Recent Work on Autoclave Methods in the United States

Recent Work on Autoclave Methods in the United States

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RJ Lee Group’s Eric Giannini presented at the 2018 spring meeting of RILEM TC 258-AAA on recent and current research activities in the United States on autoclave methods for alkali-silica reaction (ASR) potential of concrete aggregates. The research builds upon work performed primarily in Canada and Japan during the 1980s and 1990s, and includes both an autoclaved mortar bar test and an autoclaved concrete prism test.

In 2010, Dr. Giannini began research on the autoclaved concrete prism at The University of Texas at Austin with funding from the Portland Cement Association. Collaboration and equipment purchases across seven different laboratories was enabled by additional funding support from The University of Alabama, Federal Highway Administration, Wyoming Department of Transportation (WYDOT), and US Army ERDC. The latter of which is supporting an extensive multi-laboratory study of the autoclaved mortar bar test.

The two autoclave methods make use of similar mix designs, specimen molds, and measurement apparatus as those utilized for the ASTM C1260 and ASTM C1293 tests. However, these use greatly increased alkali loading and saturated steam pressure so that aggregates can be tested for ASR potential in a very short period of time. As a result, the autoclave tests are completed in less than one week from the time of mixing (including a 48-hour pre-autoclave curing period), compared to 16 days for ASTM C1260 and one year for ASTM C1293. Key aspects of the tests are highlighted in the table below, comparing the autoclave tests to ASTM standard tests. As with ASTM C1260 and ASTM C1293, aggregate reactivity is determined by measuring expansion of the specimens during the test.

Interest in further investigating autoclave methods remains strong in the US, with WYDOT funding two projects at the University of Wyoming led by Dr. Jennifer Tanner, and the potential for follow-on research at US Army ERDC. The relative speed of these autoclave tests continues to drive interest, and they generally exhibit positive agreement with the ASTM C1260 and ASTM C1293 standard tests for classifying aggregate reactivity for a wide range of reactive aggregates, and a few non-reactive aggregates tested to date.

However, before the autoclave methods can themselves be standardized, there remains open questions about the relative contribution of ASR vs. other, as-yet unidentified mechanisms, to the measured expansions of test specimens. The use of pressurized high-temperature steam to accelerate the development of ASR may also induce other causes of expansion in the specimens. Additional research may help confirm whether the primary cause of expansion in the test is ASR. More testing of non-reactive and borderline/moderately-reactive aggregates is also needed to gain greater confidence in the viability of these tests to distinguish between reactive and innocuous aggregates.

RILEM TC 258-AAA, Avoiding Alkali-Aggregate Reactions in Concrete – Performance Based Concept  began its activities in 2014. The committee is working to provide state-of-the-art guidance on the use of laboratory testing to evaluate the ASR potential of concrete mixtures for new construction, drawing upon the expertise and contributions of committee members from over 15 countries. In-person meetings are held twice yearly, and foster the international collaboration and knowledge exchanges that are key to the committee’s mission. The photo below shows the participants at the 2018 spring meeting of the committee in Reykjavik, Iceland.