Performance Comparison of Recycled Pavement Foundation Layers

Abstract

This paper describes results from a study comparing the performance of side-by-side test sections of pavement foundation layers constructed with on-site recycled materials and surfaced with hot-mix asphalt (HMA). Test sections included recycled materials blended with subgrade to create a mechanically stabilized subgrade layer and recycled materials placed in an overexcavated subgrade layer. In situ falling weight deflectometer (FWD), dynamic cone penetrometer (DCP), and laboratory freeze–thaw tests were used to assess the performance of the test sections, in comparison with a control section where recycled materials were not used. Field testing was conducted at seasonal intervals over 2 years after construction, and the results were statistically analyzed with two-tailed Welch's t-tests to account for unequal variances. Findings indicated that test sections with on-site recycled materials provided improved support conditions for the pavements during both before and after freeze–thaw conditions, when compared with the control section. FWD and DCP test results indicated that recycled material blended with sub-grade showed more thaw-weakening compared with recycled material alone. Laboratory freeze–thaw test results corroborated the comparisons observed in the field test results. Correlations between FWD test measurements on the foundation layer and on the pavement yielded a statistically significant regression relationship, which indicated the importance of support conditions on the surface layer performance. Analysis of bid prices to construct the test sections indicated no statistical evidence to suggest that the unit costs for the test sections were different from one another.

Seasonal Performance Evaluation of Pavement Base Using Recycled Materials

“…In summary, these laboratory findings indicated that seasonal freeze-thaw cycles had a significant effect on weakening the mechanical properties of pavement foundation materials, including unstabilized and stabilized recycled pavement materials. On the other hand, there are fewer field studies studying the recycled pavement materials as pavement foundations under seasonal freeze-thaw cycles [28,38]. The field test results matched the laboratory freeze-thaw test results [30,38].…”

“…The main difference between cold and hot recycling techniques refers to whether the existing bitumen in recycled materials is heated to restore its viscosity prior to compacting [23,24]. Overall, the investigated topics of these studies on recycled pavement materials are categorized into three aspects: (i) characterizing the mechanical properties, such the strength and stiffness that may represent the capacity to bear traffic loading [25,26]; (ii) evaluating their durability to freeze-thaw and wet-dry cycles [27,28]; and (iii) environmental impacts such as the leaching of metals and high alkalinity and pH [29,30]. Generally, findings from these laboratory investigations demonstrated that recycled pavement materials are able to provide comparable performance to normally used aggregate base materials, such as crushed limestone and granite [31][32][33][34][35][36].…”