Sulfur species in geological materials––sources and quantification

Groundwaters containing dissolved sulfates and sulfuric acid can lead to chemical attack on construction materials such as steel and also concrete and cement stabilized soils forming complex hydrated calcium sulfo-aluminate species such as ettringite and thaumasite. Many factors contribute to aggressive conditions that need to be adequately determined prior to construction. The identification of acid environments is generally tested for, although in some circumstances corrosion may also take place under apparently neutral or alkali conditions. Sulfur reducing bacteria can give rise to such conditions. They thrive under acidic and aerobic conditions within the range of ambient temperatures found in the UK and where there is an availability of reduced sulfur and carbon compounds. As present methods of assessment for aggressive conditions tend to concentrate on sulfate and pH determinations, the problems posed by reduced sulfide species are not fully addressed.This paper describes research by the TRL Limited and the University of Sheffield for the Highways Agency to develop better test methods for sulfur compounds in structural backfills which may cause problems to buried steel and concrete structures.