| Concrete Experts International has extensive, world-wide experience with deteriorated concrete suffering
from acid attack caused by acid smoke, rain and exhausting gasses.
Diagnosing acid attack is an integrated part of our petrographic
analysis of concrete.
What is Acid Attack?
Concrete is susceptible to
acid attack because of its alkaline nature. The components of the cement
paste break down during contact with acids.
Most pronounced is the
dissolution of calcium hydroxide which occurs according to the following
reaction:
2 HX + Ca(OH)2
-> CaX2 + 2 H2O
(X is the negative ion of the
acid)
The decomposition of the
concrete depends on the porosity of the cement paste, on the
concentration of the acid, the solubility of the acid calcium salts (CaX2)
and on the fluid transport through the concrete. Insoluble calcium salts
may precipitate in the voids and can slow down the attack. Acids such as
nitric acid, hydrochloric acid and acetic acid are very aggressive as
their calcium salts are readily soluble and removed from the attack
front. Other acids such as phosphoric acid and humic acid are less
harmful as their calcium salt, due to their low solubility, inhibit the
attack by blocking the pathways within the concrete such as
interconnected cracks, voids and porosity. Sulphuric acid is very
damaging to concrete as it combines an acid attack and a sulfate attack.
Microscopic appearance
An acid attack is
diagnosed primarily by two main features:
Please to not hesitate to
contact CXI if you have some problems regarding acid attack or any other
deterioration mechanisms.
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