under water concrete
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Cyprus International UniversityCollage of EngineeringCivil Engineering Department
CLE532 Concrete TechnologyTitle : UNDERWATER CONCRETE
Submitted to : Dr. Salaheddin Sabri
By : Muftah Aljoat
ID : 20153680 Dec/2015
table of contents
1. Introduction2. Types of materials used in underwater concrete 2.1 Cement 2.2 coarse aggregates 2.3 Fine aggregates 2.4 Admixtures for UWC3. Placement methods 3.1 Tremie method 3.2 Pump method 3.3 Bagwork method4. Construction Techniques 4.1 Caissons 4.2 Cofferdam5. Production of underwater concrete6. Quality control & Cost7. Damages and Maintanance8. Conclusion9. References2
Concrete is the construction material across the world and the most 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 most likely to lie underwater, we have to opt for UWC.construction in water poses many difficulties especially in the places where there the depth is large .Therefore should be follow proper mix design, concrete production and placement and quality control.3
2. Types of Materials used in (uwc):
2.1 Cement : Types of cements used in Underwater concrete :Ordinary Portland Cement (OPC)Sulphate Resisting -Portland Cement( SRPC )Low Heat - Portland Cement ( LHPC )
2.2 Coarse Aggregates The coarse aggregate for intruded in concrete shall conform to the following gradation: Maximum Size - 1.5-2 inch (100% shall pass a 75 mm sieve ) Minimum Size - material passing a 19 mm sieve shall not exceed 5% by mass of the coarse aggregate.
2.3 Fine Aggregates The sand for the intruded grout shall be well graded, preferably of round grains and shall conform to the following gradation: Passing 1.18 mm sieve 95 - 100% Passing 600 mm sieve 60 - 85%
2.4 Admixtures for UWC:
Anything that improves workability should be considered. Slump approximately 7in .MSA should be 45% of total aggregate .Use air-entraining admixture . Requires the use of an antiwashout , Some of these admixtures are formulated from either Cellulose ether or Whelan gum, and they work simply by increasing the cohesion and viscosity of the concrete.
3. PLACEMENT METHODS:
7It is a process in which the prepared concrete is poured below thewater surface by using suitable methods.
3.1 TREMIE METHOD
8A Tremie is a water tight pipeGenerally 250mm in diameter.Funnel shaped hopper at its upper end and a loose plug at the bottom.It is supported on a working platform above water level.
(Figure 1) Tremie Method
Tremie Concrete is done by using a formwork/pipe which will have one end of the formwork/pipe above water and other bottom endimmersedunder the water and with the help of gravity.Before concreting air and water must be excluded keeping the pipe full of concrete all the time.For this the funnel and the pipe should have equal capacity.Firstly plug is inserted in the pipe with pressure of fresh concrete so that the air is displaced.9
Laying of concrete by using Tremie
(Figure 2) Tremie method10
Tremie method (video 1)11
Tremie method (video 2)12
Specifications of concrete to be used in Tremie method:Coarse Aggregate: Gravel of 3/4 (20mm) max. size. Use 50-55 % of the total aggregate by weight.Sand, 45-50% of the totalaggregate by weight.Cement: Type II ASTM (moderate heat of hydration), 600 lbs./yd3Water/Cement Ratio: 0.42 (0.45 Maximum).Water-Reducing Admixture (preferably it is also plasticizer): Do not use super plasticizers.Air-Entrainment Admixtures: To give 6% total air.Retarding Admixture: To increase setting time to 4-24 hours, as required.Slump: 6 1/2" 1"This mix will develop compressive strength in the range of 5,600 7,000 psi at 28 days.13
3.2 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.
(Figure 3) PUMP METHOD OF LAYING CONCRETE15
163.3 BAGWORKBags 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. (Used only in special cases like repair works, etc.)
(Figure 4) Bagwork used to form a dam
4. CONSTRUCTION TECHNIQUES
4.1 Caissons :Used to work on foundation of bridge pier, construction of concrete dam or for the repair of ships.Watertight retaining structure .Constructed in such a manner so that the water can be pumped out.Keeps working environment dry.17
18(Figure 5) working area of caissons
TYPES OF CAISSONSBox caissonPre fabricated concrete box, it is set down on the prepared basesOnce in place it is filled with concrete as part of placement workMust be ballasted or anchored to prevent this phenomenon the floating of hollow concrete structuresOpen caissonsimilar to a box caisson but does not have bottom face Used in soft clays not having large obstructions beneathDuring sinking it may filled with water
21(Figure 6) Suction Caissons
advantages of caisson :
Economic.Slightly less noise and reduced vibrations.Easily adaptable to site conditions.High axial and lateral loading capacity.Minimal handling equipmentis required for placement ofreinforcing cage.22
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 structuresFordamconstruction, two cofferdams are usually built, one upstream and one downstream
(Figure 7) working area of cofferdams
24(Figure 8) working area of cofferdams
advantages of cofferdam
Allow excavation and construction ofstructures in otherwise poor environment.provides safe environment to work contractors have design responsibilty steel sheet piles are easily installed and removedmaterials usually reused on other projects25
5. PRODUCTION OF UNDER WATER CONCRETE Proper mix designProportion underwater concrete are same as conventional concreteProduction and delivery system be capable of producing concrete at the required placement rateIt is essential that the materials can be supplied to the batch plant at the required rate26
Performance requirements for UWCWorkability & self compactionCohesion against washout & segregationLow heat of hydrationControlled set timeCompression strength Problems facedSegregation of fine aggregates from coarse aggregatesWater pollutionIncreased (w/c) ratiowashout
6. Quality control & cost
Five critical items should be observed throughout concrete placement :Rate of concrete placement.Depth of concrete in different locations.Size of concrete produced opposite volume of in-place concrete measured by sounding.Concrete delivery system.
Cont.Specific recommendations for quality control, include: The workers should have been properly trained. Contractor should conduct frequent testing of concrete .The concrete placement rate should be carefully monitored and controlled. checking of concrete delivery and placement equipment.29
COST Consideredunderwaterconcrete is highcostcompared toplain concrete, due to thehighcost of equipmentandmaintenancein addition tothe cost ofthecaring. In the UnitedKingdomalsoit estimatedthe cost of repairingthe bridgesas a result ofcorrosioninrebarat about616 millionpounds and isonly 10%of the totalbridgesin the UnitedKingdom. 30
7. DAMAGES AND MAINTENANCE
Damage and ProblemsRebar corrosionSpalling concreteScour Scaling and Cracks31
Cont.1. Rebar corrosionHappen when chloride ions migrate to material like steel bars,that is Type of corrosion that happen in most highway bridges.2. Spalling concreteThe concrete that has broken up or flaked.This happened because of poor installation and environmental factors .It can also result in structural damage32
Cont..3. ScourScour is the removal of sediments from aroundbridgefoundationsorpiersIt caused by swiftly moving water, can scoop outscour holesIt is one of the three main causes ofbridge failure.4. Scaling and CracksIt is very common forconcrete to have cracks, scaling.Concrete expands and shrinks with changes in humidity and temperature.Irregular cracks are ugly and difficult to maintain but generally do not affect the safety of concrete.
Maintenance :Maintenance procedure consists of initial inspection, deterioration prediction, inspection, evaluation.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.34
if 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. The essential difference between underwater concrete and conventional concrete is in the workability requirements.Underwater concrete must flow horizontally and compact itself under its own weight, while conventional concrete is compacted with mechanical vibration.
www.ce.berbley.edu/~parmont/165/tremie www.vulcanhammer.net www.ce.gatech.edu/~kk92/classpress