Kinetics-based aging evaluation of in-service recycled asphalt pavement
Introduction
The use of reclaimed asphalt pavement (RAP) has become a common practice in pavement structural rehabilitations due to its symbiotic environmental and economic benefits. RAP refers to pavement materials generated when an asphalt pavement is removed for reconstruction or resurfacing. The general benefits of using RAP include reduction in energy consumption and emission generation, conservation of natural resources, and savings in rehabilitation cost (Robinette and Epps, 2010; Ding et al., 2018). However, concerns have also arisen about premature distresses and the longevity of recycled pavements. This is because RAP is a type of material that already suffers long-term aging in the field. Aging is known to have a significant effect on pavement performance and has been investigated with numerous efforts. An asphalt pavement is inevitably aged when loss of volatile oils and oxidation occur in the field. The aged asphalt pavement becomes more brittle and is prone to cracking, such as fatigue cracking, reflection cracking, longitudinal cracking, etc.
The most common way to evaluate aging of RAP is to examine the results of binder or mixture testing in the laboratory. For example, Mohammad et al. (2003) used the extraction and recovery technique to obtain asphalt binder from an eight-year old polymer modified pavement. The field aged binder was characterized by binder tests. It was found that extensive age hardening occurred and changes in both chemical and rheological properties were noted. Hamzah and Shahadan (2011) performed a physico-chemical analysis on RAP. They obtained recovered asphalt binder from RAP and incorporated into virgin asphalt with the percentages of 15% and 30%. The RAP modified binders were subjected to different aging conditions and tests to measure the physical and chemical properties. They concluded that the RAP modified binders were further aged as the measured properties distinctly changed. Tarbox and Daniel (2012) prepared four plant-produced mixtures containing different percentages of RAP (0%, 20%, 30%, and 40%), which were aged long-term in the laboratory oven. The dynamic modulus test was conducted on each mixture. The results showed that the oven aging had less effect on dynamic modulus when the content of RAP increased. Compared to the virgin mixtures (0% RAP), the mixtures with RAP stiffened at slower rates in terms of the change of the dynamic modulus. Besides, Colbert and You (2012) and Poulikakos et al. (2014) also utilized laboratory aging procedures and testing methods to quantify the effects of short-term and long-term aging on chemical, physical, and mechanical properties of RAP materials. Clear evidence of aging was observed in terms of the increase of the oxidized products, viscosity, and modulus. In the laboratory tests to evaluate performance like low temperature behavior, fatigue or rutting, the test results showed that a well-designed mixture with 40% RAP produced similar trend with the mixture with virgin materials (Poulikakos et al., 2014).
As recycling techniques mature, pavement analysts and engineers become more and more interested in using high percentages of RAP. An asphalt mixture containing RAP above 25 percent is considered to be a high RAP content mixture. To design such a mixture, an appropriate procedure is needed to address the key issues like selection of rejuvenators and determination of heating methods. Knowing aging characteristics of high RAP content mixtures plays an important role in making these decisions. Rejuvenation of aged asphalt means restoring the performance of the binder. Ali and Mohammadafzali (2015) identified five different recycling agents to rejuvenate recycled asphalt binders, and studied their long-term aging behaviors through extended Pressure Aging Vessel (PAV) aging and the Superpave Performance Grade (PG) test. The level of aging was represented by the high temperature PG. A significant difference was observed in the aging rates of the samples recycled with different rejuvenators.
Another example about high RAP content asphalt mixtures is the process of heating, which prepares RAP samples for mix design and characterization tests. A recent study on incorporating RAP in the Superpave mix design recommended that heating RAP should be minimum to avoid changes in material properties due to aging (McDaniel and Anderson, 2001). In another study about improved mix design of hot mix asphalt (HMA) with high RAP content (West et al., 2013), the heating experiment was designed to evaluate how different heating times and temperatures affected the properties of RAP samples. After heating and mixing, the RAP binder samples were extracted, recovered, and graded. The true grade reflected the extent of aging induced by heating. They found that additional aging of the RAP binder occurred when heating more than three hours.
Section snippets
Motivation and objectives
A brief review of existing literature above demonstrates the important role of aging in applying RAP in pavement rehabilitations. It also reveals that most of the studies of RAP aging are carried out in the laboratory on asphalt binders. In addition, a process of binder extraction and recovery is usually involved. There are some concerns raised from these approaches. First, laboratory aging conditions are certainly different from those in the field. Secondly, aging of asphalt binders differs
Kinetics-based aging modeling with FWD for asphalt pavements
This section aims at explaining the methodology used in this study to evaluate the field aging of in-service asphalt pavements. More specifically, the following two aspects are discussed:
- 1)
The concept and formulation of kinetics-based aging modeling of asphalt mixtures that are developed in the previous work (Luo et al., 2015, 2017); and
- 2)
The factors that affect the validity of the proposed method as well as the actions to mitigate the influence.
Collection of field deflection and climate data
The LTPP database is utilized to collect the FWD data and part of the climate data. Eight pavement sections in Texas are chosen from the SPS-5 (rehabilitation of asphalt concrete pavements) of the LTPP, an experiment to examine the effects of existing pavement condition, traffic, and climate on pavements rehabilitated by different methods with overlays. The sections are located on US highway 175. Details of these sections are given in Table 1 in terms of overlay material, surface preparation,
Separation of FWD modulus for asphalt overlays
A rehabilitated pavement with overlay exhibits a unique aging feature since it consists of several asphalt layers with different aging speeds. The original asphalt layer has a slower or faster aging rate than the asphalt overlay depending on the nature of overlay materials. However, the FWD modulus is a single value that represents the net effect of mechanical responses of all asphalt layers. When the FWD modulus is used to evaluate aging, it indicates the net effect of aging speeds of all
Aging characteristics of asphalt overlays
After separating the FWD modulus, the kinetics-based model can be applied to the moduli of each asphalt layer to determine the aging kinetic parameters.
Conclusions and future work
This study aims at investigating aging characteristics of in-service recycled asphalt pavements using field backcalculated modulus and climate data. The kinetics-based aging modeling approach developed in the authors’ previous studies is applied to RAP materials herein. The following findings and conclusions are drawn:
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An asphalt pavement with overlay has a composite aging process since the aging speeds of different asphalt layers are different. The FWD modulus of an asphalt overlay must be
References (33)
- et al.
The properties of asphalt binder blended with variable quantities of recycled asphalt using short term and long term aging simulations
Construct. Build. Mater.
(2012) - et al.
Reclaimed asphalt binder aging and its implications in the management of RAP stockpiles
Constr. Build. Mater.
(2015) - et al.
Blending efficiency evaluation of plant asphalt mixtures using fluorescence microscopy
Construct. Build. Mater.
(2018) - et al.
Influence of short and long term aging on chemical, microstructural and macro-mechanical properties of recycled asphalt mixtures
Construct. Build. Mater.
(2014) - et al.
Intrinsic temperature sensitive self-healing character of asphalt binders based on molecular dynamics simulations
Fuel
(2018) - et al.
Effect of aging on adhesion properties of asphalt mixtures with the use of bitumen bond strength and surface energy measurement tests
Transport. Res. Rec.
(2015) - et al.
Long-term aging of recycled binders
(2015) - et al.
New apparatus and procedure for the extraction and recovery of asphalt binder from pavement mixtures
Transport. Res. Rec.
(1993) Surface Free Energy of Asphalt-aggregate System and Performance Analysis of Asphalt Concrete Based on Surface Free Energy
(2002)EVERSERIES User's Guide: Pavement Analysis Computer Software and Case Studies
(2005)
Effects of aging on the physical, rheological and chemical properties of virgin bitumen incorporating recovered reclaimed asphalt pavement binder
Aust. J. Basic Appl. Sci.
Modeling pavement temperature for use in binder oxidation models and pavement performance prediction
J. Mater. Civ. Eng.
Long-term performance evaluation of recycled asphalt pavement results from Texas: pavement studies category 5 sections from the long-term pavement performance Program
Transport. Res. Rec.
Feasibility of using high RAP contents in hot mix asphalt
Aging characteristics of RAP blend binders: rheological properties
J. Mater. Civ. Eng.
Fast-rate–constant-rate oxidation kinetics model for asphalt binders
Ind. Eng. Chem. Res.
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