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TECHNICAL PAPER

reactions that enhance the formation of C-S-H gel, thereby Split tensile strength tests unveiled a significant reduction with
improving the strength and durability of the concrete despite 40 % pumice replacement: M30-PA40 decreased by 59.9 % and
its higher porosity. Additionally, the mixes could be used in M50-PA40 by 51.8 %. This underscores the need to consider
environments where moderate strength and durability are fibers to maintain adequate tensile strength, especially for M30
required but with the added benefit of enhanced thermal concrete, which is more affected by pumice replacement.
properties. The early-stage ettringite formation suggests these The modulus of rupture tests revealed a reduction of about
mixes might be favorable in scenarios where early strength gain 14.85 % for M30 concrete and 17.93 % for M50 concrete with
is necessary. 40 % pumice replacement. Despite these reductions, the
strength remained sufficiently high, demonstrating the viability
The X-ray diffraction (XRD) analysis of various concrete mixes
of pumice as a replacement material. Further improvements
revealed critical insights into their crystalline structures. in tensile strength and crack resistance could be achieved by
Concrete mix A exhibited prominent peaks in the 2θ range of incorporating fibers and reinforcement.
25° to 35°, indicating abundant and well-crystallized phases
such as calcium silicate hydrates (C-S-H) and calcium hydroxide, Increase in the pumice content reduces sulphuric acid resistance
alongside smaller peaks for other minerals. The spectra and compressive strength in both M30 and M50 series
comparison showed consistent peak positions, with variations concretes. The M30 control mix showed minimal strength loss
in intensity reflecting differences in phase quantities or sample (8.3 %), while M30-PA40 performed best among pumice variants
with a 13.14 % reduction. The M50 control mix had a 17.1 %
preparation. A slight baseline increase towards lower 2θ angles strength loss, with M50-PA40 showing the best performance
was noted, likely due to amorphous content or measurement among pumice mixes at 4.14 %. Based on literature benchmarks,
noise. In the M30-PA40 mix, the introduction of pumice led pumice aggregates enhance thermal insulation due to their
to increased background noise and reduced sharpness of key low density and porous structure, making them suitable for
peaks like C-S-H and portlandite, suggesting a dilution of these energy-efficient buildings or structures in hot climates and a
phases and a potential decrease in mechanical performance strength loss below 15 % under 5 % sulphuric acid exposure is
due to diminished quartz peaks. Additional peaks indicated generally considered acceptable for moderate durability. For
the formation of new crystalline phases introduced by the high acid resistance and strength, the M30 control is ideal, while
pumice. Concrete mix B displayed a simpler XRD pattern, M50-PA40 offers a good balance for applications where some
dominated by an intense quartz peak at approximately 26° 2θ, compromise on acid resistance is acceptable for improved
with a higher concentration of crystalline quartz typical of thermal insulation such as external walls, non-load-bearing
high-strength concrete. The absence of significant additional components, or industrial buildings where moderate acid
peaks suggested a straightforward mineralogical composition, exposure occurs but thermal performance is also a key design
primarily of quartz and standard hydration products like calcite criterion.
and ettringite. The M50-PA40 mix, despite pumice replacement, EDS spectra of 28 day cured concretes reveal that both M30 and
retained prominent peaks for C-S-H, portlandite, and quartz, M50 series, along with their pumice replacements (M30-PA40
with less background noise compared to M30-PA40, indicating and M50-PA40), show significant Oxygen and Calcium peaks,
a more stable microstructure. The resilience of the M50 mix indicating hydration products like C-S-H. Pumice replacement
to pumice replacement was evident in its retention of the introduces Sodium while reducing Calcium, without significantly
original crystalline structure, crucial for maintaining strength and altering Aluminum and Silicon levels. Thus M30-PA40 and M50-
durability. PA40 both maintain balanced performance, with M30-PA40
providing good insulation and durability, and M50-PA40 offering
excellent strength retention.
7. CONCLUSION
SEM analysis concluded that the pumice aggregates increase
The following conclusions are drawn from the study’s findings porosity but also enhance strength and durability through
and experimental investigation.
pozzolanic reactions, making them suitable for applications
where thermal insulation and improved performance are desired
Compressive strength tests exhibited that increasing pumice
aggregate replacement decreased strength in both M30 and despite higher porosity.
M50 concrete mixes. A 40 % replacement level was found to be XRD analysis revealed that introduction of pumice affects the
optimal, as it maintained relatively high compressive strength, crystalline phases and stability of the concrete mixes, with the
with the M50 mix effectively balancing strength and the benefits M50-PA40 mix showing better resilience and suitability for
of pumice aggregate for producing structural lightweight applications requiring higher strength and durability than the
aggregate concrete. M30-PA40 mix.

66 THE INDIAN CONCRETE JOURNAL | FEBRUARY 2026