Volume 26, Issue 4

Self-consolidating concrete (SCC) is very sensitive to delays or stoppages between successive lifts during casting, especially given that vibration is prohibited with this highly flowable type of concrete. The investigation reported in this paper seeks to quantify the effect of mixture proportioning on thixotropy along with the resulting effect on interfacial bond strength of hardened material that could result from successive lifts. The suitability of the equivalent mortar phase to simplify testing protocols and appropriately predict SCC properties was given particular attention; the concrete-equivalent-mortar (CEM) mixtures are derived from SCC by eliminating the coarse aggregate fraction and replacing it by an equivalent quantity of sand having equal surface area. Tests results have shown that SCC and CEM mixtures prepared with combinations of increased cement content, silica fume, and/or viscosity-modifier led to higher levels of thixotropy. Yet, the responses determined using SCC were higher by around 1.6 times than those of CEM, given the differences in unit weight and air content between both materials. Good correlations are established between thixotropy and interfacial bond strengths of SCC and CEM mixtures.

Former studies show that the coarse particle plays a very important role in the determination of the yield stress of fluid-solid mixtures such as debris flows. The characteristics of the coarse particle in these mixtures include particle size, gradation, shape, and type of material. To assess the influence of these coarse particles on the yield stress the concept of equivalent volumetric solid concentration C is introduced. The equivalent concentration can be derived from the volumetric solid concentration by considering the particle size, gradation, shape, and type of material. Laboratory experiments to determine the yield stress of various mixtures were conducted to calibrate the coefficients of these coarse particle characteristics. A yield stress phenomenological expression is proposed using the refined volumetric solid concentration (equivalent concentration), which could be calibrated by the experiments in this study. The validation of this phenomenological expression with data from literature shows good agreements, especially for higher volumetric concentrations of the sediments.

Rheology of Microfibrillated Cellulose (MFC) suspensions is useful for designing equipment to transport, mix, or process them. Pressure-driven flow behavior is particularly important for MFC suspensions if they are to be pumped, extruded or coated. Herein, we report use of slot and pipe geometries for determination of MFC suspension rheology and compare the results to boundary-driven flows. MFC flow behavior in a slot with varying gaps was studied at mass concentrations of 1, 2, and 3% and up to shear rates of 100 000 s -1 . The suspensions exhibited yield stress and were highly shear thinning (pseudo-plastic) with apparent power law indices of 0.22 - 0.43. The shear thinning behavior can be explained by a microstructural picture in which a non-yielding center plug is surrounded by a yielded layer and a fiber-depleted water rich boundary layer.

This paper describes the effects of irradiation on the rheological and electrical properties of a 7.7% mass fraction of native bovine collagen in water. The radiation dose was in the range of 0 - 500 Gy. Rheological oscillation measurements were done at temperatures of 10, 20, and 30 °C. There was a statistically significant dependency of storage and loss moduli on irradiation dose and oscillation frequency. There was no significant change in the electrical conductivity of collagen during oscillation movements or any dependence on irradiation dose.