Concrete has not traditionally been an economic material for most landfill barriers. Most barriers have been made with clay and many materials that have the potential for use as constituent materials concrete have been disposed of within the landfills. Recent increases in disposal costs including the introduction of the landfill tax have, however, made low cost low strength concrete a financially attractive option. In this paper the required properties of concrete mixes for this purpose are discussed. The results of an extensive investigation into potential mixes are presented and the measured properties are compared with.those, which are required. All of the mixes which have been investigated have large amounts of secondary materials in them. If these secondary materials were treated as wastes their disposal costs would be high so the mixes may be defined as 11 negative cost concretes 11• The results indicate that some of these mixes are well suited to the application.