Design features of the mastic asphalt composition

Abstract

Mastic asphalt concrete is a type of hot asphalt concrete that differs significantly from hot asphalt concrete in terms of particle size distribution, nomenclature of indicators used to assess quality, and technology for manufacturing, transporting, and paving. These features of mastic asphalt concrete must be taken into account when designing its composition. One of the operations performed during the design of a mastic asphalt concrete composition is the manufacture of samples, with the subsequent establishment of physical and mechanical quality indicators and comparison of the results with regulatory requirements. Unlike traditional hot asphalt concrete, the design of which (in particular, the determination of the amount of bitumen) is based on strength indicators (compressive strength at 50 °C and 20 °C), the optimal bitumen content in the composition of mastic asphalt concrete according to the requirements of the national standard DSTU 9290-6 is determined by the residual porosity and operational plasticity (stamp indentation). In the presented work, the optimal content of bitumen of the BND 35/50 brand in the composition of a mastic asphalt mix of the LABS-10 type was selected. According to the data obtained, it was found that the optimal amount of bitumen is 11 %, and the temperature of preparation of the mixture is 180 - 200 ºС. In the case of taking into account the serviceability of mastic asphalt concrete, determined by the stamp indentation index, the optimal amount of bitumen is reduced to 9 %, and the mixture preparation temperature is increased to 220 - 240 °C. Based on the results of the assessment of technological plasticity determined by the Luer method, at a temperature of 200 - 230 °C, the mastic-in-place mixture used in the work will be too stiff, which will make it impossible for it to spread during the process of laying on the road surface. Taking into account the three main quality indicators of mastic asphalt concrete, such as residual porosity, operational and technological plasticity, it is advisable to use a mastic asphalt concrete mixture with 10 % BND 35/50 bitumen produced in the temperature range from 235 to 270 °C. When designing the composition of mastic asphalt mixtures, it is necessary to take into account the value of technological plasticity, since this approach allows ensuring the manufacturability of pavement construction and compliance of physical and mechanical parameters with the standardized values.