Detection and Assessment of Sulfates in the Pavement Subgrade

The ability to accurately detect sulfates in an existing subgrade has been a major challenge for INDOT’s pavement maintenance and rehabilitation projects. Although naturally occurring sulfates in soil pose a significant construction challenge, detecting sulfates in an existing subgrade may be problematic and costly, given that the presence of sulfates could result in expensive treatments or even removal of the subgrade. The project evaluated the performance of the ITM-510 test, a colorimetric test method utilized by INDOT to detect sulfates in soils. Soils collected from different Indiana road construction projects and two ASTM reference soils were treated with lime and lime kiln dust and tested for sulfates after being cured for 7 and 28 days. The sulfate content obtained from the ITM-510 test was compared with levels obtained from the ion chromatography (IC) test, an analytical test method used to separate, identify, and quantify ions in solution. Test results indicated that ITM-510 was adequate for identifying the presence of sulfates and for providing accurate values of sulfate concentration at <5,000 ppm sulfate concentrations. For larger concentrations, the errors may be large. It was also found that about 3% sulfate concentration in lime products can raise the sulfate concentration of lime-treated soils by as much as 2,000 ppm.