Page 12 - ICJ Jan 2026

TECHNICAL PAPER

4.1.2 Internal factors

Internal factors correspond to the constituents of cement
paste and their interactions. Among them, several factors,
like w/c ratio, aggregate content, aggregate, and admixtures,
are well explained in the literature . One new observation is
[28]
regarding the fibre dosage. In rubber fibre-added mortars, after
a critical volume, the relative motion of fibres causes greater
interaction with other fibres, as compared to aggregates present
[30]
in the mix . This increased interaction results in mechanical
interlocking, significantly increasing the static yield strength .
[30]
In a conventional rheological test, one-directional shearing is
applied; on rearrangement, the interaction reduces significantly,
and a sudden increase in shear thinning can be observed . The
[30]
mechanical interaction can also result in cluster formation or
balling effect and affect the homogeneous distribution of fibre
during mixing (Figure 9). Further investigation in this direction is
needed to determine whether the effect is limited to stiff fibres
or extends to flexible fibres.

Key contributions: The extensive review identified several
experimental factors affecting the rheology of cement
composites, which have been reported to exhibit contradictory
phenomena. The review shows that the different trends occurred
at different experimental ranges, which were reported as
contradictory phenomena in the available literature. The review
further draws parallels from cement hydration and the rheology
of non-cementitious pastes to explain the difference in trends at
different experimental ranges.
Figure 8: Dominant effect of temperature on rheology at different w/c
ratios Limitations: The study is based on an extensive review and only
theoretically explains the changes in rheological behaviour.
In theory, the changes appear to be reversible if structural Further studies are needed to validate the theoretical
breakdown exceeds structural buildup. However, the cement explanation through controlled experimental protocols.
mix also experiences irreversible changes due to hydration
[28]
and resulting microstructural changes . An alternate
mathematical expression is proposed as Equation 7 to account
for irreversible changes . The expression consists of two parts,
[29]
τ 0 + μ(α) × γ + τ 1 (α), describing the behaviour in a fully broken-
down state of cement, and net structural buildup based on shear
history, ∫A(α,γ) × (1–B(γ,t)) × dt. The fully broken-down state uses
the degree of hydration, α, to account for irreversible changes in
viscosity, μ(α), and yield stress, τ 1 (α). An extended discussion on
the development of this expression is given in Section 4.2.

τ t = τ 0 + μ(α) × γ + τ 1 (α)+ ∫ A(α, γ) × (1–B(γ, t)) × dt (7)

Here, τ t represents shear stress at any given time t under the
applied shear rate γ. A(α, γ) and B(γ, t) represents the function of
reversible structural buildup and breakdown, respectively. A(α, γ)
uses different mathematical expressions based on the stage of
hydration. Whereas, B(γ, t) follows exponential decay functions
to represent decay and inertial lag. Figure 9: Cluster formation at high fibre dosage

74 THE INDIAN CONCRETE JOURNAL | JANUARY 2026