The watertight concrete composition is characterized by its high resistance to water penetration. Water impermeability is determined by its capillary porosity. The decisive factors for capillary porosity are the water/cement ratio, as well as the content and type of cement. In order to reduce the water content of the mixture, special chemical additives are added, while improving its workability. It is recommended to use puzzolan or latent hydraulic mineral additives in order to bind chemically soluble compounds.
To reduce the risk of chemical attack, preliminary soil and water studies that are in contact with the structure are recommended. In the BDS EN 206:2014+A1:2016/NA:2017 concrete standard, in the Environmental Impact Classes table 2 - Limit values for classes of chemical impacts from natural soil and soil water, chemical characteristics are specified, on which studies should be carried out.
To achieve a watertight structure, not only the concrete composition, but also its proper laying, compacting and aging should be taken into account.
In the contact areas between old and new concrete, water-stopping and water-repellent construction bands must be used. It is also necessary to provide for pouring of concrete elements and their maximum dimensions. This is done in order to reduce the risk of cracks in its inevitable contraction. As a rule, a 1:3 aspect ratio (a 3m x 9m element), which is particularly recommended for walls, can be accepted.