article · Alexandria Engineering Journal
This study evaluates underwater concrete mixes formulated with anti-washout admixtures at concentrations ranging from 0.0% to 0.5% by cement weight, paired with cement contents between 400 and 550 kg/m3. The concrete mixes incorporated 15% silica fume, 4% high-range water reducers, and a one-to-one ratio of fine aggregate to steel slag coarse aggregate. Performance was assessed by measuring slump, slump flow, compressive strength, and washout resistance. Testing utilized both the standard CRD-C61 plunge test and a newly manufactured pressurised air tube designed to simulate the impact of water pressure on washout. Compressive strength was compared between specimens cast underwater and those cast in air. The findings confirm that adding anti-washout admixtures facilitates mix production, with dosages between 0.3% and 0.5% satisfying Japanese Society of Civil Engineers standards, while the novel pressurised simulation technique proved reliable for assessing concrete properties.
Pouring concrete directly into water creates severe technical challenges, as water pressure can dilute the mixture and erode cement particles. Demonstrating effective admixture ratios and introducing a reliable method to simulate water pressure allows civil engineers to better predict material performance and maintain structural integrity during underwater construction projects.
This research is applicable to marine construction contractors, concrete suppliers, and testing laboratories involved in underwater infrastructure. It presents applied and tested mix designs utilising steel slag alongside a purpose-built pressurised testing apparatus. Because the testing apparatus and specific mix ratios were evaluated in an experimental environment, further industrial standardisation and field validation would be required before direct commercial implementation.
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Under-Water Concrete (UWC) contains Anti-Washout Admixtures (AWA) (0.0%, 0.2%, 0.3%, 0.4% and 0.5%) by weight of cement with cement contents (400, 450, 500 and 550 kg/m3). All concrete mix contains silica fume and high-range water reducing (15% and 4%) respectively by weight of cement. The fine to steel slag coarse aggregate was 1:1. The concrete mix was tested for slump, slump flow, compressive strength and washout resistance using two test methods based on different principles. The first method is the plunge test CRDC61 which is widely used in North America, and the second method is the pressurized air tube which has been manufactured for this research and developed to simulate the effect of water pressure on washout resistance of underwater mix. The results of compressive strength test were compared to concrete cast underwater with that cast in air. Test results indicated that the use of an AWA facilitates the production of UWC mix with the added benefit of lower washout resistance. New technique of simulating pressurized UWC is reliable for detecting UWC properties. Adding AWA (0.3–0.5%) by weight of cement makes all mix acceptable according to Japanese Society of Civil Engineers.
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DOI: 10.1016/j.aej.2015.03.017
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