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2016SummerShotcreteEMag

Table 5—Plastic properties Mixture No. Mixture description Placement method Mixture ID Air content, % (as-batched) Air content, % (as-shot) A1 Portland cement Cast concrete C-Cast 5.50 Not applicable 85 A2 Portland cement Cast wet-mix C-Wet-Mix- Cast 4.50 Not applicable 120 0.40 15 7 A3 Portland cement Shot wet-mix C-Wet-Mix- Shot 4.50 3.20 120 0.40 15 7 A4 Portland cement Shot wet-mix 5% Accelerator C-Wet-Mix- Shot-5% 5.90 3.60 190 12 min 1 h 20 min 0.40 14 9 B1 Fly ash modified Cast concrete FA-Cast 5.30 Not applicable 155 B2 Fly ash modified Cast wet-mix FA-Wet-Mix- Cast 5.60 Not Applicable 180 0.40 Not available 8 B3 Fly ash modified Shot wet-mix FA-Wet-Mix- Shot 5.40 3.50 80 0.40 14 7 B4 Fly ash modified Shot wet-mix 5% accelerator FA-Wet-Mix- Shot-5% 5.60 3.90 180 32 min 2 h 0.40 13 8 C1 Silica fume modified Cast concrete SF-Cast 7.20 Not applicable 40 C2 Silica fume modified Cast wet-mix SF-Wet-Mix- Cast 5.10 Not applicable 100 0.40 14 7 C3 Silica fume modified Shot wet-mix SF-Wet-Mix- Shot 5.10 3.40 100 0.40 15 7 C4 Silica fume modified Shot wet-mix 5% accelerator SF-Wet-Mix- Shot-5% 6.60 4.00 220 10 min 1 h 15 min 0.40 13 8 A5 Portland cement Shot dry-mix C-Dry-Mix- Shot C-Dry-Mix- Shot-3% 4.20 6 min 16 min 16 10 modified Shot dry-mix FA-Dry-Mix- Shot 2.60 Not available Not testable A6 Portland cement Shot dry-mix 3% accelerator B5 Fly ash B6 Fly ash modified Shot dry-mix 3% accelerator FA-Dry-Mix- Shot-3% 4.10 6 min 38 min 16 12 C5 Silica fume modified Shot dry-mix SF-Dry-Mix- Shot 4.10 Not available C6 Silica fume modified Shot dry-mix 3% accelerator SF-Dry-Mix- Shot-3% 2.60 5 min 15 min 14 12 Note: 1 mm = 0.039 in.; 1°C = 5(F – 32)/9. Cast concrete versus cast wet-mix shotcrete versus shot wet-mix and dry-mix shotcretes—The RCP results for cast concrete and cast wet-mix shotcrete are similar for each of the cement, fly ash, and silica fume mixtures. However, RCP results for the shot wet-mix shotcretes are consistently lower than for comparable cast concrete and cast shotcrete mixtures. This is attributed to the superior compaction achieved during the shooting process compared to casting. When 5% accelerator is added, the RCP results for shot wet-mix shotcrete increase for the cement-only and fly ash mixtures, but not for the silica fume mixtures. This shows that the 5% accelerator has little effect on the chloride penetration resistance for mixtures with silica fume. The wet-mix shotcrete with 5% accelerator has similar RCP results to the cast concrete and cast shotcrete mixtures. This shows that the negative effect of accelerator addition on Slump, mm Initial set, h:mins Final set, h:mins w/cm Shotcrete temperature, oC Air temperature, oC Not available 0.40 21 19 Not available 0.40 21 19 Not available 0.40 22 19 Not Testable Not available 3 h 30 min 3 h 25 min 14 10 Not testable 15 10 3 h 30 min 14 10 permeability tends to be offset by the beneficial effect of superior compaction achieved by the shooting process. The dry-mix shotcrete with no accelerator produced the lowest RCP test results of all the mixtures tested. When 3% accelerator was added to the dry-mix shotcrete, the RCP test results were still lower than for similar cast concrete, cast wet-mix shotcrete, or shot wet-mix shotcrete mixtures. It should be noted that the w/cm of the dry-mix shotcrete is not predetermined and is dependent on the nozzleman. The results herein are attributed to two factors—that is, first, the shooting process improves compaction, which reduces permeability, and second, the actual w/cm for the dry-mix shotcrete might be lower than that for like cast concrete, cast wet-mix shotcrete, or shot wet-mix shotcrete. Table 10 also shows the CSA A23.1 performance requirements of the significance of RCP Coulomb numbers. All the cement mixtures (with the single exception of the dry-mix 3.20 40 Shotcrete • Summer 2016 378 ACI Materials Journal/May-June 2016


2016SummerShotcreteEMag
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