Experimental studies on ettringite-induced heaving in soils

Sulfate-induced heaving in soils is primarily attributed to ettringite formation from the reactions between calcium of a lime or cement stabilizer, reactive alumina in soils, and sulfates in soils. Ettringite formation and subsequent heaving in soils are complex topics that are not well understood. This research is an attempt to advance the state of the knowledge on these topics. Ettringite was successfully synthesized in the laboratory by simulating conditions close to those in chemically treated sulfate-bearing soils. Soils spiked and compacted with the synthesized ettringite did not undergo heaving in one-dimensional free swell tests. However, heaving was observed when ettringite was formed inside the lime-treated soil specimen by including ionic reactions. Mineralogical studies including x-ray diffraction and scanning electron microscope studies were used to evaluate the presence of ettringite. Experimental investigations showed that the ettringite or sulfate-induced heaving was higher in clays than in sands under similar chemistry and environmental conditions. This is attributed to the void sizes of soil types and crystalline ettringite formation in the voids. Also, the effects of soil type, lime and sulfate amounts on this type of heaving, and hypothesized threshold levels of chemical ions to form ettringite mineral in treated soils, are addressed.