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Effect of Water Velocity on Performance of Underwater, Self-Consolidating Concrete

Although considerable advances have been made in enhancing in-place properties of concrete cast in standing water, little is known about the performance of concrete cast in flowing water. A hydraulic channel measuring 6 m in length was constructed in the laboratory to cast concrete in water flowing at velocities up to 1.0 m/s. A detailed investigation was carried out to determine the effect of the dosage of welan gum and cellulose-based antiwashout admixtures on the washout resistance of concrete placed in flowing water. The investigated mixtures were prepared with a water-cementitious materials ratio (w/cm) of 0.41 and 0.47 and contained up to 10% silica fume replacement. The high-range water reducer dosage was adjusted to maintain an approximate slump flow consistency of 500 mm to ensure self-consolidation and obtain relatively flat underwater surfaces. A concrete having a slump flow and a standard washout mass loss of 500 mm and 5%, respectively, was cast in water circulating at 0.0 m/s, 0.10 m/s, 0.40 m/s, and 0.65 m/s to evaluate in-place strength and unit weight. The selected mixture incorporated a medium dosage of welan gum and 8% silica fume and had a w/cm of 0.41. Test results show that despite the highly fluid nature of the concrete, considerably greater washout resistance can be secured when the dosage of antiwashout admixture is increased, the w/cm is reduced, and 10% silica fume is incorporated. The increase in water velocity can lead to a net reduction in in-place strength. The optimized high-performance concrete developed an in-place compressive and splitting tensile strength greater than 70% of control samples along the 5-m blocks cast in water current inferior to 0.4 m/s. Such strengths ranged between 50-65% and 70-80%, respectively, when the velocity increased to 0.65 m/s.