Effects of seasonal weathering on dewatering and strength of an oil sands tailings deposit

Considerable research has been conducted over the past decade by oil sands mining companies to improve the dewatering and strength properties of fluid fine tailings deposits in an effort to meet the regulatory and closure requirements. Commercially employed dewatering treatment technologies (inline flocculation, thickening, and centrifugation) may not be sufficient to develop the strength for the creation of trafficable landscape without the use of soft soil capping technologies. These treated tailings are continuously deposited creating soft and saturated deep deposits. Seasonal weathering may be an additional promising technology to further dewater the treated tailings and promote the development of shear strength at the surface. The effects of seasonal weathering on dewatering and strength were investigated in this paper by performing multiple cycles of freeze-thaw and alternate drying-wetting cycles on two types of treated tailings deposit. The results indicate that multiple cycles of seasonal weathering significantly increased the dewatering and strength properties. However, different parameters such as freezing gradient, number of seasonal cycles, and pore water chemistry play an influential role in changing the magnitude of the strength. The results also suggest that a minimum threshold strength value is required where the effects of rainfall rewetting had a minimal impact on strength reduction (the strength corresponding to the moisture content approaching the plastic limit).

Wide-area low-energy surface stimulation of large mammalian ventricular tissue

The epicardial and endocardial surfaces of the heart are attractive targets to administer antiarrhythmic electrotherapies. Electrically stimulating wide areas of the surfaces of small mammalian ventricles is straightforward given the relatively small scale of their myocardial dimensions compared to the tissue space constant and electrical field. However, it has yet to be proven for larger mammalian hearts with tissue properties and ventricular dimensions closer to humans. Our goal was to address the feasibility and impact of wide-area electrical stimulation on the ventricular surfaces of large mammalian hearts at different stimulus strengths. This was accomplished by placing long line electrodes on the ventricular surfaces of pig hearts that span wide areas, and activating them individually. Stimulus efficacy was assessed and compared between surfaces, and tissue viability was evaluated. Activation time was dependent on stimulation strength and location, achieving uniform linear stimulation at 9x threshold strength. Endocardial stimulation activated more tissue transmurally than epicardial stimulation, which could be considered a potential target for future cardiac electrotherapies. Overall, our results indicate that electrically stimulating wide areas of the ventricular surfaces of large mammals is achievable with line electrodes, minimal tissue damage, and energies under the human pain threshold (100 mJ).

The effect of fibers on the loss of water by evaporation and shrinkage of concrete

Shrinkage is one of the least desirable attributes in concrete. Large areas of exposed concrete surfaces , such as in shotcrete tunnel linings, where it is practically impossible to make a moist cure, are highly susceptible to plastic shrinkage at early ages. The autogenous and drying shrinkage can lead to states of greater than threshold strength, causing fracture, mechanical damage and lack of durability of concrete structures. The addition of fibers can greatly reduce plastic shrinkage, but has limited effect in mitigating autogenous and drying shrinkage. To evaluate the performance of polypropylene and steel fibers to understand their effect on shrinkage of concrete, a study was carried out to relate the loss of water from the paste and the shrinkage during the first 28 days of age, and compare it with a control mix without fiber. The loss of water was obtained by the weight loss of the specimens at different ages, since the only component that could contribute for the loss of weight was the water lost by the paste of the concrete. And the paste itself is the only source of shrinkage. Uniaxial compressive tests from very early ages enabled the determination of time when plastic shrinkage ended. It was observed that the control concrete mix lost three times more water and developed plastic and drying shrinkage 60 % higher than the fiber reinforced concrete mixes. It was possible to demonstrate that the reduced loss of water caused by the incorporation of fibers is related to the mitigation of plastic shrinkage. It was observed that the fibers are effective to restrain the movement of water through the cement paste in the plastic state, however such effect is limited after concrete starts the hardening state.

Properties Related Phase Evolution in Multilayer Silicate Ceramics

The use of ceramic processes inducing a microstructural organization at the grain scale favors the improvement of strength and toughness. With layered structures, it is possible to design the microstructural characteristics of materials, leading to increased threshold strength. Layered structures can be arranged to control the local residual stresses causing elastic mismatches between dissimilar materials and crack deflection at interfaces. In this way, multilayer composites from kaolinite and alumina or mullite fibers were shaped by tape casting and staked by thermo-compression, or by centrifugation. During sintering, they show at strong anisotropic behavior, which is in correlation with different activation energy for sintering. Mullite growth is also anisotropic, inducing the formation of an organized micro composite microstructure. The mechanical and elastic properties are correlated with the organization degree of mullite crystals, due to the formation of an interconnected mullite network in the microstructure. It is also shown that variations of mechanical and elastic properties are correlated with the texture index obtained by Quantitative Texture Analysis from X-ray data. The anisotropy of the elastic properties is evidenced by different values of Young’s modulus in directions parallel and perpendicular to the casting direction. Beside, the crack growth resistance is governed by discontinuities along layer boundaries and fiber interfaces.