Multiscale imaging and characterization of the effect of mixing temperature on asphalt concrete containing recycled components.

When producing asphalt concrete mixture with high amounts of reclaimed asphalt pavement (RAP), the mixing temperature plays a significant role in the resulting spatial distribution of the components as well as on the quality of the resulting mixture, in terms of workability during mixing and compaction as well as in service mechanical properties. Asphalt concrete containing 50% RAP was investigated at mixing temperatures of 140, 160 and 180°C, using a multiscale approach. At the microscale, using energy dispersive X-ray spectroscopy the RAP binder film thickness was visualized and measured. It was shown that at higher mixing temperatures this film thickness was reduced. The reduction in film thickness can be attributed to the loss of volatiles as well as the mixing of RAP binder with virgin binder at higher temperatures. X-ray computer tomography was used to characterize statistically the distribution of the RAP and virgin aggregates geometric features: volume, width and shape anisotropy. In addition using X-ray computer tomography, the packing and spatial distribution of the RAP and virgin aggregates was characterized using the nearest neighbour metric. It was shown that mixing temperature may have a positive effect on the spatial distribution of the aggregates but did not affect the packing. The study shows a tendency for the RAP aggregates to be more likely distributed in clusters at lower mixing temperatures. At higher temperatures, they were more homogeneously distributed. This indicates a higher degree of blending both at microscale (binder film) and macroscale (spatial distribution) between RAP and virgin aggregates as a result of increasing mixing temperatures and the ability to quantify this using various imaging techniques.

Three-dimensional reconstructed glomerular capillary network: blood flow distribution and local filtration.

We developed a mathematical model to simulate blood flow and filtration in individual capillary segments of a glomerular network reconstructed from a normal Munich-Wistar (MW) rat. Three-dimensional geometric reconstruction was obtained by semithin serial sections (1 micron) of one glomerulus after perfusion fixation of kidney. Photomicrographs of each section were digitized and processed, using a computer-based image-analysis system, to derive the topological organization of the capillary network and mean diameter and length of individual capillary segments. Blood flow rate in capillary segments was calculated using a theoretical model that considers apparent viscosity of blood in small capillaries as a function of local rheological parameters, partition of cells at bifurcations, and local filtration dependent on transmembrane hydraulic and oncotic pressure gradients along the network. In accord with previous observations, the topological organization of the capillary network disclosed a three-lobular structure. The ultrafiltration coefficient (Kf) calculated for the euvolemic MW rat with the present network approach was compared with that derived from a theoretical model that assumes identical capillaries in parallel. The latter model is shown to underestimate Kf, particularly under conditions in which filtration pressure equilibrium is approached. Calculation of local blood flow and filtration along the network indicates a heterogeneous distribution of these parameters and that some parts of the capillary network operate at filtration pressure equilibrium even if the overall network operates at filtration disequilibrium.