Moisture Sensitivity of Warm and Hot Mix Asphalt: Comparison of Loaded Wheel Tracking and Modified Lottman Tests

Concerns about ever-increasing construction costs coupled with the negative impacts on the environment have led the asphalt industry to search for alternatives that can potentially mitigate these effects. One type of technology that addresses both production cost and environmental issues is the warm mix asphalt (WMA). It allows for mixing, production, placing, and compaction of asphalt mixtures at significantly lower temperatures than conventional hot mix asphalt (HMA). The goal of this study is to compare the laboratory moisture susceptibility and permanent deformation performance of HMA and WMA mixtures. Further, to ascertain early field performance of HMA and WMA. Six field rehabilitation projects across Louisiana were selected for the evaluation of WMA technologies. Several chemical additives and processes were evaluated. A total of 18 mixtures were included in this study. The field experiment included three types of WMA technologies, chemical additives (Evotherm and Rediset), organic (Sasobit), and foaming processes (astec double barrel green system and accu-shear system), two mixture compaction levels (design traffic levels 1 and 2), two asphalt binder types (PG70-22M and PG76-22M per Louisiana Department of Transportation and Development (DOTD) specifications), two projects where higher reclaimed asphalt pavement (RAP) contents were evaluated; and two nominal maximum aggregate sizes (12.5 mm [1/2 in] and 19.0 mm [3/4 inch]). The results of this study showed comparable performance of conventional HMA and WMA in terms of moisture sensitivity tests. The modified lottman and loaded wheel tracking (LWT) tests had, in general, good agreement for mixture evaluation in terms of moisture sensitivity and field performance results. The field performance confirmed the prediction of the moisture sensitivity tests, modified Lottman and the LWT.