Laboratory Evaluation of a Unique Anti-Washout Admixture in Grouts

New construction or repair of existing structures dealing with the placement of concrete underwater poses certain challenges that require special placement techniques, and more specifically, specialized mixture proportions. Anti-washout admixtures (AWA), based on water-soluble polymers of various types, have been developed for use in concrete placed underwater in order to minimize cement washout and provide in-place concrete of satisfactory quality. These admixtures create a cohesive paste phase either by binding free mix water or by enhancing interparticle attraction. Hence, they are finding additional uses such as segregation or bleed control agents, and viscosity modifiers. Recently, the need for a viscosity modifying agent arose in a dam rehabilitation project in Alabama where a grout curtain was being placed to control seepage under the dam. To verify the feasibility of using an AWA in the grout mixtures for this project, a preliminary study was performed in the laboratory to investigate the performance of fluid grouts treated with a unique cellulose-based liquid AWA developed for underwater concreting. The effect of this unique AWA on the plastic properties of fluid and flowable grouts are presented in this paper. The results indicate that it is possible to use this admixture to modify grout viscosity, minimize bleeding characteristics, and improve washout resistance of fluid and flowable grout mixtures. Applications that might benefit from these improvements include: grouting riprap in tidal zones; and placement of grout curtains to minimize water seepage under dams.