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2016SummerShotcreteEMag

Fig. 5—Ionic migration test setup illustration (left) and laboratory setup (right). Table 11—Results for ionic migration test and drying test Mixture ID Coefficients of diffusion, DiffOH– (10–11 m2/s) Effective coefficient of diffusion, DiffOH– × VPV% (10–11 m2/s) Tortuosity K, permeability, 10–22 m2 C-Cast 18.49 2.35 28.5 9.31 FA-Cast 8.67 1.06 61.0 8.51 SF-Cast 4.92 0.51 107.5 3.94 C-Wet Mix-Cast 10.78 1.33 49.0 9.65 FA-Wet Mix-Cast 10.23 1.23 51.5 8.05 SF-Wet Mix-Cast 6.05 0.64 87.0 6.53 C-Wet Mix-Shot 10.37 1.27 51.8 4.84 FA-Wet Mix-Shot 7.35 0.87 71.9 4.76 SF-Wet Mix-Shot 5.7 0.63 92.6 2.66 C-Wet Mix-Shot-5% 11.45 1.69 46.1 5.02 FA-Wet Mix-Shot-5% 10.36 1.45 61.0 4.97 SF-Wet Mix-Shot-5% 5.04 0.56 104.2 2.69 C-Dry Mix-Shot 12.01 1.57 43.9 3.3 FA-Dry Mix-Shot 6.77 0.72 78.1 2.88 SF-Dry Mix-Shot 5.19 0.44 102.0 1.57 C-Dry Mix-Shot-3% 8.94 1.24 58.8 2.83 FA-Dry Mix-Shot-3% 5.97 0.79 88.5 1.45 SF-Dry Mix-Shot-3% 3.38 0.42 156.3 1.29 fume mixtures. This is inconsistent with the general understanding of the effects of supplementary cementitious materials (SCMs) on permeability—that is, the addition of the SCMs reacts with the Ca(OH)2 in the concrete to reduce the porosity and permeability of the concrete matrix, thus reducing the ECoD of the chemical species. The silica fume-modified mixtures have the lowest ECoD values. This is due to the fineness and high reactivity of the silica fume with its ability to refine the microstructure of the shotcrete, thus greatly reducing the porosity and permeability, and hence reducing the values of ECoD. In summary, the ECoD values can be significantly reduced by using SCMs. The reduction of ECoD values achieved with SCMs occurred consistently for cast-in-place concrete, cast shotcrete, shot wet-mix shotcrete, shot wet-mix shotcrete with non-alkali accelerator, as well as with dry-mix shotcrete and dry-mix shotcrete with accelerator. This demonstrates that the use of SCMs is a valuable way of enhancing the durability of shotcrete. WATER ABSORPTION/DRYING TEST A water absorption/drying test was conducted using a modified version of ASTM C1585—that is, U.S. Navy Specification UFGS 03 31 29-3, which later became the ASTM C1792 water absorption test. There are two dimensions of test samples: 50 mm (2 in.) thick x 100 mm (4 in.) in diameter and 10 mm (3/8 in.) thick x 100 mm (4 in.) diameter. All samples were kept in the drying shrinkage room and tested for weight loss over 120 days. Weight loss was recorded every 2 to 3 days and plotted as shown in Fig. 8. The mass loss curve for 50 mm (2 in.) samples was used to calculate permeability—that is, K, while the mass loss curve for 10 mm (3/8 in.) samples was used to calculate the moisture isotherm parameters at equilibrium when saturation is reached at 50% relative humidity. The moisture diffusivity model used is based on the drying process for concrete and shotcrete and has both a liquid contribution and vapor contribution that are obtained by separately measuring the mass loss of 50 mm (2 in.) samples and 10 mm (3/8 in.) samples.10 SAhCotIc Mreatet e• rSiaulms mJoeur r2n0a1l6/M ay-June 2016 38 413


2016SummerShotcreteEMag
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