Evaluation of the Sodium-Sulfate Soundness Test for Qualifying Dolomites of Northern Arkansas for Construction Aggregate

摘要

Dolomite formations constitute the sole rock type suitable for crushed-stone aggregate in a sizeable portion of the highlands region of Arkansas. Historically, an average of one-third of the samples from a great variety of quarries in these rocks have exceeded the 12 percent loss limit for the sodium-sulfate (Na-sulfate) soundness test. A study was conducted to determine if some easily identified physical features of the dolomites might distinguish dolomite that is likely to pass the test from potentially failing dolomites. Na-sulfate soundness tests were run on more than 50 samples having a variety of textures, colors, grain sizes, and accompanying features, such as chert nodules and hydrothermal dolomite pore-fillings. Soundness values were compared among rocks having these varying qualities. Some comparisons with other features determined by laboratory analysis were also made, including insoluble residue, water absorption, and X-ray diffraction analysis. None of the comparisons revealed clear trends that could reliably identify dolomite that is likely to pass the soundness test. A search of the research literature was conducted to try to understand the reasons for the difficulty in establishing correlations. One likely reason is the poor reproducibility inherent in the test itself. The literature search revealed several matters that have important implications for use of dolomite in northern Arkansas. Aggregate users should reevaluate how this test is applied for acceptance because of its poor precision, lack of relevance to actual environmental stresses, and marginal success in correlating with actual field performance records. The sodium-sulfate soundness test should be dropped as a criterion for acceptance of dolomite for asphalt surfaces and base-course applications in Arkansas, or at least limits of the test should be more lenient. We make this recommendation because Arkansas dolomites, including typical ones that fail the 12 percent loss limit, plot with dolomites from other studies that have been proven durable by field studies. Furthermore, similar dolomites across the border in Missouri have been used successfully in asphalt surface and road-base aggregate applications.