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2016SpringShotcreteEMag

• TYTRO® HC 270, a hydration control agent to provide the desired slump retention; • TYTRO® RC 430 as a pozzolanic-based rheology control agent to reduce rebound and enhance the early-age strength development rate to reduce the re-entry time (this admixture was used in all the mixtures as a silica fume replacement to reduce the cementitious materials content); • TYTRO® RM 471, a rheology-modifying agent to reduce rebound and increase pumpability; and • TYTRO® SA 530, an alkali-free shotcrete accelerator. Fibers STRUX® BT 50 was the macro-synthetic fiber used to increase crack resistance, ductility, and toughness required for this tunnel application. The performance comparison was made using an alternative 2.1 in. (54 mm) modified olefin macrosynthetic fiber. Mixture Design Mixture design was prepared in accordance with the B2 exposure classification limits set by RMS B82,1 as shown in Table 2. A total of four mixtures were tested with various mixture proportions and mixture constituents to evaluate the impact of different supplementary cementitious materials, macrosynthetic fibers, and alkali-free accelerator dosage rate on wet-mix shotcrete performance (Table 3). Results and Discussion Effect of Slag Cement on Shotcrete Performance The use of supplementary cementitious materials (SCMs) in shotcrete mixtures as a partial replacement of portland cement has several benefits, including the improved durability as a function of reduced permeability of the hydrated cementitious paste, enhanced workability due to their particle size and morphology, and increased Table 2: Minimum Cement Content and Maximum Water-Cement Ratio (after Table B82.4 in RMS B821) Exposure classification Minimum cement content, lb/yd3 (kg/m3) Maximum water-cement ratio (by mass) A 539 (320) 0.45 B1 539 (320) 0.45 B2 624 (370) 0.40 C 708 (420) 0.40 U In accordance with Annexure B82/A Clause A1 Table 3: Mixture Proportions Mixtures Mix 1 Mix 2 Mix 3 Mix 4 Ordinary portland cement, lb/yd3 (kg/m3) 570 (338) 455 (270) 759 (450) 759 (450) Fly ash, lb/yd3 (kg/m3) 189 (112) — — — Slag cement, lb/yd3 (kg/m3) — 303 (180) — — Total binder content, lb/yd3 (kg/m3) 759 (450) 759 (450) 759 (450) 759 (450) Water, lb/yd3 (kg/m3) 303 (180) 303 (180) 303 (180) 303 (180) water-cementitious materials ratio 0.40 0.40 0.40 0.40 Coarse aggregate 1, lb/yd3 (kg/m3) 876 (520) 876 (520) 876 (520) 876 (520) Coarse aggregate 2, lb/yd3 (kg/m3) 624 (370) 624 (370) 624 (370) 624 (370) Sand, lb/yd3 (kg/m3) 1214 (720) 1214 (720) 1214 (720) 1214 (720) Sand-to-total aggregate ratio 0.677 0.677 0.677 0.677 TYTRO® WR 172, oz/yd3 (L/m3) 80 (3.1) 85 (3.3) 88 (3.4) 88 (3.4) TYTRO® HC 270, oz/yd3 (L/m3) 41 (1.6) 41 (1.6) 41 (1.6) 41 (1.6) TYTRO® RC 430, oz/yd3 (L/m3) 103 (4) 103 (4) 103 (4) 103 (4) TYTRO® RM 471, oz/yd3 (L/m3) 103 (4) 103 (4) 103 (4) 103 (4) TYTRO® SA 530, % of total binder content 4, 7, 10 7, 10 7, 10 7 STRUX® BT 50, lb/yd3 (kg/m3) 12 (7) 12 (7) 12 (7) — Alternative 2.1 in. (54 mm) modified olefin macro-synthetic fiber, lb/yd3 (kg/m3) — — — 8 (5) Shotcrete • Spring 2016 23


2016SpringShotcreteEMag
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