Implementation of technology for rapid field detection of sulfate content in soils

Abstract

In roadway construction, chemical stabilization with calcium-based stabilizing materials (CBSMs) such as lime and cement can enhance many of the engineering properties of soil (subgrade) such as compressive strength, resilient modulus, shear strength, plasticity, and long term durability. However, soluble sulfate phase contained in some soils can react with CBSMs, resulting in volume expansion stability problems due to the growth of ettringite crystals on the clay particle surfaces through the chemical reaction between calcium components in stabilizer and sulfates and aluminates in the soil. The current Texas Department of Transportation (TxDOT) testing protocol in the field uses a spot test that measures sulfate content every 500-ft interval on a project (Tex-145-E). If a high sulfate zone lies between 500-ft intervals, the current testing protocol will miss this sulfate zone. The protocol using a device called Veris 3150 system (Figure 1) was developed and used as a continuous measurement of sulfate content as a function of electrical conductivity of soils.