George Way

Properties of crumb rubber concrete

Crumb rubber is a material produced by shredding and commutating used tires. There is no doubt that the increasing piles of used tires create environmental concerns. The long-term goal of this research is to find means to dispose of the crumb rubber by placement of the rubber in portland cement concrete and still provide a final product with good engineering properties. The Arizona Department of Transportation and Arizona State University have initiated several crumb rubber concrete (CRC) test sections throughout Arizona over the past few years. Laboratory tests were conducted to support the knowledge learned in the field and enhance the understanding of the material properties of CRC. Concrete laboratory tests included compressive, flexural, indirect tensile strength, thermal coefficient of expansion, and microscopic matrix analyses. The unit weight and the compressive and flexural strengths decreased as the rubber content in the mix increased. Further investigative efforts determined that the entrapped ...

MECHANISTIC-EMPIRICAL OVERLAY DESIGN METHOD FOR REFLECTIVE CRACKING

A new and innovative mechanistically based pavement overlay design method is described that considers the most predominant type of overlay distress observed in the field: reflective cracking above old cracks in the underlying pavement surface. Both dense-graded hot-mix asphalt (HMA) and gap-graded asphalt rubber (wet process) mixes were studied in the laboratory and in the field to derive the necessary mechanistic relationships and statistically based equations. The models proposed are based on a finite element model that closely approximates actual field phenomena. Many field test sections, mainly in Arizona, were studied during the course of the research. Other HMA mixes used for overlays may also be calibrated and used through the proposed method, but the relevant mix properties of any additional materials or environmental zones must first be determined. The two mix types studied are mainly used in the desert southwest region of Arizona and California. The overlay design program is available from the Rubber Pavements Association or Arizona Department of Transportation in the form of an Excel spreadsheet with an easy-to-use Visual Basic computer program (macro).

Flagstaff I-40 Asphalt Rubber Overlay Project: Nine Years of Success

In 1990 the Arizona Department of Transportation designed and constructed a large-scale asphalt rubber (AR) test project in Flagstaff, Arizona, on the very heavily trafficked Interstate 40. The purpose of the test project was to determine whether a relatively thin overlay with AR could reduce reflective cracking. AR is a mixture of 80 percent hot paving-grade asphalt and 20 percent ground tire rubber. This mixture is also commonly referred to as the asphalt rubber wet process or McDonald process. The overlay project was built on top of a very badly cracked concrete pavement that was in need of reconstruction. The AR overlay has performed beyond original expectations. After 9 years of service the overlay is still virtually crack free, with good ride, virtually no rutting or maintenance, and good skid resistance. The benefits of using AR on this project represent about

Assessment of Distress in Conventional Hot-Mix Asphalt and Asphalt–Rubber Overlays on Portland Cement Concrete Pavements: Using the New Guide to Mechanistic–Empirical Design of Pavement Structures

18 million in construction savings and 4 years’ less construction time. Strategic Highway Research Program SPS-6 test sections built in conjunction with the project further illustrate the very good performance of AR. Results of this project have led to widespread use of AR hot mixes throughout Arizona. On the basis of this work over 3333 km (2,000 mi) of successfully performing AR pavements have been built since 1990.

Noise-damping characteristics of different pavement surface wearing courses

The purpose of this study is to assess the way distresses are predicted by using the new Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures (design guide), developed under NCHRP Project 1-37A. Two pavement sections were used: a conventional hot-mix asphalt reconstruction and an asphalt-rubber overlay on a portland cement concrete (PCC) pavement. The design guide does not include rehabilitation design for asphalt-rubber overlays. However, many large-scale asphalt-rubber overlays on interstate highways in Arizona have been built and monitored for performance, providing an opportunity to determine to what degree the design guide can predict their performance. The input data for both types of pavements were derived from two different projects on the same highway, Interstate 40. The actual data measurements that summarize the pavement performance were compared with calculated values obtained by using the design guide. Three pavement performance parameters were evaluated on the basis of t...

A Mechanistic-Empirical Based Overlay Design Method for Reflective Cracking

The purpose of this research investigation was to conduct field and laboratory noise evaluation of 36 laboratory-blended and 49 field pavement cores encompassing 11 pavement types collected from Arizona and California in the USA and Sweden in Europe mainly to characterise their acoustical properties. Furthermore, a new and unique parameter referred to as damping acoustical measurement parameter (DAMP) was conceptualised and developed as part of this study to characterise noise-damping properties of the different road materials. Laboratory acoustical evaluation was performed on the samples covering nine conventional and modified asphalt and two non-asphaltic mixtures using the ultrasonic pulse velocity technique and Impedance (Z) was estimated. DAMP was established for the mixes which were inversely related to Z. Theoretically, lower Z and higher DAMP exemplified higher noise-damping capacity of the pavement. Amongst the asphaltic mixes, asphalt rubber friction course had the highest DAMP (∼20%) compared to the other mixes indicative of being the quietest pavement material, also confirmative of the field noise measurement findings. Within the non-asphaltic mixtures, poroelastic road surface showed the highest DAMP (37%), while Portland cement concrete exhibited the lowest DAMP (12%).

Asphalt-rubber gap-graded mixture design practices: a state-of-the-art research review and future perspective

ABSTRACT This paper describes a new and innovative mechanistically based pavement overlay design method that considers the most predominant type of overlay distress observed in the field: Reflective cracking above old cracks in the underlying pavement surface. Both dense-graded hot mix asphalt and gap-graded asphalt rubber (wet process) mixes were studied, in the laboratory and in the field, to derive the necessary mechanistic relationships and statistically based equations. The models proposed are based on a finite element model that closely approximates actual field phenomena. Many field test sections, in Arizona, California and Portugal, were studied during the course of the research. Other HMA mixes used for overlays may also be calibrated and used through the proposed method. However, the relevant mix properties of any additional materials or environmental zones must first be determined. The two mix types studied are mainly used in the desert southwest region of Arizona and California. The overlay design program is available from the Rubber Pavements Association or Arizona Department of Transportation in the form of an Excel spreadsheet with an easy-to-use visual basic computer program (macro).

HOT MIX ASPHALT DESIGN PREDICTION AND FIELD PERFORMANCE, AN ARIZONA STUDY

The use of asphalt-rubber gap-graded (AR-Gap) mix as a pavement material has gained importance due to its environmental benefits and enhanced performance. This paper reviews the current state-of-the-art pertinent to AR-Gap mix design research and practice. The various mix design practices of AR-Gap mixes adopted by various agencies were summarised. Furthermore, the performance characteristics of AR-Gap mixes such as drain-down, moisture susceptibility, permanent deformation, and fatigue cracking were also documented. The field performances of AR-Gap pavements were also reviewed. Due to an increased use of AR-Gap as a pavement material owing to its several benefits, there exists an extensive scope for further research to understand the material better, which will make it a promising sustainable pavement material in future. Furthermore, considering that AR-Gap mix design and construction technologies are yet to be fully implemented worldwide, the present work aims to be an up-to-date reference to provide benefits and issues associated with the AR-Gap mixes. However, based on the various research questions emanating out of the review process, it was adjudged that there is still further scope for advancing the current state-of-the-art pertaining to the AR-Gap mix design, and the contribution of rubber inclusions in assisting the mix’s augmented performance.

Noise-reducing asphalt rubber surfaces in China

The Arizona Department of Transportation in cooperation with the Federal Highway Administration and private industry designed and built numerous experimental paving projects from 1993 through 2001. Projects were built in a variety of different Arizona climatic zones representing hot desert climates and cold snowfall mountainous regions. Traffic truck loading levels also varied from state highways to major Interstate freeways. The purpose of all of these projects is to use new laboratory tests developed as part of the SHRP and the Superpave Models to characterize cracking and rutting of various hot mix asphalt types. The fatigue cracking test is the four point bending beam test. The rutting test is the repetitive simple shear test at constant height and the triaxial creep test. As a result of this early experimental work, the ADOT adopted the SHRP asphalt grading system in 1997 for all paving projects. SHRP consensus aggregate properties with regard to a greater degree of crushed coarse and fine particles and the fine aggregate angularity were also adopted in 1997. Asphalt rubber open graded friction courses and gap graded mixes continue to be used to compliment the structural HMA layers as the final wearing surface. For the covering abstract see ITRD E117423.

MODE OF LOADING ON FLEXURAL FATIGUE LABORATORY PROPERTIES OF CONVENTIONAL AND ASPHALT RUBBER MIXES: A MODEL VALIDATION

Beginning in about 2004 the state-of-the-art and practice of asphalt rubber (AR) surfaces as used and applied in the United States (US) to reduce traffic noise was presented in China. AR surfaces have been used in US for many years to reduce the traffic noise. The AR surfaces can be applied as the final wearing course on concrete or asphalt pavements. Both the US states of California and Arizona and others have successfully employed thin wearing courses (12.5 to 40 mm) of AR to reduce highway noise. Following this early exposure to the AR technology, China began to experiment and later use AR to reduce noise, as well as to provide a durable and good quality skid resistant wearing course. This paper reports on the progress of use of AR in China and the noise data from various surfaces in China. These surfaces include Stone Mastic Asphalt, Polymer Asphalt, Asphalt Rubber Asphalt Concrete and Asphalt Rubber Open Graded Friction Course.