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InInInIn----Place StrengthPlace StrengthPlace StrengthPlace Strength

• Evaluation of in-place strength� Testing cores

� Rebound hammer

� Pullout test

� Case study

� Pull-off test

�Maturity method

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PullPullPullPull----off Testoff Testoff Testoff TestASTM C1583/C1583M ASTM C1583/C1583M ASTM C1583/C1583M ASTM C1583/C1583M

Measure force required to pull off a metal disc bonded to concrete

surface.

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PullPullPullPull----off Testoff Testoff Testoff Test

• Direct tensile strength test

• Evaluate condition of concrete surface before application of overlay or repair material

• Measure bond strength of overlay or surface repair materials

ft (MPa)

fc (MPa)

Worthers, 1994

Lab testing between Lab testing between Lab testing between Lab testing between compressive and tensile strengthcompressive and tensile strengthcompressive and tensile strengthcompressive and tensile strength

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PullPullPullPull----off Test Procedureoff Test Procedureoff Test Procedureoff Test Procedure

• Use planing tool to prepare a flat surface

• Bond metal disc to surface

• Drill partial core

• Apply tensile force

Overlay

≥10 mm

50 mm

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Surface PlaningSurface PlaningSurface PlaningSurface Planing

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Grind “Button” & Brush SurfaceGrind “Button” & Brush SurfaceGrind “Button” & Brush SurfaceGrind “Button” & Brush Surface

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Prepare and Apply AdhesivePrepare and Apply AdhesivePrepare and Apply AdhesivePrepare and Apply Adhesive

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Press Disc To SurfacePress Disc To SurfacePress Disc To SurfacePress Disc To Surface& Clean Up& Clean Up& Clean Up& Clean Up

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Cut Partial Depth CoreCut Partial Depth CoreCut Partial Depth CoreCut Partial Depth Core

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Partial coring w. Suction PlatePartial coring w. Suction PlatePartial coring w. Suction PlatePartial coring w. Suction Plate

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PullPullPullPull----off Test Procedureoff Test Procedureoff Test Procedureoff Test Procedure

Fufpo =

Fu

A

• Bond metal disc to surface

• Drill partial core

• Apply tensile force

Schematic of ApparatusSchematic of ApparatusSchematic of ApparatusSchematic of ApparatusASTM C1583/C1583MASTM C1583/C1583MASTM C1583/C1583MASTM C1583/C1583M

Steel disc

Tensile loading device with slow loading rate

Swivel joint

Must eliminate bending on disc

Ring as counterpressure

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PullPullPullPull----off Test Apparatusoff Test Apparatusoff Test Apparatusoff Test Apparatus

Adhesion testing of overlayAdhesion testing of tiles

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Successful Test!Successful Test!Successful Test!Successful Test!

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PullPullPullPull----off Test Failure Locationsoff Test Failure Locationsoff Test Failure Locationsoff Test Failure Locations

• Interfacial bond failure (bond strength)

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PullPullPullPull----off Test Failure Locationsoff Test Failure Locationsoff Test Failure Locationsoff Test Failure Locations

• Cohesive failure in the existing concrete (substrate strength)

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PullPullPullPull----off Test Failure Locationsoff Test Failure Locationsoff Test Failure Locationsoff Test Failure Locations

• Cohesive failure in the repair material

• Can not predict failure location• Average the results for same failure locations

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PullPullPullPull----off Test Failure Locationsoff Test Failure Locationsoff Test Failure Locationsoff Test Failure Locations

• Bond failure at the epoxy

• Inconclusive test

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Evaluation of Surface Evaluation of Surface Evaluation of Surface Evaluation of Surface Preparation MethodsPreparation MethodsPreparation MethodsPreparation Methods

• Surfaces to receive overlay or repair material are usually prepared to ensure good bonding

• Some repair methods can damage concrete and reduce the “apparent” bond strength

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Evaluation of Surface Evaluation of Surface Evaluation of Surface Evaluation of Surface Preparation MethodsPreparation MethodsPreparation MethodsPreparation Methods

• Test substrate before applying overlay

� ACI 503R (Use of Epoxy Compounds with Concrete) recommends substrate pull-off strength > 175 psi (1.2 MPa)

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SummarySummarySummarySummary

• Pull-off test can be used to evaluate surface before applying repair materials or overlays

• Evaluate bond strength of repair materials

• Need to eliminate bending on the disk when it is being pulled off

• Good adhesive needed to provide strong bond and allow rapid testing

• Failure will occur in “weakest link”