Nonlinear Acoustic Technique of Time Shift for Evaluation of Alkali-Silica Reaction Damage in Concrete Structures

Recent studies have indicated that nonlinear acoustic techniques appear to be promising for the detection and characterization of early microcracks produced by damage mechanisms like alkali-silica reaction (ASR). Most of the nonlinear acoustic techniques currently used are not suitable for field investigation due to their complicated implementation. A research program has been developed on the theory and application of a new nonlinear acoustic technique, named Time Shift (TS), for field experiences. The technique is based on the wave interaction between high-frequency/low-amplitude probe waves and low-frequency/high-amplitude pump waves generated by an impact. Previously, this method has been validated in the laboratory on small specimens. To validate TS for further field applications, tests were conducted in a laboratory test setup involving three large reinforced concrete slabs in which the damage associated with ASR was monitored over time. The required pump waves were produced in the lab by a hydraulic actuator, which is a simulation of field traffic loads. Indeed, traffic load is a potentially suitable source for generating the pump waves in concrete structures, which may dispel the difficulty of perturbation of concrete elements in the field. Experimental results show that this approach for applying the TS method appears to be reliable for detecting ASR damage over time in reinforced concrete structures.