ASTM D7234-21 pdf free download.Standard Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers.
1.1 This test method covers procedures for evaluating the pull-off adhesion strength of a coating on concrete. The test determines the greatest perpendicular force (in tension) that a surface area can bear before a plug of material is detached. Failure will occur along the weakest plane within the system comprised of the loading tixture. glue, coating system. and substrate, and will he exposed by the fracture surface.
1 .2 This test method uses a class of apparatus known as portable pull-off adhesion Lesters. They are capable of applying a concentric load and counter load to a single surface so that coatings can be tested even though only one side is accessible. Measurements are limited by the strength of adhesion bonds between the loading fixture, coating system and the substrate or the cohesive strengths of the glue, coating layers, and substrate.
1.3 This test method is suitable t& both laboratory and field testing.
1.4 Pull-off adhesion strength measurements depend upon both material and instrumental parameters. There are diflèrent instruments used that comply with this test method. The specific instrument used should be identified when reporting results. This test is destructive and spot repairs may be necessary.
1.5 The values stated in SI units are to he regarded as the standard. The values given in parentheses are for information only.
3.2.3 loading fixture, ,z—(also referred to as dollies or studs) a metal structure that is flat on one end for bonding to the coating surface and shaped on the other end for attachment to the adhesion tester and is used to determine the pull-off adhesion strength of coatings.
3.2.4 portable pull-off adhesion testers, n—instruments that arc capable of applying a concentric load and counter load to a single surface so that coatings can be tested even though only one side is accessible.
4. Summary of Test Method
4.1 The general pull-oil adhesion test is performed by scoring through the coating down to the surface of the concrete substrate at a diameter equal to the diameter of the loading fixture (dolly, stud), and securing the loading fixture normal (perpendicular) to the surface of the coating with a glue. After the glue is cured, a testing apparatus is attached to the loading fixture and aligned to apply tension normal to the test surface. The force applied to the loading fixture is then uniformly increased and monitored until a plug of material is detached. When a plug of material is detached, the exposed surface represents the plane of limiting strength within the system. The nature of the failure is qualified in accordance with the percent of adhesive and cohesive failures, and the actual interfaces and layers involved. The pull-off adhesion strength is computed based on the maximum indicated load, the instrument calibra(ion data, and the surface area stressed. Pull-off adhesion strength results obtained using dillerent devices may be dillerent because the results depend on instrumental parameters.ASTM D7234 pdf download.