Development of the road aggregate test specifications for the modified ethylene glycol durability index for basic crystalline materials

Many basic igneous rocks contain smectite clays as a result of deuteric alteration during their formation or subsequent chemical decomposition. This has resulted in numerous failures when such materials are used in road construction due to inadequate durability. Various methods for assessing material durability have been developed and those using ethylene glycol (EG) to expand smectite clays appear to be the most effective. Protocols have been developed for a number of tests using EG, but it can be difficult to quantify the results in terms of unique values and develop specification limits for use in road construction. A simple new protocol for an EG soaking test, the modified ethylene glycol durability index (mEGDI), has been developed and the proposed interpretation of results is compared with existing specifications in this paper. The mEGDI is suitable for use as a screening test to identify poor-durability materials. However, inconsistent correlations with existing specifications exist for materials classified as durable by the mEGDI test and such materials require traditional testing before acceptance. The development of a rapid mEGDI is being investigated to reduce the time required to complete the test and therefore provide a useful screening test methodology.