Offshore Sand as a Fine Aggregate for Concrete Production

The aim of this study is to test the relevant properties of offshore sand obtained soon after dredging and to examine the effects on chloride levels of offshore sand when fresh water is drained to simulate average monthly rainfalls. The findings are valid for offshore sand that does not require washing particularly to remove organic matter and other contaminants. As per the results of sieve analysis, grading of the offshore sand is within the limits specified in BS 882:1992. The compressive strength of grade 25 concrete which is the mostly used structural concrete is also within the acceptable limits. The shell content of offshore sand for shells finer than 10 mm and coarser than 5 mm is 6.5 per cent. This is far below the 20 per cent limit specified in BS 882:1992. For grade 25 concrete produced with OPC, an allowable limit of 0.101 per cent by weight of sand was computed for chloride content in offshore sand. The chloride content of offshore sand obtained soon after dredging was 0.04%. Even a rainfall as low as 9.9 mm can reduce the chloride content (range from 0.01 to 0.05) to levels far below the allowable limit (0.101). Rainfalls as high as 581 mm could wash away chlorides almost completely (below 0.01). The study revealed that offshore sand obtained from 2 to 7 km away from the western coast, Sri Lanka soon after dredging, could be used as an alternative to river sand.