Major infrastructure projects require significant amount of natural materials, often followed by the soft soil stabilization using hydraulic binders. This paper presents the results of a laboratory study of alternative waste materials (fly ash and slag) that can be used for earthworks. Results of high plasticity clay stabilization using fly ash from Serbian power plants are presented in the first part. In the second part of the paper, engineering properties of ash and ash-slag mixtures are discussed with the emphasis on the application in road subgrade and embankment construction. Physical and mechanical properties were determined via following laboratory tests: Specific gravity, grain size distribution, the moisture–density relationship (Proctor compaction test), unconfined compressive strength (UCS), oedometer and swell tests, direct shear and the California bearing ratio (CBR). The results indicate the positive effects of the clay stabilization using fly ash, in terms of increasing strength and stiffness and reducing expansivity. Fly ashes and ash-slag mixtures have also comparable mechanical properties with sands, which in combination with multiple other benefits (lower energy consumption and CO2 emission, saving of natural materials and smaller waste landfill areas), make them suitable fill materials for embankments, especially considering the necessity for sustainable development.

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Results of laboratory research focusing on soil stabilization, using fly ash without activators, are presented in the paper. Two types of fine-grained soils were tested: low to medium plasticity clay and very expansive, medium to high plasticity clay. Soil-fly ash mixtures were prepared at optimum fly ash contents (15 and 20 %). The effects of fly ash on the soil plasticity, moisture-density relationship, unconfined compressive strength, shear strength parameters, CBR (California Bearing Ratio) values, deformation parameters, and swell potential, were evaluated. Results obtained show that the use uf fly ash can significantly contribute to the improvement of soil properties.

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У раду су приказани резултати лабораторијских испитивања стабилизације глине високе пластичности применом летећег пепела из ТЕ Костолац. Испитан је утицај пепела на однос влажности и суве запреминске тежине, једноаксијалну чврстоћу, CBR, модуле деформабилности и потенцијал бубрења. Добијени резултати су показали да се применом пепела као стабилизатора могу побољшати неке инжењерске карактеристике ове врсте тла. Највеће побољшање је пораст CBR вредности, што ово тло чини употребљивим у путоградњи.