High confining pressure works on concrete under various conditions such as concrete structures deep underground/sea, the lower floors of an extremely tall building and on the foundation concrete piles of an enormous structure such as dam. Understanding the performance of concrete and the deformation mechanism under high confining pressure is important for avoiding unexpected risks and for rationalization of design. A high-pressure triaxial test was conducted on cement paste to understand the mechanism of mechanical performance of concrete under a high confining pressure. The deviatoric stress-axial strain relationship of cement paste was independent of confining pressure during ductile deformation under confining pressures greater than 30 MPa. Ion-milled cross-sections of specimens were examined by scanning electron microscopy, and the obtained backscattered electron images were darker after the test. This darkening may indicate the alteration of hydrates at the molecular level caused by deformation involving crystal plasticity. Furthermore, the pore volume of the sample tested at 400 MPa was drastically reduced.
Despite much work on wood-cement composites, effects of wood species on the hydration of cements remain unclear until now. Thus, we herein investigated systematically effects of two typical wood species wastes on the hydration of Portland cement in this work. It was found that adding the poplar flour prominently affects the formation of the calcium silicate hydrate gel (C-S-H gel) delaying the hydration process, while the Chinese fir flour hardly retards the process due to different components. Compared with the neat cement, addition of both wood flours makes it easier to generate the ettringite. Besides, another important hydration product, calcium hydroxide Ca(OH)2, requires much longer time to form in the presence of both wood flours during hydration relative to the neat cement, e.g. nearly double time for the poplar-filled cement system. The findings provide useful information for extending the potential application of wood flours waste in cement composites..
There is an increasing demand from researchers and engineers to know the fatigue behaviors of RC bridge slabs under a moving load. Therefore, many numerical and experimental studies have been conducted to predict the fatigue life of these slabs. Most of these studies focused on the modeling of fatigue behaviors of RC slabs reinforced with deformed bars. However, many RC slabs in use today are reinforced with plain bars, and they are suffering from fatigue damages. A numerical method based on the bridging stress degradation concept is presented in this study to simulate the fatigue behaviors of RC slabs reinforced with plain bars under a moving load. The bond-slip effect between a reinforcing bar and its surrounding concrete is taken into consideration by adding equivalent bond strain to plain bar strain. The numerical model is verified using previous experimental data. This model is also able to capture the cracking pattern, change in displacement and rebar strain. The numerical results provide a good agreement with the experimental ones.
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