Simulation of composition of recycled hot-mix asphalt mixture produced in asphalt mixing plant

Abstract

Recycled hot-mix asphalt (RHMA) mixture is produced from reclaimed asphalt pavement (RAP) by adding an appropriate amount of new mineral materials improving the gradation of RHMA, a lower viscosity bituminous binder and a rejuvenator. The manufactured RHMA mixture must meet the same technical requirements as those for the hot-mix asphalt (HMA) mixture made of new materials only. It is also aimed at reducing its cost to the minimum in order to comply with technical requirements for the RHMA mixture in the asphalt mixing plant (AMP). These goals are ensured in the process of determining the composition of the RHMA mixture applying numerical and experimental methods for selecting an optimal content of old and new materials in the mixture. The article presents a method for determining the composition of the RHMA mixture, which allows calculating the maximum allowable percentage of RAP depending on its homogeneity. Setting the established maximum RAP amount as a constant size, the required content of new mineral materials is estimated thus taking into account bitumen capacities. The price of a single ton of the materials making the RHMA mixture and information on technical requirements for the composition of the RHMA mixture assist in applying certain technological restrictions, which makes it possible to calculate an optimal content of the components. The research findings obtained from the representative sample demonstrated that ready-for-use RAP was not homogeneous, and its five properties used for calculating its maximum allowable amount had different variations. The paper presents the algorithms that are actualized using mathematical programming methods upon the application of which the following objectives were solved: the assessment of technological requirements helped to obtain the RHMA mixtures of the cheapest or densest mineral part, and the mixture having the lowest content of bitumen was received. The article discusses mathematical analogues that can be used for determining whether the RHMA of the right gradation can be produced from the available mineral materials and allows analysing the mixtures that do not meet the established requirements thus identifying the causes of inappropriateness. The introduced algorithms can be applied at the initial stage of designing the RHMA mixture thus reducing the duration and cost of the design process. In order to determine whether the calculated content of old and new materials is appropriate, the standard specimens produced and examined in the laboratory need to be confirmed.