PSI - Issue 70

R. Mohanraj et al. / Procedia Structural Integrity 70 (2025) 401–408

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1. Introduction One of the most popular building materials is concrete, which is essential for projects like buildings, bridges, and roadways (Zhuang and Chen (2019); Khaloo et al. (2016); Zhang et al. (2017)). The quality of the raw materials used in its manufacture has a significant impact on its durability and mechanical performance (Balapour et al. (2018); Heidari, A., & Tavakoli, D. (2013); Wu et al. (2017); Wu et al. (2023)). As material science continues to progress, nanotechnology has drawn a lot of interest to improve the qualities of concrete (Givi et al. (2010); Ardalan et al. (2017); Nazerigivi & Najigivi (2019)). Nano- SiO₂ (nano -silica), which has been recognized for its capacity to increase concrete's microstructure, strength, and durability, is among the most effective nanomaterials in this respect (Zhang et al. (2019); Givi et al. (2011); Han et al. (2017)). Additional calcium silicate hydrate (C-S-H) gel is created when Nano- SiO₂, which functions as a pozzolanic material, combines with calcium hydroxide in the cement (Li et al. (2025); Wang et al. (2022)). This process increases the concrete's overall density, decreases porosity, and speeds up hydration, all of which increase the material's compressive strength and durability (Flores et al. 2010); Li (2004)). To evaluate its impact on mechanical and microstructural qualities, Nano- SiO₂ was added to concrete at different dosages ranging from 0% to 5% (Rong et al. (2015)). Three tests were used to evaluate these effects: the Fourier Transform Infrared Spectroscopy (FTIR) test was used to examine hydration reactions and microstructural changes; the slump test was used to investigate workability; and the compressive strength test (CTM test) was used to measure structural strength (Najigivi et al. (2013); Nazerigivi et al. (2018)). Because handling and placement may be impacted by an excessive reduction in slump, workability is a crucial component in the design of concrete mixes (Syamsunur et al. (2022); Oh et al. (2023)). While FTIR analysis aims to understand the chemical changes brought about by the addition of nano-silica to the cementitious matrix, the compressive strength test offers information on the ideal dose of nano- SiO₂ for reaching maximal strength (Cui et al. (2024); Fan et al. (2024); Gopalakrishnan et al. (2024)). The goal of this study's findings is to identify the ideal dose of Nano- SiO₂ to improve concrete's mechanical performance while keeping a balance between workability and durability. By increasing strength, decreasing porosity, and speeding up hydration, nano-silica shows itself to be a useful supplement for modern building techniques. The findings of this study aid in the creation of sustainable and high-performance concrete while offering valuable perspectives for upcoming developments in material engineering and building technology. 2. Materials and methodology In this study, Flyash-based Portland Pozzolana Cement (PPC) was collected from SRMPR Construction Haryana, and its surface area was determined using the Blain’s air method (Jing, et al. (2024)). Coarse aggregates (10 – 40 mm) with a density of 2.6 – 2.9 g/cm³ and water absorption below 2%, and fine aggregates ( ≤ 4.75 mm) with a density of 2.5 – 2.7 g/cm ³ were used (Su et al. (2025)). Six mixes were prepared by replacing cement with 0%, 1%, 2%, 3%, 4%, and 5% nano-silica by weight in M25 grade concrete (1:1:2 ratio). Each mix consisted of cubes (150 × 150 × 150 mm), beams, and cylinders, cured for 7, 14, and 28 days (Mahmoudsaleh et al. (2025); Mohanraj & Vidhya 2024)). A modified mixing procedure was adopted, using poly-carboxylic ether-based superplasticizer to enhance dispersion (Mohanraj et al. 2024; Mohanraj et al. 2024). The components were dry-mixed, followed by gradual water and SP addition (Mohanraj et al. 2023). Specimens were cast, compacted using a tamping rod, demoulded after 24 hours, and cured in water at 27 ± 2°C. The physical and chemical properties of the materials used in this study are summarized below. Cement exhibited a relative density of 3.16 g/cm³, bulk density of 1.6 g/cm³, and a specific surface area of 0.353 m²/g. Its compressive strengths were 24.5 MPa at 3 days and 47.9 MPa at 28 days, while the flexural strengths were 4.7 MPa and 8.1 MPa for the same respective durations. Nano - silica (SiO₂) showed a high specific surface area of 380 ± 30 m²/g, an average particle size of 7 nm, apparent density of 30%, tamped density of 50 g/l, and a SiO₂ content of 99.8% (Wang et al. (2025)). Another batch of nano-silica used had a diameter of 15 ± 3 nm, a surface - volume ratio of 165 ± 17 m²/g, a density of less than 0.15 g/cm³, and a purity exceeding 99.9%. Chemical analysis revealed that cement contains less than 20% SiO₂, <6% Al₂O₃ and Fe₂O₃ each, <50% CaO, <5% MgO, <3% SO₃, <1% K₂O and Na₂O, with loss on ignition below 3%, a specific gravity of 3.15, and Blaine fineness of 3260 cm²/g (Zhang et al. (2025)). In comparison, micro- silica had 93.6% SiO₂, 1.3% Al₂O₃, 0.9% Fe₂O₃, 0.5% CaO, 1% MgO, 0.4% SO₃, 1.52% K₂O, 0.45% Na₂O, 3.1% loss on ignition, specific gravity of 2.2, and a Blaine fineness of 21,090 cm²/g. The sieve analysis showed the filler had 100% passing through all sieves up to