Whether you own or manage a residential or commercial property, routine buildings inspections should be something you factor into your maintenance plans. Whether it is to ensure compliance with building or fire codes, or as part of a good maintenance schedule, property inspections help to keep you abreast of the health of your building. Done properly, they ensure your property is compliant; detect potential structural problems before they become larger (and significantly costlier); as well protecting the value of your asset into the long-term.
Structural problems and thus structural repairs are different to renovations or non-structural repairs. The need for structural repairs can vary, but the range of services usually required included a range of issues from concrete cancer, to balustrade replacement upgrades, through to carbon fibre strengthening, brick growth and waterproofing.
In the situation that you do need to hire a structural repair specialist, it is important that you find the right one, but knowing what to look for – for something you have little experience with – in a contractor can be somewhat overwhelming. To help make life that little bit easier, we have put together a cheat-sheet on hiring a structural repair specialist.
Ultimately finding the right structural repair expert to look after your building is important in ensuring the safety of everyone in and around the building as well as protecting your significant investment. If you want to make sure you’re getting reliable, long-term solutions for your building structures in Singapore, ask us how we can help you.
We have over 10 years of experience in providing specialised structural repairs work for a variety of clients in Singapore. With our considerable experience, we have also established a strong connection with structural and facade engineers who we can tap into for highly specialised situations when necessary.
Our structural repairs including:
- Coating Application
- Concrete Repair, Removal & Replacement
- Structural Waterproofing
- Structural Inspection & Strengthening
- Interior & Exterior Drain Installation
- Cracked Foundation Repair using Epoxy Crack Injection
- Pressure Epoxy Grouting
- Cement Grouting
- Joint Repair
- Building Reinstatement
We follow strict safety standards in accordance with our Occupational Health and Safety and Environmental Management Procedures. We use a range of Elevated Work platforms and access equipment. Our Personnel are fully licensed for all the tasks we undertake. All our employees are site safety induced and have induction cards.
Plaster non-structural cracks
Cementitious plasters are applied internally such as living rooms, bathrooms, kitchens, etc… And externally where they might be exposed to different environment conditions: sun light, wind…
We offer a wide range of cementitious plaster that can be applied internally and externally and are suitable for different environment conditions depending on the available substrate.
Reasons of plaster cracking or De-bonding
Many factors might affect the performance of an applied plaster.
Cracks in the plaster may result due to different reasons:
- Evaporation if the wall is not protected from sun and wind which can cause map cracking or dry shrinkage cracks.
- Suction into the walls if the blocks are absorbent and they have not been dampened which might cause drying shrinkage cracks.
- Bad or badly applied rush coat
- Bad plaster workmanship: high thicknesses, no curing…
- Insufficient curing of rush coat or plaster which can cause de-bonding.
- Bad preparation: leftover of dust, or loose particles on substrate
- Excessive water in the plaster
- Immature finishing
Non-Structural cracks may occur in the following directions:
- Crazing cracks: crazing is a network of fine cracks, usually in a hexagonal pattern. They are usually due to over-trowelling a rich mix render.
- Map crazing: is similar to crazing except that it is usually deeper (sometimes going through the plaster) and the hexagons of the pattern may measure up to 200 mm across.
- Drying shrinkage cracks: are the result of moisture loss after the plaster has hardened.
- When water is not enough in the mix, then plaster cracks will also occur.
Non-structural cracks repair: crack without de-bonding
In case of non-structural cracks, the method of repair depends on the assessment of the defect and the cause of its occurrence:
Plaster cracks without de-bonding:
- Hair cracks without de-bonding are usually best left alone.
- Large cracks without de-bonding are repaired with NSG after the opening of the cracks and thoroughly cleaning and washing them.
Plaster Non-structural cracks repair: Masonry block
Plaster de-bonding on normal block or light weight blocks:
De-bonded plaster is repaired after removal of the entire de-bonded surface and make the necessary substrate preparation for the new plaster as per below steps:
- All bases should be sufficiently rigid, clean of any surface contamination that may prevent good suction.
- Dampen the substrate before few hours from the plaster application
- Fill the empty gaps in the joints of the block wall with block mortar
Depending on the type of substrate, plaster should be recommended:
Spray the plaster on the dampened and prepared surface or apply it manually with a plastering trowel at a thickness between 10 and 20mm in one layer. For higher thicknesses kindly consult the technical department.
Follow the application method statement instructions
Finish the surface with a wooden or steel float as required
Let the product set properly on the surface before any curing
Cure for 3 days. 3 to 4 times a day
Protect the applied plaster from direct sun light and wind
Non-structural cracks repair: Concrete substrate
Plaster de-bonding on concrete with or without cracks:
De-bonded plaster on concrete substrate is repaired after removal of the entire de-bonded surface and creating a grip key with well-adhered plaster.
While removing the plaster, examine the rush coat for better repair:
if the rush coat is rough and strong, apply plaster to the rush coated surface
If the rush coat is rough and weak, remove it and apply a new rush coat
If the rush coat is smooth and strong, apply another layer of rush coat
If the rush coat is smooth and soft, remove and apply a new one according to the technical data sheet
1. Rush coat application:
According to the type of concrete, the suitable rush coat is recommended
Weak and failed rush coat should be removed properly. A new application with the convenient rush coat shall be executed on the prepared surface.
Substrate must be sound and clean. If cracks and defects are available, the substrate must be repaired before applying rush coat.
In case of significant concrete defects, it is recommended to clean the defected area and fix wire/mesh after repairing.
If joints between concrete substrate and blocks are available, it is recommended to install a wire/ fiber mesh, in addition around openings and where needed.
Substrate must be wet before application. Free water on the substrate should be allowed to dry before any application. (For dense concrete, the substrate should left without curing for a minimum 24 hours before rush coat application)
Recommended rush coat (the proper rush coat must be chosen according to substrate) is re-applied on smooth surfaces and cured for 3 days, and 3 times a day.
Make sure that the applied rush coat has a rough finish to secure the bonding of the plaster.
Allow to harden depending on site conditions.
For more details, consult the technical department
2. Plaster application:
The convenient plaster should be used according to the type of substrate and the compatibility with the applied rush coat
In case of dense concrete, it is recommended that the rush coat to be left without curing before 24 hours from the plaster application.
Mix the plaster with a clean and cool water
Apply and press firmly the plaster over the rush coat. Each plaster coat should be applied between 10 to 20 mm. If more thicknesses are required, kindly consult the technical department.
Apply the plaster according to the application method statement and cure for 3 days and 3 to 4 times a day.
Protect the plaster from direct sun light and wind.
Structural Crack Repair by Epoxy Injection
Certain things in life are inevitable. Some are said to include death, taxes, and concrete cracks! The latter is subject to volumes of literature on causes and cures. Some of the more typical causes for concrete cracking include:
- Drying shrinkage;
- Thermal contraction or expansion;
- Lack of appropriate control joints;
- Overload conditions that produce flexural, tensile, or shear cracks in concrete; and
- Restraint of movement
One of the potentially effective repair procedures is to inject epoxy under pressure into the cracks. The injection procedure will vary, subject to the application and location of the crack(s), with horizontal, vertical, and overhead cracks requiring somewhat different approaches. The approach used must also consider accessibility to the cracked surface and the size of the crack.
Cracks can be injected from one or both sides of a concrete member. If access is limited to only one side, installation procedures may include variations in epoxy viscosities, injection equipment, injection pressure, and port spacing to ensure full penetration of epoxy into the crack.
Depending on the specific requirements of the job, crack repair by epoxy injection can restore structural integrity and reduce moisture penetration through concrete cracks 0.002 in. (0.05 mm) in width and greater. However, before any concrete repair is carried out, the cause of the damage must be assessed and corrected and the objective of the repair understood. If the crack is subject to subsequent movement, an epoxy repair may not be applicable.
Note: Horizontal cracks of sufficient width can be filled by gravity-fed epoxies where suitable for the repair (See Crack Repair by Gravity Feed with Resin, RAP-2).
What is the purpose of this repair?
The primary objective for this type of repair is to restore the structural integrity and the resistance to moisture penetration of the concrete element.
When do I use this method?
Injection is typically used on horizontal, vertical, and overhead cracks where conventional repair methods cannot penetrate and deliver the specific repair product into the crack.
Prior to proceeding with a crack repair by epoxy injection, the cause of the crack and the need for a structural repair must be determined. If the crack does not compromise the structural integrity of the structure, injection with polyurethane grouts or other nonstructural materials may be a more suitable choice to fill the crack. When a structural repair is required, conditions that cause the crack must be corrected prior to proceeding with the epoxy injection. If the crack is damp and cannot be dried out, an epoxy tolerant to moisture should be considered. Cracks caused by corroding reinforcing steel should not be repaired by epoxy injection because continuing corrosion will cause new cracks to appear.
Fig. 1—Cracks must be clean and free of debris.
How do I prepare the surface? (see Fig. 1)
Clean the surface area about 1/2 in. (13 mm) wide on each side of the crack. This is done to ensure that materials used to seal the top of the crack (the cap seal) will bond properly to the concrete. Wire brushing is recommended because mechanical grinders may fill the cracks with unwanted dust. Contaminants can also be removed by high-pressure water, “oil-free” compressed air, or power vacuums. When using water to clean out the crack, blow out the crack with oil-free, compressed or heated air to accelerate drying. Otherwise, allow enough time for natural drying to occur before injecting moisture-sensitive epoxies.
Where concrete surfaces adjacent to the crack are deteriorated, “V”-groove the crack until sound concrete is reached. “V” grooves can also be used when high injection pressures require a stronger cap seal.
How do I select the right material?
The appropriate viscosity of the epoxy will depend on the crack size, thickness of the concrete section, and injection access. For crack widths 0.010 in. (0.3 mm) or smaller, use a low-viscosity epoxy (500 cps or less). For wider cracks, or where injection access is limited to one side, a medium to gel viscosity material may be more suitable.
ASTM C 881, “Standard Specification for Epoxy Resin Base Bonding Systems for Concrete,” identifies the basic criteria for selecting the grade and class of epoxies (see Table 1).
For concrete sections greater than 12 in. (305 mm), the working time may need to be increased, and the viscosity decreased, as the crack gets smaller.
In addition to the criteria used in Table 1 for epoxy selection, the following product characteristics may also have to be considered:
- Modulus of elasticity (rigidity);
- Working life;
- Moisture tolerance;
- Color; and
- Compressive, flexural, and tensile strengths.
Fig. 2—Installation of entry ports.
What equipment do I need?
Equipment for epoxy injection by high-pressure or low pressure systems includes:
- Air guns;
- Hand-actuated delivery systems;
- Spring-actuated capsules; and
- Balloon-actuated capsules.
Determine the delivery method that will best suit the repair requirements by considering the size and complexity of the injection repair and the economic limitations of the project.
What are the safety considerations?
Epoxy resins are hazardous materials and must be treated as such. Job-site safety practices should include, but not necessarily be limited to, the following:
- Having Material Safety Data Sheets (MSDS) available on site;
- Wearing protective clothing and protective eyewear where required;
- Wearing rubber gloves or barrier creams for hand protection;
- Having eye wash facilities available;
- Wearing respirators where needed;
- Providing ventilation of closed spaces;
- Secured storage of hazardous materials;
- Having necessary cleaning materials on hand; and
- Notifying occupants of pending repair procedures.
It is the responsibility of the user of this document to establish health and safety practices appropriate to the specific circumstances involved with its use. ACI does not make any representations with regard to health and safety issues and the use of this document. The user must determine the applicability of all regulatory limitations before applying the document and must comply with all applicable laws and regulations, including but not limited to, United States Occupational Safety and Health Administration (OSHA) health and safety standards.
Prior to proceeding with the repair, a pre-construction meeting is recommended. The meeting should include representatives from all participating parties (owner, engineer, contractor, materials manufacturer, etc.) and specifically address the parameters, means, methods, final appearance, and materials necessary to achieve the repair objectives.
1. Port installation (see Fig. 2).
Install the entry ports only after proper surface preparation. Two types of entry ports are available for the injection process:
- Surface-mounted; or
Entry ports (also called port adapters) can be any tubelike device that provides for the successful transfer of the epoxy resin under pressure into the crack. Proprietary injection guns with special gasketed nozzles are also available for use without port adaptors. Port spacing is typically 8 in. (40 mm) on center, with increased spacing at wider cracks. Port spacing may also be a function of the thickness of the concrete element. Surface-mounted entry ports are normally adequate for most cracks, but socket-mounted ports are used when cracks are blocked, such as when calcified concrete is encountered. Entry ports can also be connected by a manifold system when simultaneous injection of multiple port locations is advantageous.
Fig. 3—Installation of seal cap.
Fig. 4—Start injection at widest segment of the crack.
Fig. 5—Continue injection until refusal.
2. Install the cap seal (see Fig. 3).
Properly installed, the cap seal contains the epoxy as it is injected under pressure into the crack. When cracks penetrate completely through a section, cap seals perform best when installed on both sides of the cracked element, ensuring containment of the epoxy. Cap seals have been successfully installed using epoxies, polyesters, paraffin wax, and silicone caulk. The selection of the cap seal material should consider the following criteria, subject to the type of crack to be repaired:
- Non-sag consistency (for vertical or overhead);
- Working life; and
- Rigidity (modulus of elasticity).
Concrete temperature changes after installation of the cap seal but prior to injection may cause the cap seal to crack. If this occurs, the cap seal must be repaired prior to resin injection.
Prior to proceeding with installation of the cap seal, mark the location of the widest portion of the crack and pay close attention to the following:
- Use only materials that haven’t exceeded their shelf life;
- Accurate batching of components;
- Small batches to keep material fresh, and dissipate heat;
- Port spacing; and
- Consistent application of the material (1 in. wide x 3/16 in. thick [25 x 5 mm]) over the length of the crack. 3. Inject the epoxy (see Fig. 4 and 5).
For a successful epoxy injection, start with the proper batching and mixing of the epoxy components in strict accordance with the manufacturer’s requirements. Prior to starting the actual injection, be sure that the cap seal and port adapter adhesive have properly cured so they can sustain the injection pressures.
Start the injection at the widest section of a horizontal crack. (Be sure to locate and mark these areas before installing the cap seal.) Vertical cracks are typically injected from the bottom up.
Continue the injection until refusal. If an adjacent port starts bleeding, cap the port being injected and continue injection at the furthest bleeding port. Hairline cracks are sometimes not well suited to “pumping to refusal.” In those cases, try injecting the epoxy at increased pressure (approximately 200 psi [1.3 MPa]) for 5 min. Closer port spacing can also be considered. When injection into a port is complete, cap it immediately. Higher pressure can be used for injecting very narrow cracks or increasing the rate of injection. However, the use of higher pressure should be managed with care to prevent a blowout of the cap seal or ports.
4. Remove ports and cap seal (see Fig. 6).
Upon completion of the injection process, remove the ports and cap seal by heat, chipping, or grinding. If the appearance is not objectionable to the client, the cap seal can be left in place. If complete removal is required for a subsequent application of a cosmetic coating, prepare the concrete surface by grinding.
Fig. 6—Remove seal cap.
be left in place. If complete removal is required for a subsequent application of a cosmetic coating, prepare the concrete surface by grinding.
How do I check the repair?
To ensure that the injection has been successful, quality assurance measures may include test cores or nondestructive evaluation (NDE).
1. Test cores:
- Core locations should be chosen to avoid cutting reinforcing steel, drilling cores in areas of high stress, or creating core holes below the waterline. The engineer should determine core locations when these types of conditions exist;
- Be sure the epoxy has set before extracting a core;
- Take cores (normally 2 in. [50 mm] diameter) to check that the penetration of the epoxy is adequate;
- Inspect the core visually to determine the penetration of the epoxy into the crack;
- Cores can be further tested for compressive and split tensile strength per ASTM C 42; and
- Subsequently, patch the removed-core area (after proper surface preparation) with an expansive cementitious or epoxy grout compatible with the existing substrate concrete and the surrounding environment. 2. Methods for nondestructive evaluation:
- Impact echo (IE);
- Ultrasonic pulse velocity (UPV); and
- Spectral analysis of surface waves (SASW).
Restoring Concrete Structures by Recasting Using Ready to use Mortars
This method statement describes the step by step procedure for repairing concrete structures using a technique of recasting using ready to use mortar products.
The concrete repair range is a system of products consisting of a bonding primer, reinforcement corrosion protection layer; mortar repair and levelling or smoothing mortar.
- Bonding primers for promoting adhesion of a repair mortar on concrete
- Reinforcement corrosion protection applied on steel reinforcement bars in concrete (principle 11, method 11.1)
- Repair and reinstatement of damaged or contaminated concrete on buildings, bridges, infrastructure and super structure works (principle 3, methods 3.1 and 3.3)
- Increasing bearing capacity of a concrete structure by adding mortar for strengthening (Principle 4, method 4.4)
- Preserving or restoring passivity of steel reinforcement bars in concrete (Principle 7, methods 7.1 and 7.2)
- Increasing cover to reinforcement bars with additional mortar
- Repair of minor defects
- Pre-mixed for quality
- 1-component products only add water
- Adjustable consistencies
- Versatile range of performances
- Low shrinkage
- Products with classified performance classes
- Bonding primer with long open time
- Systems with high resistance to water and chloride penetration
- Products which can be poured or machine applied by pumping
- Compatible system with concrete protection products
This method statement has been written in accordance with the recommendations contained in European Standards EN 1504: Products and systems for the protection and repair of concrete structures, and the following relevant parts:
EN 1504 Part 1: Definitions, requirements, quality control and evaluation of conformity
EN 1504 Part 3: Structural and non-structural repair
EN 1504 Part 7: Reinforcement corrosion protection
EN 1504 Part 10: Site application of products and systems, and quality control of works
- Products shall only be applied in accordance with their intended use.
- Local differences in some products may result in some slight performance variations. The most recent and relevant local Product Sheet (PDS) and Material Safety Data Sheet (MSDS) shall apply
- For specific construction / build information refer to the Architects’, Engineer’s or Specialist’s details, drawings, specifications and risk assessments.
- All work shall be carried out as directed by a Supervising Officer or a Qualified Engineer.
- This method statement is only a guide and shall be adapted to suit local products, Standards, legislations or other requirements.
Materials shall be stored properly in undamaged original sealed packaging, in dry cooled conditions. Refer to specific information contained in the product data sheet regarding minimum and maximum storage temperatures.
Use professional equipment for mixing Grout.
Sufficient quantities repair materials – Refer to section 11
Sufficient clean potable water – For mixing 1-component, pre-wetting substrate & cleaning
Hand tools – Trowels, floats, brushes for mortar application For constructing formwork
Concrete removal – Traditional tools, hammer-drill or suitable mechanical equipment for removing damaged or contaminated concrete
Measuring cylinder – For accurate measurement of mixing water
Mixing equipment – Refer to section 4.4
Mixing bowl – Minimum size ~18 – 20 litres per 25 kg bag
Formwork – To profile application
Sponge or pressurised air (oil free) – Wipe/blow away excess water from substrate
Sealant – For sealing formwork
Curing – Membrane or similar to protect exposed fresh mortar
Cleaning – Brush, low pressure water
Waste disposal – For paper bags and excess material
Cleaning Equipment – Suitable for removing corrosion off reinforcement
HEALTH AND SAFETY
The risk to health and safety from falling objects or defects in the structure shall be properly assessed.
Platforms and temporary structures shall provide a stable and safe area to work. Do not take any unnecessary risks!
Handling or processing cement products may generate dust which can cause mechanical irritation to the eyes, skin, nose and throat.
Appropriate eye protection shall be worn at all times while handling and mixing products.
Approved dust masks shall be worn to protect the nose and throat from dust. Safety shoes, gloves and other appropriate skin protection shall be worn at all times.
Always wash hands with suitable soap after handling products and before food consumption.
FOR DETAILED INFORMATION REFER TO THE MATERIAL SAFETY DATA SHEET
Seek immediate medical attention in the event of excessive inhalation, ingestion or eye contact causing irritation. Do not induce vomiting unless directed by medical personnel. Flush eyes with plenty of clean water occasionally lifting upper and lower eyelids. Remove contact lenses immediately. Continue to rinse eye for 10 minutes and then seek medical attention.
Rinse contaminated skin with plenty of water. Remove contaminated clothing and continue to rinse for 10 minutes and seek medical attention.
FOR DETAILED INFORMATION REFER TO THE MATERIAL SAFETY DATA SHEET
CLEANING TOOLS / EQUIPMENT
Clean all tools and application equipment with water immediately after use. Hardened material may only be removed mechanically.
Do not empty surplus material into drains. Avoid runoff onto soil or into waterways, drains or sewers. Dispose unwanted material responsibly through licensed waste disposal contractor in accordance with local legislation and/or regional authority requirements.
FOR DETAILED INFORMATION REFER TO THE MATERIAL SAFETY DATA SHEET
The concrete substrate shall be thoroughly clean, in a good sound condition and free from dust, loose material, surface contamination and materials which reduce bond. Delaminated, weak, damaged and deteriorated concrete shall be removed by suitable means. If necessary, some sound concrete may also be removed but not to detriment of the structural integrity and only as directed by a Supervising Officer or Qualified Engineer.
Methods of cleaning, roughening and concrete removal are summarised as follows:
Appropriate tool selection will depend on the type and extent of damage as well as the substrate quality and shall be agreed with the Supervising Officer or qualified Engineer.
Note: Hydro-demolition is a preferred fast and effective method of removing concrete which can result in no micro cracks in the concrete.
As defined in EN 1504-10, water jet categories are as follows:
- Low Pressure – Up to 18 N/mm2 (MPa) / 180 bar / ~2,600 PSI
– Used for cleaning concrete and steel substrate
- High Pressure – from 18 to 60 N/mm2 (MPa) / 600 bar / ~8,700 PSI
– Used for cleaning steel substrate and for removal of concrete
- Very High Pressure –from 60 to 110 N/mm2 (MPa) / 1100 bar / ~16,000 PSI
– Used for concrete removal when low water volume is available
Where: 1N/mm2 = 10 bar = 145 PSI (lbf/in2)
Concrete removal shall be kept to a minimum and shall not reduce the structural integrity of the structure. Pneumatic equipment or tools which can damage concrete due to an intense vibration shall not be used.
The extent of concrete removal shall be in accordance with the chosen principle and method contained in EN 1504-9. In the case of repair and restoration the depth of contamination shall be established and taken into account when determining the depth of concrete removal.
Removal of concrete shall continue to expose full circumference of the steel reinforcement to a minimum depth of 15 mm behind the back of the bars.
Breaking out shall continue along the reinforcement until non-corroded steel is reached as directed by the supervising officer or qualified engineer.
Edges around the patch repair shall be cut at an angle of >90o to avoid undercutting and a maximum angle of 135o to reduce the possibility of de-bonding.
Surface of the concrete substrate shall be roughened to 2 mm to increase bonding which can be tested in accordance with EN 1766: clause 7.2 for horizontal surfaces.
Micro cracked or delaminated concrete including damage caused cleaning, roughening or removal techniques shall be removed or repaired if they might reduce bond or structural integrity. Micro cracks can be detected by wetting the surface and allowing it to dry. Dark lines on the dried surface indicate cracks as they retain the water.
The finished surface shall be visually inspected prior to application and can be tapped lightly using a metal hammer to detect delaminated concrete. The supervising officer or qualified engineer shall be informed immediately of any loose, cracked or damaged surfaces. In these circumstances repair materials shall not be applied without prior written consent of the supervising officer or qualified engineer.
If a smoothing coat is required the whole application surface shall be properly prepared. Appropriate cleaning procedures consist of low pressure water blasting, abrasive grit and sand blasting, or high pressure water blasting to remove a laitance layer.
The steel reinforcement shall be thoroughly clean and free from rust, scale, mortar, concrete, dust and other loose and deleterious material which reduces bond or contributes to corrosion. Tie wire and nails shall also be removed.
The whole circumference of the bar shall be uniformly cleaned, except where structural considerations prevent this. Cleaning shall not damage in anyway the structural integrity of the steel. Immediately notify the supervising officer or qualified engineer if there is a possibility of damaging the steel by cleaning.
Exposed bars contaminated with chloride or other deleterious material shall be cleaned by low pressure water jet (18 MPa) and checked afterwards to ensure the contamination has been totally removed.
If a reinforcement corrosion protection layer in the form of an active coating (method 11.1 as defined in the European Standards EN 1504-9) is to be applied, then the steel reinforcement shall be cleaned to Sa 2 defined by ISO 8501-1.
If reinforcement corrosion protection layer in the form of a barrier coating (method 11.2 of EN 1504-9) is to be applied, then the steel reinforcement shall be prepared to Sa 2½ defined by ISO 8501-1.
Cleaned bars shall be protected against further contamination prior to application of a reinforcement corrosion protection layer.
Loss of steel-area on reinforcement due to corrosion, or due to any other damage, shall immediately be brought to the attention of the supervising officer or qualified engineer prior to any further work. Any further action such as replacing reinforcement bars shall only be carried in accordance with the direct instruction of the supervising officer or qualified engineer. The scope of this method statement does not include replacement of steel reinforcement bars.
Concrete surfaces shall be saturated with clean low pressure water a minimum 2 hours before application ensuring that all pores and pits are adequately wet. The surface shall not be allowed to dry before application.
Formwork shall be fixed immediately after pre-wetting to avoid loss of moisture from the substrate surface. Ensure there is no standing water on the surface before closing the formwork. The surface shall achieve a dark matt appearance without glistening and surface pores and pits shall not contain water (saturated surface dry). Use pressurised air (oil free) to blow away excess water in difficult to reach areas.
Formwork shall be clean and fixed in place as soon as possible after the substrate has been prepared. If required, release agents shall be applied to the formwork before placing into position. Do not contaminate the substrate with the release agent and reduce bond of the grout material from spillage or run-off.
Openings in the formwork shall be protected to prevent ingress of debris or contamination. Formwork shall be watertight and free from obstructions to allow the free flow of pourable mortar.
Formwork shall be designed to allow the controlled escape of air and water bleed.
Mixing shall always be carried out in accordance with the recommendations contained in the latest product data sheet (PDS).
Do not use water beyond the stated maximum and minimum limits.
In determining the mixing ratio the wind strength, humidity, ambient and substrate temperature and shall be taken into consideration.
The product and system shall be appropriate for the type of substrate, structure and exposure conditions which they are required.
Working space shall be clean and tidy with no obstructions.
Record the substrate, ambient temperature and relative humidity. Check pot life information on bag or in the product data sheet and allow for climatic conditions e.g. high / low temperatures & humidity.
External applications shall be adequately protected. Do not apply mortar repair in direct sun, windy, humid or rainy conditions or if there is a risk of frost within 24 hours in unprotected areas. Ensure sure blow holes are not obstructed and can allow the escape of air.
Calculate the required volume for the application and then using the equation in section 10 of this method statement, calculate the yield of the product. Make sure there is enough material on job site to carry out the work.
REINFORCEMENT CORROSION PROTECTION
Where a reinforcement corrosion protection is required, apply material to the whole circumference of the steel reinforcement bar in two layers. Wait until the first layer has dried before applying the second layer. Use a mirror to inspect behind the back of the bars to ensure full coverage.
Take care not to splash or apply material on a dry concrete substrate behind the bars.
For small areas use two paint brushes to apply 2 layers and ensure full coverage. For larger areas use hopper gun aim the spray in different directions to ensue coverage behind the back of the bars.
The repair mortar shall only be applied when the reinforcement corrosion protection is hardened (wet on dry). Refer to the relevant product data sheet for more information.
Refer to relevant repair mortar product data sheet if a bonding primer is required. If a bonding primer is required, the substrate surface shall be pre-wetted in accordance with section 6.3.
Bonding primers can be applied by hand pressing the material firmly into the surface using a brush or using a hopper gun for larger areas.
The repair mortar shall be applied wet on wet to a bonding primer. Ensure the substrate surface is fully covered behind the reinforcement bars. For large applications use only a bonding primer with long open time.
RECASTING USING A POURABLE REPAIR MORTAR
A pourable repair material shall be applied into the prepared opening as soon as possible after mixing. A grout shall be poured into the prepared opening within 15 minutes to optimise the expansion properties of the material. Pot life shall also be taken into consideration, adjusting for climatic conditions, when planning the work duration.
Pour the grout through the “mouth” of the formwork allowing the material to flow to the opposite end. Always maintain sufficient pressure head while pouring. Ensure a process of continuous pouring to avoid air entrapment and prevent the material flow from coming to a stop before the operation is completed. Make sure air displaced by the material can easily escape.
Always pour from opposite ends to any air release (blow) holes. Maintain pouring until material escapes from the air release holes. Allow some material wastage until it is certain all air has been released and there is no air trapped air in the application.
Avoid the free fall of the material to prevent segregation of the aggregate (max ~2 cm).
Never make an application from two places as it will be difficult to determine if all air has been released, and the entire void has been filled.
Do not vibrate the formwork as this will cause segregation and bleeding.
RECASTING USING A PUMPABLE REPAIR MORTAR
Pumping is a specialist technique is recommended to be carried out by an experienced Contractor. The risk associated with pumping a fluid mortar is bleeding as the sand separates while it is under pressure and can cause a blockage. It is recommended checking the compatibility of the pump equipment and grout before the main application.
Pump-able mortars are pre-mixed in the normal way, placed into the hopper of the equipment and pumped through a hose to the point of application. Typical pump machines can be:
- Screw Pumps e.g. Putzmeister S5
- Piston Pumps
- Double Piston Pumps
- Membrane Pump (for small grain sizes, refer to machine manufacturers recommendations)
The pump machine and ancillary equipment shall be of adequate capacity for the volumes to be applied.
All moving parts, fittings and hopper shall be inspected for cleanliness and damage before use. Any hardened material shall be removed. The equipment shall not leak.
Power for the equipment shall be approved for use on job site. Always conform to local laws and restrictions when using diesel powered equipment. When using an electric motor check the voltage requirement is available on job site.
The Contractor shall keep full details and records of the type of machine and equipment used for the project. This information shall be provided to the Engineer, when requested.
The hose or pipe shall not have any dents or kinks and be long enough to reach from the pump location to the point of application. It is advisable to use the shortest hose length available to reduce the risk of blockage.
Always consult with the recommendations provided by the machine manufacturer.
The method of pumping a material must ensure complete filling of the voids, crevices. Pumping equipment shall suit the material and purpose for which they are to be used. Always read the pump manufacturer’s instructions and obtain further guidance if necessary.
Pumping shall generally be applied from the bottom of the application to force the air out of the top through controlled air release hole(s). Refer to section 9.1 for a typical example. Pumping shall only take place from one position on an application and shall continue until material escapes out of the controlled air release points. Allow some material wastage until it is certain all air has been released and there is no air trapped air in the application.
REMOVAL OF FORMWORK
The formwork shall not be removed until sufficient strength has been achieved. This time depends on the material characteristics and climate conditions. As guidance the formwork around a high performance, low shrinkage grout in normal 21°C / 55% relative humidity conditions may be removed approximately 12 to 24 hours after application.
Formwork shall only be removed with the agreement of the supervising officer or qualified engineer.
Best curing is achieved while the formwork is still in place. As soon as the formwork is removed, protect the still green material from premature drying.
Cure with proper curing methods for 3 days or spray with appropriate curing compound once any surface water has evaporated. Curing methods include jute and water, plastic sheets or other suitable membranes.
SMOOTHING / LEVELLING MORTARS
Smoothing mortars can be applied by hand, by hopper gun or by mechanical spray equipment for large areas. Refer to relevant product data sheet for further information.
A smoothing coat shall be applied over the whole prepared concrete surface (including repair and non-repaired areas). Any laitance layer on the surface shall be removed (section 6.1) and surface pre-wet in accordance with section 6.3.
Wait until the repair material has properly hardened before applying a smoothing coat.
Use a toothed trowel to apply the mortar by hand in a vertical direction onto the surface. Hold the trowel at an acute angle to the surface and use different size toothed trowels to regulate the application thickness.
Table 1 Approximate application thickness guide
When 1st layer is hard, apply the second layer between the vertical lines. The hardness can be tested by the ease at which a finger nail can be inserted into the mortar.
Finish surface with damp sponge, wooden or plastic float after material has set. Do not add apply additional water on the surface as this will cause discoloration and cracking.
Cure levelling mortars with proper curing methods for 3 days or spray with appropriate curing compound (once any surface water has evaporated) or appropriate curing method. Curing methods include jute and water, plastic sheets or other suitable membranes.
The application shall be protected from wind, rain, frost and direct sunlight. The curing period is dependent on climate conditions. In warm temperatures with low humidity the application shall be protected from premature drying.
- Avoid application in direct sun and/or strong winds
- Do not add water over the maximum recommended dosage
- Always check the material’s pot life and adjust for climate conditions
- Temperature of the repair mortar and substrate shall not differ significantly
- Where the structure is subject to dynamic loading, it is recommended for overhead applications to use repair systems specially tested for this situation
INSPECTION, SAMPLING, QUALITY CONTROL
As part of “Good Practice” the contractor shall provide a QC report containing the following recommended data. For more detailed information refer to EN 1504-10 Annex A, or any other local standards or legislation which may apply.
SUBSTRATE QUALITY CONTROL – BEFORE AND AFTER PREPARATION
The following checks should be carried out before and after preparation.
BEFORE, DURING AND AFTER APPLICATION
The following checks should be carried out before during and after the application.
|Dry product aspect
|2 bags per 10
|Loose, no lumps and not compacted
|Homogeneous, no lumps no un-mixed dry powder
|Keep records and provide protection
|Less than 8 m/sec or provide protection
Table 3 QC summary before during and after application
The following can be used on job site to check the adequacy of the application.
|Compressive Strength on 40x40x160 prisms
|3 prisms per batch
|Within PDS limits
|28 days after application
|No cracking on application
|Presence of Voids/ Delaminating
|EN 12504-1 Hammer souding or *ultrasonic testing
|No delaminating concrete
|Adhesion Bond *(pull off)
|EN 1542 (Acc EN 1504-10 Table A.2)
|Min 3 on a test area
|1.2 – 1.5 N/mm2 (Structural use)
0.7 N/mm2 (non-structural use)
* Optional testing
Table 4 QC summary of performance testing
TIELD & CONSUMPTION
The yield of a product can be determined from the following equation (assuming no wastage).
yield (litres) = (weight of powder (kg) + weight of water (kg))
density of mixture (kg/l)
Given: weight of water 1 litre = ~1 kg
Calculate consumption of a bag weighing 25 kg mixed with 3.6 litres of water, when the density of the fresh material is 2.1 kg/l.
1 bag of 25 kg yields:
(25 + 3.6) = ~ 13.6 litres of mortar
Therefore, the number of bags required for 1m3 of mortar will be:
No of bags required per 1m3 = (1/yield) x 1000
(1/13.6) x 1000 = ~ 74 bags
Consumption of a product can be calculated as follows:
Calculate how many kg of powder is required to cover a 10 mm thick application over an area 1 m2 (assuming no wastage)
Weight of mixed mortar (kg)
= volume (m3) x density (kg/m3)
= (1 x 0.01) x 2100
= 21 kg (total)
Less weight of water;
If water to powder mixing ratio = *14.5% then;
Required weight of powder
= 21 / ((100+14.5)/100)
= ~ 18.3 kg powder
* refer to PDS for exact figure
The following applications offer further guidance in specific situations.
EXAMPLES OF RECASTING
The following are two examples of recasting a concrete column for purposes of restoration, structural strengthening, preserving or restoring passivity using a pouring and pumping method.
The detail is for illustration purposes and not to be used as a construction drawing.
The detail is for illustration purposes and not to be used as a construction drawing.
INCREASING MAXIMUM LAYER THICKNESS
The application thickness of some pourable mortars can be increased with the addition of more aggregate. This technique only applies for filling voids or applications subject to static compression loads.
Method 1 – Filing a Void
It is with single sized rounded stones of between 16 – 32 mm (can be all 16mm or all 32 mm or a size in between – optional)
This method is only suitable for filing a void subject to compression loads only. Sides of the void must be thoroughly clean; the laitance layer must be removed and surface can be slightly roughened if neccessary.
Do not add additional water and do not use additional fines.
Method 2 – Adding Additional Aggregate
Step 1 – Pre-wash / wet the aggregate. The aggregate shall be saturated surface dry when adding to the mortar
Step 2 – Mix repair mortar as normal. Slowly add the aggregate and mix slowly until homogeneous. Over mixing will aerate. Leave to stand for 2 minutes.
Step 3 – Apply mix into void
Step 4 – Build up in layers. The first layer shall be hardened, exothermic reaction completed and be at ambient temperature before applying next layer
The new repair mortar’s characteristic will be affected with the addition of more aggregate, significantly the flow. These new characteristics shall be taken into account when the technique on job site. For example pot life.
Pre-testing of the modified material shall be carried out first to determine an acceptable construction method together with new material mechanical performances.
- Always pre-test the new material characteristics
- Always check no bleeding or sedimentation
- Use same aggregate and grading to be used on job site
- Consider ambient and substrate temperatures
- Check the new mechanical properties
The general rule for additional aggregate is to use a rounded clean well graded between dmax to (2 or 3 x dmax)
- Do not add more water to the mix
- Aggregate shall not be wet
The following example shows how a penetration can be sealed in a vertical concrete wall using a poured grout. The soffit of the void shall not be horizontal. It shall be profiled at an angle to allow the escape of air.
CONCRETE REPAIR FLOW CHART
The following is a guide of how to carrying out a concrete repair. This is not intended as a definitive guide to repair concrete and shall at all times be read in conjunction with all Architect’s, Engineer’s or specialist specifications together with EN 1504-10, local standards and all relevant product data sheets.
Crack injection on bridge structures
Cracks in concrete and natural stone bridge structures are usually best sealed and filled by injection.
The purpose of this crack injection is to seal the cracks so that aggressive agents, such as chlorides from de-icing salts, carbon dioxide from the atmosphere and other damaging materials, do not reach the reinforcement, which could subsequently lead to corrosion and increased concrete damage. These injection techniques are also used for high-strength concrete to concrete and/or concrete to steel bonding and strengthening, in order to restore the full structural load-bearing capacity. Much has been written in literature about crack widths that can be permitted and this is usually considered to be from 0.1 to 0.3mm dependent on the type of structure and their location. However, diagnosis of the correct maximum permissible crack width determination and the risk analysis is also dependent on the concrete specifications, the concrete cover over the reinforcement or prestressing cables and the environmental exposure conditions (industrial, urban or marine atmospheres), in which the bridge structure is located.
With regard to the form and depth of the cracks, the form is also dependent on several factors, including the size and grade of steel used and additionally, cracks do not necessarily run at right angles to the surface, they can frequently change direction, into the interior of the structure or the individual bridge component.
Methods of injection on bridge structures
Non-pressure methods (such as pouring and brushing in of the injection material)
This makes use of capillary action and suction forces. The injection material is taken into the cracks by these capillary forces. The injection material must be fed into the crack over a period of time and therefore must have the lowest possible viscosity and good surface ‘wetting’ properties.
This method of crack filling is mainly used for ensuring corrosion protection of steel reinforcement near the surface.
Injection by both low and high pressure injection techniques are the methods most frequently used for crack sealing today. Vacuum injection systems can also be used in some instances.
Low pressure injection – pressure <20bar
This technique is less commonly used than the high pressure method. Low pressure injection is generally only used where the design of the structure or low material strengths, do not allow the high pressure techniques to be used. Low pressure injection is also appropriate for wider cracks, slender components and areas of large-scale injection. Experience shows that with the right choice of material and execution (low viscosity and long pot life), crack injection with low pressure techniques can be equally successful as the high pressure systems. Adhesive bonded surface packers are usually used in the low process, where they are positioned over the slightly widened cracks and then injected through gravity or hand guns.
High pressure injection– pressure >20bar
Drilled injection packers, or ports as they are sometimes known, are used for this method. They must be installed on alternate sides of the crack and should meet the crack inside the structure at an angle of approximately 45°. The advantage of this alternate drilling is that every second packer (at least) intersects the crack, even when it runs diagonally. The length of the holes required depends on the concrete thickness and should usually be at least two thirds of the total thickness. The crack must be closed above a certain surface width so that the injection material does not emerge uncontrolled and the necessary injection pressure can be built up. The crack is injected working upwards on the structure and care must be taken to ensure that the injection material emerges sufficiently from the top packer before stopping the injection operation.
Vacuum injection method
With this method the injection material is pulled into the crack through the vacuum built up in it. This method can only work if the crack can be fully closed or clamped so that it is possible to build up a vacuum in the crack.
Guidelines exist for installation and spacing of both the drilled and the bonded packers. These are dependent on the wall thickness, pressure development and the type of packer and different packer spacing result. Generally:
- For drilled packers: packer spacing = component thickness / 2
- For bonded surface packers: packer spacing = component thickness
The injection pressure must be adapted to the grade or grades of concrete used in the structure. This is to avoid excessive injection pressure which could lead to further damage and widening of the cracks.
For the optimum adjustment of the injection pressure to the specific concrete in a structure, the following formula applies:
P max = (concrete compressive strength x 10) / 3
Types of injection material
The selection of the correct injection material is another extremely important factor in achieving the objectives and this depends on
- The crack widths
- The moisture content of the cracks and the concrete
- The nature of the crack sides
- The concrete temperature
- The concrete quality
- The stresses or loads existing during the application and to be applied later
- The viscosity of the injection material.
The three most common types of injection materials are:
Epoxy resins: For high-strength bonding requirements. The following resin properties must be considered:
- Pot life
- Adhesion on dry and damp concrete
- Glass transition temperature
Polyurethane resins: For sealing against water, water vapour and gases. PU injection resins are mainly used for elastic crack sealing.
The following properties should be considered for this type of resins:
- Pot life
- Adhesion on dry and damp concrete
- Alkali resistance
Ultrafine or ‘Micro-fine’ cement suspensions: For high-strength bonding in larger cracks. The following ultrafine micro-cement product properties must be considered:
- Particle size distribution
- Flow properties
- Setting time
- Tensile strength