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2016SummerShotcreteEMag

Fig 6—Coefficient of diffusion for all mixtures/processes. Fig. 7—Effective coefficient of diffusion (OH–) for all mixtures/processes. Table 11 and Fig. 9 show the calculated permeability (K values) of all mixtures. All test results are in the range of 1 to 10 × 10–22 m2. Effect of shotcrete process K values for similar mixtures for cast shotcrete and castin place concrete are very close (Table 11). K values for shot wet-mix shotcrete are lower than those for cast shotcrete and cast-in-place concrete. This shows that the shotcrete process, which involves high-velocity impact, results in a less permeable concrete matrix. K values for dry-mix shotcrete are very low when compared with both cast and shot wet-mix shotcrete and cast-in-place concrete. This is likely due in part to the fact that the water content is not determined by a need to provide a pumpable mixture but is controlled by the water added by the nozzleman at the nozzle to provide a shootable mixture. Effect of SCMs on permeability It is a general trend that the permeability (K values) decrease from the mixtures with cement to the mixtures with fly ash to the mixtures with silica fume (Table 11 and Fig. 9). This trend is significant with cast-in-place concrete, cast shotcrete, and dry-mix shotcrete, but less significant with shot wet-mix shotcrete and shot wet-mix shotcrete with 5% accelerator in which mixtures with fly ash show similar permeability with a mixture with cement only. Overall, mixtures with silica fume have the lowest K values; this is inconsistent with test results from ECoD and other permeability-related tests. Effect of accelerator on permeability Permeability test results (K values) for shot wet-mix shotcrete with 5% non-alkali accelerator are slightly higher than for shot wet-mix shotcrete (Table 11 and Fig. 9). This is due to the fact that the accelerator speeds up the initial 4348 2 ACI Materials JSohuortncraelt/eM •a Sy-uJmumnee r2 2001166


2016SummerShotcreteEMag
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