ASTM C1077 is the “Standard Practice for Agencies Testing Concrete and Concrete Aggregates for Use in Construction and Criteria for Testing Agency Evaluation.” Agencies such as AASHTO provide independent accreditation of laboratories that meet these criteria.
As we’ve discussed previously, in the construction industry the quality of the concrete delivered to the site is tested according to ASTM C31 and ASTM C39. For most tests, small errors in testing could make the result either artificially high or artificially low. That is, it would average out in the end. But with ASTM C31 and C39, just about any testing error yields an artificially low result.
To avoid the expense and delays that come when concrete doesn’t meet the strength requirement, producers aim for a higher average strength. Typically they add more portland cement. As we discussed earlier, that extra cement adds to both the cost and the carbon footprint. In some cases it can even detract from the performance of the concrete. For example, it may increase the concrete’s shrinkage or its tendency to crack.
Because bad testing can lead to excessive overdesign, it’s imperative to verify the laboratories we depend on for accurate testing. That’s where ASTM C1077 comes in. It sets forth minimum requirements for laboratories.
Qualifications for personnel
The laboratory must be under the full-time direction of a Professional Engineer. In addition to the license, this person must have at least 5 years’ experience in construction materials testing.
Laboratory- and field supervisors must have at least 3 years’ relevant experience, along with current certification in the test methods they are supervising.
Technicians conducting laboratory- or field testing must have current certification in the relevant tests. While various agencies may administer the certifications, they must include detailed written and performance examinations of the technicians. ASTM C1077 lists the test methods for which technicians must obtain certification for testing of aggregates and for testing of concrete in the laboratory and the field.
Test methods and procedures
Similarly, ASTM C1077 lists the test methods in which the laboratory must demonstrate capability. For concrete testing, they must at least be able to sample the concrete (ASTM C172); measure the slump (ASTM C143); obtain the unit weight, yield, air content (ASTM C138), and temperature (ASTM C1064); make and cure the test specimens (ASTM C31); measure the compressive strength (ASTM C39); and cap cylinders (ASTM C617 or C1231).
For aggregate testing, they must be able to perform a sieve analysis (ASTM C136), determine the quantity of fines (ASTM C117), and measure the specific gravity and absorption for coarse and fine aggregates (ASTM C127 and C128, respectively).
Laboratories may arrange with the certification agency to obtain certification for additional tests as well.
The laboratory must demonstrate that it has the equipment, facilities, and personnel to perform all of the tests for which it desires certification. The certification agency will witness the technicians performing the agency’s choice of additional tests to verify that they perform them in accordance with the latest version of the applicable ASTM standard. Copies of the standards must be readily available to the technicians. The agency will also verify that the testing equipment meets the requirements of the relevant standards.
Various agencies conduct proficiency sample programs in which laboratories receive samples from the same lot of material, conduct a standard test, and report the results. The agency compares the results from each laboratory to verify that its results are comparable to the others. Laboratories must participate in proficiency sample programs to maintain certification. If their results deviate significantly from the average, they must take measures to improve their procedures.
Records and reports
The laboratory needs to maintain meticulous records of it standard operating procedures, calibration of its equipment, personnel training, and audits and inspections. Current versions of all of the standards they use must be available to the technicians.
ASTM test methods specify what to include in the report of test results. In addition, ASTM C1077 requires that test reports include the name and address of the laboratory, the name of the client, the project and sample identifications, and the name of the supervising Professional Engineer. The laboratory must retain its test reports for at least 3 years.
The laboratory must also maintain a quality manual detailing in writing its quality assurance procedures. Its internal quality assurance program must include training and evaluation of personnel and maintenance and calibration of equipment.
Proficiency sample programs are an essential part of quality assurance. The organization conducting them must be independent of the laboratory. Each program must have at least 10 participants. The organization must issue a report with the laboratory’s result, the mean and standard deviation of the results, and a rating of the laboratory based on its standard deviations from the means. The programs must be conducted at least once a year, with records retained for at least 3 years. The laboratory must have procedures in place in case it receives a low rating—that is, if its results are more than two standard deviations from the mean.
The laboratory must also have a procedure to follow when it determines that its equipment was out of calibration or that it deviated from standard test procedures. This procedure must include review of all work since the last calibration or verification of testing procedures. The laboratory must also notify any clients of nonconforming test results.
Who evaluates the labs and the technicians?
The Cement and Concrete Reference Laboratory (CCRL), a division of ASTM, evaluates testing laboratories and conducts proficiency sample programs using ASTM test methods. AASHTO accredits laboratories and conducts proficiency sample programs using both AASHTO and ASTM tests. The US Army Corps of Engineers’ Vicksburg, MS, laboratory validates laboratories that perform work for the Corps. A laboratory may maintain accreditation with more than one of these agencies. Laboratories that perform work for their state DOT may need AASHTO accreditation, while those that perform work for the Corps of Engineers must have Corps accreditation. Most of the test methods used by all three agencies are either ASTM methods or based on ASTM methods. However, both AASHTO and the Corps have some tests unique to them.
The American Concrete Institute (ACI) has certification programs for field- and laboratory concrete technicians and for aggregate technicians. ACI certifies technicians for proficiency in ASTM test methods and, in Canada, CSA methods. State DOTs have their own programs for certifying technicians. As with laboratory accreditation, technicians may maintain certifications with more than one agency depending on their client base.
Avoiding a race to the bottom
Maintaining accreditation for a concrete laboratory is neither easy nor inexpensive. The engineer, supervisors, and technicians all require continuing education and periodic renewal of their credentials. The laboratory must participate in proficiency sample programs, maintain a rigorous quality assurance program, and renew its accreditation(s) every few years. The equipment requires regular maintenance and calibration.
As we’ve discussed in previous blogs, poor-quality testing may have a lower price to begin with, but the ultimate cost is high. Specifications should require that the laboratory have the appropriate accreditation and that all technicians have the necessary certifications. The contract should spell out who has responsibility for providing on-site curing to maintain specimens within the correct temperature range. The owner or Engineer of Record should verify that the lab has a full-time Professional Engineer in charge and should know how to contact that person. ACI PRC-132.1 outlines the responsibilities of the respective parties in more detail.
The Colorado Ready Mixed Concrete Association’s Concrete Testing Alliance Collaboration program collects data on field testing of concrete. Observers concentrate on four questions:
- Is the technician certified?
- Was the concrete sampled correctly?
- Were the tests done correctly?
- Were the specimens subject to proper initial curing?
This program has been expanding across North America. By highlighting correct performance, it contributes to a culture of quality in testing. That’s far more constructive than a race to the bottom.