Impact Echo Testing

Impact echo testing uses short-duration mechanical impacts to generate stress waves that propagate through concrete and reflect from internal interfaces, delaminations, voids, honeycombing, and the far surface of the element. A transducer adjacent to the impact point records the reflected waves, and frequency analysis identifies the depth and nature of reflecting interfaces. This provides a reliable method for detecting hidden defects that cannot be seen from the surface and may not be detectable by GPR.

The technique is particularly effective for assessing concrete bridge decks, car park slabs, and building floor slabs where delamination between the reinforcement layer and the surface, often caused by corrosion-induced expansion, is the critical defect. Delamination planes that are invisible from both surfaces produce characteristic frequency shifts in the impact echo response, allowing TRSC to map the extent of delamination across a slab without coring or destructive investigation.

Impact echo also provides an independent method for measuring concrete element thickness from one side only, which is valuable for verifying as-built dimensions when access to both faces is restricted. The measured thickness is compared with design drawings (where available) or used directly in structural capacity calculations. Accuracy is typically ±3% of actual thickness for well-characterised concrete.

TRSC uses impact echo as a complementary technology alongside GPR, UPV, and half-cell potential mapping. Where GPR identifies reinforcement layout and half-cell mapping identifies corrosion zones, impact echo identifies the resulting structural consequence, whether corrosion has progressed to the point of delamination. This integrated approach ensures that intervention decisions are based on actual structural condition rather than inferred condition.