by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
Concrete In Australia : March 2012
50 Concrete in Australia Vol 38 No 1 0.91 MJ/kg, respectively. Witherspoon et al 15 and Habert 16 based the sodium silicate estimates of CO2-e on earlier analyses of Fawer 18. Sodium hydroxide (NaOH) production was considered by Stengel et al 14 as an electrolysis process of saltwater, involving generation of both sodium hydroxide and chlorine gas, by one of three alternative types of electrolysis cells: (i) Mercury cell; (ii) Diaphragm cell; or (iii) Membrane Electrolysis Cell. Witherspoon et al 15 assigned similar energy consumption by the production by diaphragm or membrane electrolysis cells (9.8 MJ/kg and 9.2 MJ/kg chlorine), whereas the Mercury cell consumes approximately 30% more energy. Comparison between the studies is made difficult by the different sources of energy and also the production methods when compared with Australian conditions for the manufacturing of the alkali activators; sodium silicate and sodium hydroxide. Furthermore, Stengel et al 14 estimated the effect of elevated-temperature curing of geopolymers expends 340 MJ per m3 of concrete, whereas it was not considered by 13, 15-17. is paper reports the results of a comprehensive analysis of CO2-e generated by geopolymer concrete, including sourcing and manufacturing of raw materials, transportation and concrete production. e results are contrasted with the results of comparable concretes composed of OPC. 1.2 Research significance Concrete is the most commonly used construction material: approximately 1 t of concrete is produced each year for every human being in the world 19. e carbon footprint is significant: Meyer 4 estimates the contribution of the production of OPC is approximately 7% of global, man- made CO2 emissions. Five past studies have assessed emissions generated by geopolymer binders, however a very wide range of conclusions were reached due to exclusion of the contributions to emissions by the alkali activators that expend significant energy during manufacturing and also the significant effect of elevated-temperature curing of geopolymers, a necessary requirement for strength development. is study estimates the CO2-e that occurs when energy is expended during the activities associated with the manufacturing of raw materials, concrete production and construction. CO2-e comparisons were made for comparable concrete types that consisted of: (i) geopolymer made with 100% fly ash activated by sodium silicate and sodium hydroxide; and (ii) 100% OPC. 2.0 METHODOLOGY e study sought to quantify the carbon dioxide equivalent emissions (CO2-e) generated by all the activities necessary to obtain a non-reinforced cubic metre of concrete at a precast manufacture plant in metropolitan Melbourne. Estimates of CO2-e were compiled for concretes made with different cementitious binders, namely OPC and geopolymer (fly ash + alkali activators). e methodology followed these main steps: (i) e components of concrete construction were broken into single activities that relate to points of CO2 emission release (eg energy use). e activities and system boundary for conventional concrete based on OPC and blended cement is summarised in Figure 1 (adapted from Flower Figure 1. CO2 emissions system diagram for production of 1 m3 concrete.