A method to estimate the thermal stress build-up in an asphalt mixture from a single-cooling event

Abstract

This paper suggests a method to estimate the thermal stress build-up in asphalt from a single-cooling event based primarily on the measured bitumen rheology. In order to check the reasonableness of the calculation, first the thermal stress-restrained specimen test (TSRST) was performed on a laboratory-compacted, cylindrical asphalt specimen. Concurrent to the TSRST test, the thermal strain was measured from an unrestrained asphalt specimen. As a result, the thermal stress build-up and coefficient of thermal expansion were determined. The bitumen from the TSRST specimen was recovered and the bitumen low and intermediate temperature rheological properties were determined using a dynamic shear rheometer (DSR) technique (commonly referred to as 4-mm DSR) that allows testing to−40°C by way of a correction for instrument compliance. The estimated and measured TSRST thermal stress build-up were compared and found to be remarkably similar. Also, the TSRST thermal stress build-up was compared with the estimated thermal stress build-up using the methodology in ASTM D6816-11, which includes an empirical pavement constant (PC), and they were found to be significantly dissimilar suggesting that simply multiplying the binder thermal stress by a PC (18 in this case) does not provide a particularly good estimate of the mixture thermal stress build-up.