FEATURES OF THE THERMAL STRESSED STATE OF ROAD COATINGS WITH RUBBER INCLUSIONS

Abstract

Introduction. According to international estimates [18], 1.5 billion worn tires go to waste every year in the world. A significant part of them is stored in landfills, buried in the ground or burned, thus polluting the air, wastewater and soil with harmful and poisonous gases, as well as liquid and solid fractions. At the same time, rubber has a number of useful and valuable substances for the industry, the recycling of which will allow to significantly reduce environmental pollution and obtain material benefits. In addition, worn tire material has a number of unique thermomechanical properties attractive for industrial applications, including low density, good thermal and electrical insulating properties, mechanical elasticity and strength, etc. One of the promising directions of recycling worn tires is their use as admixtures in asphalt concrete materials for road surfaces. However, as field tests have shown, the mechanical properties of such materials largely depend on impurities in the material and modification of their properties by the bitumen fraction. Since these issues have not been sufficiently analyzed in the scientific environment, the problem of their study is urgent. Problems. The problem of recycling the material of worn car tires in road construction is largely limited by the instability of the thermomechanical properties of asphalt concrete mixtures with rubber crumb admixtures depending on its grain size, the percentage of its volume inclusions and the level of bitumen modification. Establishing rational parameters that characterize these factors can be implemented by mathematically solving the problem of the thermally deformed state of the road surface using methods of the theory of thermoelasticity. Purpose. The purpose of the article is to determine the reasons leading to a violation of the strength of asphalt concrete materials with admixtures of rubber crumb. For this purpose, the influence of the incompatibility of thermomechanical characteristics (moduli of elasticity, Poisson’s ratios and coefficients of thermal expansion) of bitumen and rubber on the concentration of additional internal thermal stresses in the system caused by seasonal and daily temperature changes is analyzed. Materials and methods. Mathematical modeling methods are used to conduct research using the main provisions of the theory of thermoelasticity. It is believed that bitumen is an elastic medium, which includes a rubber crumb modeled by an elastic ball. Equations of thermoelastic equilibrium of the system when its temperature changes are formulated, boundary equations and conditions of elastic interaction of the bituminous medium and rubber inclusion on their contact surface are formulated. Using the methods of analytical transformations, the solutions of these equations were built in a closed form, which allow determining the thermal stress in both fractions of the system and their dependence on the values ​​of the parameters of thermoelasticity. The principle of correspondence of the solutions of problems of the theory of elasticity and viscoelasticity is formulated, which allows to use the obtained solutions for the analysis of the thermal strength of real asphalt concrete road surfaces. The results. In the work, the reasons for the low thermal strength of bituminous materials with inclusions in the form of rubber crumbs were revealed using mathematical modeling methods. It is shown that it is related to the thermoelastic incompatibility of bitumen and rubber, which is due to the practical volumetric incompressibility of rubber and the difference in the values ​​of the thermal linear expansion coefficients of these materials. The positive role of modifying rubber with bitumen is noted, which allows to reduce the thermoelastic incompressibility of these materials and the resulting concentration of thermal stresses on the contact surface of bitumen and rubber grain. Conclusions. With the help of a theoretical analysis of the thermoelastic state of bituminous material with rubber inclusions, the reason for the concentration of thermal stresses on the contact surface of these fractions, which is caused by the incompatibility of their thermoelasticity parameters, has been established. The obtained results allow establishing ways of rational modification of rubber with bitumen, which make it possible to increase the thermal strength of road surfaces in conditions of seasonal and daily temperature changes and thereby increase their durability.