In many ways, concrete is a unique material. Due to its properties, possibilities of application and relatively low price, it is the most widely used building material.

Concrete has a very high compressive strength, but all its other properties, like its flexural and tensile strength, toughness, modulus of elasticity etc., are significantly weaker and limit its usefulness. When combined with reinforcing materials and the addition of new components to its composition, its inferior properties can be improved and therefore the range of its capabilities and usefulness can be increased. Impregnations and coatings are key to making reinforced concrete last longer.

Concrete corrosion

Concretes in buildings that are exposed to the weather and other aggressive environmental conditions are at the potential risk of corrosion damage.

The basis for the formation of corrosion processes is the porosity of the concrete or, more specifically, of the cement stone, which allows the penetration of aggressive substances from the environment into the concrete on the one hand, and on the other, the pore walls provide a large surface area which is extremely suitable for chemical processes to take place between aggressive substances that penetrate the pores, and the products of hydration.

Professionally installed concrete is alkaline, with a pH value of around 12.5, and its alkalinity protects the reinforcement against corrosion. However, reinforced concrete is in constant contact with air. The pores in concrete contain calcium hydroxide, which reacts with acid gases in the atmosphere, such as CO 2 . When CO 2 reacts with calcium hydroxide to form calcium carbonate, the process is called carbonatisation. As carbonation occurs, the pH of the concrete decreases and at a pH value of around 10, the conditions for corrosion of the reinforcement are given. In the presence of salts or acids, the conditions for corrosion are already present at a higher pH value. In addition to the pH value, two other conditions must be met for the reinforcement to corrode: the presence of oxygen and moisture.

Exterior concrete surfaces

Corrosion of reinforcement can be prevented by a sufficiently thick layer of covering concrete, which must be as dense as possible and free of micro-cracks, and by the use of protective coatings. Hydrophobic silicone impregnations and finishing coats such as water-based paint are used to protect external concrete surfaces.

Transparent silicone impregnations like FASADEX S are distinguished by their excellent water repellency or hydrophobicity. This is very important because moisture plays a key role in both the absorption of harmful substances (gases and salts) and in the corrosion process itself. They are also distinguished by their excellent durability, as they are resistant to external influences such as thermal loads, chemically aggressive substances, micro-organisms and ultraviolet rays.

When silicone impregnations are used, the pores of the concrete remain open, so the passage of water vapour and gases is not impeded. SPEKTRA Concrete Protect, a tinted water-based finishing coat for the protection of concrete, is also resistant to water absorption, weathering and light. Unlike silicone impregnations, it forms a surface film that also acts as a barrier to gases, including CO2, which is the cause of carbonation.
 

Interior concrete surfaces

Despite the fact that interior concrete surfaces are not exposed to aggressive environmental conditions, they have increasingly been painted in recent years for the following reasons:

• preventing the dusting of concrete (dust protection),
• easier cleaning of surfaces,
• protection of the concrete against aggressive substances such as acids, alkalis, solvents, oils,
• concrete decoration.

Wall and less load-bearing floor surfaces in spaces such as: boiler rooms, pantries, laundry rooms, garages etc., require a paint that is easy to apply, of high quality in terms of fast drying, high hardness, resistance to abrasion and chemicals (motor oil, petrol, salt solution, vinegar, etc.).

SPEKTRA Concrete Protect is an environmentally and health friendly, one-component, water-based paint suitable for painting walls and less load-bearing concrete floor surfaces in residential buildings.

Two-component epoxy and polyurethane coatings are more suitable for the protection of more mechanically and chemically stressed surfaces in industrial settings, e.g. in laboratories, workshops and warehouses where forklifts are used (e.g. SPEKTRA 2K epoxy paint for concrete and the FLOOR EXPERT industrial flooring protection programme.) These coatings are distinguished by their superior mechanical and chemical resistance.

It is important to realise that the key to the protection of concrete surfaces is the quality of the preparation of the substrate, as well as the use of an appropriate coating or coating system, depending on the required mechanical and chemical stresses, as well as the correct application of the coating.