Conventional concrete used in the construction of a waste water treatment plants has limited resistance to attack from the cocktail of chemicals to which it is exposed.
By adapting the concrete mix design to increase the watertightness and optimize the binder matrix, the resistance and therefore the durability of the concrete can be significantly improved. Impermeability of concrete against water is determined by the impermeability of the binder matrix, i.e. capillary porosity.

The critical factors that affect capillary porosity are, water/binder-ratio, content of SCM (secondary cementitious material) and type of SCM (pozzolanic or latent hydraulic materials).
Using a powerful superplasticizer such a Sika®ViscoCrete® reduces the water/binder-ratio. This decreases the volume and continuity of the capillary pores within the concrete matrix, whilst ensuring a highly workable concrete that will support placement and compaction.
The remaining capillary pores still provide a potential path for water to migrate through the concrete. With the addition of a water resisting admixture from the Sika® WT range these remaining migration paths are consequently blocked and provide effective protection even at 10 bar (100 meters head of water).

The waste water and the treatment process expose the concrete surfaces to aggressive chemicals. Through sensible planning and proper concrete design, the surfaces can be designed to be highly durable. Concrete’s resistance to chemical attack is nevertheless limited; if high exposure is foreseen it is advised that the concrete be protected by the application of a surface protection system. The concrete may also be designed to include SikaFume® a product that supports the additional densification of the binder matrix. As with all concrete that is expected to perform in an aggressive environment proper curing of the concrete is essential and the use of Sika®Antisol® is recommended for this purpose.