Correlating washout to strength loss of underwater concrete

A research project was undertaken to evaluate the effect of mixture parameters on the fresh and hardened properties of underwater concrete. Washout loss was determined using either the CRD C61 test method or a newly developed device for simulation of increased hydrostatic pressure on the concrete/water interface. Correlations between washout loss and residual compressive strength evaluated in dry conditions and after washout measurement were established. The test results showed that the incorporation of cellulose- or welan gum-based anti-washout agents can greatly reduce water dilution of underwater concrete while increasing flow resistance and cohesiveness. Increased cement and silica fume contents together with reduced free water resulted in lower washout loss. An increased depth of casting was found to increase washout loss until reaching a threshold water head beyond which significant washout loss would occur. A linear relationship with a high correlation coefficient of 0·91 was obtained between washout loss and residual compressive strength of the tested underwater concrete mixtures.