|The volume of concrete block pavements in the EU is estimated to 5300 mio. m^2. Weed in the joints has through decades been removed with pesticides amounting to 1200 tons active material/ year. Environmental authorities wish to reduce the use of pesticides. But alternative treatments, like heat treatment, are expensive, consume a lot of energy, lead to a CO_2 emission of 1.1 mio. ton/year, and shorten the lifetime of the concrete blok pavement. In order to combat this problem this project sets out to develop a joint material in which weed will not grow. In some oder joints a form of natural sealing occurs, which prevents the growth of weed. This project will investigate the mechanism behind this natural sealing in order to imitate and improve it, so that weed prevention can be obtained right after the installation of the pavement. Thorough laboratory- and field tests must be completed to optimize the properties of the joint material. The qualities of the new joint material will be documented in a handbook, which will give an exact description of the production and use of the joint material with weed control.