Effect of compressive strength and chloride diffusion on life cycle CO2 assessment of concrete containing supplementary cementitious materials

Using supplementary cementitious materials (SCMs) in concrete is considered as one of the possible solutions to making green concrete. Previous research often analyzed the environmental impact of concrete without considering the influences of compressive strength and durability simultaneously. Such a practice will lead to less rational life cycle assessment (LCA) results, since the service life of concrete could be shortened when durability is poor, especially if concrete is exposed to marine dry-wet environment where chloride ion is intensive. Moreover, Fick's second law of diffusion was always used to determine the chloride diffusion coefficient of concrete, without considering the influences of convection zone and peak value of chloride concentration. Therefore, this paper proposed an integrated functional unit combining durability (resistance to chloride ion diffusion), compressive strength and volume to evaluate the environmental impact of concrete containing SCMs. The chloride diffusion coefficient was calculated by re-scaling the "zero" of penetration axis to calibrate Fick's second law of diffusion. In addition, three other functional units (volume, combining volume and compressive strength, combing volume and durability) were also proposed and compared. Results indicate that the selection of functional unit has a significant influence on the LCA results of the studied concrete. Despite the variation with different functional units, concrete containing silica fume or silica fume as well as fly ash shows a consistently superior environmental performance over the ordinary concrete. (C) 2019 Elsevier Ltd. All rights reserved.