PSI - Issue 71

Yash Rathore et al. / Procedia Structural Integrity 71 (2025) 401–408

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these findings, the R20 mix was further optimized by substituting OPC with MK at levels ranging from 5% to 20% by weight. Additionally, natural river sand was completely replaced with Deccan basalt M-sand as given in Table 2. Superplasticizer dosage was adjusted for each mix to maintain the desired slump range of 75-100 mm. Table 2 presents the material proportions for the final concrete mixes used in this study. To assess acid resistance, 150 mm cube specimens were cured for 28 days and then immersed in a 4% sulphuric acid (H 2 SO 4 ) solution for 90 days. The acid concentration was maintained throughout the testing duration. Changes in specimen weight and compressive strength were recorded after the acid exposure period. Table 1. Concrete mix proportions for varying RHA content.

28 Days Strength (MPa)

Binder (B) Kg/m 3

Coarse Aggregate Kg/m 3

Water (W) Kg/m 3

SP Kg/m 3

River Sand Kg/m 3

W/B

Mixes

Compressive Strength

Flexural Strength

OPC RHA

CC 440.45

0

648.66 1254.09 154.16 4.84 0.35

48.33 49.98 51.57 52.22 52.71 50.24

4.41 4.58 4.76 4.90 5.03 4.94

R5 418.42 22.02 648.66 1254.09 154.16 5.31 0.35 R10 396.40 44.04 648.66 1254.09 154.16 5.86 0.35 R15 374.38 66.06 648.66 1254.09 154.16 6.04 0.35 R20 352.36 88.09 648.66 1254.09 154.16 6.32 0.35 R25 330.33 110.11 648.66 1254.09 154.16 6.57 0.35

Table 2. Concrete mix proportions for RHA, MK, and M-Sand mixes.

Binder (B) Kg/m 3

Fine aggregate Kg/m 3

Coarse Aggregate Kg/m 3

Water (W) Kg/m 3

SP Kg/m 3

Mixes

W/B

River Sand 648.66 648.66

OPC RHA MK

M-sand

CC 440.45 0

0

0 0

1254.09 154.16 1254.09 154.16

4.84 6.32 7.14 7.34 7.68 7.94

0.35 0.35 0.35 0.35 0.35 0.35

R20 352.36 88.09 0 R20MK5 330.33 88.09 22.02 R20MK10 308.31 88.09 44.04 R20MK15 286.29 88.09 66.06 R20MK20 264.27 88.09 88.09

0 0 0 0

648.66 1254.09 154.16 648.66 1254.09 154.16 648.66 1254.09 154.16 648.66 1254.09 154.16

4. Results and discussions 4.1. Compressive Strength

The compressive strength of all concrete mixtures after various curing periods is shown in Fig. 3(a). The figure reveals a noticeable initial increase in compressive strength when up to 15% MK is used to replace OPC in the control concrete (CC) mix, along with 20% RHA and 100% M-sand as fine aggregate. However, beyond this 15% MK content, the compressive strength begins to decline. The peak increase occurs at 15% MK, leading to a 23.62% enhancement during the 28-day curing period. After this point, compressive strength values gradually decrease for the concrete mixtures.

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