Laboratory study of the long-term durability of buried concrete exposed to Lower Lias Clay

• The aggressivity of Lower Lias Clay can result in severe concrete deterioration.
• The study affirms the susceptibility of both 25% PFA concrete and SRPC concretes to TSA.
• Bitumen coating was an effective barrier at preventing deterioration in all concretes even when the surface scratched.
• The amount of thaumasite formation was found to decreased significantly with increasing burial depth.

This paper describes a long-term investigation into chemical degradation vulnerability of four different types of concrete that were exposed to pyrite rich clay. In this, four 100 mm square by 1.2 m long concrete columns made from Portland cement (PC), Portland limestone cement (PLC), sulfate resisting Portland cement (SRPC) and Portland cement blended with 25% pulverised fuel ash (PC–PFA) were buried for 9 years in slightly weathered Lower Lias Clay of water soluble sulfate class DS-2. One face of each concrete column was coated with bitumen to test the performance of this method of protection. The temperature was controlled at 4.5 ± 0.5 °C using a cold water circulation system. The performance of the different concretes was assessed by means of visual observation supported by X-ray diffraction (XRD), Infra-red Scanning (IR) and Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM-EDX) to identify the deterioration products.It was found that deterioration due to the thaumasite form of sulfate attack occurred in all four concretes with PLC concrete being the worst affected. The thickness of thaumasite deterioration into the concretes over the 9-year exposure was as follows: PLC = 47; PC = 33; SRPC = 22 and PC–PFA = 10 mm. The study affirmed the susceptibility to Thaumasite Sulfate Attack (TSA) of both PC–25% PFA replacement and SRPC concretes. It was also found that, the amount of concrete deterioration decreased with increasing burial depth, which was probably due to reduced access to air. The bitumen coating, even if damaged, was an effective barrier at preventing deterioration in all concretes.