Q: What is the role and the danger of carbonation in concrete?
A: Basic carbonation reactions in concrete
Phase I Normal concrete pores contain
Water and free lime
H2O and Ca(OH)2
Phase II When carbon dioxide in the air enters the concrete pores carbonic acid is formed
Carbon dioxide + water = Carbonic acid
CO2 + H2O = H2CO3
Phase III Carbonic acid neutralizes the free lime and forms a neutral pH solid calcium carbonate
Free lime + carbonic acid = Calcium carbonate + water
Ca(OH) + H2CO3 = CaCO3 + H2O
(high pH) + (low pH) = (neutral pH)
A small drop in pH dramatically potentiates the destructive nature of chlorides present within concrete. In concrete having a pH of 12 to 13, corrosion of embedded steel begins when chlorides are present at 7,000 to 8,000 parts per million. However, if the pH is lowered to a range of 10 to 11, the threshold for chloride initiated corrosion is a significantly lower 100 ppm or less. In this way carbonation greatly accelerates the deterioration and shortens the service life of steel reinforced concrete.
Max M., Manager, Surtreat Holding, LLC contact
Surtreat Holding, LLC 437 Grant Street, Pittsburgh, PA 15219; 412.281.1202, official website www.surtreat.info
Max Merzlikin, Surtreat Holding, LLC 2015