The use of alternative materials (e.g. blast furnace slag, demolition rubble, crushed concrete, and bottom ash from municipal solid waste incinerators) in road construction reduces the consumption of scarce natural aggregates and recycles materials that would otherwise be disposed of as waste. In most European countries, use of alternative materials in road construction is relatively low at present, for several reasons, including high transport and treatment costs, uncertainties about the mechanical performance of alternative materials, and environmental concerns about potential contamination of surface and ground waters by leaching from alternative materials. There is however an increasing pressure, driven by national governments, to increase the use of alternative materials by means of taxes on material sent to landfill and on the use of natural aggregates, and by the setting of targets for increasing the amount of recycling.