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Erroneous results from improper testing can cause unnecessary rejection of good- quality concrete. Train your drivers to recognize some of the more common testing errors. This article is based on information presented in Down the Chute, the publication of Florida Independent Concrete and Associated Products Inc.The problem isn't confined to strength tests. Conducting other tests improperly can also cause rejection of in-spec concrete at the jobsite. Have your drivers learn the correct methods for sampling concrete, measuring slump and air content, and making and curing strength-test specimens in the field. They're your first line of defense against needlessly rejected loads of concrete.Some improper practices are:

  • Excessive prewetting, leaving surplus water in the container
  • Sampling from the form into which the concrete has been placed
  • Failure to remix the concrete sample in the sample container before starting the tests
  • Failure to use an aggregate correction factor
  • Use of the pressure meter to measure air content
  • Failure to firmly support the base plate
  • Base plate not large enough, allowing high-slump concrete to spill over the edge of the plate
  • Base not level
  • Dampening the slump cone and base leaving a puddle of water on the base
  • Measuring the difference between the top of the cone and the highest or lowest point on the slumped specimen
  • Failure to dislodge all concrete in the base before rolling and rocking the air meter.
  • Failure to roll and rock the air meter long enough for all air to rise to the surface of the graduated neck Keywords: test, driver, sampling, air, slump, volumetric