The alternate efflorescence method was developed for addressing those samples that have low levels of gypsum that can cause false positive test results for samples that do not effloresce under normal applications. Research shows that heating gypsum in a moist environment causes the gypsum to decompose and become mobile. As documented in the report on ASTM C67 Efflorescence Alternate Test Method (pp 3-11 of this ballot appended below), as gypsum approaches 100C, it begins to rapidly decompose. It was found that by reducing the drying temperature to a range that is seen in normal applications, the amount of gypsum decomposition is greatly reduced, and the test results correlate more closely with real life efflorescence performance of the specimens.
The specimens that were used in the original work were stored at Bishop Materials Lab for a significant amount of time before being tested. Because of this, the drying temperature and moisture level of the samples at the beginning of the efflorescence test method was not evaluated or considered. It has since been found that specimens with a high moisture level and low gypsum content can effloresce during the initial drying step at the beginning of the test.
This ballot addresses the issue found with the initial drying temperature. The initial drying procedure was not changed which causes an issue if the test samples are wet at the beginning of the test. The initial drying can cause the samples to effloresce before the testing is started due to the decomposition of gypsum. This ballot proposes changing the initial drying process to the same procedure as the final drying procedure in the alternate method.
Developed by Subcommittee: C15.02
Staff Manager: Krista Robbins
Date Initiated: 02-10-2022
Technical Contact: Michael Walker
Ballot: C15 (22-04)
Status: In Balloting