THEORETICAL MODELING OF THE NUCLEATION OF INTERNAL LATENT THERMAL DEFECTS IN A BITUMINOUS MEDIUM WITH RUBBER INCLUSIONS

Abstract

The current state and progress of the technology and science associated with the reuse and recycling of the tyre rubber worldwide in the road industry compels to study more thoroughly high and low temperature performance of the road bitumen modified with rubber crumbs, permitting to understand influence of the temperature, rubber grain size and mixture bitumen-rubber modification on the composite strength and sustainability. Below, these issues are studied taking into account the peculiarities of the thermomechanical properties of rubber associated with its low rigidity when changing shape, practical incompressibility when changing volume, and low (zero or even negative) coefficient of linear thermal expansion. The purpose of the study 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. Using the relations of the theory of thermoelasticity, a mathematical model of thermal deformation of crumb rubber in a bitumen medium has been constructed. With the possibility of complete and surface modification of rubber with bitumen, solutions for three-phase media are constructed, which make it possible to trace the influence of the parameters of each phase on the thermal stress fields in the system. It has been established that additional thermal stresses in bitumen, due to the thermomechanical incompatibility of the physical parameters of the phases, are concentrated in the zone of its contact with the surface of the rubber crumb and can cause defects and chippings in it. The influence of the effect of modifying rubber crumb with bitumen and of the depth of its penetration into crumb of different sizes on reducing thermal stresses in the system and increasing its sustainability is considered.