A comparison of classification systems for aggressive ground with thaumasite sulfate attack measured at highway structures in Gloucestershire, UK

Abstract

Part one of the BRE Special Digest 1 ‘Concrete in aggressive ground’ (2001) provides UK guidelines on assessing aggressive ground conditions with respect to the specification of concrete and protective measures required for concrete structures in contact with the ground. This supersedes the guidelines of BRE Digest 363 (1996) and the Thaumasite Expert Group Report (1999). All three publications rely in part on classifying the ground based on the chemical composition of the soil, backfill and groundwater at the location of the proposed structure. This paper provides an empirical assessment of the three classification schemes that was made possible following an extensive investigation into the thaumasite form of sulfate attack (TSA) in buried concrete highway structures in Gloucestershire. Ground classifications were made at 21 of the sites. The results of this study confirmed that whenever possible, the sulfate concentration in groundwater should be measured, and that as noted in SD1, the potential sulfate classification can be too conservative. The conclusions are limited geologically to the Lower Lias Clay Formation and to Recent Alluvium. The current classification system needs to be developed further by undertaking and reporting similar case studies from a variety of ground conditions.