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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4.2. The effect of nano-TiO 2 and nano-silica on the flexural strength of OPC concretes The flexural strength (both 7-day and 28-day) of OPC concrete with and without the addition of nanoparticles (nano-TiO 2 and a combination of E5-LFA and E5-IC nano-silica) cured at different temperatures are presented in Fig. 5. After 7-day of curing, the flexural strength of both OPC concretes was improved by the addition of nanoparticles, regardless of the type of nanoparticles and curing temperature. In addition, the relative enhancement of flexural strength (shown as xx% in Fig. 5(a)) due to the addition of nano-silica was slightly higher than that of nano-TiO 2 . At a later age (28 days), as shown in Fig. 5(b), the increase in flexural strength due to the addition of nanoparticles was less significant compared to that observed at early age (7 days). This can be explained by the fact that at a later age (28 days), most of the hydrating phases have reacted, and thus the addition of nanoparticles is not as effective as early age (7 days). Moreover, the effect of different types of nanoparticles (i.e., nano-TiO 2 and nano silica) on the flexural strength becomes comparable.

Fig. 5. The variation of the flexural strength of concretes with and without the addition of nano-TiO 2 or nano-silica (with both LFA and IC nano-silica) cured at both room and low temperatures at (a) 7 days and (b) 28 days. (adapted from (Dan Huang, 2022))

In addition, an attempt was made to establish the correlation between the measured and estimated values of the 28-day flexural strength. The estimated values of the flexural strength were obtained from the expression (see equation 6) suggested in reference ( ACI CODE-318-19: Building Code Requirements for Structural Concrete and Commentary , n.d.) (modified equation to reflect the value obtained from this study). � 12 � , (6) where is the flexural strength of concrete, and is the compressive strength of concrete. As shown in Fig. 6, the correlations between the actual and estimated values of the 28-day flexural strength of OPC concretes exhibit a strong alignment, irrespective of the type of nanoparticles and curing temperatures applied. The actual 28-day flexural strength falls within the ±10% error margin from the estimated flexural strength. This high level of correlation underscores the reasonableness of the predictive equation selected for this study.