CONTEMPORARY ISSUES

The most common contemporary remedies adopted for the stabilisation of soft and expansive sulphate-bearing soils (e.g. gypseous soil), involve the use of portland cement and lime.

Lime-treated gypseous soil however has low durability due to the formation of Ettringite, which is a highly baneful compound, that also forms in hydrated portland cement. Moisture ingress in building materials or environments containing these materials, causes Ettringite crystals to swell substantially, leading to considerable damage to construction structures and pavements.

Besides being chemically incompatible with sulphate-containing soils, from an environmental perspective, the manufacturing processes of portland cement and lime are energy intensive and contribute significantly to environmental pollution. For every tonne of portland cement manufactured almost 0.95 tonnes of CO2 is emitted and the process requires almost 5000 MJ of energy. For lime production, these values are approx. 0.79 tonnes of CO2 and approx. 3200 MJ of energy.

It is evident that alternative materials that are both environmentally sustainable and chemically compatible to repress the formation of Ettringite while effectively performing the necessary function of soil stabilisation are essential to mitigate the contemporary challenges.

The reason being that Improving the properties of soft subgrade soils is crucial in the construction of robust roads and and economical pavements. Buildings constructed on soft soils may fail due to the low strength, and an excessive settlement of the soil under a constant load. It is hence imperative, to improve sublayer soil quality and strength before construction, so as to make thinner and more mechanically robust foundation structures possible while simultaneously eliminating and or minimising the maintenance costs associated with the failure of buildings, roads and highways.