Aplicação da avaliação do ciclo de vida na otimização de projetos de concreto armado

ac Ambiente Construído Ambient. constr. 1415-8876 1678-8621 Associação Nacional de Tecnologia do Ambiente Construído - ANTAC Resumo O objetivo desta pesquisa foi avaliar a utilização da metodologia de Avaliação do Ciclo de Vida para auxiliar a tomada de decisão em projetos estruturais de concreto armado. Foram estudados modelos estruturais para um edifício de oito pavimentos, com classes de resistência à compressão (fck) do concreto variando de 25 a 50 MPa. Também foram avaliadas alterações nas dimensões dos elementos estruturais, bem como o consumo de materiais componentes da estrutura. Os resultados mostraram que os modelos estruturais para as classes C40 obtiveram os melhores resultados para 67% das categorias de potenciais impactos avaliados, com valores de potenciais impactos variando de 7,4% a 21,2%, incluindo a possibilidade de economizar 18 mil kg de CO2 emitido. Após a realização de uma análise econômica, observou-se que o modelo estrutural para o concreto C40 apresentou a solução ambiental-econômica ótima. Os resultados desta pesquisa indicam a viabilidade da utilização da metodologia de Avaliação do Ciclo de Vida e da análise econômica como ferramentas para auxiliar na tomada de decisão durante o processo de projeto de estruturas de concreto armado. Introduction The construction industry contributes strongly to global economic development and the generation of potential environmental impacts. The sector uses around 50% of all the raw materials consumed in the world, 70% of which are non-renewable. Moreover, 40% of all solid waste generated comes from civil construction, in addition to being responsible for 30% of the greenhouse gases emitted (DIVANDARI; NAJARI, 2016; YAVARI et al., 2017; ALMIRALL et al., 2019; GHAYEB; RAZAK; SULONG, 2020). Therefore, the construction industry faces the challenge of implementing a sustainable model in all its processes, from the efficient use of resources to the incorporation of less polluting materials, creating more environmental-friendly projects (LASVAUX et al., 2015; FERREIRO-CABELLO et al., 2017; SOUTO-MARTINEZ et al., 2017; MARTÍNEZ-MUÑOZ et al., 2020; BALASBANEH; RAMLI, 2020). Among the aspects to be incorporated for the development of environmentally sustainable projects, the optimization of the structural design is extremely important, since the characteristics of the structural system influence mechanical, economic, and environmental performances of the building (FRAILE-GARCIA et al., 2017; XIAO et al., 2018). Nadoushani and Akbarnezhad (2015) indicate that the selection of the best structural design alternative, in environmental aspects, depends on many specific parameters and should only be done after a detailed analysis. Moncaster et al.(2018) observed that the choice of a structural system with lower pollutant emissions has clear implications for mitigating climate change and therefore should always be considered. Reinforced concrete stands out as the most widely used structural material worldwide, with high consumption of materials, particularly concrete, steel, and wood (SALGADO; APUL; GUNER, 2020; SCOPE; VOGEL; GUENTHER, 2021). The sector of Portland cement comprises the largest production chain in civil construction, with an annual average of 20 billion tons of concrete produced worldwide. The consumption of Portland cement in this sector is approximately 3.5 billion tons per year. One should note that the production of Portland cement is extremely impactful since each ton of produced Portland cement uses approximately 1.5 tons of raw materials and between 4000 MJ and 7500 MJ of energy, in addition to the emission of about a ton of CO2. Thus, Portland cement is recognized as a major source of CO2, being responsible for about 80% of the total CO2 emitted in concrete production (DOSSCHE et al., 2016; NOPARAST et al., 2021). Regarding reinforcement, it is estimated that 30% of all steel produced is consumed by the construction sector, which represents about 400 million tons per year (SCOPE; VOGEL; GUENTHER, 2021). In addition to the high energy demand for its production, it is estimated that each ton of steel produced releases approximately 1.9 tons of CO2 (SALGADO; APUL; GUNER, 2020). One way to reduce environmental impacts in reinforced concrete structures lies in the efficient use of materials, from the in-depth study of the structural design, and through the simulation of models that contemplate the variation of concrete strength, reinforcement rate, piece dimension, and consumption of wooden forms (SHARMA et al., 2011). From these simulations, one can observe that there are several structural models for the same building, resulting in different consumption of resources and, consequently, different environmental performances (FRAILE-GARCIA et al., 2016). In the study by Fraile-Garcia et al. (2016), it was observed that the impacts generated by reinforced concrete structures are affected by numerous variables, such as the thickness of structural elements, utilized materials, and structure typology. In the work of Souto-Martinez et al. (2017), in which the objective was to quantify and reduce the possible environmental impacts of concrete buildings, the authors found that innovations in structural geometries maximize the potential of reinforced concrete elements to sequestrate CO2 by approximately 21%. Furthermore, Dossche et al. (2016), Ferreiro-Cabello et al. (2017), Balasbaneh and Ramli (2020), and Ghayeb, Razak and Sulong (2020) found that cement and steel contribute significantly to environmental impacts, therefore creating the need to optimize the consumption of these materials in structural design. Thus, knowing the importance of reinforced concrete structures in the construction sector and the high consumption of materials and pollutant emission in production processes, it is extremely relevant to implement structural design optimization tools, focusing on the assessment of environmental performance, such as Life Cycle Assessment (LCA). LCA is a tool used to identify the potential environmental impacts of a product, service, or process throughout its life cycle. In addition, the tool is often used to analyze conditions and, consequently, search for environmentally viable alternatives (FRAILE-GARCIA et al., 2016; POMMIER et al., 2016; HOLLBERG et al., 2021). Therefore, LCA is indicated to assess the potential environmental impacts of buildings, such as resource consumption, pollutant emission, and waste generation, as it is a broad methodology, applicable in all phases, internationally standardized, and widely used (CHO et al., 2012). LCA can be a methodology used in project decision-making, supporting the choices of the structural system to be used in buildings, following the guidelines for sustainable development, aiming at respecting and preserving the environment (DIVANDARI; NAJARI, 2016; MONCASTER et al., 2018; MARTÍNEZ-MUÑOZ; MARTÍ; YEPES, 2020; HOLLBERG et al., 2021). In this context, the objective of this work was to analyze the use of the Life Cycle Assessment (LCA) methodology to assist in decision-making in structural projects of reinforced concrete, aiming at improving environmental performance by using different classes of concrete strength, altering dimensions of structural elements, as well as changing the consumption of the structure materials (concrete, steel, and wooden form). Were studied structural models for an eight-story building, with six classes of concrete compressive strength (fck), ranging from 25 to 50 MPa [23], for comparative analysis. The LCA methodology and, also, an economic study was employed as tools to aid in the decision-making process. Research method The objective of this study was to estimate the potential environmental impact of a building, in all its phases, from cradle to grave, i.e., extraction of raw material, manufacture of raw material, transport to the construction site, production of the building, use phase, transport to the final destination, and final disposal. To achieve this goal, the Life Cycle Assessment (LCA) method was used. The structure of the LCA method is constructed based on the ISO 14040 (INTERNATIONAL…, 2006) standard. The four phases of an LCA study required by the ISO 14040 series are objective and scope definition, life cycle inventory analysis, life cycle impact assessment, and data interpretation. The objective and scope definition phase aims at defining the goals for LCA application. In the inventory analysis phase, mass and energy flow entering and leaving different stages are listed and, in the impact assessment phase, one calculates the environmental load of the target installation. In the end, at the interpretation stage, one identifies the significant issues of the study and defines conclusions and recommendations. In this analysis, the attempt to determine the function by columns, beams and slabs alone was not considered convenient. The structure of a building works holistically, with the interaction between all components with their interconnected functions. A structural part can perform several functions in the structure, depending on external and internal requests, depending also on the interaction between them. Thereforeforthe Life Cycle Assessment, thecompletestructureofthebuilding, thecompletestructural network, was adopted as the functional unit. Instead of analyzing the isolated sections (which in all strength classes must comply with the executive regulations), the study considers the rates of concrete and steel per m² for this evaluation. Description of the case study The LCA was performed with the functional unit of a standard eight-story Brazilian residential building (Figure 1), according to NBR 12721 (ABNT, 2006). It is worth mentioning that this building typology is widely executed in Brazil, acting as a case study for this work. The typical Brazilian residential building with eight floors is composed of a ground floor and seven standard floors. On the ground floor there is an entrance hall, elevator, stairs and four apartments with two bedrooms, living room, bathroom, kitchen and tank area. Outside, there is a waste room and thirty-two uncovered parking spaces. In the typical floors there is a circulation hall, stairs and four apartments per floor with two bedrooms, living room, bathroom, kitchen and laundry area. The total real area of the typical Brazilian residential building with eight floors is 2,078.00 m². Application of LCA in the case study Objective and scope definition This study applied LCA in a building with a reinforced concrete structure, designed with different values of characteristic resistance to compression, for comparative analysis, to account for the environmental impacts of each of the alternatives, which directly reflect on materials consumption and in the size of structural parts that make up the structure. The functional unit is defined by ISO 14040 (INTERNATIONAL…, 2006), as a quantified performance of a product system for use as a reference unit. In this assessment, as mentioned above, the functional unit adopted was a standard eight-story Brazilian residential building, with 2.078 m² structural area and the with the ability to withstand the characteristic load of 5,5 kN/m² (without counting the weight of the structure itself). For this functional unit, a comparative LCA was performed, analyzing the structural design with six different concrete classes. Figure 1 Design of the typical Brazilian residential building The structural system in reinforced concrete has the function of supporting the building, which is, absorbing and transmitting to the foundations all acting forces, with pre-defined safety, according to the minimum requirements of NBR 6118 (ABNT, 2014) and the prescriptions of NBR 6120 (ABNT, 2019). The description of the function of the structural system is shown in Table 1. The minimum expected durability of reinforced concrete structure project is 50 years for structural systems such as the one studied in this article, as estimated by NBR 15575 (ABNT, 2013) in reference to NBR 8681 (ABNT, 1984). Although the concrete classes are different, is important to the transparency of this evaluation to clarify that for this study all functional units adopted were considered with similar service life. The results obtained through the structural design of the building are valid and safe, as they resulted from the envelope of calculation requests, formed by a minimum of fifty combinations between Ultimate Limit State (ruin) and Service Limit State, which were then considered all normative requests (such as winds, accidental, permanent loads). Itshouldbenotedthattheanalysisofthesuperstructure was carried out withoutconsideringthefoundations, whichcanvary in different locations. Since the functional unit considered was the building, complete structural lattice, with 2,078.00 m², its structural design was carried out with six classes of concrete characteristic resistance to compression (fck), which are: C25 (25 MPa), C30 (30 MPa), C35 (35 MPa), C40 (40 MPa), C45 (45 MPa), and C50 (50 MPa). Was used the TQS Structural Engineering Software (version 18.17) to execute the structural project. During the process of designing the structure, was started the project using the resistance class C25. Then, there was a change in the strength class of the concrete, without changing the dimensions of the structural components, to class C30. The maintenance of dimensions in the analysis of structural parts between the values of classes C25 and C30 aimed at verifying the behavior and trends of the results obtained. The definition of the dimensions immediately results in different reinforcement rates per volume of concrete in the structure, significantly altering the consumption of materials. For concrete classes between C35 and C50, a progressive reduction was made in the dimensions of slabs, beams, and columns, until reaching the smallest possible dimensions that still met the required demands of safety and service (ABNT, 2015, 2019, 1984). When attempting to reduce the dimensions of structural parts from class C45 to class C50, it was verified that the operation was impeded due to normative prescriptions. As a result, dimensions of the concrete class C45 were maintained. It is worth mentioning that different reinforcement rates were calculated for each class of concrete studied. Quantities are shown in Table 2. As for geographic scope, the building is located in the southeast region of Brazil, in a city in the south of Minas Gerais state, with approximately 150,000 inhabitants (Poços de Caldas-MG). Table 1 Function of the structural system, according to ABNT 6118 and ABNT 6120 Environmental Aggressiveness Class Moderate II - Urban Region Reinforcement cover Beams 3 cm Slabs 2.5 cm Requests Adopted Slabs Permanent overload 1 kN/m² Accidental Overload 1.5 kN/m² Walls on slabs 5 kN/m Beams Walls 5 kN/m Wind Basic Speed (S1) 35 m/s Topographic Factor (S2) 1 Roughness Category (S2) IV Building Class (S2) B Statistical Factor (S3) 1 Table 2 Quantification of materials for the production of concrete - values considered for each m³ of concrete Materials Concrete Class C25 C30 C35 C40 C45 C50 Portland cement CP III (kg) 310 340 370 389 405 421 Sand (kg) 870 770 744 739 734 730 Gravel (kg) 930 970 960 1,031 1,035 1,038 Water (liter) 180 185 190 177 173 169 The boundaries of the system are divided into four elementary processes: reinforced concrete structure; concrete distribution on site; use phase; and final landfill. Figure 2 illustrates the product system flowchart. The descriptions of characteristics concerning impact categories and the comments on the results obtained follow the EDIP 1997 method. This method is also indicated for its global application scope, since there are no methods developed for Brazil or South America (FERRO et al., 2018; SOUZA et al., 2018). The study is mostly based on secondary data, obtained from the software GaBiand the databaseEcoinvent, concerning chains of electricity production, water extraction and processing, cement production, steel production, wood production, final deposition of civil construction, and input transportation by truck (diesel). Some primary data has been collected, replacing secondary ones. The primary data collected relate to the quantity of raw material for cement production, directly informed by the manufacturer, and the concrete production phase at the plant, including its transportation to the construction site. Was used data on the production process of crushed stone, taken from the study by Rossi (2013). Life Cycle Inventory (LCI) From the collected data and by using the studied functional unit, the Life Cycle Inventory (LCI) was carried out. As this is a comparative study, it is worth mentioning that six classes of compressive strengths of concrete were analyzed. Results of the material consumption of the functional unit, for the execution of the structure, as well as its indexes, are presented in Table 3. For this analysis, was considered the reservoir cover and bottom, the roof, the 2nd to 8th-floor types, the 1st floor, the ground floor 1, and the ground floor 2. In Table 3 it is observed that class C40 has the lowest cement consumption index/m², 66.13 kg/m², despite not having the lowest concrete consumption index/m², 17 m³/m², higher than class C45 and C50, both with 16.8 m³/m². Classes C45 and C50, despite having a greater reduction in concrete volumes compared to class C40, had a higher consumption of cement/m², but still lower than the reference class C25 and C30 (which did not suffer a reduction in structural parts in compared to C25). Such information is important in further analysis of some potential impact categories. In the case of steel consumption, through the transposition of the indices referring to the consumption of steel/m3 of concrete and steel/m² structural area, the graph shown in Figure 3 is presented. Figure 2 Product system flowchart Table 3 Consumption of materials and indexes of concrete classes C25 - C50 Concrete Class Concrete Wooden Forms Steel Consuption (m³) Rate (m³/m²) Consuption (m²) Rate (m²/m²) Consuption (kg) Rate (kg/m²) Rate (kg/m³) C25 471.4 0.23 4,596.8 2.2 41,619.2 20.0 88.3 C30 471.4 0.23 4,596.8 2.2 40,130.8 19.3 85.1 C35 401.0 0.19 4,464.6 2.1 39,596.1 19.1 98.7 C40 355.6 0.17 4,266.6 2.05 43,506.8 20.9 122.3 C45 348.9 0.168 4,266.6 2.05 43,938.3 21.1 125.9 C50 348.9 0.168 4,266.6 2.05 43,704.7 21.0 125.3 Figure 3 Consumption steel/m² and steel/m³ concrete x concrete strength class In Figure 4 its can be seen that class C35 has the lowest consumption index of steel/m², 19.1 kg/m², despite not having the lowest consumption index of steel/m³ of concrete, 98.7 kg/m³. With the reduction of the section due to the increase in the strength class of the concrete, there was a reduction in the structural mas sof steel/m². In the case of steel, the section reduction for this reference strength class. Life Cycle Impact Assessment (LCIA) From the conduction of the LCI, the Life Cycle Impact Assessment (LCIA) was implemented, defining the classification of impacts and later their characterization. The characterization factor employed was the EDIP 1997 method. The impact categories analyzed were acidification potential, global warming potential, eutrophication, ozone depletion potential, photochemical ozone formation (high and low NOx), with main characteristics observed in studies of concrete structures (YAVARI et al., 2017; MEEX et al., 2018; BALASBANEH; RAMLI, 2020; HOLLBERG et al., 2021). Characterization of the impact categories was performed using the software GaBi (PE International GmbH). The GaBisoftware and the Ecoinvent database are in line with recommendations of the documentation in the International Reference Life Cycle Data System (ILCD). The GaBi documentation also includes criteria of the ILCD format, created by JRC-IES of the European Commission, European Platform on LCA, Copyright©, European Commission. Life Cycle Interpretation In this stage, the results obtained were interpreted, generating subsidies for decision-making and highlighting opportunities to improve the environmental performance of buildings. Results and discussions General results of potential environmental impacts for the six structural models are shown below in Table 4 and Figure 4. Analyzing the results presented, one can identify that the structural models that had the higher impact potential are the resistance classes C25 and C30, while classes with the least potential impact were C40, C45, and C50. Table 4 presents the absolute values of environmental impacts for each category analyzed. One observes that there were slight differences between the models analyzed for some impact categories, such as OD (ozone depletion), and significant differences for other categories, that are indicated in the table and explained in the following paragraphs. Solvents, aerosols, foams for insulation, sand (reflection of ultraviolet radiation), emissions in the production of steel, and others are among the chemical substances used in civil construction that affect the Ozone Depletion category. However, it is worth noting that most substances that emit CFC gases are already massively prohibited, which may explain the low magnitude of the impact found in this study. Hence, this research will not delve into the discussion of this category. The C30 concrete class had the highest impact potential for 67% of the studied categories (AC, GW, ET, and HPO). These results can be explained by the increased strength of concrete in this class, concerning C25, though without reduction in the dimensions of beams and columns, as occurred progressively in the classes between C35 and C50. Although showing the same consumption of concrete as class C25, class C30 stood out due to higher cement consumption per area, with 78.2 kg/m² of cement being used, which may explain the consequent increase in the potential for impact of this resistance class compared to the reference (class C25, with consumption of 71.3 kg/m²), despite the reduction in steel consumption obtained (20.0 and 19.3 kg/m² for classes C25 and C30, respectively). Concrete consumption occurred in the range of 0.168 m³/m² and 0.17 m³/m² among structural models for the three classes with the lowest overall potential impacts (C40, C45, and C50). Steel consumption rates for these three strength classes ranged from 122.3 kg/m³ to 125.3 kg/m³ of concrete, corresponding to values from 20.9 kg/m² to 21.1 kg/m². As for the consumption rates of wooden forms, these three classes of resistance showed equal results up to the second decimal place, 2.05 m²/m² of wooden form/built area, due to regulatory limitations. Figure 4 graphically highlights the dimension of the potential environmental impacts for each resistance class analyzed in this study. From the Figure 4, can observed that the variation in the environmental performance between the classes, demonstrated by the aforementioned impact categories, in addition to the resistance class with the least potential impact for this analysis, the C40 class. Among classes C40, C45, and C50, concrete class C40 had the lowest potential environmental impacts for 67% of the impact categories analyzed, namely acidification (AC), global warming (GW), photochemical ozone formation - high NOx (HPO), and photochemical ozone formation - lower NOx (LPO). The lower impacts of the structural solution class C40 ranged from 7.4 to 21.2% for four of the six categories analyzed. These results can be explained due to the reduction of structural elements with the increase of resistance classes (C25 to C45) and the consequent reduction in the amount of concrete and steel consumed. This result is supported by the values of lower cement consumption (66.13 kg/m²) and by presenting the lowest consumption rates for steel (122.3 kg/m³) and concrete (20.9 kg/m²). Table 4 Potential environmental impacts of the structure of a standard building with eight floors [25] and 2,078 m² Impact Category Unit C25 C30 C35 C40 C45 C50 AC kg SO2 eq. 966 981 933 908 912 918 GW kg CO2 eq. 243,126 249,360 236,892 230,658 232,736 236,892 ET kg NO3- eq. 1,477 1,500 1,390 1,380 1,376 1,386 OD kg R11- eq. 0.00049 0.00048 0.00046 0.00050 0.00050 0.00050 HPO kg Ethane eq. 85 86 82 81 81 81 LPO Kg Ethene eq. 104 86 82 82 82 82 Note: AC: acidification; GW: global warming; ET: eutrophication; OD: ozone depletion; HPO: photochemical ozone formation (high NOx); and LPO: photochemical ozone formation (lower NOx). Figure 4 Distribution of potential environmental impacts for different classes of concrete strength For the GW category, the C40 class had the lowest environmental impact, while the C30 class had the highest impact potential. The percentage reduction was 7.5%, and although it seems to be a low value, converting to the value of kg of CO2 equivalent, the possible choice of class C40 for the production of this particular standard building with eight floors, instead of choosing class C30, would save approximately 18 thousand kg of CO2 equivalent emitted to the planet. By separately investigating the contribution of each of the three main components of the reinforced concrete structure (concrete, steel, and wooden forms) to the impact categories analyzed, the reference class C25 (minimum strength class for reinforced concrete structures in Brazil) was chosen for a detailed evaluation. The detailed results are shown in Table 5 and Figure 5. In general, for class C25, the wooden forms used in the construction of the building are responsible for most of the potential environmental impacts, presenting potential impacts of up to 61.7%, represented by impact categories: AC, ET, HPO, and LPO. This result is explained by the great distances involved in wood transportation from the extraction site to the consumption centers, which causes the high amount of emissions shown in Table 6. The native sawn wood from the Amazon rainforest, accompanied by a Document of Forest Origin (DOF) from the Brazilian Institute of the Environment and Renewable Natural Resources (IBAMA), from the Ministry of the Environment, is transported in Brazil over long distances by road. A large part of the volume of sawn wood, originating in the Amazon, travels between 1,500 and 3,000 km. In this research, a distance of 1,956 km was assumed, from the place of extraction to the place of consumption. In this context, the emission factor ranges being between 12.8 g of CO2/t.km and 50.6 g of CO2/ t.km, depending on the type of cargo truck (CAMPOS; PUNHAGUI; JOHN, 2011). Some works propose the replacement of sawn wood by plywood (AHMAD et al., 2013; PUETTMANN; CONSULTANTAS; ONEIL, 2013; POMMIER et al., 2016; JIA et al., 2019). Jia et al. (2019) show that plywood is a product commonly used in civil construction to replace traditional materials. Pommieret al. (2016) mentioned that plywood panels have been marketed worldwide for over 100 years, with successive innovations, from the use of environmental-friendly glues to the employment of different types of wood treatment, thus more environmentally appropriate. Table 5 Potential environmental impacts of a standard building with eight floors [25], concrete resistance class C25, and 2,078 m² Impact category Unit C25 (global value) Concrete Wooden forms Steel AC kg SO2 eq. 966 283 505 167 GW kg CO2 eq. 243,126 105,874 77,094 55,898 ET kg NO3- eq. 1,477 0,408 0,912 0,137 OD kg R11- eq. 0,00048833 0,00004209 0,00000004 0,00043430 HPO kg ethane eq. 85 16 49 20 LPO kg Ethene eq. 104 17 44 24 Note: AC: acidification; GW: global warming; ET: eutrophication; OD: ozone depletion; HPO: photochemical ozone formation (high NOx); and LPO: photochemical ozone formation (lower NOx). Figure 5 Contribution of potential environmental impacts of class C25 for the different impact categories analyzed The production of plywood in Brazil has been increasing, with an annual production of about 260,000 m³. Compared to sawn wood production centers, plywood production centers are located closer to consumer centers in Brazil. Compared to long-distance transportation, closer locations contribute substantially to the control of environmental impacts (AHMAD et al., 2013; POMMIER et al., 2016; JIA et al., 2019). The distances considered for wood transportation in this study caused an increase in the potential impact generated by the wooden forms of approximately 77,000 kg of carbon dioxide (CO2) and 500 kg of sulfur dioxide (SO2) emitted for the construction of a standard eight-story building. The use of plywood panels, which have shorter transportation distances between factories and consumer centers, can help to mitigate these impacts. The C25 class presented steel as the material with the higher impact on OD, with the contribution of 88.9%. This result is related to emissions of halocarbons, that is, CFC, HCFC, halogens, and other gases containing bromine and chlorine, during the steel production process. According to Renzulli et al. (2016), the impact caused by the manufacture of steel in the ozone layer is mainly due to emissions from the blast furnace and, depending on the geographic scope, emissions from the transportation of raw materials used. Among structure components, concrete was responsible for the higher environmental impacts in the GW category, mainly related to emissions during cement production, that was responsible for 43.5% of the potential environmental impacts. Xiao et al. (2018) studied the environmental impacts of two 12-story twin towers, one with natural aggregate and the other with recycled aggregate. The authors mention that the production of cement, together with long-distance transportation of raw materials, was the main responsible for the impact on global warming of the studied buildings. Dossche et al. (2016) still add that the production of Portland cement is largely responsible for the impacts of concrete production, with around 74% to 81% of the total CO2 emitted in the production of concrete only. According to Scrivener, John and Gartner (2018), cement is the largest mass-manufactured product on Earth and constitutes an important part of the built environment, though its environmental impact has been supporting research on mitigating CO2 emissions. The reduction in concrete consumption, by the reduction in dimensions structures in the classes studied, can mitigate the potential environmental impact, as can be noticed by the lowest GW value of the C40 class. Economic implantation analysis The results of this study demonstrated that class C40 had the lowest results of potential environmental impacts in approximately 67% of the impact categories. Complementarily to the LCA study, a total cost survey was carried out for the implantation of the structures to the different classes of concrete strength, as seen in Table 6. It is important to note that the survey was based on average values practiced in the region of the study. From Table 6, one can see that resistance classes with the lowest cost were C35 and C40, while the classes with the highest cost were C25 and C50. The C50 class, which presented the highest cost among resistance classes (U$ 53.87/m²), showed values 7.9% and 6.1% higher than the C35 and C40 classes, respectively. While class C25, used as a reference, showed higher values than classes C35 and C40, which had lower cost/area indexes, around 6.6% and 4.7%, respectively. Among structure components, steel was responsible for an average of 44% of the cost, concrete accounted for a mean value of 35%, and wooden forms were responsible for an average of 21% of the total cost of the structure. Class C30 presented a higher percentage of cost/area relative to concrete, among other classes, with a value of 37.3%. This high percentage can be explained due to the increase in the strength class and respective cement content, without reducing the dimensions of the structural elements. Figure 6 correlates two of the most used impact categories to highlight environmental impacts, global warming and acidification, and the cost per square meter for each class of concrete strength. Despite the variation of these values geographically and temporally, the resistance classes with the lowest cost in this study were C35 and C40. To the detriment of the correlation of environmental impacts and associated costs, class C40 was the second lowest cost among studied classes (only 2% above the cost of C35) and presented the lowest impact value on global warming, as can be seen in Figure 4. In this case, it should also be noted that the choice of C40, instead of C35, has a benefit related to structure durability, since an increase in concrete strength is directly related to the durability of the reinforced concrete structure. Thus, among the classes presented and the impact categories analyzed, the convergence of technical, environmental, and economic indicators presented in this study indicate class C40 as the most sustainable choice for the execution of the structure of the standard eight-story building addressed. Table 6 Structure costs/m² of the different concrete strength classes1 Resistance Class C25 C30 C35 C40 C45 C50 Material and Cost Concrete (m³/m²) 0.23 0.23 0.19 0.17 0.168 0.168 Cost (U$/m²) 19.11 19.77 17.16 16.33 17.56 19.84 Steel (kg/m²) 20 19.3 19.1 20.9 21.1 21 Cost (U$/m²) 22.64 21.83 21.60 23.67 23.87 23.78 Wooden Forms (m²/m³) 2.2 2.2 2.1 2.05 2.05 2.05 Cost (U$/m²) 11.38 11.38 10.86 10.60 10.60 10.60 Total (U$/m²) 53.12 52.98 49.63 50.60 52.03 53.87 Note: 1Unit costs based on the table of the National System of Costs Survey and Indexes of Construction (SINAP) of March 2021: steel U$ 1.13/kg; wooden form U$ 5.17/m²; concrete (pumping included): C25 U$ 83.09/m³; C30 U$ 85.96/m³; C35 U$ 90.26/m³; C40 U$ 95.99/m³; C45 U$ 104.58/m³; C50 U$ 116.04/m³. Figure 6 (a) Analysis of the impact of Acidification for concrete strength classes versus cost ($/m²); and (b) Analysis of the impact of Global Warming for concrete strength classes versus cost ($/m²) Conclusions The initial objective of this study was achieved, demonstrating that the use of the LCA methodology can assist in decision making during the design process of reinforced concrete structures, identifying critical points subject to adjustments, and aiming at the best environmental performance of the structural design. Results showed that the structural models for classes C40, C45, and C50 presented the best results for the impact categories evaluated. Particularly, the C40 class presented as the best option for the evaluated functional unit (the typical Brazilian 8-story building), with the lowest potential impact for 67% of the categories studied, including the possibility of saving 18 thousand kg of CO2 emitted to the planet, if this class is chosen instead of class C30. Analyzing the contribution for the potential impact, the wooden forms was the major contributor for four of six impact categories, mainly regards to the wood transportation. Other materials and solutions for wooden forms should be studied, such as the use of plywood panels, shorter transport distances (which varies regionally and from country to country), or even the possibility of using precast slabs, which practically do not require shoring, and can be the basis for future studies. With this assessment, suggestions can be made to the structural designers for decision-making in the design of buildings similar to the functional unit analyzed, aiming at the maximum reduction of structural parts and the verification of concrete and steel consumption rates. In the present study, it was also evident that the environmental assessment carried out in conjunction with the economic analysis enables to obtain an optimal result for resource use (concrete, steel, and wooden forms) in structures. Additionally, the reduction of the dimensions of structural elements together with the elevation of concrete strength were fundamental for the optimization of the project and, consequently, to reduce costs and potential environmental impacts of the reinforced concrete structure. Regarding the economic analysis of the structure, the lowest values obtained were for structural models C35 and C40. In this context, the C40 model presents itself as the optimal option in this study, in addition to presenting an increase in concrete durability compared to C35, since the increase of the concrete class is directly proportional to the longevity of the structure. The designer is largely responsible for the overall efficiency of the structural design, decisively influencing the performance, durability and final cost of construction. The realization of the LCA for the 5 strength classes of the evaluated functional unit showed that the reduction of structural parts, provided by the increase in the strength classes of concrete, is a favorable procedure for the better environmental performance of the structure. The recommendation to structural designers, for decision making in the design of buildings similar to the analyzed functional unit (8 floors), is to use as the first goal the maximum reduction of structural parts. Then the use of class C40 as the initial objective and the verification of the rates of concrete and steel by the structural area, in the case of this class of values on the order of 0.17 m³/m² and 20.9 kg/m² (corresponding to 122.3 kg /m³ of concrete), respectively. Consumption rate values are easily obtained using of calculation and verification programs routinely in structural design offices and often requested by contractors. Finally, some future research can be recommended after this study, such as to test different materials and constructive units, like slabs, can be evaluated for the structure design. Variations can be tested in sensitivity analyzes or in adoption of consequential LCA to expand the results obtained. This assessment focused on the economic study of the implantation of the structure, however new research shoud be encouraged to study the cost of maintaining the building. References AHMAD, S. et al. Life cycle inventory for palm based plywood: a gate-to-gate case study. AIP Conference Proceedings, Bangi, p. 569-575, 2013. AHMAD S. Life cycle inventory for palm based plywood: a gate-to-gate case study AIP Conference Proceedings Bangi 569 575 2013 ALMIRALL, C. et al. Environmental effects of using different construction codes applied to reinforced concrete beam designs based on Model Code 2010 and Spanish Standard EHE-08. Engineering structures, Barcelona, v. 179, p. 438-447, 2019. ALMIRALL C. Environmental effects of using different construction codes applied to reinforced concrete beam designs based on Model Code 2010 and Spanish Standard EHE-08 Engineering structures Barcelona 179 438 447 2019 ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 12721: avaliação de custos para incorporação imobiliária e outras disposições para condomínios edifícios: procedimentos. Rio de Janeiro, 2006. ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS NBR 12721: avaliação de custos para incorporação imobiliária e outras disposições para condomínios edifícios: procedimentos Rio de Janeiro 2006 ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 15575: edificações habitacionais: desempenho. Rio de Janeiro, 2013. ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS NBR 15575: edificações habitacionais: desempenho Rio de Janeiro 2013 ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 6118: projeto de estruturas de concreto: procedimento. Rio de Janeiro, 2014. ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS NBR 6118: projeto de estruturas de concreto: procedimento Rio de Janeiro 2014 ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 6120: cargas para o cálculo de estruturas de edificações. Rio de Janeiro, 2019. ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS NBR 6120: cargas para o cálculo de estruturas de edificações Rio de Janeiro 2019 ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 8681: ações e segurança nas estruturas. Rio de Janeiro, 1984. ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS NBR 8681: ações e segurança nas estruturas Rio de Janeiro 1984 ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 8953: concreto para fins estruturais: classificação pela massa específica, por grupos de resistência e consistência. Rio de Janeiro, 2015. ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS NBR 8953: concreto para fins estruturais: classificação pela massa específica, por grupos de resistência e consistência Rio de Janeiro 2015 BALASBANEH, A. T.; RAMLI, M. Z. A comparative life cycle assessment (LCA) of concrete and steel-prefabricated prefinished volumetric construction structures in Malaysia. Environmental Science and Pollution Research, Parit Raja, v. 27, p. 43186-43201, 2020. BALASBANEH A. T. RAMLI M. Z. A comparative life cycle assessment (LCA) of concrete and steel-prefabricated prefinished volumetric construction structures in Malaysia Environmental Science and Pollution Research Parit Raja 27 43186 43201 2020 CAMPOS, E. F.; PUNHAGUI, K. R. G.; JOHN, V. M. Emissão de CO2 do transporte da madeira nativa da Amazônia. Ambiente Construído, Porto Alegre, v. 11, n. 2, p. 157-172, abr./jun. 2011. CAMPOS E. F. PUNHAGUI K. R. G. JOHN V. M. Emissão de CO2 do transporte da madeira nativa da Amazônia Ambiente Construído Porto Alegre 11 2 157 172 abr-jun 2011 CHO, Y. S. et al. LCA application in the optimum design of high rise steel structures. Renewable and Sustainable Energy Reviews, Ansan, v. 16, p. 3146-3153, 2012. CHO Y. S. LCA application in the optimum design of high rise steel structures Renewable and Sustainable Energy Reviews Ansan 16 3146 3153 2012 DIVANDARI, J.; NAJARI, F. The structure of the building life cycle assessment (LCA) for selecting sustainable materials in residential complexes in Tehran. The Turkish Online Journal of Design, Art and Communication, Kashan, v. 10, p. 2155-2176, 2016. DIVANDARI J. NAJARI F. The structure of the building life cycle assessment (LCA) for selecting sustainable materials in residential complexes in Tehran The Turkish Online Journal of Design, Art and Communication Kashan 10 2155 2176 2016 DOSSCHE, C. et al. A plant based LCA of high-strength prestressed concrete elements and the assessment of a practical ecological variant. Cement and Concrete Composites,Ghent, v. 73, p. 192-202, 2016. DOSSCHE C. A plant based LCA of high-strength prestressed concrete elements and the assessment of a practical ecological variant Cement and Concrete Composites Ghent 73 192 202 2016 FERREIRO-CABELLO, J. et al. Sensitivity analysis of Life Cycle Assessment to select reinforced concrete structures with one-way slabs. Engineering Structures, Logroño, v. 132, p. 586-596, 2017. FERREIRO-CABELLO J. Sensitivity analysis of Life Cycle Assessment to select reinforced concrete structures with one-way slabs Engineering Structures Logroño 132 586 596 2017 FERRO, F. S. et al. Environmental aspects of oriented strand boards production. A Brazilian case study. Journal of Cleaner Production, São Carlos, v. 183, p. 710-719, 2018. FERRO F. S. Environmental aspects of oriented strand boards production. A Brazilian case study Journal of Cleaner Production São Carlos 183 710 719 2018 FRAILE-GARCIA, E. et al. Optimization based on life cycle analysis for reinforced concrete structures with one-way slabs. Engineering Structures , Logroño, v. 109, p. 126-138, 2016. FRAILE-GARCIA E. Optimization based on life cycle analysis for reinforced concrete structures with one-way slabs Engineering Structures Logroño 109 126 138 2016 FRAILE-GARCIA, E. et al. Repercussion the use phase in the life cycle assessment of structures in residential buildings using one-way slabs. Journal of Cleaner Production , Logroño, v. 143, p. 191-199, 2017. FRAILE-GARCIA E. Repercussion the use phase in the life cycle assessment of structures in residential buildings using one-way slabs Journal of Cleaner Production Logroño 143 191 199 2017 GHAYEB, H. H.; RAZAK, H. A.; SULONG, N. R. Evaluation of the CO2 emissions of an innovative composite precast concrete structure building frame. Journal of Cleaner Production , Kuala Lumpur, v. 242, p. 118567, 2020. GHAYEB H. H. RAZAK H. A. SULONG N. R. Evaluation of the CO2 emissions of an innovative composite precast concrete structure building frame Journal of Cleaner Production Kuala Lumpur 242 118567 118567 2020 HOLLBERG, A. et al. Review of visualising LCA results in the design process of buildings. Building and Environment, Gothenburg, v. 190, p. 107530, 2021. HOLLBERG A. Review of visualising LCA results in the design process of buildings Building and Environment Gothenburg 190 107530 107530 2021 INTERNATIONAL ORGANIZATION OF STANDARDIZATION. ISO 14040: environmental management e life cycle assessment e principles and framework. Geneva, 2006. INTERNATIONAL ORGANIZATION OF STANDARDIZATION ISO 14040: environmental management e life cycle assessment e principles and framework Geneva 2006 JIA, L. et al. Life cycle assessment of plywood manufacturing process in China. International Journal of Environmental Research and Public Health, Shaanxi, v. 16, p. 2037, 2019. JIA L. Life cycle assessment of plywood manufacturing process in China International Journal of Environmental Research and Public Health Shaanxi 16 2037 2037 2019 LASVAUX, S. et al. Comparison of generic and product-specific Life Cycle Assessment databases: application to construction materials used in building LCA studies. The International Journal of Life Cycle Assessment,Yverdon-les-Bains, v. 20, p. 1473-1490, 2015. LASVAUX S. Comparison of generic and product-specific Life Cycle Assessment databases: application to construction materials used in building LCA studies The International Journal of Life Cycle Assessment Yverdon-les-Bains 20 1473 1490 2015 MARTÍNEZ-MUÑOZ, D.; MARTÍ, J. V.; YEPES, V. Steel-concrete composite bridges: design, life cycle assessment, maintenance, and decision-making. Advances in Civil Engineering, Valência, v. 2020, p. 1-13, 2020. MARTÍNEZ-MUÑOZ D. MARTÍ J. V. YEPES V. Steel-concrete composite bridges: design, life cycle assessment, maintenance, and decision-making Advances in Civil Engineering Valência 2020 1 13 2020 MEEX, E. et al. Requirements for applying LCA-based environmental impact assessment tools in the early stages of building design. Building and Environment , Diepenbeek, v. 133, p. 228-236, 2018. MEEX E. Requirements for applying LCA-based environmental impact assessment tools in the early stages of building design Building and Environment Diepenbeek 133 228 236 2018 MONCASTER, A. M. et al. Why method matters: temporal, spatial and physical variations in LCA and their impact on choice of structural system. Energy and Buildings, Edinburgh, v. 173, p. 389-398, 2018. MONCASTER A. M. Why method matters: temporal, spatial and physical variations in LCA and their impact on choice of structural system Energy and Buildings Edinburgh 173 389 398 2018 NADOUSHANI, Z. S. M.; AKBARNEZHAD, A. Effects of structural system on the life cycle carbon footprint of buildings. Energy and Buildings , v. 102, p. 337-346, 2015. NADOUSHANI Z. S. M. AKBARNEZHAD A. Energy and Buildings 102 337 346 2015 NOPARAST, M. et al. Development of a non-dominated sorting genetic algorithm for implementing circular economy strategies in the concrete industry. Sustainable Production and Consumption, Teheran, v. 27, p. 933-946, 2021. NOPARAST M. Development of a non-dominated sorting genetic algorithm for implementing circular economy strategies in the concrete industry Sustainable Production and Consumption , Teheran 27 933 946 2021 POMMIER, R. et al. LCA (Life Cycle Assessment) of EVP - Engineering veneer product: Plywood glued using a vacuum moulding technology from green veneers. Journal of Cleaner Production , v. 124, p. 383-394, 2016. POMMIER R. LCA (Life Cycle Assessment) of EVP - Engineering veneer product: Plywood glued using a vacuum moulding technology from green veneers Journal of Cleaner Production 124 383 394 2016 PUETTMANN, M.; CONSULTANTS, W. E.; ONEIL, E. Cradle to Gate Life Cycle Assessment of Softwood Lumber Production from the Pacific Northwest. Consortium for Research on Renewable Industrial Materials (CORRIM), 2013. Available: Available: https://corrim.org/pubs/reports/2013/phase1_updates/PNW%20Glulam%20LCA%20report%201_7_13%20final.pdf . Accessed: 15 jun. 2022. PUETTMANN M. CONSULTANTS W. E. ONEIL E. Cradle to Gate Life Cycle Assessment of Softwood Lumber Production from the Pacific Northwest . Consortium for Research on Renewable Industrial Materials (CORRIM) 2013 Available: https://corrim.org/pubs/reports/2013/phase1_updates/PNW%20Glulam%20LCA%20report%201_7_13%20final.pdf 15 jun. 2022 RENZULLI, P. A. et al. Life cycle assessment of steel produced in an Italian integrated steel mill. Sustainability, v. 8, n. 8, p. 719. 2016. RENZULLI P. A. Life cycle assessment of steel produced in an Italian integrated steel mill Sustainability 8 8 719 719 2016 ROSSI, E. Avaliação do ciclo de vida da brita para a construção civil: estudo de caso.São Carlos, 2013. Dissertation (Master in Urban Engineering) - Federal University of São Carlos, São Carlos, 2013. ROSSI E. Avaliação do ciclo de vida da brita para a construção civil: estudo de caso São Carlos, 2013 Dissertation (Master in Urban Engineering) Federal University of São Carlos São Carlos 2013 SALGADO, R. A.; APUL, D.; GUNER, S. Life cycle assessment of seismic retrofit alternatives for reinforced concrete frame buildings. Journal of Building Engineering, v. 28, p. 101064, mar. 2020. SALGADO R. A. APUL D. GUNER S. Life cycle assessment of seismic retrofit alternatives for reinforced concrete frame buildings Journal of Building Engineering 28 101064 101064 03 2020 SCOPE, C.; VOGEL, M.; GUENTHER, E. Greener, cheaper, or more sustainable: Reviewing sustainability assessments of maintenance strategies of concrete structures. Sustainable Production and Consumption , v. 26, p. 838-858, 2021. SCOPE C. VOGEL M. GUENTHER E. Greener, cheaper, or more sustainable: Reviewing sustainability assessments of maintenance strategies of concrete structures Sustainable Production and Consumption 26 838 858 2021 SCRIVENER, K. L.; JOHN, V. M.; GARTNER, E. M. Eco-efficient cements: Potential economically viable solutions for a low-CO2 cement-based materials industry. Cement and Concrete Research, v. 114, p. 2-26, 2018. SCRIVENER K. L. JOHN V. M. GARTNER E. M. Eco-efficient cements: Potential economically viable solutions for a low-CO2 cement-based materials industry Cement and Concrete Research 114 2 26 2018 SHARMA, A. et al. Life cycle assessment of buildings: a review. Renewable and Sustainable Energy Reviews , v. 15, p. 871-875, 2011. SHARMA A. Life cycle assessment of buildings: a review Renewable and Sustainable Energy Reviews , 15 871 875 2011 SOUTO-MARTINEZ, A. et al. A mathematical model for predicting the carbon sequestration potential of ordinary portland cement (OPC) concrete. Construction and Building Materials, v. 147, p. 417-427, 2017. SOUTO-MARTINEZ A. A mathematical model for predicting the carbon sequestration potential of ordinary portland cement (OPC) concrete Construction and Building Materials 147 417 427 2017 SOUZA, A. M. et al. Wood-based composite made of wood waste and epoxy based ink-waste as adhesive: A cleaner production alternative. Journal of Cleaner Production , v. 193, p. 549-562, 2018. SOUZA A. M. Wood-based composite made of wood waste and epoxy based ink-waste as adhesive: A cleaner production alternative Journal of Cleaner Production 193 549 562 2018 XIAO, J. et al. A recycled aggregate concrete high-rise building: Structural performance and embodied carbon footprint. Journal of Cleaner Production , v. 199, p. 868-881, 2018. XIAO J. A recycled aggregate concrete high-rise building: Structural performance and embodied carbon footprint Journal of Cleaner Production 199 868 881 2018 YAVARI, M. S. et al. Environmental Impact Optimization of Reinforced Concrete Slab Frame Bridges. Journal of Civil Engineering and Architecture, v. 11, p. 313-324, 2017. YAVARI M. S. Environmental Impact Optimization of Reinforced Concrete Slab Frame Bridges Journal of Civil Engineering and Architecture 11 313 324 2017