Gneisses and Charnockite form crushed rocks is our main source of coarse aggregate and is available in abundance. River sand is the first choice fine aggregate type for structural concrete in Sri Lanka. However, due to scarcity and regulation in sand mining, quarry dust and offshore sand are now being increasingly used as an alternative to fine aggregate in concrete. River sand has long been considered as an unsustainable solution for the fine aggregate requirement of the country. Quarry dust which is a byproduct of metal crushing amounts only between 20-30% of the total aggregate being crushed. Furthermore demand for lot of other uses like masonry block and paving block making, quarry dust doesn’t provide a comprehensive solution for the fine aggregate requirement of the country. However, being an island nation with substantial offshore sand deposits, offshore sand has a great potential to cater the country’s demand for fine aggregate. Fig. 5 shows the usual sources of fine aggregate (River sand) and coarse aggregate (Crushed stones) of concrete and alternative sources of fine aggregate types
(Quarry dust and Offshore sand) for concrete.