Non-dispersible concrete in underwater concreting

Abstract

The growing need for constructing diverse marine structures, such as harbours, has led to the need of developing a sufficient material that will render such projects viable. For the past years concrete has been the material of choice given that, if designed correctly, it would offer ease or placement, sufficient resistance to the harsh marine environment and will be able to develop desirable strength. When designing concrete to be placed underwater, the methods adopted and the parameters designed for, are the same as those that apply for dry land concreting. The only exception is that underwater concrete must be able to offer resistance against the action of washout. In an attempt to ensure such qualities, non-dispersible concrete mixes have been developed. Such mixes are made by the incorporation of anti-washout admixtures to the mix. The primary objective of this research is to investigate the changes in the qualities of concrete, such as; workability, flowability, washout resistance and compressive cube strength at twenty eight days, which is brought about upon addition of anti-washout admixtures. Two anti-washout admixtures were obtained and tested and in doing so it was observed that both additives led to an increase in the viscous nature of the base mix to which they were added. The increase in viscosity led to a reduction in the degree of workability and flowability of the mix, which for underwater concrete works is not very desirable. The addition of these additives to a base mix, containing a superplasticizer, led to the production of a satisfactory, non-dispersible mix having the necessary qualities.