An Epitome of Building Floor Systems by Means of LCA Criteria

Studies of the elements that make up the structure of a building have generally focused on topics related to their physical and structural capacities. Although research has been carried out into environmental impact during the life cycle stages, the environmental profile is far from established. This research aims to reduce the gap in the knowledge of this subject, offering useful information to professionals in the construction industry, which will enable them to consider environmental aspects when choosing the best construction systems. The present study applies the methodology of the life cycle assessment (LCA), to analyze and compare four floor construction systems in two different scenarios (“A” with a functional homogeneous unit of 1 m2 and “B” with 1 m2 made up of the percentages of the floor system and the special areas of the building). The analysis is performed using the LCA Manager software, along with the Ecoinvent 3.1 database and with a cradle to handover perspective (A1–A5). Comparison was made using two environmental impact methodologies, Eco-indicator 99 and CML 2001. The results highlight the stages A1–A3 as those that generate the greatest environmental impact. Comparing the environmental profiles of the different floor systems, one-way floor systems I and II had the best environmental scores, 30% less than two-way floor system III and 50% less than slab floor system IV.


Introduction
The European Commission has identified the construction industry as being one of the greatest causes of environmental impact, due to its consumption of resources and energy as well as the generation of emissions and residues [1]. Regarding this, the so-called construction and demolition waste (CDW) account for a third part of the total flow of waste generated in the European region [2]. At local level, in the location used in the research, this percentage is not far from the European, representing approximately 25% of the total waste generated [3]. As this sector is constantly growing, it is necessary to try new proposals and initiatives to help identify (by analyzing the stages in each process) the causes of the impact generated. Consequently, it will be possible to design strategies that apply more sustainable building practices to reduce these affectations.

Aim and Scope of the Study
The aim of the work is to apply the methodology of the LCA to study and compare the environmental impact of the four types of floor systems-those most representative in a Spanish context-in two evaluation scenarios: Scenario "A" (theoretical-homogeneous) and "B" (application to a specific building type).
The structural systems to be analyzed fulfill the principal function of being resistant elements used as floor systems in buildings. The functional unit chosen for analysis is one square meter (1 m 2 ) of each type of floor system; as this is a widely used measurement in the construction regulations and is one of the recommended units by the standards [11], it facilitates comparison of different systems and allows verification of compliance with the regulations applicable to the type of construction involved.
To identify the environmental impact caused by the building process, and not those resulting from the building's use, the scope of the analysis was set as the modules known as "from cradle to handover" [33], which include the stages of raw material extraction (A1), transport to the factory Sustainability 2020, 12, 5442 4 of 25 (A2), production (A3), transport to site (A4), and construction (A5). The selection of the stages to be analyzed has been made based on the guidelines established by International Energy Agency [33], based on the criterion that the development in regulations and the state of knowledge related to the Use Stage of the building is such that it has been possible to decrease the affectation derived from it, achieving the design and construction of buildings with high energy efficiency [62][63][64] and even zero-energy buildings (NZEB) [65][66][67].
As a complement to the "from cradle to handover" approach, the analysis of the end-of-life stages of the building has been added (C1-C4), in order to contribute and expand the information described in the article in relation to the damages derived from the demolition, transportation from the site to the landfill, and disposal of waste. In addition, a sensitivity analysis related to the maintenance and replacement stages has been included, in order to analyze the repercussions of scenarios with a high degree of uncertainty. The results are shown separated according to two approaches; on the one hand, the results obtained from the "from cradle to handover" approach are exposed, and on the other hand, the end-of-life stages.

Case Studies
This work studies two construction scenarios for four different floor system building methods. The constructive solutions of floor systems were selected based on the analysis of the most common systems in the Spanish context, previously performed by Ortega [68], and by the recommendations of the Spanish Regulations available in the Catalog of Constructive Elements [69]. These constructive solutions are interchangeable within the structural system of a building and comply with all the current applicable regulations [70]. Figure 1 shows the constructive details of the floor system types, which are: One-way prestressed concrete joist with ceramic hollow slab blocks (I); one-way precast lattice joist and concrete hollow bricks (II); two-way joist with cast in place concrete and expanded polystyrene filler block (EPS); (III) and reinforced concrete slab (IV).
Sustainability 2020, 12, x FOR PEER REVIEW 4 of 26 handover" [33], which include the stages of raw material extraction (A1), transport to the factory (A2), production (A3), transport to site (A4), and construction (A5). The selection of the stages to be analyzed has been made based on the guidelines established by International Energy Agency [33], based on the criterion that the development in regulations and the state of knowledge related to the Use Stage of the building is such that it has been possible to decrease the affectation derived from it, achieving the design and construction of buildings with high energy efficiency [62][63][64] and even zeroenergy buildings (NZEB) [65][66][67]. As a complement to the "from cradle to handover" approach, the analysis of the end-of-life stages of the building has been added (C1-C4), in order to contribute and expand the information described in the article in relation to the damages derived from the demolition, transportation from the site to the landfill, and disposal of waste. In addition, a sensitivity analysis related to the maintenance and replacement stages has been included, in order to analyze the repercussions of scenarios with a high degree of uncertainty. The results are shown separated according to two approaches; on the one hand, the results obtained from the "from cradle to handover" approach are exposed, and on the other hand, the end-of-life stages.

Case Studies
This work studies two construction scenarios for four different floor system building methods. The constructive solutions of floor systems were selected based on the analysis of the most common systems in the Spanish context, previously performed by Ortega [68], and by the recommendations of the Spanish Regulations available in the Catalog of Constructive Elements [69]. These constructive solutions are interchangeable within the structural system of a building and comply with all the current applicable regulations [70]. Figure 1 shows the constructive details of the floor system types, which are: One-way prestressed concrete joist with ceramic hollow slab blocks (I); one-way precast lattice joist and concrete hollow bricks (II); two-way joist with cast in place concrete and expanded polystyrene filler block (EPS); (III) and reinforced concrete slab (IV).  The technical specifications and the functional properties of the four floor systems are shown in the Table 1. In Scenario A, the floor system for analysis is considered an entirely homogeneous element, without specially reinforced areas, where the square meter is composed of the materials shown in Figure 1. This scenario is studied to obtain a result that may be applied generically in building projects.
Scenario B proposes an analysis of the floor systems used in Scenario A but applied to a typical Barcelona building [68]. In this case, the analysis includes the areas of special reinforcement specified in the plans of the adopted building solution, such as lift shafts and interior patios, perimeter beams, slab zones in stairs and sloped slabs on parking ramps, reinforcements in irregular areas, etc. Therefore, in order to model the functional unit in this scenario-composed of a real representative percentage of all the project's elements-it was necessary to weigh and apportion the area of each surface of special reinforcement indicated on each floor, also considering its representativeness in the total area of the building (calculations and details available in [71]). This obtained the characterization of each square meter of floor system, as shown in Figure 2. Surfaces of less than 5% were considered part of the analyzed floor system, as they were considered unimportant for the results of the LCA.  In Scenario A, the floor system for analysis is considered an entirely homogeneous element, without specially reinforced areas, where the square meter is composed of the materials shown in Figure 1. This scenario is studied to obtain a result that may be applied generically in building projects.
Scenario B proposes an analysis of the floor systems used in Scenario A but applied to a typical Barcelona building [68]. In this case, the analysis includes the areas of special reinforcement specified in the plans of the adopted building solution, such as lift shafts and interior patios, perimeter beams, slab zones in stairs and sloped slabs on parking ramps, reinforcements in irregular areas, etc. Therefore, in order to model the functional unit in this scenario-composed of a real representative percentage of all the project's elements-it was necessary to weigh and apportion the area of each surface of special reinforcement indicated on each floor, also considering its representativeness in the total area of the building (calculations and details available in [71]). This obtained the characterization of each square meter of floor system, as shown in Figure 2. Surfaces of less than 5% were considered part of the analyzed floor system, as they were considered unimportant for the results of the LCA. The nomenclature used to characterize each constructive solution is defined by the type of floor system analyzed (I, II, III and IV) and the corresponding scenario (A-B). The nomenclature used to characterize each constructive solution is defined by the type of floor system analyzed (I, II, III and IV) and the corresponding scenario (A-B).

Impact Assessment Method and Categories
The results will be analyzed using two evaluation methods: That of the Eco-indicator 99-to obtain easily interpreted and comparable results, which from an "endpoint" focus, offers results expressed in comparable eco-points focused on the damage approach of three categories [73]. The methodology CML 2001 [74], with a "midpoint" focus, is used in order to identify the indicator at a level of Sustainability 2020, 12, 5442 6 of 25 cause-effect chain between the analyzed processes and the LC stage in which they occurred. Table 2 shows the impact categories considered in the study. The LCA Manager 1.3 software has been used as a support for developing the LCA [18], as it enables evaluation according to regulation ISO 14044 [14] and facilitates the analysis of results by means of different impact categories.

Data Inventory
The data of the environmental impact to be used come from the Ecoinvent 3.1 database [75], developed by the Swiss Federal Offices and the ETH Zurich. This is globally recognized for containing information on a broad spectrum of activities, as well as being constantly updated and having reliable and transparent calculation processes. As there are no specific data for the Spanish area, the use of reliable European area data was deemed acceptable for the purpose of this research [76].
The BEDEC database, developed by the Catalonia Institute of Construction Technology (ITeC), was used for quantifying the materials and machinery needed for constructing each system to be analyzed. This database contains detailed information about constructive elements, contract specifications, and building products from all provinces of Spain [77]. For the CDW calculation and the quantification of the machinery necessary for the demolition, the software-database CYPE was used [78].

Assumptions
The following assumptions were made for this study. According to the established in the Spanish regulations, the reference service life of the elements is considered as 50 years [72]. Stage A4: For calculating the corresponding distances, Barcelona (41 • 23 56.2" N 2 • 09 42.9" E) was established as the reference location due to its central geographic position in the city [66]. In Stage A5: The use of a tower crane for lifting materials and the use of auxiliary machinery for the construction process were considered. Due to the lack of specific information in Ecoinvent, the available generic machines were used, which implicate all the processes, maintenance, and energy consumption of the machinery involved. Specifically, in the absence of a specific process on the production of ceramic hollow slab blocks, the "brick production" dataset has been used as a substitute, because the process followed by the manufacture of the bricks and the slab blocks are similar and the results can be extrapolated (according to what is specified by Ecoinvent [75]).
The analysis of the end-of-life stages represents more complexity in its definition than other stages of the Life Cycle; mainly due to the higher level of uncertainty in the processes that have to be considered in the analysis. This uncertainty is linked to the future development or advance in the measures and Sustainability 2020, 12, 5442 7 of 25 technologies used for demolition, and to the development of new material recovery scenarios [79]. However, in this analysis, the environmental impacts assigned to the module C (end-of-life), are considered to begin when the activity that generates the waste takes place, and consider the waste management as a process that generates materials to be "discarded, recovered, recycled or reused" [10]. The impacts assigned to this module refers to this waste management and the disposal of waste to the landfill. If this were not the final destination of the waste, at the end of their condition as waste, the resulting materials would be analyzed in module D-"Benefits and loads beyond the system" (recovery, reuse, and/or recycling) [80].

Life Cycle Inventory (LCI)
Once the study cases have been established and the technical specifications and regulations complied with, along with the constructive details of the solutions, specific databases of the construction industry were used to quantify the materials that make up each floor system (considering the totality of the elements both individually and specifically). To obtain significant results and simplifying the LCA process, those materials with a representative percentage of less than 5% of the total were discarded, as it has been shown that their non-consideration does not generate significant alterations in the results [44]. Figure 3 shows the flow diagram of the life cycle inventory (LCI) studied in the analysis. blocks, the "brick production" dataset has been used as a substitute, because the process followed by the manufacture of the bricks and the slab blocks are similar and the results can be extrapolated (according to what is specified by Ecoinvent [75]).
The analysis of the end-of-life stages represents more complexity in its definition than other stages of the Life Cycle; mainly due to the higher level of uncertainty in the processes that have to be considered in the analysis. This uncertainty is linked to the future development or advance in the measures and technologies used for demolition, and to the development of new material recovery scenarios [79]. However, in this analysis, the environmental impacts assigned to the module C (endof-life), are considered to begin when the activity that generates the waste takes place, and consider the waste management as a process that generates materials to be "discarded, recovered, recycled or reused" [10]. The impacts assigned to this module refers to this waste management and the disposal of waste to the landfill. If this were not the final destination of the waste, at the end of their condition as waste, the resulting materials would be analyzed in module D-"Benefits and loads beyond the system" (recovery, reuse, and/or recycling) [80].

Life cycle Inventory (LCI)
Once the study cases have been established and the technical specifications and regulations complied with, along with the constructive details of the solutions, specific databases of the construction industry were used to quantify the materials that make up each floor system (considering the totality of the elements both individually and specifically). To obtain significant results and simplifying the LCA process, those materials with a representative percentage of less than 5% of the total were discarded, as it has been shown that their non-consideration does not generate significant alterations in the results [44]. Figure 3 shows the flow diagram of the life cycle inventory (LCI) studied in the analysis. Production stage (A1-A3): The calculation and quantification of the materials needed for each square meter of the floor system analyzed was carried out using the BEDEC database [77], and this was based on the plans, sections, and construction details of the project. The data corresponding to the input and output flows of energy and material supplies, resource extraction, transport of raw Production stage (A1-A3): The calculation and quantification of the materials needed for each square meter of the floor system analyzed was carried out using the BEDEC database [77], and this was based on the plans, sections, and construction details of the project. The data corresponding to the input and output flows of energy and material supplies, resource extraction, transport of raw materials to the production center, their handling in the factory, and the residues generated by the process were obtained by weighing the quantified data regarding the units required by the Ecoinvent V3.1 database. Table 3 shows the detailed characterization of the materials and quantities that make up the functional unit of each of the analyzed floor systems and their positioning in the Ecoinvent database, which was used to establish the input and output flow of materials and energy.  Table 4 shows the distances for each type of material considered in the analysis; they were made by averaging the distances used in previous studies and the real distances from the available factories in the local environs [45,81]. It was also assumed that the materials were transported by a normal, diesel-powered, 28-ton lorry [82]. The performance and wear associated with transporting the materials were calculated based on a service life of 540,000 km. Table 4. Distances considered for transport of machinery [45,81].

Factory
Round Construction stage (A5): Table 3 shows the amount of supplementary machinery and materials required for building one square meter of each type of floor system. To carry out the quantification, the data available in the BEDEC database and the basic properties of the materials were considered (such as density, volume, composition, etc.), as well as the performance and wear of the machinery and the reuse of the wood formwork.
To obtain the proportional quantity of wood formwork to be used, the amount of wood required for each system (m 3 ) was divided by 10, representing the total number of possible reuses [77]. For the calculations regarding the concrete pump, a pump with a capacity of 63 m 3 /h and average service life of 10,000 h was considered [83]. A performance of 20 m 3 /h with an electric motor of 1.3 kW was considered in the case of the vibrations of the concrete elements, as this was the recommended machinery for these elements [84]. A 40-m high tower crane with a 40-m arm was considered for lifting the materials within the building. This had a load capacity of 2 tons, speed of 35 m/min, and an average 10,000 h of average service life [85].
Maintenance-replacement Stage (B2-B4): The use and maintenance manuals of a building establish that, in the case of conventional structural elements, a higher level of inspection is not required than the regular routine of a building, which is established as a visual inspection every 10 years [78,86]. Therefore, theoretically, the maintenance needs or replacement actions of elements for damages presented during the time are null. However, to know the repercussion of this variable, a sensitivity analysis has been carried out including different scenarios of replacement of percentages of the functional unit (Section 3.1.3).
Demolition Stage (C1): For the analysis of the Demolition stage of the building, it has been considered that it will be demolished "element by element", which allows visualizing the demolition implications and requirements of the functional unit used in the research (one square meter of floor system). The CYPE software was used to quantify the machinery necessary for the demolition of each element (pneumatic hammer, cutting equipment, and portable compressor) [78]. The quantification of the machinery in "Scenario A" focuses solely on the demolition of the floor system; while in "Scenario B", the machinery necessary for the demolition of each element that is included in the functional unit, has been quantified relatively to its percentage (refer to " Figure 2", where the percentages of the elements in the functional unit are specified). Table 5 shows the inventory of the machinery considered. Table 5. Inventory of machine use per square meter of floor system for the demolition stage.

Dataset Unit I-A II-A III-A IV-A I-B II-B III-B IV-B
Machine operation diesel, <18. 64  Transport from site to disposal (C2): Following the principle of proximity indicated in the regulations, it is established that the CDW are transported within a radius of 15 km from the urban center under study, the transport used is containers of 7 cubic meter of capacity [87]. This corresponds to the average distance of the closest recycling plants to the study location [88]. Table 6 specifies the inventory of materials and its transportation to the landfill. Waste processing and Disposal (C3-C4): Once the quantification of the machinery required for the demolition has been carried out, the types of waste generated are quantified and identified-based on the weight of the materials that are considered in each floor system. Using the CYPE database [78], the classification of the waste generated has been established, most of which correspond to the CDW level II group: CDW of non-petrous nature (metals) and CDW of petrous nature (concrete and ceramic materials) [89]. As being of petrous, metallic, and petroleum origin, the materials are considered inert and its processing does not represent a potential risk to the environment [90]. Table 7 specifies the inventory of the CDW generated in each group of waste. It is necessary to highlight that the local regulations establish that the segregation of construction waste "in place" is mandatory when, individually, the expected quantity generated exceeds 80 t of concrete; 40 t of bricks, tiles, and ceramic materials; 2 t of metals, etc. [78]. Such quantification is outside the scope of this investigation, due to the nature of the functional unit. Therefore, for the analysis of the final stage, the waste treatment is only established until its final disposal.

Results of the Life Cycle Impact Assessment (LCIA)
The LCIA aims to characterize the input and output elements of the flows modelled in the LCI, assigning these results to the environmental impact categories chosen for analysis. The results obtained from the methodologies Eco-indicator 99 and CML 2001 are presented below, where the environmental impact of the different systems in each scenario is identified, which of them have the greatest contribution to the categories of damage or environmental indicators, and the stages that produce the greatest impact. The presentation and analysis of results have been separated; on the one hand, the results of the "from the cradle to handover" approach are shown, and on the other, the stages with potential for waste generation are shown (replacement stage (B4) and the end-of-life stages of the building (C1-C4)). In order to provide a complete overview of the environmental impact, a differentiated visualization by the different stages was generated, allowing the relationship of each stage with the impact generated to be clearly identified.
3.1.1. Results of the Eco-Indicator 99 Method Figure 4 shows the results obtained by the Eco-indicator 99 method in the approach of "from cradle to handover". In general, of all the systems analyzed, A1-A3 was the stage with most environmental impact. The greatest contribution came from the category HH, with 55% of the average score of the total eco-points, followed by RC with 34%. The category of EQ had the lowest effect, with 10% of the average.
It is necessary to highlight that the local regulations establish that the segregation of construction waste "in place" is mandatory when, individually, the expected quantity generated exceeds 80 t of concrete; 40 t of bricks, tiles, and ceramic materials; 2 t of metals, etc. [78]. Such quantification is outside the scope of this investigation, due to the nature of the functional unit. Therefore, for the analysis of the final stage, the waste treatment is only established until its final disposal.

Results of the Life Cycle Impact Assessment (LCIA)
The LCIA aims to characterize the input and output elements of the flows modelled in the LCI, assigning these results to the environmental impact categories chosen for analysis. The results obtained from the methodologies Eco-indicator 99 and CML 2001 are presented below, where the environmental impact of the different systems in each scenario is identified, which of them have the greatest contribution to the categories of damage or environmental indicators, and the stages that produce the greatest impact. The presentation and analysis of results have been separated; on the one hand, the results of the "from the cradle to handover" approach are shown, and on the other, the stages with potential for waste generation are shown (replacement stage (B4) and the end-of-life stages of the building (C1-C4)). In order to provide a complete overview of the environmental impact, a differentiated visualization by the different stages was generated, allowing the relationship of each stage with the impact generated to be clearly identified.
3.1.1. Results of the Eco-Indicator 99 Method Figure 4 shows the results obtained by the Eco-indicator 99 method in the approach of "from cradle to handover". In general, of all the systems analyzed, A1-A3 was the stage with most environmental impact. The greatest contribution came from the category HH, with 55% of the average score of the total eco-points, followed by RC with 34%. The category of EQ had the lowest effect, with 10% of the average. Scenario A: In Figure 4a, it can be seen that the floor system that generated the greatest environmental effect in the scenario was IV-A, with a total of 10.66 eco-points; the floor system with the lowest impact (and therefore the most sustainable in terms of LCA in this comparison) was I-A, with a total of 5.60 eco-points. Scenario A: In Figure 4a, it can be seen that the floor system that generated the greatest environmental effect in the scenario was IV-A, with a total of 10.66 eco-points; the floor system with the lowest impact (and therefore the most sustainable in terms of LCA in this comparison) was I-A, with a total of 5.60 eco-points.
Stages A1-A3: The greatest contribution to the environmental impact occurred in this stage, with floor system IV-A generating the most, a total of 9.31 eco-points. HH was the category with the biggest impact, in which IV-A continued generating the most effect, with 5.59 eco-points, while I-A generated the least, with 2.74 eco-points.
Stage A4: Transport of the materials to the building site was the most important stage after that of A1-A3. The category generating the most impact was RC, with fuel consumption being the principal Stage A5: This building stage had its greatest contribution in category EQ, in which the floor systems generating the biggest effect were I-A and II-A, with 0.15 and 0.16 eco-points, respectively. The building process and the generation of residues from the system had the greatest effect.
"Comparison by each category scenario A: The category HH was the one that had more environmental damage, with the IV-A being the system with more eco-points (5.94 eco-points), followed by III-A with 3.65 eco-points, II-A with 3.20 eco-points, and, lastly, I-A with 2.90 eco-points. In the RC category, it can be seen that IV-A continued to have the bigger environmental impact with 3.51 eco-points, followed by III-A with 2.89 eco-points, I-A with 2.03 eco-points, and II-A with 1.95 eco-points. Lastly, in the EQ category the floor system IV-A gets 1.21 eco-points, followed by II-A with 0.77 eco-points, III-A with 0.71 eco-points and I-A with 0.67 eco-points." Scenario B: Figure 4b shows a strong similarity with the results obtained in Scenario A, with floor system IV-B being the least environmentally efficient, with a total of 11.02 eco-points, while the most sustainable scenario was I-B, with 7.56 eco-points.
Stage A1-A3: The floor system with the biggest contribution in this stage is IV-B, with 9.69 eco-points, followed by III-B with 8.76 eco-points; the floor systems with least environmental impact are I-B and II-B, with 6.78 and 6.97 eco-points. Category HH produces 59% more effect regarding the categories of EQ and RC. Floor system IV-B has the greatest impact in EQ (0.91 eco-points) and HH (5.83 eco-points) and system III-B has the greatest impact in RC (2.97 eco-points).
Stage A4: This stage shows minimal variations regarding Scenario A, with effect values remaining at similar levels where, despite being reduced, the greatest effect is from floor system IV-B with 1.22 eco-points, followed by III-B with 0.79, II-B with 0.79, and I-B with 0.69.
Stage A5: The environmental impact in this stage is still mainly generated in category EQ. In this scenario, the environmental impact of the floor systems was more balanced, with floor system IV-B continuing to generate the biggest impact with 0.08 eco-points, followed by III-B with 0.069 eco-points, II-B with 0.067, and I-B with 0.067.
Comparison by each category scenario B: The category HH was the one that had more environmental damage, with the IV-B the system with more eco-points (6.17 eco-points), followed by III-B with 5.24 eco-points, II-B con 4.41 eco-points and, at last, I-B with 4.14 eco-points. In the RC category, it can be seen that IV-B continues to have the bigger environmental impact with 3.60 eco-points, followed by III-B with 3.40 eco-points, I-B with 2.60 eco-points, and II-B with 2.56 eco-points. Lastly, in the EQ category, the floor system IV-B generates 1.25 eco-points, followed by III-B with 1.01 ecopoints, II-B with 0.89 eco-points and I-B with 0.82 eco-points.
Analysis of the Stages A1-A3: Since stages A1-A3 obtained the highest score in the stages of the LC, an analysis of the contribution to the impact of the materials used in each construction system has been carried out ( Figure 5), in order to identify the material with the higher environmental impact in each floor system. It was observed that steel is the material that generates a greater contribution to the environmental impact in all the systems and scenarios analyzed. In scenario A, in the floor system I-A, steel generated 2.98 eco-points of impact, while concrete and ceramic hollow slab blocks generated 0.959 and 0.956, respectively. In II-A, steel generated 2.98 eco-points, followed by concrete with 1.14 eco-points and concrete hollow bricks with 0.93 eco-points. In III-A, steel obtained 3.86 eco-points, followed by concrete and EPS with 1.39 and 1.31 eco-points, respectively. Finally, in IV-A, the steel generated 6.34 eco-points and the steel 2.97 eco-points.
Sustainability 2020, 12, x FOR PEER REVIEW 13 of 26 points, followed by concrete with 1.57 eco-points and concrete hollow bricks with 0.69 eco-points. In III-B, steel obtained 6.00 eco-points, followed by concrete with 1.96 and EPS with 0.78 eco-points, respectively. Finally, in IV-B, the steel generated 6.76 eco-points and the steel 2.92 eco-points. It can be seen when comparing the scenarios that in scenario B, the eco-points corresponding to steel and concrete increases, and this is due to the characterization of the functional unit and, therefore, the amount of this materials increased, decreasing the quantity of lightening elements used. Figure 6 shows the results of the environmental impact in the Eco-indicator 99 methodology of the end-of-life stages, where it can be seen that the stage that generates the greatest impact is the Demolition stage (C1), followed by the stage of Waste Disposal (C3-C4). Scenario A: The same trend that had been occurring in the "from cradle to handover" stages can be observed, where the floor system IV-A was the one that generated the greatest environmental impact, with a total of 1.89 eco-points. This was followed by III-A with 1.40 eco-points, II-B with 1.23 eco-points, and I-A with 1.14 eco-points. In scenario B, in the floor system I-B, steel generated 4.63 eco-points of affectation, while concrete and ceramic hollow slab blocks generated 1.43 and 0.70, respectively. In II-B, steel generated 4.70 eco-points, followed by concrete with 1.57 eco-points and concrete hollow bricks with 0.69 eco-points. In III-B, steel obtained 6.00 eco-points, followed by concrete with 1.96 and EPS with 0.78 eco-points, respectively. Finally, in IV-B, the steel generated 6.76 eco-points and the steel 2.92 eco-points.
It can be seen when comparing the scenarios that in scenario B, the eco-points corresponding to steel and concrete increases, and this is due to the characterization of the functional unit and, therefore, the amount of this materials increased, decreasing the quantity of lightening elements used. Figure 6 shows the results of the environmental impact in the Eco-indicator 99 methodology of the end-of-life stages, where it can be seen that the stage that generates the greatest impact is the Demolition stage (C1), followed by the stage of Waste Disposal (C3-C4).
Sustainability 2020, 12, x FOR PEER REVIEW 13 of 26 points, followed by concrete with 1.57 eco-points and concrete hollow bricks with 0.69 eco-points. In III-B, steel obtained 6.00 eco-points, followed by concrete with 1.96 and EPS with 0.78 eco-points, respectively. Finally, in IV-B, the steel generated 6.76 eco-points and the steel 2.92 eco-points. It can be seen when comparing the scenarios that in scenario B, the eco-points corresponding to steel and concrete increases, and this is due to the characterization of the functional unit and, therefore, the amount of this materials increased, decreasing the quantity of lightening elements used. Figure 6 shows the results of the environmental impact in the Eco-indicator 99 methodology of the end-of-life stages, where it can be seen that the stage that generates the greatest impact is the Demolition stage (C1), followed by the stage of Waste Disposal (C3-C4). Scenario A: The same trend that had been occurring in the "from cradle to handover" stages can be observed, where the floor system IV-A was the one that generated the greatest environmental impact, with a total of 1.89 eco-points. This was followed by III-A with 1.40 eco-points, II-B with 1.23 eco-points, and I-A with 1.14 eco-points. Scenario A: The same trend that had been occurring in the "from cradle to handover" stages can be observed, where the floor system IV-A was the one that generated the greatest environmental impact, with a total of 1.89 eco-points. This was followed by III-A with 1.40 eco-points, II-B with 1.23 eco-points, and I-A with 1.14 eco-points.
Scenario B: In this scenario, the floor system III-B generates a greater environmental impact with 2.60 eco-points, followed by the floor system IV-B with 2.31 eco-points. The floor systems I-B and II-B had the lower environmental impact with 1.61 y 1.68 eco-points, respectively. The increase in the impact generated by III-B is mainly due to the stage C1, which indicates that it requires a greater amount of demolition work and, therefore, requires greater use of machinery. This is also directly related to the constitution of the percentages included in the functional unit (Figure 2), where it can be observed that a higher percentage of reinforcements is included. Figure 7 shows the environmental impact obtained from the CML 2001 evaluation method in the approach "from cradle to handover". In order to visualize the effects generated by the different categories and to compare the proportional contribution in each indicator, the results are presented in stacked columns for each slab in both scenarios. Scenario B: In this scenario, the floor system III-B generates a greater environmental impact with 2.60 eco-points, followed by the floor system IV-B with 2.31 eco-points. The floor systems I-B and II-B had the lower environmental impact with 1.61 y 1.68 eco-points, respectively. The increase in the impact generated by III-B is mainly due to the stage C1, which indicates that it requires a greater amount of demolition work and, therefore, requires greater use of machinery. This is also directly related to the constitution of the percentages included in the functional unit (Figure 2), where it can be observed that a higher percentage of reinforcements is included. Figure 7 shows the environmental impact obtained from the CML 2001 evaluation method in the approach "from cradle to handover". In order to visualize the effects generated by the different categories and to compare the proportional contribution in each indicator, the results are presented in stacked columns for each slab in both scenarios. It can be seen in Scenario A that IV-A was the floor system generating more environmental impact and that in all the floor systems, the impact categories with the greater percentage were the GWP and HTP, while the impact categories AP, EP, POCP, ODP, and ADP had percentages that are barely visible on the graph. It can be observed that the indicator GWP was the one with the bigger contribution in all the floor systems in scenario A, representing the 51.91% in I-A, 54.64% in II-A, 53.19% in III-A, and 49.8% in IV-A; followed by the indicator HTP, representing 47.41% in I-A, 44.74% in II-A, 46.19% in III-A, and 49.5% in IV-A. In the category ADP, the floor system with a higher impact percentage is IV-A with 0.34%, while I-A has 0.35%, II-A has 0.27%, and III-A has 0.34%. In the category AP, the floor systems IV-A and II-A had the bigger impact, but represent 0.17% and 0.19%, respectively, from their total environmental impact generated, while in I-A, the impact represents 0.17% and in III-A 0.18% of their total impact. In the category EP, the floor system with higher impact was IV-A and the impact represented 0.14% regarding its total, followed by II-A with 0.14%, III-A with 0.15%, and I-A with 0.14%. In POCP, the percentage of impact generated within each floor system was 0.15% for III-A and 0.14% for I-A, II-A, and IV-A. Lastly, ODP had the smaller impact by percentage in the impact of each floor system, where it was 0.001% in all the systems (I-A, II-A, III-A, and IV-A).

Results of the CML 2001 Method
In the scenario B, it can be observed that the indicator HTP was the one with the bigger contribution in the floor systems II-B, III-B, and IV-B, followed by the indicator of GWP (which has the biggest contribution in I-B), unlike the scenario A. It can be observed that the percentages of the category indicator AP, EP, POCP, ODP, and ADP continue being considerably smaller than the indicators of HTP and GWP. In the category HTP, the floor systems IV-B and II-B had similar percentages, with 51.17% and 51.23%, respectively; followed by III-B with 50.68% and I-B with 48.49%. The category GWP was second relative to percentage, except for the floor system I-B, which had the biggest contribution by 50.78% of its total, followed III-B with 48.65%, IV-B with 48.16%, and It can be seen in Scenario A that IV-A was the floor system generating more environmental impact and that in all the floor systems, the impact categories with the greater percentage were the GWP and HTP, while the impact categories AP, EP, POCP, ODP, and ADP had percentages that are barely visible on the graph. It can be observed that the indicator GWP was the one with the bigger contribution in all the floor systems in scenario A, representing the 51.91% in I-A, 54.64% in II-A, 53.19% in III-A, and 49.8% in IV-A; followed by the indicator HTP, representing 47.41% in I-A, 44.74% in II-A, 46.19% in III-A, and 49.5% in IV-A. In the category ADP, the floor system with a higher impact percentage is IV-A with 0.34%, while I-A has 0.35%, II-A has 0.27%, and III-A has 0.34%. In the category AP, the floor systems IV-A and II-A had the bigger impact, but represent 0.17% and 0.19%, respectively, from their total environmental impact generated, while in I-A, the impact represents 0.17% and in III-A 0.18% of their total impact. In the category EP, the floor system with higher impact was IV-A and the impact represented 0.14% regarding its total, followed by II-A with 0.14%, III-A with 0.15%, and I-A with 0.14%. In POCP, the percentage of impact generated within each floor system was 0.15% for III-A and 0.14% for I-A, II-A, and IV-A. Lastly, ODP had the smaller impact by percentage in the impact of each floor system, where it was 0.001% in all the systems (I-A, II-A, III-A, and IV-A).
In the scenario B, it can be observed that the indicator HTP was the one with the bigger contribution in the floor systems II-B, III-B, and IV-B, followed by the indicator of GWP (which has the biggest contribution in I-B), unlike the scenario A. It can be observed that the percentages of the category indicator AP, EP, POCP, ODP, and ADP continue being considerably smaller than the indicators of HTP and GWP. In the category HTP, the floor systems IV-B and II-B had similar percentages, with 51.17% and 51.23%, respectively; followed by III-B with 50.68% and I-B with 48.49%. The category GWP was second relative to percentage, except for the floor system I-B, which had the biggest contribution by 50.78% of its total, followed III-B with 48.65%, IV-B with 48.16%, and II-B with 48.09%. In the category ADP, the percentage from the total of the environmental impact was considerably smaller, representing 0.40% of I-B and 0.36% for II-B, III-B, and IV-B. In the category AP, the contribution in each floor systems represented 0.18% for I-B, 0.17 for II-B, and 0.16% for III-B and IV-B. In the category EP, the percentage in each of the floor systems represented 0.13% (I-B, II-B, III-B, and IV-B). In POCP, the percentage of impact generated within each floor system was 0.03% for I-B and 0.02% for II-B, III-B, and IV-B. Lastly, ODP had the smaller impact by percentage in the impact of each floor system where IV-B and III-B had 0.0006%, II-B and I-B had 0.0005%. Table 8 shows the results of each category indicator mentioned in Figure 7. In both scenarios, the most important categories regarding quantity of emissions were GWP and HTP; floor system IV-A had the greatest effect in Scenario A, generating 138.81 kg CO 2 eq and 138.10 kg 1.4-DB eq, respectively, while in Scenario B, floor system IV-B generated 196.96 kg CO 2 eq and 209.26 kg 1.4-DB eq, respectively, followed very closely by floor system III-B with 193.77 kg CO 2 eq and 201.87 kg 1.4-DB eq. Studying the two scenarios, the floor systems in Scenario A showed the least impact compared with those in Scenario B. From the perspective of the CML 2001 method, the floor systems of Scenario A generated less environmental impact per impact category indicator than Scenario B, while floor systems I and II contributed least to the environmental impact in general.
In Figure 8, the environmental impacts for the "end-of-life" stages are quantified with the CML methodology, complemented with Table 9, which shows the results in the values of each indicator.  Table 8 shows the results of each category indicator mentioned in Figure 7. In both scenarios, the most important categories regarding quantity of emissions were GWP and HTP; floor system IV-A had the greatest effect in Scenario A, generating 138.81 kg CO2 eq and 138.10 kg 1.4-DB eq, respectively, while in Scenario B, floor system IV-B generated 196.96 kg CO2 eq and 209.26 kg 1.4-DB eq, respectively, followed very closely by floor system III-B with 193.77 kg CO2 eq and 201.87 kg 1.4-DB eq. Studying the two scenarios, the floor systems in Scenario A showed the least impact compared with those in Scenario B. From the perspective of the CML 2001 method, the floor systems of Scenario A generated less environmental impact per impact category indicator than Scenario B, while floor systems I and II contributed least to the environmental impact in general.
In Figure 8, the environmental impacts for the "end-of-life" stages are quantified with the CML methodology, complemented with Table 9, which shows the results in the values of each indicator.   kg CO 2 eq. kg SO 2 eq. kg PO 4 eq. kg C 2 H 4 eq. kg CFC-11 eq. kg 1.4-DB eq. kg Sb eq. I-A 1.2 × 10 1 3.7 × 10 0 5.7 × 10 −2 8.4 × 10 −2 3.2 × 10 −3 2.3 × 10 −6 9.1 × 10 −2 II-A 1.4 × 10 1 4.2 × 10 0 6.5 × 10 −2 9.5 × 10 −2 3.7 × 10 −3 2.7 × 10 −6 1.1 × 10 −1 III-A 2.6 × 10 1 4.8 × 10 0 7.2 × 10 −2 1.1 × 10 −1 4.1 × 10 −3 2.9 × 10 −6 1.1 × 10 −1 IV-A 2.1 × 10 1 6.6 × 10 0 9.9 × 10 −2 1.4 × 10 −1 5.6 × 10 −3 4.2 × 10 −6 1.7 × 10 −1 I-B 1.8 × Finally, a proportional increase in the affectations of scenario B was observed. When comparing both scenarios, it was observed that the floor systems with the least contribution to the environmental impact at the end-of-life stages were I and II. It was also observed that in scenario A, the floor system with the greatest environmental impact was IV-A, while in scenario B, the floor system with the greatest impact was III-B 3.1.3. Sensitivity Analysis of Maintenance-Replacement stages (B2-B4) As discussed in Section 2.6, the building maintenance regulations and manuals only establish, for stage B2, visual inspections of the structural element [78], which, in a utopian approach, would mean that the floor systems of the building would remain unchanged until the end of life. However, in order to know the variability of the environmental impact generated by specific situations that may arise in a building, where total or partial replacement needs might be required, a sensitivity analysis was carried out, incorporating percentage replacement scenarios in the analysis. These scenarios are proposed by including in the total environmental impact of the functional unit, a percentage relative to the environmental impact generated by the substitution scenario. The hypothesis proposed for the scenario considers: The need to replace a percentage of the functional unit, passing through the demolition of the element, handling and management of generated waste, and subsequent reconstruction. For this, the following percentages were established: Replacement of 25% of the functional unit, replacement of 50% of the functional unit, replacement of 75% of the functional unit, and replacement of 100% of the functional unit; compared to a base scenario where no substitution was generated (0%).
In Figure 9, can be seen that the inclusion of these scenarios generated a significant variation in the results, which is relative to the percentages considered. The replacement of constructive elements within a building for reasons other than deterioration is usually not establish within its initial conception. Therefore, it was observed that the selection of elements with less environmental impact would decrease the escalation in environmental loads related to these unforeseeable situations. The foregoing shows that a correct choice of materials, a tight realization or construction of the elements, and an adequate use of them can avoid, in the maintenance phase, the environmental impacts caused by the total or partial replacement of the element analyzed. percentage relative to the environmental impact generated by the substitution scenario. The hypothesis proposed for the scenario considers: The need to replace a percentage of the functional unit, passing through the demolition of the element, handling and management of generated waste, and subsequent reconstruction. For this, the following percentages were established: Replacement of 25% of the functional unit, replacement of 50% of the functional unit, replacement of 75% of the functional unit, and replacement of 100% of the functional unit; compared to a base scenario where no substitution was generated (0%). In Figure 9, can be seen that the inclusion of these scenarios generated a significant variation in the results, which is relative to the percentages considered. The replacement of constructive elements within a building for reasons other than deterioration is usually not establish within its initial conception. Therefore, it was observed that the selection of elements with less environmental impact would decrease the escalation in environmental loads related to these unforeseeable situations. The foregoing shows that a correct choice of materials, a tight realization or construction of the elements, and an adequate use of them can avoid, in the maintenance phase, the environmental impacts caused by the total or partial replacement of the element analyzed.

Discussion of the LCIA Results
Comparative analysis of the floor systems: The floor system with greatest environmental impact was IV, with a value of around 5 points more in scenario A than the points obtained by the systems I and II (5.06 and 4.75, respectively). This is because the quantities of materials needed in its construction, such as concrete and steel, are greater than in the other floor systems mentioned. In addition, the floor systems with lower impact (I and II) contain lightening elements, which reduce the use of these materials (although they increase the amount of wood formwork, making their effect in stage A5 greater than the other floor systems). The floor system with the second highest effect is III, which has a score very similar to that of IV. In this case, the system also contains a high amount of concrete and steel, as well as including the use of EPS as a lightening element. This means that its

Discussion of the LCIA Results
Comparative analysis of the floor systems: The floor system with greatest environmental impact was IV, with a value of around 5 points more in scenario A than the points obtained by the systems I and II (5.06 and 4.75, respectively). This is because the quantities of materials needed in its construction, such as concrete and steel, are greater than in the other floor systems mentioned. In addition, the floor systems with lower impact (I and II) contain lightening elements, which reduce the use of these materials (although they increase the amount of wood formwork, making their effect in stage A5 greater than the other floor systems). The floor system with the second highest effect is III, which has a score very similar to that of IV. In this case, the system also contains a high amount of concrete and steel, as well as including the use of EPS as a lightening element. This means that its environmental impact is related to the production and consumption of this material of petrous origin [92]. The results obtained agree with the conclusions reached in similar research [93][94][95].
Comparative analysis of Scenarios A-B "from cradle to handover": Comparing each floor system in the two scenarios, it can be seen that applying the floor system to a real case increases the environmental impact caused by the system. Figure 10 shows the differences in eco-points of the same floor system in the two scenarios. It is noticeable that, in floor systems I, II, and III, the generated environmental impact increased significantly, by 33-35%, while in floor system IV, the increase was lower, with a total increase of 3%.
Sustainability 2020, 12, x FOR PEER REVIEW 18 of 26 environmental impact is related to the production and consumption of this material of petrous origin [92]. The results obtained agree with the conclusions reached in similar research [93][94][95]. Comparative analysis of Scenarios A-B "from cradle to handover": Comparing each floor system in the two scenarios, it can be seen that applying the floor system to a real case increases the environmental impact caused by the system. Figure 10 shows the differences in eco-points of the same floor system in the two scenarios. It is noticeable that, in floor systems I, II, and III, the generated environmental impact increased significantly, by 33-35%, while in floor system IV, the increase was lower, with a total increase of 3%. The increase in score in Scenario B is due to the increase in the quantification and characterization of the materials used, as a larger amount of steel and concrete are used in constructing the special areas; this in turn leads to a proportional increase in the environmental impact generated. In the case of floor system IV, the lower percentile increase is because the use of these materials does not increase as much, as this floor type is made exclusively of concrete and steel. Additionally, the importance of the lightweight elements for the sustainability of the floor systems is evident, as it has been seen that decreasing the quantities of these materials (such as EPS panels, hollow ceramic, or cement bricks) and using more concrete and steel will generate greater impact (the difference between scenario A and B).
By analyzing the end-of-life stages, a perspective of the environmental repercussions derived from the demolition and disposal of waste in the construction can be obtained. In the results, it can be observed that the increase in Scenario B, related to Scenario A, is different for all the floor systems, showing the variability in the results that can be generated when different construction systems are combined in the analysis of a building. In the Eco-indicator 99 methodology, the floor system "I" had an increase of 29% from scenario A to B, the floor system "II" increased 27%, the floor system III presented the greatest difference in the result obtained between the two scenarios, obtaining an increase of 46%. Finally, the scenario IV had the lowest percentage of increase, this being 18%. Using the CML methodology, it can be seen that the highest impact is due to the contribution in greenhouse gas emissions-kg CO₂ eq. The increase in score in Scenario B is due to the increase in the quantification and characterization of the materials used, as a larger amount of steel and concrete are used in constructing the special areas; this in turn leads to a proportional increase in the environmental impact generated. In the case of floor system IV, the lower percentile increase is because the use of these materials does not increase as much, as this floor type is made exclusively of concrete and steel. Additionally, the importance of the lightweight elements for the sustainability of the floor systems is evident, as it has been seen that decreasing the quantities of these materials (such as EPS panels, hollow ceramic, or cement bricks) and using more concrete and steel will generate greater impact (the difference between scenario A and B).
By analyzing the end-of-life stages, a perspective of the environmental repercussions derived from the demolition and disposal of waste in the construction can be obtained. In the results, it can be observed that the increase in Scenario B, related to Scenario A, is different for all the floor systems, showing the variability in the results that can be generated when different construction systems are combined in the analysis of a building. In the Eco-indicator 99 methodology, the floor system "I" had an increase of 29% from scenario A to B, the floor system "II" increased 27%, the floor system III presented the greatest difference in the result obtained between the two scenarios, obtaining an increase of 46%. Finally, the scenario IV had the lowest percentage of increase, this being 18%. Using the CML methodology, it can be seen that the highest impact is due to the contribution in greenhouse gas emissions-kg CO 2 eq.

Conclusions
This study has made a comparison of the four most commonly used floor systems in the Spanish ambit, from two perspectives: Scenario A, which considers each system as a homogeneous element, and Scenario B, which considers the system applied in a real building conditioned by the different types of surfaces involved in the project. The results corroborate that the LCA method is a suitable tool for analyzing and comparing the environmental impact generated by the different building systems.
Consequently, the comparison of the floor system's life cycle stages shows that those that generate most environmental impact are A1-A3, as the floor systems that use more concrete and steel have the greatest effect, due to their production process.
The development of Scenario A allows the floor system generating the least environmental impact to be identified from a theoretical perspective, considering that in reality the elements are not strictly homogeneous. The results led to the conclusion that the one-way floor systems (type I-A and II-A) generate the least impact, with the results being more sustainable as the homogeneity of the project increases. In this scenario, it can be seen that the reinforced concrete slab floor system generates the biggest impact; therefore, the floor systems with lightening elements are more sustainable from the LCA perspective.
The development of Scenario B allows for obtaining a more realistic approach in the results, because it is closer to the reality of the construction industry; however, these results are subject to the variations inherent to each construction project. In this scenario, the results showed that the differences in the environmental impact of the different floor systems were reduced as a consequence of mixing with other constructive systems. Therefore, the influence of the specific elements can be identified, with the conclusion being that the sustainability of construction systems depends on the specific and geometric characteristics of a building.
According to the results of the stages "from cradle to handover", the floor systems with the best environmental results in terms of LCA are the one-way types I and II. The difference in the environmental impact of the functional unit on both is minimal (with values of 5.60 and 5.91 eco-points in Scenario A and 7.56 and 7.86 eco-points in Scenario B, respectively), and is related to the system of blocks and slabs used. In comparison with floor system III, the two-way waffle system, they generate between 18.49% and 23.88% less impact in Scenario A and from 21.70% to 18.61% less in Scenario B. When compared with floor system IV (reinforced concrete slab), the difference in the impact rises to a reduction of between 55% and 53% in the environmental impact generated in Scenario A and 31.38% to 28.67% in Scenario B. In the end-of-life stages, it can be seen that the demolition works and the waste management of the floor systems I and II continue to be those with the least environmental impact, with a difference from the floor system IV of 40% and 35% in Scenario A, and 30% and 27% in Scenario B, respectively.
The two-way floor system III had values of 7.25 and 9.66 eco-points in Scenarios A and B, the results being due to the quantities of concrete and steel required for the reinforced slabs used in its construction. However, it can be seen that the impact is from 10% to 30% lower than the reinforced concrete slab (type IV) due to the lightweight element (EPS panels). In the end-of-life stages, in Scenario A, it is observed that it generates less impact than IV-A by 26%, while in Scenario B, the environmental impact is greater than IV-B by 11% due to the work required to demolish the floor system.
Floor system IV, the reinforced concrete slab, obtained the highest impact of the eco-points for each scenario (10.66 and 11.02 eco-points). This represented a considerable difference regarding the other floor systems, 47% more than the floor system with the best environmental performance in Scenario A. Despite the results, this floor system is essential in buildings with difficult geometric areas. Therefore, as its use cannot be excluded, efforts must be made to find more sustainable solutions in order replace the process of obtaining raw materials, such as adding lightening agents that adapt to the geometric context or using the system as an auxiliary system in the building rather than as the main construction system.
In the results obtained from the present investigation, it is observed that the environmental impact relative to the end-of-life stages represents 15-21% of the total, if they are analyzed together with the stages "from cradle to handover".
The importance of the analysis of the end-of-life stages in the construction sector has been evidenced in the development and implementation of rules and regulations regarding CDW. However, the uncertainty in the data and the hypotheses that must be stipulated for its calculation condition the results obtained. Being for a future prospective, these results may be affected by the development of new technologies or techniques for the recovery of materials, which could manage to reincorporate a greater percentage of CDWs in the production chain, which will potentially decrease the overall impact of the sector.
Currently, at European level, the recycling and reuse rates of materials vary between each country, where some have achieved percentages of up to 70% (such as Netherlands) [96]; others are far from this percentage. In the case of Spain, the percentage of revalorization of materials has reached 43% [97]. However, the use of recycled materials (such as those from concrete) have been practically used only as aggregates in asphalt or in road construction [96]. Furthermore, its use in the construction of structural elements is currently only in a "recommendations for its use" stage, mostly due to the lack of guarantees of its proper application that ensure the quality of the structural concrete [98]. The foregoing shows the need to carry out studies on the behavior of these recycled concretes as part of a structural system. In addition, in the proposal for future research using the LCA methodology, the inclusion of the analysis of different waste management, as well as the stages of module D-benefits and loads beyond the system (reused, recovery, and/or recycling), can enhance the interest in the inclusion of these aggregates in the constructive elements.
However, the realization of projections and waste management plans must prevail in all construction projects, following the hierarchy of: Prevention of waste generation, preparation for reuse-recycling, and other final recovery scenarios [96]; both in the development of the construction stage, and in the demolition of buildings, to achieve a potential reduction in the damage generated.
Finally, the comparison of the building elements carried out in this work allows the most efficient building system in terms of environmental impact to be identified, as well as generating useful information, which can be studied by construction industry professionals when making decisions about building design. Additionally, it contributes to the awareness of the environmental impact generated by the different systems, to extend the research to other construction systems, and analyze the implementation of measures that reduce the impact located at each stage analyzed.