Currently a combination of varied methods of both intermittent and continuous monitoring have to be employed in the integrity assessment of safety-critical heterogeneous structures such as reinforced-concrete pressure-vessels, buildings or bridges, and those methods vary from simple visual inspection to embedded vibrating-wire strain-gauge techniques. This paper presents ongoing work based on a concept that utilises comparisons of intermittent vibrational response measurements. The non-destructive method employed compares energy-signatures transmitted through a region of material to establish any differentials in response and it then assesses any change-of-state (CoS) from that behaviour observed.