Problems have been experienced on recent highway schemes with corrosion of galvanised steel buried structures (CSBS) due to chemical reaction from structural backfill. The corrosion has been attributed to the presence of sulfates and sulfides in the structural backfill. A reveiw by TRL (Reid and Perry, 1996) indicated that improvements could be made in the identification and assessment of sulfur compounds in the current Specification for Highway Works (MCHW1) and related documents. The present project was undertaken to develop appropriate test methods for sulfur compounds in structural backfills, to determine appropriate limiting values for the various sulfur compounds and to prepare modifications to MCHW1 and related documents. This report includes a review of existing specifications and test methods for sulfur compounds in soils and rocks and describes the development of new test methods which allow a fuller characterisation of sulfur species. The concept of oxidisable sulfides content is introduced, as the amount of sulfate which would be produced by complete oxidation of the reduced sulfur in a material. Limiting values are given for oxidisable sulfides and total potential sulfate. Detailed protocols for the new test methods and suggested amendments to the MCHW and DMRB are given. The updated 2005 edition contains revised limiting values for backfill to concrete.

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