Validation of New Asphalt Cement Specification Test Methods Using Eastern and Northeastern Ontario Contracts and Trial Sections
Subramani, Sathish Kumar
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This thesis discusses and documents the validation efforts related to two new test methods developed for the grading of asphalt cement. Asphalt cements that were recovered from a large number of regular paving contracts and trial sections in eastern and northeastern Ontario were tested according to LS-299 and LS-308 test methods. The LS-308 Extended Bending Beam Rheometer (BBR) Method involves testing of asphalt cement in a regular BBR after specific times of conditioning at –10ºC and –20ºC. The LS-299 Double-Edge-Notched Tension (DENT) Test involves testing of asphalt cement in DENT configuration at 15ºC and 50 mm/min. Both these methods improved the ranking of asphalt more than that of regular BBR protocol as in AASHTO M320 method. Pavement contracts and trial sections showing little or no distress were made with asphalt cements having low grade losses in LS-308 and high strain tolerances as measured in LS-299. Hence, future implementation of these methods should reduce thermal cracking distress in Ontario roads. Besides, a number of other properties were investigated. All recovered regular contract materials were tested at –10ºC, –20ºC, and –30ºC after various periods of conditioning. Samples were loaded for 240 s, followed by unloading for 720 s in BBR, allowing the separation of elastic and viscous creep deformations. The regular specification parameters, stiffness (S) and relaxation ability (m-value) and also other performance-related properties were determined. It was found that the confounding effect of simultaneous elastic and viscous deformations and inadequate conditioning prior to testing in the BBR protocol are the most important reasons for the observed inconsistency in grading. These findings are in general agreement to those from the earlier LS-308 tests. The main reason for the poor performance is asphalt physically age during extended periods of exposure to low temperatures. Hence, those that are graded according to the current AASHTO M320 protocol are often under-designed for thermal cracking. The slow crystallization of waxes and precipitation of asphaltenes from oily phase is the primary cause for deterioration of properties. Besides, waste engine oils with other gelling agents like PPA, increase the chemical ageing tendency of asphalts and hence, thermal cracking distress.