Abstract
Compaction of Hot Mix Asphalt (HMA) is a process aimed at obtaining the desired performance properties. Attainment of the required compaction can be hampered by external factors, which includes the presence of water. Water is known to cause quick lowering of the HMA temperature. The bottom face of the asphalt layers of a pavement is a sensitive point from the fatigue life point of view. In the site conditions, it is often difficult to obtain the required air void content at the bottom of an asphalt layer and excessive moisture content in the base course lying beneath the asphalt layer can be one of the causes. This article presents the results of tests carried out on a test section on which HMA was placed on an unbound aggregate base layer of varying moisture content. The material used for the binder course was asphalt concrete mixture composed of aggregate of minus 16 mm grading and 35/50 bitumen. Being relatively hard it is the most often specified bitumen for binder courses and also base courses. One of its characteristics is a considerable increase of viscosity with decreasing temperature, which hampers the process of compaction. The bulk specific gravity was measured to determine the variations in the air void content through the specimens. The complex modulus of elasticity and fatigue life were the other parameters which were determined on the specimens with different air void contents. The test results show worsening of the properties which have a decisive bearing on the service life of pavement.
Highlights
The Hot Mix Asphalt (HMA) micro-structure and performance characteristics are determined during the compaction process
The effectiveness of this process depends on the applied compaction effort, which is closely related to the mixture temperature [1,2,3]
The in-place air void content and compaction values were determined for the complete layer according to EN 12697-8 (Section 4) [29]
Summary
The Hot Mix Asphalt (HMA) micro-structure and performance characteristics are determined during the compaction process. The effectiveness of this process depends on the applied compaction effort, which is closely related to the mixture temperature [1,2,3]. The second parameter, namely temperature, depends on the rate of heat transfer inside the HMA layer and the dissipation of heat to the outside environment [4]. Precipitation can occur during the process of HMA placement. If it is only a light rain the contractor often takes a risk and, ignoring any prohibitions, decides to place the already delivered HMA anyway. After a direct contact of HMA with water occurs, the viscosity of the bitumen increases abruptly and reduces the temperature
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