtures containing up to 40% of RAP. However, an increase in auto correlation length (ACL) was found for RAP mixtures in comparison with the conventional mixtures.

Development of Rutting Model for Unbound Aggregates Containing Recycled Asphalt Pavement

Abstract The use of recycled materials for construction is beneficial to both the environment and the economy. Recycled asphalt pavement (RAP) is one of the most commonly used recycled materials. Different state departments of transportation allow the use of RAP in base materials using various RAP percentages. Unlike conventional crushed aggregate, RAP exhibits a high resilient modulus, but also low resistance to permanent deformation, which contradicts the relationship between the modulus and permanent deformation in the permanent deformation model for unbound materials found in the mechanistic-empirical pavement design guide (MEPDG). In this study, repeated triaxial tests are conducted on samples containing different percentages of RAP and crushed aggregate. Permanent deformation prediction models for granular base course materials, introduced in 1989 by Tseng and Lytton, are modified by adding the RAP percentage as a parameter for base course materials containing RAP. The results indicate that the proposed model accounts for the effects of RAP reasonably well. Further studies are needed to validate the new rutting model by including different virgin aggregates and RAP mixtures under various testing conditions.

Stiffness of High-RAP Asphalt Mixtures: Virginia’s Experience

In the year 2006, the price of asphalt binders in the United States increased by almost 50% over the 2005 prices. The use of higher recycled asphalt pavement (RAP) percentages with locally available binders was adopted as an approach to reduce the demand on specialty more expensive virgin binder and virgin aggregates in Virginia. The purpose of this study was to investigate concerns that the performance of these higher RAP mixtures could be compromised because of excessive mixture stiffening due to the aged RAP binder. The results indicated that measured binder stiffnesses of high-RAP mixtures are not significantly affected by RAP amount, high temperature true grade of high-RAP mixtures averaged only approximately 2.0°C above that of base virgin binder, and that the correlation between binder stiffness and flow number for the selected high-RAP mixtures considered was good. The study concludes that the addition of higher amounts of RAP to asphalt-concrete mixtures currently produced in Virginia has not resulted in excessively stiffened mixtures as previously thought; the stiffnesses of high-RAP mixtures are primarily governed by the virgin binder stiffness.

Methodologies for Estimating Effective Performance Grade of Asphalt Binders in Mixtures with High Recycled Asphalt Pavement Content

In 2009, hot-mix asphalt pavement sections containing 0%, 15%, and 50% recycled asphalt pavement (RAP) were built in a collaborative effort between Manitoba Infrastructure and Transportation and the Asphalt Research Consortium. Two types of 50% RAP mixtures were evaluated: one with no grade change in asphalt binder (PG 58-28) from mixtures with lower RAP content and one with a grade change in asphalt binder (PG 52-34). The following methodologies were used to determine the effective binder properties of the evaluated field-produced mixtures: grading of the recovered binders, blending chart process, mortar procedure, and backcalculation of binder properties from the measured dynamic modulus of mixtures with the Hirsch model and the modified Huet–Sayegh model. Overall, good correlations were observed between the estimated critical temperatures from the blending chart process and the measured ones from the recovered asphalt binders. Of the various evaluated methods, the mortar procedure provided promising results when used to estimate the mixture binder properties at critical pavement temperatures. The findings from the mortar procedure were consistent with the mixtures' resistance to thermal cracking and their current field performance. The procedure indicated that a partial blending was occurring between the virgin and RAP binders of the evaluated mixtures. Although some difficulties arose with the use of the Hirsch model, the backcalculated binder shear moduli were reasonable. The modified Huet–Sayegh model requires further evaluation to assess the true relationship between the characteristic times of the binders and mixtures.

Effects of Recycled Asphalt Pavement Amounts on Low-Temperature Cracking Performance of Asphalt Mixtures Using Acoustic Emissions

Significant increases in the cost of asphalt paving and increased awareness of the need for sustainable infrastructure in recent years have in turn increased the use of recycled asphalt pavement (RAP) in the manufacture of hot-mix asphalt (HMA). The use of RAP reduces the overall cost of HMA and provides significant environmental benefits. Experience has shown, however, that the addition of RAP to HMA can have a negative effect on the low-temperature fracture characteristics of the pavement. The purpose of this study was to determine the effects of RAP amounts on the low-temperature cracking performance of asphalt mixtures. Different percentages of RAP material, ranging from 0% to 50%, were studied. The embrittlement temperature of mixtures was determined with the use of an acoustic emissions technique. The disk-shaped compact tension [DC(T)] test was used to determine the fracture energy of asphalt mixtures. DC(T) fracture tests were conducted on two control mixtures with no RAP and mixtures that contained 10%, 20%, 30%, 40%, and 50% RAP. Both control and RAP mixtures were manufactured with PG 64-22 and PG 58-28 as the virgin binders, which brought the total number of mixtures tested to 12. In addition to DC(T) fracture testing, indirect tensile testing was conducted on HMA specimens that contained 20% and 40% RAP. Test results clearly indicated the effects of the presence of RAP materials on the low-temperature performance of mixtures. This study demonstrates the benefit of performing fracture tests before RAP is added to the asphalt mixture, and it demonstrates the use of an acoustic emissions-based testing procedure to screen mixtures susceptible to cracking at low temperatures.

Evaluating Recycled Asphalt Pavement Mixtures with Mechanistic–Empirical Pavement Design Guide Level 3 Analysis

The main objective of this study is to assess the sensitivity of the predicted performance of recycled asphalt pavement (RAP) mixtures to the assumed binder grade. That is achieved with the Mechanistic–Empirical Pavement Design Guide (MEPDG) software to predict the performance of a specific flexible pavement structure with a RAP-modified hot-mix asphalt surface layer. Different design runs are conducted for which all the pavement properties and conditions are held constant except the properties of the surface layer. Specifically, a near-full factorial experiment is performed in which RAP content and effective binder PG grade are the main variables. Comparison of the predicted performance of the various runs reveals important findings on the extent and manner in which those two properties affect pavement distresses and performance. The influence of the assumed PG binder grade on the RAP mixtures, particularly the high-temperature grade, has a significant effect on the predicted amount of thermal cracking and rutting for the given structure. The predicted performance is especially sensitive to changes in assumed PG grade in the range in which the true effective PG grade is expected to fall; the difference from one PG grade to another can be the difference between a well-performing mixture and one that requires redesign. Results emphasize the importance of determining the effective binder grade of RAP mixtures. An added benefit of conducting the numerous MEPDG software runs is the identification of issues that need to be considered when incorporating RAP mixtures in pavement design using the software.

Evaluating Recycled Asphalt Pavement Mixtures with Mechanistic-Empirical Pavement Design Guide Level 3 Analysis

The main objective of this study is to assess the sensitivity of the predicted performance of recycled asphalt pavement (RAP) mixtures to the assumed binder grade. That is achieved with the Mechanistic-Empirical Pavement Design Guide (MEPDG) software to predict the performance of a specific flexible pavement structure with a RAP-modified hot-mix asphalt surface layer. Different design runs are conducted for which all the pavement properties and conditions are held constant except the properties of the surface layer. Specifically, a near-full factorial experiment is performed in which RAP content and effective binder PG grade are the main variables. Comparison of the predicted performance of the various runs reveals important findings on the extent and manner in which those two properties affect pavement distresses and performance. The influence of the assumed PG binder grade on the RAP mixtures, particularly the high-temperature grade, has a significant effect on the predicted amount of thermal cracking a...

Mechanistic and Volumetric Properties of Asphalt Mixtures with Recycled Asphalt Pavement

This research examines how the addition of recycled asphalt pavement (RAP) changes the volumetric and mechanistic properties of asphalt mixtures. A Superpave® 19-mm mixture containing 0% RAP was the control for evaluating properties of mixes containing 15%, 25%, and 40% RAP. Two types of RAP were evaluated: a processed RAP and an unprocessed RAP (grindings). Testing included dynamic modulus in tension and compression, creep compliance in compression, and creep flow in compression. Dynamic modulus and creep compliance master curves were constructed with the use of the time–temperature superposition principle to describe the behavior of each mix over a range of temperatures. The voids in mineral aggregate (VMA) and voids filled with asphalt (VFA) of the RAP mixtures increased at the 25% and 40% levels, and there was also an influence of preheating time on the volumetric properties. The dynamic modulus of the processed RAP mixtures increased from the control to 15% RAP level, but the 25% and 40% RAP mixtures had dynamic modulus curves similar to that of the control mixture in both tension and compression. The creep compliance curves showed similar trends. A combination of gradation, asphalt content, and volumetric properties is likely the cause of these trends.

Mechanistic and Volumetric Properties of Asphalt Mixtures with Recycled Asphalt Pavement

This research examines how the addition of recycled asphalt pavement (RAP) changes the volumetric and mechanistic properties of asphalt mixtures. A Superpave® 19-mm mixture containing 0% RAP was the control for evaluating properties of mixes containing 15%, 25%, and 40% RAP. Two types of RAP were evaluated: a processed RAP and an unprocessed RAP (grindings). Testing included dynamic modulus in tension and compression, creep compliance in compression, and creep flow in compression. Dynamic modulus and creep compliance master curves were constructed with the use of the time-temperature superposition principle to describe the behavior of each mix over a range of temperatures. The voids in mineral aggregate (VMA) and voids filled with asphalt (VFA) of the RAP mixtures increased at the 25% and 40% levels, and there was also an influence of preheating time on the volumetric properties. The dynamic modulus of the processed RAP mixtures increased from the control to 15% RAP level, but the 25% and 40% RAP mixtures...

Louisiana Experience with Foamed Recycled Asphalt Pavement Base Materials

Utilization of existing recyclable materials has always been key to more efficient and economical highway construction. Use of the foamed-asphalt (FA) technique to stabilize recycled asphalt pavement (RAP) is one strategy for an efficient use of salvaged construction materials. The main objective of this study is to investigate the potential use of FA-treated RAP as a base course material in lieu of a crushed-limestone base beneath a concrete pavement layer. Test sections were constructed at US-190 near Baton Rouge, Louisiana, and used for field evaluation of the FA RAP base. The laboratory mixture design of the FA RAP, the construction of the experimental base section, and the field evaluation of the stiffness of the FA RAP base layers using different in situ testing devices are presented. Preliminary results of both laboratory and field tests showed that the FA-treated RAP mixtures are very promising and can be used as an alternative to the traditional limestone base beneath a concrete pavement layer.