CEMENTITIOUS PATCH REPAIR OF CONCRETE – SPECIFICATION AND
QUALITY CONTROL TESTING
Fred Andrews-Phaedonos, GeoPave, VicRoads
ABSTRACT
The repair of concrete structures has rapidly increased since the accelerated
construction boom of the 1960s, 70s and 80s which was also associated with the
premature deterioration of many concrete structures around the world. As such the
repair, rehabilitation and routine maintenance of deficient or deteriorated concrete
structures has since become an industry in its own right. Specifications and quality
control have not kept pace thereby leading to poor practices and consequently
premature failure of many concrete repairs. Prior to the commencement of any patch
repair of concrete, the affected concrete structure or component must be assessed to
determine the influence of spalled, deteriorated, damaged or honeycombed concrete
on load bearing capacity, serviceability and durability. A cementitious patch repair
method must be selected based on an assessment of the cause(s) and extent of the
spalled, deteriorated, damaged or defective concrete; the location of the patch repair
on the concrete structure or component; and the proposed repair material properties,
likely patch behaviour and the effect on load capacity and structural safety,
serviceability and durability. A patch repair method must be prepared which includes
requirements for surface preparation, method of application, curing and surface
finish.
This paper presents the main types of patch repair of concrete structures using
cementitious repair materials and discusses the various specification requirements
for the supply, quality and performance criteria of materials, surface preparation,
mixing and application, curing and protection, finishing and surface condition,
relevant inspection and quality control testing and acceptance criteria for the repair of
concrete structures using cementitious repair materials. The paper also covers
OH&S and environmental issues, outlines the main phases of a cementitious repair
and presents a step by step repair sequence for the main types of patch repair.
ACKNOWLEDGMENTS: The author wishes to thank the Chief Executive of
VicRoads for his permission to publish this paper. The views expressed in this
paper are those of the author and do not necessarily reflect the views of VicRoads.
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1.
INTRODUCTION
A well organised and thorough investigation is a vital part of a successful repair of
concrete structures. The first requirement for a lasting repair is to establish the
cause and extent of concrete deterioration. For a repair to be successfully completed
it must eliminate the cause, repair the full extent of the damage and ensure that the
structure is protected from further damage or recurrence of the original cause for the
whole of its projected lifespan. It is therefore important that a thorough initial
investigation should be carried out before any repair work is undertaken. It must be
emphasised that failure to carry out a detailed investigation/assessment can lead to
an incorrect diagnosis of the problem with subsequent unsuitable and ineffective
methods of repair (1, 2).
Inspection and testing of concrete structures which are thought to be deteriorating is
normally done in two stages. An initial inspection comprising global/visual survey
techniques is organised to establish whether there is a need for repair and identify
any immediate safety problems. A detailed survey and specialised testing of
representative parts of the structure is carried out to allow a repair scheme to be
designed and its cost to be estimated.
A visual inspection will only locate the more obvious symptoms and causes of
concrete deterioration. It can not reveal the extent of deterioration and corrosion
beneath apparently sound concrete. If repairs are limited to the visible areas only,
more work could be required later as the undetected defect progresses (corrosion,
chlorides etc). For this reason a number of specialised survey techniques and
equipment incorporating both physical/electrical and chemical diagnostic methods
(non-destructive, structural sampling etc) are available and can be used to reveal the
full extent of the problem in a concrete structure (1, 2).
A key issue that needs to be highlighted in any repair is the importance of
maintaining the structural integrity of structures. Work should be done safely and
excessive material should not be removed, particularly from load bearing members.
Consideration should be given to whether the concrete to be removed provides
essential support for the structure. A structural check or professional structural
advice should be considered and where necessary propping and temporary supports
should be provided (1, 2).
2.
METHODS OF REPAIR AND APPLICATION
2.1
General
For the purposes of repair of concrete structures, patch repairs can be grouped into
two general categories, namely the ones associated with corrosion deteriorated
concrete, and the ones associated with non-corrosion deteriorated concrete (i.e.
accidental damage which does not incorporate the corrosion process). The major
difference in the repair process is associated with the initial stages of the repair,
where some aspects of the total exposure and de-rusting of steel reinforcement may
not be relevant to non-corrosion deteriorated concrete (i.e. accidental damage) repair
(1, 3).
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In addition, the initial stage of removal of concrete and overall surface preparation is
generally relevant to all methods of application. For obvious reasons the remaining
repair stages are different which reflects the difference of the various methods of
application and the materials associated with these methods.
2.2
Factors Contributing to Selection of particular Method of Application
Methods of application of repair materials are mainly dictated by the prevailing inservice conditions, by relative costs, the specified performance characteristics of
suitable repair materials, as well as, the level of in-service performance required from
such materials (1, 3).
Furthermore, some specific factors which contribute to the selection of a particular
method of application can be summarised as follows:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
2.3
Horizontal, vertical or overhead repair conditions
Confined and tortuous repair areas (i.e. insufficient room etc)
Restricted access
Ease and practicality of erection of formwork
Structural limitations on amount of existing concrete that can be removed at one
time to
enable repairs to be undertaken
Area and volume of repairs to be undertaken
Underwater requirements
Prevailing traffic conditions
Immediate operational requirements
Tidal and splash zone repairs
Height and amount of scaffolding required
Vibration and compaction requirements, particularly of new concrete
Setting and curing times
Appearance requirements
Relative costs
Methods of Application
There are several different methods of application of repair materials in the repair of
concrete structures (1, 3).
(a)
Repairing of cracks (dead or live cracks)
VicRoads Standard Specification Section 687 “Repair of Concrete Cracks”, covers
different types of repairs depending on type and extent of crack and subject to proper
assessment.
(b)
Recasting with new concrete
Design of special concrete mix, shrinkage compensating admixtures, need formwork
and vibrators, restricted areas difficult to vibrate.
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(c)
Patching with cementitious repair mortars
Polymer modified designed for ease of application under a range of in-service
conditions (i.e. horizontal, vertical, overhead etc), suitable consistencies and
adhesion, trowelled or hand applied non-shrink as part of an overall repair system.
Major advantage is properties of cementitious mortars are compatible with parent
concrete in terms of modulus of elasticity, co-efficient of thermal expansion,
shrinkage movement and permeability (breathability).
(d)
Patching with free-flowing grouts and fluid micro-concretes
Useful for extensive and large repairs where access for hand/trowelled mortars is
difficult, fixing of tight formwork, pumped or hand poured into formwork, very
workable and self-compacting, feed from lowest or furthest point.
(e)
Sprayed of new concrete or specially formulated cementitious mortar
Shotcrete, gunite, dry process spraying, wet process spraying.
(f)
Pre-packing Dry Aggregates which are subsequently grouted
Single size coarse aggregate (10-20mm), grout subsequently pumped from the
furthest or lowest point to fill spaces between the aggregate, simple formwork, no
vibration, suitable for underwater conditions.
(g)
Underwater Placement Methods
Covered by Standard VicRoads Specification Section 610 “Structural Concrete”
3.
CEMENTITIOUS PATCH REPAIR OF CONCRETE
3.1
General
Prior to commencement of any patch repair of concrete, an assessment of the
affected concrete structure or component should be undertaken to determine the
influence of spalled, deteriorated, damaged or honeycombed concrete on load
bearing capacity, serviceability and durability (1, 3, 4, 5).
A cementitious patch repair method should be selected based on:
•
an assessment of the cause(s) and extent of the spalled, deteriorated, damaged
or defective concrete;
•
the location of the patch repair on the concrete structure or component;
•
the proposed repair material properties, likely patch behaviour and the effect on
load capacity and structural safety, serviceability and durability.
A step-by-step patch repair procedure should address the concrete surface
preparation, method of application, curing and surface finish and exposure
classification requirements. The application of a decorative/anti-carbonation and/or
anti-graffiti coating where required should also be considered as part of the overall
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patch repair procedure.
3.2
Types of Patch Repairs
The following main types of patch repair of concrete structures using cementitious
repair materials are considered (1, 3, 5):
(a)
Corrosion deteriorated concrete repair
This is associated with deterioration, delamination, cracking or spalling of concrete
due to contamination by deleterious substances such as chlorides and carbon
dioxide associated with the overall mechanism of corrosion of steel reinforcement.
The corrosion deteriorated concrete repair works must involve:
• the breaking back to sound and dense concrete by at least 20 mm behind the
steel reinforcement;
• preparing both the steel reinforcement and concrete substrate;
• the application of an appropriate steel primer and substrate bonding coat;
• rebuilding to the original surface profile.
(b)
Non-corrosion deteriorated concrete repair
This is associated with deterioration or damage due to accidental or physical
loadings, damage through temporary overloading, impact and other mechanical or
uncontaminated damage, excessive early shrinkage or thermal stresses and low
quality honeycombed or off form voided concrete.
The non-corrosion deteriorated or defective concrete repair works must involve the
breaking back to sound and dense concrete. The depth of removal of non-corrosion
deteriorated or defective concrete and the amount of exposure of the steel
reinforcement should be subject to review at the time of the concrete repair
assessment.
(c)
Filling of blowholes and surface imperfections
This is associated with small regular or irregular cavities, usually not exceeding
15mm in diameter or 5mm in depth, resulting from entrapment of air bubbles in the
surface of formed concrete during placement and consolidation.
Blowholes and surface imperfections should be filled with a scrape coat application of
a single component polymer modified cementitious fairing coat repair mortar. A
cementitious fairing coat repair mortar could also be used in a thin layer where a
uniform concrete surface is required prior to the application of a protective or
decorative coating.
4.
MATERIALS REQUIRED AND PERFORMANCE CRITERIA
The requirements for the supply and quality of materials, surface preparation,
application, relevant inspection and testing and acceptance criteria for the patch
repair of concrete structures using cementitious repair materials must always be
specified in a very clear and succinct way to avoid any misinterpretations which may
affect the long term performance of the product in place (1, 3, 5). The application of
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any anti-graffiti or decorative/anti-carbonation coatings as part of the concrete repair
work must also be specified as necessary.
The repair materials used for reinstatement should be single component polymer
modified cementitious non-shrink repair mortars, or be part of an approved complete
polymer modified cementitious repair system. All materials should be manufactured
by an acceptable material supplier and should be supported by relevant test
certificates, material data sheets and health and safety data sheets. Only whole bags
of material should be used for mixing.
In general repair materials should be capable of being hand applied in vertical and
overhead locations up to 30mm thick in one application with no slumping and be able
to achieve strength conforming to the requirements as presented in Table 1 (5).
Single component polymer modified cementitious mortars should also be able to
achieve a drying shrinkage in accordance with ASTM prism at 23 oC and Relative
Humidity of 50% of less than 600 micro strain at 28 days, have a minimum wet
density of 1700 kg/m3 and a maximum water/powder ratio of 0.16.
Table 1:- Strength of Repair Material and corresponding Concrete
Structure Strength
Concrete
Strength
Structure
Repair Material Strength
@ 1 day
@ 7 days
@ 28
days
MINIMUM COMPRESSIVE STRENGTH
(in accordance with BS 6319 Pt 2:1983 – dry cure)
15 MPa to 30 MPa
5 MPa
19 MPa
23 MPa
Greater than 30 MPa to 50
10 MPa
25 MPa
35 MPa
MPa
Greater than 50 MPa
15 MPa
40 MPa
60 MPa
MINIMUM FLEXURAL STRENGTH
(in accordance with BS 6319 Pt 3:1990)
15 MPa to 30 MPa
4 MPa
Greater than 30 MPa to 50
6 MPa
MPa
Greater than 50 MPa
10 MPa
MINIMUM TENSILE STRENGTH
(in accordance with BS 6319 Pt 7:1985)
15 MPa to 30 MPa
1.8 MPa
Greater than 30 MPa to 50
2.8 MPa
MPa
Greater than 50 MPa
3.8 MPa
MINIMUM BOND OR PULL-OFF STRENGTH TO CONCRETE
SUBSTRATE
@7 days
(in accordance with EN 1542 (CEN 1999c))
All
Concrete
Structure
0.75 MPa
Strengths
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Both the steel reinforcement primer and the substrate-bonding coat must be
compatible with the repair mortar and be part of the same range of proprietary repair
system.
Single component polymer modified fairing coat cementitious repair material used to
fill blowholes and imperfections on concrete structures should be capable of being
applied at 0 – 3 mm thick and fill blowholes and imperfections flush with the finished
concrete surface and be able to be applied over a large area without being subject to
shrinkage cracking.
5.
HANDLING AND STORAGE OF MATERIALS
Repair materials should be stored in dry conditions not exposed to direct sunlight, in
strict accordance with the material manufacturer’s data sheet requirements and
within the manufacturer’s specified maximum and minimum temperature range. It is
also important that materials remain in their original, sealed moisture resistant bags
or containers until time of use to ensure the quality performance required (1, 3, 5).
All material should be brought to site in the original sealed bags or unopened
containers and should be labelled with the appropriate manufacturer’s name, product
type, reference number and batch number. All repair materials should be used in the
order of date of manufacture (from earliest to latest) and any materials stored beyond
the manufacturer’s recommended shelf life should not be used.
6.
PREPARATION AND APPLICATION
6.1
General
All areas of damaged or delaminated concrete associated with corrosion should be
repaired and where necessary incorporate new reinforcing steel into the structure to
compensate for any existing reinforcing steel which is exhibiting loss in excess of
25% of its original cross-sectional area (1, 3, 5). Steel reinforcement incorporated
into the structure should comply with the requirements of relevant standards (i.e.
VicRoads Standard Specification Section 611 “Steel Reinforcement”).
6.2
Preparation
The long term performance of concrete patch repairs is largely dependent on a sound
concrete and proper preparation of the concrete surface in order to enhance the
intimate contact and adhesion strength at the interface. Inadequate surface
preparation can result in de-bonding and premature failure of the patch repair (1, 3,
5). For all types of patch repair all defective and delaminated concrete and existing
repair materials should be broken back to a sound and dense concrete surface.
Hammer sounding should be repeated on completion of breakout to ensure that all
delamination has been removed. A perpendicular saw cut of at least 15 mm should
be provided around the perimeter of the area to be repaired to prevent featheredges.
The saw cut surface should be roughened by removing the surface layer to expose
small particles of well-bound aggregate (Refer Fig.1). Defective concrete should be
removed using light hand held percussive equipment or high pressure water jetting.
Care should be taken to ensure that any steel reinforcement exposed is not cut or
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damaged. The method of breaking back or scabbling should ensure that excess dust
does not form a hazard in the surrounding area.
The overall cleaning process for the concrete substrate and any exposed steel
reinforcement should be completed by giving a final wash down or by blowing down
with oil free compressed air to ensure removal of all residual contamination. The
prepared concrete substrate should be thoroughly pre-wetted with clean fresh water
and should be surface dry prior to repair material application.
(a)
Corrosion Deteriorated Concrete Repair
In addition to the general preparation requirements, for corrosion deteriorated
concrete repair all defective and delaminated concrete and existing repair materials
should be broken back to a sound and dense concrete surface to at least 20 mm
behind and around the rusted steel reinforcement (Refer Fig.1)
Removal of concrete should also continue along the length of visibly corroding steel
reinforcement and extend until at least 50 mm of sound rust free metal is showing at
both ends of the rusted section. All corrosion products should be removed from the
exposed steel reinforcement and cleaned to a bright metal. Preparation of the steel
reinforcement should be effected by using power driven tools or wet abrasive
blasting.
(b)
Non-corrosion Deteriorated or Defective Concrete Repair
In addition to the general preparation requirements, the depth of removal of concrete
for non-corrosion deteriorated or defective concrete repair and the amount of
exposure of steel reinforcement should be subject to review during the assessment
of the deteriorated or defective concrete.
Figure 1 – Surface preparation, saw cut and exposure of steel reinforcement
6.3
Application of Reinforcement Protection and Substrate-Bonding Coat
The next step in the repair sequence is for the steel reinforcement to be coated with
a suitable primer which forms part of the proprietary repair system to provide
immediate protection against corrosion (Refer Fig.2). A substrate-bonding coat
which also forms part of the proprietary repair system should also be applied by
working into the concrete substrate using a short bristle brush to enhance the bond at
the repair interface (Refer Fig.3). The repair material should be applied while the
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bonding coat is still tacky (1, 3, 5).
It is essential that the steel primer and substrate bonding coat are thoroughly mixed
to achieve a uniform colour and consistency using a spiral paddle in a slow speed
heavy-duty electric drill. Materials should not be thinned and the whole container
contents should be mixed without split mixing between mixes to ensure the accuracy
of the various proportions and therefore the right consistency and final quality of the
mixed mortar.
6.4
Application of Repair Mortar
The material manufacturer’s specifications for use of the repair materials, and test
plans that meet the requirements of the relevant standards and specifications should
form part of any quality procedures prepared, prior to the commencement of any
repair work. All materials should be applied in accordance with the directions for use
issued by the manufacturer. The clean concrete substrate should be rebuilt to the
original surface profile using a cementitious repair material (Refer Fig.3) and where
the existing concrete cover to the steel reinforcement is less than the design
requirements, the new repair must be profiled as required to ensure that a minimum
polymer modified repair material cover to the steel reinforcement is achieved,
namely, for benign to moderate exposure classifications a minimum cover of 20 mm
and for severe exposure classifications a minimum cover of 50 mm (Refer Fig.2). As
mentioned previously the repair mortar must be mixed thoroughly in whole bags in a
suitably sized drum using a spiral paddle in a slow speed heavy-duty electric drill. It
is advisable that a joint measurement of the repair be undertaken to ensure the
accuracy of the repaired areas.
Figure 2 – Application of steel primer, re-profiling with additional cover
Figure 3 – Pre-wetting, substrate bonding coat, repair mortar, curing
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6.5
Filling of blowholes and surface imperfections
All concrete surfaces and mortar substrates must be sound, clean and free from dust,
oils, and grease and surface contaminants and all loose materials and surface
laitance must be removed. It is vital that the prepared concrete substrate be
thoroughly pre-wetted with clean fresh water and be surface dry prior to repair
material application.
7.
FINISHING AND SURFACE CONDITION
All surfaces should match the surrounding surface finish by use of plywood, steel
forms or steel trowel finish. In order to ensure the integrity and long term
performance of the patch repairs no cracks of width greater than 0.10 mm, measured
at the concrete surface, or craze cracking covering a significant area of the repair
should be visible, at the completion of the curing period or at any stage after
construction. Furthermore, no cracking should be allowed at the concrete repair
interface with the existing concrete. Any remedial works required should be
performed in an acceptable manner (5).
8.
CURING AND PROTECTION
The cementitious material should be applied and cured with a curing compound in
accordance with the material manufacturer's specification. However, for concrete
patch repairs greater than 500 mm x 500 mm in size the curing compound should
also be supplemented with heavy duty polyethylene sheeting fastened and sealed at
the edges (Refer Fig.3). It is further advisable that for chloride affected concrete
structures or components the requirement for both curing compound and heavy duty
polyethylene sheeting should apply to all concrete patch repairs. Curing compounds
should comply with the requirements of AS 3799 (1, 3, 5).
Curing compounds should be removed prior to the application of any protective or
decorative coatings, unless it can be demonstrated that the applied curing compound
is compatible with those coatings. The repair material should be cured and protected
from drying out and against the harmful effects of water movement and weather,
including rain and rapid temperature changes for a minimum of 7 days after placing.
9.
END PERFORMANCE TESTING
9.1
General
Testing for the performance of patch repairs should include ongoing testing for
compressive strength, adhesion (pull-off) testing, delamination survey to check for
drummy areas and testing for flatness and placement tolerances of the finished
product (5).
9.2
Compressive Strength of Cementitious Repair Material
The compressive strength of cementitious repair material should be tested by
procuring test cube samples at a prescribed frequency. In general three, 75 mm test
cubes should be taken from the first batch of material mixed, cured and tested in
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accordance with AS 1478.2, followed by three, 75mm cubes for every 100 kg of
material used thereafter. The cubes should be cured for 7 days under laboratorycontrolled conditions. Two cubes should be tested at 7 days and the third cube at 28
days to confirm compliance with the minimum compressive strength requirements as
shown in Table 1.
9.3
Bond Strength (Pull-Off) Testing
The bond strength of patch repairs can be undertaken on partially cored direct pull-off
tests of the fully cured in-situ repair material to verify the tensile bond between the insitu repair material and the existing concrete substrate, 7 days after the completion of
application (Refer Fig. 4). The pull-off testing can be undertaken in accordance with
the European Standard EN 1542 (CEN 1999c) although reference to concrete test
specimens in the standard should be replaced by the in-situ concrete substrate.
Testing should be carried out at a frequency of three tests per 10 m2 of repair area.
The mean bond strength at 7 days must not be less than 0.75 MPa, provided no
individual result is below 90% of 0.75 MPa.
The mode of failure of the pull-off test
must be in the concrete substrate. Mean bond strengths less than 0.75 MPa or
failure between the in-situ repair material and the concrete substrate should be
raised as a non-conformance and be the subject of further assessment.
9.4
Testing for Drummy Areas
A visual inspection of all concrete repair areas should be conducted immediately
prior to the application of any decorative / anticarbonation coating and checked for
delaminations and any defects recorded. The test for drummy areas can be
conducted using a small hammer along the whole surface area of the concrete patch
repairs and delaminated areas should be characterised by a “drummy” or hollow
sound. Delaminated patch repairs should be removed and repaired in an acceptable
manner.
9.5
Tolerances
Control of dimensional tolerances is an important part of the overall quality control
and aesthetic appearance of patch repairs. As such the tolerance on edges and
surfaces in plan and level should be ± 3 mm. The maximum allowance for
irregularities when measured with a 2.0 metre straightedge should be 3 mm. In
addition, evenness should not deviate by more than 1 mm when checked with a 300
mm straightedge.
Figure 4–Cores into repair/substrate, pull-off tests, and core samples on dollies
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10.
OCCUPATIONAL
MANAGEMENT
HEALTH
AND
SAFETY
AND
ENVIRONMENTAL
It is of paramount importance that health and safety have a top priority at all times
during all repair operations (1, 5). Rules and regulations for the health and safety of
personnel, as well as safety for traffic must always be adhered to. Special care is
needed when handling or applying the different types of proprietary materials. In
general, all mandatory and recommended industrial hygienic procedures should be
followed. Specific provisions for the material manufacturer’s occupational health and
safety directions should be included within the required Site Safety Plans. Specific
provisions regarding the collection, segregation, handling, control and disposal of
waste generated during concrete patch repair works, and clean up should also form
part of an Environmental Management Plan.
11.
STEP BY STEP REPAIR SEQUENCE OF CEMENTITIOUS APPLICATION
11.1
Corrosion Deteriorated Concrete
The following provides a systematic and organised step by step guide of a typical
repair for trowel applied mortars (1, 3, 5).
(a)
Investigation and Assessment
• Establish the cause and extent of the concrete deterioration problem using both
physical and chemical diagnostic methods.
• Determine areas and depths of concrete to be removed.
(b)
Surface Preparation Completion (Refer Fig.1)
• Remove unsound and contaminated concrete to expose a sound and
uncontaminated concrete substrate by at least 20 mm behind and around the
rusted steel reinforcement.
• Continue removal of concrete along the length of visibly corroding steel
reinforcement and make sure it extends until at least 50 mm of sound rust free
metal is showing at both ends of the rusted section.
• Provide a perpendicular saw cut or equivalent to a depth of at least 15 mm
around the perimeter of the area to be repaired in order to prevent featheredging.
• Remove all products of corrosion from exposed steel reinforcement preferably
clean to bright metal and add new steel reinforcement (or ligatures) if required.
Wet sandblasting is preferable. This will also assist with the removal of any other
contaminants present on the bars.
• Complete the cleaning process by giving a final wash down or by blowing down
with compressed air of both the concrete substrate and steel reinforcement to
ensure the removal of all residual contamination.
• Thoroughly pre-wet the prepared concrete substrate with clean fresh water.
(c)
•
•
•
Application of Reinforcement Protection and Substrate Bonding Coat (Refer
Fig.2 & 3)
Steel reinforcement coated with a suitable primer to provide immediate protection
against renewed corrosion.
Remove excess or standing water from earlier pre-wetting operation.
Apply a concrete substrate bonding coat by working into substrate using a short
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bristle brush, to enhance the bond at the repair interface.
(d)
Application of Repair Mortar (Refer Fig.2 & 3)
• Erection of formwork or profiles if required (Refer Fig.3).
• Apply repair material. Ensure that substrate bonding coat is in correct condition
to ensure good adhesion.
• Apply normal curing procedures. That is applying a curing compound complying
with the requirements of AS 3799 and in accordance with the material
manufacturer's specification. For concrete patch repairs greater than 500 mm x
500 mm in size the curing compound should also be supplemented with heavy
duty polyethylene sheeting fastened and sealed at the edges (Refer Fig.3).
(e)
Application of Protective Coating (if required)
• Final surface preparation.
• Apply final protective coating or system of coatings.
(f)
Supervision and Quality Control (Refer Fig.4).
• Proper construction practices, procedures and standards.
• Re-inspect at suitable intervals to confirm the success of the repair.
11.2 Non-Corrosion Deteriorated Concrete (i.e. Accidental Damage)
The following provides a systematic and organised step by step guide of a typical
repair for trowel applied mortars.
(a)
Investigation and Assessment
• Establish the cause and extent of the concrete damage or distress.
• Determine areas and depths of concrete to be removed.
(b)
Surface Preparation Completion (Refer Fig.1).
• Remove spalled and unsound concrete to expose a sound and dense concrete
substrate and where necessary the steel reinforcement.
• Provide a perpendicular saw cut or equivalent to a depth of at least 15 mm
around the perimeter of the area to be repaired in order to prevent featheredging.
• Complete the cleaning process by giving a final wash down or by blowing down
with compressed air of both the concrete substrate and steel reinforcement to
ensure the removal of all residual contamination.
• Thoroughly pre-wet the prepared concrete substrate with clean fresh water.
(c)
•
•
•
Application of Reinforcement Protection and Substrate Bonding Coat (Refer
Fig.2 & 3)
Steel reinforcement coated (if exposed) with a suitable primer to provide
immediate protection against corrosion.
Remove excess or standing water from earlier pre-wetting operation.
Apply a concrete substrate bonding coat by working into substrate using a short
bristle brush, to enhance the bond at the repair interface. Where a proprietary
pourable cementitious grout is used, instead of a mortar consistency some repair
systems may not require the application of a primer or concrete substrate bonding
coat.
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(d)
Application of Repair Mortar (Refer Fig.2 & 3).
• Erection of formwork or profiles if required (Refer Fig.3).
• Apply repair material. Ensure that substrate bonding coat is in correct condition
to ensure good adhesion.
• Apply normal curing procedures. That is applying a curing compound complying
with the requirements of AS 3799 and in accordance with the material
manufacturer's specification. For concrete patch repairs greater than 500 mm x
500 mm in size the curing compound should also be supplemented with heavy
duty polyethylene sheeting fastened and sealed at the edges (Refer Fig.3).
(e)
Application of Protective Coating (if required)
• Final surface preparation.
• Apply final protective coating or system of coatings.
(f)
Supervision and Quality Control (Refer Fig.4)
• Proper construction practices, procedures and standards.
• Re-inspect at suitable intervals to confirm the success of the repair.
12.
SUMMARY
A thorough investigation is an important ingredient in achieving a lasting repair of
concrete structures. Correct interpretation of visual observations and testing is
essential to enable a correct diagnosis and prognosis of the problem, and thus
enable appropriate corrective measures to be taken. The use of sound materials,
thorough preparation and proper application of materials, satisfactory finishing and
curing are vital components of the step-by-step repair sequence required to
achieving a satisfactory repair, with adequate strength, durability, appearance and
economy.
13.
REFERENCES
1.
Fred Andrews-Phaedonos (1990), “Manual for Assessment, Maintenance and
Rehabilitation of Concrete Bridges”, VicRoads.
Fred Andrews-Phaedonos (1990, 2004), “Investigation of Concrete
Structures”, VicRoads.
Fred Andrews-Phaedonos (1990, 2004), “Methods of Repair and Repair
Sequence”, VicRoads.
Fred Andrews-Phaedonos (1990, 2004), “Durability of Concrete Structures”,
VicRoads.
VicRoads Standard Specification Section 689 (2005), “Cementitious Patch
Repair of Concrete”.
2.
3.
4.
5.
Cementitious Patch Repair Of Concrete, Andrews-Phaedonos
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