Page 5 - ICJ Jan 2026

TECHNICAL PAPER

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of dissolved phases and reaction kinetics The hydrated cement dosage, cluster II starts to disturb the effective w/c available for
phases precipitate on available surfaces, in a phenomenon hydration, reducing the observed strength improvement . At
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known as nucleation. Nucleation over a surface hinders its higher dosage, group I (silicate) and group II (alumina silicate)
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dissolution and acts as a limiter to the first stage of hydration . exhibit better sustainability without negatively affecting the
2+
SCMs with higher specific surface area and Ca content tend strength . Furthermore, group I (silicates) are recommended
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to attract precipitating phases and reduce nucleation over in concrete with higher portlandite availability, like C 3 S cement
unreacted cement phases . composite, as they can produce more pozzolanic reactions .
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Higher concentration of soluble aluminium in alumina silicate,
2.1 Characterisation-based assessment
calcareous alumina silicate and slag can limit the solubility of
Higher clinker substitution through SCM has always been silicates and overall pozzolanic activity . Group II (alumina
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advocated for improved sustainability . However, an extensive silicates) are recommended for concrete with lower portlandite
review of the legal framework, availability of raw materials and availability, like C 2 S cement composite, for achieving high clinker
consumption patterns revealed a major challenge associated substitution .
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with the selection of SCM and optimisation of its dosage [1,2] .
It is important to note that higher clinker substitution is Key contribution: The results clearly demonstrate that SCMs
permitted within the legal framework, but requires additional with similar specific surface area and elemental composition
testing for material safety, which increases the project cost . can be grouped together irrespective of their nature of origin.
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The stakeholders further face the challenge of different types The study, for the first time, demonstrated the application of
of SCMs with disproportionate geographic availability . grouping across materials from different sources of origin. The
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Furthermore, most available literature classifies SCMs based classification helps in optimising the use of new and alternative
on the source of their origin. Several studies show that SCMs materials as SCMs, based on the desired concrete application.
from a similar source can perform significantly differently in
concrete, limiting the replicability of results and stakeholder Limitations: Assumptions were taken to account for the limited
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confidence . As an alternative strategy, the article advocates reporting of characterisation data. In the case of limited
for a characterisation-based assessment approach to select and reporting, it has been assumed that the missing properties of
optimise the dosage of SCMs in concrete. any given SCM will be within the range reported across other
reported studies on the same material. Due to the assumption,
In one of the previous studies, an extensive meta-analysis the study fails to establish a correlation between material
was carried out to correlate the physical, chemical, and
microstructural characteristics of SCMs with their effect on the characteristics and the relative performance of different SCMs
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properties of concrete . The study showed that specific surface within the same group of materials. Furthermore, the effect
area and elemental composition have a strong correlation with of amorphous content, electrical conductivity, pH and carbon
mechanical, rheological and durability properties of concrete as content was reported for very limited SCMs. Further inclusion
compared to specific gravity, mineral composition and chemical of these parameters may improve the characterisation-based
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composition . The particle morphology affects the rheological classification.
properties of fresh concrete, but does not correlate with other
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properties . Different SCMs were then grouped based on
specific surface area and elemental composition, as shown in
Figures 1 and 2 .
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The groups demonstrated a strong correlation with the
resulting properties of concrete in terms of workability, strength
(compressive, flexural, split tensile), and durability (permeability,
sulphate attack, chloride ion penetration, carbonation, and
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wetting-drying cycles) . The study shows that, to improve
workability, cluster I (similar particle size) with a smooth, spherical
morphology should be used, such as fly ash, ground granulated
blast furnace slag (GGBS), silica fume, marble powder, and glass Clusters I II
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powder . To improve strength and durability, it is recommended Trait Similar specific surface area Fine particles
2
2
to use cluster II (very fine particles) and materials with high Ca <1100 m /kg (typically 200 – >1100 m /kg (typically 12000
2
2
content, i.e., group III (calcareous alumina silicate), group IV 600 m /kg) – 20000 m /kg)
(slag) and group V (calcites) . It is interesting to note that at high Figure 1: Grouping of SCMs based on specific surface area
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THE INDIAN CONCRETE JOURNAL | JANUARY 2026 67