Louisiana experience with crumb rubber-modified hot-mix asphalt pavement

A comparative study of laboratory and field performance of several applications of crumb rubber-modified (CRM) hot-mix asphalt in Louisiana is presented. Eight CRM asphalt pavement sections were constructed by eight different CRM processes or applications. These eight CRM sections were built at five state highway projects. A control section with conventional asphalt mixture was constructed at each project to compare with the 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 and strain, and indirect tensile resilient modulus were conducted on field compacted Marshall specimens. Comparisons of the field performances of the pavements were achieved through roadway core air void analysis, rut-depth measurement, international. roughness index, pavement structure numbers measured through the Dynallect (dynamic deflection determination) system, and visual inspections of cracks. The results 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 performance indices (rut depth, fatigue cracks, and international roughness index numbers) than the corresponding control sections after 5 to 7 years of traffic.