AGRICULTURE TESTING TARGETS POTENTIAL SULFATE HEAVE AREAS

By: Matthew W. Singel, PE
When stabilizing soils with calcium-based additives (cement, lime, etc.), accurately determining the presence and concentration of sulfates (gypsum) is important.  If high sulfate concentrations are present and not recognized in advance, sulfate-induced heave can occur.  

To identify the presence of sulfates, testing labs will collect random soil samples from a project site and test them individually.  The testing procedures are reliable; however, on-site soil conductivity measurements may offer a targeted approach for obtaining the soil samples.  A breakthrough study by three Texas researchers shows that measuring the bulk electrical conductivity eliminates low-risk areas, allowing testing professionals to narrow their focus on a smaller area in question.

Soil conductivity testing, adapted from the agricultural industry, does not guarantee the presence of sulfates as other salts can also exhibit a high bulk soil conductivity.  It does, however, allow us to eliminate sampling in areas that exhibit a low conductivity readings and target areas where a higher probability exists.  Using field-acquired soil conductivity data in conjunction with existing geological maps, (USDA/NRCS) soil maps and data available from state and local agencies will increase awareness, reduce unnecessary testing and reduce the potential for surprises during construction.
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Presented at the 91st (2012) Transportation Research Board Meeting in Washington, D.C., the research was conducted by Pat Harris of Sam Houston State University along with Omar Harvey and Stephen Sebesta of the Texas Transportation Institute.  
"This blog was previously posted in the Cement Council of Texas' "Texas Cement and Concrete Blog" (now inactive) and was carried forward to the current blog ("Cementx Pavement Blog") as it contains content that may be of interest to the reader".