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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Fig. 6. Comparison between the actual and estimated 28-day flexural strength for OPC concretes with and without nanoparticles cured at (a) 23°C and (b) 4°C. (adapted from (Dan Huang, 2022))

4.3. The effect of the addition of nano-TiO 2 and nano-silica on the total pore volume and formation factor of OPC concretes To investigate the effect of different types of nanoparticles on the characteristics of porosity of OPC concretes, the total pore volume and formation factor of concretes were measured. Fig. 7 compares the relationship between the values of total porosity (pore volume) and formation factor for 28-day-old OPC concretes with and without nanoparticles cured at two different temperatures. When comparing the reference OPC concretes (those without nanoparticle additions), it is observed that concretes cured at low temperatures exhibit a higher total porosity volume and a lower formation factor, indicating increased pore connectivity. This is as expected as low curing temperature delays the hydration process, thus the microstructure is more porous compared to samples cured at standard temperature. Furthermore, in addition to the above observations, it is noted that the reference OPC concrete with a lower water-to-cement ratio (OPC1-0nT) demonstrates a reduced total porosity and a higher formation factor when cured at low temperatures, as opposed to the OPC2-0nS reference concrete. However, contrary to the expected trend, the formation factor of the OPC1-0nT concrete cured at 23°C is lower than the formation factor of the reference concrete with higher w/c ratio OPC2-0nS cured at the same temperature. This unexpected result is likely an outlier.

Fig. 7. Comparison of relationships between total porosity and formation factor values for 28-day-old OPC concretes with and without nano TiO 2 (red labels) and nano-silica (black labels) cured at the temperature of (a) 23°C and (b) 4°C. (adapted from (Dan Huang, 2022))