Effects of monovalent and divalent metal sulphates on consistency and compaction of lime-stabilised kaolinite

The factors influencing the durability of compacted lime-stabilised clay soils depend in part on the short-term material properties that emanate from the immediate changes that occur (within a few hours) during the initial part of the stabilisation process. The long-term properties take a much longer period to develop and small changes are still occurring after several years. In both cases, the genesis of the properties may be directly linked to the properties of the parent soil and the cationic process that takes place as soon as the mix materials are in contact with water. Thus, the significance of the constitution of the parent material and the factors influencing the cationic exchange process cannot be overemphasised. Both these factors are affected by the presence of sulphates in the soil. This paper shows how the commonly occurring monovalent metal sulphates of sodium and potassium, and the divalent ones of calcium (gypsum) and magnesium, affect the consistency and dynamic compaction properties of an industrial kaolinitic clay soil of high purity, to which sulphates have been artificially introduced. The results clearly illustrate that the effects of the presence of sulphate depend strongly on the sulphate cation type. Some cations (Ca2+ and Mg2+) enhance the effects of lime addition while others have the tendency to reverse these effects (Na+ and K+).