Underwater concrete

1. UNDERWATER CONCRETE SANTHINI K.P S8, CE 28 GUIDED BY MANASWI C.M

2. Introduction Concrete is the premier construction material across the world and the most widely used in all types of civil engineering works. During the construction of bridges , dams or any other structure where the foundation part of the structure is lie underwater, we have to opt for underwater construction When concrete is placed under water, it induces concrete to deteriorate uniformity Therefore should be follow proper mix design, concrete production and placement and quality control .

3. PRODUCTION OF UNDER WATER CONCRETE Proper mix design Proportioning underwater concrete are same as conventional concrete According to its performance there are two classes of concrete mixture standard mixture high-performance mixture Concrete placed underwater is susceptible to cement washout laitance Segregation

4. Cont……. Mix design influence certain workability characteristics such as Flowability Self-consolidation Cohesion Mix design also influence by rheology It describes flow and deformation of materials The behaviour of fresh concrete can be described by two parameters-yield stress and plastic viscosity

5. Cont…. water content is the important factor affecting the rheology of concrete water content in a mixture can be classified into two categories water absorbed in the aggregate free water

6. PLACEMENT METHODS Tremie method. Pump method Toggle bags Bags work.

7. TREMIE METHOD A Tremie is a watertight pipe Generally 250mm in dia. Funnel shaped hopper at its upper end and a loose plug at the bottom. It is supported on a working platform above water level.

8. Laying of concrete by using Tremie Fig. 2.2 Tremie method

9. PUMP METHOD: Pumping concrete directly into its final position, involving both horizontal and vertical delivery of concrete. Pumping concrete has the advantage of operational efficiency with potential savings of time and labour. For massive underwater concrete construction of navigation structures, the pump method should be prohibited.

10. PUMP METHOD OF LAYING CONCRETE

11. Cont…. TOGGLE BAGS Toggle bags are ideal for small amounts of concrete placement. The bag is filled in the dry with wet concrete Used for repair work. The concrete is squeezed out by a diver. BAGWORK Bags are made of open weave material. Diver-handled bags are usually of 10 to 20 litres capacity but 1cub.m bags can be placed using a crane .

12. Concrete production The standard requirements of underwater concrete is same as conventional concrete Production and delivery system be capable of producing concrete at the required placement rate It is essential that the materials can be supplied to the batch plant at the required rate The logistical planning should include Provision for alternative supplies Provision of all the accessory items

13. CONSTRUCTION TECHNIQUES Caissons Watertight retaining structure . Permanent in nature. Used to work on foundation of bridge pier, construction of concrete dam or for the repair of ships. Constructed in such a manner so that the water can be pumped out. Keeps working environment dry.

14. Cont….. Box caisson Pre fabricated concrete box, it is set down on the prepared bases Once in place it is filled with concrete as part of placement work Must be ballasted or anchored to prevent this phenomenon the floating of hollow concrete structures Open caisson similar to a box caisson but does not have bottom face Used in soft clays not having large obstructions beneath During sinking it may filled with water

15. Cont……. Compressed-air caisson It has the advantage of providing dry working conditions Compressed air is used to keep the water and mud out Used to work on river bed Monolithic caisson It is more suitable for off shore construction larger than the other types of caisson, but similar to open caissons

16. Cofferdam Temporary enclosure Built within or in piers across a body of water Allows the enclosed space to be pumped out, creating a dry work environment . Cofferdams are usually welded steel structures With components consisting of sheet piles, and cross braces For dam construction, two cofferdams are usually built, one upstream and one downstream

17. Fig. 3.2 coffer dam

18. Quality control Five critical items should be observed throughout concrete placement Rate of concrete placement Depth of concrete at various locations Volume of concrete produced versus volume of in-place concrete measured by sounding Concrete delivery system Embedment depth of the tremie

19. Cont……. Specific recommendations for quality control include The workers should have been properly trained Contractor should conduct frequent testing of concrete Continuous soundings should be taken The concrete placement rate and sequence should be carefully monitored and controlled Compare vol.of concrete produced and fed into the tremie Periodic checking of concrete delivery and placement equipment

20. DAMAGES AND MAINTANANCE Damage and Problems Rebar corrosion Scaling and Cracks Spallingconcrete Scour

21. Cont…. Rebar corrosion Rebar is steel reinforcement bars passively embedded within the concrete before it sets Occurs when chloride ions migrate to material like steel bars Type of corrosion that occurs in most highway bridges Spalling concrete The concrete that has broken up, flaked, or become pitted It is occurred due to poor installation and environmental factors It can also result in structural damage

22. Cont….. Scour Scour is the removal of sediments from around bridge abutments or piers It caused by swiftly moving water, can scoop out scour holes It is one of the three main causes of bridge failure Scaling and Cracks It is very common for concrete to have cracks, scaling, crazing and pitting Concrete expands and shrinks with changes in moisture and temperature Irregular cracks are unsightly and difficult to maintain but generally do not affect the integrity of concrete.  

23. Maintenance Maintenance procedure consists of initial inspection, deterioration prediction, inspection, evaluation, and remedial measures During construction the engineering as well as social and economical aspects should be required. Adequate protection from corrosion can be achieved by using anticorrosion or protective products By placing concrete carefully spalling of concrete can be avoid up to an extend

24. CONCLUSION For in-the-wet construction of navigation structures, underwater concrete construction is a critical component underwater concrete construction can be accomplished with the same degree of reliability as above water construction it is not carried out properly, with the proper concrete mixture and placement, it can result in a major overrun in construction cost and schedule.

25. Cont….. The essential difference between underwater concrete and conventional concrete is in the workability requirements Underwater concrete must flow laterally and compact itself under its own buoyant weight, while conventional concrete is compacted with mechanical vibration

26. REFERENCES Yao, S.X., Berner, D.E., Gerwick, B.C., “Assessment of Underwater Concrete Technologies for In-the-Wet Construction of Navigation Structures”, U.S. Army Corps of Engineers Publication, TR INP-SL-1, 1999. Neeley, B. D, Netherlands Committee for Concrete Research, “Underwater Concrete”, HERON, 1973 ACI 304R-00, "Guide for Measuring, Mixing, Transporting, and Placing Concrete", Chapter 8 "Concrete Placed Under Water", American Concrete Institute, 2000 Yao, S. X., and Gerwick, B. C., “Underwater Concrete Part II: Proper Mixture Proportioning” and “Underwater Concrete Part III: Construction Issues”, Concrete International, February and March 2004 Nagataki, S. (1992). "Use of antiwashout underwater concrete for marine structures," Tokyo Institute of Technology, Tokyo, Japan. Saucier, K. L., and Neeley, B. D. (1987). "Antiwashout admixtures in underwater concrete," Concrete International 9(7), 42-47. Strange, C. (1970). "Submarine placing of concrete by the tremie method," Offshore Technology Conference 2(1311), 813-18.

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