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2016SpringShotcreteEMag

Sustainability is an additional benefit, as it would allow shorter cycle time for shotcrete applications (Fig. 3). Longevity is an important parameter for sustainability, as it determines the service life of structures; therefore, durability aspects of the shotcrete mixtures were also evaluated. As shown in Fig. 4, mixtures with lower paste content (reduced by 56 lb/yd3 33 kg/m3 of cementitious materials content that was supplemented with the addition of 6 lb/yd3 3.6 kg/m3 of TYTRO RC 430) had slightly higher (or equal at minimum) durability compared to the mixtures having higher paste content. The improved durability of the mixtures with lower paste content is likely due to the impact of TYTRO RC 430 pozzolanicbased rheology control agent on improving the interfacial transition zone (ITZ) and reduced porosity. Furthermore, the impact of using supplementary cementitious materials such as metakaolin, slag cement, and fly ash is also significant on the reduction of the conductivity, which is consistent with what has been reported in the literature. Outcome 2—Increased Cement Efficiency Based on the obtained test results, cement efficiency was calculated by dividing the strength at 6 hours per unit mass of total cementitious material content in a mixture. Figure 5 supports the findings discussed previously (that the addition of 6 lb/yd3 3.6 kg/m3 of TYTRO RC 430 provided 32% more efficiency for the portland cement available in these mixtures than adding 56 lb/yd3 33 kg/m3 of ordinary portland cement to achieve equivalent strength at 6 hours). The most benefit was observed in the mixtures containing 8% metakaolin and 100% portland cement, as the cement efficiency was improved as much as 43% for similar strength performance. Outcome 3—Reduced Carbon Dioxide Emissions Because the production of each ton of portland cement clinker emits approximately 1 ton (900 kg) of carbon dioxide, reducing 56 lb/yd3 (33 kg/m3) of ordinary portland cement would result in a reduction of 0.033 metric ton CO2. If this approach is applied on a middle-size project with a shotcrete production volume of 6500 yd3 (5000 m3), the carbon dioxide emissions of the project would be reduced by 182 tons (165 metric tons) CO2 as a result of reducing the cement content by 7% with the addition of 0.8% of TYTRO RC 430 by total Fig. 3: Comparison of compressive strength at early ages Fig. 4: Comparison of bulk conductivity at 28 days Fig. 5: Cement efficiency cementitious materials content. 34 Shotcrete • Spring 2016


2016SpringShotcreteEMag
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