ASTM_D_7234-21.pdf

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.Designation:D7234-21NTERNATIONALStandard Test Method forPull-Off Adhesion Strength of Coatings on Concrete UsingPortable Pull-Off Adhesion Testers1This standard is issued under the fixed designation D7234:the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.7 This international standard was developed in accor-1.1 This test method covers procedures for evaluating thedance with internationally recognized principles on standard-pull-off adhesion strength of a coating on concrete.The testization established in the Decision on Principles for thedetermines the greatest perpendicular force(in tension)that aDevelopment of International Standards,Guides and Recom-surface area can bear before a plug of material is detached.mendations issued by the World Trade Organization TechnicalFailure will occur along the weakest plane within the systemBarriers to Trade(TBT)Cprised of the loading fixture,glue,coating system,andsubstrate,and will be exposed by the fracture surface.2.Referenced Documents1.2 This test method uses a class of apparatus known as2.1 ASTM Standards:3C1583 Test Method for Tensile Strength of Concrete Sur-portable pull-off adhesion testers.They are capable of apply-ing a concentric load and counter load to a single surface sofaces and the Bond Strength or Tensile Strength ofConcrete Repair and Overlay Materials by Direct Tensionthat coatings can be tested even though only one side is(Pull-off Method)accessible.Measurements are limited by the strength of adhe-D16 Terminology for Paint,Related Coatings,Materials,andsion bonds between the loading fixture,coating system and thesubstrate or the cohesive strengths of the glue,coating layers,Applicationsand substrate.D2651 Guide for Preparation of Metal Surfaces for AdhesiveBonding1.3 This test method is suitable for both laboratory and fieldD3933 Guide for Preparation of Aluminum Surfaces fortesting.Structural Adhesives Bonding(Phosphoric Acid Anodiz-1.4 Pull-off adhesion strength measurements depend uponing)both material and instrumental parameters.There are differentD4541 Test Method for Pull-Off Strength of Coatings Usinginstruments used that comply with this test method.ThePortable Adhesion Testersspecific instrument used should be identified when reportingE177 Practice for Use of the Terms Precision and Bias inresults.This test is destructive and spot repairs may beASTM Test Methodsnecessary.E178 Practice for Dealing With Outlying ObservationsE691 Practice for Conducting an Interlaboratory Study to1.5 The values stated in SI units are to be regarded as theDetermine the Precision of a Test Methodstandard.The values given in parentheses are for informationonly.3.Terminology1.6 This standard does not purport to address all of the3.1 The terms and definitions in Terminology D16 apply tosafety concerns,if any,associated with its use.It is thethis test method.responsibility of the user of this standard to establish appro-3.2 Definitions:priate safety,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.3.2.1 concrete,n-with respect to this test method,refers toall forms of concrete including masonry units.3.2.2 glue,n-with respect to this test method,glue refers tothe material that bonds the bottom of the loading fixture to theThis test method is under the jurisdiction of ASTM Committee DOI on Paintand Related Coatings,Materials,and Applications and is the direct responsibility oftop surface of the coating to be tested.Subcommittee D01.46 on Industrial Protective Coatings.Current edition approved July 1.2021.Published August 2021.Originallyapproved in 2005.Last previous edition approved in 2019 as D7234-19.DOI:3 For referenced ASTM standards,visit the ASTM website,www.astm.org.or10.1520/D7234-21.contact ASTM Customer Service at serviceastm.org.For Annual Book of ASTM2 The term adhesion tester may be somewhat of a misnomer,but its adoption byStandards volume information,refer to the standards Document Summary page ontwo manufacturers and at least two patents indicates continued usage.the ASTM website.Copyright ASTM Intemational,100 Barr Harbor Drive,PO Box C700.West Conshohocken.PA 19428-2959.United StatesD7234-213.2.3 loading fixture,n-(also referred to as dollies or studs)6.Apparatusa metal structure that is flat on one end for bonding to the6.1 Adhesion Tester;including the components and accesso-coating surface and shaped on the other end for attachment tories described in 6.1.1-6.1.5.the adhesion tester and is used to determine the pull-off6.1.1 Loading Fixtures,having a flat surface on one end thatadhesion strength of coatings.can be adhered to the coating and a means of attachment to the3.2.4 portable pull-off adhesion testers,n-instruments thattester on the other end.The bonding surface may be round,are capable of applying a concentric load and counter load tosquare or rectangular.The round loading fixtures are usuallya single surface so that coatings can be tested even though only50 mm(2.0 in.)in diameter but may range from 20 mm(0.75one side is accessible.in.)to 75 mm(3.0 in.)in diameter.6.1.2 Detaching Assembly,having a central grip for engag-4.Summary of Test Methoding the loading fixture.4.1 The general pull-off adhesion test is performed by6.1.3 Base,on the detaching assembly,for uniformly press-scoring through the coating down to the surface of the concreteing against the coating surface around the fixture eithersubstrate at a diameter equal to the diameter of the loadingdirectly,or by way of an intermediate bearing ring.A means offixture(dolly,stud),and securing the loading fixture normalaligning the base is needed so that the resultant force is normal(perpendicular)to the surface of the coating with a glue.Afterto the surface.the glue is cured,a testing apparatus is attached to the loading6.1.4 Force Applicator;means of moving the grip awayfixture and aligned to apply tension normal to the test surface.from the base in as smooth and continuous a manner asThe force applied to the loading fixture is then uniformlypossible so that a torsion free,co-axial(opposing pull of theincreased and monitored until a plug of material is detached.grip and push of the base along the same axis)force resultsWhen a plug of material is detached,the exposed surfacebetween them.represents the plane of limiting strength within the system.The6.1.5 Force Indicator and Calibration Information,fornature of the failure is qualified in accordance with the percentdetermining the actual force delivered to the loading fixture.of adhesive and cohesive failures,and the actual interfaces andThe force indicator shall be verified to be within 5%of thelayers involved.The pull-off adhesion strength is computedforce measured by a calibrated testing machine at a frequencybased on the maximum indicated load,the instrument calibra-determined by the user,typically once a year.tion data,and the surface area stressed.Pull-off adhesion6.2 Timer;or means of limiting the rate of stress to less thanstrength results obtained using different devices may be differ-or equal to 0.2 MPa/s(30 psi/s)so that the maximum stressent because the results depend on instrumental parameters.(failure)is obtained in about 5 to 30 s.5.Significance and Use6.3 Solvent,or other means for cleaning the loading fixture5.1 The pull-off adhesion strength and mode of failure of asurface.coating from a concrete substrate are important performance6.4 Fine Sandpaper;or other means of cleaning or preparingproperties that are used in specifications.This test methodthe coating that will not alter its integrity.serves as a means for uniformly preparing and testing coated6.5 Glue,for securing the fixture to the coating that does notsurfaces,and evaluating and reporting the results.affect the coating properties.Two-component epoxies and5.2 Variations in strength results obtained using differentacrylics have been found to be the most versatile.instruments,different substrates,or different loading fixtures6.6 Mechanical Clamps,if needed,for holding the fixture inwith the same coating are possible.Therefore,it is recom-place while the glue cures.mended that the specific test instrument and loading fixture bemutually agreed upon between the interested parties.6.7 Cotton Swabs,or other means for removing excess glue.5.3 It is recommended that the coating be sufficiently cured6.8 Core Bit with Drill Press or Hand Drill,and means toto ensure cohesive strength and adhesion.This required mini-ensure that the scoring is normal to the coating for themum cure time before testing should be provided by theprocedures that use a round loading fixture.The core bit insidecoating manufacturer,and may require an extension due todiameter should equal the diameter of the loading fixture.If aatmospheric conditions on site(for example,low temperature,core bit with an inside diameter equal to the diameter of theand low or high humidity).loading fixture is not available,the closest size available shouldbe used.The diameter of the scored area should be measured5.4 This test method may be adapted to determine surfaceand recorded for performing the calculations.The core bit orstrength of uncoated concrete(see X2.1).Test Method C1583saw blades should be diamond tipped and,when required tois also suitable for that determination.minimize heat and suppress dust,supplemented with water5.5 The objective of this method is to determine the adhe-sion of a coating to concrete(or adapted for surface strength asstated in 5.4)and will result in failure in the coating or near theThe sole source of supply of the acrylics known to the committee at this timesubstrate surface.If evaluating the cohesive strength of theis Versiloc 201 and 204 with accelerator,available from Lord Corp.,Industrialsubstrate or cementitious surfacers is the purpose of the testing.Adhesive Div.,2000 W.Grandview Blvd.,P.O.Box 10038,Erie,PA 16514.If youare aware of alternative suppliers,please provide this information to ASTMor if the substrate or cementitious surfacers have low strength,International Headquarters.Your comments will receive careful consideration at athen Test Method C1583 may be more suitable.meeting of the responsible technical committee,which you may attend.2D7234-21lubrication.For the test procedures that use a square orin a manner that does not twist or torque the test area andrectangular loading fixture,a circular saw is required instead ofminimizes heat generated and edge damage or microcracks toa core bit and drill.Alternately,for thin or elastomeric coatings,the coating and the concrete substrate.For thick coatings it isa sharp knife or hole saw may be sufficient to score around therecommended to cool the coating and substrate during theloading fixture.cutting process with water lubrication.If any defects of thecoating due to the scoring are observed,the test location shall7.Test Preparationbe discarded and not recorded in the results.When using a7.1 The method for selecting the coating sites to be preparedround loading fixture,scoring shall be performed before thefor testing depends upon the objectives of the test andloading fixture is attached(see Fig.1).When using square oragreements between the contracting parties.There are,rectangular loading fixtures,scoring is typically performedhowever,a few physical restrictions imposed by the generalafter the loading fixture is attached(see Fig.2).method and apparatus.The following requirements apply to allNorE 1-Since it is difficult to score the coating precisely down to thesites:surface of the substrate.especially for thicker coatings,it is acceptable to7.1.1 The selected test area must be a flat surface largeallow a range.This range for the whole circumference or edge should,atenough to accommodate the specified number of replicate tests.the top end,ensure touching the surface of the substrate,and at the bottomThe surface may have any orientation with reference toend,be no more than 3 mm in.)below the substrate surface.In casesgravitational pull.Each test site must be separated by at leastwhere the substrate is very rough,the surface of the substrate would be thelowest depth of continuous substrate with this same tolerance.the distance needed to accommodate the detaching apparatus.NoTE 2-(For concrete surfacers/patching materials under coatings.)ItThe size of a test site is essentially that of the secured loadingis common in recoating projects to apply asurfaceror patching materialfixture.At least three replications are required in order toto the concrete substrate to repair or level,or both,the concrete prior tostatistically characterize the test area.recoating.This surfacer/patching material layer can range in thicknessfrom very thin(essentially immeasurable on top of the remaining7.1.2 The selected test areas must also have enough perpen-concrete),up to 12 mm or more in small repair pockets.It is the option ofdicular and radial clearance to accommodate the apparatus,andthe specifier of the project to define the surfacer/patching material as eitherbe flat enough to permit alignment.It should be noted thatpart of the coating system(where the underlying concrete would be themeasurements close to an edge may not be representative of thesubstrate)or as the substrate itself.This distinction would be relevant incoating as a whole.determining the depth of scoring as detailed in 7.2.NorE 3-For vertical and overhead surfaces it is recommended to use7.2 Scoring the coating down to the surface of the substratean attached template to ensure scoring is performed with a tool securedis required for all coatings thicker than 0.5 mm(20 mils)andand guided in a perpendicular angle.for all reinforced or elastomeric coatings.While scoring is7.3 Clean the surfaces in a manner that will not affectrecommended for coatings thinner than 0.5 mm(20 mils),theintegrity of the coating or leave a residue.Clean the loadingtest may be performed without scoring,but the results shouldfixture surface as indicated by the apparatus manufacturer.note this exception.Scoring shall be performed in a mannerFailures at the fixture-glue interface can often be avoided bythat ensures the cut is made normal to the coating surface andtreating the fixture surfaces in accordance with an appropriateConcrete SubstrateScoring around the perimeterLoading fixture bonded to theLoading fixture pulled fromof the loading fixture prior tocoating surface to be testedthe substrateattachmentwith appropriate adhesiveFIG.1 Scoring Around the Loading Fixture Prior to Attachment of the Fixture(Round Loading Fixtures)3D7234-21Concrete SubstrateLoading fixture bonded to theScoring around the loadingLoading fixture pulled fromcoating surface to be testedfixture to the substratethe substratewith appropriate adhesiveFIG.2 Scoring Around the Loading Fixture After Attachment of the Fixture(Square or Rectangular Fixtures)ASTM standard practice for preparing metal surfaces for8.Test Procedureadhesive bonding.Fingerprints,moisture,and oxides tend to bethe primary contaminants.8.1 Select an adhesion tester having a force calibrationspanning the range of expected values along with its compat-NorE 4-Guides D2651 and D3933 are typical of well-proven methodsible loading fixture.Mid-range measurements are usually thefor improving adhesive bond strengths to metal surfaces.best,but read the manufacturers operating instructions before7.4 Prepare the glue in accordance with the glue manufac-proceeding.turers recommendations.Apply the glue to the fixture or thesurface to be tested,or both,using a method recommended by8.2 If a bearing ring or comparable device is to be used,the glue manufacturer.Be certain to apply the glue across theplace it concentrically around the loading fixture on the coatingentire surface.Position fixture on the surface to be testedsurface.If shims are required when a bearing ring is employed,centered directly over the scored section with the fixture outerplace them between the tester base and bearing ring rather thansides lined up with the inside circumference of the scoredon the coating surface.section.Carefully remove the excess glue from around thefixture.(Warning-Movement,especially twisting,can cause8.3 Carefully connect the central grip of the detachingtiny bubbles to coalesce into large holidays that constituteassembly to the loading fixture without bumping,bending,orstress discontinuities during testing.)otherwise prestressing the sample and connect the detachingassembly to its control mechanism,if necessary.For nonhori-NoTE 5-Adding about 1%of#5 glass beads to the glue assists in evenzontal surfaces,support the detaching assembly so that itsalignment of the test fixture to the surface.weight does not contribute to the force exerted in the test.7.5 Based on the glue manufacturers recommendations andthe anticipated environmental conditions,allow enough time8.4 Align the device according to the manufacturers in-for the glue to set up and reach the recommended cure.Duringstructions and set the force indicator to zero.the glue set and early cure stage,a constant contact pressureNoTE 6-Proper alignment is critical.If alignment is required,use theshould be maintained on the fixture.Mechanical clampingprocedure recommended by the manufacturer of the adhesion tester.systems work well,but systems relying on tack,such asmasking tape,should be used with care to ensure that they do8.5 Increase the load to the fixture in as smooth andnot relax with time and allow air to intrude between the fixturecontinuous a manner as possible,at a uniform rate of less thanand the test area.or equal to 0.2 MPa/s(30 psi/s)so that failure occurs or themaximum stress is reached before 30 s.7.6 Note the temperature and relative humidity during thetime of test.8.6 Record the force attained at failure.D7234-218.7 When the plug of material is detached,label and store9.3.1 Describe the specimen as substrate A,B,C,uponthe fixture for qualification of the failed surface in accordancewhich successive coating layers D,E,F,etc.,have beenwith 9.3.applied,including the glue,Y,that secures the fixture,Z,to the8.8 Report any departures from the procedure such astop coat.possible misalignment,hesitations in the force application,etc.9.3.2 Designate cohesive substrate failures by the quantityand type of substrate removed(see Fig.3).9.Calculation and Interpretation of Results9.3.3 Designate cohesive coating failures by the layers9.1 If provided by the manufacturer,use the instrumentwithin which they occur as D,E,F,etc.,and the percentage ofcalibration factors to convert the indicated force for each testeach.into the actual force applied.9.3.4 Designate adhesive failures by the interfaces at whichthey occur as A/B,B/C,C/D,etc.,and the percent of each.9.2 Either use the calibration chart supplied by the manu-facturer or compute the relative stress applied to each coating9.4 A result that is very different from most of the resultssample as follows:may be caused by a mistake in recording or calculating,amongother things.If either of these is not the cause,then examine the4FX=d2(1)experimental circumstances surrounding this run.If an irregu-lar result can be attributed to an experimental cause,drop thiswhere:result from the analysis.However,do not discard a resultX=pull-off adhesion strength achieved at failure in MPaunless there are valid nonstatistical reasons for doing so or(psi).unless the result is a statistical outlier.Valid nonstatisticalF=Maximum force applied to the test surface at failure andreasons for dropping results include alignment of the apparatusas determined in 9.1 in N(lb),andthat is not normal to the surface,poor definition of the aread=diameter of the loading fixture in mm(in.).stressed due to improper application of the glue,poorly definedNorE 7-d should be the inside diameter of the scored sample if thisglue lines and boundaries,holidays in the glue caused by voidsdoes not equal the diameter of the loading fixture.or inclusions,improperly prepared surfaces,and sliding or9.3 Estimate the percent of adhesive and cohesive failures intwisting the fixture during the initial cure.Dixons test,asaccordance to their respective areas and location within the testdescribed in Practice E178,may be used to detect outliers.system comprised of substrate,coating and glue layers.A9.5 Disregard any test where glue failure(between the glue,convenient scheme that describes the total test system isY,and the loading fixture,Z or the coating surface)representsoutlined in 9.3.1-9.3.4.more than 25%of the area.Loading FixtureGlueTop(second)coatBottom(first)coatConcrete SubstrateSubstrate Failure ASubstrate Failure BSubstrate Failure CBulk Cement Paste andBulk Cement Paste WithoutThin Layer of CementitiousFractured AggregateFractured AggregateMaterial or LaitanceFIG.3 Substrate Failure Classification5