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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4.5. The effect of nano-TiO 2 and nano-silica on the scaling resistance of OPC concretes The effect of nano-TiO 2 and nano-silica on the scaling resistance of concretes (assessed by the cumulative mass loss during the scaling test) cured at two different temperatures is shown in Fig. 12. As previously mentioned, the Ontario Ministry of Transportation (MTO) established a criterion that states the cumulative mass loss due to scaling should be no higher than 0.8 kg/m 2 after 50 freeze-thaw cycles for the concrete to be considered scaling resistant. In this study, all concrete samples, irrespective of curing temperatures, types, or dosages of nanoparticles, demonstrated excellent scaling resistance, as illustrated by the fact that after 50 freeze-thaw cycles, the observed mass losses were much lower than 0.8 kg/m 2 . This outcome was anticipated, given that scaling is typically not a major concern for OPC concrete, especially if the concrete is air-entrained. Nonetheless, the addition of nanoparticles (both nano-TiO 2 and nano-silica) reduced the mass loss of concrete, regardless of the curing temperature. However, the data for OPC1-0nT reference concrete cured at 23°C appears to be an outlier, as the observed mass loss exceeded that of OPC2-0nS reference concrete cured at the same temperature. This is difficult to explain considering that a lower w/cm ratio typically indicates higher scaling resistance compared to concrete with a slightly higher w/cm ratio. This discrepancy suggests a possible experimental error, particularly since the mass loss value obtained from specimens cured at 23°C should theoretically be lower than those cured at 4°C.

OPC1-1nT OPC1-0.5nT OPC1-1nT

OPC2-0nS OPC2-12nS OPC2-8nS OPC2-4nS

(a) Cumulative mass loss, kg/m 2 0.00 0.05 0.10 0.15 0.20 0.25 0.30

(b) Cumulative weight loss, kg/m 2 0.00 0.05 0.10 0.15 0.20 0.25 0.30 23°C

4°C

23°C

4°C

Curing Temperature

Curing Temperature

Fig. 12. Cumulative mass losses due to the scaling for OPC1 and OPC2 concretes with and without (a) nano-TiO 2 and (b) nano-silica cured at different temperatures (adapted from (Dan Huang, 2022)).

As shown in Fig. 12(a) and (b), the scaling resistance appears to depend on both the dosage and type of nanoparticles. As an example, the addition of 0.5 wt.% of nano-TiO 2 to concrete cured at 23°C reduced the cumulative mass loss and enhanced the scaling resistance of the concrete. This is due to the fact that the microstructure of concrete was densified, and the permeability of concrete was reduced due to the addition of nano TiO 2 prior to the exposure of FT cycles. However, concrete cured at the same temperature but containing 1.0 wt.% of nano-TiO 2 had lower scaling resistance (as indicated by higher mass loss). This might be related to the fact that a higher dosage of nano-TiO 2 can limit the space available for the growth of various hydration products (Jalal et al., 2013; Nazari & Riahi, 2010; Zhang & Li, 2011), thus making it less effective with respect to enhancing the strength and densifying the microstructure of concrete. When samples were cured at a lower temperature before the scaling test, it was observed that incorporating a higher dosage (1.0 wt.%) of nanoparticles proved more effective than using a lower dosage (0.5 wt.%). This can be attributed to the reduced formation of hydration products in concrete cured at lower temperatures. Consequently, such concrete required a higher nanoparticle dosage to achieve the desired beneficial effects on scaling resistance. On the other hand, when nano-silica was introduced, it appeared that the E5-LFA variant exhibited less effectiveness compared to the E5-IC nano-silica. Despite previous evidence demonstrating a synergistic effect of combining both LFA and IC nano-silica in enhancing compressive strength and diminishing pore connectivity in concrete, such a phenomenon did not translate to improved scaling resistance in OPC concrete. There are many