With time the concrete production and technology is increasing with processing methods that need better understanding of concrete in its fresh state. This is when the study of flow matter called the rheology takes its place.
How to apply rheological study in concrete?
Rheology study can be applied to fresh and hardened concrete state. In hardened state, the plastic behavior of the concrete is considered for rheological study. Rheological study on fresh concrete has more scope compared to hardened state.
Rheology of fresh concrete
Fresh concrete is a dispersion of aggregates on a liquid medium containing cement paste. As cement paste is itself a combination of solid materials, a fresh concrete forms a multiphase material.
The determination of rheological characteristics or parameters of fresh concrete are based on the assumption that:
 The concrete as a multi phase material is a continuum. This means, a material with no discontinuity between any two points on it.
 The concrete as a multi phase material is a homogeneous mix. This means a material with uniform composition throughout.
 The concrete as a multi phase material is an isotropic material. This means, material of the same properties in all directions
Yes, you have doubted the right!! How can all these assumptions together satisfy. It won’t. The degree of compliance with the assumptions i mentioned above is dependent on
 the type of concrete mix
 the microscale study performed
 the state of concrete when the measurement is carried out
It also depends on how the mix is observed, i.e. The microscale study performed. Because in micro scale the concrete is unlikely to have a continuum.Representation of Rheological behavior of Concrete
As we are relating concrete study with fluid study, i will start explaining with “newton’s law of viscous flow”.
The newton’s law of viscous flow states that “the shear stress is proportional to the shear strain when we study the forces between the layers of the fluid”.
Shear stress Î± shear strain
Shear stress (Ï„) = constant x shear strain (Î³)
Those fluid that obeys newton’s law of viscous flow is called as Newtonian liquids. The constant obtained by the above relation is a “physical constant” that represent the characteristic of the material studied.
Bingham Model for Rheology of Concrete
Concrete is a nonNewtonian fluid whose rheological properties is represented by Bingham model. When we relate with the concrete material, the constant is related to the shear rate at which concrete is measured and the shear history of the same.

Bingham Model Representation of Concrete Rheology 
When the concrete is studied at a lower shear stress value, that is the practical case of fresh concrete, it is observed that, the linear curve obtained when drawing shear stress to strain curve do not pass through the origin. Instead, it starts at a particular value from the xaxis as shown. This intercept formed at the xaxis is the minimum stress value below which the concrete will not flow.
No time to Read??Watch the Video on this Article: Rheology of Concrete
Consider an experimental condition, where the concrete can stay in a pile while conducting slump test. This means, a minimum stress value for this concrete will make the concrete to flow. This minimum stress value of concrete to start flowing is called as the yield stress and it is designated by the symbol, Ï„0.

Concrete Slump Test 
Then the simplest flow equation can be given as:
Ï„= Ï„o + Î¼Î³’
Here, , Ï„o. Is the yield value that indicates the cohesion of the material. is the Î¼ plastic viscosity that is a constant value giving dimensions of viscosity and this relation is called as Bingham model.
In a Bingham model, the parameters that represent the flow properties of the material are Ï„0 and Î¼. Bingham fluid, which is a nonNewtonian fluid which is most frequently used for the study of concrete.
Note: NonNewtonian fluid is the fluid that does not obey newton’s law of viscosity.
In Bingham model a single point test like workability only gives a single value. But to form a line we need minimum of two points. So we need to perform two or more tests like vee bee tests etc.
Watch the Video on this Article: Rheology of Concrete
Tattersal Model for Rheology of Concrete
The Tattersal model overcomes the shortcoming of the Bingham model. The Tattersal tests measures the mobility characteristics of the fluid that provides us two point value of shear conditions.

Tattersal Model for rheology of concrete 

In this method, the power required to run the concrete mixer at different speeds are calculated. After this, the torque ‘t’ is calculated by dividing the power by speed. Hence, Tattersal provided a relation as:
T = g + hN
Where, T= torque;
N is the number of r.p.m , g and h are constants proportional to the cohesion and plastic viscosity of the mixture.
It has been observed that two different mixtures with same g and h values shows identical values for consistency, veebee time and compacting factor test.
Comparison of Bingham model and Tattersal model of concrete
Compared to Bingham model, the yield stress is not well defined in the case of Tattersal model. Second important difference is that, the flow curve obtained in Tattersal model is not linear (except in some of the portions).
Also Read:
0 Comments
Commenting Spam Links Are Against Policies