Rapid evaluation of alkali–silica reactivity of aggregates using a nonlinear resonance spectroscopy technique

A new nonlinear acoustic technique — Nonlinear Impact Resonance Acoustic Spectroscopy (NIRAS) — is developed and used to characterize the alkali-reactivity of different aggregates. Cementitious materials such as mortar and concrete exhibit a hysteretic and nonlinear elastic behavior in their constitutive relations. This hysteretic nonlinearity is associated with interfacial debonding between the different constituents, and it changes with the progress of damage such as that induced by the alkali–silica reaction (ASR). One of the consequences of the hysteretic nonlinear property of these materials is the decrease in resonance frequencies, with increased excitation amplitude. This shift in the resonance frequency as a function of the material nonlinearity parameter can be used to directly characterize the damage state of the material. This research tracks the variation of the nonlinearity parameter during a standard accelerated mortar bar test (AMBT) to assess the potential for alkali-reactivity of aggregates. The results show that the NIRAS technique is more sensitive than conventional linear acoustic methods and is capable of accurately characterizing the reactivity of the aggregates examined. Furthermore, the results show advantages over standard expansion measurements for differentiating various aggregates having similar levels of reactivity, particularly at early test ages. These changes in the nonlinearity parameter are benchmarked against results from a petrographic analysis. Thus, the proposed NIRAS is a promising technique for the rapid identification of alkali-reactive aggregates.