Q. We're designing a concrete structure in Egypt, and I received test results for the aggregate to be used in the concrete. The report lists chloride and sulfate content, but I don't know how to evaluate these numbers because ASTM C 33, "Standard Specification for Concrete Aggregates," doesn't give limits for them. Where can I get information about permissible levels of chlorides and sulfates in coarse and fine aggregates used in concrete?

A. "Aggregates in Saudi Arabia: A Survey of Their Properties and Suitability for Concrete" was published in a 1987 issue of the RILEM publication Materials and Structures. It quotes the following maximum limits from the Ministry of Public Works and Housing's General Specifications for Building Construction:

  • 0.1% for aggregates

  • in reinforced concrete

  • 3

  • maximum value=0.4%

Reader Response:

Your answer regarding permissible levels of chlorides and sulfates in aggregate might be OK for Saudi Arabia but certainly not for most of the United States. A limit on NaCl is meaningless: Does one measure sodium, or chloride, or both? Don't other chlorides count?

What if both the coarse and fine aggregates contain chloride?

(If so, you could have nearly 2 pounds of chloride per cubic yard, or 0.4% chloride by weight of cement, enough to reject the concrete even if all other components contain no chloride at all.) For the SO3 limit, 0.4% SO3 by weight of concrete may be equivalent to about 3% by weight of cement, doubling the equivalent SO3 in the portland cement and effectively surpassing any ASTM C 150 limit. For U.S. designers, call on your friendly cement chemist for advice. Mine is: It depends on the type of chloride and sulfate in the aggregate, so have it analyzed.

William G. Hime
Erlin Hime Associates,
Northbrook, Ill.