## 4 Conclusions  
This review paper aimed at analysing the process of preparing a LCA for concrete and identifying potential sources of discrepancies. The purpose was to standardize the concrete LCA methodology in order to be able to judge the environmental impact in absolute terms across industries, which is a prerequisite for the rising demands to cut down the environmental impact of concrete to combat the rising global warming issues. As seen in Table 7 upon reviewing 146 references, it is apparent that there are 13 most-common sources of discrepancies that spread across the four stages of an LCA study. More than half of these sources are user-based choices, such as depending on a cradle-to-gate scope, selecting a basic volume-based functional unit, ignoring the impact allocation and relying on a single indicator. Throughout the paper, it was shown that based on these choices, the results of the concrete LCA study are not deemed reliable and are not comparable either to other concrete studies, nor in absolute terms to other products and services. Hence, it was concluded that the errors need to be addressed by following an inclusive methodology. In order to cater for the intrinsic uncertainty in some of the elements of the methodology proposed, such as the means of transportation, the expected service life and fluctuations in market prices, it is advised to perform scenario analyses on each of these elements and run a Monte Carlo simulation to aggregate the uncertainty in the final presented LCA outcome. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \# & **LCA Stage** & \ \begin{tabular}{c} **Source of** \\ **Discrepancy** \\ \end{tabular}  & **Description** & **Outcome** & **Frequency** & **Category** & \begin{tabular}{c} **Impact on LCA** \\ **Outcome** \\ \end{tabular}  & **Potential Solution** \\ \hline
1 & & & \ \begin{tabular}{c} Ignoring potential \\ carbon sequestration \\ by concrete \\ \end{tabular}  & 90\% & Reliability & 2-20\% & \begin{tabular}{c} Daduct the sequestered \\ carbon by predicting the \\ carbon potential of \\ concrete throughout its \\ expected service life \\ \end{tabular}  \\ \hline
2 & & & \begin{tabular}{c} Disregarding \\ the “use” phase \\ \end{tabular}  & \begin{tabular}{c} Assuming same \\ service life for \\ concrete alternatives \\ \end{tabular}  & 75\% & Reliability & \ \begin{tabular}{c} Underserstimulation \\ (variable) \\ \end{tabular}  & \begin{tabular}{c} Induct maintenance/and/or \\ replacement impact \\ depending on the difference \\ between the required and \\ expected service life of \\ concrete \\ \end{tabular}  \\ \hline
3 & & \begin{tabular}{c} System \\ Boundaries \\ \end{tabular}  & \begin{tabular}{c} Ignoring the \\ operational energy \\ consumed by concrete \\ \end{tabular}  & 75\% & Precision & \ \begin{tabular}{c} 1-10\% \\ underestimation \\ \end{tabular}  & \begin{tabular}{c} Add an estimate of the \\ operational energy consumed by concrete thought its \\ service life \\ \end{tabular}  \\ \hline
4 & & & \begin{tabular}{c} Disregarding \\ the “end-of-life” & \begin{tabular}{c} Ignoring the impact of \\ demolishing concrete \\ \end{tabular}  & 75\% & Precision & \ \begin{tabular}{c} 1-10\% \\ underestimation \\ \end{tabular}  &
\begin{tabular}{c} Add an estimate of the \\ emissions and energy \\ required to denol