PSI - Issue 70

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

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0.3 mm, and 90.9% through 0.15 mm (Xia et al. 2025); Ravikumar et al 2024; Ravikumar et al. 2023). Fine aggregates had 98.38% passing 4.75 mm and 3.62% passing 0.15 mm. Coarse aggregates showed 97.9% passing 12.5 mm, decreasing progressively to 13.2% at 4.75 mm and 0% below 2.36 mm. These detailed properties are crucial for mix design and evaluating the mechanical behavior of concrete incorporating nano-silica. 3. Experimental study To evaluate the mechanical and chemical behavior of cement paste incorporating nano-silica, compressive strength and FTIR tests were conducted. The compressive strength test was performed using a Compressive Testing Machine (CTM) as per ASTM C109/C109M and IS 516:1959 standards. Specimens were dried after curing and tested under a loading rate of 140 kg/cm²/min until failure, ensuring uniform load distribution. The FTIR (Fourier Transform Infrared spectroscopy) test was carried out to analyze the chemical structure and hydration products (Shanmugasundaram et al. 2022). Finely powdered concrete samples with varying nano-silica content were mixed with potassium bromide (KBr) and tested using an FTIR spectrometer at SRM University's C4D Lab (Velumani et al. 2023; Pattusamy et al. 2023). This analysis helped identify functional groups and compounds such as C-S-H, CH, carbonates, and sulphates, offering insights into microstructural changes influenced by nano-silica and TDS levels in mixing water. 4. Results and Discussion 4.1 Effect of Nano-Silica on Compressive Strength Nano- Sio₂ reduces workability due to an increase in surface area. Because of its large surface area, Nano- Sio₂ makes concrete less workable, which raises water requirement and lowers slump value (Fig. 1). Also, Nano-SiO ₂ speeds up hydration, which results in a quicker setting time, which can also be a challenge at the site. This can help with early strength increase, but it may not be fruitful at the site but adding 1 – 1.5% Nano-SiO ₂ to admixtures helps to keep a balance between good concrete and workability. Although Nano- Sio₂ increases strength and durability, but mix design should be taken care off. Changing the content (0%, 1%, 2%, 3%, 4%, and 5%), allowed for a systematic analysis of the impact of SiO₂ on cement paste's compressive strength. Because of its strong pozzolanic reaction and fine particle size, nano-silica promotes the hydration process and results in the creation of denser microstructures. Due to improved particle dispersion and decreased porosity, the test results showed that the addition of nano silica meaningfully increased compressive strength, especially at the ideal dispersion time and permissible dosage. But when the nano silica content increased above a certain point, it led to the collection, which negatively impacted the strength characteristics. At different curing ages, there are notable patterns in the compressive strength of concrete with different percentages of Nano SiO₂. Improved early - age hydration is indicated by the strength increasing with Nano SiO₂ content at 7 days, peaking at 2% (~7.91 MPa). The strength decreases beyond 2%, though, indicating that too much Nano SiO₂ can hurt the early setting process. The strength once more peaks at 2% (~9.96 MPa) after 28 days, indicating better particle packing and ideal pozzolanic activity. Curiously, there is an additional peak at 4%, which might be the result of improved cement matrix densification. But at 5%, the strength drastically decreases, most likely because of the nanoparticles clumping together and losing their ability to improve hydration. According to the 56- day data, the maximum strength is attained at 0% (~15.73 MPa), suggesting that too much Nano SiO₂ could counteract the long-term hydration benefits. between 2% (~12.84 MPa), the strength starts to decline. It then varies between 3% and 4% until settling around 13.9 MPa. The strength drops significantly (around 10.8 MPa) at 5%, highlighting the detrimental effects of too much Nano SiO₂. Higher concentrations (over 3%) may result in strength reduction due to poor dispersion and particle aggregation, but overall, 2% Nano SiO₂ seems to offer the optimum balance for early and mid-term strength enhancement. A 2% – 3 % Nano SiO₂ content is advised for optimal performance, which will increase concrete strength.