Since 1970 unbound gravel or crushed stone has been the most widely used pavement material in Irish roads. Between 1970 and 1985 unbound glacial gravel was the preferred construction material because of its low cost but was then replaced by crushed rock, mainly limestone aggregate, which has generally performed well. Irish experience in the use of unbound aggregates indicates that pavements constructed with high quality granular layers can give long service if strong stable materials are specified and care is taken during construction to ensure adequate compaction and control of moisture content. The importance of moisture content in the performance of granular materials and the need to provide an impervious surfacing for unbound pavement material is emphasised. The different approaches identifying high quality granular materials for specifications purposes are described. Recent performance based laboratory tests on crushed aggregate from nine quarries throughout the country indicate that different rock types will perform differently in road pavements.
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