Many producers get the impression that, while not nearly as risky as buying a lottery ticket, testing labs often hold their company's future in a plastic mold. Since Beltway-area municipal building departments have adopted BOCA #1705, producers and building owners have had to rely on the quality of third-party engineering labs to inspect and test all aspects of the construction process. The absence of a municipal testing program created a void in the customary cycle of checks and balances.
Frustrated by a lack of an interlaboratory precision standard in ASTM, Teck Chua, a registered professional engineer in charge of QC/QA for Florida Rock Industries, proposed that the Ready Mixed Concrete Producers Technical Committee initiate a program to generate the precision standard. Now 30 to 40 testing facilities participate annually.
The program evaluates variability in test results attributable to differences in laboratory curing, capping and cylinder testing methods. Seeing five years of good results, lab managers now consider the round-robin program a good business practice. "Program results provide lab managers a baseline for quality," says Tom Cohn, executive director of the Washington Area Council of Engineering Laboratories. By comparing their individual results against the group's precision, managers can adjust their lab procedures.
A summary of the 1998 test results for low- and medium-strength tests results are given.
For the past five years the interlaboratory round-robin program has provided participating lab managers good opportunities to evaluate their testing procedures and to compare results with those of other area labs. Test-precision estimates are particularly important when compressive-test results are used for acceptance and payment decisions, since precision is a major factor affecting the required overdesign needed to avoid penalties.
WACEL officials maintain test-result confidentiality by assigning sample identification numbers to laboratories and not revealing individual results. Labs pay no fees to participate.
Chua says the program has helped. He now finds it easier to explain strength test differences. But as successful as the program has been, Chua thinks there's still work to be done.
Keywords: Virginia Concrete, round robin, Ready Mixed Concrete Producers Technical Committee, Washington Area Council of Engineering Laboratories, WACEL, National Ready Mixed Concrete Association, NRMCA, compressive, test, ASTM C 802, ASTM C 39.