US Patent 7704011 Structural module

A sub-base layer for use in construction, comprises a plurality of connected substantially cuboid modules each having spaced-apart, substantially parallel top and bottom walls joined by a peripheral sidewall defining an enclosed volume. The connection between the modules is effected by a plurality of tie members which prevent lateral movement of the modules relative to one another. The layer is particularly useful as a lightweight replacement for aggregate sub-base layers in foundations, roadways, pavement, carparks, and the like.