Research of efficiency of ferrous metallurgy slag use in pavement base layers

Introduction. The results of research of metallurgical slags characteristics are presented, the possibility of their application in organomineral mixtures for pavement base layers is considered, taking into account technological features of their preparation and indicators of operational properties. The research topic is relevant both for individual regions and for the country as a whole. The amount of waste from metallurgical production increases annually and is estimated in hundreds of millions of tons. The main direction of reducing production waste is their disposal. This problem is becoming even more urgent against the background of constantly decreasing reserves of natural materials, the increase in demand for which is due to the high rates of development of material production and the acceleration of scientific and technological progress. Thus, the use of slag materials in road construction will not only contribute to waste disposal, but will also solve a number of environmental and economic problems. The aim of the research is a comprehensive study of the influence of ferrous metallurgy slags on the physical, mechanical and operational properties of organomineral mixtures of pavement base layers and substantiation of their effective application in road construction. To achieve this goal, it is necessary to perform the following tasks: 1) to determine the chemical analysis of the studied slags and to study the mechanism of interaction of slag materials with binders; 2) to assess the degree of influence of slag materials on the physical, mechanical and operational properties of organomineral mixtures; 3) to develop a methodology for determining the accumulation of residual deformations in organomineral mixtures and to establish patterns of their change over time; 4) to determine the modulus of stiffness and the number of cycles to failure in the studied organomineral mixtures, depending on the nature of the origin of the material. Steelmaking slags of ferrous metallurgy can contribute to the production of organomineral mixtures with increased physical, mechanical and operational properties due to the increased content of calcium compounds, microporous additions of the crystal structure and active hydration processes, which can have a beneficial effect on the durability of the structural layer of the pavement when used.Materials and methods. All materials used in this study were subjected to tests to determine their physical and mechanical parameters, and materials representing industrial by-products were additionally subjected to chemical analysis. This approach made it possible to assess the compliance of inert materials with the requirements imposed in the Russian Federation for starting materials for their use in organomineral mixtures, and to identify critical characteristics of materials that can affect the strength and performance properties. The use of waste from the metallurgical industry has a number of advantages over conventional natural materials, including low economic and environmental costs. Converter and blast furnace slags of various granulometry were used as waste products of the metallurgical industry. An X-ray fluorescence test was performed to assess the chemical composition of steelmaking slags. The sulfur content was determined on an elemental analyzer by burning a specimen at a temperature of 1350 °C. Carbon content was determined on a total organic carbon analyzer by burning a specimen at a temperature of 950 °C. The analysis of other components was carried out on an atomic emission spectrometer with inductively coupled plasma after decomposition of the specimen with a mixture of inorganic acids. To select the compositions of organomineral mixtures based on a complex binder, studies were carried out to study the nature of the interaction of an organic binder with slags. To assess the effectiveness of the use of the studied slag materials, optimal compositions of organomineral mixtures were selected in accordance with GOST 30491–2012, from which cylindrical specimens were made and tested for indicators of physical and mechanical properties, as well as plate specimens and beam specimens for performance properties. During the experimental studies, a universal device for compression and bending testing, Unifame 70-TO108E, and a test press were used. The degree of stability of specimens from organomineral mixtures to the accumulation of residual deformations was assessed using a dynamic testing device (patent No. RU 152287 U1), in accordance with the test procedure developed for this purpose. To assess the performance parameters in terms of modulus of rigidity and the number of cycles to failure and water resistance, the test methodology used to assess the quality of asphalt concrete properties was adapted, taking into account the technological conditions characteristic of organomineral mixtures. For these purposes, the CRT-RC-H2 device was used, simulating the operation of a roller, and the CRT-SA4PT-BB device, which is a servo-pneumatic system that supplies a sinusoidal load with constant deformation and frequency to the specimen beam.Research results. The chemical and elemental composition of slag materials is analyzed, on the basis of which the main directions of the possibility of using metallurgical industry waste in the road industry are determined. The mechanism of interaction of slag gravel and sand with binders was studied. It was established that the use of steelmaking slags makes it possible to increase the strength and performance properties of organomineral mixtures. Test conditions were developed and a method for evaluating the water resistance of specimens from an organomineral mixture according to the tensile strength under indirect tension and resistance to the accumulation of residual deformations was tested. A method for assessing the stability of organomineral mixtures to the accumulation of residual deformations on a dynamic test device is proposed and the dependence of the change in the indicator over time is established. According to the results of experimental studies, the expediency, economic and environmental efficiency of using waste from the metallurgical industry in the layers of the base of the pavement structure was confirmed.Conclusions. A chemical analysis of steelmaking slags was performed, their positive sides were noted and the mechanism of their interaction with binders was studied. Steelmaking slags of ferrous metallurgy made it possible to obtain organomineral mixtures with increased physical, mechanical and operational properties relative to similar mixtures of natural mineral materials. For the first time, within the framework of experimental studies, the actual values of operational properties were obtained in terms of “residual deformations”, “modulus of rigidity” and “number of cycles to failure” in organomineral mixtures of natural and slag materials, which can be used in making design decisions. The use of organomineral mixtures of slag materials in the base layers slows down the accumulation of residual deformations by 30–35 % relative to similar mixtures of natural mineral materials, which makes it possible to extend the service life of the structural layer of the pavement.

slags, metallurgical waste, residual deformations, organomineral mixtures, stiffness modulus, indirect tensile strength, water resistance, long-term water resistance