Microstructural characteristics of bituminous mix using X-ray CT

Abstract

The study of internal structure of bituminous paving mixes is very essential to understand its air void (AV) characteristics, which ultimately influences the structural and functional performances of bituminous mixture. The present study is an attempt to investigate the AV properties and their distribution in a profound and precise manner using an effective and quick three dimensional (3-D) high resolution technology such as X-ray micro computed tomography (X-ray CT) combined with the digital image processing tools. Using 3-D images obtained from imaging technique, the internal structure of bituminous mix was visualized and then image analysis was done to determine various AV parameters such as AV content, number of AV, AV size and shape of AV of the compacted bituminous specimen. Two compaction methods, namely Marshall method and Superpave gyratory compaction (SGC) methods were used to prepare dense graded bituminous concrete (BC) specimens. With the help of continuous spatial data obtained from volumetric X-ray CT images, the variation of AV parameters were assessed along the vertical, horizontal and radial directions of the specimens. The results show that the distribution of various AV parameters is quite uniform in radial direction as compared with vertical and horizontal directions. For both compaction methods, higher percent AVs are present in top and bottom parts of the specimens as compared with the middle part of the specimens. Besides, Marshall specimens exhibit more heterogeneity in the distribution of AV parameters in the horizontal direction as compared with SGC specimens.