While most concrete jobs are done on dry land, there are many uses for concrete underwater, like building dams, bridges, sea walls, underwater foundations, repairing coral reefs and more. The first successful attempt to build under water is credited to the Greeks and dates as far back as 600 BC with the discovery of pozzualana, a
special calcined lime found on the island of Santorini.
Coral Reef in Florida
One interesting case was the underwater project that repaired the Molasses Reed, the third largest barrier reef in the world, that was damaged by a shipwreck 6 miles Southeast of Key Largo, Florida. This accident caused the destruction of a major habitat for fish, marine and coral life. The solution was to create modules by combining small lime stone boulders, fiberglass reinforcement bars, concrete and sand. Then to lower the modules underwater and pour concrete in these modules with a hydraulic concrete pump to tie them to the damaged reef. A Putzmeister Katt-Kreter pump was used to complete this project along with a 4-yard mixer truck on the barge. Its ability to reverse the concrete back to the hopper was essential to the success of the operation.
Putzmeister Katt Kreter Pump (Side-view)
THE PROCESS
Usual settings include a boom pump or placing boom either land based or large barge mounted. In addition, there are a few challenges operators must keep in mind:
1) Placing the line below water surface requires the line to be grouted or “primed” in a way so that no water is in contact with the priming material before the prime reaches the discharge end of the pumping system. If this doesn’t happen, the grout can become too diluted and no longer properly lubricates the system, which will cause plugs. This will cause costly delays and extra steps to clear them.
2) To grout a water filled line, we recommend using 2 sponges suited for the size of the pipe line placed above the water level. Concrete must be pumped slowly so that it never passes the sponges and the water is displaced by the concrete without ever contaminating one another. Another way to achieve this is to place the concrete line inside existing concrete. Even though concrete is poured in water, the line must be kept out of the This is essential to the integrity and strength of the resulting poured concrete.
3) In terms of cement material content, operators must include a high volume of fly ash and silica fume and chemical admixtures.
4) One of the biggest risk is overloading the pumping boom.This requires close collaboration between the pump and crane operators. Both should check to see a droop in the hose between the placing boom and the additional system to make sure it doesn’t happen.
If you are looking for a great deal on concrete pumps for a job on dry land or underwater, don’t hesitate to call Dick at (503)283-2105.
Recommended further reading:
http://www.concretepumping.com/dictionary/index.php?title=Under_Water_Concrete_Pumping
http://www.ce.berkeley.edu/~paulmont/165/tremie.pdf
ftp://dfi.org/OneMine/Marine%20Foundations%20Book%20-%20individual%20papers/29-5.4%20Underwater%20Concrete%20-%20Mix%20Design%20and%20Construction%20Practices.pdf
