Top down cracking appears to be a common mode of HMA pavement distress in at least several states and countries. Traditionally, pavement cracking is thought to initiate at the bottom of the HMA layer where the tensile bending stresses are the greatest and then progress up to the surface (a bottom-up crack). Most traditional transfer functions used in mechanistic-empirical structural design are based on this concept. However, the late 1990s saw a substantial focus on a second mode of crack initiation and propagation: top-down cracking.
Water bleeding (left two photos) occurs when water seeps out of joints or cracks or through an excessively porous HMA layer. Pumping (right-most photo) occurs when water and fine material is ejected from underlying layers through cracks in the HMA layer or out the sides of the HMA layer under moving loads.
Pavement rutting is defined as surface depression in the wheelpath. Pavement uplift (shearing) may occur along the sides of the rut. Ruts are particularly evident after a rain when they are filled with water. There are two basic types of rutting: mix rutting and subgrade rutting. Mix rutting occurs when the subgrade does not rut yet the pavement surface exhibits wheelpath depressions as a result of compaction/mix design problems. Subgrade rutting occurs when the subgrade exhibits wheelpath depressions due to loading. In this case, the pavement settles into the subgrade ruts causing surface depressions in the wheelpath.
Since the advent of Superpave mix design technology and the follow-on predictive testing now used in hot mix asphalt (HMA) design evaluation, rutting has largely been eliminated as a concern when the pavement structure and HMA are properly designed. In Washington State, the Hamburg Wheel Test device has been in use since 2010 to evaluate HMA designs for rut resistance prior to approval for use. The exception to the rule, for both asphalt and concrete pavements, is in areas where extensive studded tire use is common.