Confusion over freeze-thaw testing

After the publication of the article, “The Crowning Touch: Concrete Tile Roofs Combine Esthetic Expression with Sustainable Performance” by Rich Thomas, LEED AP, and Steven H. Miller, CDT, in the September 2017 issue of Construction Canada, we received a letter from one of our readers.

Bob Merchant, MAAA (retired) wrote:

I was the Western Regional Architect for Parks Canada for 20 years before I retired, so I have quite a bit of experience with materials and construction issues in difficult Canadian climates. I found the article on concrete roofs very interesting, but potentially very misleading.

Parks Canada installed several concrete tile roofs on projects in the early 1970s. The product was Alberta-produced and promised many of the advances noted in the article, particularly the fire protection advantages in very-high-risk forest fire zones of Banff, Jasper, Yoho, Kootenay, Glacier, Waterton, and Revelstoke. The article notes at one point the need for freeze-thaw testing, but does not provide details of what standard other than ASTM C1492, Standard Specification for Concrete Roof Tile, should be applied.

In the high moisture and frequent freeze-thaw environment of Lake Louise in particular, the concrete tiles installed in 1970s crumbled and turned to sand within five to eight years—similar deterioration occurred at less-sensitive sites in other Parks in longer time frames. These were roofs placed on kiosks, staff housing, visitor centres, and public washrooms.

ASTM C1492 requires 50 cycles freeze-thaw testing by Test Method C67, Test Methods for Sampling and Testing Brick and Structural Clay Tile, for severe weather areas. Note that 95 per cent of Canada is considered “severe weather” by the ASTM definitions. Parks Canada found the Test Method C67 testing may not truly represent the severity of weather found in Canada, and that caution is needed in using concrete-based roof tiles in our climate.

The article outlined many advantages of the product, but I fear it glossed over the very real freeze-thaw weakness experienced in severe climate conditions.

For clarification, we reached out to the article’s authors. Thomas offered this response:

Mr. Merchant makes an excellent point about some materials that may pass the ASTM-required tests, but still may not be appropriate for climates with severe weather. While the ASTM standard exists to demonstrate a minimum acceptable performance level, it may not be completely appropriate for extreme conditions, such as regions of North America where freeze/thaw cycles are frequent. For this reason, testing at the manufacturer with which I am employed goes far beyond the ASTM standard.

As Mr. Merchant stated, ASTM C1492 only requires 50 cycles of freeze-thaw testing. With its long history of manufacturing concrete and clay tile, the roofing tile manufacturer has found weather can cycle from freezing to thawing and back many times over a single winter season in certain regions, reaching 50 cycles in just a few years. Therefore, it tests freeze-thaw for 500 cycles—10 times the ASTM standard—and only regards its products as being freeze/thaw resistant for such climates after passing the ASTM C67 test for 500 cycles. Specifiers with concerns about freeze-thaw resistance of roof tile should contact tile manufacturers for details of their testing regime.

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