The laboratory investigation of concrete affected by TSA in the UK

Abstract

Abstract Procedures that have been successfully employed by Geomaterials Research Services Ltd. in the determination of the distribution of the thaumasite form of sulfate attack (TSA) in concrete samples taken from bridge and other motorway structures throughout the UK are described. Electron microprobe analysis has been used to provide confirmation of the presence of thaumasite and to investigate the distribution of sulfate compounds including gypsum and ettringite in cement paste at the surfaces of concrete affected by sulfate attack. Electron microprobe analysis has the advantage that it is capable of detecting very small quantities of thaumasite. Electron microprobe analysis used in conjunction with petrographic analysis is regarded as the most effective tool for the diagnosis of TSA and other forms of sulfate attack. The analysis of numerous cores taken from bridge foundations throughout the UK shows that the development of TSA is often accompanied by the formation of calcium carbonate in cement paste. High levels of chloride in the cement paste of TSA damaged concrete suggest the importance of run-off moisture as a contributory factor in the development of TSA.