Rebar location and mapping survey will determine the exact location of reinforcement within concrete.
Ground Penetrating Radar (GPR) is an ideal technology for reinforcement
steel location and rebar mapping. Please note that for this type of service,
you can also come across names such as rebar survey or GPR rebar scanning.
In GPR rebar mapping, Ground Penetrating Radar will
determine reinforcing steel location but also the locations of reinforcement
bars made of fibre reinforced polymer; named after the material used, fibre
reinforced polymer-FRP rebar.
Except rebar distribution (spacing and depth of the
different rebar layers), rebar survey will also verify rebar diameters and
concrete cover thickness.
For more in depth information about concrete slab, like
finding out overall slab thickness or detecting other features within concrete
including post tension cables, conduits, ducts, and voids you should request
concrete imaging survey. Concrete scanning is used to produce highly detailed
images at the specific locations which will also include information about
rebar arrangement.
What is rebar?
Rebar, or reinforcement bar is a type of reinforcement which
strengthens and stabilises concrete structures and because of that it is
regularly used in construction. Rebar is a crucial element of reinforced
concrete- which essentially is made from concrete with embedded reinforcement.
Rebar comes in different shapes and sizes and is typically made
from steel (but not always).
A good alternative to steel rebars is for example carbon
fibre reinforced polymers (CFRP).
The primary function of rebar is to add extra tensile
strength to the concrete structures and maintain their structural integrity.
Reinforced concrete is used in various types of infrastructure
such as roads, bridges, tunnels, dams as well as commercial and residential
buildings, and in specific structural applications such as concrete slabs,
foundations or retaining walls.
Except rebar, there are other types of reinforcement available
namely mesh reinforcement, also called ‘welded wire mesh’ and fibre
reinforcement. Similarly to rebar, mesh reinforcement is used for increasing
tensile strength to the concrete. The application of fibre reinforcement
however is different- it is added to the concrete mix to increase concrete
strength but post cracking.
How does rebar strengthen concrete structures?
Concrete is widely used construction material which on one
hand is substantially strong in bearing compressive loads and stresses. On the
other hand, it is relatively weak if subjected to tensile forces. In
construction projects, that weakness in tensile strength will manifest itself
in structural cracking, deflection or, in worst case scenarios, collapse.
To alleviate tensile weakness, concrete is routinely
reinforced with steel.
Reinforced concrete will resist tensile stresses caused by
bending forces when the heavy load is applied and therefore it is commonly used
in most construction work.
Adding rebar to the concrete will also prevent concrete from
cracking, which can occur when the concrete expands and contracts due to the
changes in temperature and moisture level. In that case rebar helps to keep
concrete in place.
Why use GPR for rebar mapping and concrete imaging?
Ground Penetrating Radar (GPR) is a completely non-invasive
and non-destructive technology (NDT) that can reliably detect reinforcing steel
bars and other features in concrete up to a depth of 50cm. The penetration
depth can be greater if necessary, however it will depend on two factors:
-the antenna frequency of the GPR used for the rebar survey
-the spacing between the rebars
GPR is ideal for concrete imaging and rebar mapping survey
because concrete is a homogeneous material and there is a strong contrast in
the dielectric properties of concrete and metal rebar.
GPR can detect multiple layers of reinforcement (depending
on the spacing of bars and presence of fibre reinforcement which might obstruct
the deeper view) and due its small size it can be used to detect reinforcing
bars to within 10cm of an obstruction. For majority of GPR rebar scanning
surveys, it is only necessary to access a slab from one side only.
If rebar locations are required in a real time, a GPR rebar
survey can be used to locate the reinforcing steel bars and mark the positions
directly on site.
Rebar survey deliverables
Typical deliverables from a rebar mapping survey will be a CAD drawing and/ or short report which clearly details the requested information. In the case of rebar location with on-site mark out, the deliverable will be the marks left on site.
Limitations of GPR for concrete imaging and rebar mapping survey
GPR although great technology, does have some limitations.
It is not able to penetrate through a closely spaced mesh, concrete reinforced
with metal fibres, and very closely spaced reinforcing bars. The results will
also depend on the condition of the rebar eg. damaged screed, caused by debonding
from the substrate.
GPR has limited resolution therefore it is not possible to
confidently determine the condition of the reinforcement bars such as the extent
of the corrosion* (if corrosion is present).
For this type of information, it is recommended that the GPR rebar scanning is followed by either electrochemical testing eg. half-cell potential test (for detecting likelihood or speed of rebar corrosion), other magnetic NDT methods like self-magnetic flux leakage (SMFL) or destructive testing, which as it causes secondary damage to the reinforced concrete structure is chosen as the last resort.
*GPR is used for corrosion testing, but in the academic environment. In the commercial environment there are other, better suited methods intended for that purpose which we have briefly mention in the above text.
How a GPR rebar mapping survey works?
For post-processing rebar survey, our GPR surveyor will
attend your site and mark the surface in paint, crayon or chalk to indicate
accurately referenced scan locations. We will then make passes of the GPR
across the surface in a series of sequential scans to collect and save GPR data
until the area has been thoroughly scanned in an orthogonal grid. Collected
data is recorded for post-processing and interpretation.
At our office, the data is imported to into our advanced GPR
imaging software and the scans are processed and referenced into a 3D image
showing the locations of all the rebar and structural features within the
concrete. This image is used to produce a map of the locations and distribution
of rebars and other identified features in CAD. A short report will be included
if you request it.
On-site GPR rebar location survey
If survey results are required directly on site, the survey
will be performed in a similar way, however, we perform interpretation of the
GPR data in real time and mark the locations of the individual rebars directly
on the surface. On-site rebar location survey is often requested to avoid rebar
prior to drilling or coring activities.
Ground Penetrating Radar (GPR) vs other electromagnetic technology for detecting reinforcing bars (Cover Meter and Ferroscan)
KB Surveys recommend the use of GPR for rebar location
survey. Although GPR requires more expertise to use and interpret the output,
it offers deeper penetration, better resolution and unlike Cover Meter and
Ferroscan can detect non-metallic objects.
See our blog for further information and comparative
equipment tests.
What is rebar?
Rebar, or reinforcement bar is a type of reinforcement which strengthens and stabilises concrete structures and because of that it is regularly used in construction. Rebar is a crucial element of reinforced concrete- which essentially is made from concrete with embedded reinforcement.
Rebar comes in different shapes and sizes and is typically made from steel (but not always).
A good alternative to steel rebars is for example carbon fibre reinforced polymers (CFRP).
The primary function of rebar is to add extra tensile strength to the concrete structures and maintain their structural integrity.
Reinforced concrete is used in various types of infrastructure such as roads, bridges, tunnels, dams as well as commercial and residential buildings, and in specific structural applications such as concrete slabs, foundations or retaining walls.
Except rebar, there are other types of reinforcement available namely mesh reinforcement, also called ‘welded wire mesh’ and fibre reinforcement. Similarly to rebar, mesh reinforcement is used for increasing tensile strength to the concrete. The application of fibre reinforcement however is different- it is added to the concrete mix to increase concrete strength but post cracking.
How does rebar strengthen concrete?
Concrete is widely used construction material which on one hand is substantially strong in bearing compressive loads and stresses. On the other hand, it is relatively weak if subjected to tensile forces. In construction projects, that weakness in tensile strength will manifest itself in structural cracking, deflection or, in worst case scenarios, collapse.
To alleviate tensile weakness, concrete is routinely reinforced with steel.
Reinforced concrete will resist tensile stresses caused by bending forces when the heavy load is applied and therefore it is commonly used in most construction work.
Adding rebar to the concrete will also prevent concrete from cracking, which can occur when the concrete expands and contracts due to the changes in temperature and moisture level. In that case rebar helps to keep concrete in place.
Why use GPR for rebar mapping and concrete imaging?
Ground Penetrating Radar (GPR) is a completely non-invasive and non-destructive technology (NDT) that can reliably detect reinforcing steel bars and other features in concrete up to a depth of 50cm. The penetration depth can be greater if necessary, however it will depend on two factors:
-the antenna frequency of the GPR used for the rebar survey
-the spacing between the rebars
GPR is ideal for concrete imaging and rebar mapping survey because concrete is a homogeneous material and there is a strong contrast in the dielectric properties of concrete and metal rebar.
GPR can detect multiple layers of reinforcement (depending on the spacing of bars and presence of fibre reinforcement which might obstruct the deeper view) and due its small size it can be used to detect reinforcing bars to within 10cm of an obstruction. For majority of GPR rebar scanning surveys, it is only necessary to access a slab from one side only.
If rebar locations are required in a real time, a GPR rebar survey can be used to locate the reinforcing steel bars and mark the positions directly on site.
Limitations of GPR for concrete imaging and rebar mapping survey
GPR although great technology, does have some limitations. It is not able to penetrate through a closely spaced mesh, concrete reinforced with metal fibres, and very closely spaced reinforcing bars. The results will also depend on the condition of the rebar eg. damaged screed, caused by debonding from the substrate.
GPR has limited resolution therefore it is not possible to confidently determine the condition of the reinforcement bars such as the extent of the corrosion* (if corrosion is present).
For this type of information, it is recommended that the GPR rebar scanning is followed by either electrochemical testing eg. half-cell potential test (for detecting likelihood or speed of rebar corrosion), other magnetic NDT methods like self-magnetic flux leakage (SMFL) or destructive testing, which as it causes secondary damage to the reinforced concrete structure is chosen as the last resort.
*GPR is used for corrosion testing, but in the academic environment. In the commercial environment there are other, better suited methods intended for that purpose which we have briefly mention in the above text.
How a GPR rebar mapping survey works?
For post-processing rebar survey, our GPR surveyor will attend your site and mark the surface in paint, crayon or chalk to indicate accurately referenced scan locations. We will then make passes of the GPR across the surface in a series of sequential scans to collect and save GPR data until the area has been thoroughly scanned in an orthogonal grid. Collected data is recorded for post-processing and interpretation.
At our office, the data is imported to into our advanced GPR imaging software and the scans are processed and referenced into a 3D image showing the locations of all the rebar and structural features within the concrete. This image is used to produce a map of the locations and distribution of rebars and other identified features in CAD. A short report will be included if you request it.
On-site GPR rebar location survey
If survey results are required directly on site, the survey will be performed in a similar way, however, we perform interpretation of the GPR data in real time and mark the locations of the individual rebars directly on the surface. On-site rebar location survey is often requested to avoid rebar prior to drilling or coring activities.
Ground Penetrating Radar (GPR) vs other electromagnetic technology for detecting reinforcing bars (Cover Meter and Ferroscan)
KB Surveys recommend the use of GPR for rebar location survey. Although GPR requires more expertise to use and interpret the output, it offers deeper penetration, better resolution and unlike Cover Meter and Ferroscan can detect non-metallic objects.
See our blog for further information and comparative equipment tests.
What are main benefits of rebar mapping survey?
Why choose us for your rebar survey?
Our senior surveyors have over 20 years of experience in rebar survey | |
We are trusted sub-contractor for larger surveying companies | |
We participated in university studies for applying GPR in rebar corrosion testing | |
We offer outstanding customer service and build relationships |