Cracking of Asphalt Concrete at Low Temperatures

Abstract

The objectives of this research are (1) to characterize the fracture resistance of asphalt concrete at low temperatures and (2) to develop a simple test method for laboratory testing. Cracking of asphalt concrete at low temperatures is a major problem in the Upper Midwest. The cold temperatures in the winter months impart a brittle behavior to an otherwise ductile (viscous) material. The formation of cracks in the pavement provides a pathway for the migration of water, which may refreeze and cause more damage. The conventional three-point-bend (3PB) load configuration is proposed for conducting fracture tests. The entire 3PB fixture is placed in an environmental chamber, where the temperature is controlled and maintained at -18° (0°) and -34°C (-30°F). The experimental apparatus and test procedure are described in detail, and the corresponding formulae are derived. Following linear fracture mechanics, the fracture toughness of a particular asphalt concrete at 10% air voids is about 0.5 MPa-m° s at both temperatures, although the nonlinear response is more pronounced at -18"C. This means that less energy is needed to initiate a crack at -34°C compared to -18"C. Furthermore, it appears that the toughness of the asphalt concrete is increased with an increase in compactive energy, which is indicated by a decrease in air voids content.