Aging of bitumen on the surface of crushed granite at high temperatures

Abstract

When exposed to high temperatures, bituminous materials including mixtures of crushed stone and bitumen (black gravel) quickly change their physical and mechanical properties. In the process of heating up, the structure and composition of the bitumen binding agent go through complex transformations due to the processes of polymerization, polymerization of carbons, evaporation of volatile components, etc. These processes depend on the thickness of bitumen films on the surfaces of mineral particles, depending on the type and size of mineral particles, exposure to air, magnitude and intensity of the process, high temperatures and other factors. Since bitunomineral mixtures contain mineral particles that can vary in size hundreds of times, films of different thickness and directivity are formed on their surfaces in the process of mixing with bitumen. This raises the need for a differential study of their behavior at high temperatures and changes in their adhesive properties in particular. At this, due to the lack of a standard methodology for analysis of these processes, a special estimating experimental method has been developed (see the Patent of the Russian Federation for the invention No. 2654954 [22]). The aging of the bitumen binding agent on the surfaces of mineral materials was analysed using a dimensionless aging factor for local indicators of physical and mechanical properties. According to the research based on this method, the most sensitive indicator is the compressive strenght limit at 50 degrees Celsius for standard cylindrical samples, formed from bituminous mixtures pre-heated at high temperatures. The aging of crushed granite mixtures of fr. 5…10 mm with petroleum road bitumen 90/130 was calculated at various ratios – 1:25; 1:30; 1:35; 1:40, pre-aged at + 150 °C. The aging dynamics was assesed by the values of aging intensity according to the aging coefficient. Due to the experiments, the optimum ratio of bitumen and mineral part (crushed granite) with the best resistance to aging at high temperatures and the dynamics of changing the aging intensity at different time intervals was determined. The results also include mathematical models describing the aging of mixtures under study, analysis of the experimental results and conclusions.