Andrew Dawson[7], Niki Kringos, Tom Scarpas and Primoz Pavsic
Abstract Pavement surfaces provide a key route of ingress of rain water into the pavement construction. Thus, permeability of asphaltic materials and the water ingress capacity of cracks in the pavement are very important. A range of equipment exists to determine the permeability of asphaltic mixtures both by in-situ and laboratory testing. Sometimes porous asphalt surfacing is provided to deliberately allow water into the pavement to limit spray from vehicles and to limit tyre-pavement noise generation. These porous surfaces can become clogged with fines, but rehabilitating without causing premature damage is a challenge. Except for this planned acceptance of water into the pavement, water is generally undesirable as it often causes ravelling (stripping) of the asphalt whereby aggregate and binder separate. The mechanisms behind this separation are becoming better understood due to advances in computational engineering and mechanical and physio-chemical testing.
Keywords Asphalt ■ cracking ■ infiltration ■ stripping ■ ravelling ■ porous asphalt ■ permeability
The topmost layer of most pavements is comprised of a bound layer. The vast majority of pavements have an asphaltic surface. A far lower proportion have a Portland cement concrete (PCC) surfacing. Whilst it is usually a design aim of these surfaces that they provide an impermeable covering to all the lower pavement layers, water does penetrate such surfacings. It may do so either through intact, but not impermeable, bound material or through cracks and joints in the surfacing. Although the emphasis of this book is on water movement and its impact in the unbound material and subgrade layers of the pavement, some information on the movement and response in the upper, bound layers is indispensable. Apart from any other consideration, any
complete analysis of water in the road and foundation structure must consider the input conditions — which are significantly affected, perhaps even controlled, by the surface layer. In this chapter the emphasis is on asphaltic mixtures, their permeability and the damage that they suffer from water. Consideration is also given to the ingress of water through joints and cracks. Some of this may also be applicable to the ingress through construction joints and cracks in Portland concrete surfacings. In addition, some consideration is given to porous asphalt mixtures — surfacing that is designed to prevent runoff flowing over the surface.
