In transportation engineering, earthwork is the main structural material which geotechnical properties can be positively modified withadmixtures. This article focuses on the application of energy by-products in earthwork of transportation line structures and summarizes their advantages and define the scope of their utilization. Earthwork construction demands the considerable volume of qualitymaterial and therefore, the effort to optimize traditional material substitution is made. One possibility is to apply solid by-productsemerging when combusting coal, which is referred to as secondary energy products. These include various types of fly-ash, slag, bottomash or gypsum. Requisite for their further widespread utilization is the application in the construction and modernization of transportinfrastructure, including road and rail construction, or in the case of flood control dams within the framework of water managementmeasures against flooding. They can be utilized also as municipal waste dumps covering. However, the application of fly ashes inearthwork constructions delivers certain limits. When contacting with rain ingress or groundwater, the leaching containing heavy andtoxic metals depending on energy by-product type may occur. Alternatively, the limitation of their application can be relatively lowmechanical resistance to cyclic saturation and frost effect and consequent volume changes. This article deals with long-term observation results of the energy by-products saturation and additivity influence on volume changes. For the investigation purpose of failurecauses, the phase composition using X-ray crystallography and Raman spectroscopy was determined.