Laboratory Investigation of Underwater Concreting

About the report:

Concrete and grout with minimal washout are required for underwater placements from both a structural and environmental perspective. Resistance to washout and consolidation are factors difficult to achieve underwater using conventional concretes or grouts.  Cohesive and self-consolidating concrete and grouts could provide the needed washout resistance and omission of consolidation efforts with mechanical vibration. 

Cohesive concrete and grout mixtures with high flowability that have satisfactory strength and durability would satisfy both the structural and environmental needs of underwater placement.  This study investigated the performance of both concrete and grout mixtures with and without self-consolidation in addition to various types of viscosity modifying admixtures for cohesiveness in an underwater environment.  The laboratory study investigated concrete and grout mixtures resistant to washout and segregation underwater. 

The study found that mass loss can be reduced through the choice of mixture ingredients, especially viscosity modifying admixtures; proper mixture proportions; use of grout bags; and the lowering of the slump or slump flow of the mixture.  However, reduction of mass loss was not directly related to reduction of pH.  To reduce the pH that is harmful to aquatic life, alternative cementitious materials—such as rapid set cements or magnesium phosphate binders—can be used.  In addition, the increase of pH underwater mainly occurs while concrete is still plastic; thus, reducing the setting time would limit the pH exposure. The study recommends that the Virginia Department of Transportation update existing special provisions on underwater concreting to include the findings of this study.

Authors