Interim results of a long-term investigation on the durability of steel reinforcement embedded in expanded slate structural lightweight concrete are reported. The influence of concrete cover, cement content and of partial replacement of lightweight fines with natural sand was studied. Surface crazing was found to increase with cement content and increasing fine particles. The carbonation depth, and the relative permeability measured by alcohol absorption, were found to decrease with increasing cement content. Inclusion of natural sand in the mix reduced the permeability and the penetration of the carbonation front into the concrete. No instance of damage due to corsosion was found in embedded steel reinforcement after two year's exposure to industrial atmosphere.