A revised ethylene glycol test for assessing the durability of basic crystalline materials for road aggregate

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Paige-Green, Philip
Holding Date 15 September 2008

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. Additionally, the size of the sample (eg, Method CRD C 148-69, which uses about 5 kg of 19 to 76 mm aggregate) makes it impracticable for many road construction material investigations where only limited drill core is available for testing.
As a result, a number of investigations using different treatments and soaking techniques have been pursued. By carrying out various strength and impact tests (eg, 10% fines aggregate crushing test (10%FACT), Aggregate crushing value (ACV), aggregate impact value (AIV), etc) on dry, water soaked and EG soaked materials, useful results can be obtained. However, these tests are not without problems: they use a relatively small, single sized fraction (9 – 13 mm), which is often difficult to obtain in sufficient quantities during the early stages of projects (eg, from drill cores), some dispute exists over how long the material should soak in the EG (4 days seems to be the optimum), spurious results are commonly obtained (eg, materials soaked in water are weaker than those soaked in EG), etc.
Tests using the direct soaking of cores or particles in EG with descriptions of the behaviour are commonly used and seem to be good indicators of performance. However, their interpretation (particularly quantitatively) is often difficult. Based on a number of recent investigations, the following simple protocol for an EG soaking test has been developed:
40 pieces of more or less equidimensional aggregate (20 to 25 mm in diameter) are placed in a tray and covered by ethylene glycol. The aggregate pieces are placed in a fixed pattern (five rows of eight pieces) so that each particle can be individually assessed and its behaviour with time recorded. The material is inspected after 1, 5, 10 and 20 days and the number (and location in the tray) of pieces of spalled (shed small fragments from their edges), fractured (split into two or three pieces) and disintegrated (spilt into more than 3 pieces) aggregate are recorded at each assessment. A value of the EG Durability Index (EGDI) is calculated by weighting the number of pieces affected after 5 days and their degree of disintegration.
This can then be related to the expected performance of the material as a road aggregate according to the following tentative criteria:
Subbase - EGDI<20
Base course - EGDI<10
Surfacing - EGDI<35
EGDI after 20 days<1.5xEDGI after 5 days