4. Conclusions
A structural analysis embedded within a Life Cycle Analysis (LCA) methodology has been used to assess the influence of certain key variables on the environmental impacts of the construction of concrete shallow foundations (CSFs). These variables were: built cast in situ or precast; rigid or flexible; and calculated with structural design code EC-2 or EHE-08.
One main conclusion drawn from the results is that decisionmakers should consider some key aspects of the traditional design and construction of CSFs, because they can significantly affect environmental performance. For instance, steel and concrete had the highest impacts in all impact categories, accounting for around 95% of GWP emissions for cast-in-situ CSFs and 85% for precast CSFs. In addition, careful selection of the variables in the study might vary all indicators of the environmental impacts of CSFs by 45e60%. The optimization of concrete and steel amounts, when considering the variables selected for this study, is therefore a crucial element to minimize the impacts.
Compared with the cast-in-situ CSFs, the precast CSFs resulted in increases of up to around 35% in all impact categories, when both types had the same volume of concrete but different amounts of steel. These higher impacts are partly due to the higher cement content of precast concrete. In addition, precast products require lengthier transport distances and the use of on-site mechanized installation, as well as tending to require more reinforcing steel for higher concrete strengths. In this regard, the different minimum quantities of steel established by each structural code (EC-2 and EHE-08) for precast CSFs might affect the environmental impacts with variations of up to 48%. Nevertheless, when precast concrete volumes are greatly reduced and steel reinforcement is not significantly increased, the findings make it clear that precast CSFs can achieve similar environmental impacts to cast-in-situ CSFs. For instance, the precast rigid sloped CSF calculated with EC-2 (PR-DEC2*) had impacts that were around 2% higher than the best option in the study (IF-S13-EHE). This observation is principally explained by the use of sloped shapes and because it was calculated with EC-2 that permits greater reductions of concrete than EHE-08, as the minimum depth of the CSF is not limited. This code-dependent variability comes from the different assumptions adopted in each one. These assumptions, deduced from specific behavioural models, are basically structural or related to durability.
