Deterioration of Concrete and Remedial Measures

Decomposition of Concrete Depends on:

1. Porosity of concrete
2. Concentration of the acid
3. Solubility of the Acid Calcium Salt
4. Fluid Transport through the concrete, its temperature and pressure

Remedial Measures:

Following are some remedial measures to increase the resistance of concrete or prevent it from acid attack:

1. Calcium silicates can be used to fill the pores and decrease the permeability. This can be done by treating calcium hydroxide with diluted sodium silicate (also known as Water-Glass)
2. Pores can also be filled by treating Calcium Hydroxide with Magnesium Fluosilicate followed by the formation of Colloidal Silicofluoric Gel to withstand acid attack
3. Allowing the concrete to dry before exposure causes the formation of a calcium carbonate film produced by the action of CO₂ on lime. This film blocks the pores and reduces the permeability of the surface layer. Thus a precast concrete is appreciated.
4. The above method is not a permanent solution. For more protection the concrete is subjected in vacuum to silicon tetra fluoride gas which reacts with the lime as follow.

2Ca (OH)₂ + SiF₄ ------> 2CaF₂ + Si (OH)₄

This treatment can only be applied to precast concrete, which is then known as Ocrat-Concrete.

Surface treatments:

1. Coal-Tar Pitch
2. Bituminous Paints
3. Epoxy Resins

Degradation of Concrete