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This research quantified the temporal mesostructural evolution of bitumen emulsion–cement composites using the time-lapse high-energy X-ray tomography of a fine-aggregate matrix. The image post-processing and analysis showed that the mastic's significant temporal decrease in volume complemented the expansion of the pore space. Nevertheless, the volume fractions determined by the image analysis essentially differed from the physical composition of specimens and were several times less sensitive to curing. Because of the extremely heterogenous microstructure and the abundance of calcium, the mastic phase had the highest attenuation of X-rays, but the attenuations of bitumen- and cement-dominated systems experienced contrary temporal trends. The sand and pore space had typically smooth and oppositely evolving axial distributions with the highest-density plateau in the middle, while the mastic was distributed uniformly. The radial distributions evolved less irregularly and notably interfered with the post-processing of beam hardening. The temporal increase in the pore space's local thicknesses was extremely unevenly distributed across diameters. Except the sand particle size distributions, all results were almost excellently repeatable. Finally, the interaction with X-rays was identified as crucial for the interpretation and validity of the results. Moreover, although water could not be segmented using the conventional X-ray tomography, its discrete signature was present throughout the behaviour of other phases. [ABSTRACT FROM AUTHOR]

The theory of small-angle scattering is reviewed with special attention paid to the anomalous scattering and multiphase systems. A general equation is derived that describes the scattering of a multiphase system as a sum of scattering functions of each of the phases, as if it scattered alone in a two-phase system, and interphase interference scattering functions. These scattering functions depend only on the spatial distribution of the phase boundaries, but not on the scattering density. Contrast variation techniques are most rewarding when the scattering density of only one phase can be varied. For anomalous small-angle X-ray scattering (ASAXS), this means the most favourable is the case in which resonant atoms are contained in one phase only. The general equation involves n(p - 1) unknown partial atomic number density differences, where p is the number of phases and n the number of the different atom types in the sample. These partial atomic number density differences can be found if a suitable structure model is applied to calculate the phase scattering functions. Then, the phase compositions and densities can be calculated by solving a system of linear equations incorporating the atom number conservation law. The partial structure factors formalism is also reviewed. Corresponding equations for a system of n types of atoms and p phases are derived. The number of independent partial structure factors is p(p - 1)/2 and depends on the number of phases, but not on the number of the types of the atoms in the sample, as in the case of wide-angle scattering. [ABSTRACT FROM AUTHOR]

An ultrasonic technique is being developed to detect the dispersed phase holdups in multiphase systems. This technique is based on the fact that the transmission time and attenuation of ultrasound in suspensions differ from those in pure liquids. Experiments were carried out at three probe gap spacing, (2.04, 4.27, and 6.31 cm) in a fluidized bed of 7.6 cm diameter. Water was used as the continuous phase and air and 500 µm glass beads as the dispersed phases. The time-averaged amplitude ratio decays exponentially with gas and solid holdups, whereas the transmission time increases slightly with gas holdup but decreases with solid holdup. It is also observed, for the first time, that the fluctuations of the instantaneous ultrasonic signals can be correlated with the solid and gas holdups in a multiphase system. This correlation may provide a basis for the development of a new approach for phase holdup analysis in multiphase flow systems. [ABSTRACT FROM AUTHOR]