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
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,