American Society for Testing and Materials

The detrimental effects of hardening in asphalt pavements were first recognized by pioneering pavement engineers in the 1900s and have been studied extensively during the last 70 years. This hardening process, referred to as asphalt aging, is generally defined as change in the rheological properties of asphalt binders/mixtures due to changes in chemical composition during construction and its service life period. Aging causes the asphalt material to stiffen and embrittle, which affects the durability and leads to a high potential for cracking. This paper presents the state of the art on asphalt and asphalt mixture aging and use of antioxidant additives to retard the aging. A picture of complex molecular structure of asphalt and its changes due to atmospheric condition and various protocols used to simulate aging in laboratory environment are also discussed. Emphasis is given on recent studies on simulation of aging of asphalt mixtures as there has been limited research on mixtures compared to the asphalt binder. Finally, this paper presents the application of antiaging techniques and its mechanism, use of various types of antioxidant additives to retard aging of asphalt and, hence, improve the performance of asphalt pavements.

/pdf/state-of-the-art-study-on-aging-of-asphalt-mixtures-and-use-4ebplgc6uu.pdf

State of the Art Study on Aging of Asphalt Mixtures and Use of Antioxidant Additives

Use of recycling agents in asphalt mixtures with high recycled materials contents in the United States: A literature review

Open-graded friction courses (OGFC), or porous friction courses (PFC) as defined by the Texas Department of Transportation (TxDOT), are a special gap-graded asphalt mixture characterized by a large interconnected air void content. In general, the voids content is at a minimum of 18%. Similar mixtures [porous asphalt (PA)] with voids contents as high as 25% are successfully applied in Europe. These interconnected voids make these mixtures highly permeable with the capacity to reduce tire-pavement noise. These characteristics are associated with the following advantages that can be obtained from the use of PFC as a surface layer: safety improvements, economic benefits, and environmental benefits. On the other hand, the following aspects are identified as disadvantages of PFC: reduced performance, high construction costs, winter maintenance issues, and limited structural contribution. Substantial efforts have been undertaken to correct previous failures in OGFC, and significant advances have been made since the 1990s with respect to mixture performance and service life. This report summarizes the current state of the practice related to mixture design methods (proposed by different U.S. and international agencies and institutions), construction, maintenance, and performance of surface courses using OGFC and PA identified from a worldwide literature review. In addition, the report presents a synthesis of the relevant aspects related to the current practice and application of PFC in Texas based on the interviews conducted with selected TxDOT districts. The report represents the baseline for a research project aimed to improve the PFC mixture design method using advanced research tools and develop guidelines for construction and maintenance of PFC. In this project, special efforts will be directed to address functionality in terms of permeability and noise reduction, and durability in terms of moisture damage and aging potential.

/pdf/synthesis-of-current-practice-on-the-design-construction-and-2tzw32r5vh.pdf

Synthesis of Current Practice on the Design, Construction, and Maintenance of Porous Friction Courses

The effect of long-term aging on the rheology of warm mix asphalt binders

This project was a comprehensive study directed at developing an improved method of screening asphalt binders for long-term pavement performance. A new dynamic shear rheometer (DSR) function, G'/(eta'/G'), and a new aging procedure should warn of premature asphalt hardening and resulting fatigue cracking. For unmodified asphalts the new DSR function correlated well with ductility (at 15 deg C, 1 cm/min) below 10 cm. The correlation was originally developed for DSR measurements at 15 deg C and 0.005 rad/s. These conditions were time-temperature superposition shifted to 44.7 deg C and 10 rad/s to produce a method that is easily accessible to standard laboratory rheological equipment and methods. The recommended aging procedure uses the pressure aging vessel (PAV) apparatus but takes advantage of the higher average aging rate when the asphalt is aged in thinner films. This change, combined with somewhat longer aging, results in a more rigorous test of durability than the standard PAV method. At the same time, the resulting rankings of aged materials are more representative of rankings that are obtained from aging at atmospheric air pressure and 60 deg C. For modified asphalts, the results were complex. Generally for a given value of the DSR function, the ductility was better than indicated by the unmodified asphalt DSR-ductility correlation. Larger amounts of modifier produced increasing values of ductility for a given function value. This result was very asphalt dependent, however, so no general correlation could be found. As modified binders oxidize, the asphalt hardens and the improvement to ductility imparted by modifiers decreases. After enough aging, the improvement is gone and modified binders perform no better than their aged unmodified counterpart. A critical issue is whether the life extension produced by modifiers is life-cycle cost effective. Long-Term Pavement Performance (LTPP) and SH 21 binders indicate: sealcoats may provide an opportunity for significant and very cost-effective in-place binder rejuvenation; G'/(eta'/G') is an excellent function for tracking pavement aging; pavements can oxidize rather uniformly with depth; brittle binders can be tolerated in stiff pavements; aggregates appear to have little effect on asphalt oxidation reactions; rolling thin-film oven tests plus PAV aging is not severe aging, in the context of pavement life.

Development of a New Method for Assessing Asphalt Binder Durability with Field Validation

This project was a comprehensive study directed at developing an improved method of screening asphalt binders for long-term pavement performance. A new dynamic shear rheometer (DSR) function which correlates well with ductility was coupled with a new aging procedure in a tentative specification which should guard against failure caused by premature asphalt hardening and consequent fatigue cracking. The correlation was found for unmodified asphalts between ductility (at 15 deg C, 1 cm/min) below 10 cm and the DSR function G'/(eta'/G'). The correlation was originally developed for DSR measurements at 15 deg C and 0.005 rad/s. These conditions were shifted to 43 deg C and 10 rad/s by using time-temperature superposition to produce a method that is easily accessible to standard laboratory rheological equipment and methods. The developed method is not adequate for modified asphalts. The aging procedure that is recommended uses the pressure aging vessel (PAV) apparatus but is modified by taking advantage of the higher average aging rate when the asphalt is aged in thinner films. This, combined with somewhat longer aging, results in more extended binder aging and thus a more rigorous test of durability than the standard PAV method. At the same time, the resulting rankings of aged materials is more representative of rankings that are obtained from aging at atmospheric air pressure and 60 deg C. For modified asphalts, the results were complex. Generally for a given value of the DSR function, the ductility was better than indicated by the DSR function correlation for unmodified asphalts. Larger amounts of modifier produced increasing values of ductility for a given function value. This result was very asphalt dependent, however, so no general correlation could be found. As modified binders oxidize, the asphalt hardens and the improvement to ductility imparted by modifiers decreases. After enough aging, the improvement is gone and modified binders perform no better than their aged unmodified counterpart. A critical issue is whether the life extension produced by modifiers is life-cycle cost effective.

/pdf/development-of-a-new-method-for-assessing-asphalt-binder-15ww8e6l02.pdf

Chris H. Domke

Papers

Development of a New Method for Assessing Asphalt Binder Durability with Field Validation

Development of a new method for assessing asphalt binder performance durability