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TECHNICAL PAPER

Table 1: Complex combination of characteristics necessary in special concrete

TYPE OF CONCRETE FRESH PROPERTY HARDENED PROPERTY
High strength / high Workability requirements may be different based on application; Typically used aggregate gradations may not
performance concrete however, achieving and maintaining workability at low w/c is be optimized with respect to the needs of high
difficult-optimizing of chemical admixture combination and dosage strength concrete; durability requirements may not
is important be met just with low w/c, and would require the use
of suitable supplementary cementitious materials
Self-compacting Control of segregation for highly flowable concrete needs to Optimizing the mixture design to achieve a
concrete be achieved by the use of suitable chemical and/or mineral range of concrete strengths (mainly in the low to
additives; further, the material needs to exhibit diagonally opposite moderate range) may be difficult because of the
characteristics while in movement (low yield stress and viscosity) and usually low w/b used for such concretes
while at rest (high yield stress and viscosity)-therefore, selection and
optimization of chemical admixtures plays a large role; additionally,
the control of workability needs to be exercised in different
applications to avoid cracking
High density concrete Because of the high density nature of the aggregates, controlling the Distribution of aggregate across the cross section
segregation at high workability can be difficult-aggregate gradation could be non-uniform, leading to strength
and chemical admixture selection play a crucial role in the control of variations-this requires a careful control of the
the behavior particle gradations
3D printed concrete Contradictory set of characteristics need to evolve in a short time The concrete needs to evolve ‘green’ strength and
span: for pumping and material delivery, the concrete needs to have stiffness, that gives it the ability to stay in place
low yield stress and plastic viscosity; when the material is extruded without failure; on the other hand, the interface
through the nozzle, it needs a moderate yield stress, but when between layers requires the material to be relatively
layer-on-layer deposition occurs, considerable increase in the yield fresh in order for the bond to be good
stress and viscosity of the material needs to happen; therefore, a
proper control needs to be exercised on the selection of appropriate
chemical admixtures and printing strategy

A common particle packing model used in concrete studies is The exponent q value in the Andreassen equation could be
[2]
the Modified Andreassen model which is preferred because varied from 0.21 to 0.37 depending upon various workability and
of its relevance, simplicity and availability. The ideal gradation strength requirements. The previously available EMMA software
as per the Modified Andreassen model is defined in terms of was based on this model. However, the model can be easily
Equation 1. coded into a spreadsheet to obtain the parameters for the ideal

q
q
q
q
CPFT = 100 * (d -d m ) / (D -d m ) (1) gradation.
where, CPFT is the Cumulative (Volume) Percent Finer than, Studies on particle packing involve investigations into the
d is the particle size, problem of selecting appropriate sizes and proportions of
particulate materials to get the suitable combination for optimal
d m is the minimum particle size of the distribution,
packing. As the particle packing is directly controlled by the
D is the maximum particle size, and particle size distribution of the material, a system of aggregate
q is the distribution coefficient (the exponent). or powders can never pack better than the maximum possible

Figure 1: Elements of a systematic approach to designing special concrete

50 THE INDIAN CONCRETE JOURNAL | JANUARY 2026