Page 38

2016SpringShotcreteEMag

Sustainability Table 3: CO2 Emission Factor17 Activity Emission factor Unit Portland cement 0.8200 t CO2/1000 kg Coarse aggregates 0.0357 t CO2/1000 kg Fine aggregates 0.0139 t CO2/1000 kg Concrete batching 0.0033 t CO2-e/m3 Concrete transport 0.0094 t CO2-e/m3 On-site placement activities 0.0090 t CO2-e/m3 Table 4: Estimated CO2 of Shotcrete Production Activity Dosage, lb/yd3 (kg/m3) CO2 emission, t/m3 Portland cement 759 (450) 0.3690 Coarse aggregates 905 (537) 0.0192 Fine aggregates 1960 (1161) 0.0161 Concrete batching — 0.0033 Concrete transport — 0.0094 On-site placement activities — 0.0090 Total — 0.4260 When the listed factors are applied to calculate the carbon footprint of shotcrete production, for a mixture containing 759 lb/yd3 (450 kg/m3) of portland cement, a total of 0.47 tons (0.43 metric tons) CO2 emission is expected to batch, transport, and place 1.3 yd3 (1 m3) of concrete, as shown in Table 4. Therefore, for a project with a shotcrete production volume of 6500 yd3 (5000 m3), reducing rebound by 15% (from 20 to 5%) would result in reducing CO2 emissions by 350 tons (320 metric tons). Outcome 3—Cost Savings The reduction of rebound by 15% would result in providing more than 15% cost savings, as it would not only prevent 15% of the ordered concrete from being waste material but also save from efficiency of the operation and reduced labor time. Considering many shotcrete applications are composed of fibers, high-range water-reducing admixtures, and set accelerators, 15% cost savings due to rebound reduction would be significant. Conclusions and Recommendations Based on the obtained test results, the following conclusions can be drawn: • Performance—When the cementitious materials content was reduced by 7% with the aid of a pozzolanic-based rheology control agent, an equivalent 28-day strength was achieved compared to the mixture containing higher cementitious materials content. Furthermore, mixtures with lower paste content supplemented with the addition of TYTRO RC 430 had slightly higher durability and 15% lower rebound compared to the mixtures having a higher paste content. The cement efficiency was improved as much as 43% for early strength performance. • Carbon dioxide emission—When cement content was reduced by 56 lb/yd3 (33 kg/m3), a reduction of 0.034 tons (0.031 metric tons) CO2 is expected; and when the rebound rate is reduced by 15%, a further reduction of 0.071 tons (0.064 metric tons) CO2 is expected for 1.3 yd3 (1 m3) of shotcrete production. • Cost savings—When 7% silica fume is replaced with the addition of 0.8% of TYTRO RC 430 by total cementitious materials content, at least 10% less expensive shotcrete is produced. Furthermore, more than 15% cost savings would be obtained with the reduction of rebound. 36 Shotcrete • Spring 2016


2016SpringShotcreteEMag
To see the actual publication please follow the link above