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As example, the selection of the repair material and techniques can be based on the various principles described in the EN 1504-9.

All over the world, some companies can provide repair materials that meet the local and international standards requirements such as ASTM, EN etc.

In Europe, repair material selection will need to be carried out with products complying with the forthcoming EN 1504-3 that are compulsory since 1st January 2009. Classification of this standard is based on 4 different levels R4 & R3 for Structural repair works and R2 & R1 for non structural works mainly cosmetic repair.

The products performances are differentiated based on compressive strength, bond strength in various conditions (after long freeze thaw cycles, long term immersion, etc…), elastic modulus etc.

According to the definition of EN 1504-2, a coating is a treatment to produce a continuous protective layer on the surface of concrete. Its typical thickness can range from 100 µm to 5mm. Some applications may use thickness bigger that 5 mm.

The most important components of the coating are its conglomerates which give to the coating the main characteristic. These conglomerates may be, organic polymers, organic polymers with fillers cement or hydraulic cement modified with a polymer dispersion.

Any selected protective coating shall have good resistant to weathering and ageing, shall exhibit good hiding power and low dirt pick up. Protective coatings cover all the different requirements for almost all project types and can performed in completely opposite environmental conditions, from very cold countries to the very hot and dry climates through the hot and wet climates.

When selecting a protective coating, designers/ engineers shall consider the following parameters:

• Level of water tightness to liquid water, e.g. is the project near the sea? The ability to reduce or prevent chloride migration.
• Permeability to water vapor, e.g. Highly breathable or restricting vapor exchange?
• Barrier against CO2 diffusion, e.g. At which thickness?
• Crack bridging, e.eg Static or dynamic? Which minimum temperature?

So, they will have to choose between:

Elastic protective coatings, it shall retain their elastic properties at very low temperature (as elastomeric material trends to become more brittle when temperature is decreasing) this parameter is important for countries with heavy winter.

Protective coatings, the use of highly elastic coatings may not be desirable in some structures or part of them in order to be able to be in the position to detect potential development of severe structural cracks. These coating nevertheless may be able to bridge surface crazing in order to be able to provide the relevant protection.

Reactive coatings are sometime used for the protection of concrete against normal aggressive atmospheric influences (preventing CO2, chlorides and water ingress) as well as when additional chemical protection is needed. Therefore, for particularly aggressive or special exposure situations such as in tunnels, or marine structures or bridges, they can potentially be used for both requirements. However, if epoxy resin-based coating is considered, consideration must give to their poor resistance to UV light exposure then an additional top coat of a lightfast UV resistant polyurethane coating may be required in these situations.

Some designers would prefer using cement based protective coating as they prefer to maintain a “mineral look” at their structure whilst protecting it against aggressive environment.

Concrete has been the most common building material of the 20 th century and still being largely used nowadays. Many famous internationally known arquitects used concrete as decorative elements. These magnificent structures required sometimes to be protected. However, the use of organic coating may denature the original aesthetic of the bare concrete.

Therefore, some designers will prefer to use cement based protective coatings to protect their structures against aggressive environments. Additionally, to comply to EN-1504-2, some of these cement bases coatings are also used as surface repair materials and as such shall also to comply to EN-1504-3.

According to the definition of the European Standard EN 1504-2, an impregnation is a treatment of concrete to reduce the surface porosity and to strengthen the surface.

The pores and capillaries are partially or totally filled.

According to the definition of the European Standard EN 1504-2, hydrophobic impregnation is a treatment to produce a water-repellent surface.

Hydrophobic impregnation is a surface applied, invisible, non-film forming protection system to increase the durability. Because of the small size of mono-molecular layer, there is little or no change in its aesthetic appearance. Compare to film forming systems as coatings, the surface applied hydrophobic impregnations penetrates the surface pores and capillaries, so that they are internally coated but not filled.

In Europe, the hydrophobic impregnations need to comply with EN 1504-2. Outside Europe, the hydrophobic impregnations need as well to comply to various specifications/standards such as in USA the NCHRP 244 (National Council Highway Research Program) or Federal Specification SS-W-110C, or in Canada, the Alberta B388 or MTQ standard 3601.