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RECO2006 Construction IV

Concrete Repair

Edward CY YIUDepartment of Real Estate and Construction

January 2007

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Intended Learning Outcomes

• How to repair concrete?• What are the common

concrete repair methods?

• How to determine which repair methods to be used?

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Anatomy of Concrete Repairs

Emmons, 1993, p.99

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Repair Strategy• Material

selection• Method

selection• Support

Design• Safety

Precaution• Costs• Logistics

Emmons, 1993, p.98

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Process• Re-bars

– Undercutting– Cleaning– Repair– Protect

• Concrete– Surface

preparation– Bonding– Apply new

material

Emmons, 1993, p.98

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Performance Requirements of Concrete Repair

• Protection of Rebars• Aesthetics• Integrity and Compatibility (with substrate)• Carry loads• Waterproofing

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Repair Systems Selection Criteria

• Stability of element• Cost• Disturbance to users• Existing concrete condition• Exposure condition• Compatibility of repair material to

substrate

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Concrete Repair Methods

• Buildings Department (1998) lists the followingcommon repair techniques for concrete:– Patch Repair– Recasting/Partial Recasting– Sprayed Concrete– Micro-concrete– Pre-packed concrete– Non-shrinkage grout– Sealing system– Protective Coating

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Traditional Repair Methods

– Patch Repair• Cementitious mortars • Resin-based mortars

– Recasting/Partial Recasting– Sprayed Concrete

• Dry process spray• Wet process spray

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Preparation Before Work– Preparation of concrete surface– Cleaning of reinforcement– Coating reinforcement– Bond Coat

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Preparation• Marking out, Hack back to 10-20mm behind re-bars,

ensure concrete cover• Saw cut the edge, Brush/grind the re-bar • Prime coat for re-bar, bond coat for substrate• Batching of repair mortar and apply.• Dowel bars:• Holes drilled with rotary-percussive drills to provide

keys• Air blown by pneumatic device• Required length of insertion• Give it a 1/2 turn and then turn back to original position • Give 2 hrs initial set off time

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Cleaning of reinforcement

• For cleaning of reinforcement rust, high pressure water-abrasive blasting should be the best ways of ensuring a chloride-free surface for the reinforcement. Probably, it is the only way of removing chlorides from the pits in rusting reinforcement.

• If the damage is caused by carbonation, it is less critical to remove rust from the reinforcement. Coating with a layer of firmly adhering cement paste will be sufficient to prevent further deterioration. Other material for coating can be used if the repair is not in a cementitiousone.

http://www.sadgrovesquay.com.au/abrasive/sandblast1.jpg

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1. Patch Repair• It is most suitable for small-volume repairs as to

restore concrete’s durability. The damaged concrete should be removed and patched up with appropriate repair mortars.

• In general, there are two common repair mortars used for repairing works:

– Cementitious mortars– Resin-based mortars

• i. Cementitious mortars:• Cementitious mortars is one type of repair mortars for

patch repair on small-volume repairs. It is used to restore durability of the structure. The damaged concrete is removed and these areas will be patched up with appropriate repair mortars.

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1. Patch Repair

Emmons, 1993

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1. Patch Repair (Cont’d)• Mailvaganam and Taylor (1994) prefers resin based mortars. It is

because the resin based mortars have an elastic modulus of aboutone-tenth of concrete.

• The coefficient of thermal expansion is five times more than that of concrete.

• It has the strongest compressive strength than the other type of cementitious based mortars.

• Recently, polymer is added into the mortar in order to increase their strength.

• However, there are some limitations in polymer repair materials e.g. it may cause delamination or blistering when applied on the damped areas; and

• It is not recommended to be applied in areas where fire resistance is required. It has poor fire resisting property and it has thermalincompatibility with substrate concrete.

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Properties of typical concrete repair materials

• (Mays, G. and Wilkinson, W., 1987)

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Emaco S66Emaco S88C; Emaco

S88C with MCI

For repair load-bearing concreteSilica fume-modified repair mortar

Silica fume-modified

Lanko 731For repair of spalling, honeycombing, stair nosing, ramp etc.

Fibre-reinforced, non-shrinkage mortar

Renderoc GP; Renderoc HB40 (with higher performance)

For area where superior resistance is required to chlorides and carbon dioxide.

For general purpose concrete reinstatement.

Medium-weight cementitious mortar

ReferenceSuitabilityTypes of cementitiousmortars

Types of Mortar

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Types of Mortar (Cont’d)

Unicell 25; Unicell 40, and unicell ultra rapid.

Suitable for concrete repair. It can be applied in thick section and is suitable for structural and non-structural application.

Polymer modified repair mortar for high build with different classes of strength

Barra Mortar HL; Nitomortar HB; Renderoc HB; HB25

For high build, vertical and overhead repairs (rather low compressive strength will be developed)

Polymer modified repair mortar, feature lightweight

Emaco R740Restore concrete and inhibit further deterioration before significant structural damage occurs.

Polymer modified repair mortars, feature shrinkage compensating properties

Barra 80; Barrafill; Renderoc S; RonafixMix A; Ronafix Mix D

For locations where required high compressive strength, and reinstatement of concrete.

Polymer modified repair mortar suitable for different degree of exposure

Polymer modified

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Renderoc Plug 1; Renderoc Plug 20 (20mins setting)

Rapid patching and plugging of concrete segments.

Rapid setting waterstoppingmortar

Emaco S90UWSpecifically developed for underwater repair and restoration work.

Rapid setting underwater mortar

Rapid Setting

Types of Mortar (Cont’d)

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Nitomortar PEFor fast and emergency reinstatement of concrete, bedding, jointing and reprofiling of concrete

(cannot be applied to damp or wet surface)

Polyester resin mortars with high strength jointing and multi-purpose repair compounds

Polyester resin mortars

Nitomortar SFor fast and permanent reinstatement of concrete

High strength, abrasion-resistant epoxy reinstatement mortar

Expocrete UAFor use in exceptionally wet conditions and for underwater applications

Expocrete GPLow slump for general repair workTwo-part epoxy resin mortars (possesses outstanding strength and adhesive powers)

Expoxy resin mortars

ReferenceSuitabilityTypes of resin-based mortars

Types of Mortar (Cont’d)

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8 tests on Repair Mortar:

• compressive strength (28 days) 30-60 MPa• Tensile strength (7 days) 2 MPa• Mod of Elasticity (28 days) 15-25 kN/mm2• Bond Strength (7days) 2.0 MPa• Shrinkage Cracking (7 days) Coutinho ring test• Permeability• Workability• Chemical Analysis• Open-up inspection: 1 / 25sm patch repair• Pull-off test (bond coat adhesion strength): 1/ 50sm patch repair

– Pass if 1/2 fracture in substrate or pull-off stress > 1/4 of the 7-day bond str

– Core a 75mm dia. Full thick of the repair with 7days age.

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Bond Strength of Patch Repair –tested by pull-off test

• Pull-off test on the adhesion strength of the bond between the repair mortar and the substrate concrete, aided by any bond coat

• identify re-bar position– Repair area shall have a

minimum age of 7 days– Re-bar sensor to identify

the location of reinforcement bars

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Core

• A 75mm dia. Core containing the full thickness of the repair was produced

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Detail of the core

Repair Mortar

Substrate

Cored hole

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Dummy

• A suitable metal plate was glued to the cored hole and let it dry for one hour;

• this attachment was pulled with increasing tensile force using a calibrated device until failure occurs.

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Result 1• Criteria:

– fracture shall be at least half in the substrate concrete, unless

– the pull-off stress is not less than 1/4 (i.e. 0.5 MPa) of the minimum 7 days bond strength of the repair mortar (2.0 MPa).

• Result 1– Fracture at bond surface,

bond strength = 27psi (0.9 MPa) - PASS

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Result 2

• Half of the fracture at substrate, bond strength = 18psi (0.6 MPa) - PASS

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Results 3 & 4

• Result 3: less than half of the fracture at substrate, bond strength = 12psi (0.4MPa) - FAIL

• Result 4: fracture at surface material, bond strength = 9psi (0.3 MPa) - FAIL

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2. Recasting• In this method, the damaged part of the structural element will be

demolished, replace corroded reinforcement and recast it with same or even better grade concrete in order to restore its structural strength.

• Considerations for practical uses• Pay attention to the discontinuity which causes any instability to the

linked structural elements due to demolition. • Dowel bars and/or replacement steel bars should be placed on the

cleaned reinforcement bars.• For recasting of slabs, evacuation may be required for flats above or

below the element.• The joint between old and new concrete should be paid with special

attention. Poor joints will result easy seepage of water and causes of corrosion.

• Shear key is required for large areas of recasting.• Pre-soaking of substrate is necessary• Avoid air trapping by thorough compaction of repair mortar.

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Recasting by form and pump

• Application ranges• When defective

depth is ranges from 75mm to 100mm.

• Also for vertical members e.g. wall and column.

• When structural restoration is required.

Emmons, 1993, p.168

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Full Depth Recast

Emmons, 1993, p.168

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3. Sprayed Concrete• Sprayed concrete is a technique which is widely

used in high-volume concrete repair work. • The concrete mix will be sprayed with or without

admixture or polymers to the defected areas under high air pressure. This process can be done by means of nozzle gun.

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Dry Spray Concrete• There are two different methods of spraying:

– Dry process spraying– Wet process spraying

• Dry process spraying is the process which the mixture of damp sand and cement is passed through the delivery hose to the nozzle and the water is mixed at that time.

• This process is often used for repair work. • It is because of its fast application process and restoration of structural strength at an

early stage. • The performance characteristics of dry sprayed concrete are they have good density

and high strength. • It has very good bond to a suitable substrate. • These advantages make it more variable than conventional concrete and wet process

sprayed concrete. (SCA, 1999)

(SCA, 1999)

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Wet Spray Concrete• Wet process spraying means all the ingredients

including water are mixed together before transporting to the site for repairing works.

• It is not normally applied for building repairs since the size of equipment is much larger than that of dry process spraying.

(SCA, 1999)

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Cracks prevention

• Concrete surface must be reinforced with small-mesh small diameter reinforcement before carrying out sprayed concrete. This can prevent developments of cracks when the concrete shrinks.

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Spray Concrete• Considerations for practical uses• The process should be in a continuous process.• Concrete mixed should be complied with acceptable standard and quality.• The operation should be carried by experienced nozzleman.• Acceptance test should be carried out to test the skill of the nozzleman.• The process should be held at right angle to and at one meter from the

surface of the repair areas.• Min. spray concrete thickness should be considered before spraying

process. • Reference should be made to Code of Practice for Structural Use of

Concrete. • Good surface preparation should be done.• Sufficient safety precautions must be taken.

• Application ranges• Large areas of repairs with thickness > 50mm• In vacant flats and/or public areas, this can minimize the nuisance to

peoples.• Partial strength is to be restored.

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Sika Mono Top-612; Optimix RM770

General concrete repair work

Wet Spary

Sika Rock 30Specially prepared for use in dry shotcrete applications.

(compressive strength: 30-40 N/mm2)

Gunite mortar (cementitious based)

Renderoc DS (aggregates used are classified as ‘non-reactive’.); Renderoc SC; Optimix RM770

For large area repairs (rather low compressive strength developed)

Should not be used when the temperature is <5C and falling.

Should not be exposed to moving water.

Polymer modified cementitious repair mortar

Dry Spray

ReferenceSuitabilityTypes of sprayed concrete

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Other Repair Methods

– Micro-concrete– Pre-packed concrete– Non-Shrinkage Grout – Joint Sealing System

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1. Micro-concrete• By applying this method, the contaminated or damaged concrete are removed and

replaced by fluid micro-concrete. • It is used to re-form desired concrete profiles. • Usually, prescribed mixes are available in the market with shrinkage compensators to

control shrinkage in plastic and hardened states.

• Considerations for practical uses• It needs special design by the supplier and specialist advice is required.• Formwork with leakproof is required.• Pre-soaking of the formwork and substrate is required. • Aggregates used should not be greater than 10mm.• In order to improve workability, aggregates should be rounded in size.• Good curing of the repair is essential.

• Application ranges• For use in area with limited working space or congested reinforcement• For use in thin sections where the use of normal concrete is impractical

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Renderoc LA27Low alkali, non-reactive micro-concrete

Renderoc LA55High performance shrinkage compensated

Renderoc LAFor area where access to the repair zone is restricted or where reinforcement is congested which unable to carry out compaction and vibration.

Difficult access which make hand/trowel-applied mortars impractical.

Shrinkage compensated

ReferenceSuitabilityTypes of micro-concrete

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2. Pre-packed Concrete• Graded aggregates similar to the substrate concrete will

be placed firstly in the formwork. • After the placement of graded aggregates, cement grout

will be injected into the formwork from THE BOTTOM. • The resulting concrete will be in excellent quality in

proper implication.

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• Considerations for practical use• All loose and spalled concrete should be repaired prior to the application.• Target compressive strength of the pre-packed concrete should be compatible with

that of the substrate. • Trials on compressive strength before operation are recommended.• Careful design on aggregate size and grading is recommended.• Aggregate size shouldn’t be too fine in order to avoid blockage of grout patch.• Similar to micro-concrete, formwork with leakproof is required.• Pre-soaking of the substrate with water is necessary.• Aggregate should be clean and free from silt before application.

• Application ranges• For use at areas where concrete placing is difficult, e.g. at beam soffits.• For areas with congested reinforcement or depth of repair is greater than 75mm

where patch repair is not suitable.• For where the structural strength have to be restored.

• Advantages• Compare to sprayed concrete, it has greater density, greater uniformity, lesser

permeability, lower shrinkage, less dependence on personal skills of equipment operators, less dust, less clean-up work, and more economical.

• Limitations• All works in vertical surfaces require formwork. At least 3 to 4 inches of space is

required for replacement.

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3. Non-shrink grout• cementitious, epoxy resin or polyester

resin based• In repair works, non-shrink grout is used in

crack injection repair. • Also, it is used to repair porous concrete

and in those areas with very congested reinforcement.

• Usually, it has a very high workability, it can be applied either flowable or in fluid.

• If mixtures are according to specified instruction, the compressive strength of non-shrink grout can be higher than 50 N/mm2 although it has high workability.

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Non-shrink grout• Considerations for practical use• Please refer to micro-concrete

• Application ranges• used in crack injection repair,• To repair porous concrete,• Very congested reinforcement or in limited

working spaces,• Thickness of repair is thin.

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Conbextra GP; ConbextraConbextra HES; Conbextra HF; ConbextraUW; Calgrout No 1

For general purpose of crack injection. Different kinds of cementitiousgrout are available such as, rapid set, high strength, high performance or specifically for underwater application

Non-shrink cementitiousgrout

Cementitious based

Ronabond EP 22UWCapable of restoring structural integrity and can be used under water

Epoxy resin suitable for structural element (suitable for use underwater)

Ronabond EP 22S; High strength resin and capable of restoring structural integrity

Epoxy resin suitable for structural element

Nitofil THFor injection of cracks of about 0.5-9mm wide.

Permits injection of open-ended cracks

Thixotropic epoxy resin injection grout

Ronabond EP 21SLV; Ronabond EP 21 FLV (more flexible)

As resin binder in flooring screeds or for repair of cracks subject to movement.

Ultra low viscosity expoxyresin injection

Nitofil LV; Sikadur 752; HI-Crete 85; Conbextra EP; Expocrete S

For injection of cracks of about 0.25-9mm wide.

Permits maximum resin penetration

Low viscosity epoxy resin injection grout

Epoxy resin based

ReferenceSuitabilityTypes of non-shrink grout

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4. Joint Sealing System• This system is generally applied for repairing active

cracks. • The crack must be widened and sealed as joints if any

measurements or circumstances suggested that it is live crack.

• When those live cracks cannot successfully be glued together with resin injection, the joints must be widened at the surface and sealed as a joint.

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ERTOBLOC 224; Ronabond PU 10; Ronabond PU 20 (High strength); Ronabond PU

Sealing of waterwaysFast setting, Used underwaterHigh resistance to pressure. Some of

the products are with different properties, such as, high strength, flexible and elastic for use in different situation.

Instant-setting hydraulic mortar/grout

Sikaflex-11FCAs an elastic adhesive and elastic joint sealant.

One component polyurethane sealant/adhesive

Sikaflex PRO 2HPPermanent elastic one-compound joint sealing compound

Joint sealing compound (Polyurethane base)

Sikadur CombiflexFor joints and cracks subject to normal or large movements

Versatile sealing system

ReferenceSuitabilityTypes of joint sealing system

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Protection Methods

• Protective Coating• Apply Cathodic Protection• Provide Additional Concrete Cover• Realkalization or Desalination• Overcladding and Insulation• Protection with Corrosion Inhibitors

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5. Protective Coating• The protective coating is a thin outer layer which used to

protect the substrate concrete by acting as an impermeable barrier or slowing the rate of penetration of active components from the surrounding environment.

• Three main functions of protective coating are:– Change appearance;– Improve surface properties;– Barrier against the penetration of aggressive gases, liquids and

vapours.• Good protective coating should allow water vapour to

pass out through it in order to stop the building up of vapour pressure in the substrate concrete which causes blistering. (BSIS)

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• Considerations for practical use• Good surface preparation before application of the coating, such as

completed repairing of concrete and removal of surface contaminations and voids.

• Remove all loose part of existing painting and check the compatibility of the existing paints before application.

• If a solvent based protective coating is selected, it should be in an open space with good ventilation for coating to evaporate.

• Application ranges• It should be applied on repaired concrete substrate to prevent

further deterioration.• In those areas where frequent wetting of concrete surface is

unavoidable.• On surfaces where exposed to aggressive surroundings.

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SikaTop Seal 107; Ronabond JoltecFinish; RonabondJotec Transparent; Ronabond Nigatex

Provides an effective barrier against the transmission of liquid water. It should be applied on concrete, brickwork and blockwork.

Waterproof protective coating

Sikagard-62; RonabondCover Plus 150

As a barrier to resist chemical resistance, such as carbon ion.

Protective coating with moderate chemical resistance

Sikagard 680 S-Concrete Cosmetic

Protection and enhancement of concrete and asbestos cement building elements, especially facades.

Acrylic resin protective coating for concrete

Nitoprime Zincrich; Frianzinc EPE

As an anti-corrosion primer for exposed steel reinforcement for use with concrete repair mortars

Single component epoxy zinc primer (corrosion protection)

ReferenceSuitabilityTypes of protective coating

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6. Cathodic Protection

• The purpose of applying cathodicprotection is to stop the setting up of anodes on the reinforcement by applying a low voltage electric current or by a sacrificial anode.

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Sacrificial Anode System• There are two main systems of

cathodic protection:– Sacrificial Anode System– Impressed Current System

• In sacrificial anode system, the steel is connected to a metal which is less stable in electro-chemical series, e.g. zinc. Since zinc is more anodic than steel, the current will flow from zinc to steel and zinc will be corroded instead of steel.

Sacrificial anodes fixed to the rebar with tie wires. (Fosroc: Galvashield XP)

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Impressed Current System

• In impressed current system, an external current with sufficient intensity is applied to over-ride the corrosion current.

Discrete impressed current cathodicprotection (ICCP) anode. (Fosroc: Ebonex)

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Pros and Cons

• Advantages:– The only way to completely stop steel

corrosion– Permanent solution

• Disadvantages:– Ongoing cost to maintain– Many structures not suitable (access, non-

continuous reinforcement, pre-stressing steel, etc.)

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Cathodic Protection• Considerations for practical use• Installation and maintenance costs for the systems are much higher

than other repair methods.• It needs special design by the supplier and specialist advice is

required.• Defects must be repaired before implication of cathodic protection.• Electrical continuity has to be assessed before implication.

• Application ranges• In area where corrosion is active or chloride content is high.• Recasting or large scale patch repair is not feasible.• Corrosion of steel reinforcement is not that serious while application.

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EbonexFor protection of steel corrosion in reinforced concrete structures and steel framed buildings

Discrete cathodic protection anodes

Impressed Current System

Galvashield XPTo be embedded within repairs performed in chloride contaminated concrete to protect adjacent steel from the onset of corrosion.

Embedded zinc anode which acts to prevent corrosion of reinforcing steel in concrete:

Galvashield CC45, Galvashield CC65

For pre-stressed/post tensioned structures (Not for use with epoxy and polyester repair mortars or primers.

Drilled in sacrificial anode for reinforced concrete structures

Sacrificial Anode System

ReferenceSuitabilityTypes of cathodicprotection

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Realkalization

• Advantages:– Based on reversing the principles of cathodic

protection– Limited concrete removal– No ongoing maintenance

• Disadvantages:– Very high installation cost– Not all structures are suitable– Environmentally unsound

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Overcladding

• Advantages:– Greatly improves appearance– Provides the additional benefit of insulation– Provides a long-term solution

• Disadvantages:– Very expensive– Can hide latent defects– Extended contract period

• The Jardine House case

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Corrosion Inhibitors

• See Sika FerroGard-903 Corrosion Inhibitor or Tyfo CIS Inhibitor

Tyfo® CIS Inhibitor Layer 2 DESCRIPTIONTyfo® CIS Layer 2 is a single-component, clear, waterbased liquid with a mild odor. It may be applied by roller or spray following the application of Tyfo® CIS Layer 1. Layer 2 controls the pH, purges and encapsulates water-soluble chlorides, fills voids in the concrete, and inhibits further penetration of moisture. Layer 2 also acts as a contact corrosion inhibitor on the reinforcing steel. After receiving both Layers 1 & 2, the exposed surfaces are cleaned by washing with fresh water or by abrasive blasting. All exposed steel is then treated with the Tyfo® CB material and the concrete section is restored using Tyfo® P or Tyfo® PF as required.

USETyfo® CIS Layer 2 is used with the Tyfo® Concrete Repair System on new or old concrete surfaces to seal porosity, increase compression strength, maintain pH, protect from acid and alkali attack, pacify and extract chlorides, and inhibit embedded steel corrosion.

ADVANTAGES• Ease of application• Can be applied to horizontal, vertical or overhead surfaces• Restores properties of deteriorating Portland concrete cement• Can penetrate concrete 2 to 3 inches, depending upon existing porosity• Dramatically improves condition of substrate prior to repairs• Protects new concrete• For new and old structures• Non-toxic

14%C-418New concrete

Hardness Increase

Increases 2,000 psi(13.8 MPa)C-42Compression

Strength

50% reduced voltage in 14 days (400 to 200mV)

C-876Corrosion Inhibition

Typical Test Value* ASTM Method Property

MATERIAL PROPERTIES

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European Standards for Repair and Protection of Concrete

• The standards related to the repair and protection of concrete of concrete currently available as standards or under development by CEN TC104 SC8-Protection an Repair an Repair of Concrete. It was updated on 6 November 2001.

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State-of-the-art Repair and Protection Methods

• Concrete– Patch repair with phosphate-based– Cathodic protection– Chloride extraction– Concrete re-alkalization– Concrete strengthening plates/sheets– Surface-applied penetrating sealer and coating

• Re-bar– Fusion-boned epoxy bar coatings– Inhibitive primer

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1) Patch Repair: Magnesium phosphate-based

• It is a unique, two-component with rapid setting concrete repair and grouting system. It cures faster than concrete and it has a very good bonding with new and old concrete. The repair system can be applied at any temperature without shrinkage and is freeze/thaw and deicing salt resistant since it does not require water as an additive.

•• loctite.com.hk.

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2) Concrete strengthening• An advanced technology of concrete

strengthening techniques which do not need to recast the concrete structure for strengthening.

• This technique apply the use of placing an bonding CIFIRP (Fibre Reinforced Polymer) plates or sheets to surfaces of structural concrete members.

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Examples of Concrete Strengthening Materials

Ronacrete FRP systemFor structural strengthening for post-reinforcement of structural members, such as beams, columns, slabs)

Fibre reinforced polymer (FRP)

system

SikaWrapShear strengthening in a building beam and slab

Flexural strengthening of slab

Composite fabrics for structural and

seismic strengthening

ReferenceSuitabilityTypes of concrete strengthening

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3) Chloride Extraction• If there is a presence of chloride ion, the concrete will

deteriorate at a faster rate. It is mainly due to the depassivating effect of chloride ions. Usually, a value of 0.8% (a critical acceptance value) is adopted for practical use.

• In this method, chloride ions are removed from concrete by dissolving in electrolyte and drawing it to an external electrode by an electrical potential. The external electrode being used in this method is a titanium wire mesh which is embedded in electrolytic paste of cellulose fibre. The paste is adhered onto the surface of concrete.

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4) Concrete Re-alkalization• Alkaline is a substance which can protect

reinforcement from corrosion. When concrete is carbonated, its alkalinity decreases and hence the protection of reinforcement is decreased. This method is used by diffusing alkaline chemicals like metallic hydroxides into concrete for increasing pH value and cause re-passivation.

• Recently, this technique is still under testing and not yet been developed for field test. Therefore, it is difficult to find this service in the market.

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5) Surface-applied Penetration Seal

• Aquron® CPT-2000 is a highly reactive catalytic agent which reacts with free alkali and/or alkaline hydrates by internally producing a silica hydro-gel which fills the pore spaces and the voids around aggregate. Furthermore, alkali is converted to a neutral compound structure, reducing the potential for internal chemical reactions. More density is added, additional bonding strength is provided and concrete is permanently hydrostatically sealed from within.

http://www.aquron.com/2000_tech_sheet.htm

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– prevents ingress and migration of moisture and damaging corrosive

– Deplete soluble chlorides in concrete and inhibit corrosion of imbedded reinforcing steel

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6) Corrosion Inhibitor

• With the addition of calcium nitrite, the standard threshold of corrosion is elevated

• i.e. the protective passivity layer can tolerate a higher level of chloride ions.

• http://www.na.graceconstruction.com/concrete/

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Reading

• Rostam, Steen. (1996) High performance concrete cover – why it is needed, and how to achieve it in practice, Construction and Building Materials, 10(5), 407-421.

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References• Buildings Department, (1998), Interim Technical Guidelines on The Inspection,

Assessment and Repair of Buildings for The Building Safety Inspection Scheme, The Government of the Hong Kong SAR.

• Mays, G. and Wilkinson, W., Polymer Repairs to Concrete: Their Influence on Structural Performance, ACI-SP 100-22 Katherine and Bryant Mather International Conference 1987, pp.351-338.

• Mailvaganam, N.P. and Taylor, D.A., Compatibility of Repair Systems for Concrete Structures, CANMET/IRC Symposium on Advanced Materials, Ottawa, 1994, 11 p.

• Pullar-Strecker, P., (1988). Corrosion Damaged Concrete: Assessment and Repair. London: Butterworths, 1988.

• Buildings Department, (1998), Interim Technical Guidelines on The Inspection,• Assessment and Repair of Buildings for The Building Safety Inspection Scheme,• Highway Department, HKSAR Govt (2002) Guidance Note on the Repair of Spalled

Concrete Road Joints, GN028. The Government of the Hong Kong SAR.• Currie, R. J. (1994). Repair and Maintenance of Reinforced Concrete. Building

Research Establishment Report. Watford: BRE publication.• Schmick, Bonnie L. Pollington, Annette. (2002) Concrete repair manual

American Concrete Institute. Imprint Farmington Hills, Mich. : ACI International, [2002?] 2nd ed.[HKU 624.18340288 C7 S]

• The Australian Corrosion Association and The Asian Pacific Materials and Corrosion Association, (2001). Fosroc galvashield: New ways to repair and protect reinforced concrete, Corrosion & Materials, vol 26 (4), 6-7.

• The Sprayed Concrete Association, (1999), Introduction to Sprayed Concrete, The Sprayed Concrete Association.

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The End

For enquiries, please send email to Edward CY YIU

Department of Real Estate and ConstructionThe University of Hong Kong

ecyyiu@hkucc.hku.hk