## 2 Materials and Methods Considered in the Research
### Materials Considered in the Research
#### 2.1.2 Chemical Stabilisers
Although it is still most often used for the production of concrete products (approximately 65%), its use is increasingly common for the purpose of soil and waste stabilisation, approximately 7% [19]. Due to its significant application in this century, some of the eminent researchers included fly ash in conventional stabilisers [5; 7]. Although it could be used in combination with lime or cement to stabilise soil, a number of research works have confirmed that fly ash can improve soil properties without additional activators [20; 21]. In thermal power plants in Serbia, 35 to 40 million tonnes of coal are consumed annually, and around 7 million tonnes of fly ash are produced. This makes up almost 80% of industrial waste in Serbia. Of this amount, only 3% is used in the production of cement, so there is a huge potential for the application of fly ash for the purpose of soil stabilisation during construction on weak soils of lower bearing capacity. The fly ash used in this research was deposited from the thermal power plant Kostolac, with the chemical composition SiO\({}_{2}\) (56.38%), Al\({}_{2}\)O\({}_{3}\) (17.57%), Fe\({}_{2}\)O\({}_{3}\) (10.39%), CaO (7.46%), and MgO (2.13%). The success of soil improvement with fly ash depends on soil properties, the content of fly ash in the soil, the time interval since treatment, and the amount of water at the time of compaction. Some previous studies have shown that the optimal content of fly ash can range from 10% to 30%, depending on the type of soil and fly ash [21; 22]. With an aim of determining the optimal content of fly ash, in this research, samples of clayey soil with the addition of 10%, 15%, and 20% fly ash were tested. **Rock flour** is waste from stone quarries and is successfully used as a finishing material on highways. It is produced during the extraction of stone and production of crushed stone, whereby about 20% of the rock material is turned into waste material--rock flour. Research has shown that adding rock flour can successfully contribute to the improvement of the geotechnical properties of expansive soils [23] and lateritic soils [24]. The obtained results indicate the possibility of reducing the plasticity and increasing the bearing capacity of the soil with an increase in the content of rock flour. According to some recent studies [24; 25], the optimal content of rock flour is not higher than 15%. Therefore, in the present research, clayey soil samples with the addition of 5%, 10%, and 15% rock flour were tested. The rock flour was deposited from the stone pit Gradac (\"Strazevica\"-Batocina), which is located near Nis. It consists of dolomite (CaMg(CO\({}_{3}\))\({}_{2}\)), which makes up 99% of the rock, whereas secondary minerals include calcite (CaCO\({}_{3}\)) and muscovite ((KF)\({}_{2}\)(Al\({}_{2}\)O\({}_{3}\))\({}_{3}\)(SiO\({}_{2}\))\({}_{6}\)(H\({}_{2}\)O)). * Alternative chloride-based reagents  
Chloride-based compounds are categorised as non-traditional or alternative stabilisers. Non-traditional stabilisers are chemical compounds that do not contain a large amount of calcium [26]. Furthermore, these are mostly reagents in liquid state, which are more economical for transport than traditional ones and are diluted with water on site. They can be applied directly to the soil layer before compaction or injected under pressure into deeper layers [27]. Strong electrolytes such as potassium chloride (KCI), calcium chloride (CaCl\({}_{2}\)), and ferric chloride (FeCl\({}_{3}\)) were used as alternative stabilisers in the present research. Some recent studies have shown that these electrolytes can be effectively used instead of lime or cement in soil stabilisation, owing to their better solubility, their easier mixing with soil, and the fact that they provide the necessary cations for the cation exchange process [28; 29; 30].