Volume 41, Issue 2 (March 2013)
Exploration of a Performance Test for Emulsion Treated Asphalt Surfaces
Asphalt emulsions are a key material used for pavement preservation. Over time, asphalt concrete pavements become oxidized, which can lead to cracking and other surface deterioration. The addition of pavement maintenance treatments, such as scrub seals, chip seals, or fog seals, can rejuvenate the pavement surface as the asphalt emulsion penetrates the oxidized layer of pavement. However, most existing test methods for asphalt emulsions are empirical in nature and do not directly address field performance. With the aim of improving material characterization and testing so as to better capture field properties, this research explored using a bending beam rheometer (BBR) to measure the stiffness and rate of change of the stiffness (or m-value) of asphalt concrete mixture beams treated with asphalt emulsions. There were three components of this study. First, procedures for fabricating BBR beams from field asphalt concrete samples were developed, as the top portion of pavement is often brittle after field aging and oxidation. It was determined that beams could be successfully fabricated with reasonable geometric variability. Second, asphalt concrete BBR specimens compacted and fabricated in the laboratory were sawn and tested, with and without asphalt emulsion, to determine whether the addition of emulsion could be detected. Third, the same emulsion applied to the laboratory fabricated specimens was applied to field mixes to determine the influence of asphalt emulsion on candidate materials for pavement preservation. Overall, beam fabrication was repeatable, and coefficient of variation values for test results were lower for the laboratory compacted plant mix (10 % to 25 %) than for the field mixtures (9 % to 57 %). Emulsion addition increased the m-value and decreased the stiffness of all pavements, which indicates rejuvenation of the asphalt concrete. BBR mixture beams appear to be able to capture the effect of adding emulsion to both lab produced and field specimens, but more types of emulsions, a more comprehensive conditioning regime, and more asphalt concrete mixtures should be examined in order to determine the effectiveness of the measured performance properties of asphalt concrete with the addition of asphalt emulsion.