Using the alkaline fly ash after combustion of lignite as the acid soils neutralizer is a technique known for decades. Due to many disadvantages of the direct fly ash application it is sought to modify this material prior to its use. The process of fly ash modification in the magnetic activator involved breaking up fly ash to small grain sizes in order to obtain a material with a very large specific surface and modified properties. The purpose of the research was to compare the properties of unmodified fly ash with those of ash modified in the magnetic activator in terms of its usefulness in the neutralization of acidic soils. Unmodified fly ash was classified as a medium-grained calciferous material. The basic components of ash were silicates (33.28% of SiO2) and calcium compounds (31.26% of CaO). It has a low heavy metal content falling within a range characteristic of coal ash and meeting soil quality standard requirements. As a result of activation, the following changes were obtained in the properties of modified ash compared with unmodified ash: sand fraction content – reduced to 0.40, silt fraction content – increased by 1.40, silt fraction content – increased by 1.68, content of the sum of the dust and silt fractions – increased by 1.49, specific surface – increased by 1.65, fineness – reduced by 0.48. Modification of fly ash in the magnetic activator was found to have improved the physical properties of ash as acidic soil neutralizer, and its chemical properties make such an application possible.

Certain soils encountered in practice are difficult or impossible to use for road building. To improve their mechanical properties, various methods of soil stabilization are applied. A widely used means of soil stabilization is the addition of hydraulic binders. In the methodology of designing of soil-binder mixtures it is important to determine how, based on variable parameters characterizing a sample of soil, to predict the grade of the binder and the quantity in which it is to be added to the soil in order for defined requirements to be met. This work describes an application of statistical logit model in designing soil-binder mixtures intended to be used for road foundations, subject to defined requirements as to their strength and frost resistance.

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The development of an appropriate soil-binder composite (stabilized soil) is associated with the selection of the appropriate strength class of the hydraulic binder (e.g. ash-cement) and its amount to stabilize the soil. Advanced statistical methods based on the use of the spline function were used in the analysis of tests of soil--binder composites. The analysis presents statistical modelling as a tool helpful in the design of soil-binder composites, showing possible interactions between the components of materials included in the mineral composition of composites. A logarithmic model of the compressive stress forecast was developed for soil-binder composites both with freezing cycles of the soil composition and without freezing cycles, in which the composites hardening time and the addition of ash-cement binders to the soil were continuous variables.