## 2 Materials and Methods Considered in the Research
### Materials Considered in the Research
#### 2.1.2 Chemical Stabilisers
The reaction induced by the mentioned cation exchange is very fast, so immediately after the addition of lime to the soil, the soil properties change significantly. Finally, there is a long-term reaction of lime with active silica and alumina from clay minerals--the porzolamic reaction. The silica and alumina break down, forming a new crystalline stage known as hydration, the products of which are calcium silicate hydrates CSH (Ca2+ 2 OH- + SiO2 \(\rightarrow\) CSH) and calcium aluminate hydrates CAH (Ca2+ 2 OH- + Al2O3 \(\rightarrow\) CAH) as gel-like materials with highly binding properties. For the purpose of determining the optimal lime content, samples of clayey soil with the addition of 3%, 5%, and 7% lime were examined in this research, whereby commercial hydrated lime marked CL 90 S was used, with the following chemical composition: CaO (71.01%), MgO (3.05%), and SiO2 (2.14%). When it comes to **cement**, although there are almost no restrictions on its application in soil stabilisation, the stabilisation of coarse-grained and fine-grained soils can be distinguished. In order for the cement binder to be successfully applied during stabilisation, it is necessary that the content of organic ingredients in the soil is at most 2% and that the pH value of the soil is not less than 5.3 [18]. In the case of coarse-grained soil mixed with a cement binder, with the presence of water, there is hydration of the cement, the formation of certain compounds (primarily calcium hydrate and aluminum hydrate), and the binding of the grains. Due to the relatively small amount of cement, covering the grains with the binder cannot be achieved completely, so the soil is highly porous, but despite this, it is still firm and stable. With a mixture of fine-grained soil and cement, hydration as well as binding of soil particles occurs. As the particles are of smaller size, the cement can cover the grains completely. With larger amounts of cement, a fine cement skeleton is formed, which extends through the soil and improves its mechanical properties. There is also an additional stabilising effect for this type of soil material. During hydration, a certain amount of CaO is released from the cement, which reacts with active silica and alumina from clayey soil minerals, and then, in a longer, slower process, it further contributes to the increase in soil  
Figure 1: A schematic presentation of cation exchange and stabilisation mechanism by adding lime to a clayey soil [17]. strength. When it comes to the optimal content of cement, a very wide range can be found in the literature; however, it depends primarily on the properties of the natural soil. The cement HRB E2 was used in this research. The chemical composition of cement is CaO (51.73%), SiO\({}_{2}\) (15.20%), Al\({}_{2}\)O\({}_{3}\) (5.13%), Fe\({}_{2}\)O\({}_{3}\) (2.39%), SO\({}_{3}\) (1.87%), and MgO (1.02%). This type of cement binder is primarily used to stabilise coarse-grained soil. For this reason, tests were carried out with a higher percentage share of cement binder compared to the percentage share of lime. For the purpose of determining the optimal cement content, samples with 5%, 10%, and 15% cement were tested. * Waste materials  
With urbanisation and great industrial growth, the operation of various plants generates a huge amount of industry waste, such as fly ash and rock flour. **Fly (electro-filter) ash** is produced in thermal power plants, where it is separated from waste gases using filter devices. Fly ash is a material that needs to be disposed of and treated as construction waste, only in cases when it does not belong to the class of hazardous waste, that is, if it does not have increased radioactivity. In civil engineering, its application was initially related exclusively to production of concrete; in recent decades, however, it has a much wider application, increasingly gaining importance.