Meeting the grade

Masonry Construction, Jan, 2003 by Norbert V. Krogstad

Q I received a test report from a brick manufacturer on a unit with an average saturation coefficient of 0.83. The average maximum water absorption by 5-hour boiling was 11%. However, the manufacturer certified that these brick units met ASTM C 216 Grade SW.

Is this certification possible?

A It appears that these units do not meet the requirements for Grade SW listed in ASTM standard specification C 216. The average saturation coefficient exceeds 0.78, which is the maximum value for Grade SW. The saturation coefficient is the ratio of 24-hour cold water absorption to 5-hour boiling absorption. This ratio provides an indication of the available void space within the pore structure of the brick unit to accommodate freezing expansion.

The absorption alternate in ASTM C 216 states that the saturation coefficient does not apply if the units meet the strength requirements and the 24-hour cold water absorption of each unit if a random sample of five brick does not exceed 8%. The strength requirements for SW are an average 3000-psi minimum compressive strength for five brick with an individual 2500-psi minimum compressive strength.

The average value of the cold water absorption is determined by multiplying the average maximum water absorption by the average saturation coefficient. The result is a value of 9.1, which exceeds 8%. Even if the average value by this calculation was slightly less than 8%, it is likely that at least one of the five brick in the random sample would exceed 8%, thereby eliminating the use of this alternate.

These brick units, however, may still be classified as Grade SW if a sample of five brick units meets the strength requirements and passes the freezing and thawing test described in the Rating Section of the Freezing and Thawing test procedures of ASTM Test Method C 67. The brick in this test are subjected to 50 cycles of freezing and thawing of saturated units.

Require the brick manufacturer to provide test reports, preferably less than 1 year old, showing that the units successfully passed the requirements listed in the ASTM C 67 freeze/thaw test. Test reports that are more than 1 year old may not be representative of the units currently being produced because over time, the clay composition, firing times, and temperatures may vary.