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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4. Results and discussions 4.1. The effect of nano-TiO 2 and nano-silica on the 28-day compressive strength of OPC concretes Fig. 4 illustrates the impact of incorporating nano-TiO 2 and nano-silica on the 28-day compressive strength of OPC concretes subjected to varying curing temperatures. Upon comparing the compressive strength of the reference concrete (without the addition of either type of nanoparticles), it is evident that the concrete with a lower water-to cement ratio (OPC1, w/c=0.44, depicted in Fig. 4(a)) achieved a comparable 28-day compressive strength to that of the concrete with a higher water-to-cement ratio (OPC2, w/c=0.45) displayed in Fig. 4(b)) when cured at room temperature. However, there is a significant difference in the compressive strength between reference concrete with different w/c values when cured at low temperature (4688 psi for OPC1 vs 4168 psi for OPC2, though results from OPC2 concrete presents a higher standard deviation). This discrepancy can be attributed to the inherent porosity of concrete with higher water-to-cement ratios, coupled with the deceleration of the hydration process at lower curing temperatures. Consequently, the concrete with greater porosity exhibits a delayed strength development compared to its counterpart cured at room temperature. Hence, a disparity in the 28-day compressive strength (fc') of reference OPC concrete with different water-to-cement ratios is observed under low curing temperatures.

Fig. 4. The 28-day compressive strength of OPC concretes (OPC1, w/c=0.44, and OPC2, w/c=0.45) with and without the addition of (a) nano TiO 2 and (b) nano-silica cured at different temperatures. (adapted from (Dan Huang, 2022)) Analysis of Fig. 4 (a) and (b) suggests that the incorporation of both nano-TiO 2 and nano-silica leads to improved 28-day compressive strength in OPC concretes, irrespective of curing temperature. Notably, when examining the relative increases in 28-day compressive strength (fc’) at low curing temperatures compared to reference OPC concrete, denoted as xx% at the top of the bars in both Fig. (a) and (b), nano-silica appears to be more effective compared to nano-TiO 2 (~16.9% vs. 11.6%). This can be attributed to the fact that in addition to its "nucleation effect," nano-silica undergoes a reaction with calcium hydroxide (CH), resulting in the formation of additional calcium-silicate-hydrate (C-S-H). This additional C-S-H contributes significantly to the enhancement of concrete strength. Furthermore, it is notable that the increase in compressive strength attributed to nanoparticle addition is more pronounced when the concrete is cured at low temperatures. Moreover, when comparing different categories of nano-silica nanoparticles, it appears that the combination of both LFA and IC (OPC2-12nS) is more effective with respect to enhancing concrete’s compressive strength compared to using either one of them alone (OPC2-8nS or OPC2-4nS). Considering both types of nano-silica nanoparticles yield beneficial effects, it is reasonable to assume that the simultaneous addition of both types will yield synergistic effects (El-Sadany et al., 2023; Liu et al., 2021; Uthaman et al., 2018). For nano-TiO 2 nanoparticles, while 1% of nano-TiO 2 outperformed 0.5% in improving the compressive strength of concrete cured at room temperature, 0.5% of nano-TiO 2 appears more effective in concrete cured at low temperature.