As exposure to weathering processes or other changes in moisture content can be the cause of troublesome breakdown of many mudrocks, it is essential to have reliable means of predicting this behaviour. Although the ISRM slake durability test is the standard test used to distinguish between durable and non-durable mudrocks, the test does not always identify problematic materials. The dynamic nature of the test and the use of an arbitrary 2 mm drum mesh size are particular short falls. The test is too aggressive to characterize properly the behaviour of low durability mudrocks and slaking of samples to a fragment size greater than 2 mm is not measured. This paper reviews the various tests that have been used for predicting slaking potential. Comparative durability testing of 49 selected UK mudrocks ranging in age from Cambrian slates to Carboniferous Coal Measures is described. An evaluation of the performance of these materials in the one- and three-cycle ISRM slake durability test confirms the greater value of the latter. The modified jar slake test was found to be a suitably simple and accurate means of determining the durability of these mudrocks. Comparisons with the results of natural slaking trials confirm that the modified jar slake test presents a more detailed evaluation of the slaking potential of samples. In practice it is anticipated that the described test procedure will be used to provide data that would augment sample evaluation based on the ISRM slake durability test.

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The presence of sulphur compounds in soils and rocks can lead to chemical attack on construction materials such as steel and concrete when these materials are used as backfill to structures. Sulphate attack on concrete is a well-known phenomenon and BRE guidance to some of the causes and prevention measures has been available for some time. However, recent cases of the corrosion of corrugated steel buried structures and thaumasite attack on concrete bridge foundations have highlighted the role played by sulphides such as pyrite. The sulphides can oxidise, producing high sulphate concentrations and acid conditions, which can then attack construction materials. Present methods of assessing corrosion potential tend to concentrate on sulphate and pH, and do not fully address the problem of sulphides. This paper describes research carried out by TRL Limited and the University of Sheffield for the Highways Agency that aimed to develop better test methods for sulphur compounds in structural backfills. Advances in chemical test methods such as direct determination of sulphur by ICP-AES and novel methods of extraction have been investigated and compared with traditional methods for a range of materials with widely varying sulphur contents and mineralogy. The research led to recommendations for a revised suite of tests for sulphur compounds in structural backfills, appropriate methods of sampling and storage and limiting values for species such as reduced sulphur which are not covered by existing guidance. The research will be implemented by means of revisions to the relevant sections of the Specification for Highway Works and Design Manual for Roads and Bridges. The paper also aims to highlight the distribution of naturally occurring sulphur species within the UK geological materials. As a result of inadequate sampling, storage and assessment procedures, these sulphur species may cause problems to buried steel and concrete structures.