Factors determining the inhomogeneity of reclaimed asphalt pavement and estimation of its components content variation parameters

With a view to saving bitumen and mineral substances and also for the purpose of preventing environmental pollution, the old asphalt pavement (AP) may be milled without increasing the thickness of pavement structure and subjected to hot recycling for reuse in the same or any other location. However, the suitability of reclaimed asphalt pavement (RAP) for reuse depends on its composition (the content and gradation of bitumen) and the properties of its components. Hence, the present study aims at providing a systematic analysis of factors that determine the inhomogeneity of RAP. To this end, RAP samples, taken from RAP being loaded from the milling machine onto the transport means and from RAP stored in the territorial storage facilities of asphalt concrete (AC) plants, were examined in an accredited laboratory to determine, for each sample unit, the composition (the content and gradation of aged soluble bitumen), the content of moisture and the gradation of non-extracted granules. The statistical characteristics showing the actual homogeneity of RAP sampled from different sources were also estimated and analysed. Further, there was elaborated a model for comparing the homogeneity of RAP from different sample sets by the max values of standard deviations in the percentage mass passing the sieves and, based on the experimental data, derived the respective regression equation. The results of the performed comparison showed the absence of any statistically significant difference in terms of homogeneity between the three different RAP sample sets, i.e. RAP-1 sampled from the road, RAP-2 taken from the stockpiles being formed in different locations and RAP-3 obtained from RAP kept stockpiled in an open storage facility. The study was finalized by determining, in line with the Specification of Technical Requirements TRA ASFALTAS 08, the max content of RAP allowed for inclusion in a hot mix asphalt (HMA) mixture depending on the actual homogeneity of RAP determined.