Sulfate Attack on Concrete - Chapter 9 potx

9 Assessment of cement and

concrete performance under

sulfate attack

The assessment of the expected performance of cement and concrete to be

exposed to sulfates may be based on tests or predictions or both. The purpose

of assessment is to avoid concrete damage or shortened life due to the use of

an inappropriate binder or concrete mixture. An ideal test should be as simple

as possible, yield results within a short period of time, and present reliable

information about the concrete performance that may be expected under

field conditions.

Basically, for convenience, two different types of sulfate attack may be

defined, with the testing procedure and method of evaluation of the test

results being different for each:

• In internal sulfate attack, the deleterious action of sulfates is brought about

by an excessive SO3 content in the binder or, less often, in the aggregate

used. Under these conditions the whole volume of the material is affected

more-or-less uniformly. The extent of damage depends on the composition

of the mixture, the curing conditions, and the environment to which the

object of concern is exposed.

• In external sulfate attack, the sulfates responsible for the damage migrate

into the concrete from an outside source. Under this condition, an altered

layer resulting from the action of sulfates develops on the surface in con￾tact with the sulfate-containing water or soil, while as the material in

deeper regions stays unaffected. The performance of the concrete will

depend not only on the binder employed, but to a great degree also on

the mixture proportions and the resultant permeability to the sulfate

solution.

The following facts have to be considered in assessing the expected

performance under sulfate attack:

• A cement may perform differently if exposed to different forms of sulfate

(e.g. alkali sulfates, magnesium sulfate, sulfuric acid, etc.).

© 2002 Jan Skalny, Jacques Marchand and Ivan Odler