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2016SpringShotcreteEMag

Sustainability fill the voids between aggregates). However, once the paste content of a mixture reaches an optimum value (which should be determined based on the desired pumpability, sprayability, durability, and strength requirements), the use of more cementitious material does not further increase the performance. 12,13 In fact, in some cases, excessive amounts of cementitious materials may adversely affect durability and shrinkage due to the increased risk of cracking. Outcome 1—Improved Shotcrete Performance With the advancements in chemical admixture technology, it is now possible to replace a portion of cementitious materials with a pozzolanic-based rheology control agent (TYTRO® RC 430) to reduce the total cementitious materials content without compromising the performance. A recent study was conducted on a few shotcrete mixtures under laboratory conditions to assess the performance of mixtures containing 6 lb/yd3 (3.6 kg/m3) of TYTRO RC 430 to replace 56 lb/yd3 (33 kg/ m3) of ordinary Type I portland cement in mixtures incorporating various supplementary cementitious materials, as shown in Table 1. Early- and later-age strength results indicate that regardless of the binder type presence in a given mixture, the addition of 0.8% TYTRO RC 430 by weight of binder content was able to reduce the cementitious materials content by 7% and still achieve equivalent cylinder compressive strength at 28 days (Fig. 2). Furthermore, mixtures containing the reduced paste content supplemented with a small addition of TYTRO RC 430 pozzolanicbased rheology control agent provided higher strength at very early ages of 6 and 8 hours, which Fig. 2: Comparison of 28-day cylinder compressive strength Table 1: Mixture Design Mixture components Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6 Mix 7 Mix 8 ASTM C150 Type I ordinary portland 642 698 642 698 513 569 703 759 cement, lb/yd3 (kg/m3) (381) (414) (381) (414) (304) (337) (417) (450) Silica fume, lb/yd3 (kg/m3) 61 (36) 61 (36) 0 0 0 0 0 0 Metakaolin, lb/yd3 (kg/m3) 0 0 61 (36) 61 (36) 0 0 0 0 Slag cement, lb/yd3 (kg/m3) 0 0 0 0 190 (113) 190 (113) 0 0 Total binder content, lb/yd3 (kg/m3) 703 (417) 759 (450) 703 (417) 759 (450) 703 (417) 759 (450) 703 (417) 759 (450) Water-cementitious materials content 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 Sand-to-total aggregate, % 68.4 68.4 68.4 68.4 68.4 68.4 68.4 68.4 High-range water-reducing admixture: TYTRO® WR 157, % of total binder 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 Set-accelerator: TYTRO® SA 530, % of total binder 5 5 5 5 5 5 5 5 Pozzolanic-based rheology control agent: TYTRO® RC 430, % of total binder 0.8 0 0.8 0 0.8 0 0.8 0 Shotcrete • Spring 2016 33


2016SpringShotcreteEMag
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