## 3 Sources of Discrepancies in LCA Stages
### Stage 3: Impact Assessment  
The third stage of an LCA is the assessment of the impact of the concrete mix by simply multiplying the functional unit by the aggregates impact of the concrete from the three life phases. As seen in Equations (3) and (4), the emissions and energy use are calculated by adding up all the emissions and energy uses of the products and processes involved in the production, use and end-of life stages. \[\text{Total emissions for mix }(\mathrm{x})=\mathrm{FU_{x}}\times\sum_{n=1}^{3} \text{ emissions of all products and processes of stage n} \tag{3}\]  
\[\text{Total energy use for mix }(\mathrm{x})=\mathrm{FU_{x}}\times\sum_{n=1}^{3} \text{energy use of all products and processes of stage n} \tag{4}\]  
In order to contextualize the information about the concrete mix being studied, an environmental impact indicator is needed. An impact assessment method is vital to producing judgements on the severity of the impact of concrete on the three main areas of protection: (i) ecosystem quality, (ii) human health and (iii) natural resources [59]. This is done through three steps: characterization of the impact, which is a must-do; then, normalization and weighing, which are both optional [49]. According to [PERSON] et al. [99], there are two main types of indicators: mid-point indicators, which correlate the calculated impact to a specific change in the environment, such as global warming potential, and end-point indicators which correlate the same increase to damage occurring later-on in the cause-effect chain, such as human health. The significance of this differentiation is that the same comparison between products or processes could result in different scores if looked upon by a mid-point or an end-point indicator, due to the exaggeration of damage that happens to reach the latter [100]. By examining the references reviewed, it was noticed that out of 107 papers, as seen in Figure 11 only six chose to rely on end-point indicators to present the concrete LCA findings. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & \multirow{2}{*}{**Author**} & \multirow{2}{*}{**Year**} & \multicolumn{8}{c}{**Kilometes**} \\ \cline{3-10}  & & & **OPC** & **Aggregates** & **FA** & **GGBS** & **SP** & **SH** & **SS** \\ \hline
[53] & [PERSON] & 2015 & 50 & 50 & 50 & & & & \\
[20] & [PERSON] & 2017 & 25 & 1 & & 0.01 & & & \\
[93] & [PERSON] & 2017 & 45 & 36 & & & 39 & & \\
[75] & [PERSON] & 2012 & 90 & 30 & 945 & 9317 & & & \\
[98] & [PERSON] & 2018 & 50 & 50 & & 10 & & & \\
[24] & [PERSON] & 2016 & & 100 & & & & & \\
[29] & [PERSON] & 2013 & 32 & 12 & 180 & 1640 & 724 & & \\
[64] & Kim and Chae & 2016 & 106 & 32 & & & 77 & & \\
[69] & [PERSON] & 2018 & 60 & 65 & 160 & & 15 & & \\
[89] & [PERSON] & 2015 & & & & 177 & & & \\
[17] & [PERSON] & 2017 & 100 & 100 & 50 & & & 50 & 20 \\
[39] & [PERSON] & 2018 & 6 & 10 & 10 & 493 & & 53 & 192 \\
[41] & [PERSON] & 2018 & 5 & 5 & & & & 12 & 64 \\
[13] & [PERSON] & 2015 & 50 & 1 & & & & & \\ Van den & & & & & & & & \\
[46] & Heede and De & 2010 & 113 & 193 & 38 & & 118 & & \\  & [PERSON] & & & & & & & & \\
[78] & [PERSON] & 2014 & 277 & 43 & 322 & 339 & 70 & & \\ \hline  & mean & & 72.1 & 48.5 & 195.9 & 1498.0 & 173.8 & 38.3 & 92.0 \\  & St dev & & 68.5 & 51.0 & 299.2 & 3205.7 & 271.8 & 22.9 & 89.4 \\  & St. dev (\% of mean) & 95.0 & 105.2 & 152.7 & 214.0 & 156.4 & 59.6 & 97.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: A sample of the inventory data for the transportation distances of concrete raw materials in km. In terms of relying on mid-point indicators to represent the environmental profile of concrete, the majority of the papers only selected global warming potential. The first reliability issue is that 10% of the papers opted to use the carbon dioxide emissions value as equivalent to the global warming potential [37; 64; 78; 79; 101; 102].