LITERATURE REVIEW

The environmental impacts of buildings sector are reaching a percentage that cannot be ignored of negative influence on the planet, such as 38% of summer smog and 20% of heavy metal categories.

Therefore, predicting the environmental impacts of construction materials in the design stage is playing a crucial role in reducing the environmental impacts of the materials that are used in buildings during all their life cycle (Coelho & de Brito, 2012). According to these facts, this prediction process needs to be based on LCA methodology, which performs as an important task in calculating the essential impacts of the construction, such as global warming and climate change, during the entire life cycle (Bragança and Mateus 2012) and (Ghattas et al., 2016). LCA is an environmental methodology that has been used and developed to analyse the environmental impacts of products, materials and even for buildings. It is recognized as an innovative method, which helps applying and improving sustainability concept in the construction industry throughout all stages of the building life cycle, considering raw materials’

extraction, construction, use and maintenance/final disposal or demolition. Therefore, it can be used to decide more sustainable and environmental friendly alternatives among the construction materials (Ortiz et al., 2009). To help classifying the different kinds of LCA studies, several authors have used a simple classification described as follows (Ferreira et al., 2015) and (Kulahcioglu et al., 2012):

1. Building Material and Component Combination (BMCC) LCA;

2. Whole process construction (WPC) LCA.

LCA studies in the world

Globally, LCA has had a gradual increment in the studies and the publications as the consciousness of its necessity is rising. Figure 1 presents statistics according to Scopus database that shows the increasing interest in LCA studies in buildings around the globe since 2013.

Figure 1. Scopus statistics of LCA publications in buildings around the world (source: Scopus database) LCA research has been different from country to country, depending on the requirements of each one to find out more sustainable materials that consume as less as possible from the natural limited sources. Therefore, implementing LCA in building has been growing in parallel with the increase in requiring more buildings with less resources and materials demand. As an evidence, Figure 2 shows the different numbers of LCA studies applied in buildings in some countries around the world.

Figure 2. LCA publications in buildings in different countries (Source: Scopus)

These studies have focused not only on reducing the increasing cost of energy demands but also on minimising the drop of natural resources, the environmental impacts of the materials in addition to decrease the health impacts of the products (Patrick, 1998) and (Reza et al., 2014). For example, Reza et al. (2014) found out a comprehensive framework to enhance the sustainability of building considering quantitatively the environmental impacts during its whole life cycle related to social and economic costs. They pointed out that regarding an annual energy use, a multi-unit residential building would be more sustainable than a single-family house. Furthermore, the total life cycle energy per unit area of the multi-residential building is 2-3 times higher than the single-family house.

They conclude in both types of buildings that the production phase is the 2^ndafter the operation energy consumption, registering 5.3 and 7.4 % of the operation energy.

Another example of this kind of studies is the Assefa and Ambler (2017) publication. It studied the environmental impacts of a building in two case-scenarios; either reuse it or demolish it and construct a new one, considering the reuse the materials and the structure again. Thus, the refurbishment scenario was more positive than the demolishing scenario, since it saved (33 and 34) % in GWP and fossil fuel consumption further than reducing (20 to 41) % of the environmental impacts categories such as Eutrophication potential and Human Health Criteria, among others.

(Basten et al., 2017) provide an evaluation of green building rating tools based on existing green building achievement in Indonesia using Life Cycle.

LCA studies in Portugal

In Portugal, the number of LCA studies in buildings has been increasing gradually. In fact, the last four years have registered much more considerable number of publications than the previous, which can point out that LCA has started to be an important matter of research among the scientific and technical community. This increment is expected to grow even more in the following years in Portugal due to the increasing consciousness toward applying LCA in the design phase to implement more alternatives and sustainable solutions. As far as statistics are concerned, Figure 3 presents the increment of Portuguese LCA publications in the Scopus until now in Portugal.

Figure 3. LCA publications in Portugal (Source data: Scopus database)

For instance, Silvestre. et al (2016) performed a cradle to cradle LCA analyzing the environmental impacts of insulation cork boards using site-specific data and showing they could be a sustainable insulation material for buildings from an environmental point of view. Raw material extraction cause 88,9% of the primary energy and 33,9% of Ozone depletion. Silvestre. et al (2016) obtained the following points: (i) manufacturing process contributes to up to 65% of LCA environmental impacts categories; (ii) 40% of direct air emissions from the boiler in the expansion phase and (iii) electricity consumes up to 10% of Eutrophication Potential, whereas disposal the wood ash residue of the boiler causes up to 48.2% of it. However, this study suggests reducing the needed energy to produce insulation cork boards in a further research, since it has higher impacts in primary renewable energy and in water consumption comparing with polymers, wool minerals and polyurethane.

Brás and Gomes (2015) performed a (cradle to gate) LCA used to compare mortars with thermal insulation materials in its composition (EPS and cork granules) with common cement and lime ordinary mortars. These comparisons were made in a rehabilitation case study of a school in Baixa da Banheira, Setúbal, Portugal. This study obtains that adding thermal insulation materials into mortars can reduce the Operational Energy and the GHG LCA emissions without compromising the service behavior of the mortar.

Rodrigues and Freire (2017) integrated LCA and LCC with thermal dynamic simulation to study the insulation strategies of roof and exterior wall applied in a residential building in Portugal with two scenarios of low/high occupancy and another scenario of using it as an office. It is strongly suggested to improve the retrofit behavior of historic European buildings by considering their use type and occupancy level. Nevertheless, further research is needed to study other materials that influence the environmental and the economic impacts of the building retrofit, such as structural materials, electricity mix or heating/cooling systems, among others. Those studies show that most of the LCA studies in the building sector in Portugal analyzed (i) the environmental impacts, (ii) the cost savings and (iii) the thermal performance of insulation materials such as panels and boards. Therefore, further researches and studies of the construction materials and their environmental impacts need to be done.

LCA studies in structural materials (in Portugal)

The structural materials differ from one building to another and according to the region.

Therefore, the alteration of the structural construction materials must be compatible with the needs of each region and country to achieve the required safety and the stability of the building (Silvestre et al., 2013). In Portugal, LCA studies in buildings and especially in the structural solutions were few.

Indeed, most of the LCA studies focused on enhancing the efficiency of the thermal insulations and minimising energy requirements more than the environmental impacts as explained before. Even though, there are some interesting studies for LCA structural solutions in Portugal, which will be briefly summarized in the following paragraphs.

Gervásio and Silva (2008) aimed to integrate LCA with sustainability approach by comparing

steel composite bridge with a common concrete bridge, analysing the energy demands and environmental impacts of its materials. It was concluded that using recycled materials, such as steel can grant savings of more than 50% in embodied energy whereas in Portugal it is not yet common to reuse the concrete debris. They insisted on the need for further researches in the service life and the life cycle deterioration of the structure (concrete and steel). Regarding the global environmental categories, the steel solution showed better results than the concrete one. On the other hand, the concrete solution was more economically preferable than the steel one (20% cheaper) (Gervásio and Silva, 2008).

Bastos et al. (2014) analysed the primary energy and GHG emissions of a building located in Lisbon considering the construction, the use and the retrofit phase. It was commented that the use of the building over 75 years would be responsible for 69 to 83 % of the primary energy and GHG burdens. Moreover, the energy demands and the GHG emissions were decreased as more as the area was bigger, whereas these impacts were increased as more as the building had higher occupancy.

Bastos et al. (2014) highlighted the importance of the functional unit when LCA is used to compare the environmental impacts of variant buildings. It was also suggested to utilise the occupancy based-area as a functional unit in LCA calculations. Besides, they also endorsed using the primary energy to predict the energy requirements in future LCA calculations.

Ferreira et al. (2015) performed LCA and LCC (cradle to grave) analysis in two cases: the 1^stone was the refurbishing of one old existing building located in Lisbon; and the 2^ndone was demolishing it and building a new equivalent one using a common reinforced concrete solution with clay brick walls.

Ferreira et al. (2015) results showed that considering the GWP, refurbishment solution was 13% better than the solution of demolishing and constructing a new building, likewise, the refurbishment saved up to 10% of the primary energy compared with the other solution. Moreover, the refurbishment was preferable than the construction solution, since it saves around 542% of production waste and 266% in eutrophication potential. In contrast, the demolishing and constructing new palace solution is economically better than the refurbishment, since it saves around 47.32 €/m².

Santos et al. (2016) collaborated to create a tool to reach more steel sustainable design based on energy analysis, LCA calculations and the climatic condition/location, which influence the energy demands of the building. They focused on the steel buildings, since it could bring many losses in heat and high gains due to the thermal characteristic of the steel itself and, since the steel is an essential recyclable material. They show the importance of their tool according LCA importance, and recommended to do LCA during the design phase. It was commented that this tool could help choosing better structural materials, insulations and design strategies, and consequently saving energy up to 60%.

Concluding, it could be summarised from LCA studies of structural materials and solutions in Portugal that using concrete and steel in the building structure brings many negative impacts. The works insist on further research and attention that should be paid on the structural materials such as steel, concrete and brick to improve the sustainability of the construction sector. In fact, to reach a sustainable building with low life cycle environmental impacts it is not enough to study only the insulation materials, but also the structural solutions, since their right choice, based on LCA calculations, could reduce up to 60 % of the environmental impacts of the construction sector. To fill the gaps of research here highlighted, this work will use LCA to predict the environmental impacts of structural materials (instead of the insulation materials widely studied in Portugal) and evaluate the most sustainable solution for the structure of a real building in Aveiro University.

METHODOLOGY

LCA study follows the definitions and methods described in ISO 14040, ISO 14041 and ISO 14042 which are the four mandatory steps:

1. Goal and scope definition: The goal of this study is to assess the environmental impacts of three different structural alternatives of the case study building. On the other hand, the scope of this LCA

study is analysing six different physic alternatives. All of them represent possible types of structures for a scholar building of the University of Aveiro. Although, the final functional unit is the building, each material has its own functional unit, which will be analysed in the life cycle inventory phase.

2. Inventory analysis: Identification of resources consumption and emission to air water and soil.

3. Life cycle impact assessment: After collecting the data, the impact categories must be defined and assigned, since it is the first step to do life cycle impact assessment. Therefore, the impact categories that will be considered in this study are: (i) The global warming potential (kg CO2 eq); (ii) Ozone depletion potential (kg CFC eq); (iii) Acidification Potential Total (kg SO2eq); (iv) Eutrophication Potential Total (kg NOxeq) and (v) Smog potential (kg O3eq). To calculate the total impacts of each alternative, the impacts’ indicators for each functional unit of each construction material must be multiplied by the quantities provided in the inventory stage. The sum of all environmental impacts of each material gives the global environmental impacts of the alternative, which represents the global functional unit of this LCA: 1 building.

4. Interpretation phase: it is the phase where the results are discussed and explained.