under water concreting
Post on 24-Jul-2015
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BANGALORE INSTITUTE OF TECHNOLOGYDEPARTMENT OF CIVIL ENGINEERINGUNDER THE GUIDEANCEOFB S KARTHIKAsst.professorPRESENTED BYAGNESH B S1BI11CV008
Introduction Concrete specificationLaying techniquesRepair worksConclusion
Introduction There are often situations such as basements , sewerage ,ducts , harbours , bridges and marine works ,in which concrete is to be placed underwater. Special precaution need to be taken whenever the concrete is to be placed underwater. The concrete should be plastic and cohesive but should have good flowability.
Performance requirements for UWCWorkability & self compactionCohesion against washout & segregationLow heat of hydrationControlled set timeCompressive strengthAdequate bondProblems facedSegregation of fine aggregates from coarse aggregatesWater pollutionIncreased w/c ratiowashout
Types of Materials used :
Cement Coarse Aggregates Fine Aggregates Admixtures
CEMENT : Types of cements used in UNDERWATER CONCRETING :
Ordinary Portland Cement (OPC)
Sulphate Resisting -Portland Cement ( SRPC )
Low Heat - Portland Cement ( LHPC )
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.
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 um sieve 60 - 85% Passing 300 um sieve 20 - 45% Passing 150 um sieve 15 - 30% Passing 75 um sieve 0 - 10%
Use of Different Admixtures
Anti-washout admixturesHydrocem Mellose
Viscosity modified admixturesNaphthalene FormaldehydeSulfonated Melamine Formaldehyde
Concrete Particles with adding MELLOSE
Concrete Particles without MELLOSE
* Black Dots Indicates Water
Concrete laying techniques
A Tremie is a watertight pipeGenerally 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.
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 weightWater/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.
Laying of concrete by using Tremie *Basic principle behindMethod of underwater concreting - Tremie methodMethod of underwater concreting Tremie method (inside view)
Divers Using Tremie Concreting
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.
*PUMP METHOD OF LAYING CONCRETE
Defining the AreaCleaning the Affected AreaEquipment HaulagePersonnel requirementsInspection methodsEnvironment considerations
At present, the Tremie placement method is the standard way of placing high-quality concrete underwater. The other placement method are not able to reliably place high-quality underwater concrete for major structures, although they may find application in special cases.
www.ce.berbley.edu/~parmont/165/tremie www.vulcanhammer.net www.ce.gatech.edu/~kk92/classpress/uwater/index.htm www.scanecm.com.au/products/additives/hydrocem/index.htm www.ce.ecn.purdue.edu/cem/cliproj/civil/mellose.htm www.masterbuilder.com/uc.htm