Nondestructive In Situ Characterization of Elastic Moduli of Full-Depth Reclamation Base Mixtures

Abstract

State highway agencies are searching for more cost-effective methods for rehabilitating roads. One sustainable solution is full-depth reclamation (FDR), which is a pavement rehabilitation technique that involves pulverizing and reusing materials from existing distressed pavements in place. However, there is little information on the long-term properties of these recycled materials. An important property, the elastic modulus, indicates the structural capacity of pavement materials and is highly recommended for design purposes by the Mechanistic–Empirical Pavement Design Guide. The elastic modulus directly affects selection of the overall pavement thickness; therefore, an accurate estimation of the modulus is key to a cost-effective pavement design. This research investigated the elastic modulus trends of three in-service pavements rehabilitated with the FDR technique during the 2008 Virginia Department of Transportation construction season. Foamed asphalt (2.7% with 1% cement), asphalt emulsion (3.5%), and portland cement (5%) were used as stabilizing agents for the FDR layers. The results of the moduli measured for the recycled base materials varied significantly over time. These changes were attributed to curing after construction, seasonal effects, and subgrade moisture. The structural capacity of the pavements improved irrespective of the stabilizing agent used.

Input Parameters for the Mechanistic-Empirical Design of Full-Depth Reclamation Projects

“…Following AASHTO's recommendations, the back-calculated modulus (E FWD ) obtained from deflection data were adjusted to laboratory conditions of resilient modulus for M-E design by applying a coefficient of 0.62 (24). The resilient modulus of FDR obtained in this project have more variability that the ones found in the literature, with values ranging from 38 to 50 kips per square inch (ksi) for non-stabilized FDR and 48 to 112 ksi for emulsion-stabilized FDR (12,16,23,26). This variability may be a result of compounding factors including the variability of FWD testing, the back-calculation process, and, even more importantly, the variability related to the in-place recycling process of FDR (27,28).…”

“…This study included laboratory and field performance evaluations that showed a good performance of the pavement 4 years after construction and derived recommendations of M-E level 1 and level 2 inputs for cement-stabilized FDR. Amarh et al investigated three FDR projects that included foamed, asphalt emulsion and cement stabilizers to analyze changes in the elastic modulus over time and its sensitivity to temperature and seasonal effects (12). The authors found that the backcalculated modulus of FDR bases increased over time and they developed regression models to predict the short-term strength gains.…”

“…The authors found that the backcalculated modulus of FDR bases increased over time and they developed regression models to predict the short-term strength gains. One of the novelties of Amarh et al's study is that they analyzed the actual performance of FDR projects and calibrated deterioration curves of the critical condition index (CCI) used by Virginia DOT based on performance data over 7 years (12). This analysis found that FDR projects with stiffer base materials do not necessarily perform better, although they highlighted the need to analyze a longer time period to confirm these findings because of the high variability of the CCI measurements.…”

“…Previous studies have mainly focused on determining the mechanical properties of FDR from laboratory and in situ testing to inform M-E design (2,3,21). However, limited studies have actually compared the resulting M-E predictions with the actual performance of FDR projects (6,12,16,23). Previous efforts addressing this comparison have focused on the short-term and do not derive conclusions on the longterm differences between M-E predictions and actual FDR performance.…”

“…Several studies have recently been completed to address this limitation, such as the comprehensive report Material Properties of Cold In-Place Recycled and Full-Depth Reclamation Asphalt Concrete (3). Different DOTs, such as the ones in Maryland and Virginia, have also completed projects to assess the mechanistic structural properties of stabilized base materials (10)(11)(12). These studies have advanced the design of FDR base mixtures by providing reference values of the modulus of FDR materials.…”