PSI - Issue 70

Shashikant Kumar et al. / Procedia Structural Integrity 70 (2025) 501–508

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1. Introduction Self-compacting concrete (SCC), a modern form of high-performance concrete, is distinguished by its ability to flow and compact under its own weight, even with complex reinforcement, without segregation or migration of coarse aggregates, and to uniformly fill formwork without the need for external vibration (Okamura & Ouchi, 2003). Researchers have described self-compacting concrete (SCC) as a highly flowable material that meets the essential requirements of passing ability, filling ability, and segregation resistance (Kumar & Rai, 2018). Various approaches have been employed to develop SCC. One common method to achieve self-consolidating properties, compared to conventional concrete, involves significantly increasing the quantity of fine materials, such as fly ash or silica fume, without changing the water content. Adding a viscosity modifying admixture (VMA) to improve stability is one other strategy. High deformability and sufficient workability can be ensured by using VMA in conjunction with a suitable concentration of superplasticizer (SP), which results in an excellent resistance to segregation. Over the last 20 years, SCC has been further improved utilising a range of supplementary cementitious materials (SCMs), such as fly ash (FA) (Kumar & Rai, 2019) and silica fume (Kumar & Rai, 2022). The inclusion of various SCMs can have a significant influence on the fresh and hardened characteristics of SCC (Kumar & Rai, 2022). All SCMs have two things in common: they are pozzolanic, meaning they participate in hydration processes, and their particles are either smaller or the equal size as ordinary Portland cement (OPC). A naturally diverse byproduct of coal combustion, fly ash is frequently utilized in concrete in place of Portland cement. With both crystalline and amorphous phases, fly ash is a complex substance with distinct reactivity in the concrete environment. A better knowledge of the effects of fly ash on the characteristics of concrete and, consequently, a higher-quality final product could be achieved by identifying and defining the distinct phases in this highly variable and frequently complicated material. Pozzolans such as FA a nd SF, which are reactive forms of silica (SiO₂), possess minimal cementitious properties when used independently. Introducing a secondary mineral additive to the cementitious system can help counterbalance the drawbacks of relying solely on one mineral source. A silica fume-fly ash blend added as an additive to cement compositions has the potential to be highly beneficial since it increases the strength of concrete and reduces permeability and corrosion. The effects of fly ash and silica fume on cement hydration have each been extensively researched, and there isn't much disagreement on how they work. Ternary blended cement concretes are frequently made using a mixture of low and high reactive pozzolana to advance the rheological properties, sulphate resistance, chloride ion permeation, pore structure, and higher early age strength (Kumar et al., 2020). Furthermore, adding nanoparticles helps to improve the micropore structure. Shashikant and Rai (Kumar & Rai, 2022) discovered that SCC combinations with 8% silica fume worked better mechanically and in terms of durability than any other SCC mix when they substituted SF and HVFA for some of the cement. Using class C fly ash, Ashtiani et al. (Soleymani Ashtiani et al., 2013) produced an SCC and discovered that it had a comparable water-binder ratio and a significant compressive strength as compared to conventional concrete. The addition of silica fume (SF) can enhance the properties of concrete in both its fresh and hardened states. For financial reasons, it is usually used in place of cement (Neville, 2011). Because of its large surface area and amorphous shape, silica fume is perfect for use in binder systems that aim to increase heat conductivity (Demirboǧa, 2003) . The rapid reaction between silica fume and lime results in the formation of a higher silica hydrated layer. The delicate nature of this layer causes it to rapidly transform into calcium silicate hydrate (C-S-H) gel. During the 7 – 28 day curing period, free lime disappears because of the higher reactivity of amorphous particles of silica fume. However, the C-S H gel produced by this process is much more crystalline than the C-S-H gel produced by cement hydrating (Tayeh et al., 2013). A sequence of complex chemical reactions results from the reaction of cement and water. Le Chatelier made the initial observation that the cement's hydration products were a blend of the separate compounds' products under comparable circumstances over a century ago (Neville, 2011). Bogue and Lerch (Bogue & Lerch, 1934) and Senior (Steniour, 1952) then added to Le Chatelier's observation. According to the supplement, the reaction's byproducts might interact with the other cement-related chemicals. The primary constituents of cement are two calcium silicates, namely dicalcium silicate and tricalcium silicate, which exhibit comparable physical characteristics to cement when it hydrates. Dadsetan and Bai examined the microstructural and mechanical characteristics of SCC mixtures made of metakaolin, GGBS, and FA (Dadsetan & Bai, 2017). They discovered that SCC mixtures containing FA had a reduced compressive strength at 28 and 56 days. For mechanical performance and mix design, Haung et al. produced