What is concrete repair?
Concrete repair means restoring the load-bearing capacity, durability and appearance of concrete and reinforced concrete structures damaged by reinforcement corrosion, an aggressive environment, loads, fire or construction errors. A good repair eliminates not only the visible defect but also its cause: if the reinforcement is corroding because of carbonation or chlorides, simply filling a spall with cement mortar will produce new spalls next to the patch within a few years.
That is why a repair always starts with diagnosis, and the materials are chosen as a system: substrate preparation — reinforcement protection — reinstatement of the section — crack filling — levelling — surface protection. Each layer has its own class of materials and its own requirements.
Which standards apply to concrete repair and protection — EN 1504, GOST 32016 and 32017, GOST R 56378, ShNK 2.03.11-24 — is summarised in the section Concrete repair and protection standards.
Selecting a repair system. On the basis of a survey, or of photographs and a description of the damage, we will propose a repair method, materials and consumption rates. Protective coatings engineering →
Why reinforced concrete deteriorates
- Carbonation. Carbon dioxide in the air gradually neutralises the alkaline environment of the concrete. When the carbonation front reaches the reinforcement, the steel loses its passivity and starts to rust; the corrosion products take up a larger volume and spall off the concrete cover.
- Chlorides. De-icing salts, saline soils and groundwater, salt-laden dust, sea water. Chlorides break down the passive film locally, so corrosion takes the form of pitting and can weaken a bar before any noticeable spalling appears.
- Freeze–thaw, especially in combination with salts: scaling and breakdown of the surface layer.
- Chemical attack: sulphates, acids, wastewater, process spills.
- Mechanical causes: overloading, impact, abrasion, settlement, thermal movement, shrinkage — hence cracks and spalls.
- Construction defects: insufficient cover, honeycombing, inadequately vibrated concrete, cold joints.
A survey answers the questions that determine the choice of materials: what the concrete strength is, what the carbonation depth and the chloride content at the reinforcement are, how much section the bars have lost, whether the cracks are live, whether water is present, and what environment acts on the structure now and will act on it after the repair.
EN 1504: how the standard is structured
The European EN 1504 series covers products and systems for the protection and repair of concrete structures: definitions, requirements for materials, quality control and rules of application. It is the standard referred to in the technical data sheets of Sika, Fosroc and Mapei, and the CE marking of repair materials is based on it.
| Part | Scope |
|---|---|
| EN 1504-1:2005 | Terms and definitions |
| EN 1504-2:2004 | Surface protection systems: hydrophobic impregnation, impregnation, coating |
| EN 1504-3:2005 | Structural and non-structural repair — repair mortars and concretes |
| EN 1504-4:2004 | Structural bonding |
| EN 1504-5:2013 | Concrete injection |
| EN 1504-6:2006 | Anchoring of reinforcing steel bars |
| EN 1504-7:2006 | Reinforcement corrosion protection |
| EN 1504-8:2016 | Quality control and assessment and verification of constancy of performance |
| EN 1504-9:2008 | General principles for the use of products and systems |
| EN 1504-10:2017 | Site application and quality control of the works |
Part 9 sets out the logic of selection. It identifies eleven principles of repair and protection: six relate to defects in the concrete — protection against ingress, moisture control, concrete restoration, structural strengthening, physical resistance and resistance to chemicals; five relate to reinforcement corrosion — preserving or restoring passivity, increasing resistivity, cathodic control, cathodic protection and control of anodic areas. Each principle has its methods, and each method has materials from the other parts of the standard. In technical data sheets this appears as an entry such as “principle 3, method 3.1” — this is how the manufacturer shows which task a product is intended for.
EN 1504 is a European standard. CE marking and a declaration of performance confirm that a material has been tested by its methods, but they do not replace the requirements of the codes of Uzbekistan and other Central Asian countries: for projects here, the design and the material documents are checked against national rules. In Uzbekistan, requirements for the corrosion protection of building structures are set by ShNK 2.03.11-24.
Sequence of work
- Survey and diagnosis: damage mapping, concrete strength, carbonation, chlorides, condition of the reinforcement, cracks and whether they are live, moisture.
- Selection of principles and methods to EN 1504-9 and development of the repair procedure — taking into account loads, environment and timescales.
- Substrate preparation: removal of deteriorated and contaminated concrete back to sound concrete, exposing the reinforcement, cleaning the steel, giving the repair areas a simple shape.
- Reinforcement protection with products to EN 1504-7 and, where necessary, corrosion inhibitors or cathodic protection.
- Reinstatement of the section with repair mortars to EN 1504-3: by hand, by spraying or by pouring into formwork.
- Crack injection to EN 1504-5.
- Levelling and pore filling before painting.
- Surface protection to EN 1504-2: hydrophobic impregnation, anti-carbonation and elastic coatings.
- Strengthening as designed — with CFRP, section enlargement or bonded-in reinforcement.
- Quality control to EN 1504-10 and the design requirements: substrate preparation, temperature and humidity during the work, bond tests, coating thickness, work log.
Sections of the guide
- Concrete repair mortars — structural repair in classes R3 and R4: thixotropic, flowable, rapid-hardening and sprayed mortars, and epoxy mortars.
- Levelling and finishing compounds — thin-layer mortars, pore fillers and putties applied before painting.
- Reinforcement corrosion protection — anti-corrosion and bonding coatings for bars, penetrating inhibitors.
- Crack injection — epoxy resins for restoring monolithic integrity and compounds for sealing.
- Protective coatings and impregnations — water repellents, anti-carbonation and crack-bridging coatings.
- Strengthening with composites — CFRP plates, fabrics and structural epoxy adhesives.
Anchoring of reinforcement and grouting of equipment are covered in the “Grouts” section, chemical-resistant linings for concrete bunds and tanks in the “Chemical protection” section, and waterproofing of structures in the “Waterproofing” section.
Repair mortar classes to EN 1504-3
EN 1504-3 divides repair mortars and concretes into four classes. R3 and R4 are structural: they are used to reinstate the section of load-bearing members. R1 and R2 are non-structural: they are used to level surfaces and fill defects that play no part in the structural behaviour. The class is determined not by strength alone but by a set of properties. The requirements that manufacturers quote in their data sheets alongside the test results:
| Property | R4 | R3 | R2 |
|---|---|---|---|
| Compressive strength at 28 days | at least 45 MPa | at least 25 MPa | at least 15 MPa |
| Bond strength to concrete (pull-off) | at least 2.0 MPa | at least 1.5 MPa | at least 0.8 MPa |
| Elastic modulus in compression | at least 20 GPa | at least 15 GPa | no requirement |
| Chloride ion content | no more than 0.05 % | ||
For structural repair, besides strength, carbonation resistance, limited shrinkage and compatibility with the existing concrete are important: a mortar that is too strong and too stiff for a weak substrate performs worse than one selected to match the strength of the structure.
Common mistakes
- Repair without diagnosis: a patch where the spall was, while reinforcement corrosion continues under the adjacent areas.
- Not all of the damaged and contaminated concrete has been removed; the reinforcement has not been exposed all round or cleaned on the back.
- A dry substrate under a cementitious mortar — the mortar loses water, sets poorly and debonds; or, conversely, puddles on the surface.
- Extra water added to the mix “to make it easier to work”, cement or sand added to a ready-mixed product.
- No curing of the fresh mortar — shrinkage cracks appear in hot and windy weather.
- Materials from different systems without confirmed compatibility: a bonding coat from one manufacturer, a mortar from another and a coating from a third.
- Cracks filled with a rigid resin without establishing whether they are moving.
- A repaired area left without surface protection in an aggressive environment.
Materials in the guide
We have collected repair materials from Sika, Fosroc and Mapei — manufacturers whose systems are used in Uzbekistan and neighbouring countries. For Sika, the cards are based on the data sheets of its subsidiaries in Europe, Turkey and Kazakhstan; for Fosroc, on the data sheets of the UK and the manufacturer’s other regions; for Mapei, on the parent company’s international data sheets. Examples: the repair mortars Sika MonoTop-412 N, SikaEmaco S 488, Fosroc Renderoc S and Mapegrout Thixotropic; reinforcement protection SikaTop Armatec-110 EpoCem and Mapefer 1K; the injection resins Sikadur-52 Injection and Epojet; the water repellent Sikagard-705 L; the CFRP plates Sika CarboDur S and Carboplate. Full lists are on the section pages.
How to request a selection
To get an accurate proposal, please send us:
- what is to be repaired: the type of structure (slab, beam, column, wall, tank, bridge superstructure), its age and purpose;
- photographs of the damage with a scale, approximate areas and depths of spalls, crack widths and lengths;
- survey results, if available: concrete strength, carbonation depth, chlorides, loss of reinforcement section;
- service conditions: indoors or outdoors, contact with water, salts or chemicals, temperature, loads and movement;
- constraints: an operating plant, the date for return to service, the season, access (soffits, height), whether spraying is possible;
- design and client requirements: codes, material classes, approved manufacturers.
Based on this information, we will propose a repair method and 1–3 material options from different manufacturers with consumption rates and, where necessary, a strengthening scheme, which is calculated by a structural engineer.
About supply
We supply concrete repair and protection materials across Uzbekistan and to neighbouring Central Asian countries: we help check the project requirements, obtain the current technical data sheets from the manufacturer and put together a complete system — from the reinforcement coating to the topcoat. We select the repair method and consumption rates for your project and, where needed, organise the works through partner contractors experienced in reinforced concrete repair.
Frequently asked questions
Can concrete be repaired with ordinary sand and cement mortar?
Sometimes, for non-critical areas, but ordinary mortar has no specified shrinkage, bond or carbonation resistance. Repair mortars to EN 1504-3 are formulated to work together with the old concrete and to protect the reinforcement — for load-bearing structures this is essential.
How is R4 better than R3?
R4 is the higher class, with higher requirements for strength, bond and elastic modulus. But “better” depends on the task: a repair mortar is selected to suit the existing concrete. Fosroc, for example, recommends the lightweight Renderoc HB30 mortar instead of Renderoc S for compatibility with lower-strength concrete.
Does concrete need protection after repair?
If the damage was caused by carbonation or chlorides, yes: without an impregnation or a coating, the processes will continue in the adjacent areas. The type of protection is chosen to suit the environment — hydrophobic impregnation, an anti-carbonation or elastic coating and, in a chemically aggressive environment, a chemical-resistant system.
Can repairs be carried out in winter or in hot weather?
Cementitious and epoxy materials have a working temperature range stated in the data sheet; there are also rapid-hardening mortars that allow work in freezing conditions. In hot weather, materials are stored in the shade and mixed with cold water, and curing of the fresh mortar is organised straight away.
Need materials selected for concrete repair or a supply quotation? Call us or message us on WhatsApp/Telegram: +998 94 094 52 27.