Rheology in Self Compacting Concrete

Rheology is the science of the deformation and flow of materials. It is a complex discipline used to understand the workability characteristics of Self Compacting Concrete (SCC). Special test devices called RHEOMETERS are used in the laboratory to research the workability properties of Self Compacting Concrete. The two most important properties of Self Compacting Concrete’s rheology are:

Yield stress: the measure of the amount of energy required to make Self Compacting Concrete flow. To be considered Self Compacting Concrete, concrete must flow easily under its own weight, so its yield stress must be very low.

Plastic viscosity: the measure of the resistance of Self Compacting Concrete to flow due to internal friction. SCC must have a high viscosity in order to suspend aggregate particles in a homogenous manner within the concrete matrix without segregation, excessive bleeding, excessive air migration, or paste separation.

 In summary, Self Compacting Concrete must have low-yield stress and high viscosity.

How does an understanding of Self Compacting Concrete’s rheological properties help in the field?

In practice,  rheological properties of Self Compacting Concrete are manifested in three ways:

1. Filling ability: Self Compacting Concrete must flow into forms and around obstacles such as reinforcing steel under only the force of gravity. This does not mean that all Self Compacting Concrete is self-leveling, however.

2. Passing ability (resistance to blocking): Self Compacting Concrete must pass through various obstacles and fill open spaces in the formwork without blockage due to aggregates being restricted from passing through narrow openings. Typical aggregate size to opening size relationships are at least 1:2, such that, for example, a 6.4 mm (1⁄4 in.) maximum nominal size aggregate would require a 12.5 mm (1⁄2 in.) or larger opening.

 3. Stability (segregation resistance): Self Compacting Concrete must have dynamic stability by remaining homogenous throughout mixing, transportation, placing, and have static stability during finishing and curing