Page 6 - ICJ Jan 2026

TECHNICAL PAPER

level defined by the particle size distribution alone. Proper the flow behavior of concrete. In simple practical terms, the
control of interparticle chemistry, however, can help to achieve shear yield stress is reflective of the effort to get the material
maximum packing and can be used to modify rheological or moving (for example, vibrating the normal concrete), while the
other properties. The objectives of particle packing research are plastic viscosity is the resistance of the material to flow once it
to understand how the given combination of particles packs in moves.
a system, systems of particle-packing, to develop models for
calculating packing densities and porosities of various systems, While the shear yield stress is a function of the interparticle
spacing between the aggregates and the fluidity of the paste,
behavioral and performance study of the operations which use
the plastic viscosity of the concrete depends on the paste to
such systems.
aggregate ratio as well as the viscosity of the paste fraction. In
Optimization of aggregate blends for concrete production other words, the rheology of concrete is closely related to the
[3]
can also be performed through an experimental approach paste rheology.
and application of statistical techniques to select the correct
While a complete assessment of the rheology includes the
combination of different sized aggregates that leads to
use of specialized rheometers, the need for accessible and
maximum packing density, or in other words, minimum void
economical alternatives has led to the development of simple
content (which is = 1– packing density). The calculation of
test methods based on the use of common equipment such
voids content enables the determination of the minimum paste
content required to completely fill the voids left behind by the as the slump cone. A full range of alternative methods for
[5]
aggregate combination. Further, the quantity of excess paste to self-compacting concrete (SCC) is available , with some
produce the desired workability can then be assessed. guidance on how the empirical results can be connected to the
rheological parameters. The concept of rheological control is
further necessary for 3D printable concrete, which often presents
1.2 Control of rheology in cementitious systems
contradictory demands for workability at different stages of the
Since the early 2000s, or more precisely from the advent of Self- process.
Compacting Concrete, the term ‘workability’ has been gradually
replaced by ‘rheology’. As the name describes, rheology is the It must be understood that a comprehensive understanding
science of flow of matter. Conventional workability tests adopted of mixture design resulting in the right combination of fresh
for concrete only give an indication of the consistency of the properties in SCC and 3D printable concrete would require the
material, and do not essentially capture all elements involved application of multiple types of assessment, going beyond just
in workability, which consists of the ease of mixing, placing, the rheology control.
consolidating and finishing the concrete. Especially where
The purpose of this paper is to unravel the complexity of mixture
concrete with special fresh characteristics is involved, such as
design and materials selection for special concretes by utilizing
flowable concrete or SCC, it becomes imperative to design
a simplified and systematic approach that combines the use
concrete appropriately and test it to actually reflect all the
of particle packing and rheology. The discussions presented
aspects of workability. This is only possible through a rheological
in the paper include the work performed by IIT Madras in high
approach. While a detailed treatise on rheology is beyond
performance concrete (HPC), self-compacting concrete (SCC),
the scope of this paper and is presented in much better terms high density concrete (HDC) and 3D printed concrete (3DPC).
[4]
elsewhere , it would suffice to say here that for most practical
purposes, concrete is treated as a Bingham material with respect
2. PRODUCING HPC WITH LOW CEMENT
to its rheology. As per this model, the shear stress is related to
CONTENT
the shear strain rate as per Equation 2,
Senthil Kumar and Santhanam attempted the use of the
[6]
τ = τ 0 + µѓ (2) particle packing approach using the modified Andreassen
where τ = shear stress model to design HPC with cement contents as low as 240 kg/m .
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τ 0 = shear yield stress Two series of concretes were prepared, with w/b ranging from
µ = plastic viscosity, and 0.33-0.36, and coarse to fine aggregate ratio of 1.2:1. In the
� = shear strain rate first series (cement replacement trials), an equivalent volume of
cement (for 60 kg material) was replaced by quartz powder, fly
Hence, there are two principal parameters in this equation, ash, and microsilica-the control mixture had a cement content
namely the shear yield stress and plastic viscosity, which define of 420 kg/m . In the second series, special design mixtures
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