Quick lime-gypsum interactions in stabilized soil bases for concrete highways

Lime stabilization of clayey soils is very common throughout many parts of the world. Typically if heaving is observed after quick lime (CaO) stabilization, then one may think that insufficient lime and/or poor slaking and mixing techniques may be the root of the problem. Actually, there are several other reasons for the observed heaving. One explanation is that the lime may have been hard burnt, thus rendering the lime inactive until months later. Another explanation is due to the interaction of the quick lime with gypsum (CaSO₄ . 2 H₂O) in the soil to be stabilized.One may conclude that lime, Type I portland cement, or Class C fly ash stabilization of high gypsum bearing soils would at best produce poor results because of the possibility of expansion due to the formation of ettringite.