IAEG2006 Paper number 38 © The Geological Society of London 2006 1 Use of quarry dust instead of river sand for future constructions in Sri Lanka

Abstract: The construction industry of Sri Lanka expects a serious shortage of sand in the near future due to over exploitation of river sand. Then, the entire construction industry will be paralyzed if there are no alternative sources instead of river sand. Near-shore marine sand, dune sand and quarry dust (crushed rocks) are the other alternative sources available for it in Sri Lanka. Quarry dust may not be suitable for the civil constructions due to the mixture of various broken minerals. Hence, research was initiated to find out the mineralogical quality of the quarry dust. Fresh rock samples from different quarries were collected for the laboratory tests. Thin sections were prepared from each sample and studied under the petrographic microscope. Mineral composition of each sample was counted using a point counting instrument attached to the microscope. The minerals present in fresh rocks were quartz, feldspar, biotite mica, hornblende and hypersthene as major and a very few other minerals as minor. There are not any reactive forms of silica minerals such as opal and chalcedony in these rocks. Hornblende biotite gneiss, biotite gneiss, migmatite and migmatitic gneiss showed mica percentages higher than 5 % (5%-20%). Mica percentages in charnockite, charnocktic gneiss and granitic gneiss are always less than 5%. Generally, sand with less than 5 % of mica is considered as suitable for civil engineering construction. Therefore, charnockite and charnockitic gneiss and granitic gneiss are suitable rock