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2016SpringShotcreteEMag

Case Study The Use of Slag Cement, Alkali-Free Accelerator, and Macro-Synthetic Fibers in Wet-Mix Shotcrete for Tunnel Applications By Ezgi Yurdakul, Klaus-Alexander Rieder, Niki Jackson, Mick Pawelski, Arthur Kyriazis, and Lukasz Debny This paper presents the results of a case study conducted in a wet-mix shotcrete application of a major tunnel construction located in Sydney, Australia. The total concrete production volume of this project is estimated to be 1,300,000  yd3 (1,000,000 m3), of which 330,000 yd3 (250,000 m3) will be shotcrete. The performance specifications were developed to comply with RMS B82, “Shotcrete Works,” that is set by the Roads and Maritime Services. According to these specifications, slump was targeted to be a minimum of 6.25 in. (160 mm). The compressive strength at 28 days for both cored and cylinder samples was required to be a minimum of 6000 psi (40 MPa) and a maximum of 10,000 psi (70 MPa). In addition, a compressive strength of 145 psi (1 MPa) was desired to be reached within 3 to 4 hours after spraying. The material selection was based on the cost and listed performance criteria. Macro-synthetic fibers were preferred, as they provide the desired post-crack energy absorption while eliminating the corrosion potential associated with steel fibers. In addition, the performance of slag cement was evaluated as a replacement material due to the shortage of fly ash in this region. Materials Aggregates The combined particle size distribution of all coarse and fine aggregates used in this case study was within the gradation limits shown in Table 1. Cementitious Materials Ordinary portland cement (OPC) and various supplementary cementitious materials were used in accordance with RMS 32112 to compare the performance of slag cement as a replacement of fly ash. Chemical Admixtures The following admixtures were used: • TYTRO® WR 172, a polycarboxylate-based high-range water reducer to maintain the target workability; Table 1: Combined Coarse and Fine Aggregate Particle Size Distribution (after Table B82.1 in RMS B821) Sieve size Mass of sample passing, % Specification Mass of sample passing, % Case study 0.5 in. (13.2 mm) 100 100 3/8 in. (9.5 mm) 90 to 100 95 0.25 in. (6.7 mm) — 76 No. 4 (4.75 mm) 70 to 85 69 No. 8 (2.36 mm) 50 to 70 56 No. 16 (1.18 mm) 35 to 55 42 No. 30 (600 μm) 20 to 40 31 No. 50 (300 μm) 8 to 20 19 No. 100 (150 μm) 2 to 10 9 22 Shotcrete • Spring 2016


2016SpringShotcreteEMag
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