Limes and derivates Calcinor - Stabilisation FAQ

What kind of limes can be used to stabilise soil?

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).

What are the specifications of limes for use in soil stabilisation?

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

How are soils classified?

There are various soil classifications, the most commonly used being the following.

· P.R.A (Public Road Administration, United States).
· CASAGRANDE (created by Arthur Casagrande). This is the most well-known and has been adopted by various entities.
· L.C.P.C.- SETRA (created by the French entity L.C.P.C.- SETRA in the Seventies, it appears in the French standard NFP 11300).
· ARTICLE 330 of the General Technical Specifications for Road and Bridge Works (PG3) from the Spanish Ministry of Public Works.

These classifications generally adopt as their main criteria the granulometry and plasticity of soils, and some of them include the parameters of humidity in accordance with the natural state of the soil.

The characterisation of a soil is carried out by using two types of parameters, known as natural parameters (analysis of granulometry, plasticity and swelling) and condition parameters (compaction analysis using the Proctor test and load-carrying capacity using the CBR- California Bearing Ratio test).

What types of soils are suitable for stabilisation with lime?

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.

Can you combine lime with pulverised fuel ash in soil stabilisation?

Adding pulverised fuel 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.

Can you use lime in soils that have a high soluble sulphate content?

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.