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A proposed kinetic-based method for interpreting ASTM C 1260 test results is introduced that appears capable of overcoming some of the shortcomings currently encountered using a percent expansion criterion for defining potentially reactive aggregate. The method is based on nucleation and growth or phase transformation reaction kinetics where the percent expansion is exponentially related to a power of time. Solving the logarithmic form of the kinetic equation by a least-squares fit yields two parameters, lnk and M, where lnk is the intercept and M is the slope of the regression line, which can be used to determine potential reactivity. A plot of M versus lnk yields two separate domains—one containing reactive aggregate and one containing innocuous aggregate. Values of lnk < -6 are associated with innocuous aggregate. The method successfully differentiated between several reactive aggregates with 14-day expansions of less than 0.1% as reactive and indicated that one aggregate with a 14-day expansion of 0.278% was innocuous. The method also appears promising with regard to determining effective levels of pozzolans and other admixtures for mitigation of ASR reactive aggregate.
South Dakota Department of Transportation, Pierre, SD
FMC Corporation, Bessemer City, NC
Federal Highway Administration, Denver, CO
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