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2013FallShotcreteEMag

Sustainability the form of ground-granulated blast-furnace slag mixture Designs (GGBFS).3* It is produced alongside pig iron Dry-mix shotcrete was selected for this project, when iron ore, limestone, and coal are heated in as it offers users more control over placement an enormous blast furnace at temperatures parameters. It is better suited for lightweight reaching around 3450°F (1900°C). As the molten aggregate mixtures and is a current placement iron sinks to the bottom of the furnace, impurities method in many mines.13 The two mixture designs containing silicates and sulfates are captured by used in the experimental phase of this project are the calcium carbonate of the limestone and float shown in Table 1, with pictures of the ground to the top. The pig iron is separated out at the blast-furnace slag aggregates in Fig. 1 and their bottom of the furnace, while the slag is skimmed combined gradations in Graph 1. off the top of the molten pig iron.4-6 After accounting for marketable pig iron recovery, about 10 to 15% by mass of pig iron output is slag.7 Blast-furnace slag has steadily gained popularity for various uses, making it an economically viable option. GGBFS has been studied, used, and proven to be a useful addition to concrete mixtures as a supplementary cementitious material.8 Blast- furnace slag has been studied as both a coarse aggregate, as expanded blast-furnace slag,9 and as a fine aggregate10,11 under the form of non- ground-granulated blast-furnace slag (n-GGBFS) in concrete mixtures, but not in shotcrete mixtures. Fig. 1: Pelletized coarse (1.15 to 9.50 mm 0.05 to 0.37 in.) (right) and This project investigated the feasibility of using pelletized fine (0 to 2.36 mm 0 to 0.09 in.) (left) blast-furnace slag aggregates blast-furnace slag, in multiple forms, to produce dry-mix shotcrete mixtures with the explicit goals of sustainability and meeting basic performance Graph 1: Comparison of Shotcrete Mixture Design Gradations and criteria for underground shotcrete. Blast-furnace ACI 506R Limits slag aggregates and supplementary cementitious material (SCM) are also as safe to use in shotcrete applications as conventional aggregates and cement, thus meeting the safety objective.12 *Note: ACI and ASTM International now use the term “slag” in place of “ground-granulated blast-furnace slag,” but to eliminate confusion in this article, we will use the older term GGBFS because we are also discussing pelletized slag as well as the cementitious GGBFS. Table 1: Mixture designs for dry-mix shotcretes Control mixture Sustainable mixture Dry ingredient, Quantity, Dry ingredient, Quantity, Ingredients (%, weight) lb/yd3 (kg/m3) (%, weight) lb/yd3 (kg/m3) Type GU cement 20.40 656 (389) 22.10 649 (385) GGBFS cement (90% BFS, 10% GU) 1.75 56 (33) 1.90 56 (33) Silica fume 1.85 59 (35) 2.00 59 (35) Concrete sand (0.08 to 5.00 mm) 57.00 1831 (1086) 0.00 0 (0) n-GGBFS fine (0.15 to 2.36 mm) 0.00 0 (0) 59.30 1743 (1034) BFS coarse (1.18 to 9.50 mm) 19.00 610 (362) 14.70 432 (256) TOTAL DRY 100.00 3211 (1905) 100.00 2936 (1743) Water (e/c = 0.45 theoretical) 347 (206) 344 (204) TOTAL WET 3558 (2111) 3282 (1947) Shotcrete • Fall 2013 33


2013FallShotcreteEMag
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