The Effect of Additional Byproducts on the Environmental Impact of the Production Stage of Concretes Containing Bottom Ash Instead of Sand

Abstract

This study aims to assess whether using byproducts as additional binders can reduce the environmental damage of concretes that already contain bottom ash instead of sand. In particular, two concretes in which sand had been replaced by coal bottom ash at varying percentages (from 0 to 100 wt %) were evaluated in which (i) silica fume was an additional binder, and (ii) silica fume and blast furnace slag were additional binders. Consequential life cycle assessment was applied to environmentally evaluate the effect from the production stage of these byproducts. We used the ReCiPe2016 midpoint hierarchist and single-score (six methodologies) methods. A two-stage nested mixed analysis of variance was used to simultaneously evaluate the results of six ReCiPe2016 methodologies. The ReCiPe2016 midpoint hierarchist results indicate that using additional binders in both bottom ash-based concretes decreases global warming potential, terrestrial ecotoxicity, water consumption, and especially, fossil resource scarcity environmental impacts. The bottom ash-based concrete with silica fume and blast furnace slag as additional binders shows more environmental benefits than the bottom ash-based concrete with only silica fume. The ReCiPe2016 single-score method results indicate that the bottom ash-based alternatives with 40–100 wt % (with silica fume as an additional binder) and 75–100 wt % (with silica fume and blast furnace slag as additional binders) of sand replacement seem to cause the least environmental damage.

End-of-Life Materials Used as Supplementary Cementitious Materials in the Concrete Industry

“…By this way, we may be able to reduce the adverse environmental impacts stemming from cement (74%-93%) and sand (0.3%-2%) consumption in the total LCA of EOL material-based concretes. The minimum contribution of sand to the entire environmental assessment of concrete makes this issue important to concrete design [111][112][113].…”

“…Structural concrete has life expectancy differentiated by application, such as in pillars, beams and walls. While the durability over time for foundation or load-bearing structural elements is 50-300 years, the corresponding lifetime for cover walls is only 20-50 years [111]. Therefore, sufficient data is not presently available for the EOL stage of structural concrete and its disposal conditions [111,[114][115][116].…”

“…Cradle-to-gate life cycle assessment (LCA): studied system boundaries of the concretes (plain line-included processes; dashed line-non-included processes)[111].…”

Modern trends in the development of the construction industry in the production of building materials

“…The moisture content of bauxite sludge samples should be within 20-30 %, density -2.6 -2.86 g/cm 3 , bulk density in a loosened state -from 1.1 to 1.3 g/cm 3 Metallurgical slag of fraction 0-5 (Figure 3a) and coarse fractions 20-30 (Figure 3b) were used as fillers. The slag is gray, a porous microstructure is observed, the presence of a crystallized glassy component is noted [15][16][17]. Brown inclusions indicate the presence of iron oxide.…”