Water is the source of all life as well as a scarce commodity. Clean drinking water should therefore be protected against contamination, while waste water must be treated before being released into a discharge system. The waste water itself as well as the treatment measures undertaken represent an exposure to chemicals for concrete surfaces.
Through sensible planning and proper concrete design concepts, the surfaces can be designed for durability. Concrete’s resistance to chemical attack is nevertheless limited, therefore surface protection systems must be considered in case of heavy exposure.
Chemical resistance in this case signifies resistance to corrosion and erosion of concrete. Alongside known types of spalling attack such as frost (with and without de-icing agents), ASR (Alkali-Silicate-Reaction), sulfate exposure and mechanical surface abrasion, in wastewater treatment facilities particularly, chemical and solvent aggression is also prevalent. The water treated in such facilities, however, varies too greatly to describe the attack on concrete surfaces as uniform. Decisive in addition to the general quality of the water is also its hardness (°fh or °dH).
On one hand the surface of the concrete is attacked by a cocktail of chemicals, while on the other mechanical stress (e.g. high pressure cleaning) also occurs at the surface. Thereby fines are washed out that have already been dissolved, but remained adhered within the concrete structure. This entire process is additionally accelerated by softened water (hardness < 15°fh or 8.4°dH) and the reduction of the pH value on the surface of the concrete (e.g. in biofilm). The concrete design, curing and foremost the cleaning of the surface must be adapted to the respective exposure.
While for resistance to mechanical cleaning a hard and compact concrete surface is considered optimal, chemical cleansing is best tolerated by concrete with a high calcite content. Concrete’s chemical resistance is limited. If exposure limits are exceeded, concrete surfaces can only be durably protected with appropriate coatings.
