A study was carried out to improve knowledge of movement of water into and out of road pavement layers under UK conditions. The theoretical background and results of recent international studies were reviewed. Field and laboratory studies were carried out to obtain data to test the theoretical models and to trial various investigative techniques. A section of existing trial concrete pavement was instrumented and rainfall, runoff, sub-base drainage and pore pressures in the sub-base and subgrade measured over a full year. The chemical composition of the rainfall, runoff and sub-base flows was measured and compared with laboratory leaching tests to assess the factors controlling the chemical composition of the flows. The permeability of the pavement layers was estimated from laboratory-based experiments. Cracks were induced in the concrete after one year, to see if the sub-base flows increased as a result. Ground probing radar was used to investigate changes in sub-base moisture content, and a tracer study using saline solution performed to find if water from the surface could be detected at the sub-base outflow. Theoretical modelling methods, identified by the literature review, were compared with the field data. The models predict greater flows than those measured. Difficulties were encountered in obtaining reliable data for some parameters, but several of the investigative techniques showed promise. Attempts to obtain an indication of the water fluxes from a combination of models and the field data are described.

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