دانلود رایگان مقاله لاتین جریان شروع ملات تازه در روانه سنج از سایت الزویر
عنوان فارسی مقاله:
جریان شروع ملات تازه در روانه سنج: سهم لخته خمیر و مهاجرت ذرات شن و ماسه
عنوان انگلیسی مقاله:
Flow onset of fresh mortars in rheometers: Contribution of paste deflocculation and sand particle migration
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Most studies on the rheology of cement-based materials thus far have focused on the paste phase and the concrete phase [1]. Paste is investigated because it is the phase that embodies the colloidal and hydration effects. However, the rheology of concrete is heavily influenced by the characteristics of the granular phase. Many experimental rheological studies investigate concrete systems directly to capture the critical aspects of particle packing and grain-to-grain contact. Sophisticated measurements are challenging, though, due to the limited sensitivity of large-scale viscometers and increased likeliness of inhomogeneity within the suspension, although some modified geometries have been proposed [1–3]. Mortar is an intermediate scale that exhibits both colloidal and granular behavior. They can be prepared in relatively small batches, and tested on rotational rheometers with precise shear and measurement control, allowing for more complex flow situations. Serving as the suspending phase for the coarse aggregates, the rheological properties of the mortar are important in regards to the stability of fresh concrete systems [4]. Particularly for self-consolidating concrete (SCC), the mortar phase makes up a greater part of its composition compared to conventional concrete. Thus testing the rheological properties of mortar is an integral part of SCC design [5]. However, a widely recognized challenge in characterizing fresh cement mortar through shear rheological methods is shear-induced particle migration [6–8]. This has invoked studies that explore the influence of various parameters, e.g. setup geometries and solid inclusions, on sedimentation and migration under rotational shear [9]. However, more investigation is needed. In particular, it would be useful to develop a method to quantify sand particle migration in fresh mortars to help guide the design of protocols for dynamic rheological characterization. Further, it can help determine the range of shear rates within which migration can be minimized or held constant. It can also be used to evaluate the effect of various mix parameters, e.g. mix proportioning and use of mineral/chemical admixtures, on dynamic segregation. As part of a wider investigation on the thixotropy of fresh mortar systems, in the present paper we discuss the potential of a thixotropy/migration model to quantify shear-induced particle migration in fresh mortars. The idealized shear stress response of a fresh cement-based suspension under a constant intermediate shear rate can be described as follows: an initial increase to a peak value, considered to be the static yield stress as measured by the stress growth protocol, followed by a decay until steady-state is reached. The shear stress decay from the peak value to the equilibrium value captures the process of structural breakdown and is related to the thixotropy of the material. Thixotropy is defined as a decrease in viscosity under shear, followed by an increase upon removal of shear. From a microstructural point of view, it can be described as paste deflocculation and breakage of CSH bridges under flow, and reflocculation and formation of CSH bridges over time at rest [10]. Meanwhile, sand migration induces structural heterogeneity. In investigating stress decay, we focus on paste deflocculation and sand migration. The stress decay curve of cement paste is found to be fitted well by an exponential curve. Empirically, Tattersall [11], Papo [12] and Lapasin et al. [13] measured the difference between the maximum shear stress, τmax, needed to initiate flow and the steady-state equilibrium value, τe, at constant shear rate, then proposed simple thixotropy models thatpredict an exponential decrease of the shear stress. A logarithmic evolution of the shear stress was obtained, as follows:
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کلمات کلیدی:
[PDF]Flow onset of fresh mortars in rheometers: Contribution of paste ... https://academiccommons.columbia.edu/.../ccr2016_qian__shear_migration_.pdf Sep 30, 2016 - Flow onset of fresh mortars in rheometers: Contribution of paste ... terizing the stress decay process during constant shear flow with the aid of a ... Academic paper (PDF): Flow onset of fresh mortars in rheometers ... https://www.researchgate.net/.../308787566_Flow_onset_of_fresh_mortars_in_rheomete... Dec 9, 2016 - Download research paper: Flow onset of fresh mortars in rheometers: Contribution of paste deflocculation and sand particle migration on ... Flow onset of fresh mortars in rheometers: Contribution of paste ... isi-dl.com/item/140420 Flow onset of fresh mortars in rheometers: Contribution of paste deflocculation and sand particle migration. sciencedirect.com ... Flow onset of fresh mortars in rheometers: Contribution of ... - DeepDyve https://www.deepdyve.com/.../flow-onset-of-fresh-mortars-in-rheometers-contribution... Read "Flow onset of fresh mortars in rheometers: Contribution of paste deflocculation and sand particle migration, Cement and Concrete Research" on ... The rheology of Portland cement pastes - IOPscience iopscience.iop.org/article/10.1088/0508-3443/6/5/304/meta by GH Tattersall - 1955 - Cited by 66 - Related articles Flow onset of fresh mortars in rheometers: Contribution of paste deflocculation ... Modelling thixotropic behavior of fresh cement pastes from MRI measurements Handbook of Adhesives Raw Materials https://books.google.com/books?isbn=081551185X Ernest W. Flick - 1989 - Reference Slip is a common problem aggravated by the plastic flow behavior and by the ... There are several rheometers available for testing fresh concrete and mortar. PRO 33: 3rd International RILEM Symposium on Self-Compacting Concrete https://books.google.com/books?isbn=291214342X Ólafur H. Wallevik, Indriði Níelsson - 2003 - Concrete Rheological measurements are essential, to determine the flow behaviour ... of a low concentration of coarse aggregates dispersed in the viscous fluid of a mortar matrix. The fresh concrete properties of SCC are influenced mostly by the ... during a time consuming placing of SCC, the authors developed a rheometer ... Simulation of Fresh Concrete Flow: State-of-the Art Report of the ... https://books.google.com/books?isbn=9401788847 Nicolas Roussel, Annika Gram - 2014 - Technology & Engineering Cement and Concrete Research 40, 77–84 (2010) Coussot, P.: Rheometry of ... Limited, Great Britain (1983) Banfill, P.F.G.: The Rheology of Fresh Mortar. Mag.
