## 2 Materials and Methods
### Life-Cycle Assessment  
The LCA of concrete considers the following four stages: (i) Design, (ii) production/execution, (iii) usage phase, and (iv) end-of-life [16]. However, the execution of all these stages for concrete was not possible as different types of concrete are used for different specific building elements, such as columns, beams, walls, floors, and slabs [17]. Therefore, the usage phase could differ. For example, the concrete structure could serve as the foundation and load-bearing elements from 50 to 300 years, and the skin could serve as an exterior surface from 20 to 50 years [18]; thus, this stage is typically excluded from the LCA of concretes [19]. The LCA of the end-of-life stage is highly uncertain and \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Material** & **CBA0** & **CBA25** & **CBA50** & **CBA75** & **CBA100** \\ \hline Portland cement (kg/m\({}^{3}\)) & 386 & 386 & 386 & 386 & 386 \\ water content (kg/m\({}^{3}\)) & 205 & 190 & 170 & 150 & 130 \\ sand (kg/m\({}^{3}\)) & 652 & 494 & 318 & 138 & 0 \\ Coal bottom ash (CBA) (kg/m\({}^{3}\)) & 0 & 167 & 343 & 529 & 725 \\ coarse aggregate (kg/m\({}^{3}\)) & 1110 & 1127 & 1126 & 1135 & 1184 \\ water/cement ratio & 0.53 & 0.49 & 0.44 & 0.39 & 0.34 \\ slump (mm) & 65 & 65 & 70 & 75 & 67 \\
28-day compressive strength (MPa) & 56 & 65 & 70 & 75 & 67 \\ Drying shrinkage (microstrain) & 690 & 650 & 590 & 510 & 420 \\ Chloride–ion penetration (total charge passed in coulombs) & 5600 & 5200 & 5050 & 4700 & 4300 \\ \hline \hline \end{tabular} Note: Sand-CBA replacements were performed by mass. Mix designs were based on saturated surface dried conditions.  
\end{table} 
Table 1: Mixture with a fixed slump range (MIX-fixed-SLUMP): Concrete mixture design with a fixed slump range of 60–80 mm and the concrete’s properties (based on [15]). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Material** & **CBA0** & **CBA25** & **CBA50** & **CBA75** & **CBA100** \\ \hline Portland cement (kg/m\({}^{3}\)) & 386 & 386 & 386 & 386 & 386 \\ water content (kg/m\({}^{3}\)) & 205 & 205 & 205 & 205 & 205 \\ sand (kg/m\({}^{3}\)) & 652 & 457 & 262 & 67 & 0 \\ Coal bottom ash (CBA) (kg/m\({}^{3}\)) & 0 & 163 & 326 & 489 & 545 \\ coarse aggregate (kg/m\({}^{3}\)) & 1110 & 1127 & 1126 & 1135 & 1184 \\ water/cement ratio & 0.53 & 0.53 & 0.53 & 0.53 & 0.53 \\ slump (mm) & 68 & 85 & 120 & 155 & 195 \\
28-day compressive strength (MPa) & 56 & 52 & 45 & 39 & 32 \\ Drying shrinkage (microstrain) & 690 & 650 & 640 & 690 & 720 \\ Chloride–ion penetration (total charge passed in coulombs) & 5600 & 5800 & 5900 & 6000 & 6200 \\ \hline \hline \end{tabular} Note: Sand-CBA replacements were performed by mass. Mix designs were based on saturated surface dried conditions.  
\end{table} 
Table 2: Mixture with a fixed water/cement ratio (MIX-fixed-W/C): Concrete mixture design with a fixed water-cement ratio of 0.53 and the concrete’s properties (based on [15]). influenced by the applied demolition and disposal practices [20]. Moreover, the environmental damage estimated from this stage was smaller than that of the production/execution stage [21]. Therefore, this study only conducted a \"cradle-to-gate\" LCA that evaluated the production of the concrete mixtures. The FU is a reference unit, to which the inputs and outputs must be connected [11]. The production and use of 1 m\({}^{3}\) of a concrete mixture with a designed 28-day compressive strength is an appropriate FU in the LCAs of concrete with the partial replacement of cement by byproduct additives [22]. However, the environmental performance of the compared structural concretes should be based on the same mechanical properties. Therefore, [PERSON] and [PERSON] [14] normalized the FU by dividing the environmental assessment of 1 m\({}^{3}\) of concrete according to the 28-day concrete compressive strength.