Moisture susceptibility of high and low compaction dry process crumb rubber modified asphalt mixtures

The field performance of dry process crumb rubber-modified (CRM) asphalt mixtures has been reported to be inconsistent with stripping and premature cracking on the surfacing. One of the concerns is that, because achieving field compaction of CRM material is difficult due to the inherent resilient nature of the rubber particle, nonuniform field compaction may lead to a deficient bond between rubber and bitumen. To assess the influence of compaction, a series of CRM and control mixtures was produced and compacted at two levels: 4% (low, optimum laboratory compaction) and 8% (high, field experience) air void content. The long-term durability, in regard to moisture susceptibility of the mixtures, was assessed by conducting repeated moisture conditioning cycles. Mechanical properties (stiffness, fatigue, and resistance to permanent deformation) were determined in the Nottingham Asphalt Tester. Results indicated that compared with conventional mixtures, the CRM mixtures, regardless of compaction effort, are more susceptible to moisture with the degree of susceptibility primarily depending on the amount of rubber in the mixture, rather than the difference in compaction. This behavior is different from that of conventional mixtures in which, as expected, poorly compacted mixtures were found to be more susceptible to moisture than were well-compacted mixtures

Static and dynamic elastic moduli of concrete : a comparative study

Peer reviewed: YesNRC publication: Ye

Semi-automated crack analysis system for the heavy vehicle simulator

The condition of Florida roadways is documented through annual surveys conducted by the State Materials Office (SMO) of the Florida Department of Transportation (FDOT). This survey has shown that the majority of the deficient flexible pavements are due to cracking. Based on these circumstances, FDOT\u27s Accelerated Pavement Testing (APT) program has placed a greater focus on deficiencies in the evaluation of crack development and crack resistance. As part of this effort, a computer based program has recently been developed to assist with the identification and quantification of pavement cracks from digital images. A digital camera mounted in front of the wheel carriage on the Heavy Vehicle Simulator (HVS) collects the images at regular intervals during testing to document initiation and the progression of crack development. This paper provides a description of the crack analysis system and offers an example of its use. © 2012 Taylor & Francis Group