Kostin D. Increasing of the resistance to the plastic deformations accumulation of stone mastic asphalt pavements

The thesis covers an important scientific and practical problem which lies in the increase of the durability of the road pavements made of stone mastic asphalt mixtures on the criteria of strength and rutting formation resistance. The paper theoretically substantiates and experimentally confirms that the spatial mineral skeleton in stone mastic asphalt concretes plays a key role in providing of their resistance to the accumulation of plastic deformations. According to the results of comparative studies of rutting resistance of stone mastic asphalt concretes of different granulometrical types in the conditions of repeated cyclic loadings at different temperatures and wheel load levels it is established that with increasing of the crushed stone grain size and their content in the mineral part the rut depth decreases. The thesis presents the results of comparative experimental studies of resistance to rutting formation of fine-graded and coarse-graded stone mastic asphalt concretes. It has been shown that stone mastic asphalt concretes based on bitumens of higher grade viscosity have higher rutting resistance. It has been experimentally established that more intensive increase of rut depth with the increase of asphalt pavement temperature from 50 °C to 65 °C is proper to stone mastic asphalt concretes with smaller crushed stone grain size. The obtained results of experimental researches testify to bigger resistance to rutting formation in the operational range of temperatures of stone mastic asphalt concretes with the bigger maximum size of grains of crushed stone in comparison with SMA with the minimum size of grains of crushed stone. Comparative studies of rutting resistance of stone mastic asphalt concretes of different granulometric types showed that the increase in the composition of the mineral part of the maximum grain size of crushed stone from 10 mm to 40 mm causes a decrease of rut depth by 1,8 times. It was experimentally established that more intense increase of the rut depth with increasing of pavement temperature is further facilitated by the increase of the vehicle wheel pressure on the surface of the layer of stone mastic asphalt pavement. It is established that the use of bitumen modified by polymers of the thermoelastoplast class for the preparation of stone mastic asphalt concrete mixtures has a greater effect on the increasing of the rutting resistance of stone mastic asphalt concrete with a smaller crushed stone size. It is experimentally proved that the usage of natural bitumens for modification of bitumens and stone mastic asphalt mixtures directly in the asphalt mixer at the stage of their preparation causes an increase of strength and rutting resistance in comparison with SMAM prepared on the initial bitumen. The dependences of the design characteristics of stone mastic asphalt concrete of different granulometric types on the grade viscosity of bitumens used for their preparation are determined. The growth of the values of the modulus of elasticity and bending tensile strength of stone mastic asphalt concretes based on the polymer-modified bitumens, which are the design characteristics required for the calculation of non-rigid pavement structures, has been experimentally confirmed. It is established that with the decrease of the maximum grain size of crushed stone in the composition of stone mastic asphalt concrete and the increase of the grade viscosity of bitumen used for preparation of the mixture the values of calculated modulus of elasticity and bending tensile strength increase. The research and production check of the research results in the road-building organizations during the construction of pavement layers of the increased durability by criterion of rutting stability is carried out. The results of the research are implemented in production conditions during road maintenance on highways in Kharkiv, Volyn and Ivano-Frankivsk regions by arrangement resistant to accumulation of plastic deformations of stone mastic asphalt concrete pavement layers. The results of the thesis research were implemented during the development of three standards and two industry recommendations.