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The Illinois Department of Transportation (IDOT) uses the sodium sulfate (Na2SO4) soundness test as one of its main aggregate acceptance tests. Unfortunately, many accusations concerning the lack of reproducibility and validity of the soundness test are continually voiced by aggregate producers and specifying agencies.
In order to better understand the sodium sulfate soundness test, IDOT conducted an evaluation program to identify the major problem areas in the test method. The evaluation program consisted of eight separate evaluations. Samples from a number of different Illinois aggregate sources were tested for each evaluation. The evaluations looked at (1) temperature control, (2) different Na2SO4 materials, (3) repeatability, (4) validity, (5) increased cycles, (6) cooling of samples, (7) pan versus basket soaking, and (8) the method used to interrupt the test.
Several general conclusions were drawn from the evaluations on the sodium sulfate soundness test. These conclusions identify areas of the test procedure which could produce erratic and erroneous results. One area was that temperature must be accurately controlled, both during soaking and during cool down of the samples. Another was that the specified method of interrupting the test produces results that do not correlate with running the test straight through to completion. There are also several other items that indicate potential problems and that should have additional research run on them.
The overall summary concluded that when tighter control, especially temperature, is maintained, the sodium sulfate soundness test seems to provide valid test results.
Geologist/Aggregates, Bureau of Materials and Physical Research, Illinois Department of Transportation, Springfield, IL
Stock #: CCA10105J