Thread:Glflegolas/@comment-26041296-20151009014248/@comment-4750818-20151009152659

This is based off research I did in a second-year analytical chemistry course.

And yes, the salt can damage the concrete over time. This is because the component of concrete that holds it together, cement, is mostly composed of CaCO3, which is insoluble in water. However, when salt is used for de-icing concrete, the following reaction can occur:

CaCO3 + 2Cl- <--> CaCl2 + CO32-

Keq=<<1

Unfortunately, the calcium chloride produced from this reaction is water-soluble. That means that the water produced from the melting ice starts to dissolve the concrete, and, even if the calcium chloride turns back into calcium carbonate almost immediately, it's lost its structural role; the re-formed calcium carbonate is simply deposited as a powder on the surface of the concrete, which washes off in the next rain or blows away.

So, the case of salt causing concrete to become rough is a case of reversible reactions. Although the equilibrium greatly favours calcium carbonate over calcium chloride, there is still sufficient reaction going on between the concrete and the salt to gradually destroy it over the years (this is particularly true when concrete is used in the ocean).

Although salt can damage concrete, acid rain is also a major factor. The calcium carbonate reacts with hydronium ion (the product when any acid is added to water) in the following manner:

CaCO3 + 2H3O+ --> Ca2+ + CO2 + 3H2O

(limestone and marble also undergo this reaction, but to an even greater extent, since they're made of almost pure calcium carbonate, while concrete contains about 75-80% aggregate)

Hope this answers your question!

Glflegolas (admin) Send a Messenger  15:26, October 9, 2015 (UTC)