Reliability-Based Design for Feeeze-Thaw Concrete

by J. M. Pitt, Iowa State Univ, Ames, United States,
M. Seshadri, Iowa State Univ, Ames, United States,
D. L. Covey, Iowa State Univ, Ames, United States,

Abstract: Observation of pavements in Iowa shows results from the test for freezing and thawing of concrete, ASTM C-666, is not always consistent with field performance. Similar concrete made with coarse aggregates from different sources have the same durability factor but demonstrate service lives differing by as much as ten years. ASTM C-666 was intended to provide a relative measure of concrete serviceability and makes no attempt at predicting service life, particularly when deicers are used. This paper presents preliminary research aimed at applying reliability analysis to estimate time to failure of concrete subject to frost action. Four carbonate aggregates with service lives ranging from ten to thirty years were tested by embedding randomly selected single stones in the neck of dog-boned shaped mortar briquettes of mortar proportioned to represent paving concrete. These specimens were subjected to cyclic freeze-thaw in water and deicing brine until failure. Failure was defined as rupture by gravity when specimens were lifted for inspection. Failure was observed to occur by one of three mechanisms: the aggregate itself, the bond between aggregate and mortar phases, and the mortar itself. When tested in water, failure tended to be aggregate dependent, except in one case where the aggregate outlasted the mortar. When tested in deicers, failure occurred at the bond, regardless of aggregate type. Test interpretation involves plotting cumulative failures vs. the number of cycles to failure, which gives a failure rate and expected number of cycles to failure. General trends include a dormant period before any failures occur, and varying rates of failure depending on aggregate source and test fluid. Deicers reduced expected cycles to failure and increased failure rate.

Subject Headings: Failure analysis | Concrete | Aggregates | Freeze and thaw | Mortars | Material failures | Deicing | Concrete pavements | Iowa

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