PSI - Issue 67

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

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factors affecting the scaling resistance of concrete. Such discrepancies between the influence of nano-silica on the mechanical properties and scaling resistance might be related to the impact of nano-silica on the chemical composition of cementitious matrix. The nature of this impact is unknown, as the chemical composition of the paste matrix plays an important role in affecting the scaling resistance of the concrete (Dan Huang et al., 2023; John J. Valenza & Scherer, 2007b). Additionally, because the nano-silica product was proprietary, its precise chemical composition was not available. 4.6. Performance index of nanoparticles on the performance of OPC concretes Table 5 presents an overview of the impact of both nanoparticles studied (i.e., nano-TiO 2 and nano-silica) on the performance of concrete, including compressive strength, flexural strength, total volume of porosity, pore connectivity, water absorption, and scaling resistance. Quantitative comparisons are presented with respect to the reference concrete (i.e., without any usage of nanoparticles) except for the results from the scaling resistance test. Though both types of nanoparticles enhanced the scaling resistance of concrete (~56% by nano-TiO 2 and ~25% by nano-silica/with type IC), a quantitative analysis may undermine the fact that reference concrete already has a fairly good scaling resistance (with a cumulative mass loss much less than 0.8 kg/m 3 ).

Table 5. Performance index of the nanoparticles (nano-TiO 2 and nano-silica) on the properties of concrete. Properties Nano-TiO 2 Nano-silica Cured at 23°C Cured at 4°C Cured at 23°C Cured at 4°C Compressive strength at 28 days ↑ 15.3% ↑ 11.5% ↑ 14.5% ↑ 16.9% Flexural strength at 7 days ↑ 35% ↑ 42% ↑ 33% ↑ 40% Flexural strength at 28 days ↑ 6.3% ↑ 6.5% ↑ 7.8% ↑ 7.5% Total volume of porosity ↓ 7.3% ↓ 5.8% ↓ 6.5% ↓ 8.3% Pore connectivity - - ↓ 6.2% ↓ 7.9% Water absorption ↓ 17.5% ↓ 14.5% ↓ 13.2% ↓ 27.3% Scaling resistance Improved Improved Improved Improved

5. Conclusions This paper presents a study focused on comparing the effects of different types of nanoparticles (i.e., nano-TiO 2 and nano-silica) on the strength, porosity, water absorption, and scaling resistance of OPC concretes cured at different temperatures. It was found that the addition of both types of nanoparticles is beneficial in enhancing the mechanical properties and durability of concrete, as manifested by improvement in the values of the compressive and flexural strengths, reduction in the porosity and water absorption, and improvement of the scaling resistance, irrespective of the curing temperature. However, it should be noted that these effects were more pronounced in concretes cured at lower temperature. The following detailed conclusions can be drawn from this study: i) The extent of property enhancement varied depending on the type of nanoparticles employed. Specifically, the increase in compressive strength appeared slightly more pronounced with the addition of nano-silica compared to nano-TiO 2 . Conversely, no significant differences were observed in the case of flexural strengths regardless of the type of nanoparticles used. Furthermore, there appears to be a synergistic effect when both types of nano silica were used in the concrete in enhancing the compressive strength of concrete. ii) The impact of nano-silica addition was also notably more significant in increasing the formation factor values compared to nano-TiO 2 , regardless of level of dosages. This suggests that incorporating nano-silica into concrete is more effective in reducing pore connectivity. iii) Both types of nanoparticles were approved to decrease the total amount of porosity in concrete. Similarly, both nanoparticles were also found to be effective in reducing the overall permeability of concrete, as both the values of the initial and secondary absorptions, as well as the rates of initial and secondary absorptions of concrete were reduced. iv) Furthermore, the scaling resistance of OPC concretes was improved by adding either type of nanoparticles (i.e.,