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TECHNICAL PAPER

suggesting pumice adds sodium and enhances pozzolanic This has an impact on mechanical performance but enhance
reactions, which improve strength and durability. Silicon content qualities like thermal insulation. Higher oxygen concentration
was high, with M50-PA40 at 12.9 %, indicating a pozzolanic in M30-PA40 is shown by the EDS analysis, indicating significant
reaction that enhances C-S-H gel formation. The M50 pumice cement hydration and the presence of oxides within aggregates
mixes also had a small potassium peak (0.6 %), which was absent and cement paste.
in mix B, contributing to C-S-H gel formation. Both spectra
showed significant calcium peaks, with 8.1 % in mix B and SEM pictures of M50-PA40 and 28 day-cured concrete mix B are
2.8 % in M50-PA40, suggesting pumice replacement does not displayed in Figures 8(c) and 8(d). A strong cement matrix and
significantly affect calcium availability for hydration and strength effective cement hydration are indicated by mix B’s smooth,
development. dense, and compact microstructure with minimal voids, which
adds to the material’s mechanical strength and longevity. On the
5.7 Scanning electron microscopy (SEM) other hand, the M50-PA40 SEM picture has a rougher surface

SEM pictures of M30-PA40 and 28 day-cured concrete mix A are with more apparent voids, suggesting that pumice aggregates
displayed in Figures 8(a) and 8(b). Mix A’s excellent mechanical have increased porosity. The M50-PA40 mix, while having a
qualities and durability are attributed to its thick microstructure larger porosity, gains from the pozzolanic interactions that occur
with fewer holes, which indicates effective compaction plus high between the silica in pumice and the calcium hydroxide from
levels of hydration products such as C-S-H. The SEM picture cement hydration. This process increases the silicon content
of M30-PA40, on the other hand, reveals a rougher and more of the mix and encourages the production of C-S-H gel, which
porous surface, indicating higher porosity from pumice particles. strengthens and prolongs the concrete.

(a) Mix A-M30 control concrete SEM report (b) M30-PA40 concrete SEM report

(c) Mix B-M50 control concrete SEM report (d) M50-PA40 concrete SEM report
Figure 8: Scanning electron nicroscopy (SEM) report

THE INDIAN CONCRETE JOURNAL | FEBRUARY 2026 63