Get Consistent Results in the Plant Lab—Part 1 for Gyratory Specimens

For the toolbox tips this month, we’re concentrating on quality control/quality assurance, which means attention to detail. For the lab, let’s look at the way you make gyratory specimens. Quality results stem from a quality start. Here are a few ideas to improve the uniformity of the asphalt specimen.

Consistency in the specimens will build confidence in the test results down the line. To improve all of this, start with the consumables in the process.

It’s surprising how such a simple thing can affect the result, but studies have shown that the non-glossy paper disks you use in preparing the specimens matter. Paper disks with different surface textures and thicknesses will generate different specimen densities. If your lab produces its own paper disks from whatever paper stock is available, you’re not saving money; you’re adding variability and inconsistencies.

Three Steps Can Improve Your QC

You might not have thought of your mold assemblies as consumables, but the components may need replacing after time and wear. Monitor the wear of the mold and end plate so all mold assemblies remain consistent in size. Minimum clearance between the end plate and the mold surface should be 0.15 mm. Maximum clearance is 0.70 mm. If one assembly is at the minimum allowable size and another is at the maximum allowable size, you have variation creeping in. One source showed you can expect to see a bulk specific gravity difference of 0.020 per millimeter.

Next week, we’ll look at handling and compacting the gyratory specimen.

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