guidelines on crack repair in concrete structure

7/30/2019 Guidelines on Crack Repair in Concrete Structure

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Structural Engineering Branch, ArchSD Page i of ii File code : SEBGL-MT3Guidelines on Crack Repair of Concrete Structure CTW/MKL

First Edition: August 1990

Edition No./Revision No. : 2/- Second Edition: May 2013

SEB GUIDELINES

SEBGL-MT3

Crack Repair of Concrete Structure

STRUCTURAL ENGINEERING BRANCH

ARCHITECTURAL SERVICES DEPARTMENT

May 2013


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Structural Engineering Branch, ArchSD Page ii of ii File code : SEBGL-MT3Guidelines on Crack Repair of Concrete Structure CTW/MKL



Content Page

1 Introduction ........................................................................................................ 1

2. Evaluation of Cracks .......................................................................................... 1

3. Classification of Cracks ..................................................................................... 5

4. Repair Options and Methods ............................................................................ 6

5. Option 1: Injection and Grouting ..................................................................... 6

6. Option 2: Stitching ........................................................................................... 12

7. Option 3: Changing a Crack into a Joint ....................................................... 13

References

Copyright and Disclaimer of Liability

This Guideline or any part of it shall not be reproduced, copied or transmitted in any

form or by any means, electronic or mechanical, including photocopying, recording,

or any information storage and retrieval system, without the written permission from

Architectural Services Department. Moreover, this Guideline is intended for the

internal use of the staff in Architectural Services Department only, and should not berelied on by any third party. No liability is therefore undertaken to any third party.

While every effort has been made to ensure the accuracy and completeness of the

information contained in this Guideline at the time of publication, no guarantee is

given nor responsibility taken by Architectural Services Department for errors or

omissions in it. The information is provided solely on the basis that readers will be

responsible for making their own assessment or interpretation of the information.

Readers are advised to verify all relevant representation, statements and information

with their own professional knowledge. Architectural Services Department accepts no

liability for any use of the said information and data or reliance placed on it

(including the formulae and data). Compliance with this Guideline does not itself

confer immunity from legal obligations.


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Structural Engineering Branch, ArchSD Page 1 of 15 File code : SEBGL-MT3Guidelines on Crack Repair of Concrete Structure CTW/MKL



1 Introduction

1.1 SEBGL-MT1: Structural Survey and Appraisal of Existing Structures (being

revised as at May 2013) details the procedures of structural survey in order to

identify defective areas in buildings for further investigation. One of the aims

of such investigation is to identify any defects in order to devise a cost-effectiverepair strategy. SEBGL-MT2: Causes of Concrete Deterioration, Investigation

and Repair Methods supplements it by listing out the common causes of defects

and deterioration of rc structures, and the principles and methods to repair such

defects and deterioration.

1.2 In SEBGL-MT2: Causes of Concrete Deterioration, Investigation and Repair

Methods, it has been mentioned that concrete deterioration is commonly due to

corrosion of steel reinforcement, which is accelerated by the presence of cracks

through the ingress of moisture and air. It also mentioned that such cracks may

be caused by overloading, poor workmanship, incorrect detailing, shrinkage,

thermal effect, AAR, etc. It is therefore necessary to seal such cracks in theirearly stage in order to restore its structural integrity, to prevent the ingress of air

and moisture into the concrete causing the corrosion of the steel reinforcement,

etc.

1.3 In 1990, SEB issued a set of guidelines entitled Cracks in Concrete Structure

providing guidelines on crack repair. The present set of guidelines (Guideline)

is intended to update it taking into account of the technological advancement

and our experience in the past two decades. This Guideline will describe:

a) the different repair methods of both structural and non-structural cracks in

an existing rc structure;

b) salient features in carrying out the repair on site.

2. Evaluation of Cracks

2.1 Before proceeding with repairs, an evaluation should be made to determine the

location and extent of crack, the cause(s) of crack, the likelihood of further

movement, and the need for repair. The location, extent and further movement

of a crack are useful information for identifying the cause(s) of the crack.

Location and extent of crack can be determined by visual inspection and non-

destructive testing.

2.2 Crack widths can be measured using a crack width meter formed by a

transparent card having lines of specified width marked on the card (Figure 1(a)

and Figure 1(b)). More accurate measurement can be carried out by a crack

width microscope, and one piece of this equipment with magnification of 10X is

available for loan at SEB Equipment Store (available:

http://asdiis/sebiis/2k/booking/frame.htm). The microscope can measure crack

widths to an accuracy of 0.02mm, and consists of a high definition microscope

with a light source (Figure 1(c)). A knob on the side of the microscope is used

to focus the image, and the eyepiece graticule can be rotated through 360o to

align with the direction of the crack being examined.
http://asdiis/sebiis/2k/booking/frame.htmhttp://asdiis/sebiis/2k/booking/frame.htmhttp://asdiis/sebiis/2k/booking/frame.htm


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(i) newly installed telltale (ii)after movement(a)Telltale

(Source: ACI 2007)

(b)Demec Gauge(Source: Mayes Group) (c)

Demec gauge with digital dialgauge (Source: Capco Test

Equipment)

Figure 2 Crack movement measurement

2.4 More advanced monitoring devices are available in the market, including: crack

monitoring device (CMD), and displacement transducer, which can monitor

crack movement with time. A CMD (Figure 3(a)) consists of a three-point

rosette, in the shape of an equilateral triangle with 50-mm side lengths, bonded

to the concrete surface. Two of the rosette points are positioned parallel to the

crack, and the third one is positioned on the opposite side of the crack

approximately half the distance to the base line. A displacement transducer(Figure 3(b)) can be surface mounted or installed in drilled holes across

existing cracks on structures, and it works the principle of measuring changes in

electrical properties in proportion to the relative displacement between the

transformer and armature (Buenfeld et al2008).

(a) Continuing monitoring device

(Source: Avantech Engineering

Consortium Pvt Ltd)

(b)Displacement transducer(Source: Geokon Inc)

Figure 2 Continuous device for crack movement measurement


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2.5 Besides indentifying the location, extent and further movement of the cracks,

PSE should also review the drawings, specifications, and construction and

maintenance records, and calculations can be made to determine the stresses due

to applied loads. Information on the location, extent, movement, desk study, etc

should then be assessed to determine the cause(s) of the cracks. The common

causes of cracks in rc structures have been described in SEBGL-MT2: Causes ofConcrete Deterioration, Investigation and Repair Methods. Determination of

the cause(s) of the cracks is vital to assess whether repair is required and to

devise a cost-effective remedial proposal. For example, if the cracks are caused

by overloading and such excessive loading is not removed, it is first required to

carry out strengthening work. Similarly, for cracks caused by corroding

reinforcing bars, the deterioration should be repaired by using patch repair

technique. Indeed, using injection to repair cracks caused by corroding bars is

not recommended because continuing corrosion will cause new cracks to appear

(ACI 2003).

2.6 Following the evaluation, it may be found that the crack is not a cause forconcern and no treatment is needed. For example, if the crack width is very

small, the crack may not have to be repaired. As a general rule, cracks in rc

structures with crack width smaller than 0.3mm (0.2mm for liquid retaining

structures) need not be repaired or sealed (Table NA.4 of the UK National

Annex toBS EN 1992-1-1 (BSI 2004a)).

2.7 Autogenous healing

One common phenomenon is that fine cracks may seal themselves naturally

through the process of autogenous healing in the first few days or weeks after

casting. Autogenous (means self-produced in Greek) healing occurs in

concrete in the presence of moisture. Healing occurs by the following two

mechanisms (Neville 2002):

a) by formation of calcium hydroxide generated from the hydration oftricalcium silicate and dicalcium silicate in concrete leading to hydration of

the unhydrated cement;

b) formation of calcium carbonate within cracks in the presence of water andcarbon dioxide when cement reacts with carbon dioxide in the atmosphere

and the calcium hydroxide at the cracked surface, resulting in the formationof calcium carbonate crystals. Gradually these crystals accumulate and grow

in these tiny cracks and form bonding so that the cracks are sealed

As autogenous healing depends on cement hydration, saturation of the crack and

the adjacent concrete with water is essential. Alternatively, water may be

ponded on the concrete surface so that the crack is saturated. PSE should further

note that the use of hydrophobic admixture in the concrete mix, which reduces

the molecular attraction between water and concrete, will affect the autogenous

healing mechanism to seal fine crack naturally, and SEB therefore promulgated

SEI No. 02/2010: Using and Specifying Concrete Admixtures in Construction

Contracts (available: http://asdiis/sebiis/) advising PSE to exercise care in thechoice and use of waterproofing admixture in the concrete mix.
http://asdiis/sebiis/http://asdiis/sebiis/http://asdiis/sebiis/


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2.8 However, in some instances, remedial measures may be necessary; especially

when the cracks adversely affect the structure in terms of one or more of the

following properties:

(i) structural strength,

(ii) ingress of moisture to reinforcement,

(iii) watertightness,(iv) appearance.

3. Classification of Cracks

3.1 Once it is determined to carry out repair to cracks, it is required to classify the

cracks in order to choose the appropriate repair method. There are a number of

classifications of cracks. For example, cracks may be classified into non-

structural and structural. There has not been consensus on precise definitions

for non-structural and structural cracks. For this Guideline, non-structural

cracks refer to those that are not structural concern; whilst structural cracks referto those that are structural concerns, e.g. those affecting the structural integrity,

those affecting durability of the structure.

3.2 Alternatively, for the purpose for deciding upon the method of repair cracks are

usually classified into three classes, as changes of crack width are of importance:

(a) dormant (or dead) cracks, which are unlikely to open, close or extend

further. These include cracks formed as a result of plastic shrinkage and

occurred settlement, or cracks caused by one-off overload or under-design

which has subsequently been strengthened. They may be repaired by

filling them with a rigid material.

(b) active (or live) cracks, which do not remain constant in width but open

and close, as the structure is loaded or with changes in temperature or

seasonal shrinkage. Typical causes of live cracks include those due to

thermal effect. The repairs must either be flexible enough to allow for

movement or steps must be taken to eliminate the movement.

(c) growing cracks, which are increasing in width because the original source

for their occurrence is continuing, e.g. cracks caused by reinforcement

corrosion, or long-term drying shrinkage. Any repair to a growing crackmust also eliminate the cause of the crack.


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4. Repair Options and Methods

4.1 There are many crack repair methods available in the market, including epoxy

injection, polyurethane injection, gravity filling, routing and sealing, near-

surface reinforcing and pining, grouting, drilling and plugging, crack arrest, etc.

These methods may be grouped into three basic types (Newman 2001; Li et al2009)):

Option 1: Seal the crack by injection or grouting with suitable materials to suit

the different types of cracks

Option 2: Stitch the cracked concrete with dowels

Option 3: Enlarge the crack first and then caulk it with a flexible or semi-rigid

sealant

These options together with the repair methods will be described in the

following paragraphs.

5. Option 1: Injection and Grouting

5.1 Cracks are now usually repaired by injection. BS EN 1504-9: Products and

Systems for the Protection and Repair of Concrete Structures. Definitions,

Requirements, Quality Control and Evaluation of Conformity. General

Principles for Use of Products and Systems (BSI 2008) lists injection as Method

1.4 and Method 4.5 under Principle 1 protection against ingress and

Principle 4 structural strengthening respectively.BS EN 1504-5: Products and

Systems for the Protection and Repair of Concrete Structures. Definitions,

Requirements, Quality Control and Evaluation of Conformity. Concrete

Injection (BSI 2004) describes the details of injection of cracks, defects and

voids in concrete. ACI also published Field Guide to Concrete Repair

Application Procedures: Structural Crack Repair by Epoxy Injection (Keane et

al 2003) providing guidelines on crack repair by injection. As injection is

widely used in Hong Kong to seal cracks, ArchSD promulgated ArchSD OI No.

02/2011: Particular Specifications for Concrete Repair (available:

http://asdiis/cmbiis/CMBIIS_a/manuals/manuals/oi/asdoi02-11.pdf), providing

a specification Particular Specification for Concrete Repair by Chemical

Injection(the PS) for carrying out crack repairs using chemical injection.
http://asdiis/cmbiis/CMBIIS_a/manuals/manuals/oi/asdoi02-11.pdfhttp://asdiis/cmbiis/CMBIIS_a/manuals/manuals/oi/asdoi02-11.pdfhttp://asdiis/cmbiis/CMBIIS_a/manuals/manuals/oi/asdoi02-11.pdf


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5.2 Materials

5.2.1 Various injection materials are available for injection, and the choice depends

on the types of crack. For dormant cracks, cement grout or epoxy resin (EP), are

commonly used to rebond the substrate; whilst for live cracks, polyurethane

resin (PUR) is usually used to act as void fillers (Concrete Society 1992).Clause 5 of the PS specifies two types of materials for injection, namely epoxy

resin and polyurethane resin.

5.2.2 Epoxy resin

Epoxy resin consists of two components - a resin and a hardener, and is usually

delivered in 2-packed (Figure 4). It is of low viscosity and is usually used to

seal dormant cracks with widths down to 0.1mm. As its tensile strength and

adhesion strength on the concrete is greater than the tensile strength of concrete,

the component will fail outside of the injected crack in the event of overloading.

Figure 4 2-packed epoxy injection resin

5.2.3 Polyurethane resin

Epoxy resin injection has a serious limitation if the crack is not dormant. The

crack will recur. If the crack does not affect the structural integrity of the

structure, injection with polyurethane resin may be a more suitable choice to fill

the crack. Polyurethane resin may consist of two components - a resin and a

hardener, or one component (moisture cured). One of the advantages of using

polyurethane resin is that it can be used to seal live cracks that experience some

small degree of movement. A rule of thumb is that a maximum change in crackwidth of 0.05 mm applies for cracks of between 0.3 mm and 0.5 mm in width,

or at a maximum change of 0.1 mm for cracks of over 0.5 mm in width.

Moreover, polyurethane resin can also be used in damp and wet cracks, and

even in cracks subject to water pressure. Wet or actively leaking cracks and

joints are therefore preferred to be injected with polyurethane resin.

Polyurethane resin cannot be used for very fine cracks, and the width of the

crack must be at least 0.3mm. Moreover, polyurethane resin usually has low

strength as compared with epoxy resin, and is not used to structurally re-bond

cracked concrete.


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5.2.4 Properties of injection resin (PS Clause 5)

Injection resin is delivered as a proprietary product and will seldom be tested

prior to injection. The desirable qualities for repair resin include low viscosity,

ability to bond to damp concrete, suitability for injection in as wide a

temperature range as possible, low shrinkage, and toughness rather than highstrength (Perkins 1986).

Clause 5.1 of the PS specifies the tensile strength and bond strength for epoxy

resin, which is referenced from ASTM C881: Standard Specification for Epoxy-

Resin Based Bonding Systems for Concrete (ASTM 2008) with modifications to

suit the availability of such products in the market of Hong Kong. ASTM C881

classifies the various epoxy resins by Type, Grade and Class. There are seven

types (Type I to VII) of epoxy resins, which designates the type of epoxy for

that specific type of repair. Each type of epoxy resin has three grades which

denote its viscosity (Grade 1 (low viscosity), Grade 2 (medium viscosity) and

Grade 3 (non-sagging consistency)) and three classes which specifies thetemperature range in which the epoxy is used (Class A (below 5oC), Class B

(515oC) and Class C (above 15oC)). The specified properties for epoxy resin

in Clause 5.1 of the PS generally meet the requirements for epoxy material Type

IV specified for structural repairs load bearing applications for bonding

hardened concrete to hardened concrete inASTM C881. Though viscosity is not

specified in the PS, PSE should note that low viscosity epoxy resins are best for

hairline cracks. PSE may also note that the specified properties for epoxy resin

do not currently tally with the properties for epoxy resin in the Schedule of

Rates for Term Contracts for Building Works 2010 Edition Volume 1 (Builder's

Works) issued by ArchSD, and arrangement is currently being made to amend

the requirements in the latter one to tally with those in the PS.

Clause 5.2 of the PS also specifies the elongation and bond strength for

polyurethane resin used for repair of live cracks. PSE should check the product

information sheet of the proprietary product submitted in the submittal under

Clause 2 of the PS against the specified properties.

5.3 Injection Procedures

5.3.1 ACI published Causes, Evaluation, and Repair of Cracks in Concrete

Structures (ACI 2007) details the injection procedures, and the PS also specifiesthe necessary steps in carrying out injection. Videos (e.g. at

http://www.youtube.com/watch?feature=player_embedded&v=TSogjFQPksc,

www.youtube.com/watch?v=aUeKs1akSlw (accessed: 15 April 2013)) were

uploaded by suppliers showing the main injection procedures. The procedures

may be summarised as follows, and the detailed procedures and the salient

features will then be described:
http://www.youtube.com/watch?feature=player_embedded&v=TSogjFQPkschttp://www.youtube.com/watch?feature=player_embedded&v=TSogjFQPkschttp://www.youtube.com/watch?v=aUeKs1akSlwhttp://www.youtube.com/watch?v=aUeKs1akSlwhttp://www.youtube.com/watch?v=aUeKs1akSlwhttp://www.youtube.com/watch?feature=player_embedded&v=TSogjFQPksc


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Clean the cracks

Install the entry and

venting ports

Seal the surfaces

Mix and inject the resin

Remove the surface seal

5.3.2 Cleaning of the crack (PS Clause 7.2)

The surface around a crack should be cleaned such that it can be sealed by the

cap seal. Usually, wire brushing (instead of mechanical grinding) is used, as

mechanical grinders may fill the cracks with unwanted dust. The crack may then

be flushed with water, and should then be allowed to dry.

5.3.3 Installation of ports and cap seals (PS Clause 7.3.1)

Before injection, ports are required to be installed. Ports are usually surface

mounted. They act to transfer the injection resin under pressure into the crack.

They are usually spaced at 400 mm c/c (Figure 5(a)). After installing the

injection ports, the surface of the cracks should be sealed by cap seal (Figure5(b)), which serves to contain the resin as it is injected under pressure into the

crack. As the detailed procedures are to be designed and specified by the

specialist sub-contractor, Clause 3 of the PS specifies that the specialist sub-

contractor to submit the equipment, tools and materials required for the

application, the application procedures including crack preparation, spacing of

injection points, mixing procedures, injection sequence and curing regime, etc.

for the approval of the SO.

Figure 5(a) Installation of surface

mounted ports

Figure 5(b) Application of cap seal(Source: Lincoln Company)


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5.3.4 Mixing of injection resin (PS Clause 7.3.2)

Mixing is specified to be done by continuous method. In the continuous mixing

system, the hardener and resin in liquid form pass through metering and driving

pumps before passing through an automatic mixing head. The continuous

mixing system applies for all epoxies, including fast-setting adhesives that havea short working life.

5.3.5 Injection (PS Clause 7.3.3)

Injection methods aim to fill a crack completely, and the experience and skill of

the personnel executing the injection is of paramount importance. Hence, the PS

does not specify the exact methods of injection, and leaves it at the discretion of

the specialist sub-contractor. The injection resin is to be introduced under

pressure with the ports (Figure 6). Usually, the injection is started at the port in

the widest section of a horizontal crack, and at the bottom for vertical cracks.

The injection at that port can be stopped and capped if an adjacent port startsbleeding, and the process continues until all the ports are capped. If the crack

is vertical or inclined, the injection process should begin by pumping injection

resin into the entry port at the lowest elevation until the injection resin level

reaches a predetermined entry port above. The lower injection port is then

capped, and the process is repeated until the crack has been completely filled

and all ports have been capped. It may be required to repeat this process several

times until the crack is sealed. The crack is full if the pressure can be

maintained. If the pressure cannot be maintained, the injection resin is still

flowing into unfilled portions or leaking out of the crack.

Figure 6 Injection of epoxy resin

Upon completion of the injection process (Figure 7), the ports and cap seal can

be removed by heat, chipping, or grinding. Pressure for injection should be kept

to minimum in order to allow the resin to flow into the crack. Excessive

pressure is likely to force the resin along the path of least resistance, leaving

voids.


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Figure 7 Completed injection work

Another injection method involves the use of a vacuum. There are two

techniques. One technique is to entirely enclose the cracked member with a bag,

introduce the liquid adhesive at the bottom, and apply a vacuum at the top. The

other technique is to inject the cracks from one side and pull a vacuum from theother. Vacuum injection may be used for dead-end cracks where access to the

cracks can only be from one side of the structural elements, or for multiple

cracks with random pattern.

5.3.6 Quality control and testing (PS Clause 2, Clause 3 and Clause 6)

As the injection resin is proprietary product, PSE usually approves the materials

and method statement based on the submittal (Clause 3 of the PS). An

additional safeguard is to ensure that personnel with appropriate experience are

employed to carry out the injection work and the work is also supervised by

staff with appropriate experience (Clause 2 of the PS). Moreover, before large-scale field injection, a trial injection on specified area should be arranged

(Clause 6 of the PS). To ensure that the trial injection has been successful, test

cores of 50 mm diameter are taken to check the penetration of the injection resin

into the crack.

For completed works, the PS also specifies that test cores may be ordered to test

the penetration of the injection resin into the crack (Clause 6 of the PS). The

PSE may note that instead of taking cores, nondestructive tests (NDT), though

are not specified in the PS, may be considered. Possible NDTs include impact

echo, ground penetrating radar, and ultrasonic pulse measurement, and these

techniques have been described in SEBGL-MT2: Causes of Concrete

Deterioration, Investigation and Repair Methods.

5.5 Gravity filling

BS EN 1504-9 identifies the purposes of filling as meeting Principle 1

protection against ingress and Principle 4 structural strengthening, and lists

gravity filling as Method 1.5 and Method 4.6 respectively. Gravity filling can

be used to seal cracks with surface widths of 0.03mm to 2mm. This method

employs low-viscosity monomers and grouts (e.g. high-molecular-weight

methacrylates, urethanes, low-viscosity epoxies) to fill the cracks that can befilled. ACI published Crack Repair by Gravity Feed with Resin (ACI 2003)


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giving the theories and procedures for crack repair using polymer resin to fill

the crack under gravity alone. The procedures of gravity filling are similar to

those in injection, except that no pressure is required. After cleaning the surface,

the monomer or resin can be poured onto the surface and spread with brooms,

rollers, or squeegees. The material should be worked back and forth over the

cracks to obtain maximum filling as the monomer or resin recedes slowly intothe cracks (Figure 8).

Figure 8 Gravity filling of crack on on-grade slab

6. Option 2: Stitching

Instead of gluing a crack together, repair can be done by stitching a crack

(Figure 9), in which the crack is stitched by steel dogs. BS EN 1504-9 identifies

the purposes of changing a crack into a joint as meeting Principle 4 structural

strengthening and lists this option as Method 4.2. Stitching can be consideredas one of the crack arrest techniques. The principles of stitching are that the

series of stitches are sufficient to make the total tensile strength of the repaired

concrete equal to or greater than the tensile strength of the original concrete.

Before stitching, it is first required to clean and seal the crack. Holes are then

drilled on both sides of the crack. The holes should not be in a single plane, and

the spacing should be reduced near the ends of the crack (because of the stress

concentration at the crack tip). However, limited use, if ever, of such repair

method has been carried out for repairs in ArchSD projects.

Figure 9 Stitching


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7. Option 3: Changing a Crack into a Joint

7.1 BS EN 1504-9 identifies the purposes of changing a crack into a joint as meeting

Principle 1protection against ingress and lists as Method 1.3 and Method 1.6.

This option is generally applicable to live cracks with expected significant

movement. As there are signs of continuing movement at a crack, it is usuallynecessary to make provision for it to continue after repair. The above options

are not feasible, because as the crack is locked solid, another crack will often

form nearby. The movement must be considered in terms of strain rather than

absolute magnitude, and the strain capacity of the sealant must be at least as

great as the strain that has to be accommodated. If the movement cannot be

arrested, then the following two methods are available:

1. route and seal the crack, thus treating it as a joint;

2. form a joint that will accommodate the movement; and

7.2 Routing and Sealing

Routing and sealing of cracks can be used for repair of cracks where structural

repair is not necessary. This method involves enlarging the crack along its

exposed face and filling and sealing it with a suitable joint sealant. Figure 10(a)

shows the procedures for repairing a crack by routing and sealing, and Figure

10(b) shows an example of routing and sealing of crack in an ArchSD venue.

Figure 10(a) Procedures of routing and sealing for non-structural crack(Source: modified from ACI 2007)

Figure 10(b) Routing and sealing of crack on on-grade slab


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7.3 Forming a new joint

This principle is usually employed in long parapet with insufficient steel

reinforcement to cater for the thermal movement, and in such case it is

necessary to insert movement joints back to such long wall at regular intervals.

Most of the sealant manufactures assign a movement accommodation factor(MAF) to each of their products to provide a value for the calculation of joint

dimensions. The MAF is the total movement range between the maximum

compression and the maximum extension that a sealant can accommodate. It is

expressed as a % of the minimum design joint width. The minimum joint width

Wmin is therefore calculated by:

Wmin = anticipated movement MAF100

In forming such movement joints, it is necessary to have joint sealant with

width-to-depth ration of 2:1. Figure 11(a) illustrates the importance of

maintaining the ratio 2:1 for the sealant. If W, the width of the joint, is set to be

equal to D, the bead is too deep and is not free to stretch properly when the twosides contract. If movement is excessive, the sealant will probably fail. On the

other hand, if D is set to be half of the width W of the sealant, the force exerted

will be considerably reduced (Figure 11(b)).

(a)W/D=1 (b)

W/D=2Figure 11 Dimensions of Joint Sealant

(Source: modified from Allen and Edward 1993)

Moreover, in forming a joint over a crack (indeed in both contraction and

expansion joints), a bond breaker is required to be inserted at the bottom of the

joint. The bond breaker may be a polyethylene strip or tape which will not bond

to the sealant. Figure 12 illustrates the function of a bond breaker in a

contraction joint.

(a) Crack closed (b) No bond breaker

(c) With bond breaker

Figure 12 Function of Bond Breaker

(Source: modified from Woodson 2009)


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References

ACI (2003), ACI RAP Bulletin 1: Field Guide to Concrete Repair Application Procedures -

Structural Crack Repair by Epoxy Injection (Detroit: American Concrete Institute).

ACI (2007),ACI 224.1 R07: Causes, Evaluation, and Repair of Cracks in Concrete Structures (Detroit: American Concrete Institute).

Allen, R T L and Edwards, S C (1993), Repairs to Cracked Concrete, in Allen, R T L,

Edwards, S C and Shaw, J D N (1993), The Repair of Concrete Structures (London: Blackie

Academic & Professional, 2nd

ed).

BSI (2004), BS EN 1504-5: Products and Systems for the Protection and Repair of Concrete

Structures. Definitions, Requirements, Quality Control and Evaluation of Conformity. Concrete

Injection (London: BSI).

BSI (2004a), BS EN 1992-1-1: Design of Concrete Structures. General Rules and Rules for

Buildings (London: BSI).

BSI (2008), BS EN 1504-9: Products and Systems for the Protection and Repair of Concrete

Structures. Definitions, Requirements, Quality Control and Evaluation of Conformity. GeneralPrinciples for Use of Products and Systems (London: BSI).

Buenfeld, N R, Davies, R D, Karimi, A and Gilbertson, A L (2008), CIRIA Publication No.

C661: Intelligent Monitoring of Concrete Structures (London: CIRIA).

Concrete Society (1992), Concrete Society Technical Report No. 22: Non-Structural Cracks inConcrete (Wexham, Slough: Concrete Society, 3

rded).

Concrete Society (2000), Concrete Society Technical Report No. 54: Diagnosis of Deterioration

in Concrete Structures: Identification of Defects, Evaluation and Development (Crowthorne:

Concrete Society).

Concrete Society (2009), Repair of Concrete Structures with reference to BS EN 1504

(Crowthorne: Concrete Society).

Neville, A (2002), Autogenous Healing a Concrete Miracle?, Concrete International,

November, pp. 76-82.

Schiessl, P (ed) (1988), Report of the Technical Committee 60: Corrosion of Steel in Concrete

(London: Chapman and Hall).

Woodson, R D (2009), Concrete Structures: Protection, Repair and Rehabilitation (Amsterdam;

Boston: Butterworth-Heinemann).

guidelines on crack repair in concrete structure

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