PREDICTION AND PREVENTION OF SURFACE CRACKING IN ASPHALTIC PAVEMENTS. SIXTH INTERNATIONAL CONFERENCE, STRUCTURAL DESIGN OF ASPHALT PAVEMENTS, VOLUME I, PROCEEDINGS, UNIVERSITY OF MICHIGAN, JULY 13-17, 1987, ANN ARBOR, MICHIGAN

In several relatively new road pavements premature cracking in the top layer(s) has occurred. It has been found that this type of cracking could be surveyed both in and outside the wheelpaths. According to the currently used mechanistic design procedures with linear elastic multilayer programs the greatest tensile strains are predicted in the bottom of the asphalt layers and not at the surface. To search for causes of this type of distress and to provide recommendations for the prevention, theoretical analyses, laboratory experiments and field studies have been conducted. In the theoretical analyses the currently used traffic models and fatigue parameters have been evaluated. The tentative results show that radical shear forces under rubber tyres can attribute to surface cracking. Secondly, it is shown that energy parameters can be useful in the structural analysis of top layers. Experiments have covered aspects such as mix composition, mix properties, fatigue, strength, thermal stresses and dynamic load induced residual stresses. The fatigue characteristics of the mixes appeared to be not sufficient mainly due to excessive hardening of the bitumen. The mixes have been tested for their response on low temperatures. Tests on stress relaxation could be desribed very well by the Burgers' model. This enabled the use of the model for investigating the influence of loading time, temperature, and load repetitions on the asphalt mix. Field studies containing visual condition surveys and falling weight deflection measurements have been conducted to check the results of the laboratory experiments. Tentative recommendations are presented to prevent premature cracking of asphalt wearing courses.