Assessment of sulphates effect on the classification of soil-lime-natural pozzolana mixtures based on the Unified Soil Classification System (USCS)

According to the Unified Soil Classification System (USCS), fine-grained soils, such as clays and silts, can be classified by plotting the values of their plasticity index and liquid limit on a plasticity chart. However, soil classification can be affected by mineral additives and sulphates. The effect of both sodium (Na2SO4) and calcium (CaSO4 center dot 2H(2)O) sulphates on the soil classification of soil-natural pozzolana, soil-lime and soil-lime-natural pozzolana mixtures has been studied. The results showed that in the absence of sulphates, the addition of lime and limenatural pozzolana to both clayey soils improved considerably their soil classification. However, a negligible change in soil classification was recorded when natural pozzolana was used alone. The presence of sulphates influenced significantly the soil classification of these mixtures, especially with the curing period. The modification in the soil classification was more pronounced with the Na2SO4 than with the CaSO4 center dot 2H(2)O. Furthermore, the sensitivity of the soil classification to the sulphate effect was also more pronounced with the Na2SO4 than with the CaSO4 center dot 2H(2)O. The utilisation of CaSO4 center dot 2H(2)O as on additive is highly recommended for obtaining the best class soil. In general, the transformation in the class soil of both stabilised grey and red soils depends largely on the type of additive and its amount, the type of sulphate and its amount, the mineralogical composition of the stabilised soil and the curing period.