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Concrete In Australia : March 2012
52 Concrete in Australia Vol 38 No 1 FEATURE: CEMENT TECHNOLOGIES EC = energy content of the particular fuel type; GWP = total global warming potential of the fuel type, comprised of the sum of the individual components, comprising carbon dioxide, methane, nitrous oxide, and synthetic gases. (v) For each fuel type, values of EC and GWP were obtained from the Australian National Greenhouse Accounts (NGA) Factors 20 and the emission factors, expressed as the product of EC by GWP, are summarised in Table 1. Each activity through the life cycle was analysed in terms of energy expended and calculation of CO2-e at the point of emission release. e records of fuel use were obtained from the relevant manufacturers, suppliers and contractors, where possible. Equation 1 was calculated using the emission factors shown in Table 1. (vi) e estimation of CO2-e due to cement manufacturing is complicated due to the chemical liberation of CO2 due to decomposition of limestone during calcination, limestone source variability and also the use of calorific wastes in cement kilns which provide energy as a substitute fuel. Within Australia, the most recently reported emission factor for cement production, including transport of cement to concrete batching plants, is 0.82 kg CO2-e/kg 6 and we have used this emission factor in our calculations. (vii) We have examined the CO2 footprint of obtaining 1 m3 of Grade 40 concrete in the Melbourne metropolitan area. e concrete mixtures that were utilised in the calculations are summarised in Table 2. Energy source Emission factor1,2 EC*GWP Unit Diesel 2.68 kg CO2 -e/L Electricity3 1.35 kg CO2-e/kWh Liquid Petroleum Gas (LPG) 1.54 kg CO2 -e/L Explosives4 (ANFO Ammonium nitrate and fuel oil slurry) 0.44 kg CO2-e/kg product Notes: 1. Includes the net effects of ECO2, ECH4, and EN2O, taking into account the relevant oxidation factors and energy content of the fuel (i.e. -- EC*GWP) 2. Source: Reference (19) 3. Calculated as indirect emissions for the consumption of purchased electricity. Appropriate for Melbourne, Australia, and may vary elsewhere due to differences in energy or fuel production methods Material Concrete type Geopolymer Sumajouw et al 21 100% OPC 22 Mass (kg/m3) Coarse aggregates 1202 1242 Fine sand 647 781 Fly ash 408 Sodium hydroxide 41 (16M) Sodium silicate 103 (Na2O=14.7%, SiO2=29.4%, and water=55.9%) OPC 328 Superplasticiser 6 -- Free water* 26 190 Curing Steam curing at 60 °C for 24 h Moist curing * Note: Allowance was made for free water contained in the alkali activators and aggregates (to saturated surface dry condition). Table 2. Mixture proportions for 40 MPa concrete. Table 1. Emission factors utilised to estimate CO2 liberated for different fuel types.