Laboratory and Field Procedures for Measuring the Sulfate Content of Texas Soils (0-4240-1)

Project 0-4240 was initiated to provide guidelines on how to effectively stabilize sulfate rich soils. The first tasks in this project involved evaluating the various methods of measuring the sulfate content of soils both in the laboratory and in the field. In the laboratory, two test procedures were investigated, namely Texas Department of Transportation (TxDOT) Test Method Tex-620-J gravimetric approach and the Ion Chromatography approach. For this comparison, control samples with known sulfate contents were fabricated in the laboratory. The samples were treated with known amounts of fine-grained and coarse-grained sulfate crystals. A range of samples was sent to TxDOT and several private laboratories. In terms of both accuracy and repeatability, the researchers concluded that the Ion Chromatography approach is superior to TxDOT Test Method Tex-620-J. Recommendations are submitted to improve the Tex-620-J procedure. The main conclusion is that TxDOT should consider replacing Tex-620-J with the Ion Chromatography approach. Sulfate swell problems are frequently localized, so substantial effort was placed on evaluating rapid field tests. Four potential tests were evaluated, two were found to provide good results. Both the Colorimetric/Spectrophotometric and Conductivity tests should be considered for full-scale implementation. A survey of both automated and map systems revealed that the existing geological maps provide a good first-cut indication of locations with potentially high sulfate contents. The automated Soil Survey Geographic (SSURGO) maps hold great potential for future use, however, they are available for less than half of the Texas districts and some errors and inconsistencies were found.