PROBLEMS WITH SODIUM SULFATE SOUNDNESS OF DOLOMITE AGGREGATES OF NORTHERN ARKANSAS

On the average, 1/3 of the dolomite aggregate samples from northern Arkansas that are evaluated by the sodium sulfate soundness test exceed the 12% loss limit set by the Arkansas Highway and Transportation Department (AHTD) for acceptance. To aid in exploration for acceptable dolomite in this region where dolomite constitutes the sole rock type available for construction aggregate we conducted soundness tests on more than 50 samples of dolomite from the Cotter Dolomite. We compared results of the soundness test with various visible rock features, such as rock texture, grain size, color, presence or absence of chert, and the presence or absence of hydrothermal dolomite pore fillings. We also compared the Na-sulfate soundness with results from several lab tests including insoluble residue, water absorption, and X-ray diffraction analysis. The goal was to find easily identifiable attributes that would characterize dolomite that would likely pass the soundness test. However, none of the comparisons revealed trends consistent enough to establish reliable indicators. One likely factor for the failure to establish consistent trends is the very poor precision inherent in the sulfate soundness test itself, as is well documented in the research literature regarding this test. An extensive search in the literature revealed several factors that lead us to recommend that the AHTD and any other users of dolomite aggregate reconsider their acceptance criterion with respect to this test. The soundness test’s most serious flaws are its poor precision and reproducibility, a lack of relevance to the environmental stresses it is supposed to simulate, and marginal success in correlating with field performance data. The Na-sulfate soundness test limits should be made more lenient for Arkansas dolomites or perhaps the test should be dropped altogether, at least for asphalt surfaces and for road base applications. We recommend this because the dolomites we studied, including ones that failed according to the 12% loss limit, have a similar range of soundness values as field-proven durable dolomites from other studies. Furthermore, identical dolomites in neighboring Missouri have been used successfully in asphalt surface and base-course aggregate applications.