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Benefits of Cover Meter System in Pre-Cast Yards

This post will guide you through how to select the Correct Positector Probe based on your application and the use of a Cover Meter in a pre-cast yard environment. On top of it, we are excited to announce that the Noggin Utility GPR is now supplied with the new DVL-500, bringing its performance to an all new level.

With the new DVL, operators will be able to save and retrieve project data with this touch screen unit. Noggin is known for its flexibility, with a number of different antenna options, and cart, drag kit or handle based scanning arrangements. The new DVL improves the ability to control the exact data collection parameters such as the size and spacing of grid scan, speed of data acquisition and the use of encoder etc. More info about the Noggin GPR can be found at our Noggin Webpage.

Achieving design concrete cover for Precasters with the Use of Cover Meters

Precast-MouldIt is a commonly held belief that bar chair/spacers will ensure that concrete cover to reinforcing is controlled and the specified level is achieved in concrete elements. However, the placement of concrete into the formwork (or moulds) and subsequent vibration of the concrete can inevitably move the reinforcing and therefore affect the cover achieved.

Precast concreters are extremely reliant on pre-pour checks to achieve cover and overall the quality control is much higher for this type of construction. However, in the authors experience it has been demonstrated in many precast yards the use of a cover meter or destructive testing can show that the reinforcing has moved during the pouring of the concrete.

As such insufficient cover can still be an issue even where pre-pour checks are completed.  It is common sense that on occasion there will not be enough spacers/chairs or that the work method is moving the reinforcing. It is not possible to discount the likelihood of insufficient cover occurring.

The prudent approach is to use a tool like a cover meter to measure the cover after the first few elements are poured, check that the specified cover is being achieved and if there are any issues remedy them before you have created a large problem involving a whole production run of elements. This small investment upfront could be a huge money saver in the long run.

Many will say that if they need to check every element being cast they will incur themselves a lot of time and money spent checking for a non-existent problem. The solution here is also simple. When you change design or start making a new element check with a high frequency. If no problems occur in the first number of elements then the frequency can be reduced. Rather than checking every single unit the engineer could check every tenth. The work method has now proved successful so this reduction in frequency is easily justified.

Engineers on site complete JSA or SWMS every day. They assess the risk and likelihood of a myriad of dangers and where a danger is identified it is mitigated by using steps to lower the rating. This approach is no different but instead of safety you are protecting your reputation and your bottom line with proactive quality control.

A few extra points on this subject:

  • Recognise that covermeters don't work in all circumstances without adjustment. They are particularly inaccurate where the reinforcing layout is dense. Peruse the plans and locate areas that are relevant and lend themselves to the use of covermeters, or use site calibration such as offered by the Profometer 630 AI upgrade. 
  • A number of organisations have already started instituting the requirement for mandated cover checks post-pour. Vic Roads for example have directive 610.33 which stipulate 20 mandatory checks per unit. Why not stay ahead of the curve?

The cost and time impingement on a company who creates hundreds of an element with cover defects is huge. The cost of purchasing a cover meter and instituting work methods with regular checks is much less in comparison.

Selecting the Correct Probe for a PosiTector system

Positector-RangeThe PosiTector range by DeFelsko is one of the best known ranges of coating inspection equipment on the market but its flexibility and large selection of test probes can make selecting the best system for current and future jobs difficult. This article will provide some guidelines on the most important information to gather before selecting a system along with a quick overview of the range and the correct probe selection for unique applications like testing the thickness of anodizing.

Remember if you need any support on selecting equipment your local PCTE manager always has time to discuss testing requirements and recommend equipment.

Important questions to answer

  • Determine the measurement required e.g. coating thickness, material thickness, humidity, etc. 
  • Establish minimum and maximum values, e.g. half the thinnest coating expected, 1.25x the largest coating expected
  • Establish all materials to be tested over
  • If the system may be used for other jobs confirm details for them as well
  • Determine geometry and access to test spots, e.g. if testing on the inside of a drilled hole a special thin, 90deg angle probe may be required
  • Determine data logging requirements,

The PosiTector body range universally accepts all PosiTector probes, easily converting from a coating thickness gauge for nonmetallic substrates to metallic substrates (ferrous and non-ferrous), or to other relevant tests such for environmental humidity or surface profile testing.

The Positector 6000 probe range is appropriate for determining the coating thickness on metallic substrates. The probe employs one of two technologies depending on the nature of the metallic substrate:

Ferrous coating thickness gauge

RedTank RGBMagnetic induction instruments use a permanent magnet to generate a magnetic field. Changes in magnetic flux density at the probe surface are directly related to the distance from the steel substrate. By measuring these changes, it is possible to determine the coating thickness. 

Non-Ferrous coating thickness gauge

Eddy current techniques employ a coil of fine wire to conduct a high frequency alternating current. When the probe is brought near to the conductive surface, the alternating magnetic field produces eddy currents on the surface. The magnitude of the eddy currents is measured and the coating thickness is determined.

Coating thickness over nonmetallic substrates

Positector200 TheoryThe PosiTector 200 probe range is appropriate for this application.

High frequency sound pulses are emitted which travel the coating via a coupling gel. The sound pulses reflect from any surface that is different in density. Coating thickness readings are obtained by measuring the time taken for the ultrasonic signal to propagate to the coating/substrate interface and back.

Guidance on specific probe selection

Depending upon a users requirements specific models of probe should be sellected, some common criteria and a recomendation of the suitable probe are listed below:

  • Testing galvanizing - like a normal test using a Positector 6000 Ferrous coating thickness probe
  • Testing anodizing on aluminium - The Positector 6000 NAS probe is specifically designed for this application, it offers high precision under 100 micron
  • Multi-layer test over non-metallic substrate - The Positector 200 range can be used to measure the thickness of individual layers in a multilayer coating system, the advanced body is require. 
  • Underwater Use – The standard, cabled stainless steel Positector 6000 probes are hermetically sealed to be totally waterproof, please note that the PosiTector Basic or advanced bodies are not waterproof. Longer cables can be obtained on request.
  • Rough Steel – For rugged applications the Positector 6000 FXS & FHXS Xtreme probes have a toughened alumina wear face. 
  • Duplex coatings – The Positector 6000 FNDS probe measures individual thicknesses of both layers of a duplex system, defined as a combined Zinc and power/paint system. 
  • Small parts, hard to reach areas or close to edges - The  Positector 6000 Microprobe range has very small heads angled to reach odd places such as inside bolt holes.
  • Thick protective coatings – The Positector 6000 Thick and Very Thick probes can be used for thick coating systems such as epoxy, rubber, concrete liners, intumescent fireproofing and more

Other Positector Probes

In addition to the broad range of coating thickness probes available Defelsko also manufacture a number of other probes for the Positector base, each is explained below:

Thickness of steel or other homogenous materials

PosiTectorUTG-MThe Positector UTG easures the wall thickness of materials such as steel, plastic and more using ultrasonic technology. This range is ideal for measuring the effects of corrosion/erosion on tanks, pipes or any structure where access Is limited to one side or for measuring steel thickness behind coatings. 

Dew Point

DPM-Web-AccessThe Positector DPM measures and records climatic conditions including relative humidity, air temperature, surface temperature, dew point temperature and the difference between surface and dew point temperatures. Ideal for qualifying surface preparation to international standards.

Shore Hardness

shd-probe-yellowThe Positector SHD measures the indentation hardness of non-metallic materials. Two durameter models are available depending on the hardness range – Shore A and Shore D.

 

Soluble Salts

SST-Flex-PatchThe Positector SST evaluates the concentration of soluble salts on metal surfaces by measuring the conductivity of water washed over the surface. This is done before coating and after surface blasting. The user is able to confirm that the surface salt levels are low enough to prevent corrosion and water attraction issues beneath a permeable coating.

Surface profile

BurnishingSurface profile gauges are used to record the surface profiles on blasted or otherwise prepared metals before coating are applied. The gauges measure and record peak to valley surface profile heights and conform to international standards. The Positector SPG is an electronic Needle-Type Depth Micrometre, the Positector RTR is a Replica Tape Reader.

 

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