How to Test Concrete Structures Using Impact Echo method

Impact Echo is a non-destructive testing (NDT) method for structural integrity testing of concrete and masonry structures. This method was first developed to locate flaws and voids in plate-like concrete structures (such as bridge decks, retaining walls, and slabs). Impact-echo test basically works based on the generation of stress waves through a short-duration mechanical impact on the surface of concrete element. Followed by the mechanical impact, reflection and refraction of stress waves from internal interfaces (concrete-crack, concrete-air, concrete-rebar) or external boundaries (echo) is recorded through a proper transducer (e.g. piezoelectric accelerometer or geophone). The reflectogram is analyzed in either time-domain or frequency-domain.
The test method was first adapted in 1998 as a standard test procedure by the American Society of Testing Materials (ASTM C 1383) “Standard Test Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using the Impact-Echo Method.”
The impact-echo method can be utilized for Thickness Evaluation, Localization of Subsurface Defects, and Crack Depth Estimation in various types of concrete elements such as:
heritage/new buildings (retaining wall, masonry wall, floor slab, column, beam), bridges & culverts (bridge deck, bridge abutment, bridge pier, culvert walls), dames (water-retaining wall, dam crest, spillway, sluice way),
tunnels (tunnel lining segments), and offshore structures (sea walls).
How Does Stress Waves Propagate within Concrete?
When a short-duration impact is applied on the surface of concrete, the applied disturbance (stress) propagates through the member. The wave propagation happens through propagation of three main types of waves: primary (compression) waves or P-waves, secondary (shear) waves or S-waves, and Rayleigh (surface) waves or R-waves. While P- and S- waves travel into the concrete along expanding spherical wave fronts, R-waves travel away from the impact point along the “near-surface”. As P- and S- waves propagate within concrete element, they get reflected by internal flaws or external boundaries. The impact-echo testing is commonly looking into reflection of P-wave, since the P-waves causes much larger displacement when compared to displacement due to other waves forms (e.g. S-waves).
How Does Impact Echo Work?
The concept of the Impact-Echo test is illustrated in the Figure blow. An Impact-Echo test system is mainly composed of three main components: an impactor, a transducer, and a data logging system. The impact source is a small steel ball of different sizes capable of producing varying short-duration impacts. To conduct a test, an impulse is applied by the impactor at one-single point on the surface of concrete element. The resulting stress waves (P-wave, S-wave, and R-wave) propagate into the concrete medium in all directions; and travel back and forth between the test location and all existing boundaries and interfaces. The arrival of these echos on the surface of concrete element induces displacement.
Because of the high propagation speed and amplitude of P-waves, surface displacement caused by the arrival of reflected waves is dominated by the displacements caused by P-wave arrivals. The subsequent displacement associated with P-waves is measured using a sensitive transducer located near the impact point. The transducer converts the measured displacement into an analog signal of amplitude vs. time, called “waveform”. The waveform is recorded by a data logging system, which then proceeded for data analysis in either time-domain or frequency-domain.
Applications of Impact Echo Method
Impact-Echo is a very practical testing solution with a wide range of applications in condition assessment of concrete structures. The test can be used to:
1. Estimate Thickness of Concrete Elements
Impact Echo is widely used by engineers to assess the thickness of concrete elements. This is specially important in concrete elements with one-side access (Single Side Access), such as:
Tunnel linings: Thickness measurement is critical in the QC process for tunnel linings. It is also an important parameter for structural evaluation purpose.
2. Locate Sub-Surface Defects
IE can be used to assess certain defects in concrete elements. IE can pinpoint the following defects:
Delamination: IE method can be used for detection of subsurface progressive defects such as delamination due to corrosion of steel reinforcement in concrete bridge decks, parking garage slabs, and concrete tanks.
Honeycombing: IE is a great tool in the Quality Control and Quality Assurance of new construction. IE can be used to localize honeycombs in concrete.
Flaws/Voids/Debonding: IE can be utilized in different structural members in order to determine the location and depth of internal flaws (e.g. flaws and voids) and debonding in plain, reinforced, and post-tensioned concrete structures
3. Estimate Crack Depth

[@irshad_khan_civil]

hi professor thanks for guidance sir i am studying impact echo for my master research professor i want to know what's new i can add to this in order to write a good proposal for research? currently studying in china.

[@BGIS2000]

Thanks for sharing your video. Is there any standard requirement in the industry for tgis type of units? Do you also use proceq for finding depth of crack, void etc?