UNDERWATER CONCRETE. PART 3: CONSTRUCTION ISSUES

This paper examines some technical considerations in the production and delivery, placement and protection, and form pressure of underwater concrete. Selecting a concrete batch plant is a crucial decision, since the choice has a significant impact on construction cost, risk and quality control. The benefits and limitations of an offshore batch plant, a batch plant on shore that requires concrete to be transported by barge, and a remote batch pant with concrete delivery by trucks to the shore and then by pump line over the water, are discussed. Once a concrete batch plant is selected, the minimum mixing time required is critical in determining the peak concrete production and placement rates. A field mock-up test for determining the mixing time is desirable. A proper underwater concreting plan for a project also depends on the site conditions, engineering requirements, availability of equipment and cost. The tremie method and the pump method are the most common placement methods. Since unique features define the characteristics of underwater concrete form pressure, the authors propose a calculation for form pressure that requires only the performance of a slope retention test and the recording of the time for the concrete to reach zero slump.