Assessing the Rut Performance of Warm Mixes in North Dakota

Abstract

New emerging technologies in asphalt production and placement with the premise of saving fuel, reducing plant emissions, and extending the paving season into colder weather have been gaining popularity in recent years. These technologies, namely Warm Mix Asphalts (WMA), are produced by incorporating additives into asphalt mixtures to reduce the viscosity of the asphalt binders and allow aggregate coating at temperatures well below of those of the conventional hot-mix asphalts (HMA). Due to the short paving season in North Dakota, North Dakota Department of Transportation (NDDOT) has initiated WMA research in hopes that the use of WMA will lead to the extension of the paving season into colder weather. Also since previous WMA research was not conclusive on rutting and moisture issues, NDDOT constructed WMA and HMA overlays to evaluate the WMA resistance to rutting and moisture sensitivity. The WMA overlay sections were constructed using Evotherm 3G chemical additive. The primary purpose of the research study was to evaluate and compare the rut resistance performances of the WMA and HMA overlays under dry and wet conditions. Twenty four field core samples representing the WMA and the control HMA sections were selected and tested for rut resistance under dry and wet conditions using the asphalt pavement analyzer (APA). The APA results indicate that the average rut values for WMA samples were 13 percent and 29 percent higher than those of the HMA mixes under dry and wet conditions, respectively. The slight increases in rut values of the dry specimens were expected due to the reduced stiffening of WMA binders. On the other hand, the elevated rut values of WMA specimens under wet testing may suggest reduced durability of warm mix overlays.