A Kinetic-Based Method for Interpreting ASTM C 1260

Abstract

Abstract 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.