under water concreting

BANGALORE INSTITUTE OF TECHNOLOGY

DEPARTMENT OF CIVIL ENGINEERING

UNDER THE GUIDEANCEOF

B S KARTHIKAsst.professor

PRESENTED BY

AGNESH B S1BI11CV008

Topics coveredTopics covered

Introduction Concrete specificationLaying techniquesRepair worksConclusion

Introduction 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 bond

Problems facedSegregation of fine aggregates from coarse aggregatesWater pollutionIncreased w/c ratiowashout

Types of Materials Types of Materials used used ::

Cement Coarse Aggregates Fine Aggregates Admixtures

CEMENT :CEMENT : Types of cements used in UNDERWATER

CONCRETING :

Ordinary Portland Cement (OPC)

Sulphate Resisting -Portland Cement ( SRPC )

Low Heat - Portland Cement ( LHPC )

AGGREGATES AGGREGATES :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 Use of Different AdmixturesAdmixtures

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 Concrete laying techniquestechniques

Tremie method

Bucket Placing

Pump method

TREMIE METHOD

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 total aggregate 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 14

Basic principle behind Method

of underwater concreting -

Tremie method

Method of underwater concreting— Tremie method (inside view)

Divers Using Tremie Concreting

Bucket placingBucket placing

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.

17

PUMP METHOD OF

LAYING CONCRETE

Repair worksRepair works

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.

ReferencesReferences::

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