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2016SummerShotcreteEMag

Table 4—As-batched cast concrete mixture proportions Mixture No. Mixture description Placement method Mixture ID Cement (Type GU), kg Fly ash (Class F), kg Silica fume, kg A1 Portland cement Cast concrete C-Cast 415 0 0 1027 691 168 0 0.40 2329 5.50 B1 Fly ash modified Cast concrete FA-Cast 334 79 0 1023 688 166 0 0.40 2319 5.30 C1 Silica fume modified Cast concrete SF-Cast 379 0 34 1003 671 167 0.538 0.40 2263 7.20 Notes: 1 kg/m3 = 1.68556 lb/yd3; 1 L/m3 = 29.5 fl oz/yd3. Fig. 2—Dry-mix shotcrete gun with pre-dampener. shot in the field (refer to Fig. 3). Wet-mix shotcrete mixtures A4, B4, and C4 were shot with 5% by mass of cement of a non-alkali accelerator added at the nozzle during shooting. Dry-mix shotcrete was also dry batched and supplied in 0.76 m3 (1 yd3) bulk bin bags. It was discharged into a predampener and then into the dry-mix machine (gun). The moisture content of the predampened dry-mix shotcrete was estimated to be between 4 and 6%. The dry-mix shotcrete predampener and machine (Fig. 2) are typical of the dry-mix shotcrete setup used in the shotcrete industry and conformed to ACI 5065 requirements. Dry-mix shotcrete mixtures A5, B5, and C5 and A6, B6, and C6 were shot in the field. Mixtures A6, B6, and C6 contained 3% by mass of cement of a chloride-free dry powder accelerator added to the mixture at the time of batching. An ACI Certified Nozzleman (certified for shooting wet-mix overhead and vertical, and dry-mix overhead and vertical) conducted the shooting (Fig. 3). Rebound and overspray were properly controlled. The nozzleman controlled the nozzle angle, nozzle distance, air flow from the air compressor, and water addition for the dry-mix process in a proper way, as required by ACI 506. It is estimated that approximately 4 to 6% rebound occurred with the wet-mix process, and less than 15% rebound occurred with the dry-mix process. In summary, the shotcrete application met ACI 5065 recommendations and was representative of proper application. The mixing and shooting were conducted at the first author’s laboratory in Vancouver in October 2013. On-site monitoring Mixture proportions for 1.0 m3 Coarse aggregate (ten 5 mm) SSD, kg Fine aggregate SSD, kg Water, L Water reducing admixture, L w/cm Total mass, kg Air content, as-batched, % of shotcrete batching, mixing, and test panel production was provided by experienced shotcrete engineers. Testing for plastic properties of the concrete and shotcrete was provided by an ACI Certified Concrete Testing Technician. BASIC CONCRETE AND SHOTCRETE TEST RESULTS AND DISCUSSION Test results for basic plastic and hardened concrete and shotcrete properties and for transport properties are presented and discussed in this section. Test results for three transport properties—that is, ASTM C642 boiled absorption test, ASTM C1792 water absorption test, and U.S. Navy Specification UFGS 03 31 29-3 ionic migration test—are also presented and discussed in this section. These transport properties results will be input into the STADIUM8 service life model to provide a comparative evaluation of the predicted service life of the concretes and shotcretes tested in this study. The results of this service life analysis are not included in this report, but will be presented in a separate paper. Fresh properties Plastic properties of shotcrete were tested according to ACI 506 requirements and are summarized in Table 5. The air contents for as-batched shotcrete and as-shot shotcrete were tested separately. The as-batched air content was tested on samples from the shotcrete pump. The as-shot air content was tested on samples extracted from the in-place shotcrete. Slumps for non-accelerated wet-mix shotcrete ranged from 80 to 120 mm (3 to 5 in.). For the accelerated wet-mix shotcretes, the slump was increased to the 180 to 220 mm (7 to 9 in.) range to allow for proper dispersion of the accelerator at the nozzle, as is standard industry practice. This increase in slump was achieved by increasing the high-range water-reducing admixture dosage, with no increase in the w/cm. Compressive strength For each mixture, two cores were extracted and tested for compressive strength at 7 days, and three cores were extracted and tested for compressive strength at 28 days. Seven-day and 28-day compressive strength results are listed in Table 6. The 28-day compressive strength for cast concretes and wet-mix shotcretes, including results from both cast and shot wet-mix shotcretes’ processes, ranged from 35 to 64 MPa 38 Shotcrete • Summer 2016 376 ACI Materials Journal/May-June 2016


2016SummerShotcreteEMag
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