Quantifying the Workability of Cold In-Place Recycling in the Laboratory

The Dongre Workability Test (DWT) is a method for determining an asphalt pavement's relative workability based on stress-strain relationships during compaction in a Superpave gyratory compactor. Although the DWT has seen favorable results with warm-mix and hot mix asphalt, there has been limited attempts to apply it to cold-mix asphalt (CMA), and those limited attempts did not provide conclusive results. This research re-examined the curves developed during the DWT data collection in order to better quantify the workability of CMA, specifically, cold in-place recycling (CIR). Phase one consisted of defining ten possible metrics from the stress-strain curve and applying them to samples with three different curing conditions. From these preliminary results, the five metrics that showed the greatest differences between curing conditions with small relative coefficients of variation were chosen for continued evaluation. In phase two, these five metrics were applied to three different asphalt emulsions at four different curing conditions (temperature-minutes: 10C-30, 10C-120, 60C-30, and 60C-120). Two metrics based on different areas under the stress-strain curve yielded the most logical and consistent results, with higher values indicating a more workable mixture. Samples cured for 30 minutes at either 10 degrees C or 60 degrees C showed the most noticeable distinction between workability of each asphalt emulsion. Moving forward, it is recommended these metrics be applied to additional asphalt emulsions, reclaimed asphalt pavement sources and gradations, and curing conditions to determine if the DWT method can be modified for application to CIR mixtures.