Determining the Embrittlement Temperature of Asphalt Binders Using an Acoustic Emission Approach

An acoustic emission (AE) approach to estimate the embrittlement temperature of asphalt binders is presented. Thin films of asphalt binders were bonded to various substrates and exposed to decreasing temperatures, starting at 20 °C and decreasing to approximately -50 °C. Differential thermal contraction between the substrate and asphalt binder sample under this cooling regimen induces thermal stress in the binder resulting in thermal crack formation, which is accompanied by a release of elastic energy in the form of transient waves. Using piezoelectric sensors (Digital Wave, Model B-1025), a four-channel acoustic emission system was used to record the acoustic emission activity during the cooling process. Assuming the embrittlement temperature to be the temperature at which the AE signal energy exceeds a pre-selected threshold energy level, this AE testing approach was found to be sensitive and repeatable for predicting this parameter for a wide range of asphalt binders. Unlike existing protocols for determining the low temperature cracking behavior of binders, the presented AE approach does not require the use of sophisticated software for predicting thermal stresses, and no assumption is required regarding the testing cooling rate and the binder coefficient of thermal contraction. The paper also explains how the procedure is being broadened to include asphalt mixture materials, and how the procedures developed may be used in a comprehensive pavement management system to accurately plan preventive maintenance and rehabilitation of asphalt surfaces to prevent propagating cracks and expensive repairs. The work is being conducted under the National Cooperative Highway Research Program (NCHRP) program titled Ideas Deserving Exploratory Analysis (IDEA).

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