Near Surface Mount (NSM) or Externally Bonded - Which method ?

No one method for structural strengthening fits all situations. When FRP strengthening is a good option, there are three distinct product types to consider. Near Surface Mount, where the Carbon FRP bar or tape is embedded in the concrete cover using a high strength structural adhesive. Externally bonded strengthening, where the surface of the structure is prepared and either a pre-cured laminated plate is bonded to the surface or a field wet-layup FRP composite is formed onto the structure in-situ. Aslan FRP offers two NSM products, the Aslan 200 CFRP bar and the Aslan 500 CFRP Tape and for externally bonded strengthening, the Aslan 400 CFRP laminate plate.

Why use Near Surface Mount (NSM) CFRP?

Pro

  • More effective than externally bonded
  • No special training or know-how required to perform
  • Eliminates issue with surface prep
  • FRP material is more protected
  • Fire performance will be better
  • Verifiable FRP properties prior to installation

Con

  • Cutting of grooves may be more challenging overhead
  • Field QA testing not as simple as externaly bonded
  • Requires adequate concrete cover
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Why use Externally Bonded CFRP?

Pro

  • Surface prep may be easier than cutting NSM grooves
  • Easier to perform overhead surface prep & installation
  • Wet lay-up can be formed to varying geometries
  • Validating bond pull-off tests straight forward to perform

Con

  • For wet-layup FRP, specialized training required
  • Implementation generally limited by de-bonding
  • Success depends on caliber of surface prep
  • Material properties vary more than pre-cured
  • More susceptible to fire & mechanical degradation than NSM
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NSM - Near Surface Mount

Two Choices for Near Surface Mount (NSM) Strengthening Round Bar - Aslan 200 or Rectangular Bar - Aslan 500

Characteristic

Aslan 200 CFRP Bar

Aslan 500 CFRP Tape

Cross Sectional Area

#2 (6mm), #3 (10mm) & #4 (13mm)
Equivalent Areas

#2 (6mm) & #3 (10mm)
Equivalent Areas

Minimum Groove Dimensions

1.5 X bar diameter square groove

3 X narrow dimension
1.5 X wide dimension

Bendable Along Axis

Yes

No

Available Lengths

Up to 40ft lengths

Up to 40ft lengths

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Aslan 200 CFRP Bar Properties

SizeNominal Dia - mmNominal Dia - inNominal Area - mm2Nominal Area - in2f*ffu - Guaranteed Tensile Strength - MPaf*ffu - Guaranteed Tensile Strength - ksiUltimate Load - kNUltimate Load - kipsEf - Tensile Modulus - GPaEf - Tensile Modulus - msiUltimate Strain - %
26_31.670.04922432570.815.92124181.81%
310_71.260.112172315154.134.65124181.75%
413_126.70.1962068300261.658.8124181.67%

Aslan FRP reserves the right to make improvements in the product and / or process which may result in benefits or changes to some physical-mechanical characteristics. The data contained herein is considered to be representative of current production and is believed to be reliable and to represent the best available characterization of the product as of July 2011. Tensile tests per ASTM D7205.

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A comprehensive list of physical & mechanical properties of Aslan 200 carbon bar is found in our Brochure & Data Sheet

Aslan 500 CFRP Tape Properties

Size- ImperialSize - metricDimensionNominal Area - mm2Nominal Area - in2f*ffu - Guaranteed Tensile Strength - MPaf*ffu - Guaranteed Tensile Strength - ksiUltimate Load - kNUltimate Load - kipsEf - Tensile Modulus - GPaEf - Tensile Modulus - msiUltimate Strain - %
260.079" x 0.63" 2mm x 16mm31.670.049224132570.815.92124181.81%
3100.079" x 0.63" 2mm x 16mm71.260.112172315154.134.65124181.75%

Aslan FRP reserves the right to make improvements in the product and / or process which may result in benefits or changes to some physical-mechanical characteristics. The data contained herein is considered to be representative of current production and is believed to be reliable and to represent the best available characterization of the product as of July 2011. Tensile tests per ASTM D7205.

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A comprehensive list of physical & mechanical properties of Aslan 500 CFRP Tape is found in our Brochure & Data Sheet

Aslan 400 CFRP Externallly Bonded Plate Properties

Width - mmWidth - inThickness - mmThickness - inNominal Area - mm2Nominal Area - in2f*ffu - Guaranteed Tensile Strength - MPaf*ffu - Guaranteed Tensile Strength - ksiUltimate Load - kNUltimate Load - kipsEf - Tensile Modulus - GPaEf - Tensile Modulus - msiUltimate Strain - %
2500.0551.4700.1102240035016838.57131191.87%
41000.0551.41400.224240035033677.14131191.87%

Aslan FRP reserves the right to make improvements in the product and / or process which may result in benefits or changes to some physical-mechanical characteristics. The data contained herein is considered to be representative of current production and is believed to be reliable and to represent the best available characterization of the product as of July 2011. Tensile tests per ASTM D7205.

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A comprehensive list of physical & mechanical properties of Aslan 400 externally bonded CFRP Plate in our Brochure & Data Sheet

Installation Instructions for Near Surface Mount or NSM Strucctural Strengthening

NSM strengthening is a superior method in situations that allow the ability to cut shallow grooves into the concrete cover. The method eliminates many of the surface preparation issues, critical to successful implementation and efficacy, associated with field lay-up externally bonded FRP systems. Since the bar is bonded to the member on three sides, development length is much shorter and it is possible to utilize the full strength of the bar. The Aslan 200 NSM bar is furnished to the job site pre-cured with verifiable design properties. Unlike field layup FRP systems, there is no need for highly skilled and trained FRP installation experts. Design is dictated by ACI 440.2R.

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Step #1: Grooves are cut after marking the layout as per the Engineer of Records’ specifications. Generally the final groove dimension is 1.5 times the bar diameter in depth and width. Dado cuts are also effective if possible.

Note: Proper equipment such as diamond crack chasing blades, guide rails and sufficiently sized power tools make cutting of the grooves easier. Rather than cut the groove in a single pass, sometimes its more effective to cut parallel grooves and remove the concrete between the saw cuts.

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Step #2: Chisel any remaining concrete between cut paths.

Step #3: Clean the groove and eliminate any residual dust with compressed air or vacuum. Note: It is not necessary to roughen the interior of the groove with additional abrasion, or brushing.

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Step #4: For a clean appearance, mask the concrete adjacent to the groove. Note: A time saving tip is to mask over the groove and then trim the masking to each edge.

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Step #5: Fill the groove approximately half way with adhesive. Note: Consider bulk dispensing of adhesive when making your choice of adhesive for the project.

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Step #6: Press the Aslan bar or tape into the groove partially filled with adhesive. The objective is to ensure adhesive is well consolidated around the bar without air pockets. Note: Some contractors have developed their own system based on epoxy crack injection methods using a low viscosity epoxy crack injection resin.

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Step #7: Completely fill the groove with adhesive ensuring the bar is fully covered.

Step #8: Level off the excess adhesive with a trowel or putty knife.

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Step #9: Remove masking. Note: pull the masking off before adhesive is fully cured.

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Finished Product

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