Performance of various modified binders in road trials and under simulated crack movement in the laboratory

Abstract

The use of bitumen-rubbers and other modified binders to inhibit reflection cracking, highlighted the need to investigate the phenomena of load-associated crack movement and crack reflection and the evaluation of the field performance of modified binders. The development of the Crack-activity Meter (CAM)and its use with the Heavy Vehicle Simulator (HVS) has led to an improved understanding of crack movement behaviour. The N3 trial sections, which were built to determine the field performance of various modified binders under normal traffic, as well as initial rsults from this experiment are discussed in this paper. To date, fatigue testing under simulated crack movement in the laboratory was conducted on four of the binders used in the N3 trials. Initial results from this work, including fatigue curves of the four materials, are reported. Guidelines are suggested for the identification of sections on pavements where crack reflection problems can be expected. Models were also developed to predict crack movement from a knowledge of block sizes and structural parameters such as basin of deflection and an example of this is shown. It is also shown that these models can be used to predict the decrease in crack movement due to the overlaying of a pavement with a structural layer. It is concluded that the measurement of an analysis of crack movement can aid rehabilitation design.