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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Table 4. The initial and secondary rate of absorptions data for concretes with and without nano-additives cured at different temperatures. (adapted from (Dan Huang, 2022)) Curing Temperature Sample Rate of initial absorption, ×10 -4 R 2 Rate of secondary absorption, ×10 -4 R 2

OPC1-0nT OPC1-0.5nT OPC2-0nS OPC2-12nS OPC2-8nS OPC2-4nS OPC1-0nT OPC1-0.5nT OPC2-0nS OPC2-12nS OPC2-8nS OPC2-4nS

102

0.9974 0.9970 0.9976 0.9905 0.9941 0.9944 0.9974 0.9966 0.9948 0.9958 0.9946 0.9934

31 25 41 39 36 36 33 27 44 47 39 32

0.9801 0.9809 0.9802 0.9882 0.9839 0.9811 0.9813 0.9763 0.9818 0.9861 0.9844 0.9828

85

106

23 °C

93 98 90

103

94

128 105

4 °C

88 92

From Table 4, it is evident that irrespective of the curing temperature, OPC reference concretes featuring a lower w/cm ratio (OPC1) exhibited a reduced rate of both initial and secondary absorption. Furthermore, when comparing differences in the rate of initial absorptions at different curing temperatures, OPC1 reference concrete demonstrates a lower difference compared to OPC2 reference concrete (102×10 -4 vs 103×10 -4 , and 106×10 -4 vs 128×10 -4 , respectively). This is, again, an indication that concretes with higher w/cm values are more sensitive to low curing temperatures. The addition of nanoparticles (both nano-TiO 2 and nano-silica) reduced both the initial and secondary rates of absorption, more significantly when cured at low temperature. Another prevailing observation is that the R 2 of the initial absorption tends to be higher than that of the secondary absorption. This is related to the fact that the initial degree of saturation of the sample is the lowest during the period of testing, and the suction force due to the capillary porosity is the highest. Consequently, water absorption tends to exhibit more linear behavior during the initial stage compared to the second phase of the test. To better illustrate the comparison between the two types of reference OPC concretes, Fig. 11 displays only the absorption curves for both. OPC1 reference concrete exhibits lower initial and secondary absorptions as well as rates of absorption, validating the effectiveness of the modified sample conditioning method in providing suitable sample conditions for the water absorption test. Moreover, the distinction between these reference OPC concretes becomes more pronounced at lower curing temperatures, indicating that the influence of w/cm values on water absorption is particularly notable under such conditions.

Fig. 11. The results of the water absorption test for the 28-day reference OPC concretes cured at (a) 23°C and (b) at 4°C. (adapted from (Dan Huang, 2022))