Illiash S. Improvement of asphalt pavement hot recycling technology

The dissertation solved an important scientific and practical task which is to improve the technology of asphalt pavement hot recycling. This allowed obtaining the new scientific results for a more accurate setting of the technological process parameters and provided the development of more economically efficient solutions for the current repair of asphalt pavements. Analysis of foreign experience in application of hot asphalt concrete recycling technologies on the road enabled to establish the rational area of their application - current repair when it is necessary to restore riding qualities of the road pavement, eliminate its damages and deformations and increase the service life at the expense of small costs. Theoretical background for determining the main parameters influencing the physical and mechanical characteristics of the reclaimed asphalt concrete was generalized. On the basis of expert assessment using the factor analysis, the choice of the most important parameters was substantiated which are the mixing technology and the regenerating additive content. The conducted theoretical and experimental studies using the theory of planning of experiments allowed developing the mathematical models of changing the main physical and mechanical characteristics of the reclaimed asphalt concrete depending on changing the most important parameters. Realization of the developed mathematical models allowed determining the rational ranges of changing the preparation temperature (125-135) ⁰С and the regenerating additive content (0,26-0,28)% at the average weighted bitumen content of 6%. The obtained results of mathematical modeling allow determining the additive content at different content of residual bitumen in the existing asphalt concrete. Basing on the research results, the rational range of bitumen content in the reclaimed asphalt mixtures was determined (5,70-6,85) to preserve the standard indicators of water saturation and durability. The results were also proved by rutting tests. The research results have shown that the most rut is the reclaimed asphalt concrete prepared from the asphalt concrete with the service life of about 10 years. The experimental data obtained confirm the results of theoretical studies and analysis of world experience, which show that the hot regeneration of road clothing is most effective when its service life does not exceed (8-10) years. We have conducted field studies and developed a mathematical model of asphalt pavement heating with the use of infrared heating. The implementation of the mathematical model and the obtained graphic dependencies made it possible to determine the heating time depending on the ambient temperature (in the range from 10 °С to 30 °С) and the necessary mixing temperature. The use of a regenerating additive and a rational mixing temperature during the preparation of the mixture increase machine productivity by 20-25%. The minimum permissible duration of mixing was established which allowed to provide the normative indicators of water saturation and strength. Generalized recommendations on the calculation of the grading of the reclaimed asphalt mixture with or without limiting the maximum thickness of the reclaimed asphalt concrete layer. On the basis of the feasibility study, the expediency of using the hot recycling technology for the inter-repair period for the current repair was confirmed. The technological process of hot recycling was optimized which allowed the reducing of the cost of works performance by 16%. One of the results of scientific research is the developed recommendations for the restoration of layers of asphalt pavement by the technology of hot regeneration on the road. The developed Recommendations establish: - classification of methods of hot regeneration of asphalt concrete on the road; - the characteristics of the hot regeneration processes depending on the type of defects in the coating and the degree of damage to the coating; - material requirements; - a methodology for choosing the rational parameters of asphalt pavement hot recycling technology on the road (heating temperature of the coating, speed of movement, regenerating additive content, mixing time). The research results were implemented in the development of the state and branch regulations, in particular, the state standard on the estimated norms, recommendations, flowcharts, in the repair of the international highway of state importance M-01 Kyiv – Chernihiv - Novi Yarylovychi (km 103+010 - km 103+628).