Introduction. One of the most important characteristics of asphalt concrete that characterizes its properties is the elasticity modulus. The elasticity modulus of asphalt concrete is used in the design of pavement structures to calculate its permissible elastic deflection, under the condition of shear resistance of the working subgrade layer and the layers of non-cohesive materials, as well as bending tensile strength.
Problem statement. Today, the calculated value of the elasticity modulus of asphalt concrete is taken in accordance with Handbook No. 2 «Design Characteristics of Asphalt Concrete» [2]. In this Handbook, the calculated value of the elasticity modulus of asphalt concrete is given depending on the bitumen grade, temperature, type of asphalt mixture, and time of load action. Numerical design values of the elasticity modulus of asphalt concrete are provided only for asphalt concrete type B; for other types of asphalt concrete, it is proposed to reduce or increase the design value of the elasticity modulus by the value that depends on the type of asphalt concrete and temperature. Since 2020, a new standard on technical requirements for bitumen has been in force in Ukraine, which brings bitumen grades in line with the European classification [4]. At the same time, in the Handbook No. 2 [2], the calculated value of the elasticity modulus of asphalt concrete is given in accordance with the previous bitumen grades, which necessitates their adjustment.
Objective. To adjust the calculated value of the elasticity modulus of asphalt concrete on the basis of known calculation models.
Materials and methods. The Witczak E* Predictive Model and asphalt mixtures in accordance with DSTU B B.2.7-119 [6] were used for the adjustment.
Results. The elasticity modulus of asphalt concrete is a combination of the binder viscosity, asphalt concrete grading, effective binder content, residual porosity of asphalt concrete, and deformation frequency. The elasticity modulus of asphalt concrete is significantly affected by the viscosity of the binder and its temperature sensitivity. Increasing the viscosity of bitumen leads to a gradual increase in the elasticity modulus of asphalt concrete: the lower the temperature sensitivity of bitumen is, the lower the elasticity modulus of asphalt concrete at temperatures below 25 °C is, and the higher the elasticity modulus of asphalt concrete at temperatures above 25 °C is. The residual porosity of asphalt concrete also significantly affects the elasticity modulus of asphalt concrete. A decrease in residual porosity from 2.0 % by volume to 10.0% by volume leads to a decrease in the elasticity modulus by an average of 36 %. The elasticity modulus of asphalt concrete is least significantly affected by the content of bitumen and aggregate. A general increase in the content of coarse aggregate leads to a decrease in the elasticity modulus of asphalt concrete, but in the case of an increase in the content of coarse aggregate larger than 10 mm, the elasticity modulus increases. The elasticity modulus of asphalt concrete significantly depends on the frequency of deformation, and hence the speed of traffic.
Conclusions. Existing documents provide numerical calculated values of the elasticity modulus of asphalt concrete only for type B of asphalt concrete; for other types of asphalt concrete, it is proposed to reduce or increase the calculated value of the elasticity modulus by the value that depends on the type of asphalt concrete and temperature. According to the data obtained, the elasticity modulus of asphalt concrete of type A is greater than the elasticity modulus of asphalt concrete of type B, i.e., the data obtained do not confirm the dependencies provided in existing documents.
None of the existing documents classify asphalt concrete by type, but the data obtained indicate a significant difference in the elasticity modulus of asphalt concrete of different types, which necessitates changes to existing documents.
