Multi-Phase Characterization of Asphalt Concrete using X-ray Microfluorescence
The objective of this study was to develop a microstructure characterization technique to capture the multi-phase nature of asphalt concrete using x-ray microfluorescence. This study examines the morphology and positions of aggregates, sand mastic and air void phases of asphalt concrete. Three different samples with targeted air void levels of 4%, 7%, and 10% were analyzed using an X-ray microscope. The cylindrical asphalt specimens were cut into slabs and then polished, and finally white zinc-oxide powder was pressed into the voids. The zinc-oxide powder helped to discern air voids from aggregate and mastic. After sample preparation, elemental maps were constructed using characteristic K x-rays from the following elements: aluminum, silicon, sulfur, chlorine, potassium, calcium, iron, zinc, and strontium. The relative intensities of pixels in the elemental maps were used to categorize pixels in each image according to sand mastic, air voids, and aggregate using multi-spectral analysis techniques. Air void contents in the three images (A, B and C) are correlated to those computed from the asphalt concrete. It was found that the air void contents in the three images (A, B) are highly correlated to those computed from the asphalt concrete. The images were utilized to calculate aggregate gradations and compared with the real gradation. It is concluded that the microstructure characterization technique to capture the multi-phase nature of asphalt concrete using x-ray microfluorescence was moderately successful.
International Journal of Pavement Research and Technology, Vol. 6, No. 2: 117-122.