Investigation of concrete–clay interaction with regards to the thaumasite form of sulfate attack

•The aggressivity of Lower Lias Clay result in concrete deterioration exceeded that observed in standard test solutions.•Temperature can be considered to be a secondary factor for thaumasite formation in concrete exposed to Lower Lias Clay.•The route of TSA formation for concrete exposed to Lower Lias Clay differs from that seen in standard sulfate solutions.

The influence of clay composition on the severity of attack due to thaumasite sulfate attack (TSA) on concrete made with CEM I and CEM I blended with 10% Limestone Filler (LF) was investigated. Concrete specimens were exposed to weathered Lower Lias Clay (LLC), for which the water soluble sulfate corresponded to the BRE sulfate class of DS-2, for 12 months at 5 and 20 °C. A parallel study was carried out in which specimens of the same concretes were placed in sulfate solutions equivalent to DS-2 and DS-4 at the same temperatures. It was found that concrete exposed to clay with sulfate design class DS-2 deteriorated at a faster rate than corresponding specimens in DS-2 solution and at a similar or greater rate to those exposed to the DS-4 sulfate solution. This suggests that the aggressively of clay and resulting concrete deterioration could exceed what might be observed in concrete exposed to equivalent standard test solutions.