Evaluation of Concrete Mixtures for Underwater Pile Repairs

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Abstract Repair of submerged concrete piles that have undergone considerable loss in cross section and strengthening of existing marine piles often involves jacketing the piles and filling the annular spacings between the jackets and the piles with concrete. In this paper, physical and mechanical properties that are deemed necessary to secure high-quality concrete under water were evaluated for numerous mixtures. Four concrete mixtures were selected to repair 2.4-m (8-ft)-high mock-up piles located above water. Rigid rectangular forms were erected around the 203-mm (8-in.)-square mock-up piles. The resulting annular spacings between these forms and the mock-up piles were first filled with water and then with concrete. The concrete was discharged within previously placed unhardened concrete to minimize segregation and water dilution rather than allowed to fall through water. Once the repair had set, the exposed surface of each underwater-cast pile was examined for any signs of segregation. Cores were obtained to evaluate the in-situ density and compressive strength of the concrete, as well as the bond strength between the underwater-cast concrete and the central mock-up pile. The testing program indicates that concrete mixtures containing antiwashout admixtures and either silica fume or fly ash can secure higher quality repairs, at equal or lower costs, than similar concretes made with high silica fume or high cement contents and no antiwashout admixtures. Properly proportioned concrete mixtures resulted in exposed repair surfaces free of segregation, with mean in-place compressive strength in excess of 58.6 MPa (8500 psi). The in-situ density of such concrete was identical to that cast and consolidated above water, and the bond strength to existing mock-up piles was in excess of 2.1 MPa (300 psi).