دانلود رایگان مقاله لاتین پروتکل بازیابی خزش از سایت الزویر
عنوان فارسی مقاله:
استفاده از پروتکل بازیابی خزش برای اندازه گیری تنش های استاتیک و بازسازی ساختاری از خمیر سیمان تازه
عنوان انگلیسی مقاله:
Use of creep recovery protocol to measure static yield stress and structural rebuilding of fresh cement pastes
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Yield stress has been extensively studied in non-Newtonian fluids, including colloidal gel, bentonite, polymer suspension, food, paints, waxy crude oil, pastes, foams, etc. [1–5]. Specifically in cementitious materials, yield stress is important in quantifying flowability [6] and is correlated to conventional field-friendly measurement methods such as slump flow and flow table test, both experimentally and in simulation [7]. The large application and research on self-consolidating concrete (SCC) has aroused great interest and study on yield stress because it is closely related to formwork pressure [8–14], stability of coarse particles in self-consolidating concrete (SCC) [15] and multilayer casting [16]. Since the publication of the Bingham model [17], many models have been proposed to fit the equilibrium flow curve. The most common models for cementitious materials are Bingham, τ ¼ τy þ ηplγ_ , where τ is the shear stress, γ_ is the shear rate, τy is the Bingham yield stress and ηpl is the plastic viscosity; and Herschel-Bulkley, τ ¼ τy þ kγ_ n , where k and n are constants based on material properties. Mortar and SCC are usually regarded as Bingham materials, showing a linear relationship between shear stress and shear rate [8,18,19]. While, because of shear thinning of cement paste [20] and shear thickening of normal concrete [21], cement paste and normal concrete are commonly fitted with the Herschel-Bulkley model, in which n b 1 for shear thinning and n N 1 for shear thickening. With these models, the equilibrium flow curve quantifying the relationship between equilibrium shear stress and shear rate is fitted and the dynamic yield stress is obtained. In contrast to the dynamic yield stress obtained from the steadystate flow curve, thixotropic materials also exhibit a static yield stress [22,23]. The dynamic yield stress is the stress necessary to terminate flow, measured after the material has been sheared and the microstructure has been broken down. In contrast, the static yield stress is the stress necessary to initiate flow, corresponding to a well-connected microstructure. A common protocol to characterize static yield stress is to apply an intermediate constant shear rate and to record the resultant shear stress [23,24]. The typical response of cement-based materials is an initial increase to a peak and subsequent decrease to an equilibrium value over time. The increase in stress is related to the gradual deformation of the material and the peak stress marks the static yield stress of the suspension that must be overcome to initiate continuous flow. However, this method is shear rate dependent [25]. This presents an experimental challenge when attempting to characterize systems that exhibit very high rates of flocculation. For instance, systems modified with highly purified attapulgite clays were found to significantly accelerate thixotropic rebuilding kinetics [26]. As a result, the stress growth protocol is not a suitable approach to characterize such systems. Another method is to apply creep recovery, which was implemented by Struble and Schultz on cement paste systems [20]. This is a stress-controlled test, where the material will not flow until the applied creep stress is higher than the critical creep stress. They observed the transition from solid-like behavior to liquid-like behavior with a slight increase in applied stress. They compared the measured stress at which this transition occurs to the dynamic yield stress measured through fitting the flow curve with a steady-state flow model. Here, we adopt their approach and tie it to static yield stress, then extend it to characterize thixotropic rebuilding over time. In this study, strain and viscosity development of cement paste under a creep recovery test will be presented and discussed. Through incrementally increasing applied stress, a viscosity bifurcation is found to occur beyond a critical stress. Through low amplitude oscillatory shear, the critical strain at which the solid-liquid transition occurs is measured and is compared to the shear strains measured in the creep recovery test. The strains at which the material transitions to either flow or no flow were found to exceed the critical strain only once the critical stress had been exceeded. This supports that the critical stress measured through the creep recovery test is static yield stress. The test is extended to characterize thixotropic rebuilding of cement pastes modified with attapulgite clays by measuring the development of static yield stress over time, up to 60 min.
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کلمات کلیدی:
Use of creep recovery protocol to measure static yield stress and ... www.sciencedirect.com/science/article/pii/S0008884616304306 by Y Qian - 2016 - Cited by 2 - Related articles In this study, a creep recovery shear rheological protocol was applied to fresh cement pastes. A viscosity bifurcation behavior was observed through applying a. Use of creep recovery protocol to measure static yield stress and ... https://academiccommons.columbia.edu/catalog/ac:206269 by Y Qian - 2016 - Cited by 2 - Related articles In this study, a creep recovery shear rheological protocol was applied to fresh cement pastes. A viscosity bifurcation behavior was observed through applying a ... Use of creep recovery protocol to measure static yield stress and ... isi-dl.com/item/102477 Use of creep recovery protocol to measure static yield stress and structural rebuilding of fresh cement pastes. sciencedirect.com ... Use of creep recovery protocol to measure static yield stress and ... https://www.deepdyve.com/.../use-of-creep-recovery-protocol-to-measure-static-yield... Read "Use of creep recovery protocol to measure static yield stress and structural rebuilding of fresh cement pastes, Cement and Concrete Research" on ...
