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This study developed a simple and rational mixture proportioning procedure for low-CO2 concrete using supplementary cementitious materials (SCMs) such as fly ash (FA), ground-granulated blast-furnace slag (GGBS), and condensed silica fumes (SF). Life-cycle CO2 reduction ratio was critically considered as one of the targeted requirements. The effect of SCMs on CO2 reduction and the compressive strength of concrete was examined by a nonlinear multiple regression analysis using a total of 12,537 datasets, which produced schematized data allowing for the straightforward design of SCMs for satisfying the targeted requirements. Considering the determined substitution level of SCMs for a targeted CO2 reduction ratio, unit binder content and water-binder ratio (W/B) were formulated for the designed compressive strength and entrained air content of concrete. The fine aggregate-to-total aggregate ratio (S/a) was determined from the quadratic formula of a parametrized value for a targeted initial slump of concrete. Overall, the developed procedure is expected to encourage the practical production and application of low-CO2 concrete in the ready mixed concrete field.
Keywords: life-cycle assessment; low-CO2 concrete; mixture proportions; supplementary cementitious materials.
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INTRODUCTION
Given the global awareness and efforts for reducing greenhouse gas emissions, there have been growing social and/or specific needs for assessing the environmental impact of the concrete production phase and concrete structures.1,2 In general, the production of 1 ton (2.2 kip) of ordinary portland cement (OPC) is estimated to emit 0.8 to 0.9 tons (1.76 to 1.98 kip) of CO2 and deplete 0.25 ton (0.55 kip) of abiotic resources during the plasticity process under the temperature being over 1300°C (2372°F).3 Some estimates indicate that the amount of CO2 emitted from the worldwide OPC production corresponds to 7% of the total global CO2 emission.4 For these reasons, the concrete industry has further invested expense and labor to partially replace OPC with supplementary cementitious materials (SCMs) such as fly ash (FA), ground-granulated blast-furnace slag (GGBS), and condensed silica fumes (SF). It is commonly accepted that SCMs have sound environmental performance in terms of the recycling of by-products, low carbon dioxide emissions, and low energy consumption. However, there are few studies that quantitatively evaluate the effect of SCM substitution on reducing CO2 emissions from OPC concrete production.5,6
In general, the 28-day compressive strength and initial...