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One of the emerging solutions to enhance the durability of asphalt pavements is the use of a French asphalt mix known as "High-Modulus Asphalt Concrete (HMAC)." This mix uses a hard asphalt binder, high binder content (about 6%), and low air voids content as compared to Superpave mixtures. The key objective of this study was to develop a cost-effective HMAC mixture using crumb rubber and local materials in Louisiana. To achieve this objective, four HMAC mixtures were prepared using two asphalt binders (PG 82-22 and PG 76-22 plus 10% crumb rubber) and two Reclaimed Asphalt Pavement (RAP) contents (20% and 40%); additionally, a conventional Superpave mixture in Louisiana was prepared as a control mixture. The laboratory performance of these five mixtures was evaluated in terms of workability, dynamic modulus, rutting resistance, and cracking resistance. The AASHTOWare Pavement ME Design software was also used to estimate the long-term field performance of these mixtures. Results indicated that the HMAC mixture prepared with 10% crumb rubber and 20% RAP successfully met the French mix design specifications for HMAC and LaDOTD specifications. This HMAC mix outperformed the control Superpave mix in terms of dynamic modulus, rutting resistance, and cracking resistance. Additionally, this HMAC mixture can reduce the required asphalt thickness by 1.5 or 2 inches based on the traffic level. The cost-effectiveness analysis indicated that this HMAC mixture was more cost-effective than conventional Superpave mixtures in Louisiana. In addition, this mixture is environmentally-friendly since it can reduce the disposal of scrap tires in landfills.
The objective of this project was to develop an asphalt mix design method incorporating crumb rubber and using the "Wet" or "Dry" method of producing Crumb Rubber Modified Asphalt (CRM). Several resurfacing projects have been constructed using both the "Wet" and "Dry" methods. Based on this study, the Kansas Department of Transportation could use CRM mixes with a binder content between 7.5% and 9.0% depending on the percent air voids, with 19% to 22% rubber content. In this study, it was observed that using 24% rubber produced mixes that were too sticky to manage. With a rubber content of less than 18% combined with AC-5 it was difficult to satisfy the minimum viscosity requirements. Fracture tests can be used as a basis to determine the optimum binder content for any asphalt-rubber mix.
This report deals with pavement mixture designs and construction operation of field trials on U.S. 69 north of Lufkin, Texas. The binders used in this field trial consisted of pure asphalt cement for the control sections and 30/70 weight percent of a sulphur/asphalt emulsion as the test binder. All elements of the structural (thickness) design were produced in pairs for comparison purposes with the exception of two thinner sections selected to possibly show distress in two or three years. Otherwise, the thickness designs used in the test sections were those specified by the State Department of Highways and Public Transportation in the conventional section of this highway. Preconstruction laboratory evaluations of mixture properties and field laboratory control measurements are included as a part of this report.
This research program was based on laboratory and field studies. All work was limited to the use of a 10-mesh crumb rubber in the dry process. An evaluation of the asphalt-rubber interactions indicated that there should be a reasonable level of interaction between the crumb rubber and the asphalt cement selected for the project. A suggested criterion for defining an acceptable level of interaction would be to establish a minimum viscosity of 15 Poise (Brookfield viscosity) for a neat asphalt cement modified with 20% crumb rubber. When designing a crumb rubber modified mixture, the aggregate gradation should be substantially gapped. The target gradation used in the construction of the Babbit, Minnesota test sections should be adjusted for crumb rubber gradations volumetrically; generally, 1 gram of crumb rubber occupies the same volume as 3 grams of aggregate for a given sieve size. The optimum asphalt content for crumb rubber mixtures should be based on air voids from 1.5 to 3%.
3 test lanes constructed at the Louisiana Pavement Research Facility (PRF) to study the performance of Asphalt Rubber Hot Mix Asphalt (AR-HMA) materials, and determine the best possible location of AR-HMA materials within the pavement structure.
TRB's National Cooperative Highway Research Program (NCHRP) Report 752: Improved Mix Design, Evaluation, and Materials Management Practices for Hot Mix Asphalt with High Reclaimed Asphalt Pavement Content describes proposed revisions to the American Association of State Highway and Transportation Officials (AASHTO) R 35, Superpave Volumetric Design for Hot Mix Asphalt, and AASHTO M 323, Superpave Volumetric Mix Design, to accommodate the design of asphalt mixtures with high reclaimed asphalt pavement contents.
The mixture design and performance characteristics of crumb rubber modified asphalt concretes were investigated in this research project to meet the requirements of the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991, which has required each State to incorporate scrap tire rubber into its asphalt paving materials. Specifically, the objectives of this research encompass the following: (i) investigation of the rheological properties of asphalt-rubber binder to determine optimum content of crumb rubber; (ii) development of optimum mix design for various applications, including both wet and dry mix processes; (iii) characterization of mechanical properties of recommended paving mixtures, including resilient modulus, fatigue cracking behavior, low-temperature thermal cracking resistance, water sensitivity test, incremental creep test and loaded wheel track test; and (iv) comparison of performance of selected paving mixes.