CONSIDERATIONS CONCERNING THE DETERMINATION AND INTERPRETATION OF MARSHALL FLOW VALUES IN ASPHALT CONCRETES

ABSTRACT

In Romania, the European technical standards concerning the quality control of the primary materials and asphalt mixtures used in road and highway works have been harmonized. In the same time, Romanian norms were adopted. These norms set limits within which every characteristic must range, without the possibility of adopting other values, even if laboratory tests prove, in many cases, that the imposed limits do not correspond to the practical reality.
Also, most Romanian road laboratories own automatic Marshall equipment for the determination of Marshall stability and flow. The software of this equipment offers two modalities of determining the flow: in relation to the maximum load reached or the displacement of the tangent to 1.5mm. In many cases there are significant differences between these two values, from fitting to the standardized values and by far exceeding these values.
Based on these general considerations, the article presents the results of some laboratory research on three different grading of natural aggregates corresponding to the standards for asphalt concrete for the wearing course of public roads. Two issues that are in the Romanian specialists’ attention are being discussed: if the minimum binder content required by the Romanian standard corresponds to practical conditions (bitumen types used and correlation with the other physical and mechanical characteristics), and which is the correct methodology for determining the flow, respectively.

Keywords: asphalt concrete, Marshall flow, bitumen content, deformation stress ratio