Concrete Slab Scanning

If you know where the steel reinforcing bars, post tension cables and electricity lighting is within a concrete slab, then it’s safe to say you DO NOT require the help of Geoscope when planning to make holes or cuts with diamond tipped equipment.

If you ARE planning to carry out any core drilling or cutting works, and you would like to make the safest cut possible by avoiding potential electric shocks or damage to structural tendons, you may want to carry out concrete scanning before you begin.

Here’s where Geoscope can help with our GPR concrete slab scanning service which covers the Sydney metropolitan area and beyond.

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If you’re planning on cutting or drilling into a slab, carrying out a comprehensive concrete scan can help eliminate the risk of damage or injury from striking an embedded object or service. Concrete scanning using GPR and electromagnetic devices can help you identify any post tension cables, steel, rebar or services that might lie within the concrete structure.

If you want to protect workers and fulfil your duty of care in eliminating risks in the workplace then scanning the concrete before beginning any planned works is the way to do it.

The cost of having concrete slab scanning done far outweighs the cost of repairing a damaged service or the structural integrity of a suspended slab level.

Remember, planning makes perfect!

Risks of cutting concrete slabs

Cutting or drilling through post tension cables or steel reinforcement has the potential to effect the structural integrity of the concrete structure and also cause injury to workers and damage to equipment.

Post tension cables are used in concrete slabs to provide strength while reducing the need for the amount of steel in a non-post tension slab. It’s for this reason damaging PT cables can reduce the strength of the slab.

Post tension cables are also under great tension, which means that when severed, they have the potential to fling back into the path of workers and operators cutting into the slab. Personal safety and equipment safety is also at risk in these situations.

Live electrical cables can cause serious injury to personnel if drilled or cut through. Even if a cable appears to have no voltage running through it, it can be very dangerous if you accidentally damage the cable. As the need to power the cable through lights or machinery can be intermittent, the cable may seem safe when first damaged, but become live at a later stage causing serious injury.

Advantages of scanning before coring

Concrete scanning saves time, money, and prevents injuries and unnecessary damage. By choosing to locate and map the position of post tension cables, voids, rebar and electrical conduits embedded in concrete you can be sure that any cutting or coring is carried out consequence free.

How does concrete scanning work?

Finding objects or services that might be hidden within a concrete slab requires specialist equipment operated by fully trained technicians. At Geoscope, our highly trained technicians use the most up to date GPR and electromagnetic devices to ensure that you get the most comprehensive concrete scan possible.

Using a combination of GPR and electromagnetic service locating methods is the most effective and efficient way to detect services and objects. The electromagnetic locator can identify metallic services like water pipes by using a transmitter to induce a traceable current which travels through the pipe or cable.

Once any traceable services have been identified, we then confirm them and also identify any embedded steel rebar and reinforcements using ground penetrating radar. The GPR device is passed over the work area in a grid fashion to make sure that all the angles are covered.

The device emits a signal that reflects off any embedded objects in the slab, which is captured on the monitor of the GPR device. Experienced technicians are able to read this data to identify any objects which are embedded in the concrete structure.

How does GPR scanning work?

When the concrete slab or structure is scanned using the GPR locating device, it transmits electromagnetic radar into the ground. These signals reflect off any subsurface materials that match the frequency and are communicated back to the receiver where they are stored.

These radar waves are projected into the soil in a cone-like shape from under the antenna, where if they encounter underground structures, they reflect the energy back. This energy comes back at a different wavelength depending on the material and type of structure – which is how the different utilities can be identified.  It also measures the depth and location of the target by analysing the time taken for the radar signal to be returned.

As these GPR waves are passing through the concrete, they are also contacting objects within the slab such as steel mesh and rebar or even electrical and post tension cables, they reflect off of these targets very well due to the differing dielectric constants.

GPR is an ideal concrete scanning method as it is relatively easy to setup without the need for bulky equipment. Most of the time the gear is confined to a suitcase size pelican hard case and a shoulder bag.

Locating post tension cables

Concrete ground penetrating radar is the ideal method to locate post tension cables.

Using a higher frequency of radar system than typically used in utility locating means we can focus our attention on targets within the first 0-400mm of concrete.

Can GPR detect voids?

Building on top of a void can cause failures of the overlying strata. Voids underneath roads can cause eventual sinkholes.  Voids located underneath concrete slabs eventually lead to cracking and potential failure of the slab. Detecting voids in the subsurface before construction works can avoid expensive repair work and potentially disastrous consequences later.

Ground Penetrating Radar is also useful for locating voids. Voids located underneath concrete slabs eventually lead to cracking and potential failure of the slab. Detecting voids before starting any works can avoid expensive repair work and potentially disastrous consequences later.

GPR units can find even small voids at small penetration depths. Voids that are located very deep below ground need to also be quite large to be located with GPR.

There are certain considerations when scanning for voids located underneath reinforced concrete, as the GPR waves cannot pass through the steel rebar. However, experienced GPR device operators can still interpret the data that is provided and use it to indicate if there is a potential void in that area.

The frequency is the key to finding voids using Ground Penetrating Radar. The imaging is clearer at higher frequencies, and a concrete scanning friendly frequency in the 1600-2700MHz range works well to locate voiding 300-400mm below the surface.

How does electromagnetic scanning work?

Electromagnetic locating devices have a transmitter and a receiver. The transmitter sends a signal that reflects off objects that are embedded in the concrete. The receiver can pick up the reflected signal as long as the embedded object, pipe or cable material is metallic. Non-metallic objects don’t conduct a signal back to the receiver, and so these cannot be picked up.

As electromagnetic devices only pick up on conductive materials, we don’t recommend that you use these devices alone for your concrete scanning. Ideally, you should use both Ground Penetrating Radar and electromagnetic methods together, as it allows for a very high accuracy rate

What technology is used for concrete slab scan?

Ground penetrating radar has become commonplace in concrete scanning and investigations over the years as the hardware and software has become compact and refined.

This GPR slab scanning technology uses electromagnetic waves pulsed into the concrete at a nominated set frequency or multi-frequencies..

As these GPR waves are passing through the concrete, they are also contacting objects within the slab such as steel mesh and rebar or even electrical and post tension cables, they reflect off of these targets very well due to the differing dielectric constants.

This creates a clear disturbance in real-time which were able to interpret with years of experience as post tension cables or steel rebar.

This method of scanning is preferred as it is relatively easy to setup without the need for bulky equipment, most of the time the gear is confined to a suitcase size pelican hard case and a shoulder bag.

Is concrete scanning safe?

There’s a common misconception that scanning the concrete can leave behind harmful radiation in the concrete slab. It’s based on the fact that concrete scanning has previously been completed using X-Ray equipment that can be potentially hazardous if not properly controlled.

Luckily, we now have much better options available to carry out concrete scanning. Ground penetrating radar has become commonplace in concrete scanning and investigations over the years as the hardware and software has become compact and refined.

The radar signal emitted by the ground penetrating radar does not remain in the slab after the scanning is complete. It’s also completely non-destructive, so there’s no damage to the concrete or reinforcement.

The amounts of electromagnetic energy from GPR and electromagnetic devices are regulated, and so there is absolutely no risk of any harmful radiation left inside the concrete slab. You can rest assured that your site staff have nothing to worry about regarding any radiation left behind from scanning a concrete slab.

What kind of objects can we detect inside a concrete slab?

The following are all fairly common objects that can be found inside concrete structures. Using the combined detection methods of GPR and electromagnetic devices, we’re able to potentially identify these quickly and accurately:
  • Post tension cables
  • Pre-stressed cables
  • Steel mesh
  • Steel reinforcing bars
  • Structural beams
  • Electric lighting cables
  • Mains cables
  • Sub main electrical
  • Abandoned cables
  • Telstra copper
  • Conduits
  • Fire Hydrant pipes
  • Sprinkler Systems
  • Emergency Speakers
  • Fire Control Circuits
  • Copper water pipes
  • Unknown services and anomalies
  • Voids

Concrete scanning doesn’t only prevent unnecessary injuries and damage, it saves you time and money. A full concrete scan gives you the peace of mind that comes with knowing that any cutting or coring can go ahead without risking your safety, reputation, or your budget.

Site Mark up

Depending on your requirements, you may request to have the steel and cables marked right on the slab as we scan.

We can mark the GPR targets using spot marking paint, chalk, crayon, masking tape, permanent marker depending on the surface type being scanned and the need for temporary or semi permanent markings.

We find this the best for contractors doing fit outs and needing to place a penetration somewhere on a slab and having the markings right there in front of them gives them the option to place it in the safest location.

Why might I need a concrete floor slab survey?

Typically, concrete floor slab surveys using GPR are undertaken to determine or confirm the presence of the following:
  • Confirm the thickness of the slab
  • Check the depth of rebar cover.
  • Verify the construction drawings
  • Identify and mark out the reinforcement distribution
  • Check for mesh overlap
  • Identify any voiding beneath the slabs.

It can be especially important to check the depth of any concrete covering steel, especially if you are chasing cables through a slab; or for QA and quality assurance checks.

Understanding how much concrete stands between the slab and the steel can be the difference between a clean and easy job or cutting through a heap of top reinforcing steel potentially causing costly structural damage.

Once the indicated depth of steel has been established via GPR scanning, you can plan for alternative cutting or coring methods or topping of the slab to avoid potential damage.

What type of tasks require concrete scanning?

  • Electricians running new electrical cables through floor penetrations
  • Aircon ducting installation cutting
  • Plumbing floor waste and water closet points for bathroom or restaurant fit outs
  • Carpentry and commercial kitchens
  • Fire hydrant upgrades for building compliance
  • Any procedure which involves cutting into a slab

How long does concrete scanning take?

The time it takes to scan an area of slab depends on a few factors:
  • How large the area is that needs scanning
  • Whether vertical, horizontal or inverted scanning is required
  • What type of cutting or d What tasks require concrete scanning
  • Electricians running new electrical cables through floor penetrations
  • Aircon ducting installation
  • Plumbing floor waste and water closet points for bathroom or restaurant fitouts
  • Carpentry and commercial kitchens
  • Fire hydrant upgrades for building compliance a rilling is being carried out
  • If the concrete slab is on ground / sub-graded or suspended
  • How thick the slab is (too thick requires scanning on both sides)

What is involved in scanning a concrete slab?

To get started, we need to first identify the proposed area of works, activities, or investigations. Once the area has been established we clear the slab and surrounding area. It must be relatively clean so that we’re not scanning over and around debris, which can affect accuracy in the mark up.

We use a combination of electromagnetic locating methods and ground penetrating radar technology using various frequencies pulsed into the concrete to pin point embedded reinforcement and utilities.

By detecting targets with GPR inside the concrete slab, we can picture the consistent reflections and images typically gathered from rebar and steel mesh.

We perform live frequency scans and induction sweeps, as well as directly connecting to visible services in the area. This ensures all traceable services within the proposed area to be scanned have been found.

Finally, we measure the concrete thickness and locate the exit locations of core holes.

Concrete Scanning Reports

We have several options when it comes to reporting the findings from our concrete scanning.

With most of the scans we complete, a simple on-site mark up identifying any potential risks with the locating equipment is the best option. We can mark up any traceable conduits, post tension as well as the steel and rebar.

We can mark the GPR targets using spot marking paint, chalk, crayon, masking tape, or permanent marker. What we use depends on the surface type being scanned and the need for either temporary or semi-permanent markings.

This gives you the option to plan your core hole or cut in the desired location with the best possible care taken.

We also provide digital copies of the site mark up tp help you gain approval for permits. These might be a a permit to cut/drill, or a permit to excavate. The digital site mark-up may also be needed as part of your project’s engineering requirements.

However you intend to use the report, we can provide it in various forms to suit your requirements:
  • PDF photo reports
  • CAD drawings
  • 3D scanning and slices imagery

We can also customise our reports to include any additional information that you might need to complete the scanning process.

What should I look for when hiring a company to complete concrete scanning?

Hiring a specialist company to complete the concrete scanning for you is one of the best ways to ensure that it’s done quickly, accurately and cost-effectively. To get these benefits, it’s really important to make sure that the company you hire has well-trained and reputable operators.

At Geoscope, we pride ourselves on using highly trained technicians and the most up to date technology so that you can be assured of safety, accuracy, and reliability. We use both electromagnetic and Ground Penetrating Radar (GPR) methods because these are by far the most effective non-destructive methods of concrete scanning available.

When we complete a concrete scan, we gather all of the information you need and can mark any embedded objects or utilities in the slab in real time. So you get the peace of mind that comes from knowing you’ve accurately identified and marked any concrete floors or structures before you begin work.  

If you’ve got a coring or drilling project in the pipeline, get your project off to a great start with Sydney’s Concrete Scanning Specialist – Geoscope.

Geoscope Colour Coding for Concrete Scanning Markings

RED

Red – Post tension cables / Danger areas

Post tension and pre-stressed cables and tendons or areas too dangerous to cut through

ORANGE

Orange – Electricity

Electricity located within the concrete slab on power and passive scans or through direct connecting and clamping onto electrical equipment within the work area

BLUE

Blue – Steel (top bars)

Top rebar or mesh image found with GPR

GREEN

Green – Steel (bottom bars)

bottom rebar or mesh image found with GPR

PINK

Pink – Unknown service

Unknown signal or image from electromagnetic locating and or ground penetrating radar scan which was not on the existing service plans and or unable to verify trace to a known source.

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