For optimum performance, repair materials or coatings must form a strong bond with the concrete substrate. But how can you accurately measure this bond strength in the field?
Contractors often rely on portable adhesion testers, which can evaluate surface preparation during preconstruction testing and measure bond strengths throughout a project. The instruments are available from several manufacturers, but they all work the same way. A flat, circular pull stub is secured to the surface of the coating or repair material with a fast-setting adhesive. After the adhesive cures, the operator attaches the testing apparatus to the pull stub and applies tension perpendicular to the test surface. The force applied to the pull stub is gradually increased until failure or, if nondestructive testing is desired, a specified value is reached. Acceptable pull-off strengths for concrete repairs and coatings depend on the application, but specifications often require minimum pull-off strengths of 100 to 250 psi.