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TECHNICAL PAPER

Modulus of rupture
3.50 3.29
3.03
3.00 2.58 2.70
Modulus of rupture (MPa) 2.00
2.50

1.50
1.00
0.50

0.00
M30 M30-PA40 M50 M50-PA40
Specimen
(a) Universal testing machine arrangement with prism centred for loading (b) Different M30 and M50 concrete mix modulus of rupture at 28 days
Figure 5: Modulus of rupture

aggregate, the M30-PA40 mix’s tensile strength dramatically durability evaluation across multiple exposure scenarios for a
decreased to 1.42 MPa, a 59.9 % decrease. Comparably, the comprehensive understanding.
M50 concrete initial 3.82 MPa tensile strength decreased to 1.84
MPa for M50-PA40 when the same 40 % pumice substitution Concrete sample preparation and curing for a total of 28 days
was used, signifying a 51.8 % loss. The findings showed that was required for the sulphuric acid resistance test. We measured
adding pumice had a negative impact on the tensile strength of their initial weight and size. The concrete samples were
both concrete grades, with M30 exhibiting a somewhat larger completely immersed in a 5 % sulphuric acid solution that was
percentage reduction than M50. made in non-reactive containers. The samples were submerged
for a duration of 28 days, as seen in Figure 6(a). As seen in
5.4 Modulus of rupture test Figure 6(b), the pH of the solution was checked and maintained
once a week. Following the exposure time, the samples were
Modulus of rupture test was performed on control concrete taken out, carefully washed to eliminate any remaining acid,
and optimal dosage pumice aggregate concrete. Concrete dried, and remeasured. In addition to calculating the percentage
prism specimens were used for the test, as seen in Figure 5(a). of weight loss, the degree of surface damage, such as pitting,
The modulus of rupture of prisms testing findings showed cracking, or erosion, was evaluated. This information was
clear variations across the different specimens. According to recorded, and the concrete’s ability to withstand sulphuric acid
Figure 5(b), the modulus of rupture for regular M30 concrete was examined. Safety procedures were meticulously adhered to
was 3.03 MPa. The modulus of rupture dropped to 2.58 MPa throughout the operation, involving wearing PPE and working in
when pumice M30-PA40 was used in place of 40 % of the coarse an area with good ventilation.
aggregate, showing a loss in flexural strength. Likewise, the
M50 concrete had a greater modulus of rupture, at 3.29 MPa. Visual inspection, as seen in Figure 6(c), revealed that the
However, the modulus of rupture dropped to 2.70 MPa with concrete had small, crater-like holes on its surface, indicating
M50-PA40 mix having 40 % pumice substitution. These results localised areas of intense attack where the acid had dissolved
show that although adding pumice aggregate can help reduce the cement paste or aggregate. Cracks appear as a result of the
weight, it also has an impact on mechanical qualities, especially concrete’s components expanding and compressing in reaction
in blends with greater strengths, as M50. to the acid. Higher replacement rates (over 40 %) have also been
linked to spalling, which is the erosion of the surface layer by
5.5 Durability acid and subsequent loosening of the concrete components.
The surface of the concrete showed colour changes, indicating
Sulphuric acid (H 2 SO 4 ) was chosen due to its highly aggressive that chemical reactions were occurring between the components
nature and common presence in industrial and urban of the concrete and sulphuric acid.
environments. A 5 % concentration was selected to simulate
severe exposure conditions and accelerate degradation According to Table 5, When comparing the M30 pumice-
for comparative microstructural analysis. While other replaced concrete mixes to the M30 control concrete, it was
durability aspects (e.g., chloride penetration, carbonation) discovered that the resistance to sulphuric acid decreased as
are also relevant, this focused study serves as a preliminary the percentage of pumice aggregate increased. The weight of
investigation, and future work can be planned to extend the the M30 control concrete dropped from 8 kg to 7.83 kg after

60 THE INDIAN CONCRETE JOURNAL | FEBRUARY 2026