Andrea Kvasnak

Testing of Moderate and High Reclaimed Asphalt Pavement Content Mixes: Laboratory and Accelerated Field Performance Testing at the National Center for Asphalt Technology Test Track

This paper describes the performance of test sections containing moderate and high levels of reclaimed asphalt pavement (RAP) at the National Center for Asphalt Technology test track. The test sections included two with 20% RAP, four with 45% RAP, and a control with no RAP. Each mixture contained the same component aggregates and RAP. One of the 20% RAP mixes contained PG 67-22 binder, and the other contained PG 76-22 binder. Different binders in the 45% RAP mixes included PG 52-28, PG 67-22, PG 76-22, and PG 76-22 plus 1.5% Sasobit. All sections performed well for rutting and raveling. Low-severity longitudinal wheelpath cracking was documented in two sections. The 45% RAP section with PG 76-22 plus Sasobit had moderate cracking, which appears to reflect cracking from the underlying pavement. The 20% RAP section with PG 76-22 had less cracking. Other sections had no cracking. Laboratory tests included asphalt pavement analyzer (APA) rutting tests, dynamic modulus, bending beam fatigue, and energy ratio. The APA results corresponded to the effective stiffness of the binder in the mixes. Master curves of dynamic moduli showed the effects of the virgin binder grade on the stiffness of the mixtures. Beam fatigue tests indicated that the 45% RAP mixes have lower fatigue lives compared with those of the other mixes, but this is because of a lower effective volume of asphalt in these mixes.

Strategies for Design and Construction of High-Reflectance Asphalt Pavements

The occurrence of higher air and surface temperatures in urban areas is known as the urban heat island (UHI) effect. Reducing the UHI effect may decrease summer energy use and improve human and ecological health. The Leadership in Energy and Environmental Design certification system has awarded up to three points for construction projects that provide any combination of the following cool pavement strategies for up to 75% of the site landscape: (a) shading hard surfaces on the site with landscape features, (b) using high-reflectance materials with a minimum solar reflectance index (SRI) of 29, and (c) utilizing an open-graded pavement or porous pavement system. Although a guide to the design and construction of porous asphalt pavements has existed for some time, such a guide is not readily available for high-reflective asphalt pavements. The objective of this study is to identify and validate high-reflectance asphalt materials and pavement surface treatments that are suitable for use in parking lots and other large paved surfaces, have a minimum SRI of 29, and are economical. In this study, six technologies exhibited SRI values of 29 or greater: E-Krete microsurfacing, Street-Bond coating, synthetic binder, Densiphalt, and chip and sand seals using light-colored aggregates. Another technology, surface gritting using light-colored aggregate, most likely would have exhibited SRI values of at least 29 if the aggregate had adhered properly to the asphalt mat.

Full-Scale Structural Evaluation of Fatigue Characteristics in High Reclaimed Asphalt Pavement and Warm-Mix Asphalt

Warm-mix asphalt (WMA) and the inclusion of higher percentages of reclaimed asphalt pavement (RAP) are two strategies for developing environmentally friendly pavement structures that can also reduce pavement cost. Although demonstration projects have evaluated the constructability and short-term performance of these technologies in the field, questions remain about the structural characterization and longer-term field performance. As part of the 2009 National Center for Asphalt Technology test track, four sections were constructed; they included both WMA and high-RAP contents (50% RAP). A control section did not include either technology. Every section featured embedded instrumentation that facilitated strain versus temperature characterization under truck loading. Statistical comparisons of measured strain response were conducted at three reference temperatures. At the lowest temperature (50°F), the measured strain in the control section was not statistically different from the strains of the experimental sections. At the intermediate temperature (68°F), strains in the RAP with WMA section were statistically lower than the control, but the other sections were not distinguished from the control. At the highest temperature (110°F), the strain in the control section was statistically higher than all other sections. The WMA sections were next highest, and the RAP sections were the lowest. The base mixtures of each section underwent beam fatigue testing from which fatigue transfer functions were developed. Strains entered into their section-specific transfer functions showed that the RAP–WMA section would perform the best. Continued testing and monitoring of the sections are necessary to validate this finding.

Bulk Specific Gravity of Reclaimed Asphalt Pavement Aggregate: Evaluating the Effect on Voids in Mineral Aggregate

Several methods are available for determining the bulk specific gravity (Gsb) of reclaimed asphalt pavement (RAP). However, a clear recommendation has not been had for determining this property. In this study, asphalt mixes with known aggregate properties were produced and aged in the laboratory to simulate RAP. The aggregates were recovered, and the aggregate properties, including Gsb, were reassessed. The aged mixtures were also tested to determine maximum theoretical specific gravity (Gmm), from which estimated Gsb values could be calculated. The Gsb values from both the extraction and Gmm methods were compared with the known or true Gsb values for these aggregates. The effects of the RAP Gsb errors on voids in mineral aggregate values from the various methods were also evaluated. On the basis of the results of this study, it is recommended that the Gmm method be used to determine the RAP Gsb when a regional absorption value is known.