Volume 20, Issue 6

The classification of a concrete mixture as self-compacting (SCC) is performed by a series of empirical characterization tests that have been designed to assess not only the flowability of the mixture but also its segregation resistance and filling ability. The objective of the present work is to correlate the rheological parameters of SCC matrix, yield stress and plastic viscosity, to slump flow measurements. The focus of the slump flow test investigation was centered on the fully yielded flow regime and an empirical model relating the yield stress to material and flow parameters is proposed. Our experimental data revealed that the time for a spread of 500 mm which is used in engineering practice as reference for measurement parameters, is an arbitrary choice. Our findings indicate that the non-dimensional final spread is linearly related to the non-dimensional yield-stress. Finally,there are strong indications that the non-dimensional viscosity of the mixture is associated with the nondimensional final spread as well as the stopping time of the slump flow; this experimental data set suggests an exponential decay of the final spread and stopping time with viscosity.

The application of sustainability principles in construction encourages the development of new products, with new functionalities and applications, able to improve buildings environmental performance. The use of latent heat storage materials in lime mortars aims to reduce the energy consumption of buildings. This work intends to evaluate the impact of phase change materials (PCM) incorporation in rheological and hardened state properties of aerial lime mortars. A fresh state characterization was conducted through the rheological study complemented with flow table tests of different mortar formulations. To complete the mortar characterization some hardened state properties (porosity, mechanical strength and microstructure) after 28 days, were also evaluated. It was concluded that, the PCM microcapsules incorporation does not compromise aerial lime mortars overall performance and may help to improve some characteristics like workability and mechanical strength. Therefore, it is possible to reduce the energy demand in old buildings, improving their performance and sustainability.

Bitumen is undoubtedly the most important material in the construction and rehabilitation of flexible road pavements. By increasing the temperature, bitumen changes from brittle solid, to viscoelastic solid and finally to Newtonian fluid. The rheological characteristics of bitumen also vary greatly due to aging, which is a phenomenon initiated in the phases of production and application of bituminous (asphalt) mixtures and continued during the life of road pavements. The aim of this work is to study several rheological parameters in order to evaluate if they are able to quantify the aging of various types of bitumens. Four bitumens from the same distillation column in the refinery, but with different penetration grades, were aged by using the RTFOT method, which simulates the aging of the bitumen during the asphalt mixture production and pavement construction. The original (base) and aged bitumens were characterized with conventional tests used in the paving industry, and the results were compared with the rheological characteristics obtained with small amplitude oscillatory shear tests. Aging was assessed at high temperatures (110 to 180°C) through the activation energy computed from the temperature dependence of the Newtonian viscosity. However, the comparison of the characteristic relaxation times extracted from master curves measured at medium/low temperatures (between 25 to 80ºC), proved to be the most sensitive indicator of bitumen aging.

Blood rheology and hemodynamics models show positive correlation between hematocrit and hemodynamic factors that has implication to physiological and arterial disease processes. Blood flow is modeled by the Navier- Stokes equation and its non-Newtonian property by the Casson equation. Hematocrit dependent parameters in the Casson equation integrate the hematocrit level in the mathematical model. Then the mathematical model was linearized on a tetrahedral computational grid using the finite volume method. Results show strong correlation between hematocrit and hemodynamic factors. The determined hemodynamic factors and their strong correlation with the hematocrit provide explanation how these factors promote the atherosclerotic process in the right coronary artery at a steady flow and how influence arterial disease process.

An experimental set-up was used to visually observe the characteristics of bubbles as they moved up a column holding xanthan gum crystal suspensions. The bubble rise characteristics in xanthan gum solutions with crystal suspension are presented in this paper. The suspensions were made by using different concentrations of xanthan gum solutions with 0.23 mm mean diameter polystyrene crystal particles. The influence of the dimensionless quantities; namely the Reynolds number, Re, the Weber number, We, and the drag co-efficient, cd, are identified for the determination of the bubble rise velocity. The effect of these dimensionless groups together with the Eötvös number, Eo, the Froude number, Fr, and the bubble deformation parameter, D, on the bubble rise velocity and bubble trajectory are analysed. The experimental results show that the average bubble velocity increases with the increase in bubble volume for xanthan gum crystal suspensions. At high We, Eo and Re, bubbles are spherical-capped and their velocities are found to be very high. At low Weand Eo, the surface tension force is significant compared to the inertia force. The viscous forces were shown to have no substantial effect on the bubble rise velocity for 45 < Re < 299. The results show that the drag co-efficient decreases with the increase in bubble velocity and Re. The trajectory analysis showed that small bubbles followed a zigzag motion while larger bubbles followed a spiral motion. The smaller bubbles experienced less horizontal motion in crystal suspended xanthan gum solutions while larger bubbles exhibited a greater degree of spiral motion than those seen in the previous studies on the bubble rise in xanthan gum solutions without crystal.