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2016SpringShotcreteEMag

Fig. 7: Impact of TYTRO SA 530 accelerator dosage rate on early-age strength Fig. 8: Impact of TYTRO SA 530 accelerator dosage rate on ultimate strength increased from 7 to 10%. However, no strength reduction was observed on the mixture containing 10% accelerator at later ages, as shown in Fig. 8. The Effect of Macro-Synthetic Fibers on Shotcrete Performance Macro-synthetic fibers are commonly used in underground applications as they improve the following properties7: • Post-crack energy absorption; • Durability after cracking; • Strain-softening behavior under deformation; • Cost competitiveness compared to steel fibers and welded wire reinforcement; and • Elimination of corrosion potential. Figure 9 shows the comparison of average energy absorption measured according to ASTM C1550-12a8 obtained from five panels for mixtures containing STRUX BT 50 and alternative 2.1 in. (54 mm) modified olefin macro-synthetic fibers. According to the round panel test, both fibers performed similar to each other at 0.2 in. (54 mm) deflection. At 1.6 in. (40 mm) panel deflection, STRUX BT 50 met the target energy absorption of 400 Joules, whereas the alternative fiber was around 325 Joules. However, when the results are evaluated considering the energy absorption and weight of fiber content at 1.6 in. (40 mm) deflection, both mixtures perform very similarly because STRUX BT 50 had 60 J/kg while the alternative fiber had 65 J/kg. Figure 10 shows the comparison of STRUX BT 50 and the alternative fiber regarding workability. Both mixtures had comparable workability, as they had the same water reducer dosage to achieve similar slump despite the higher fiber dosage of the mixture incorporating STRUX BT 50. They both met the requirement of having a minimum of 6.25 in. (160 mm) slump. However, the aligned packaging of the STRUX BT 50 fibers (Fig. 11) helped to further reduce balling and prevented individual fibers from curling and becoming tangled prior to use, thereby enhancing placement. Conclusions Based on the obtained test results, the following conclusions are drawn: • Slag cement can be used as a replacement for fly ash or ordinary portland cement as the impact of slag cement on early-age strength is offset with the presence of a pozzolanic-based rheology control agent; • For a shotcrete mixture with desired rheology allowing sufficient consolidation, an accelerator amount used within the manufacturer’s recommended dosage rate does not necessarily decrease the 28-day strength, as demonstrated in these tests; Fig. 9: Effect of STRUX BT 50 and alternative fiber on energy absorption (Note: 1 mm = 0.0394 in.) 26 Shotcrete • Spring 2016


2016SpringShotcreteEMag
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