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2015SpringShotcreteEMag

The influence of different grades and dosage rates in Europe. It should be noted that as a result of of RC agents on the fresh and hardened properties replacing powder-based SF with liquid-based RC of shotcrete was evaluated. agents, the total cementitious materials content was 796 lb/yd3 (472.5 kg/m3) for the SF mixture Experimental Program and 758 lb/yd3 (450 kg/m3) for the mixtures An extensive experimental test program was incorporating the RC agents. The water-cemen- conducted at the Hagerbach Testing Gallery titious material ratio (w/cm) was kept constant at (VSH), which is an underground facility in Flums, 0.435 for all mixtures. Switzerland. A total of five mixtures were batched Table 2 shows the test matrix used in this as shown in the following: study. The presented results represent the • Mixture 1—A reference mixture incorporating average of two test results conducted on separate SF with the addition rate of 5% by mass of batches of the same mixture carried out on cement; subsequent days. • Mixture 2—A mixture containing RC agent Grade 1 with the dosage rate of 0.67% by mass Results and Discussion of cement; Sprayability and Pumpability • Mixture 3—A mixture containing RC agent Sprayability and pumpability are two key Grade 1 with the dosage rate of 1.30% by mass properties that reflect the distinctive process of of cement; shotcrete application and distinguish it from • Mixture 4—A mixture containing RC agent traditional cast-in-place concrete. Hence, it is Grade 2 with the dosage rate of 0.80% by mass important to understand the differences between of cement; and these two parameters. Sprayability is the effi­ • Mixture 5—A mixture containing RC agent ciency of a mixture at sticking to the applied Grade 2 with the dosage rate of 1.60% by mass surface (adhesion) and to itself (cohesion).14 of cement. Pumpability is the stability and mobility of a RC agent Grade 1 had a smaller average mixture under pressure.15 One of these two particle size compared to RC agent Grade 2. parameters is often compromised due to requiring Table 1 shows the mixture design used in this conflicting properties. For pumpability, it is experimental program for the reference mixture desired to have a mixture with low viscosity and selected to represent a generic mixture containing high flowability (usually associated with high SF that is commonly used for shotcrete applications slump). However, for sprayability, a stiff and Table 1: Mixture Design of SF Mixture Mixture design Quantity Fine aggregate 0 to 0.04 in. (0 to 1 mm), lb/yd3 (kg/m3) 238 (141) Fine aggregate 0.04 to 0.16 in. (1 to 4 mm), lb/yd3 (kg/m3) 1748 (1037) Intermediate aggregate 0.16 to 0.32 in. (4 to 8 mm), lb/yd3 (kg/m3) 855 (507) Cement (CEM I 42,5 N), lb/yd3 (kg/m3) 758 (450) SF*, lb/yd3 (kg/m3) 38 (22.5 ) High-range water-reducing admixture, % of total cementitious materials content 1.2 Hydration control, % of total cementitious materials content 0.3 Alkali-free accelerator, % of total cementitious materials content 6 w/cm 0.435 *SF was fully replaced with RC agents. Table 2: Test Matrix Tested property Method Age Slump flow EN 12350-510 N/A Early-age strength EN 14488-211 10 min, 30 min, 1 h, 3 h Later-age strength EN 12390-312 7 d, 28 d Water penetration resistance EN 12390-813 28 d Shotcrete • Spring 2015 27


2015SpringShotcreteEMag
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