Hydrophobic cement contains admixtures which decreases the wetting ability of cement grains. The usual hydrophobic admixtures are acidol, naphthenesoap, oxidized petrolatum, etc. These substances form a thin film around cement grains. Hydrophobic cement is obtained by grinding portland cement clinker with a film-forming substance such as oleic acid in order to reduce the rate of deterioration when the cement is stored under unfavourable conditions.
When water is added to hydrophobic cement, the absorption films are torn off the surface and they do not in any way, prevent the normal hardening of cement. However, in initial stage, the gain in strength is leas as hydrophobic films on certain grains prevent the interaction with water. However, its strength after 28 days is equal to that of ordinary Portland cement.
When hydrophobic cement is used, the fine pores in concrete are uniformly distributed and thus the frost resistance and the water resistance of such concrete are considerably increased.
Oxygen diffusion coefficient of Hydrophobic cement
The oxygen diffusion coefficient through hydrophobic cement-based materials fully immersed in water are determined by potentiostatic measurements on concrete and by the use of a diffusion cell on cement pastes and mortars. The obtained results show that very high oxygen diffusion occurs through cement paste, mortar and concrete made with hydrophobic admixture as opposed to negligible diffusion through the reference cement matrix without admixture. Moreover, the oxygen diffusion coefficients measured through hydrophobic cement matrices immersed in water are comparable with those reported in literature for unsaturated cement materials in air. These experimental results appear to confirm that oxygen dissolved in water directly diffuses as a gaseous phase through the empty pores of a hydrophobic cement matrix. This could explain the severe corrosion of steel reinforcement embedded in cracked hydrophobic concrete immersed in an aqueous chloride solution observed in various work.
Advantages & Disadvantages of Hydrophobic cement
The advantages of Hydrophobic cement are as follows:
- This cement can be used in the construction of water structures such as dams, spillways, or other submerged structures.
- The strength of this cement is same as that of ordinary portland cement after 28 days.
- It can be used in cold weather conditions as well.
The disadvantages of Hydrophobic cement are as follows:
- Cost is high as it is very expensive.
- Application is labor intensive.