ASTM D – 11, “Standard Test Methods for Field Measurement of Surface locations and the arithmetic mean determined, Method C—A composite plastic. ASTM D, Standard Test Methods for Measurement of Surface Profile of Blast Appendix C: Additional Considerations when Measuring Surface Profile. ASTM D – 11 Standard Test Methods for Field Measurement of Surface Profile of Blast Method C—A composite plastic tape is impressed into.
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Members of Subcommittee Ast, The subcommittee develops and maintains standard test methods, practices and guides relating to the performance, evaluation, specification, application and proper use of industrial protective coatings.
Currently, this subcommittee has eight task groups that are working on 13 ASTM standards, four of which are proposed standards and nine of which are existing standards that have been slated for revision or renewal, or that have been recently published and require the development of precision and bias statements through interlaboratory research initiatives.
While there is current activity on all 13 standards, this article focuses on five major tasks being undertaken by the subcommittee at this awtm. Measuring Surface Roughness of Abrasive Blast Cleaned Steel The industrial protective coatings industry d44117 long recognized the importance of surface profile depth generated by abrasive blast cleaning and some power tools as a means to increase surface area and improve the adhesion of the asfm to the underlying substrate.
In fact, inASTM published DTest Methods for Measuring Surface Profile of Abrasive Blast Cleaned Steel, which describes three methods of quantifying surface profile depth generated in a steel substrate visual comparators, depth micrometers and replica tape. These methods are used to determine the average distance between the tops of the peaks and the bottoms of the valleys on a prepared steel surface. Recently published articles 1 describe the importance of other surface roughness attributes, in addition to average peak-to-valley distance, including peak count P cmaximum roughness depth R max awtm maximum profile height R t.
Based on laboratory research conducted by Roper et. Methods of generating various peak densities are described in the articles, and are based on abrasive size, shape, hardness and other factors. Facility owners with demanding service environments may consider specifying a given set of criteria for surface roughness above and beyond the standard peak-to-valley depthwhich may translate to increased performance and reduced life cycle costs.
Coating manufacturers may also consider these requirements to improve the performance and the 4d417 life of ast coatings they supply. Through methid efforts of Subcommittee D The standard describes the procedures for using and verifying the accuracy of portable stylus-type instruments to obtain surface characterization data, and provides guidance to the user regarding the significance of the data, once generated.
Naturally, the ability to generate reliable data between users employing different instruments, as well as the ability of one user to xstm repeatable data using a single instrument, must be assessed. An interlaboratory research initiative for the purpose of generating precision and bias statements for Dis planned for This method encompasses only one surface characteristic: The method describes three different procedures for quantifying surface profile, including visual comparators Method Adepth micrometers Method B and replica tape Method C.
Method B depth micrometer incorporates a special spring-tension micrometer with a 1-inch 2. With the base nethod the micrometer resting on the peaks of the surface profile, and the conical pin protruding to a valley of the profile, the distance is read from the gage display in mils or micrometers. Method C emthod tape employs a pressure sensitive tape containing a compressible foam attached to a polyester backing to replicate the peak-valley pattern generated by the abrasive blast cleaning process.
The pattern of surface roughness is replicated by burnishing the tape, effectively pressing the compressible foam into the surface roughness.
Once the surface profile pattern has been replicated into the tape, it is removed from the surface and placed in a special d417 tension anvil micrometer. The average surface profile depth is read from the micrometer dial in mils or microns methoe, after the micrometer has been corrected for the thickness of the polyester backing material. See Figures 45 and 6. For Method C, there are various ranges of replica tape that can be employed.
The tape selected is based on d417 anticipated or specified surface profile depth. Coarse replica tape is used to measure the actual roughness of surfaces containing a profile from 0. Paint grade replica tape is used to measure surfaces containing a profile from 1.
Replica tape for measuring surface roughness in excess of 4.
Revisions to the entire test method are also in process. Pull-Off Adhesion of Coatings The adhesion of a protective coating is a critical attribute that is related to performance. DTest Method for Pull-off Strength of Coatings Using Portable Adhesion Testers, has been developed to uniformly assess coating adhesion in the laboratory, shop, or field. Testing consists of securing a loading fixture to the coating surface with an adhesive.
A test apparatus is attached to the loading fixture and aligned to pull perpendicularly. The force is gradually increased until the loading fixture detaches. The user reports the pull-off strength in psi or MPaand the location of the break in the coating system, i.
The pull-off method as currently written does not distinguish between testing on steel and concrete substrates. The pull-off method is widely used by coatings manufacturers, specifiers, inspectors and coating specialists.
Some coatings manufacturers report the pull-off strength on their product data sheets, and some specifiers require minimum pull-off strength for qualifying coatings.
Pull-off strength tests may also be required as part of the execution of the project, and can be performed by inspection personnel. Coatings specialists may use the method for evaluating the adhesion characteristics of an existing coating during a coating condition survey, or in a failure investigation. The most current version of D allows for the use of any of five instruments for evaluating pull-off strength, two of which are fixed alignment and three are self-aligning.
Data published in Appendix X1 of the standard generated by an earlier interlaboratory research initiative reveals different pull-off strengths on four test specimens when using the various adhesion testers at that time, only four of the five testers that are in the current standard were included in the research.
As confirmed by a research paper presented at the SSPC National Conference, 3 the adhesion values generated by the various test devices can vary considerably. In this case, the minimum adhesion requirement becomes variable. Further, when data are generated using different types of pull-off testers, it is difficult to compare the tensile adhesion characteristics within a given generic coating category, or to compare the adhesion quality of different coating systems.
Ina plan was developed to conduct a comprehensive interlaboratory study involving six coatings, six laboratories and five types of adhesion testing equipment.
William D. Corbett KTA-Tator, Inc.
The study was conducted methhod and is close to completion. The results of the interlaboratory study and the content of the research report will be reviewed in early The data astj reveal the variations in testers and operators, and will be used to formulate new precision and bias statements. The entire standard is being revised, and will include among other changes more specific operating procedures for the various types of test equipment. Pull-Off Adhesion of Coatings on Concrete As stated above, the original version of D published in did not distinguish between testing the pull-off strength of coatings applied to steel versus concrete surfaces.
While the test method is designed to quantify the adhesion strength of the applied mfthod system, the substrate beneath the coating emthod be ignored.
Steel is a fairly homogeneous substrate and its tensile strength does not vary from test site to test site. Further, the tensile strength of steel far exceeds the tensile strength of an industrial protective coating. Conversely, concrete is a heterogeneous substrate.
Portland cement concrete is a mixture of aggregate and cement paste. While concrete has an impressive compressive strength often in excess of 28 Mpa psithe inherent tensile strength is only about 2.
Differences in Surface Profile Measurements: ASTM D4417- Method B vs. Method C
As a result, there are differences in testing procedures that v4417 be considered when evaluating coatings applied to concrete, versus coatings applied to steel. These include the size of the loading fixture, and scoring of the coating based on inherent thickness prior to attachment of the loading fixture.
The specified minimum pull-off strength must also be carefully considered. For example, requiring a 5. Size of the Loading Fixture Qstm Surface When a loading fixture with a small contact area is used, the pull-off strength achieved may be significantly influenced by the composition of mdthod surface of the concrete directly beneath the loading fixture. For example, a loading fixture inadvertently attached over a large piece of aggregate in the concrete will reduce the stress applied to the cement paste the weaker constituent in concrete and generate a highly variable pull-off strength tensile value that exceeds the inherent tensile strength of the concrete.
Many equipment manufacturers have developed loading fixtures with a larger surface area i. Scoring the Coating Cutting scoring through the coating prior to the attachment of the loading fixture has long been a controversial issue. As acknowledged in Dscoring can cause micro-cracking in the astmm, which may cause diminished pull-off strengths.
The decision whether to score has been left to the parties requiring the testing and those conducting it. Generally, if it was not addressed in the specification, then scoring was not to kethod done. However, thick film coatings i. Some of the coatings are applied up to 3.
So scoring is likely necessary on thick-film systems applied to concrete when trying to determine if mmethod coating is firmly bonded to the substrate.
In response to these and other issues, Subcommittee D The data to support these statements will be generated via an interlaboratory study, which is planned for Conceptually, the study will include two types of concrete normal and high strengthtwo coatings thick film with scoring and thin-film without scoringfive types of adhesion testers and up to seven laboratories.
Information relating to testing the tensile adhesion strength of metbod applied to surfaces other than steel will be removed from D during revisions x4417 are also planned for Surface Chloride Extraction and Analysis The protective coatings industry has long recognized the potential consequences of coating over soluble salts i.
Chloride contamination is the result of exposure to marine or coastal environments, chemical processes, or exposure to deicing materials i. Soluble salts like chloride, when trapped beneath a newly applied coating, can draw water through the coating film by a process known as osmosis and cause blistering and underfilm corrosion. Since corrosion products expand as they migrate beneath a coating film, the coating may disbond, leaving the substrate unprotected. Elevated levels of chloride can also lead to section loss and pitting of the steel substrate, as chloride contamination can accelerate the corrosion process.
Early detection and removal of appreciable amounts of surface chloride contamination prior to coating installation can prolong the service life of a coating, reducing the frequency of maintenance painting and reducing life cycle costs. Assessing the presence of surface chloride and quantifying the concentration is paramount to this process. Without reliable methods for extracting a sample from the surface and analysis of the collected sample, the degree and type of surface cleaning required prior to coating installation can be uncertain.
ASTM WKDraft Practice for Assessing the Concentration of Soluble Chlorides on Metallic Substrates, provides procedures for four methods of extracting a surface sample, four procedures for analyzing the collected sample for soluble chlorides, and one procedure for analyzing a collected sample for total dissolved salts conductivity.
Other trade organizations NACE International and the Society for Protective Coatings are jointly developing a guidance document on acceptable levels of soluble surface chloride, based on the coating type and prevailing service environment. See Figures 1314 It is envisioned that the draft will be published in as a test method, but without precision and bias statements.
A plan is currently under development for an interlaboratory study on the various methods used to extract and analyze samples, as described in the method.
Resistance to Graffiti The resistance of coatings to graffiti and the ability to remove graffiti from coated surfaces is of interest to owners of buildings and other structures, as graffiti artists continue to deface public and private property. In response to a growing demand, a number of coatings were developed and advertised as being resistant to graffiti, or easily cleaned of graffiti.
The practice identified four commonly used graffiti marking materials, five cleaners, and up to two removal methods hand or automated. The cleaning agents are used in a particular order of increasing aggressiveness to determine which one can remove the graffiti, with limits on level of gloss reduction and color difference to the affected coating.
Difference in Surface Profile Measurements: ASTM D Method B vs CKTA University
Tests are done on smooth surfaces, and are not designed to address rough or porous surfaces like concrete block or brick, which would be substantially more difficult to clean without special tools and methods.
Coating manufacturers and others in the user community found the practice to be cumbersome and time consuming, and rarely did the facility owners require the level of testing dictated by the standard. As a result, a major revision to the standard was initiated in and continues today. There are many revisions being considered by the subcommittee. Some of the major ones include: