Life Cycle Assessment and Sustainability Characteristics of Built Environment Systems

Abstract

The sustainable built environment concept has recently gained enormous attention from academic and industrial organizations. The growth in climate-related disasters and pandemics, continuing difficulties in the energy sector, and consumer awareness regarding resources’ conservation and sustainability are considered the driving factors influencing participants toward supporting sustainable engineering applications. Furthermore, numerous professional standards and requirements for implementing and rating sustainable practices have been generated, such as life cycle assessment (LCA), cost analysis, project development (i.e., from planning through construction up to demolition), recycling, material preservation, and utilizing reusable materials. The LCA is a great method for examining and integrating a wide variety of environmental elements to provide a comprehensive picture of system sustainability. The research presented in this study covered significant environmental elements that are essential to deciding between two or more choices and improving the system. This research compared the OPC and AABC based on CO₂ emissions. The results showed that the AABC produces positive sustainability outcomes in terms of CO₂ emissions. The AABC emits substantially less CO₂ than the OPC, indicating that it is preferable for greenhouse buildings.

1 Introduction

In developing communities with limited resources, resilience and sustainability are crucial components for creating high-performance infrastructure [1, 2]. Prior to the 19th century, the concept of resilience as a design principle was inherent in common construction knowledge. Buildings’ resilience was increased through implicit construction knowledge such as oversizing of parts and spaces, redundancy, and reparability. One of the most important factors of sustainability is the life cycle assessment (LCA) of the built environment systems, which analyzes the environmental impact based on the phases of manufacture and production, usage, and destruction. The LCA is divided into four phases: scope definition and aim, analysis of inventory, impact evaluation, and interpretation [3, 4]. The LCA can be used to determine durability, mechanical strength, cost, energy, and emissions criteria. By providing a complete picture of the required energy and CO₂ emissions, this technique allows a thorough comparison of transit, material production, usage, and demolition implications [5, 6]. The life cycle stages for the manufacture of material feedstocks, which include collection, transporting, mining, and calcining of these feedstocks, are examined first, followed by the manufacturing process, including mixing these raw materials [7,8,9,10]. The availability of sources is also an important factor in sustainability; it has a key impact on the cost, which includes the stages of the excavating process, including extracting, transporting, forming, and construction time. Therefore, the high availability of sources activates the construction process and shortens the project’s duration to minimize purchasing effort and human potential in the alternative search [11, 12]. Furthermore, the use of waste materials from finished projects or demolished structures as recyclable materials has a good impact on the built environment, with the goal of reducing waste materials in landfill areas and using available materials [13, 14]. The availability of building materials is considered a criterion of embodied energy in selecting materials. Furthermore, in order to achieve environmental protection and decrease gas emissions during excavation and transportation, it is preferable to utilize locally available materials for the project instead of the materials available in remote areas that need time and financial potential for transportation, even if the project location is remote. Therefore, employing easily accessible building materials improves sustainability by reducing the possibility of excavation, expense, gas emissions, working time, human potential, and embodied energy [15, 16]. Despite its significance for the sustainability of built-environment systems, resilience is not explicitly considered by studies of LCA. Resilience is a design principle that is associated with a combination of sustainability and the ability to recover in the shortest time. This term becomes more tangible when unexpected disasters happen in urban infrastructure, particularly in residential buildings [17, 18]. Resilience refers to the capacity of buildings, infrastructure, and communities to endure and recover from a variety of shocks and stresses, including climate change, natural disasters, and other disruptions. Thus, resilience is a key factor in the built environment because it can mitigate the effects of climate change, reduce loss and damage, promote sustainability, and ensure long-term viability and economic stability [19, 20]. The principal objective of this paper is to investigate the techniques for monitoring resilient and sustainable construction projects and resolving difficulties and possibilities in the long-term development of resilient built-environment systems.

2 Built Environment Sustainability

The sustainable built environment system, also known as the sustainable ecosystem, can be defined as a complicated and integrated system of natural resources, processes, and elements that work together to minimize adverse environmental effects while preserving ecological balance and providing necessary services to support life on Earth. The created or man-made environments in which individuals live, work, and interact are referred to as the built environment system. It includes all of the physical features, such as gardens, roads, bridges, buildings, and other services, that comprise both urban and rural regions. This system is an important part of human civilization and has a major influence on the environment, economic growth, and standard of living. A sustainable environment system has the following essential elements: resource conservation, which includes the utilization of natural resources such as atmosphere, water, land, energy, material, and biodiversity (i.e., a wide variety of species); cost efficiency of the constructed projects in all stages (i.e., initial cost, cost in use, and recovery cost); and design for human adaptation, which could include the minimization of production waste, keeping water and air clean, and protecting human interaction with the environment [21, 22]. A schematic representation of the built-environment system is displayed in Fig. 1.

Fig. 1.

Sustainable built environment system (SBES).

The built environment system can be assessed using the meaning of the LCA of the used materials (e.g., cement, ordinary concrete, geopolymer concrete, steel, asphalt, masonry, etc.), especially in construction projects (i.e., buildings, roads, bridges, tunnels, dams, etc.). The impact of various factors such as sustainability, resilience, available opportunities, challenges, and LCA on the built environment systems is described in detail in the following subsection. The conceptualization of resilience has developed over the past decade and is frequently discussed alongside the concept of sustainability. As a result, because both of these ideas come together and are utilized simultaneously, they must be considered jointly. The philosophy of sustainability, and subsequently resilience, is part of a broader narrative that has affected a wide range of specific topics and geographic situations, including metropolitan regions. Resilience is being utilized more and more to understand extremely complex, dynamic social systems, such as metropolitan regions. This may shed light on difficult concepts related to sustainability and resilience [22,23,24].

3 Life Cycle Assessment (LCA)

The LCA is a unique tool that comprises all procedures and environmental releases, from the extraction of raw materials and the production of energy necessary to manufacture the product to its usage and final disposal. The LCA considers a wide range of environmental aspects, including energy use, resource consumption, and emissions, to provide a comprehensive view of a product’s sustainability. Thus, the LCA can assist decision-makers in comparing all key environmental impacts generated by products, processes, or services when choosing between two or more alternatives [25]. The LCA usually examines how building materials affect the environment by considering various aspects, including resource extraction, manufacture, transportation, and disposal at the end of the product’s life. It evaluates these materials’ embodied energy, carbon footprint, and environmental metrics. The LCA considers energy and emissions, which are related to site work, and evaluates the use of energy and resources during building operations [26, 27]. The LCA can also examine building demolition and disposal, which include investigating the environmental impacts of waste management, demolition, and potential material recycling or re-use. The LCA frequently examines a building’s whole life cycle, from cradle to grave, and considers a variety of environmental indicators, including carbon emissions, energy consumption, and water use, to thoroughly assess the sustainable built environment system (Fig. 2).

Fig. 2.

Typical architecture of the LCA application in civil engineering.

4 Materials and Methods

In general, applying the concept of LCA to a domestic zone can assist legislators, engineers, urban planners, architects, and developers in making choices that avoid negative environmental consequences. The tool used to apply the environmental assessment for the whole framework in this paper is CO₂ emissions. In order to apply the LCA for assessing a built environment framework, a virtual system of a compound city was taken as an example to compare the CO₂ emissions values of a city built using ordinary Portland cement (OPC) concrete and another city built using alkali activated binder (AABC) concrete. Various types of buildings were included in the study for a good evaluation of the environmental impact, and the construction site works (i.e., infrastructure works) were also included in the study data estimation. The city (i.e., compound) consists of ten 4-floor residential buildings, five 2-floor villas, four 4-floor commercial buildings, two 3-floor schools, one language center, and two 2-floor health centers. The details of each building type (i.e., number of buildings, area of each building, and total area) are listed in Table 1. A schematic representation of the studied compound with all building types is displayed in Fig. 3. The data used in the LCA analysis for various building types and two concrete types (OPC and AABC) were collected from reputable published research studies [6, 28, 29] and then applied to the constructed virtual compound. A comparison between the OPC and AABC was produced by creating each concrete type’s life cycle stages and then computing its CO₂ emissions. The numbers shown in Table 2 represent the amount of CO₂ emissions resulting from casting 1 m² of the building area using either OPC or AABC, the total amount of CO₂ emissions, and the percentage of CO₂ emissions. It can be observed that the CO₂ emissions using the AABC are significantly lower than the OPC, which attests that the use of the AABC is desirable in greenhouse construction. According to Fig. 4, the total CO₂ emissions resulting from residential buildings are the highest, since the majority of buildings in a typical built environment are residential buildings.

Fig. 3.

3D plan of the virtual compound.

Table 1. The details of each building type.

Table 2. LCA results for the various buildings and concrete types.

Fig. 4.

CO₂ emissions values for OPC and AABC concretes for various building types.

5 Conclusion

The LCA is a useful tool capable of considering and combining a wide range of environmental aspects for the purpose of providing a complete picture of system sustainability. The analysis provided in this study addressed key environmental aspects that are important for choosing between two or more alternatives as well as optimizing the system. The findings of the LCA may assist and guide stakeholders and decision-makers toward environmentally friendly and sustainable techniques for their application in the development of the built environment. A comparison between the OPC and AABC revealed that the AABC results in more favorable sustainability outcomes measured in terms of CO₂ emissions. It can be observed that the CO₂ emissions using the AABC are significantly lower than the OPC, which attests that the use of the AABC is desirable in greenhouse construction. The total CO₂ emissions resulting from residential buildings are the highest, since the majority of buildings in a typical built environment are residential buildings. This could be a direct motivation for imposing sustainability-proactive regulations on residential buildings to enhance the sustainability of the built environment.