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TECHNICAL PAPER

applications where weight reduction is a priority without a critical (Si) peaks were consistent across all spectra, implying pumice
need for maximum tensile strength, such as in non-load-bearing aggregates do not significantly alter their contents. Calcium
elements or precast concrete products. For instance, in the peaks, essential for the hydration process and C-S-H gel
construction of a multi-story building, using a concrete mix with formation, were observed at 9.7 % in mix A, 8.1 % in M30-PA40,
40 % pumice replacement for non-load-bearing walls can reduce 8.1 % in mix B, and 2.8 % in M50-PA40, indicating that pumice
the overall weight of the building, leading to lower material replacement does not drastically reduce calcium availability and
costs and potentially smaller and less expensive structural increased in silicon content. Minor Potassium (K) peaks in both
supports. This approach can result in more sustainable and pumice mixes further highlight the role of pumice in pozzolanic
efficient construction while maintaining adequate performance activity and C-S-H gel formation. For applications requiring
for the intended application. improved insulation and durability, mixes like M30-PA40 offer a
balanced performance, though the level of pumice should be
The durability and compressive strength after sulfuric acid curing chosen based on specific needs.
indicates that both M30 and M50 series concretes with pumice
replacement showed decreased acid resistance and increased The SEM analysis for mix A revealed a dense microstructure
strength loss as pumice content increased. In the M30 series, the with fewer pores, indicating well-compacted concrete with a
control mix exhibited minimal weight loss, decreasing from 8 kg higher degree of hydration products like calcium silicate hydrate
to 7.83 kg, and the lowest strength reduction of 8.3 %, indicating (C-S-H). This dense microstructure is a critical factor contributing
strong resistance to acid degradation. Among the pumice- to the concrete’s outstanding mechanical properties and
replaced variants, the M30-PA40 mix performed best with a durability. On the other hand, the M30-PA40 mix displayed a
13.14 % strength loss, while the M30-PA100 mix experienced more porous and rougher surface, with visible holes and pores,
the most significant strength reduction at 47.1 %. In the M50 suggesting that the addition of pumice particles increased
series, the control mix had slight weight loss from 7.76 to 7.6 kg the porosity and roughness. This resulted in larger aggregates
and a 17.1 % strength loss, suggesting good overall durability. with more voids and a less uniform distribution, which might
The M50-PA40 mix showed the best performance among the negatively impact the material’s overall mechanical performance
pumice-replaced concretes, with only a 4.14 % strength loss, but could enhance properties such as thermal insulation.
maintaining most of its initial strength. Higher pumice content in For mix B, the SEM analysis revealed a notable difference in
M50 mixes led to increased weight loss and strength reduction, microstructures. The control concrete mix B demonstrated
with the M50-PA100 mix showing a 44 % strength loss. For a smooth surface, fewer apparent voids, and a reasonably
applications where superior acid resistance and strength thick and compact microstructure, indicating efficient cement
retention are critical, the M30 control mix and M50-PA40 mix hydration and a robust cement matrix. This uniform mixture is
are preferable. The M30 control mix is ideal for scenarios associated with superior durability and mechanical qualities.
demanding high acid resistance, while the M50-PA40 mix offers In contrast, the M50-PA40 concrete showed a coarser surface
a good balance of strength and durability, making it suitable with more noticeable voids and imperfections, indicating an
for applications where some compromise on acid resistance is increased porous structure. This increased porosity is likely
acceptable in exchange for improved thermal insulation and due to pumice aggregates, which introduce more air pockets
overall performance.
and result in a less compact mix. Despite the higher porosity,
The EDS spectra of 28 days cured concrete mixes A and B, the M50-PA40 concrete benefits from pozzolanic reactions, as
along with their respective pumice replacements, M30-PA40 indicated by the increased silicon (Si) concentration 12.9 % in the
and M50-PA40, reveal key insights into their compositions. Both pores. These reactions occur between the silica in the pumice
mixes exhibited significant peaks of Oxygen (O) and Calcium and calcium hydroxide from cement hydration, promoting
(Ca), indicative of hydrated cementitious phases and potential the development of C-S-H gel, which aids in improving the
carbonation products. The highest peak of Oxygen was 58.9 % mechanical properties and durability of the concrete. Both
in control mix A and 60.5 % in M30-PA40, while mix B showed mixes A and B showed early-stage ettringite formation at 28
63.1 % and M50-PA40 had 56.2 %, reflecting the substantial days, which is beneficial for strength gain. The EDS analysis for
presence of oxygen, a sign of cement hydration products like the M30-PA40 mix indicated a significant presence of oxygen
calcium silicate hydrate (C-S-H). Carbon (C) peaks varied, with (60.5 %), suggesting a large portion of oxides in the aggregates
mix A having 26.7 % and M30-PA40 at 20 %, whereas mix B had and cement paste, and confirming the presence of hydration
17.8 % and M50-PA40 at 23.2 %, indicating carbonates in the products like C-S-H. The control concrete mix A had an oxygen
concrete. The presence of Sodium (Na) in the pumice mixes, content of 56 and 60.5 % in M30-PA40, while the M50-PA40 mix
replacing Magnesium (Mg) seen in the control mixes, suggests had 56.2 % oxygen content, compared to 63.1 % in the control
that pumice aggregates contribute to the pozzolanic reaction, mix B. These findings indicate that the pumice aggregates,
enhancing strength and durability. Aluminum (Al) and Silicon while increasing porosity, also contribute to beneficial pozzolanic

THE INDIAN CONCRETE JOURNAL | FEBRUARY 2026 65