Resources

The objective of this project, carried out in 2000–2001, was to study the weathering quality index (WQI), the measure used in the Transit New Zealand M/4:1999 specification basecourse aggregate, in order to determine the changes occurring when a marginal aggregate is modified with lime. (A marginal aggregate is unlikey to have the weathering characteristics necessary to comply with TNZ M/4.) The clay index (CI) test was used to measure the changes that occurred in the quantity of swelling clay minerals present at each stage of the laboratory study.

The project involved a review of recent research into the weathering of rock and its relationship to aggregate used in the construction of unbound granular road pavements. This was followed by a series of laboratory tests carried out on a selection of aggregates obtained from quarries around the Auckland region. The laboratory phase of the project involved measuring changes in the WQI and CI as the aggregate was being subjected to a number of processes including treatment with lime, curing, and then passing through a laboratory crusher to replicate the compaction and trafficking processes.

The results showed that the WQI was not sufficiently sensitive to the changes that were occurring in the aggregate, but that the CI provided a good measure. The report concludes that the potential effects of weathering should be monitored using the CI alone.

Keywords: aggregate, clay minerals, marginal aggregate, modification, stabilisation, roads, weathering