Moisture Susceptibility of High and Low Compaction Dry Process Crumb Rubber–Modified Asphalt Mixtures

Abstract

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, as achieving field compaction of CRM material is difficult because of the inherent resilient nature of the rubber particle, non-uniform field compaction may lead to deficient bond between rubber and bitumen. To assess the influence of compaction, a series of CRM and control mixtures were produced and were compacted at two levels; 4% (low, optimum laboratory compaction), and 8% (high, field experience) air void content. The long-term durability, in terms of moisture susceptibility of the mixtures was assessed by conducting repeated moisture conditioning cycles. The mechanical properties (stiffness, fatigue, and resistance to permanent deformation) were determined in the Nottingham Asphalt Tester (NAT). The results indicated that compared to conventional mixtures, the CRM mixtures, irrespective 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 behaviour is different to conventional mixtures where, as expected, poorly compacted mixtures were found to be more susceptible to moisture than well compacted mixtures.

Sublayer Strength Evaluation with FWD in Semi-Rigid Base Asphalt Pavement Rehabilitation Project

“…In the dry process, most of the previous works have considered that the wet process had sufficient interaction between asphalt and CRM due to long time blending at high temperature, while asphalt -CRM reaction in the dry process is negligible due to the shorter reaction period and larger particle sizes used (Rahman 2004). However, recent research found that during the mixing period as well as transportation and laying, the asphalt -CRM reaction in the dry process is significantly higher than previously thought and improves the performance of HMA (Singleton 2000, Rahman et al 2010, Hernández-Olivares et al 2009, López-Moro et al 2013. In addition, field performance of the dry process CRM mixture is inconsistent and the service life varies from 2 to 20 years (Rahman 2004).…”

Performance of porous European mix (PEM) pavements added with crumb rubbers in dry process

“…However, recent research found that during the mixing period as well as transportation and laying, the asphalt -CRM reaction in the dry process is significantly higher than previously thought and improves the performance of HMA (Singleton 2000, Rahman et al 2010, Hernández-Olivares et al 2009, López-Moro et al 2013). In addition, field performance of the dry process CRM mixture is inconsistent and the service life varies from 2 to 20 years (Rahman 2004).…”

Durability Evaluation Study for Crumb Rubber–Asphalt Pavement

“…Crumb rubber-asphalt mixture is a new type of deicing pavement material prepared by replacing some of the aggregates in asphalt mixture with mechanically sheared particles of waste rubber tires and mixing them uniformly with high-performance modified asphalt [1][2][3][4][5][6]. The addition of rubber crumbs changes the original structure of the mixture and the contact state between the materials so that the pavement is more easily loosened than an ordinary asphalt pavement [7].…”