Evaluation of field projects using crumb rubber modified asphaltic concrete.

State Project: 736-99-0762LTRC Project: 95-5BIn 1994, the Louisiana Department of Transportation and Development (LADOTD) initiated a research project to evaluate different crumb-rubber modified (CRM) applications in which the long-term pavement performance of the CRM asphalt pavements was compared to that of the control sections built with conventional asphalt mixtures. This report presents a laboratory, construction, and field performance evaluation study of several applications of CRM hot-mix asphalt in Louisiana. Eight CRM asphalt pavement sections were constructed using eight different CRM processes or applications. Five state highway projects were selected to construct these eight CRM sections. A control section was built with conventional asphalt mixtures on each project to compare the field performance of pavement sections built with CRM asphalt mixtures. To evaluate the mixture characteristics of the CRM and conventional mixes, laboratory tests of Marshall stability and flow, indirect tensile strength (ITS) and strain, and indirect tensile resilient modulus (M sub R) were conducted on field compacted Marshall specimens. Comparisons of the construction and field performance of the pavements were achieved through roadway core air void analysis, rut-depth measurement, international roughness index (IRI), pavement structure numbers measured through the DYNAFLECT system, and Quality Control data. Also, the final field performance evaluation used visual data acquired from Louisiana\u2019s Pavement Management Section in which the international roughness index (IRI), rut-depth measurements, and crack data were evaluated. Also, visual inspection of cracks was reported. The result of this study indicated that the conventional mixtures exhibited higher laboratory strength characteristics than the CRM mixtures. The pavement sections constructed with CRM asphalt mixtures showed overall better field performance indices (rut depth, random cracks, and IRI numbers) than corresponding control sections. Both CRM modified, wet and dry, hot mix asphalt (HMA) mix types are performing equally well, if not better, than the conventional mix types evaluated