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Development of shrinkage limits and testing protocols for ODOT high performance concrete.
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  • Abstract:
    ODOT has observed varying degrees of cracking in their concrete structures. Cracking of high performance reinforced

    concrete structures, in particular bridge decks, is of paramount concern to ODOT. Cracking at early ages (especially within

    the first year after placement) results in additional costs and a significant maintenance burden to ODOT. The causes behind

    cracking in high performance concrete are well known and documented in the existing literature. However, appropriate

    shrinkage limits and standard laboratory/field tests that allow proper criteria to ensure crack-free or highly crackingresistant high performance concrete are not clearly established either in the technical literature or in specifications. The

    purpose of this research was to provide shrinkage threshold limits for specifications and to provide a robust test procedure

    that allows easy determination of compliance with specified threshold limits. It has been shown that the “restrained ring”

    tests are the most comprehensive accelerated laboratory tests to accurately identify cracking potential. In addition,

    acceptable correlation between the ring test and the field test has been observed and documented. However, a simplified

    yet robust test procedure is in demand from materials suppliers and Departments of Transportation. Analysis of data

    obtained from this research project showed that the ratio of free shrinkage to shrinkage capacity (theoretical strain related

    to tensile strength and modulus of elasticity), referred to as a cracking potential indicator (CPI), was a promising

    assessment of cracking resistant performance. In this way, only the free shrinkage test (ASTM C157) and basic mechanical

    properties (ASTM C39, C469 and C496) are required to assess cracking risk of candidate high performance concrete

    mixture designs. This research investigation showed that a CPI less than 3.0 indicated low cracking risk when correlated to

    standard restrained ring tests. For ODOT HPC concrete bridge deck mixtures, a limit of 450 microstrain for free shrinkage

    at 28 day from initiation of drying is recommended to achieve satisfactory cracking resistance. Correlation to field

    experience is also recommended if these recommended thresholds/limits are adopted by ODOT.

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