Role of sulfates on highway heave in Lake County, Ohio.
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2014-01-01
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Abstract:Samples from borings in areas of heave on Route 2, Lake County, OH were analyzed for the amount, mineral form,
and distribution of sulfates. In addition, samples of non-stabilized (NSS) and cement-stabilized (CSS) soils from
three stations along Route 2 were analyzed for mineralogy and sulfate content. Finally, swell tests were run using
the NSS samples to evaluate the degree of swelling and the role of ettringite. The sulfate content in the natural
subgrade soil samples range from low (<3000 ppm) to unacceptable risk (>10,000 ppm) for heaving based on the
TxDOT guidelines, and 36% tested above the moderate risk level (>5000 ppm). Gypsum and/or anhydrite were
detected in 64% of the samples. The CSS samples contained white precipitates that were largely calcite, but with
measurable amounts of ettringite as well. The NSS did not contain ettringite but had sulfate levels of moderate to
high risk (4880 to 6107 ppm). Swelling of up to 8% was observed in the swell test samples; however, the amount of
swelling did not correlated with the amount of sulfate present in the soil. Ettringite crystals were found in all of the
swell test specimens after the experiment. In some cases the crystals were flat and coated the soil particles while
others were long needle-like crystals that radiate out from bundles. This difference in crystal shape is thought to
relate to the difference between primary and secondary ettringite growth in the samples.
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