Storage and Infiltration of Rain Water Through Permeable Paving Blocks a First Step to Disconnect – Results of a Belgian Research Project

Water-permeable paving is used to minimize the far-reaching adverse effects produced by sealing off the natural water balance. The risk of flooding during thunderstorms by water running off the surface or by overflow from sewer pipes is strongly reduced by the immediate absorption and subsequent storage of water in the permeable structure. Although drainage into the natural ground is possible, a water-permeable paving should be looked upon as a drainage-saving element rather than an actual drainage system. This is mainly because permeability may drop significantly as the pores become silted up [1]. Some research into the concept of water-permeable pavings has been done to render their permeability as durable as possible, but so far it has been inconclusive in this respect [2-10]. A research project funded by the Flemish Government (through IWT1) was, therefore, undertaken to model the permeability and storage capacity of structures and to optimize the preservation of permeability. This project includes laboratory tests on the paving material as well as on the base and subbase materials, and field tests on soils and water-permeable pavings. In addition, a parking area with twelve different sections (each 120 m² in area) was constructed on the premises of the Belgian Road Research Centre to test five different types of water-permeable concrete paving block and two different types of base layer. Furthermore, the water permeability of existing and new permeable pavings in Belgium is measured and monitored over time. The goal of this project is to gain a clear insight into the working mechanism of permeable pavings in storing and infiltrating water, and to provide sound guidelines for architects, engineers and constructors. The Belgian Road Research Centre, the Laboratory for Soil and Water Management of the Katholieke Universiteit Leuven and the federation of Belgian manufacturers of linear and modular paving elements in concrete (FEBESTRAL) are working together on this project. This paper focuses on the concept of water-permeable pavings and on the measurement techniques applied in the laboratory and in situ. The important role of porous block paving in avoiding surface run-off is demonstrated, as well as the need for a porous base to allow storage in the structure. The results are checked against the requirements for water infiltration and storage facilities set in a Flemish implementation decree of 1st October 2004 [12].