In distressed pavements a large proportion of ingress may be through cracks, even if the intact material is relatively impermeable. It has been suggested that there are four factors which influence infiltration rates in cracked asphaltic pavements (Ridgeway, 1976):
• the water-carrying capacity of the crack or joint,
• the amount of cracking present,
• the area that drains to each crack, and
• the intensity and duration of the rainfall.
The first of these is of particular concern in this chapter and is addressed in Section 5.4.2.
5.4.1 Laboratory Permeability Determination
Both constant head and falling head laboratory methods are available to determine the permeability of asphaltic cores, often with sides sealed using a membrane and/or a confining pressure to prevent edge-leakage (Cooley, 1999). There is some evidence (Maupin, 2000) that the falling-head device is the better device for testing both cores and moulded cylindrical specimens. There are some standardized test procedures of which the recent standard published by FDOT (2006), is an example. A schematic of their laboratory permeameter with flexible walls is given in Fig. 5.2. There is also a European standard available (CEN, 2004).
