Contradictory results have been published on the effect of sea sand and seawater in concrete as opposed to conventional river sand and freshwater. The majority of studies show equivalent, if not better, results when sea sand and seawater are used in concrete, although some studies concluded otherwise. This paper investigates the variations in the chemical and physical properties of sea sand. It has been found that each sea sand sample is unique, which might be the reason for the contradictory findings in the current literature. Chemical properties of sea sand were analyzed using a scanning electron microscope and the physical properties were observed using an optical microscope. The particle size distribution was measured. The short-term mechanical properties of sea sand-seawater concrete were compared with conventional concrete. The concrete samples were cured in natural marine conditions and atmospheric conditions and tested at 7 and 28 days. Sea sand-seawater concrete had a high early compressive strength at 7 days and remained slightly higher than conventional concrete at 28 days. The experimental procedure used all natural, unaltered, concrete constituents and curing conditions.
The use of seawater and sea-sand in producing concrete has attracted increasing research attention in recent years to address the shortage of river sand and in certain applications the shortage of freshwater. In particular, reinforced concrete structures made of seawater sea-sand concrete (SSC) and corrosion-resistant fiber-reinforced polymer (FRP) are particularly attractive for the development of coastal and marine infrastructure (e.g. on remote islands) as durable structures can be created using locally available materials. Existing studies on SSC or seawater concrete have been largely limited to the use of mixing water with a salinity level close to the world-average ocean salinity. Against this background, the present paper reports the first ever systematic study on the effect of salinity of mixing water on the properties of concrete. The present study covered a wide range of salinity levels from 16.5 g/L to 82.5 g/L, and examined a wide range of short-term concrete properties including the heat of hydration, shrinkage, compressive strength and modulus of elasticity. The test results show that the salinity of mixing water has a considerable effect on the rate of hydration heat and shrinkage at early ages, as well as the cumulative release of hydration heat. It is also shown that the water salinity has a slight negative effect on the compressive strength and modulus of elasticity of concrete at ages older than 14 days.
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