PSI - Issue 30

A.A. Vasilieva et al. / Procedia Structural Integrity 30 (2020) 186–192 Vasilieva A.A. et al. / Structural Integrity Procedia 00 (2020) 000–000

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Fig. 2. Moisture weight gain experimental data for exposed in the cold climate of the Northern Russia and warehouse BFRP rebar specimens with diameter of 6 mm and a height of 50, 70, 100 subjected to 60°C/98% RH and the solid lines represent its Fickian approximations.

Fig. 3. Moisture weight gain experimental data for exposed in the cold climate of the Northen Russia and warehouse BFRP rebar specimens with diameter of 6 mm subjected to 60°C/98% RH and the solid lines represent its Fickian approximations: (a) specimens with a height of 30 mm, (b) specimens with a height of 10 mm, (c) specimens with a height of 5 mm.. Table 1. Parameters of Fickian diffusion of exposed in the climate of the Northern Russia and warehouse BFRP rebars under 60°C/98%RH Specimens sizes eq w M (%) eq cl M (%) w D (cm 2 /day) cl D (cm 2 /day) / w M M  (%) / w D D  (%) h=100 mm 0.31 0.25 2.54·10 -4 2.95·10 -4 -19 16 h=70 mm 0.35 0.25 2.54·10 -4 3.55·10 -4 -22 39 h=50 mm 0.30 0.25 2.54·10 -4 3.97·10 -4 -17 56 h=30 mm 0.31 0.3 2.54·10 -4 2.81·10 -4 0 10 h=10 mm 0.24 0.24 2.54·10 -4 7.2·10 -4 0 183 h=5 mm 0.17 0.3 2.54·10 -4 1.48·10 -4 76 -42 In Fig 2 kinetics of moisture uptake are plotted for the specimens with a height much larger than its diameter. As can be seen in Table 1 in this case the equilibrium moisture uptake is almost independent of the size of the specimen in both the climatic specimens and the warehouse. With this, the moisture saturation level of climatic specimens is 20% less than the level of warehouse specimens. This comparative decrease is related to the fact that atmospheric moisture catalyzed the additional curing of the epoxy binder by the molecular mechanism (Kablov et al. (2010, 2018); Startsev et al. (2009)). The diffusion coefficients of the warehouse specimen are the same and do not depend on the size of the specimen, and the diffusion coefficients of climatic specimens ranging from 16 to 56% downwards with height of the specimen. Such a sensitivity of the diffusion coefficient is associated with uneven fracture surface layer in climatic specimens under the influence of numerous seasonal and daily thermal cycles during exposure in the North of Russia. The moisture uptake kinetics for a specimen height commensurate with its diameter are shown in Fig. 3. The kinetics of warehouse specimens is monotonous and the level of moisture saturation decreases with height because