New directions in concrete health monitoring technology

The NSF-sponsored Center for Advanced Cement-Based Materials is actively in volved in research aimed at the development of technologies for health moni toring and nondestructive evaluation of the concrete infrastructure. This p aper summarizes pertinent research performed at the center. Basic findings from several new laboratory-based nondestructive evaluation techniques for concrete are reported. The described techniques are based on measurements o f mechanical waves that propagate in the concrete. First, ultrasonic longit udinal wave (also called the L-wave or P-wave) signal transmission (attenua tion) measurements are shown to be sensitive to the presence of damage in t he form of distributed cracking in concrete. Next, experimental procedures that enable practical one-sided wave signal transmission measurements to be performed on concrete structures are described. The utility of the signal transmission measurement is demonstrated by two experimental test series; t he depths of surface-opening cracks in concrete slabs are estimated and the extent and nature of autogenous healing in concrete disks are studied. Fin ally, an approach by which fatigue-induced damage in concrete structures is nondestructively monitored is described. Vibration frequencies are shown t o be sensitive to the presence of fatigue-induced cracking in concrete spec imens; changes in the vibration frequency of a concrete specimen during fat igue tests are related to the remaining fatigue life of the test specimens.