Repair Strategy
Process
Performance Requirements of Concrete Repair
Repair Systems Selection Criteria
Concrete Repair Methods
Buildings Department (1998) lists the following common repair techniques for concrete:
– Patch Repair
– Recasting/Partial Recasting
– Sprayed Concrete
– Micro-concrete
– Pre-packed concrete
– Non-shrinkage grout
– Sealing system
– Protective Coating
Traditional Repair Methods
– Patch Repair
– Recasting/Partial Recasting
– Sprayed Concrete
Preparation Before Work
– Preparation of concrete surface
– Cleaning of reinforcement
– Coating reinforcement
– Bond Coat
Preparation
Cleaning of reinforcement
1. Patch Repair
1. Patch Repair (Cont’d)
Types of Mortar
Types of cementitious mortars | Suitability | Reference |
Medium-weight cementitious mortar | For area where superior resistance is required to chlorides and carbon dioxide. For general purpose concrete reinstatement. | Renderoc GP; Renderoc HB40 (with higher performance) |
Fibre-reinforced, nonshrinkage mortar | For repair of spalling, honeycombing, stair nosing, ramp etc. | Lanko 731 |
Silica fume-modified | ||
Silica fume-modified repair mortar | For repair load-bearing concrete | Emaco S66 Emaco S88C; Emaco S88C with MCI |
Types of Mortar (Cont’d)
Polymer modified | ||
Polymer modified repair mortar suitable for different degree of exposure | For locations where required high compressive strength, and reinstatement of concrete. | Barra 80; Barrafill; Renderoc S; Ronafix Mix A; Ronafix Mix D |
Polymer modified repair mortars, feature shrinkage compensating properties | Restore concrete and inhibit further deterioration before significant structural damage occurs. | Emaco R740 |
Polymer modified repair mortar, feature lightweight | For high build, vertical and overhead repairs (rather low compressive strength will be developed) | Barra Mortar HL; Nitomortar HB; Renderoc HB; HB25 |
Polymer modified repair mortar for high build with different classes of strength | Suitable for concrete repair. It can be applied in thick section and is suitable for structural and non-structural application. | Unicell 25; Unicell 40, and unicell ultra rapid. |
Types of Mortar (Cont’d)
Rapid Setting | ||
Rapid setting underwater mortar | Specifically developed for underwater repair and restoration work. | Emaco S90UW |
Rapid setting waterstopping mortar | Rapid patching and plugging of concrete segments. | Renderoc Plug 1; Renderoc Plug 20 (20mins setting) |
Types of Mortar (Cont’d)
Types of resin-based mortars | Suitability | Reference |
Expoxy resin mortars | ||
Two-part epoxy resin mortars (possesses outstanding strength and adhesive powers) | Low slump for general repair work For use in exceptionally wet conditions and for underwater applications |
Expocrete GP Expocrete UA |
High strength, abrasionresistant epoxy reinstatement mortar | For fast and permanent reinstatement of concrete | Nitomortar S |
Polyester resin mortars | ||
Polyester resin mortars with high strength jointing and multipurpose repair compounds | For fast and emergency reinstatement of concrete, bedding, jointing and reprofiling of concrete (cannot be applied to damp or wet surface) | Nitomortar PE |
8 tests on Repair Mortar:
Bond Strength of Patch Repair – tested by pull-off test
Core
Dummy
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
Result 2
Results 3 & 4
2. Recasting
Recasting by form and pump
3. Sprayed Concrete
Dry Spray Concrete
Wet Spray Concrete
Cracks prevention
Spray Concrete
Types of sprayed concrete | Suitability | Reference |
Dry Spray | ||
Polymer modified cementitious repair mortar | 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. | Renderoc DS (aggregates used are classified as ‘non-reactive’.); Renderoc SC; Optimix RM770 |
Gunite mortar (cementitious based) | Specially prepared for use in dry shotcrete applications. (compressive strength: 30-40 N/mm2) | Sika Rock 30 |
Wet Spary | ||
General concrete repair work | Sika Mono Top-612; Optimix RM770 |
Other Repair Methods
– Micro-concrete
– Pre-packed concrete
– Non-Shrinkage Grout
– Joint Sealing System
1. Micro-concrete
Types of micro-concrete | Suitability | Reference |
Shrinkage compensated | For 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. | Renderoc LA |
High performance shrinkage compensated | Renderoc LA55 | |
Low alkali, non-reactive micro-concrete | Renderoc LA27 |
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.• 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.
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.
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.
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.
Types of joint sealing system | Suitability | Reference |
Versatile sealing system | For joints and cracks subject to normal or large movements | Sikadur Combiflex |
Joint sealing compound (Polyurethane base) | Permanent elastic one-compound joint sealing compound | Sikaflex PRO 2HP |
One component polyurethane sealant/adhesive | As an elastic adhesive and elastic joint sealant. | Sikaflex-11FC |
Instant-settinghydraulicmortar/grout | Sealing of waterways Fast setting, Used underwater High resistance to pressure. Some of the products are with different properties, such as, high strength, flexible and elastic for use in different situation. | ERTOBLOC 224; Ronabond PU 10; Ronabond PU 20 (High strength); Ronabond PU |
Protection Methods
• Protective Coating
• Apply Cathodic Protection
• Provide Additional Concrete Cover
• Realkalization or Desalination
• Overcladding and Insulation
• Protection with Corrosion Inhibitors
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)
• 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.
Types of protective coating | Suitability | Reference |
Single component epoxy zinc primer (corrosion protection) | As an anti-corrosion primer for exposed steel reinforcement for use with concrete repair mortars | Nitoprime Zincrich; Frianzinc EPE |
Acrylic resin protective coating for concrete | Protection and enhancement of concrete and asbestos cement building elements, especially facades. | Sikagard 680 S-Concrete Cosmetic |
Protective coating with moderate chemical resistance | As a barrier to resist chemical resistance, such as carbon ion. | Sikagard-62; Ronabond Cover Plus 150 |
Waterproof protective coating | Provides an effective barrier against the transmission of liquid water. It should be applied on concrete, brickwork and blockwork. | SikaTop Seal 107; Ronabond Joltec Finish; Ronabond Jotec Transparent; Ronabond Nigatex |
6. Cathodic Protection
The purpose of applying cathodic protection is to stop the setting up of anodes on the reinforcement by applying a low voltage electric current or by a sacrificial anode.
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.
Impressed Current System
In impressed current system, an external current with sufficient intensity is applied to over-ride the corrosion current.
Pros and Cons
Advantages:
– The only way to completely stop steel corrosion
– Permanent solution
Disadvantages:
– Ongoing cost to maintain
– Many structures not suitable (access, noncontinuous reinforcement, pre-stressing steel, etc.)
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.
Types of cathodic protection | Suitability | Reference |
Sacrificial Anode System | ||
Drilled in sacrificial anode for reinforced concrete structures | For pre-stressed/post tensioned structures (Not for use with epoxy and polyester repair mortars or primers. | Galvashield CC45, Galvashield CC65 |
Embedded zinc anode which acts to prevent corrosion of reinforcing steel in concrete: | To be embedded within repairs performed in chloride contaminated concrete to protect adjacent steel from the onset of corrosion. | Galvashield XP |
Impressed Current System | ||
Discrete cathodic protection anodes | For protection of steel corrosion in reinforced concrete structures and steel framed buildings |
Ebonex |
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
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
Corrosion Inhibitors
See Sika FerroGard-903 Corrosion Inhibitor or Tyfo CIS Inhibitor
Tyfo® CIS Inhibitor Layer 2
DESCRIPTION
Tyfo® 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.
USE
Tyfo® 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
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.
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
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.
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
Examples of Concrete Strengthening Materials
Types of concrete strengthening | Suitability | Reference |
Composite fabrics for structural and seismic strengthening | Shear strengthening in a building beam and slab Flexural strengthening of slab | SikaWrap |
Fibre reinforced polymer (FRP) system | For structural strengthening for post-reinforcement of structural members, such as beams, columns, slabs) | Ronacrete FRP system |
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.
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 repassivation.
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.
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.
– prevents ingress and migration of moisture and damaging corrosive
– Deplete soluble chlorides in concrete and inhibit corrosion of imbedded reinforcing steel
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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