You can use either quicklime or slaked lime. Quicklime reacts with the humidity in the soil (the hydration process) and then acts on the stability and characteristics of the soil. Quicklime allows the level of humidity in the soil to be reduced almost immediately. If the soil to be stabilised does not have a high humidity level, you can use slaked lime directly (calcium hydroxide).

There is a Spanish standard (UNE 80.502) that defines the characteristics of limes to be used for soil stabilisation.

Before starting any work with soil, it is essential to have the most accurate possible information on the characteristics of the materials that make it up, the problems that these materials may generate, and the solutions that can be adopted (for example, stabilisation treatment with lime).

As a general rule, in order for soil stabilisation with lime to be effective, the soil should be quite plastic, and in this sense it is considered that soils with a Plasticity Index (PI) equal to or greater than 10 are suitable for reacting satisfactorily to stabilisation with lime, given that this is crucial for the chemical reactions to take place that improve the properties of the soil both immediately and in the long term.

Adding pulverised fly ash can significantly increase the resistance to compression of lime-treated soils. Pulverised fuel ash contributes additional elements such as aluminates and silicates, reacting with the calcium in the lime to form calcium aluminates and silicates thanks to the pozzolanic action of combining the lime with pulverised fuel ash. This kind of mixture is particularly suitable for soils with very low plasticity indices and a high content of very fine materials or silt.

When looking at a soil stabilisation project, you need to pay special attention to the sulphate content of soil. In addition, you need to take great care when using lime or any other limestone-based stabilisation product with soils whose clay content is higher than 10% and 1% of soluble sulphates. For your information, we offer you this address www.lime.org/factsheets.html where you can consult publications from the US Lime Association.