Asphalt Thermal Cracking Analyser (ATCA)

Abstract

The Asphalt Thermal Cracking Analyser (ATCA) is a device that can simultaneously test two asphalt mixture beams while undergoing selected thermal history. The first beam is unrestrained and thus the change of its length with temperature can be used to obtain glass transition temperature (T_g) and coefficients of thermal expansion or contraction. The second beam is restrained at the ends and can be used to measure the thermal stress build-up as a function of time and temperature. The measures of length change and stress in beams can be used to get a comprehensive evaluation of the low temperature performance including change in strain, stress as a function of time and temperature.

The ATCA is considered an important advancement when compared to other existing thermal or mechanical cracking tests in which either thermal stress or moduli are measured, while making assumptions about coefficients of contraction and ignoring glass transition change. These assumptions are believed to cause serious errors in estimating thermal stresses.

Nine asphalt mixtures obtained from field sections in Minnesota, USA were used for the development of the ATCA. It is shown that the device can be used to estimate cracking temperature and strength. Further, the relaxation modulus of mixes can be directly estimated by solving the convolution integral using the measured thermal stress and strain from the restrained and unrestrained specimen, respectively. The ATCA can also be used to investigate response of asphalt mixtures to thermal cycles and isothermal conditions.