PSI - Issue 71

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

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ettringite. The formation of ettringite causes internal expansion and microcracking, compromising durability. Therefore, the moderate MK level in R20MK10 prevents such adverse effects while maintaining sufficient refinement of the pore structure, leading to improved acid resistance. A similar trend has been reported in earlier

studies on MK-rich mixes under acidic conditions (Kannan & Ganesan, 2014). Fig. 4. Heatmap for concrete mixes subjected to acid attack (a) Compressive strength loss %; (b) Weight loss %. 4.4 Microstructural Analysis SEM images of 28-day water-cured samples for CC, R20MK10, and R20MK15 are shown in Fig. 5(a–c). The CC displays a slightly porous and irregular matrix, contributing to its lower strength and durability. R20MK10 shows a denser and more uniform microstructure due to the synergistic action of RHA and moderate MK content, which improves pore refinement and acid resistance. R20MK15 exhibits the most compact matrix with minimal porosity and well-formed hydration products, explaining its highest mechanical strength. Despite this densification, R20MK15 showed reduced durability under sulphuric acid attack compared to R20MK10. This is likely due to higher alumina content at increased MK levels, which can lead to ettringite formation in acidic environments, causing expansion and microcracking. This behaviour has been reported in similar studies (Kannan & Ganesan, 2014). Thus, R20MK10 offers a better balance between strength and acid resistance under aggressive conditions.

Fig. 5. SEM images of different concrete mixes (a) CC; (b) R20MK10; (d) R20MK15.

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