Top-down cracking has become an asphalt surface course distress of growing concern that must be dealt with during the design, construction, maintenance, and resurfacing of long-life asphalt pavements. The surface course is designed for heavy vehicle loadings and general traffic conditions in terms of rutting, resistance, durability, noise levels, smoothness, and frictional characteristics. The surface course must be properly maintained and should be renewable on an 18 to 22 year cycle. A pavement management and maintenance system is very important to achieving this objective. It is very important that top-down cracking, which is a rather complex surface distress mode related to tensile and shear stresses associated with non-uniform tire stresses, interlayer slippage, thermal stresses, stiffness gradients, construction problems such as segregation, and premature asphalt binder age hardening, is mitigated in order to achieve satisfactory overall pavement performance. While improved methods for pavement designs and rehabilitation to deal with top-down cracking are being developed, the most effective current approach appears to be enhanced asphalt materials and construction technology. The use of stone mastic asphalt and polymer modified asphalt binders have been shown to be very effective on a life-cycle performance and cost basis for instance.
