The Potential of Thermal Energy Obtained from Exhaust Gases in the Production of Hot Mix Asphalt (HMA)

The increasingly stringent environmental requirements, as well as the tendency to achieve significant savings of energy products in HMA production processes, prompted researchers to investigate the possibility of reducing the moisture of the stone aggregate which is used in production of hot asphalt mixtures. The goal of this paper is to determine the effect of various drying parameters on the aggregate moisture loss. The parameters which were analyzed and observed in various combinations were selected on the basis of the production process of an asphalt plant, and they are as follows: the air flow speed (3.86 m/s, 4.53 m/s and 5.94 m/s), the drying temperature (basic temperatures 33.1 °C, 50.4 °C and 71.7 °C) and the time of exposure of the aggregate to drying (30, 45 and 60 s). In order to research the effect of reduction in moisture of the stone material, a laboratory model of a belt dryer (chamber with a cover) was conceived and made with a drying device that can control the air flow speed from 3.86 m/s to 6.32 m/s and the temperature, ranging from 33 °C to 110 °C. Tests were carried out in order to determine the moisture loss of different aggregate fractions, namely 0/2, 2/4, 4/8, 8/11, from the total (natural) moisture of fractions that are used as aggregate in the production of hot mix asphalt (HMA). In all, there were 162 samples of aggregate prepared and tested. Results showed that for different aggregate fractions, the ranges of the value of the moisture loss are considerably different and that they depend on the parameters of drying and the natural moisture of the aggregate. It was noticed that there was less moisture loss in fractions at a lower air flow speed (3.86 m/s) than there was at higher speeds, while the highest aggregate moisture loss was noticed at an air flow speed of 5.94 m/s. For all duration times of drying, regardless of the drying temperature or speed, it is noticed that, with the prolongation of the drying time, the aggregate moisture loss becomes more intense. The drying temperature directly affects the reduction in the aggregate moisture; the higher the air flow temperature is, the more significant the moisture loss is during drying of the aggregate. The results of the linear regression and the coefficient of determination R2 indicate a very firm connection between the loss of the aggregate moisture and the duration of the drying time. From the obtained equations, it is possible to calculate the reduction in the aggregate moisture for different lengths of drying duration and different drying temperatures.