Reinforcement
Can help locate the bars and qualitatively reconstruct their arrangement.
Technical guide · Methodology
Structural GPR
Investigating the inside of structural elements without demolition.
Ground Penetrating Radar applied to structural diagnostics uses high-frequency electromagnetic pulses to identify elements, discontinuities and variations in material properties inside concrete structures.
How GPR applied to structures works
GPR is an indirect, non-invasive method. An antenna sends short electromagnetic pulses into the concrete; their propagation depends on the electrical properties of the material crossed.
When the signal encounters an interface between materials with different electromagnetic properties, part of the energy is reflected and received by the antenna. The response recorded along the profile is processed and represented as a radargram, whose interpretation requires comparison with known geometry, materials and conditions of the element.
01
Antenna
Emission and reception on the surface of the element.
02
Electromagnetic pulse
High-frequency signal sent into the material.
03
Propagation
Path conditioned by electromagnetic properties.
04
Reflector / discontinuity
Variation encountered in the investigated volume.
05
Reflection
Part of the energy returns to the surface.
06
Radargram
Representation of signals along the acquired profile.
07
Interpretation
Technical reading correlated with known geometry and conditions.
What it can reveal
The evidence depends on electromagnetic contrast, the frequency used and acquisition conditions. The radargram provides indications to be interpreted: it does not automatically diagnose corrosion, moisture or deterioration.
Metallic elements
Can reveal inserts, ducts or other elements with strong electromagnetic contrast.
Voids and cavities
The response may indicate volumes with properties different from the surrounding concrete.
Honeycombing and discontinuities
Local signal variations may suggest areas to investigate further with targeted checks.
Stratigraphy and variations
Can help distinguish interfaces, thicknesses and changes in internal configuration.
Possible anomalies associated with deterioration
The radargram may show variations to be interpreted together with other data, without automatic diagnosis.
Mapping reinforcement inside concrete
Metal bars produce recognisable reflections which, when acquisition geometry and signal quality are adequate, can help locate their position and qualitatively reconstruct their arrangement within the structural element.
Reading coordinated profiles allows the evidence to be organised spatially and supports the choice of areas in which to carry out subsequent checks, local tests or further investigation with other methods.
GPR or covermeter? Two methods with different functions
| Aspect | Structural GPR | Covermeter |
|---|---|---|
| Principle | Electromagnetic waves | Local magnetic or electromagnetic principle |
| Acquisition | Coordinated profiles and grids | Point measurements or local scans |
| Reporting | Radargrams and mappings | Position of reinforcement and measurement/estimate of concrete cover |
| Reading | Interpretation of internal configuration | Local verification of metallic elements |
GPR and the covermeter can be used in a complementary way when the objective of the survey requires it.
From a single scan to mapping
A traceable mapping requires a reference system with origin and longitudinal and transverse axes. Grid spacing and scan directions are chosen based on the expected size of the elements and the level of detail required.
Grid
Reference, origin, axes and spacing defined.
Scans
Longitudinal and transverse profiles.
Radargrams
Recording of the response along each profile.
Processing
Corrections and treatment consistent with the survey.
Mapping / interpretation
Spatial correlation of evidence.
Which factors influence the result?
Measurement conditions
- Antenna frequency and configuration
- Dielectric constant of the material
- Electrical conductivity
- Moisture content
- Signal attenuation
- Geometry of the element
- Depth of targets
- Density and arrangement of reinforcement
- Surface conditions
Materials with high conductivity can rapidly attenuate the signal and reduce the depth that can be investigated. Rapid attenuation may be associated with different conditions and does not, by itself, constitute a diagnosis of moisture, corrosion or deterioration.
How is a structural GPR survey designed?
The survey configuration is not standard: frequency, grid, directions and processing procedures must be defined starting from the diagnostic question and the element to be investigated.
Defining the objective
Clarifying which information must support the technical decision.
Choosing the antenna
Balancing resolution, depth and characteristics of the element.
Defining the reference system
Establishing origin, axes and coordinate system of the survey.
Grid design
Defining spacing and directions based on the scale of the targets.
Acquisition
Collecting traceable profiles consistent with the survey plan.
Processing
Applying appropriate procedures without separating the data from its context.
Interpretation
Reading reflections and anomalies considering geometry and material.
Reporting
Delivering results, limitations and indications useful for subsequent decisions.
When GPR can guide a tomographic survey
In specific campaigns GPR can provide preliminary information on internal geometry and the position of elements, helping to select the areas in which to further investigate the concrete's response using ultrasonic tomography.
This is an example of documented integration, not a mandatory procedure: methods and sequence must be chosen based on the diagnostic question.
Discover ultrasonic tomographyGPR
Location and geometry
Ultrasonic tomography
In-depth investigation
Data correlation
Integrated reading of information
Structural GPR on a viaduct
In 2019 Novatest conducted a diagnostic campaign on the Via Mario de Bernardi Viaduct, at Fiumicino Airport. GPR was used to qualitatively define the arrangement of the rebars in the central beam and organise subsequent investigations.
116 radar sections were acquired on the central beam. The radargrams were subsequently organised by sector, maintaining correspondence with the reference system adopted on site.
The contribution of GPR was the qualitative reading of the internal configuration: the data guided the diagnostic programme without replacing correlation with ultrasonic tomography and digital radiography.
Discover the full case study on bridge and viaduct surveys:
Limitations and conditions of applicability
- Highly conductive materials
- Moisture content
- Signal attenuation
- High density of reinforcement
- Complex geometries
- Surface conditions
GPR is a diagnostic tool whose effectiveness depends on the correct choice of frequency, acquisition geometry and the characteristics of the investigated element.
GPR systems for structural diagnostics
Concrete diagnostics requires high-frequency systems and configurations consistent with the required resolution, depth and accessibility. Instrumentation remains subordinate to survey design, acquisition quality and technical interpretation.
Discover Novatest GPR solutionsFrequently asked questions
- What is structural GPR?
- It is an indirect, non-invasive method that uses high-frequency electromagnetic pulses to acquire information on the internal configuration of structural elements. Interpretation of radargrams can help locate reinforcement, embedded elements, discontinuities and material variations.
- Does GPR measure concrete cover?
- GPR can help estimate the position and depth of reinforcement when the electromagnetic parameters of the material are known or correctly estimated. For dedicated local cover measurements, a covermeter may be appropriate; the choice depends on the objective and the context.
- Does GPR automatically detect corrosion and moisture?
- No. Variations in amplitude, velocity or signal attenuation may be associated with different conditions and do not alone constitute a diagnosis. Data must be interpreted taking into account material, geometry, moisture, reinforcement and acquisition conditions.
- What is the difference between GPR and ultrasonic tomography?
- GPR uses electromagnetic waves and is effective for locating and qualitatively mapping elements and internal geometries. Ultrasonic tomography uses elastic waves to investigate the internal response of concrete in greater depth. In specific campaigns the two methods can provide complementary information.
- How is a GPR survey on concrete designed?
- It starts from the diagnostic question, after which antenna frequency, reference system, grid, directions and scan spacing are defined. Acquisition, processing and interpretation must be consistent with geometry, expected depth and the condition of the element.
Do you need to know what is inside a structure?
The choice of GPR system and acquisition mode depends on the element to be investigated, the information required and the operating conditions.