Local cavity injection and crack injection is part of common activities related to concrete in the building industry. Correctly chosen injection material type depending on the environment and and type of crack of the concrete structure and compliance with the technologic procedure are the basis for effectively implemented injection. We use polymer hardening and hydraulic hardening injection materials. Choice of correct injection material depends on mechanical properties at given temperature.
Humidity of concrete is an important factor at the choice of injection material. Injection materials react to water in the process of hardening differently. Categorization of humidity state: dry, humid and water permeable (the degree of permeability is categorized according to the amount of water flowing through the deformed site depending on the pressure). Dry cracks and cavities are places where it is impossible to detect the presence of water. Humid cracks and cavities are places which show change of colour hue in the area of crack or cavity (visible water spout). With water flowing in drops it is flowing of water without pressure (water permeable without pressure). With flow of water in an uninterrupted stream or water splashing through the crack, we assess the site as a water flow under pressure (water permeable under pressure). We primarily assess the appearance of the surface or structure and its malfunctions. In certain cases, we perform sampling by core boreholes.
An important factor at the choice of injection material is viscosity of the mixture. With polymer injection materials (reactive resins) we can, according to viscosity, execute crack injections with width from 0.1 mm. Artificial resins (with regard to capillary rising) are able to penetrate into the roots of cracks and their branching. Mineral suspension and its use is limited to injection of wider cracks (depending on the structure of binder particles). It is impossible to ensure sealing of cracks in this way, because with mineral suspensions it is not possible to fill cracks up to their roots.
Elastic injection materials on the basis of polyurethane (PUR) belong to sealing injections with the widest range of use. Cracks or cavities (regardless of their humidity status) can be sealed with elastomer elastic and porous resins with low viscosity. In the case of variable crack widths sealing injection can be executed with elastic products with a viscosity of about 100 mPa. In some cases of unacceptable injection pressure we use resins with higher viscosity (the same crack widths with higher pressure).
Cracks with width from 0,1 mm can be sealed with a low-viscosity system. Viscosity of materials in case of all polymer injections quickly increases after mixing of all compounds. Fast foaming resins on the same material basis (SPUR) are used to temporarily stop the pressure water seepage. After their use a sealing injection with a lasting effect must also be carried out to close their pores.
Elastomer foams react very quickly and they need ony a few seconds (or minutes) to react with water.
Aj pri dokonale realizovaných stavebných prácach dochádza pri betónových konštrukciách k tvorbe nežiadúcich trhlín. Úspešná injektáž poškodenej štruktúry a správny výber injektážneho materiálu zaručujú trvalú opravu a utesnenie poškodeného miesta konštrukcie.