Rheological behaviour of fresh concrete mixtures

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F68407700%3A21220%2F22%3A00362996" target="_blank" >RIV/68407700:21220/22:00362996 - isvavai.cz</a>

Nalezeny alternativní kódy

RIV/68407700:21610/22:00362996

Výsledek na webu

<a href="https://www.e-congress.events/AERC2022" target="_blank" >https://www.e-congress.events/AERC2022</a>

DOI - Digital Object Identifier

—

Jazyk výsledku

angličtina

Název v původním jazyce

Rheological behaviour of fresh concrete mixtures

Popis výsledku v původním jazyce

Knowledge of the rheological behaviour of UHPC (ultra-high-performance concrete) is required when studying processes that run in the mixture during its preparation, transport, and application. The mixture consists of water, powdered compounds, plasticizer, and metal or organic fibres. The presence of additives makes it impossible to measure the flow properties using classical rheometers with common geometries, e.g. coaxial cylinders. We used a measuring system consisting of a cylindrical flat-bottomed vessel and an eccentrically placed screw agitator to measure the flow properties of UHPC. The shaft torque and the rotations of the agitator were measured to determine the apparent viscosity of the mixtures. A power characteristic of the agitator (dependence of power necessary for reaching a steady state rotation on Reynolds number) has to be known for the used agitator. Moreover, the dependence of the Reynolds number on the shear rate of the liquid flowing around the agitator surface must be known. A Metzner-Otto concept was used for this purpose. Newtonian (silicon oil) and non-Newtonian power-law liquid (CMC) were used to actualize constants of the power characteristic as well as the Metzner-Otto constant of the used agitator. The flow properties of the model fluids were determined using the modular compact rheometer MCR 102 with standard coaxial cylinders (CC27) in the range of shear rates corresponding to the values that can be expected in the observed processes (order of tenths to units of reciprocal seconds). The rheological properties of fresh concretes and also their change during the solidification process were determined. The results showed that the mixtures can be divided into two groups that differ in the value of the yield stress. A Herschel-Bulkley model was used for practical description of the flow behaviour. The contribution presents the results of the methodology used to measure the flow properties of fresh concretes or similar inhomogeneous mixtures in which a solidification process can occur.

Název v anglickém jazyce

Rheological behaviour of fresh concrete mixtures

Popis výsledku anglicky

Knowledge of the rheological behaviour of UHPC (ultra-high-performance concrete) is required when studying processes that run in the mixture during its preparation, transport, and application. The mixture consists of water, powdered compounds, plasticizer, and metal or organic fibres. The presence of additives makes it impossible to measure the flow properties using classical rheometers with common geometries, e.g. coaxial cylinders. We used a measuring system consisting of a cylindrical flat-bottomed vessel and an eccentrically placed screw agitator to measure the flow properties of UHPC. The shaft torque and the rotations of the agitator were measured to determine the apparent viscosity of the mixtures. A power characteristic of the agitator (dependence of power necessary for reaching a steady state rotation on Reynolds number) has to be known for the used agitator. Moreover, the dependence of the Reynolds number on the shear rate of the liquid flowing around the agitator surface must be known. A Metzner-Otto concept was used for this purpose. Newtonian (silicon oil) and non-Newtonian power-law liquid (CMC) were used to actualize constants of the power characteristic as well as the Metzner-Otto constant of the used agitator. The flow properties of the model fluids were determined using the modular compact rheometer MCR 102 with standard coaxial cylinders (CC27) in the range of shear rates corresponding to the values that can be expected in the observed processes (order of tenths to units of reciprocal seconds). The rheological properties of fresh concretes and also their change during the solidification process were determined. The results showed that the mixtures can be divided into two groups that differ in the value of the yield stress. A Herschel-Bulkley model was used for practical description of the flow behaviour. The contribution presents the results of the methodology used to measure the flow properties of fresh concretes or similar inhomogeneous mixtures in which a solidification process can occur.

Druh

O - Ostatní výsledky

CEP obor

—

OECD FORD obor

20302 - Applied mechanics

Projekt

<a href="/cs/project/GA21-24070S" target="_blank" >GA21-24070S: Model segregace vláken v závislosti na reologických vlastnostech čerstvého HPC</a><br>

Návaznosti

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Rok uplatnění

2022

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů