INTRODUCTIONMany of the techniques available for above waterrepair can be used underwater with only minormodifications. The materials specified for use inair, however, are often completely unsuitable forunderwater use.The major effects that underwater working hason repair operations are summarized as follows:The cost & difficulty of underwater workingrequires that operations to be carried out atthe repair site be minimized & made as simpleas possible. The method of repair must betailored to suit the available methods ofaccess.
INTRODUCTIONPreparation of the damaged area requiresspecially adapted techniques. Care must be takento ensure that the area is not contaminated priorto application of the repair material.The material selected for the repair must becompatible with underwater use both duringplacing & curing. Many resin-based repairmaterials are not suitable for use underwater;cementitious systems are however in an idealmedium.Placement methods & formwork must be adoptedthat minimize mixing between repair material &water.
INTRODUCTIONChecking during the repair operation and regularinspection on completion is difficult and costly toachieve underwater.The cost of underwater repair is far greater thanfor similar repairs carried out in the dry. The costof failed repairs is also therefore high. Hence it isimportant that laboratory trials on both repairmethods and materials be carried out to identifypossible problem areas and ensure smooth siteoperations.
PREPARATION OF DAMAGED AREASURFACE CLEANINGAll marine encrustations to be removed.Necessary to determine extent of damage andto ensure bond.Small areas: Hand held tools, mechanical wirebrushes, needle guns or scabbing tools.Large areas: High pressure jets;Encrustations – Abrasive slurryOil contamination – Detergent.After cleaning determine extent & type ofdamage.
PREPARATION OF DAMAGED AREAREMOVAL OF DAMAGED CONCRETEHIGH PRESSURE WATER JETTING• Most common for underwater work.• A thin high pressure jet of water directedon the concrete surface removes mortarfrom between the aggregates• The reinforcement is itself cleaned but notcut by the water jet.
PREPARATION OF DAMAGED AREASPLITTING TECHNIQUES• Hydraulic or Pneumatic expansive devicescan be used to split concrete.• Hydraulic expanding cylinders are insertedinto predrilled holes & pressurized untilsplitting occurs.• Expansive cements are also effective.Cement mixed into a paste & poured intoplastic bags, which are put into predrilledholes. In 24 hours it expands and splitsconcrete.
PREPARATION OF DAMAGED AREAMECHANICAL CUTTINGUnderwater cutting using hydraulicallypowered diamond tipped saws & drills havebeen used extensively for minor works formany years.THE CARDOX SYSTEMHoles are drilled into concrete.Into these cartridges of pressurized CO2 areplaced.The pressure is then released by electricallydetonating a small initiating charge in eachcartridge, producing a comparatively gentleexplosion which bursts the concrete apart.
PREPARATION OF DAMAGED AREATHERMIC LANCEComprises long steel tube packed with steelrods.O2 is passed down centre of the tube & lance isignited by external heat source.Temperature goes up to 3500 deg C, enablingthe tip of the lance to quickly melt throughconcrete or steel.EXPLOSIVE CUTTINGExplosives using contact demolition chargeshave been used for many years.The size & placing of charge is matter ofexperience. The resulting cut/tear in concrete isirregular.Shaped charges provide precise cut.
CUTTING OF REINFORCEMENTOXY-FUEL GAS CUTTINGAs Acetylene becomes unstable with risk ofexplosion, Oxy-hydrogen flame is used forunderwater steel cutting.OXY-ARC CUTTINGSame as above, only that an electric arcinstead of a flame is used.MECHANICAL CUTTINGDiamond tipped saws can be used for smallworks.FINAL PEPARATIONReplace reinforcement rods surface flushedwith clean water to remove bacterial ormicrobiological growth.
PATCH REPAIRSMinor damages can be repaired by specialcementitious or resin based materials.CEMENTITIOUS MORTARSConventional mortar when immersed in water,washout of the top surface will occur.Special admixtures can be added to resistwashout of cement.Self-leveling, Self-compacting mortars to beused.
PATCH REPAIRSRESIN MORTARSNormal epoxy or polyester resin mortarsunsuited for underwater works.By careful formulation of the base resin & thecuring agent, special epoxy & polyester resinmortars have been developed which can beused underwater.
INJECTION INTO CRACKSGeneral procedure for underwater crack repairsame as for dry workings.Drill 50 mm deep injection points along thecrackLine of crack thoroughly cleaned by highpressure water jetting.Line of crack is sealed using epoxy putty.Injection pipes sealed into injection points.Width > 3mm Cementitious grout< 3mm Epoxy grout (low viscosity,solvent free, underwater grade)Injection achieved by pressure pot.
INJECTION INTO CRACKSStart with lowestpoint till resinflows out of thenext highestinjection point.Lock lowerinjection point andinjection istransferred to thenext point.
LARGE SCALE PLACEMENTWhere large volumes of material are required,consideration must be given to bulk placementunder water.Precast high density concrete mats for renewingballast can be obtained in various sizes & offermany advantages over wet cast systems.
FORMWORKShould be simple toerect under waterShould be tolerant tovariations.Figure shows steelformwork fitted todamaged surface.Flexible seals ensureleak-tight fit.Formwork is completewith inlet pipes,external vibrators, etc.
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