Guide for the Preparation of Concrete Surfaces for Repair Using Hydrodemolition Methods

8/20/2019 Guide for the Preparation of Concrete Surfaces for Repair Using Hydrodemolition Methods

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1 7.10 Hydro-Demolition Induced CrackingDescription:

The process of hydro-demolitionexploits the existence of micro-cracks, voids, capillaries and cracks to enable concrete demolitionusing high pressure water jets. This raises the question of potential damage to concrete in adjoining area through direct pressure,vibrations,or crack propagation.

This document is intended to determine if hydro-demolition can cause cracking and if any occurred at CR3.

Note that issues of vibration induced by hydro-demolition are covered in depth in FM 7.2.

Data to be collected and Analyzed:

1. Review literature (FM 7.10 Exhibit 1 is a "Guidefor the Preparation of Concrete Surfaces for Repair Using Hydrodemolitionmethods , FM 7.10 Exhibit 2 includes selected pages from ACI 546R-04 Concrete Repair Guide", FM 7.10 Exhibit6 includesselected pages from the book "Hydrodemolitionof Concrete Surfaces and Reinforced Concrete by Andreas Momber, FM 7.10Exhibit 7 is a published article, and FM 7.10 Exhibit 8 is a research report from MoDOT);

2. Interview personnel involved in the Hydrodemolitionat CR3 (FM 7.10 Exhibit3 is a summary of interviews);3. Review physical data collected from the structure (FM 7.10 Exhibit 4and FM 7.10 Exhibit 5 are photos taken of areas impacted

by the demolition process).

Verified Supporting Evidence:

a. Hydro-demolitionworks through the introduction ofhigh pressure water into cracks (FM 7.10 Exhibit 6). If a delamination crack isencountered during demolition, the water will fill it and exert pressure internally, potentiallyaccelerating propagation. Eyewitnessreport large volume of water exiting the wall through a moon-shaped crack that developed outside the demolition area (FM 7.10

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Exhibit 5).

Verified Refuting Evidence:

a. Literature review shows a consensus that hydro-demolitiondoes not cause significant damage to adjacent material (seehighlighted sections of FM 7.10 Exhibits 1, 2, 7, and 8);

b. Hydro-demolition removes concrete not by impact, but by introducing high-pressure water into existing voids (FM 7.10 Exhibit 6).The high internal pressure in these voids causes the concrete to fail, spalling the surface material;

c. Cores taken adjacent to the demolition area did not show degradation of strength properties (see discussion b. below).

Discussion:

a. Published information about the principles of hydro-demolition (FM 7.10 Exhibit 6, page 3 of 21) describes the three modes offailure established in quoted research. These include water flow into crack, creating stress at the tip, water flow into capillarieswhich result in internal pressure amplification, and water flow through open pore system creating friction forces to the materialgrains. The exhibit provides research information and formulas that may be used to estimate parameters of failure;

b. Nine (9) cores were taken through the edge of the SGR opening following the discovery of the delamination. Three (3) of thecores were tested for splitting tensile strength and averaged 615 psi (compared to average of 604 psi for fourteen (14) corestested from the structure). Three (3) of the cores were tested in compression and averaged 7390 psi (compared to average of

7460 psi for fourteen (14) cores tested). These results confirm that there was no degradation to the concrete adjacent to thehydro-demolitionarea.

Conclusion:

Hydro-demolitiondid not cause cracking and degradation of the concrete adjacent to the demolition area. However, it may haveplayed a role in the propagation of existing cracks and may have been a contributing factor to the extent of the delamination.

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FM 7.10 Exhibit 1 page 1 of 16

TECHNICAL

GUIDELINESPrepared by the International Concrete Repair Institute September2004

Guide for the Preparationof Concrete Surfacesfor Repair UsingHydrodemolition MethodsGuideline No. 03737

Copyright © 2004 International ConcreteRepair Institute

All rights reserved.

International ConcreteRepair Institute3166 S. River Road, Suite 132, Des Plaines, IL 60018Phone: 847-827-0830 Fax: 847-827-0832Web: www.icri.orgE-mail: [email protected]

92 5


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926 FM 7.10 Exhibit 1 CONCRETEREPAIR MANUAL

About ICRI Guidelines

page 2 of 16

The International Concrete Repair Institute (ICRI)was founded to improve the durability of concreterepair and enhance its value or structure owners. Theidentification, development, andpromotion of he most

promising methods and materials s a primary vehiclefor accelerating advances in repair technology.Working through a variety offorums, ICRI membershave the opportunity to address these issues andto directly contribute to improving the practice ofconcrete repair

A principal component of this effort is to makecarefully selected information on important repairsubjects readily accessible o decision makers. Duringthe past several decades, much has been reported in

Technical ActivitiesCommitteeRick Edelson, Chair

David Akers

Paul CarterBruce Collins

William Bud Earley

Garth FallisTim Gillespie

Fred GoodwinScott GreenhausRobert JohnsonKevin Michols

Allen RothJoe Solomon

SynopsisThis guideline is intended to provide anintroduction to hydrodemolition for concreteremoval and surface preparation, the benefitsand limitations of using hydrodemolition,and an understanding of other aspects to beaddressed when incorporating hydrodemolitioninto a repair project. This guideline providesa description of the equipment, applications,safety procedures, and methods of watercontrol and cleanup.

literature on concrete repair methods and materialsas they have been developed and refined Neverthe-less, it has been difficult to find critically reviewedinformation on the state of the art condensed intoeasy- o-useJbrmats.

To that end, ICRI guidelines are prepared bysanctioned task groups a nd approved by the ICRITechnical Activities Committee. Each guidelineis designed to address a specific area of practicerecognized as essential to the achievement ofdurable repairs. All ICRI guideline documentsare subject to continual review by the membershipand may be revised as approved by the TechnicalActivities Committee.

Producers of this GuidelineSubcommitteeMembers

Pat Winkler, Chair

Don CapleBruce CollinsEric EdelsonKen Lozen

Bob NittingerSteve Toms

ContributorsScott Greenhaus

Rick TomanMike Woodward

KeywordsBond, bonding surface, bruising, chippinghammer, coating, concrete, delamination,deterioration, full depth repair, hand lance,high-pressure water, hydrodemolition, impactremoval, mechanical removal, micro-fracture,post-tensioning, rebar, reinforced concrete,reinforcing steel, robot, rotomill, safety, soundconcrete, surface preparation, surface profile,surface repair, tendon, vibration, wastewater,and water jet.

This documentis intended as a voluntary guidelinefor the owner, design professional, andconcrete repair contractor. It is not intendedto relieve the professional engineeror designer ofany responsibilityfor the specificationof concreterepair methods, materials,or practices.Whilewe believe the information contained hereinrepresents the proper means to achieve qualityresults,the International ConcreteRepair Institute mustdisclaim any liabilityor responsibilityto those whomay choose to rely on all or any part of this guideline.


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FM 7.10 ERREIRTION OFCONCRETESURFACES FOR REPAIRUSING HYDRODEMOLITIONMEJIP, 3 of 16 927

PurposeThis guideline is intended to provide owners,design professionals, contractors, and otherinterested partieswith a detailed description ofthe hydrodemolitionprocess; a list of the benefitsand limitations of using hydrodemolition forconcrete removaland surface preparation;and an

understanding of other aspects to be addressedwhen incorporating hydrodemolitioninto a repairproject. Theguideline providesa description ofthe equipment, applications, safety procedures,and methods of water control and cleanup. Thisguideline is not intendedas anoperating manualfor hydrodemolition equipmentas that informationis specific to each equipment manufacturer.

The scope of this guideline includes theuse of hydrodemolition for the removal ofdeteriorated and sound concretein preparationfor a concrete surface repair.In addition,the useof hydrodemolitionfor the removal of coatingsis discussed.

While the procedures outlined hereinhavebeen found to work on many projects, therequirements for each project will vary due tomany different factors.Each project shouldbeevaluated individually to ascertain the applica-bility and cost-effectiveness of the proceduresdescribed herein. Other methods of surfacepreparation are discussed in ICRI TechnicalGuideline No. 03732, "Selectingand SpecifyingConcrete Surface Preparation for Sealers,Coatings, and Polymer Overlays."

IntroductionHydrodemolition is a concrete removal techniquewhich utilizes high-pressure water to removedeteriorated and sound concrete. This processprovides an excellent bonding surfacefor repairmaterial. First developedin Europe in the 1970s,this technologyhas becomewidely accepted forconcrete removal and surface preparationthroughoutEurope and North America.

Hydrodemolitioncan be used for horizontal,vertical, and overhead concreteremovals and

surface preparation on reinforced and non-reinforced structures. It is effective in removingconcrete fromaroundembedded metal elementssuch as reinforcing steel, expansion joints,anchorages,conduits, shear connectors,and shearstuds. Hydrodemolitioncan beused for localizedremovals where deteriorationis confinedto smallareas and forlarge area removals in preparationfor a bonded overlay. This technologycan alsobeused to remove existingcoatings from concrete.

Hydrodemolition has beenusedon the followingtypes of structures: Bridge decks and substructures Parking structures Dams and spillways Water treatment facilities Tunnels and aqueducts Nuclear power plants

Piers and docks Stadiums Warehouses

Retainingwalls

The Effects ofMechanicalImpact TechniquesMechanical m ethods suchas chippinghammers,

, rotomills, scabblers, and scarifiersremoveconcreteby impactingthe surface. These procedurescrush(bruise) the surface, fractureand split the coarseaggregate, and create micro-fractures in the

'substrate (Fi g.d .saresult, tle abili~y ofthe fractured substrate to provide a durable

c. j vamage createa Dy cnipping nammer

Fig. 2: Damage created by rotomilling


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928 FM 7.10 Exhibit 1 CONCRETEREPAIRMANUAL page 4 of 16

bond with the repair material is compromised,requiring a second step of surface preparation toremove the damaged region.

Furthermore, impact methods may damagethereinforcing steel and embedded items such asconduit, shear studsand connectors,and ex.pansionjoint hardware.Impact methodstransmitvibrations:through the reinforcing steel, which may cause:

further cracking,delamination, and loss of bondbetween the reinforcing steel and the existing:concrete. Vibration and noise created by the:mechanical impact willtravel through the structure,disturbing the occupants. During repair of thinslabs and precast tees, chipping hammers ma yshatter the substrate resultingin unanticipatedfulldepth repairs.

For a discussion onsurface bruising and themechanics of concrete removalby impact methods,refer to ICRI Technical Guideline No. 03732,"Selecting and Specifying Concrete Surface Preparationfor Sealers, Coatingsand Polymer Overlays."

HydrodemolitionBenefitsand LimitationsThe benefitsof hydrodemolitioncan be placed intotwo groups: structural benefits that improve thequality of the repair, and environmental benefitsthat improve the quality of the work place.Hydrodemolitionalso has limitations,whichneed

to be considered.

Structural BenefitsA rough, irregular surface profile is createdto provide an excellent mechanical bond for

... r.epýairmaterials; ...................... Surface.micro-frac is eliminated;, Exposed aggregates are not fractured or split; Lower strength and deteriorated concrete is

selectivelk removedk, t . . .~r;Ywtt........v~i~brati.on.s minimal;

Reinforcementis cleaned, eliminating the needfor a second stepof surface preparation;and

0 Reinforcingand otherembeddedmetal elementsare undama, ed.

During concrete removal,the waterjet is directedat the surface, causing high-speederosion of thecement, sand, and aggregate. Thewater jet doesnot cut normalweight aggregate which remainsintact and embeddedas part of the rough, irregularsurface profile(Fig. 3). The aggregate interlockswith the .reair material to assist in developing a

Fig. 3: Surface prepared by hydrodemolition has arough irregular rofile withprotruding aggregate andis excellent for creating a mechanical bond

mechanical bondand composite action betweenthe substrate and the repair material.

The rough, irregular surface profile providedby hydrodemolitioncan result in bond strengthsthat equal or exceed the tensile strengthof theexisting concrete. The concrete surfaceprofilecan exceed CSP-9 (veryrough) as defined inICRI TechnicalGuideline No. 03732.

Rotomills and scarifiers remove concretetoa uniform depth and may leave deterioratedconcrete below the specified depth.Alterna-tively, the waterjet moves in a consistent patternover the surface and will remove unsoundconcreteeven if it is below thespecified depth.

mce flewaterjetcr~o'esn'ot'craerneý;chan;Ica1:impact,vibrationis not transmittedinto the structure:

:from the hydrodemolitionoperation. Delami-

nationbeyondthe repair area caused by vibration:,of the reinforcingsteel isgreatly reduced..During hydrodemolition, sand and cement

particlesmix withthe waterjet.Theabrasive actionof theses particles is usually sufficient to cleanuncoated reinforcing bar and embedded metalitemswithout damaging them. Corrosionmaterialis removed from the reinforcingbar and metalitems, allowing for easy inspec tion and identifi-cation of cross-sectionalarea loss.The reinforcingbar is cleanedwithout anyloss of deformations.Cleaning of the entire reinforcingbar, however,will not occurif the reinforcing barhas not been

completely exposed duringhydrodemolition.

Environmental BenefitsMinimizesdisruptions to users of occupiedspace by significantly reducing transmittedsound throughthe structure;

- Increased speedof concrete removalcanreduce construction time;

o Minimizesdust; and


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FM 7.10 EffiV8R11TIONOF CONCRETESURFACES FOR REPAIRUSING HYDRODEMOLITIONME'[Wg 5 of 16 929

* Robotic units reduce labor and minimizeinjuries as compared to chipping hammers.Concreteremoval byhydrodemolitioncan take

place insidean occupied structure,such as a hotel,apartment building, office building or hospitalwith minimalnoise disruption to the occupants.

Hydrodemolitioncan quickly removeconcrete.As such, projectduration can be reduced, mini-

mizing the impacton the users of the structure.During demolition,cleanup, and final wash

down, the concrete debrisand repairsurface remainwet, minimizingdust in the workarea. Since hydro-demolitioncleans the reinforcingsteel, the needto sandblast is eliminatedunless additional concreteremoval is required using chipping hammers.Assuch, silica dust in the work area is reduced,thereby providinga safer workenvironment.

The use of chipping hammers and otherimpactmethodsare labor intensiveand physicallydemanding, whichcan cause injuryto theemployee.Robotichydrodemolitionequipmentreduces theuse of these tools and thepossibility of injury.

LimitationsThe hydrodemolition process consumes asignificant amount of water (6 to 100 gp m[25 to 380 1pm]). A potablewater source mustbe available. The cost of the water shouldbe considered;

Wastewatercontaining sand and cement fines(slurry)must be collected, treated,and returnedto the environment.Wastewaterdisposal mayrequire a permit;

* Projectsrequiringtotal demolitioncan be donefaster and more economicallywith crushersand similar equipment;

Water can leak throughcracks in the concreteand damage occupied space belowthe repairarea. Hydrodemolitionshould notbe used overoccupiedareas due to the risk of blow-through(unanticipatedfull-depth removal);

Repair areas of varyingstrength will result innon-uniformremoval. Areas of high strengthmay need to be removed usinghand lances orchipping hammers;

The water jet is blocked by reinforcing steelresulting in concrete shadows under thereinforcing bar that may needto be removedusing hand lances or chipping hammers;

Sincethe waterjet of a roboticunit is containedin a metal shroud, some robotsare unable tocompletely remove concrete up to a verticalsurface such as a curb, wall or column. Theremainingconcrete mayhave to be removedusing hand lances orchipping hammers;

The water jet will remove the sheathing frompost-tensioningtendons and may drive waterinto the tendon;The hydrodemolition robot maybe too large toaccess small or confinedareas of the structure;Thewaterjetcan damagecoatings onreinforcingsteel and other embedded items;

The waterjet can introducewaterinto electrical

system components, especially if embeddedin the concrete and already deterioratedor notproperlysealed; and

If cleanup is not properly performed in atimely manner, further surface preparationmay be required.

The HydrodemolitionSystemThe hydrodemolition system consists of asupport trailer or vehicle, high-pressurepump(s),a robotic unitto perform the demolition,and high-pressure hoses to connect the pump (s)to the robot. Hand lances are also availableto remove concrete in areas inaccessible tothe robot.

Support TrailerHydrodemolition unitsare typically transportedon 40 to 50 ft trailers (Fig. 4). The robot may

C

Fig. 4: Hydrodemolition upport trailer A self-contained unit transports pumps, robot, hoses,and spare parts

be transported on the same trailer or separatelyon a smaller trailer. The support trailer usuallycontainsa supplyofspare parts, tools, maintenancearea, fuel and water storage, supply waterhoses, and filters. These units are designedto be self-sufficienton the job site withadequatespare parts to perform routine maintenanceand repairs.


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930 FM 7.10 Exhibit 1 CONCRETE REPAIR MANUAL page 6 of 16

High Pressure PumpsThehigh-pressurepumpsused for hydrodemolitionare capable of generating pressures from10,000 psi to 40,000 psi (70 to 275 MPa) withflow rates from6 to 100 gpm (25 to 380 1pm).The pumps are driven by a diesel or electricmotor, typically operating between 100 and700 horsepower. The engine size will varybased on the flow and pressure rating of thepump.The pumps operate mostefficientlyat theirdesign pressure and flow. High-pressure hosesconnect the pumps to the robot.The pumps ma ybe locateda significantdistance (500 ft [150 m])from the actual removal area. However, due toa drop in pressure and flow through the high-pressurehoses, the pumps should be located asclose as possible to the removal area, typicallywithin 300 ft (100 m).

Robotic Removal Unit-Horizontal SurfacesThe force created by thehigh-pressurepump(s)is controlledusing a robotic removalunit (Fig.5).The robot is a diesel or electric powered,self-propelled,wheeled or trackedvehicle. It is usedto uniformly move and advance the waterjet overthe surface duringconcrete removal.

Fig. 6: Nozzle is mounted on a traverse beam

Rotation Oscillation

Fig. 7. Rotating or oscillating nozzles

Fig. 8: Rotating nozzles are angled rom center

Fig. 5: Typicalhydrodemolition robot

The water jet is mounted on a trolley thattraversesover the removalarea along a cross feedor traverse beam (Fig. 6) perpendicular to theadvance of the robot. The water-jet nozzle mayeither oscillateor rotate (Fig.7). The oscillatingnozzle is angled forward in the direction of thetraverse. Rotating nozzles are angled from thecenter, creating a cone effect while rotating(Fig. 8 and 9).

The nozzle assemblyis enclosedwithin a steelshroudwith rubberseals around the perimeter tocontain the debrisduring demolition (Fig. 10). Fig. 9: Rotation of the angled nozzle creates a water cone


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FM 7.10 ERJMPRPITIONOF CONCRETESURFACESFOR REPAIRUSING HYDRODEMOLITIONMEPDW' 7 of 16 931

Fig. 10: Nozzle is enclosed within a steel shroud

The rotation/oscillationof the nozzlecombinedwith the traverse and advance of the robotprovide a uniformand continuousmotion of thewaterjet over theremoval area (Fig.11). Each ofthese functions is fully adjustable. The depth ofconcrete removal is determinedby the length of

time the waterjet is directed at the removal area.

3 seconds and thewaterjet may traverse only onetime before the robotadvances 2 to 4 in. (50 to100 mm).

The depth of concrete removal is controlledat the robot. Since the pumps are designed tooperate at a specific pressure and flow rate, it isunusual to reduce the pressure (and subsequentlythe flow rate) toadjust the depth of removal.

Narrow areas may be removed by adjustingsensors that limitthe movement of the water jetalong the traverse beam.The traverseand advancefunctions limitthe removalto a rectangular areaalong the advance pathof the robot. Because thewaterjet is contained within a steel shroud, mostrobots are unable to removeconcrete within3 to6 in. (75 to 150 mm) of vertical surfaces.

Specialized Robotic Equipment-Vertical and OverheadSurfacesVarious types of robotic equipmentare available

to perform removalson walls,soffits, substructures,beams, columns, and tunnels. These robots areoften built on wheeled or tracked vehicles andhave the ability to lift the traverse beam intothe vertical or overhead position.The primaryfunctions of traverse and advance are utilized inorder to provide uniform concrete removal duringvertical and overhead repairs.

As an alternativeto the robot, the waterjet mayalso be attached to a frame that allows the jet tomove in a twodimensional "X-Y" plane. TheX-Ymovementof traverseand advanceare present inthese unitsto provide uniform concrete removal.The X-Y frames can be lifted andpositionedoverthe removal area using a crane, backhoe, all-terrain forklift or other similar equipment.

Hand LanceHand lances operate at pressures of 10,000 to40,000 psi (70 to 275 MPa) while deliveringapproximately2 to 12 gpm (8 to 45 lpm) of water.Hand lances are not as fast or as precise forconcrete removal as a programmedrobot and areslower than chippinghammers.Hand lancesareeffective in performing light scarification andcoating removals. It should be noted that thewater jets on hand lances maynot be shrouded,increasing the risk of debris becoming airborne.Hand lancescan be used for removalof: Concrete shadowsbelow reinforcing bar; Concrete adjacent to walls, columns, curbs,

and in tight and confined areasnot accessibleto the robotic equipment;and

Coatings.

Fig. 11: The water et traverses back and forth perpen-dicular o the forward advance of the robot

Adjustingthe followingparameterswill increaseor decrease the depth of removal:a. Total traverse time (time of each traverse x

number of traverses); andb. Distance of the advance.

Once these parameters are set, the robot willreproducethesettings in a programmedsequenceto provide consistentremoval of the concrete.Forexample, during deep removal to expose thereinforcing bar 3 to 4 in. (75 to 100 mm), thetraverse speed may be 8 seconds (the timerequired for thewaterjet to move from one sideofthe traverse beamto the other) and the water jetmay traverse 3 times before the robot advancesforward i to 2 in. (25 to 50 mm). On the other hand,for light scarification 1/4 to 1/2 in. (6 to 13 mm)or coating removal, the traverse speed may be


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932 FM 7.10 Exhibit 1 CONCRETE REPAIR MANUAL page 8 of 16

SafetyHydrodemolitioninvolves the use of potentiallydangerous specialized eq uipment. Atall times, themanufacturer's instructionsfor the safeoperationof the equipmentand personal protective equipmentshould be followed, as well as all local, state, andfederalregulations. Hydrodem olition units should

be supervisedand operated byqualifiedpersonnelcertifiedby the equipment manufacturer.

Hydrodemolition employs high-velocitywaterjets to demolish concrete andperform surfacepreparation. E ven thoughthe waterjet is shroudedon robotic units, debriscan be propelled frombeneath the shroud with sufficient velocityto cause serious injury.Serious injury or deathcan also occur if struck by the water jet. Handlances are typically not shroudedand care mustbe exercised to avoid injurywhen using these tools.

Workers, equipment operators, and anyindi-viduals entering the work area are required towear hard hats, safety glasses, hea ring protection,safety shoes, gloves, longpants and long-sleeveshirts, and must be trained in the proper use ofpersonal protective equipment. When using ahand lance, the operator shouldwear a full-faceshield, rain suit, and metatarsal and shin guards.Additional protective clothingmay also be requiredfor usewith hand lances. Everyone involvedwiththe hydrodemolition operation should receivespecifictraining outliningthe dangers associatedwith the use of high-pressure water.

Prior to starting demolition, an inspection of

the area should be performed including the areaunder the work area. All barricades, partitions,shielding, and shoring must be installed andwarning signs posted to prevent unauthorizedentry into thework area. The area below the workarea must be closed off and clearly marked"Danger- Do NotEnter." Electrical conduitsorother electrical equ ipmentin thework area shouldbe deenergizedto avoid electricalshock.

Special precautions are required for post-tensioned structures as referred to in the section"Considerationsfor HydrodemolitionUse."

HydrodemolitionApplicationsScarificationScarificationis performedto remove the surfaceconcrete andprovide a rough profile (Fig. 12 and13). Scarificationis often used in preparationfor

Fig. 12: Scarified surface with I in. aggregate

Fig. 13: Scarified surface with 3/4 in. aggregate

a concrete overlay.If the surface waspreviouslyrotomilled, the minimum removal depth usinghydrodemolition should equal the size of thecoarse aggregate to remove all concrete micro

fracturesand damaged or crushed aggregate.Scarification may not remove all unsoundconcrete dueto the rapid rate atwhichthe waterjetmoves overthe surface. It may be necessary toresurveythe scarified surface and identifydelami-nated or deteriorated areas for further removal.

Partial Depth RemovalPartial depth removal is commonly required ifchloride contaminationhas reached the top matof reinforcingsteel ordeterioration, delaminationor spallingoccurs withinthe topmatof reinforcingsteel. Partialdepth concrete removal can exposethe top mat of reinforcing steel and provideclearance, typicallyaminimum of 3/4 in. (19 mm),below the bottom reinforcing bar of the top mat(Fig. 14 and 15). Determiningthe reinforcing barsize and concrete coverare critical to determinethe required removal depth.

Concrete removal using hand lances or chippinghammers may be required to remove shadowsunder the reinforcing bar,previously repairedareas


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FM 7.10 EP•*MAR1TION OF CONCRETE SURFACESFOR REPAIRUSINGHYDRODEMOLITIONMEPW 9 of 16 933

used. Other structural elements such as shearconnectors, shear studs, and steel beam flangescan be exposed without damage.

During full depth removal, the removal rateslows as the depth increases because thewaterjet stream dissipatesas it moves awayfrom thenozzle and the water jet must push morewaterand debris from its path prior to contacting the

surface to be removed.Full depth removal is often necessary on

waffle or pan joist slab systems(Fig. 16).

Fig. 14: Partial epth removal

Fig. 15: Partial epth removal on a retaining wall

or high areas resulting from variations in thestrength of the concrete. In addition, concreteremoval may be necessary adjacentto vertical

surfaces such as curbs, walls and columns. Sawcutting of the perimeter of the repair area, ifrequired, should be performed after hydro-demolition to prevent damage to the saw cut. Thiswill require additional concrete removalalongthe repair perimeter withhand lancesor chippinghammers. If the saw cut is made first, theareaoutside the saw cut shouldbe protected usingasteel plate. The steel platewill allow the waterjetto slightlyover runthe saw cut withoutdamagingthe surface outsidethe saw cut while completelyremoving the concrete within the repair area.

Full Depth RemovalHydrodemolition can be used for full depthremoval wheredelaminationhas occurredin thelower mat of reinforcing or chloride contami-nation exists throughoutthe entire thicknessof heslab. Full depth removal canbe performed alongexpansionjoints and other areas where thereis ahigh concentration of reinforcingsteel that maybe damaged if conventionalremoval methodsare

Fig. 16: Full depth removal-waffle slab

Coating RemovalHydrodemolition can be used for the removalof epoxy, urethane, hot applied membrane,andother coatings from concrete surfaces(Fig. 17).When performing coating removal, a multiplejet nozzle is used. The multiple jets allow thewater to penetrate the coatingwithout damagingthe concrete. However,if the concrete belowthecoating is deteriorated, it may be removed alongwith the coating.

Fig. 17: Coating removal using a spinning, multi-nozzlespray head


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934 FM 7.10 Exhibit 1 CONCRETEREPAIR MANUAL page 10 of 16

The HydrodemolitionProcessConcrete removal byhydrodemolitionis impactedby the followingfactors:

Size and density of the aggregate;Concrete strength;

Uniformityof concrete strength;* Extent of cracking; Deteriorationand delamination; Surface hardeners; Previous repairs with dissimilar strength

material; and Size and spacing of reinforcingsteel or other

embedded items.In sound concrete, the variation in the depth

of removal willgenerally equal the size of thecoarse aggregate (Fig. 18). For example, if thecoarse aggregate is 1 in. (25 mm), D = 1 in.(25 mm) and the specified depth of removal is2 in. (50 mm), the range of removal willbe 2 in.(50mm) ± D12 (1/2 in. or 13 mm), or 1-1/2 in.(38 mm) to 2-1/2 in. (63 mm).

If the strength of the concrete increases ora high-strength repair area is encounteredduring hydrodemolition, the removaldepth willdecrease (Fig.19). The decrease in depthmay notbe immediately detected bythe operator, resultingin an area of shallow removal(Fig. 20). To obtainthe required depth in higher strength concrete,the total traverse time is increased and the

advance of the robot is decreased. If the high-strength repair areais large enough, it may bepossible to set up thehydrodemolitionrobot overthe area and remove to the specified depth. This

DftWe 080W -

Nm * O~ .

),5OOw4,W0pw -

I

Fig. 18: The depth of removal depends on the size of thecourse aggregate

During hydrodemolition, a high-pressurewater jet is uniformly moved overthe surfaceand, provided the concrete is sound and thestrength does not change significantly, theremoval depth will remain consistent. Depthvariations occur when the concrete strengthchanges, cracking or delaminationis present,theconcrete is deteriorated or the surfacehas beenpreviously repaired usinga different type andstrength of material. In comparison, rotomillingor dry-milling equipmentcan be set to a specificdepth and the milling drum will mill the surfaceto that depth regardless of any variations in theconcretestrength,quality or levelof deterioration.

Fig. 19: High-strength concrete is removed at a slowerrate than normal concrete, which can result in a non-uniform removal


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FM 7.10 ERRtRITION OFCONCRETESURFACES FOR REPAIRUSING HYDRODEMOLITIONMPjTiJ 1 of 16 935

Fig. 20: High-strength repair area within the hydro-demolition area

procedure canbe problematic for two reasons.First, if the water jet overruns the high-strengthrepairarea, it may resultin a blow-through orfulldepth removalat the perimeterof the high-strengthrepair area.Second, since the water jet mustbe slowed significantly,it may cause excessiveremoval below the high-strength area once it isremoved and thesofter base concreteis exposed.For these reasons, it is often preferableto usechipping hammersin high-strengthrepair areas.

The opposite effect is encountered if theconcrete strengthdecreases or there is cracking,deterioration or delaminations(Fig.21). Concretethat is deteriorated, low strength or delaminatedis removed faster than thesurrounding soundconcrete by the water jet. For example, if the

average removaldepth is 2 in. (50 mm) and thereis a delamination that is 2 in. (50 mm) deep, theactual removalwithin the delaminatedarea couldbe 3 to 4 in. (75 to 100 mm) deep. For this reason,removal in an area that is seriously deterioratedand delaminated maynot be consistent.

This effect is often described as "selectiveremovalof deterioratedconcrete." Whilethe waterjet is traversing and advancing uniformly overthe surface, it is removingunsound, delaminated,deteriorated, cracked, and low strength concreteselectivelybelow the specifiedremoval depth.

Selective removalis not without limitations.Forexample,if the robot is traversingand advancingrapidly as during scarification,it may not removedeeper delaminations.

Size and spacing of the reinforcingsteelwillalso influence theremovaldepth. The reinforcingsteel blocksthe waterjet and shields the concretebelow, creating concrete "shadows"(Fig. 22 and23). Removalof concreteshadows becomesmoredifficultas the reinforcingbar size increases and

Fig. 21: Delaminated or deteriorated concrete isremoved at a faster rate leading o non-uniform removal

is most difficultat reinforcing barintersections.Increasing the specified depthof removal willminimize the amountof shadowing.

Pointing the water jet under the reinforcingbar can reduce concreteshadows. This can beaccomplished by using a rotating oroscillatingnozzle (refer to Fig. 7-9). Rotating nozzles aretypically angled 10' and 30' from center. Thenozzle rotates between100 and 1800 rpm, creatinga demolition cone that will undercut both thetransverse and parallel reinforcing bar providedthe specified removal depth is greater than the


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936 FM 7.10 Exhibit 1 CONCRETEREPAIRMANUAL page 12 of 16

Fig. 23: Shadow under the rebar (note tie wireundamaged and n excellent condition)

removal may result in the removal of soundconcrete, it will minimize the need forconcreteremoval under the reinforcing bar with chippinghammers or hand lances.

ConsiderationsforHydrodemolitionUseIssues that should be considered when evalu-ating the use of hydrodemolition for a repairproject include:

Limited quantity of repair: Mobilization andset up of the hydrodemolitionequipment canbeexpensive. If there are only minor repairsor alimited quantity of repairs, the mobilizationcostmay make the process uneconomical.

Increase in repair quantity.: The traverse andadvance function of the hydrodemolitionrobotresults in removalareas that are rectangular.Theremoval areas may have to be "squared up" inorder for the hydrodemolition equipment toefficiently removethe concrete. "Squaringup"the repair areas maylead to an increase in theremoval quantityand the cost of the project.

Reinforcing bar size and concrete cover.:Partial-depthremoval normallyrequiresclearancebelow the bottom reinforcing bar of the top matof reinforcing. The size and quantity of thereinforcing bar and the concrete coverover thereinforcing bar should be determinedin order tospecify the correct removaldepth to achieve therequired clearance.

Potential or ull-depthblow-throughs: Hydro-demolition of severely deteriorated structuresmay result in full-depth blow-throughs.Blow-throughs may take place where full depth slabcracks occur, especiallyif deteriorationis evidenton the slab underside. Shieldingmay be required

Fig. 22: Reinforcing steel blocks the water et leaving aconcrete shadow under the reinforcing. ncreasing heremoval depth will decrease the amount of shadowing

depth of the reinforcingbar. Similarly, the oscil-latingnozzle moves from sidetoside as it traverses,directing the water jet at an angle to the surface,cutting under the reinforcing bar. The nozzle isangled forwardas it traverses left,and at the endof the traverse,flips to face forwardas it traversesright. To minimizeconcrete shadows,the requireddepth of removalshould be at least3/4 in. (19 mm )below a #5 reinforcing bar. Larger reinforcingbars will require a greater removal depth tominimize shadowing. While this additional


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FM 7.10 ERMO'ITION OFCONCRETESURFACES FOR REPAIRUSING HYDRODEMOLITIONM P T J I 3 of 16 937

to protect the area below from damage. Shoringbelow the blow-through may be damaged ordestroyed. W henthe water jet is in the open air,as will happen whenthe waterjet blows throughthe deck, it is extremely noisy (may exceed130 db) and dangerous.Sound resistant partitionsshould be installed to contain the noise within thestructure if blow-throughsare expected.

Extent of previous repairs: Repair materialsmay have a different compressivestrength thanthe original concrete. Since the hydrodemolitionjet is set to move at a uniform rate, the presenceof dissimilar strengthsof material will result in avariation in the depthof removal.Higherstrengthareasmay require furtherconcrete removalsusingchipping hammers or hand lances to achieve thespecified depthof removal.Lower strength areasmay result in deeper removals and possibly full-depth blow-throughs.

Occupied areas adjacent o or under he repairarea: Occupied spaces such as stores or officesmay occurin the structure. Itmay not be practicalto perform hydrodemolitionadjacent to or overthese areas.Water from the hydrodemolitionmayleak to the occupied level below. As such, therepair area shouldbe protected to prevent waterfrom entering the occupied area.

Shoring requirements.: During structuralrepairs, concretemay be removed from aroundthe top reinforcing.An analysis of the structuralcapacity of the remaining slab sectionshould bemade by a qualified engineer to determine ifshoring will be required. The weight of thehydrodemolition robot should be consideredwhen determiningshoring requirements.

Equipment location: The hydrodemolitionequipment is transported on a trailer. If possible,the pumps should be located within 300 ft ofthe repair area. A suitable location next to thestructure mustbe selected. Pump units thatarepowered bydiesels engines shouldnotbe locatednext to the air intake of adjacent buildings. Incongestedmetropolitanareas, the pumps mayberemoved fromthe trailer and placed within thestructure.Diesel powered pumps will need to belocated closeto an exhaust shaftand the exhaust

from the pumps pipedto this location.A fuel tankwill also have to be placed in the pump area andprovisions made to fill the tank as required.Although electric pumps may be used insidethestructure eliminating the fueling and exhaustconcerns,theyhave a substantialpower requirementand will need an electrical service installed.Dueto the weight of the pumps, they may need to beplaced on the slab on ground or in a shored area

of the structure. Temporary shoring may beneeded to move the pumps intothe structure.

Available water sources: Pumps used forhydrodemolitionrequire a steadysupply of cleanwater at a sufficient vo lumeto performthe work.Generally, local municipal water is used forhydrodemolition.Sourcesclose tothe workarea,such as a nearbyfire hydrantor water line feeding

the structure, should beadequate. Specificwaterrequirements willvary, depending on the hydro-demolition unit used for the project and themethod of cleanup. Cleanup performedusing afire hose operating at 100 to 200 gpm (380 lpmto 760 1pm) will use substantially more waterthan an 8000 to 10,000-psi (55 to 70 MPa) waterblaster operatingat 8 to 12 gpm (30 to 45 1pm).In remote areas,water can be drawn from wells,fresh water lakes, rivers, or streams. Thiswatermust be pre-filtered to remove any suspendedsolids to avoid damage to the high-pressurepumps. Recycled waterhas been usedfor hydro-demolition, however, it can add substantiallyto the cost of the project due to collection andfiltration of the water and the added wear tothe equipment caused by dissolved mineralsinthe recycled water. When available, potablewater is used. Watermay have to be trucked intoremote locations.

Post-tensioned structures: The use of hydro-demolition on post-tensioned structures haspotentially severe risks and must be carefullyevaluatedto maintaina safe workingenvironment,maintainstructural integrity,and to preserve thelong-term durability of the structure. Suddenrelease of anchorages can result in dangerousexplosive energy and flying debriscapable ofcausing damageto equipment and serious injuryor deathtoworkers.Tendons shouldbe de-tensionedprior to removingconcrete from around anchoragesto prevent the sudden release of the anchoragesand lossof pre-stressforces. Theloss of pre-stressforces may resultin the loss of structural integrityand result in the need for shoring. Careful eval-uation must also be exercised whenremovingconcrete around post-tensioningtendons. Removalof concrete aroundtendons can result in a change

of tendon profile,which may also result in theloss of prestressingforce and structural integrity.

The wiresor strandsof post-tensioningtendonsare usually undamaged during hydrodemolition,howeverthe sheathing and protectivegrease willbe removed from unbonded tendons. In bondedpost-tensioningtendons, thewaterjet may penetratethe duct and remove the grout inside. In eithercase, the hydrodemolition water may enter the


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938 FM 7.10 Exhibit 1 CONCRETEREPAIR MANUAL page 14 of 16

tendon at the edge of the repair area and can bedriven into the tendon outside the work area.Water remaining in the tendon can cause futurecorrosion affectingthe long-term durabilityof thepost-tensioning system. Each tendon must becarefully examinedand any water thathas enteredthe tendon removed. Both the grease and theprotective sheathing mustbe restored.

It may notbe possibleto remove moisturethathas entered the post-tensioning systemduring thehydrodemolition process.In addition,verificationof the presence of moisture is difficult andmay not be possible. Refer to ICRI TechnicalGuideline No. 03736, "Guide for theEvaluationof UnbondedPost-Tensioned Concrete Structures,"for suggested proceduresto detect waterin post-tensioning tendons. Long term monitoring forfuture corrosion mayalso be prudent.

Conduit and embedded metal tems: Embeddedaluminumand steelconduit willnot be damagedby hydrodemolitionif they are ingood condition.However, deteriorated portionsof aluminumandsteel conduit will be damaged and water willenter the conduit system. PVC conduit will bedamaged during hydrodemolition. As a safetyprecaution, all conduits should be deenergizedduring demolition. Other metal items withinthe removal area suchas shear connectors,shearstuds, and anchorages will not be damagedby hydrodemolition.

Noise limitations: Hydrodemolitiondoes notproduce sound that is transmitted through astructure, however, the noise from the hydro-demolition unit in the work area is sufficientlyloud to be objectionable to the public. Further-more, noise can be excessive during full-depthrepairsor blow-throughs.Sound reducingpartitionwalls thatseparate the public fromthe work areamay be required.Acoustical studiesindicate thatthe sound waves created byhydrodemolitionarelow frequencyand are best controlled usingdensematerial such as sheet rock or concrete board.There are a variety of sound deadeningmaterialssupplied by various vendorsthat have proveneffective in controlling noise. Partition wallsshould be protected frommoisture. If properly

sealed atthe base, a waterresistant sound reducingpartition wall will also assist in containing thewater w ithin the work area.

Protection of lighting, sprinklers, and otherservices: Light fixtures, fire protection systems,and other servicesmay be damaged by airbornedebris from the hydrodemolition or clean upoperation. If full depth removalor blow-throughsare anticipated,light fixturesmay need tobe removed

and stored and temporary lighting installed.Sprinklerheads may needto beprotected.Mist andhigh humidity in the work area could damageelectricalpanelsand other services.Items remainingin the work area should be protected.

Temperature: When the temperature fallsbelow freezing, the structure mustbe heated orthe hydrodemolition stopped to prevent water

from freezing in the work area.

Test AreaA test area should be designated to establish theoperating parametersand to demonstratethat theequipment, personnel,and methods of operationare capable of producing satisfactory concreteremoval results. The test should include soundand deterioratedconcrete areas, eacha minimumof 50 ft2 (5 m2). First the robot is set to removesound concrete to the specified depth. Oncetheoperating parameters have been determined,

the equipment is moved to the deteriorated areaand a second test is performed usingthe sameoperating parameters.If satisfactory results areachieved, the quality and depth of removalwill become the standardfor the project. If handlances are to be used to perform concreteremovals, they should alsobe demonstrated toshow satisfactory results.

It is noted that the hydrodemolition robotwillmove the waterjet over the surface in a constantmotion and if the concrete is of uniform strength,the removal depth will be consistent. However,since concrete is seldom uniform, there will bevariations in the removal depth on theproject.Other factors affectingthe removal depth includethe extent and depth of deterioration,the size andquantity of reinforcing bar, the concrete coverover the reinforcing bar, and the presence ofsurface hardeners.As the equipment is used,nozzles will wear, changing the force createdby the water jet. As such, the hydrodemolitionequipment operator must monitorthe depth andquality of removal and adjust the parameters ofthe robot to provideconsistent removal through-out the project.

Wastewater ControlControllingthe wastewaterhas often beenviewedas one of the more difficulttasks associated withthe use of hydrodemolition.However, with pre-planning and proper installationof a wastewatercontrolsystem,the water can be properlymanaged(Fig.24). Hydrodemolitionwastewater shouldbe


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FM 7.10 ERRBAR*,TIONOF CONCRETE SURFACESFOR REPAIRUSING HYDRODEMOLITIONM P W I 5 of 16 939

IIFig. 24.: Typical wastewater handling system

discharged to the storm or sanitary sewer ortothe ground for absorption and/or evaporationunder permit from the controlling authority.Discharge into an existing stormor sanitary linemay occur in the structure orto a nearby storm

or sanitary line accessed througha manhole. A4-in. (100 mm) connection should be adequate.Wastewater maynot be discharged directlyto awetland, stream, river orlake.

Hydrodemolitionwastewatercontains suspendedparticlesand typicallyhas a pH of 11 to 12.5. Thewastewater is initially placed in settling tanksor ponds to reduce the suspended solids, Theparticles are heavy and settle out quickly asthe water is allowed to stand. This can also beaccomplished by allowing the water to passthrough a series of berms that are lined withfilterfabric or hay bales.

The controlling authoritiesfor dischargehavevarying requirements for the level of suspendedsolids and the range of pH for discharge into theirsystem. Typically the water should be clear andthe pH range between 5 and 10. Ponding thewater will clarify it, however, the pH of thewastewater may have to be reduced prior todischarge. This can be accomplished by theintroduction of acid, CO2 or other pH reducingmaterialsinto the wastewater. Adding flocculantscan assist in reducing suspended solids.A locationfor settling ponds or tanks and pH reducingequipment shouldbe determined.

The costto dischargewastewater ranges fromthe cost of a discharge permit to charges for theactual water consumed and discharged.The costof waterconsumed is generally thatof commercialwater usagewithin the community.The controllingauthority may require monitoring and testing ofthe wastewater. Local ordinance requirementsmustbe reviewedand met priorto discharge, includingthe obtaining of proper permits.

Water containmentand collection systems willvary dependingon thestructure. Where possible,it isbest to take advantageof gravity to move thewater to the treatment area. In many structures,the slab on groundcan beused to collect and treatthe water. The water may be allowed to flowthrough the structure to the lowest level orthrough the existing drains, which have been

disconnectedjust below the undersideof the firstsupported level. Allslab-on-grounddrains shouldbe plugged and water should notbe allowed toenterthe drainagesystem prior to treatment.Oncethe water is clear and the pH adjusted, it can bepumped directlyto the discharge point. Additionaltreatmentcapacity maybe necessary if rainwatercannot be separated fromthe wastewater.

Floorslabs and decks are commonlycrownedor sloped to provide drainage. Since waterwillrun to the low area, a simple methodof watercontrol involvestheuse of hay bales or aggregatedams,which can be set up along curblines or theperimeter of the work area.As the water pondsin front of the hay bales or aggregate dams,thesuspended solids will settle out.In areas wherethe drainsare plugged,the water is forced to passthroughthe hay balesor aggregatedams.Retentionponds can be built at the end of the structure andthe water directed or pumped to these ponds.Settling tanks can also be used and the waterpumped fromthe structure to the tanks.

Debris Cleanupand DisposalHydrodemolition debris consists of wet sand,aggregate, chips or chunksof concrete, and slurrywater.Slurry containscement particlesand rangesfrom muddy waterto a thick paste.Removal of thedebris should occuras soon as possible to preventthe debris from solidifying and adhering to thesurface, making cleanup more difficult.

Tools used for cleanup include: fire hoses,pressure washers, compressed air, sweepers, skidsteer loaders,vacuum trucks, and manual labor.

The types of cleanup willvary based on thetype of removal performedas follows:1. Above thereinforcing bar-any emoval depth

above the top reinforcingbar of the top mat ofreinforcing and the reinforcing bar remainssupported by the concrete;

2. Below the reinforcing bar-any emoval depthbelow the top mat of reinforcing bar inwhich the top reinforcing bar mat becomesunsupported by the original concrete; and


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940 FM 7.10 Exhibit 1 CONCRETE REPAIR MANUAL page 16 of 163. Full-depth emoval.

During above the reinforcing bar clean up,equipment suchas skid steer loaders, sweepers,andvacuum trucksmay be driven overthe surfaceto assist with the cleanup (providing they meetthe weight requirementsof the structure). Thedebriscan be swept, pressure washed orair blowninto piles where it is picked up by a loader. A

vacuum truck may be used to vacuum the debrisfrom the surface. In all cases, the surface mustbe pressure washed to remove any remainingcement slurry.

If the removal is below the reinforcing bar ndthe reinforcing baris unsupported,it is difficultand possibly unsafe to drive equipment intotheremoval area. The debris can be removed bywashingwith a firehose(large waterconsumption),pressure washingor blowingit onto the adjacentoriginal surface whereit can be picked up with aloader. A pressure washer operating at 8000 to10,000 psi (55 to 70 MPa) and 8 to 12 gp m(30 to 45 1pm) is effective. Vacuuming hasprovenvery effective in removing debris from aroundthe reinforcing steel, however, the surface willrequire pressure washingto remove the cementslurry and paste.

During full-depth removal, the debris simplyfalls to thefloor below whereit can bepickedupwith a loader.

The debris, which consists of wet sand,aggregate, chips or chunks of concrete, andslurry is placed in dumpsters or hauled awayintrucks andmay be recycledor placed in a landfillin accordance with the requirements of thecontrolling authority.

Removal DepthMeasurementsFollowing hydrodemolition,the surface profileis very rough and three depthmeasurementsarepossible (Fig. 25):1. Minimum removal-original surface to the

shallowest removal point.2. Maximum removal-original surface to the

deepest removalpoint.3. Average depth of removal-The difference

between the minimum and maximum removalat the same location.Measuring the depth of removal can be

accomplishedusing:1. A straight-edgeplaced on the originalsurface;2. A string-linepulledover the removalarea; and3. A surveyor's level.

Fig.: 25.: Measuring depth of removal using astraight edge

The most common practiceof measuringthedepthof removal is to place a straightedgeon topof the original surface and extend it over theremoval area. Measurementsare taken from thebottomof the straightedge to determine thedepthof removal. Thisquick and simple technique canonly be used during the removal processand isnot applicable for final measurements in largeremoval areas.

A string line maybe pulled over the removalarea and measurementstaken below the string.However, this method could provide incorrectresults if slopes or crowns occurin the originalsurface. Surveyingequipmentmay be used andis very accurate; however,to account for slopes,pitchesand crownsin theoriginal surface,a detailedsurvey must be made of the original surface

prior to removal and measurements takenat thesame locationsafter removalfor comparisonanddetermination of the actual removal depth.

SummaryEffective concrete removaland proper surfacepreparationare key elementsto a successfulrepairproject.A surface prepared usinghydrodemolitionis rough, irregular, and is excellent in creating amechanical bond with the repair material.Hydrodemolitioneliminatesmicro-fracturesanddamage to reinforcingsteel, minimizestransmitted

noise and dust, and cleansthe reinforcingsteel.The useof hydrodemolitionmay not beappro-

priate for every structure and a careful reviewofthe benefitsand limitationsof the process relativeto each structure shouldbe undertaken. Propersafety procedures mustbe observed at all timeswhen using hydrodemolition.


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FM 7.10 Exhibit 2 page 1 of 8...................

ACI 546R-04:.. . . . . . ... :

Concrete Repair Guide*

Reported by ACI Committee 546

Jay H. Paul Paul E. GaudetteChair Secretary

James P. Barlow

Paul D. Carter

Michael M. Chehab

Marwan A. Daye

Floyd E. Dimmick

Peter H. Emmons

Michael J. Garlich

Steven H. GeblerI. Leon Glassgold

Yelena S. Golod

Harald G. Greve

Robert F. Joyce

Lawrence F. Kahn

Brian F. Keane

Benjamin Lavon

Kenneth M. Lozen

James E. McDonald

Kevin A. Michols

Richard Montani

Myles A. Murray

Thomas J. Pasko

Don T. Pyle

Richard C. Reed

Johan L. Silfwerbrand

W. Glenn Smoak

Joe Solomon

Michael M. Sprinkel

Ronald R. Stankie

George I. Taylor

Alexander Vaysburd

D. Gerald Walters

Patrick M. Watson

Mark V. Ziegler

This document provides guidance on the selection and application ofmaterials and methods for the repair protection, and strengthening of concretestructures. An overtiew of ,naterials and methods is presented as a guide formaking a selection for a particular application. References are provided forobtaining n-depth information on the selected materials or methods.

Keywords: anchorage; cementitious; coating; concrete; joint sealant;placement; polymer; reinforcement; repair.

ACI Committee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in planning,designing, executing, and inspecting construction. Thisdocument is intended for the use of individuals who arecompetent to evaluate the significance and limitations of itscontent and recommendations and who will acceptresponsibility for the application of the material it contains.The American Concrete Institute disclaims any and allresponsibility for the stated principles. The Institute shall no tbe liable for any loss or damage arising therefrom.

Reference to this document shall not be made in contractdocuments. If items found in this document are desired by theArchitect/Engineer to bea part of the contract documents, theyshall be restated in mandatory language for incorporation by

the Architect/Engineer.

CONTENTSChapter 1-Introduction p. 546R-2

1. 1-Use of this document1.2-Definitions1.3-Repair methodology1.4-Design considerations1.5-Format and organization

Chapter 2-Concrete removal, preparation, andrepair techniques, p. 546R-6

2. 1-introduction and general considerations2.2--Concrete removal2.3-Surface preparation2.4-Reinforcement repair2.5-Anchorage methods and materials2.6-Materials placement for various repair techniques2.7-Bonding methods

Chapter 3-Repair materials, p. 546R-203.1--Introduction3.2--Cementitious materials

3.3-Polymer materials3.4-Bonding materials3.5--Coatings on reinforcement3.6-Reinforcement3.7-Material selection

ACI 546R-04 supersedes ACI 546R-96 and became effective Septemb er 23, 2004.Copyright © 2004, AmericanConcrete Institute.All rights reserved including rights of reproductionand use in any form or by any

means, including the making of copies by any photo process, or by electronic ormechanicaldevice, printed,written,or oral. or recordingfor sound or visual reproduc-tion or for use in any knowledgeor retrieval system or device, unlesspermission inwriting is obtained from the copyright proprietors.

663

It is the responsibility of the user of this document toestablish health and safety practices appropriate to the specificcircumstances involved with its use. ACI does not make anyrepresentations with regard to health and safety issues and theuse of this document. The user must determine theapplicability of all regulatory limitations before applying thedocument and must comply with all applicable laws andregulations, including but not limited to, United StatesOccupational Safety and Health Administration (OSHA)health and safety standards.


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664 FM 7.10 Exhibit 2 page 2 of 8CONCRETE REPAIR MANUAL

Chapter 4-Protective systems, p. 546R-304. 1-Introduction and selection factors4.2-Concrete surface preparation and installation

requirements4.3-Typical selection problems4.4-Systems concept4.5-Surface treatments4.6-Joint sealants4.7--Cathodic protection

4.8--Chloride extraction4.9-Realkalization

Chapter 5-Strengthening techniques, p. 546R-415.1--General5.2-Internal structural repair (restoration to original

member strength)5.3-Interior reinforcement5.4-Exterior reinforcement(encased and exposed)5.5-Exterior post-tensioning5.6-Jackets and collars5.7-Supplemental members5.8-Repair of concrete columns5.9-Column repair parameters

Chapter 6-References, p. 546R-486.1-Referenced standardsand reports6.2--Cited references

CHAPTER 1-INTRODUCTION1.1-Use of this document

This documentprovides guidanceon selection of materialsand application methods for the repair, protection, andstrengthening of concrete structures. The information isapplicable to repairing damaged or deteriorated concretestructures, correcting designor constructiondeficiencies,orupgradinga structure for new usesor to meet morerestrictive

building codes.This guidesummarizescurrent practices in concrete repairand providessufficient information for the initial planning ofrepair work' and for selecting suitable repair materialsandapplication methods for specific conditions. Many of thetopics covered in this guide are more extensivelycovered inother ACI committeedocuments.Readers of this guide shouldrefer to the appropriate documents of other ACI committeesand other industry resourcesfor additionalinformation.

1.2-Definitionscorrosion-destruction of metal by chemical, electro-

chemical, or electrolyticreaction within its environment.dampproofing-treatment of concrete or mortar to retard

the passage or absorption of water, or watervapor, eitherbyapplication of a suitable admixture or treated cement,or byuse of preformed film, such as polyethylene sheets, placedon grade beforeplacing a slab.

excavation-steps taken to remove deterioratedconcrete,sound concrete,or both, designatedfor removal.

nonstructural repair-a repair that addresses localdeterioration and is not intendedto affect the structuralcapacityof a member.

protection-the procedure of shielding the concrete struc-ture from environmental and other damage for the purpose ofpreserving the structure or prolonging its useful life.

repair-to replace or correct deteriorated, damaged, orfaulty materials, components, or elements of a structure.

repair systems-the combination of materials andtechniques used in the repair of a structure.

strengthening-the process of restoring the capacity ofdamaged components of structural concrete to its originaldesign capacity, or increasing the strength of structuralconcrete.

structural repair-a repair that re-establishes orenhances the structural capacity of a member.

surface preparation-steps taken after removal ofdeteriorated concrete, including conditioning of the surface ofsubstrate at bond line and the cleaning of existing reinforcingsteel.

waterproofing-prevention of the passage of water, inliquid form, under hydrostatic pressure.

1.3-Repair methodologyA basic understanding of the causes of concrete deficiencies

is essential to perform meaningful evaluations andsuccessful repairs. If the cause of a deficiency is understood,it is much more likely that an appropriate repair system will beselected and, consequently, that the repair will be successfuland the maximum life of the repair will be obtained.

Symptoms or observations of a deficiency should bedifferentiated from the actual cause of the deficiency, and itis imperative that causes and not symptoms be dealt withwherever possible or practical. For example, cracking can bea symptom of distress that may have a variety of causes suchas drying shrinkage, thermal cycling, accidental over-loading, corrosion of embedded metal, or inadequate designor construction. Only after the cause or causes of deficiencyare determined can rational decisions be made regarding theselection of a proper repair system and the implementationof the repair process (Fig. 1.1).

1.3.1 Condition evaluation-The first step in concreterepair is to evaluate the current condition of the concretestructure. This evaluation may include a review of availabledesign and construction documents, structural analysis of thestructure in its deteriorated condition, a review of availabletest data, a review of records of any previous repair work,review of maintenance records, a visual inspection of thestructure, an evaluation of corrosion activity, destructive andnondestructive testing, and review of laboratory results fromchemical and petrographic analysis of concrete samples.Upon completion of this evaluation step, the personnelresponsible for the evaluation should have a thorough under-standing of the condition of the concrete structure and beable to provide insights into the causes of the observeddeterioration or distress. Additional information onconducting surveys can be found in ACI 201.IR, 222R,224.1R, 228.2R, 364. IR, and 437R.

1.3.2 Determination of causes of deterioration ordistress-After the condition evaluation of a structure hasbeen completed, the deterioration mechanism that caused the


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668 FM 7.10 Exhibit 2 CONCRETE

behavior to evaluate and design a structural repair, strength-ening procedure, or both. Some design considerations followand arediscussed throughout this guide.

1.4.1 Current load distribution-In a deteriorated state, astructural member or system distributes dead and live loadsdifferently than first assumed when the structure was new.Cracking, deteriorated concrete and corroded reinforcementalter the stiffness of members, which leads to changes inshear, moment, and axial load distribution. As concrete andreinforcement are removed and replaced during the repairoperation, these redistributed forces are further modified. Tounderstand the final behavior of the structural system, theengineer should evaluate theredistribution of the forces. Tofully re-establish the original load distribution, a membershould be relievedof the load by jacking or other means. Therepaired member and the repair itself supports the loads differ-ently than would be assumed in the original or a new structure.

1.4.2 Compatibility of materials-If a repair and themember have the same stiffness-for example, modulus ofelasticity-the analysis of the repaired member may be thesame as a new section. If the stiffness varies, however, thenthe composite nature of the repaired system. should be

considered. A mismatch of other material characteristicsfurther exacerbates the effects of thermal changes, vibra-tions, and long-term creep and shrinkage effects. Differentcoefficients of thermal expansion of the repair and originalmaterial results in different dimensionalchanges. Theengineershould design for the different movements, or the repairsystem should be similar to the thermal and dimensionalcharacteristics of the original material.

1.4.3 Creep, shrinkage, or both-Reduction in length,area, or volume of both the repair and original materials dueto creep, shrinkage, or both, affect the structures service-ability and durability. As an example, compared with theoriginal material, high creep or shrinkage of repair materialsresults in loss of stiffness of the repair, redistributed forces,and increased deformations. The engineer should considerthese effects in the design.

1.4.4 Vibration-When the installed repair material is in aplastic state or until adequate strength has been developed,vibration of a structure can result in reduced bonding of therepair material. Isolating the repairs or eliminating thevibration may be a design consideration.

1.4.5 Water and vapor migration-Water r vapor migrationthrough a concrete structure can degrade a repair. Under-standing the cause of the migration and controlling it shouldbe part of a repair design consideration.

1.4.6 Safety- The contractoris responsible forconstructionsafety. Nevertheless, as the engineer considers a repairdesign, which may involve substantial concrete removal,steel reinforcing cutting, or both, he or she should notify thecontractor of the need and extent of shoring and bracing. Thelocal repair of one small section can affect a much largerarea, of which the contractor may not be aware.

1.4.7 Material behavior characteristics-When new andinnovative materials and systems are used for repair andstrengthening, the structural behavior of the repaired sectioncan differ substantially from the behavior of the original

REPAIR MANUAL page 3 of 8

section. For example, if a beam's steel reinforcement hascorroded extensively and lost part of its load-carryingcapacity, the steel reinforcement may be replaced by carbonfiber-reinforced polymer (CFRP) applied to the externalbottom face of the beam. The original yielding behavior of thesteel bar is replaced by FRP that is stronger, but has a moreelastic and brittle behavior. The behavior assumptions ofcodes like ACI 318 are no longer valid. The engineer shouldconsider the behavior and performance of the new repairunder the actual service and ultimate load, and design therepair to provide at least an equivalent level of safety to theoriginal design. Such a design is outside the scope of ACI 318.

1.5-Format and organizationChapter 2 discusses removal of deteriorated concrete,

preparation of surfaces to receive repair materials, generalmethods for concrete repair, and repair techniques forreinforcing and prestressing steel. Chapter 3 discussesvarious types of repair materials that may be used. Thereader is urged to use Chapters 2 and 3 in combinationwhen selecting the repair material and method for a givensituation. Chapter 4 describes materials and systems thatmay be used to protect repaired or unrepaired concretefrom deterioration. Chapter 5 provides methods forstrengtheningan existingstructurewhen repairingdeficiencies,improving load-carrying capabilities, or both. Chapter 6provides references, including other appropriate ACIdocuments and industry resources.

CHAPTER 2-CONCRETE REMOVAL,PREPARATION, AND REPAIR TECHNIQUES

2.1r-introduction and general considerationsThis chapter covers removal, excavation, or demolition of

existing deteriorated concrete, preparation of the concretesurface to receive new material, preparation and repair ofreinforcement, methods for anchoring repair materials to the

existing concrete, and various methods that are available toplace repair materials. The care that is exercised during theremoval and preparation phases of a repair project can be themost important factor in determining the longevity of therepair, regardless of the material or technique used.

Specific attention should be given to the removal ofconcrete around prestress strands, both bonded andunbonded. The high-energy-impact tools, such as chippinghammers, should avoid contact with the strand because thiswill reduce the strands' load-carrying capacity and maycause the wire(s) to rupture, which may lead to strand failure.

S2.2-Concrete removalA repair •projct uually in'volves removal of deteriorated,

damaged, or defective concrete. In most concrete repairprojects, the zones of damaged concrete are not well defined.Most references state thatall damaged or deteriorated materialshould be removed, but it is not always easy to determinewhen all such material has been removed or when too muchgood materialhas been removed. Acommon recommendationis to remove sound concrete for a defined distance beyondthe delaminated area; thereby, exposing the reinforcing steelbeyond the point of corroded steel.


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FM 7.10 Exhibit 2 page 4 of 8CONCRETEREPAIR GUIDE 669

Removal of concrete using explosives or other aggressivemethods can damage the concrete that is intended to remainin place. For example, blasting with explosives or the use ofsome impact tools heavier than 12 kg (30 lb) can result inadditional delamination or cracking. Delaminated areas canbe identified by using a hammer to take soundings. In mostcases, such delaminations should be removed before repairmaterials are placed.

small-scale microcracking damage (termed bruising) to the:surface of the concrete left in place. Unle.ss this damaged.layer is removed, a weakened plane may occur in the parentconcrete below the repair material bondline. This conditioncan result in a low tensile rupture (bond) strength betweenthe parent concrete and repair material. Thus, a perfectlysound and acceptable replacement material may fail due toimproper surface preparation. All damaged or delaminatedconcrete, including bruising, at the interface of the repair andthe parent concrete should be removed before placing therepair material. This may require one type of aggressiveremoval for gross removal followed by another type ofremoval for bruising.

a~l'a~sJsi'nNviZ1iZcncrte haZ KWii We(MeaT'From 'aaa structure by primary means such as blasting or aggressivea

impact methods, the concrete left in place should be prepared a:by using a secondary method. such as chipping, abrasive::blasting, orahigh-Vressure water jetting; to remove any°

aremalining danag:ed surface material.Careful visualispectonsof the prepared surfaces should be conducted before placingrepair materials. Wetting the surface may help to identify thepresence of cracking. Determination of the tensile strength(ACI 503R, Appendix A) by pull-off testing is advisable onprepared surfaces to determine the suitability of the surfaceto receive repair material.

Removal of limited areas of concrete in a slab, wall, orcolumn surface, requires saw-cutting the perimeter of theremoval area, providing an adequate minimum thickness ofrepair material at the edge of the repaired area, andmitigatingthe advancement of undetected incipient cracking.Featheringof repair materials generally should be avoided. The prep-aration for shotcreting is an exception. ACI 506R recom-mends tapered edges around the perimeter of such patches.Saw cutting can also improve the appearance of the repairedarea. The general shape of the repaired areas should be assymmetrical as possible (ICRI 03730). Reentrant cornersshould be avoided. Large variations in the depth of removalin short distances should also be avoided. The texture of theprepared surface should be appropriate for the intended'repair material (ICRI 03732).

Every precaution should be made to avoid cutting under-lying reinforcement. Reviewing design drawings and using acovermeter or similar device provides data as to the locationand depth of reinforcement. In addition, the removal of smallareas of concrete is commonly used to confirm the locationand depth of bars before saw cutting.

Sections 2.2.1 through 2.2.18 present descriptions of manyof the commonly used concrete removal techniques to helpin the selection process.

2.2.1 General considerations-Concrete removaladdresses deteriorated and damaged material. Some soundconcrete, however, may be removed to permit structuralmodifications and to ensure that all unsound material isremoved. The effectiveness of various removal techniquescan differ for deterioratedand sound concrete.Some techniquesmay be more effective in sound concrete, while others maywork better for deteriorated concrete.

Concrete removal techniques selected should be effective,safe, economical, environmentally friendly, and minimizedamage to the concrete left in place. The removal techniquechosen may have a significant effect on the length of timethat a structure will be out of service. Some techniquespermit a significant portion of the work to be accomplishedwithout removing the structure from service. The sameremoval technique, however, may not be suitable for allportions of a given structure.In some instances, a combinationof removal techniques may be more appropriate to speedremoval and limit damage to the remaining sound concrete.Trial field testing various removal techniques can helpconfirm the best procedures.

In general, the engineer responsible for the design of the

repair should specify the objectives to be achieved by theconcrete removal, and the repair contractor should beallowed to select the most economical removal method,subject to the engineer's acceptance. In special circum-stances, the engineer may also need to specify the removaltechniques to be used and those that are prohibited.

The mechanical properties of the concrete and the type andsize of aggregate to be removed provideimportant informationto determine the method and cost of concrete removal. Th emechanical properties include compressive and tensilestrengths. This information is also necessary for the engineerto specify the prepared surface condition and select the repairmaterial, and it should be made available to contractors forbidding purposes.

2.2.2 Monitoring and shoring during removal opera-tions It is essential to evaluate the removal operations tolimit the extent of damage to the structure and to the concretethat remains. Structural elements may require shoring,removal of applied loads, or both, before concrete removal toprevent structural deformations, possible collapse, buckling,or slippage of reinforcement. Care should be used duringremoval of concrete to avoid cutting and damaging rein-forcing steel. Because reinforcement is often misplaced,unanticipated damage may occur when saw cutting,impacting, or removing concrete.

Careful monitoring is required throughout the concreteremoval operation. This can be accomplished by visualinspection, sounding, use of a covermeter, or other means tolocate reinforcement. The project specifications should assignresponsibilities for the inspection of the prepared concrete.

Sounding is an excellent means to detect delaminatedconcrete adjacent to the outermost layers of reinforcing steel.Subsurface cracks, the extent of deterioration, or otherinternal defects, however, may not be identified by thismethod alone. Other means of evaluation should be used toproperly identify the extent of concrete to be removed. In


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FM 7.10 Exhibit 2 page 5 of 8670 CONCRETEREPAIR MANUAL

addition, sounding usually does not indicate near-surfacemicrocracking or bruising. Only microscopic examination orbond testing may disclose near-surface damage.

Subsurface evaluation (examination of the substrate) canprovide valuable information about the condition of theconcrete. This information may be obtained by thefollowing methods before, during, or after concrete removal(ACI 228.2R):

a) Taking cores for visual examination, microscopicexamination, compressive strength tests, and splitting-tensile strength tests;

b) Pulse-velocity tests;c) Impact-echo tests;d) Bond tests (pull-off testing, ACI 503R Appendix A);e) Covermeter or similar equipment to locate reinforce-

ment and determine its depth below the surface;f) Infrared thermography; andg) Ground-penetrating radar (GPR).Many of these methods are discussed in ACI 228.2R.2.2.3 Quantity of concrete to be removed-In most repair

projects, all damaged or deteriorated concrete should beremoved; however, the quantity of concrete to be removed is

directly related to the elapsed time between preparation ofthe estimate and actual removal. Substantial overruns arecommon. Estimating inaccuracies can be minimized by athorough condition survey as close as possible to the time therepair work is executed. Potential quantity overruns, basedon field-measured quantities, should be taken into account.When, by necessity, the condition survey is done far inadvance of the repair work, the estimated quantities shouldbe increased to account for continued deterioration. Becausemost concrete repair projects are based on unit prices, repairareas should be accurately measured before forms areinstalled. This is usually done jointly by the engineer and thecontractor. It is not uncommon for estimated quantities toincrease significantly between the detectable quantities andthe actual quantity removed. ICRI 03735 provides guidelinesfor methods of measurement for concrete repair work.

2.2.4 Classification of concrete removal methods-Removal and excavation methods can be categorized by theway in which the processacts on theconcrete. These categoriesare blasting, cutting, impacting, milling, hydrodemolition,presplitting, and abrading. Table 2.1 provides a generaldescription of these categories, lists the specific removaltechniques within each category, and provides a summary ofinformation on each technique. The techniques are discussedin detail in the following sections.

2.2.5 Blasting methods-Blasting methods generallyemploy rapidly expanding gas confined within a series ofbore holes to produce controlled fracture and removal of theconcrete. The only blasting method addressed in this reportis explosive blasting.

Explosive blasting is the most cost-effective and expedientmeans for removing large quantities of concrete-forexample, portions of large mass concrete foundations or walls.This method involves drilling bore holes, placing an explosivein each hole, and detonating the explosive. Controlled-blasting techniques minimize damage to the material that

remains after blasting. One such technique, cushion blasting,involves drilling a line of 75 mm (3 in.) diameter or smallerbore holes parallel to the removal face, loading each hole withlight charges of explosive (usuallydetonating cord) distributedalong its length, cushioning the charges by stemming eachhole completely or in the collar with wet sand, and detonatingthe explosive with electric blasting caps. The uniformdistribution and cushioning of the light charges produce arelatively sound surface with little overbreak.

Blasting machines and electrical blasting-cap delay seriesare also Used for controlled demolition and employ propertiming sequences to provide greater control in reducingground vibration. Controlled blasting has been used success-fully on numerous repair projects. The selection of propercharge weight, borehole diameter, and borehole spacing fora repair project depends on the location of the structure, theacceptable degree of vibration and damage, and the quantityand quality of concrete to be removed. If at all possible, apilot test program should be implemented to determine theoptimum parameters. Because of the inherent dangers in thehandling and usage of explosives, all phases of the blastingproject should be performed by qualified, appropriately

licensed personnel with proven experience and ability.2.2.6 Cutting methods-Cutting methods generallyemploy mechanical sawing, intense heat, or high-pressurewater jets to cut around the perimeter of concrete sections topermit their removal. The size of the sections that are cut freeis governed by the available lifting and transportingequipment. The cutting methods include high-pressurewater jets, saw cutting, diamond wire cutting, mechanicalshearinp, stitch drilling,,and thermal cuttinZ.. ..........

a) High-pressure water jet (without abrasives)-A high-pressure water jet uses a small jet of water driven at high:velocities, commonly producing pressures of 69 to 310 MPa(10,000 to 45,000 psi). A number of different types of water:jets are currently being used. The most promising are the:ultra high-pressure jet and the cavitating jet. Section 2.2.10 adescribes using a water jet as a primary removal method.Water jets used with abrasives are described in Section a

a 2.2.11.b) Saw cutting-Diamond or carbide saws are available in

sizes ranging from small (capable of being hand-held) tolarge (capable of cutting depths of up to 1.3 m [52 in.]).

c) Diamond wire cutting-Diamond wire cutting isaccomplished with a wire containing nodules impregnatedwith diamonds. The wire is wrapped around the concretemass to be cut and reconnected with the power pack to forma continuous loop. The loop is spun in the plane of the cutwhile being drawn through the concrete member. Thissystem can be used to cut a structure of any size as long asthe wire can be wrapped around the concrete. The limits ofthe power source determines the sizeof the concrete structurethat can be cut. This system provides an efficient method forcutting up and dismantling large or small concrete structures.

d) Mechanical shearing-The mechanical shearing methodemploys hydraulically powered jaws to cut concrete andreinforcing steel. This method is applicable for makingcutouts through slabs, decks, and other thin concrete


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FM 7.10 Exhibit 2 CONCRETEREPAIR GUIDE page 6 of 8 671

Table 2.1- Summary of features and considerations/limitations for concrete removal methodsCategory Features Considerations/Limitations

2.2.5 Blasting ExplosivesUses rapidly expanding gas confined within a seriesof Most expedient method for removing large volumes Requireshighly skilled personnelfordesignand execution.boreholes to producecontrolled fracture andremoval of where concrete sectionis 10 in. (250 mm) thick or more. Stringentsafety regulations mustbe complied withregardingconcrete. Produces good fragmentationof concrete debris for easy the transportation, storage, anduse of explosives due to

removal. their inherent dangers.Blast energy must be controlled to avoid damage tosurrounding improvements resulting from air blast

--------------------------------------- -------------------- - -- .pnegurey g--u-d-ib----..a-d'li-debpi.. ........I 2.2.6 Cutting High-pressure waterjet (withoutabrasives)I Uses perimeter cutsto remove large piecesof concrete. Applicable for making cutouts through slabs,decks, and Cutouts for removal limitedto thin sections.* other thin concretemembers. Cutting is typically slowerand more costly than diamond

Cuts irregularand curved shapes. blade sawing.U Makes cutoutswithoutovercutfingcorners. Moderatelevels of noise maybe produced.* Cuts flush with intersecting surfaces. Controllingflow of waste water maybe required.*No telatvi%•auo•,lods io d Additionalsafety precautions are required dueto the highS'Handli ng of debtisis efficient because bulk of concrete is water pressureproduced by the system.

a removed in arge pieces.S2.2.6Cutting.(continued. Diamond saw

Applicable for making cutouts through slabs,decks, and Cutouts for removallimited tothin sections.other thin concrete members. Performance is affectedby type of diamonds and the dia-Makes precisioncuts. mond-to-metalbond in blade segments (segment selec-No dust or vibrationis produced. tion is based on aggregate hardness).Handling of debris is efficient because bulk of concrete is The higher the percentage of steel reinforcementin cuts,removed in arge pieces. the sltwer and more costly the cutting.

The harder the aggregate, the slower and more costly thecutting.Controllingflow of waste water maybe required.

2.2.6 Cutting(continued) Diamond wire cuttingApplicable for cutting large and/or thickpiecesof concrete. The cutting chainmust be continuous.The diamond wire chaincan be

infinitely long. Access to drill holes throughthe concrete must be available.No dust or vibration is produced. Water must be available to the chain.Large blocks of concrete ca

Documents

Guide for the Preparation of Concrete Surfaces for Repair Using Hydrodemolition Methods