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2016SummerShotcreteEMag

Table 8—BA and VPV voids for shot wet-mix shotcrete versus cast wet-mix shotcrete and cast concrete Boiled absorption Cast-in-place concrete, % Cast wet-mix shotcrete, % Shot wet-mix shotcrete, % Decrease in BA of shot shotcrete versus cast shotcrete, % Cement 5.8 5.7 5.4 5 6.8 19 Fly ash 5.6 5.6 5.3 5 6.3 13 Silica fume 4.8 4.9 4.9 0 5.2 6 Volume of Decrease in VPV of permeable Cast-in-place Cast wet-mix Shot wet-mix shot shotcrete versus voids concrete, % shotcrete, % shotcrete, % cast shotcrete, % Cement 12.7 12.3 12.2 1 14.8 20 Fly ash 12.2 12.0 11.9 1 14.0 17 Silica fume 10.3 10.5 11.0 –5 11.2 7 Table 9—BA and VPV for shot dry-mix shotcrete versus cast concrete Boiled absorption Cast concrete, % Dry-mix shotcrete, % Decrease in BA of shot dry-mix shotcrete versus cast concrete, % Cement 5.8 5.9 -2 6.2 7 Fly ash 5.6 4.7 16 5.9 5 Silica fume 4.8 3.5 27 5.6 17 Volume of permeable voids Cast concrete, % Dry-mix shotcrete, % Decrease in VPV of shot dry-mix shotcrete versus cast concrete, % Cement 12.7 13.1 –3 13.9 9 Fly ash 12.2 10.7 12 13.2 8 Silica fume 10.3 8.4 18 12.5 21 Table 10—Rapid chloride penetration test results (Coulombs) Coulombs Cast concrete Cast wet-mix shotcrete Shot wet-mix shotcrete Cement 3052 2884 2047 2937 1582 2274 Fly ash 1108 1054 912 1259 637 752 Silica fume 374 361 305 269 250 295 Notes: CSA A23.1/23.2 performance requirements: chloride ion penetrability is high (>4000 Coulombs); moderate (2000 to 4000 Coulombs); low (1000 to 2000 Coulombs); very low (100 to 1000 Coulombs); and negligible (<100 Coulombs). ECoD values include the effects of both the CoD and VPV and are more representative for the diffusion properties for the species. Results of the coefficient of diffusion (CoD) test are plotted in Fig. 6. All CoD values for all 18 mixtures are in the range of 2 to 20 × 10–11 m2/s. Although there are various species in both upstream and downstream solutions, OH– is one of the most representative ions. CoD (OH–) values are determined by the test and are used to characterize the diffusion properties for all the species, including Cl–, SO4 –, and so on. ECoD values for the different mixtures/processes are plotted in Fig 7. Effect of shotcrete process on ECoD The cast-in-place concrete mixtures have similar ECoD values when compared with similar cast wet-mix shotcrete, except that the ECoD for the cast-in-place concrete mixture for the cement-only mixture is very high. This is attributed to the high CoD for the cast-in-place concrete mixture with cement only (Fig. 7). Shot wet-mix shotcrete with 5% accelerator, % Increase in BA of shot shotcrete with 5% accelerator versus cast shotcrete, % Shot wet-mix shotcrete with 5% accelerator, % Increase in VPV of shot shotcrete with 5% accelerator versus cast shotcrete, % Dry-mix shotcrete with 3% accelerator, % Increase in BA of shot dry-mix shotcrete versus cast concrete, % Dry-mix shotcrete with 3% accelerator, % Increase in VPV of shot dry-mix shotcrete versus cast concrete, % Shot wet-mix shotcrete with 5% accelerator Dry-mix shotcrete Dry-mix shotcrete with 3% accelerator Shot wet-mix shotcrete mixtures have similar ECoD values when compared with similar cast shotcrete mixtures. This shows that the shotcrete process, which involves high-velocity impact, does not adversely affect the ECoD of the chemical ions. Accelerated wet-mix shotcrete—that is, mixtures with 5% non-alkali accelerator—show slightly higher ECoD values compared to the equivalent shot wet-mix shotcrete mixtures and cast shotcrete mixtures. Dry-mix shotcrete mixtures show similar ECoDs values to shot wet-mix shotcrete. It is known that the w/cm of dry-mix shotcrete is dependent on the nozzleman’s skill, as it is controlled by the nozzleman during shooting. Therefore, the results presented herein provide a good indication that the dry-mix shotcrete was properly applied, as it achieved similar ECoDs values to the shot wet-mix shotcrete. Effect of supplementary cementitious materials (SCMs) on ECoD The ECoD values of all the mixture groups decreased from the cement-only mixtures, to fly ash mixtures, to silica 380 ACI Materials Journal/May-June 2016 42 Shotcrete • Summer 2016


2016SummerShotcreteEMag
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