Concrete Testing Methods
Updated: Jul 1
Concrete Surface Profile & Material Bonding Testing
The International Concrete Repair Institute (ICRI) and the American Society for Testing and Materials (ASTM) provides a variety of concrete testing methods. Below you will find an explanation of the purpose and summary of the procedure for performing each test. Resinous flooring tests can be put into 4 basic categories: Surface Profile, Material Bonding, Moisture, and Hardness. For the purposes of this article only surface profile and material bonding are discussed. If you would like to learn more about moisture testing check out my blog post "Hydrostatic Pressure."
Surface Profile Tests
Surface Profile—ICRI 310.2R
The surface preparation specification may include a CSP required profile, which can be compared with the CSP molded replicas available from ICRI. These replicas provide a visual comparison with the actual profile created during the surface preparation. Place CSP replicas on the prepared surface and visually compare the profile with the replicas. The profile of the surface should be in the range specified.
To learn more about this subject check out my blog post “ICRI Guidelines for CSP.”
Replica Putty—ASTM D7682 & Replica Tape—ASTM D4417
Visual observation of the surface profile may not provide a satisfactory determination of the surface profile. More qualitative/quantitative methods, including the Replica Putty and Sand Method, are available to further define the surface profile. The measurement of roughness can lead to the optimization of bonding strength.
Ensuring that the correct surface profile has been achieved can best be done with the use of replica putty. A permanent replication of the surface may be viewed and/or measured to form a permanent record of the surface preparation. To create this replication, replica putty is applied to the surface and allowed to cure. Once removed from the surface, the putty represents a reverse image of the surface. The peaks and valleys of the surface can be measured using a specially modified thickness gauge to accurately compare to CSP replicas.
The replica tape method uses a special tape containing compressible foam attached to a noncompressible uniform plastic film. A burnishing tool is used to impress the foam face of the tape into the surface to create a reverse replica of the profile that is measured using a spring-loaded micrometer. This method is designed for relatively smooth surfaces (CSP 1-and is not applicable for rougher surfaces.
The digital surface roughness meter (DSRM) measures the surface roughness of a prepared surface using a line laser. The DSRM is placed flush with the surface to be measured. An image of the profile is transmitted to a computer, where the image is digitized; the profiles are automatically isolated and measured for roughness. This method is rarely used on site and is more often used in laboratory conditions.
Sand Method—ASTM E965
The technical name for the sand method is the “Standard Test Method for Measuring Pavement Macrotexture Depth Using a Volumetric Technique.” This testing method measures the average surface texture by using a known volume of sand and spreading it uniformly over the surface and measuring the area covered. Using the standard formula for volume (L x W x D), the appropriate amplitude of the surface may be determined. This method will assist in determining the amount of material that is necessary to cover the surface.
The first step is to apply a known volume of sand to the surface. Carefully spread the sand in a circular motion using a large flat spreading tool, slowly increasing the diameter of the circular motion until all the sand has been spread. Measure the diameter of the circle and calculate the average depth. AD = (V sand/A area of the circle).
Petrographic Analysis—ASTM C856
While petrography can be used to detect a variety of flaws within concrete, it can also be used following surface preparation to determine if the method used to prepare the surface caused microcracking in the substrate. The test is made by extracting a sample of the concrete and observing it under a microscope. Microcracks weaken the substrate and should be removed by further surface preparation prior to installation of any materials. This test is never done on site and is exceptionally rare outside of a research setting.
Material Bonding Tests
Tensile Bond Strength Test— ICRI 210.3 and ASTM C1583/C1583M
The tensile bond test is used to assess the adequacy of the substrate prior to or following the installation of resinous material. The advantage of evaluating the substrate, prior to installation, is that additional surface preparation may be performed if necessary without additional costs of removing applied material after the installation. Performance of the test allows a resinous flooring expert to determine whether the resinous material will properly bond to the substrate.
This test is conducted by coring the substrate, attaching a metal disc to the core, and applying a load perpendicular to the surface and measuring the force required to cause failure in PSI. Additionally, if the cored sample is done after resinous material application it can indicate whether proper surface preparation was undertaken to ensure material bonded to the substrate.
Adhesion Test—ASTM D7234
This test method evaluates the pulloff adhesion 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.
The general pulloff 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 and securing the loading fixture perpendicular to the surface of the coating with an adhesive. After the adhesive is cured a testing apparatus is attached to the loading fixture and aligned to apply tension to the test surface. The force applied to the loading fixture is then increased, and monitored, until a plug of material is detached. When this happens, 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 and the fracture surface area.
Knife Adhesion Test—ASTM D6677
This test method assesses adhesion of the coating to the substrate using a utility knife. It is used to establish whether the adhesion of a coating to a substrate is at a generally adequate level. Using a utility knife and straightedge, two cuts are made into the coating with a 30-45 degree angle between them and down to the substrate which, intersects to form an “X.” At this intersection, the point of the knife is used to attempt to peel the coating from the substrate or from the coating below. This is a highly subjective test and its value depends on the experience of the resinous flooring expert.