1. Introduction
The construction sector is damaging the environment by being the primary contributor to generating Green House Gases (GHG). GHG emissions are responsible for global warming. Carbon Dioxide (CO2) is the principal GHG. The rampant growth of construction sector has therefore led to an alarming increase in global warming. As per a report by the UK Green Building Council, the CO2 content in the atmosphere is estimated to be doubled by 2100. Drainage of natural resources, environmental damage, and GHG emissions have become driving factors for initiation of sustainable construction practices. As per C.K. Chau et al. 2015, Life cycle study comprises of three sub-categories: Life cycle assessment (LCA), Life cycle energy assessment (LCEA), and Life cycle carbon emission assessment (LCCO2A).
The building sector accounted for nearly 40% of the world’s energy consumption, 30% of raw material use, 25% of solid waste, 12% of land use, and 33% of the related global greenhouse gas (GHG) emissions [SBCI, UNEP 2009]. As per the latest report by India Environmental Change [Jos G.J. Olivier et al., 2016], net annual CO2 emission for India during 2015 increased to 2.47 billion tonnes which were 5.1% more than in 2014. Energy from fossil fuels consumed in the construction and operation of buildings accounts for approximately half of the UK’s emissions of carbon dioxide [Ben Stubbs, 2008]. As concluded by Cass and Mukherjee (2011), 90% of GHG emissions throughout the construction phase were due to the production of materials. For India alone, CO2 emissions from cement and steel production increased by 4.9% and 2.4% for the year of 2015 as compared to 2014 [Ben Stubbs, 2008].
Hong et al. 2014, analyzed GHG emissions during the construction phase of a case study building in China and concluded that building material production and transportation, on-site electricity usage were three of the greatest contributors for GHG emissions. Atmaca et al. 2015 concluded that the operational phase accounted for 79-84% of total energy requirements and 86-93% of total CO2 emissions, over a lifespan of 50 years, for a residential building each in a rural and urban area of Gaziantep (Turkey). As concluded by Bribián et al., building materials are the second most energy consuming for a residential building after heat consumption during the operational phase. Seo et al. 2016, concluded that, for a building complex, materials production accounted for 94.3% of the net CO2 emission and CO2 emissions from the material transportation and on-site construction were merely 2.4% and 4.2% of the total emissions, respectively. They also concluded that choice of input materials and construction process plays a vital role in reducing CO2 emissions.
Bribián et al. 2011, concluded that the impact of construction materials can be significantly reduced by substituting the use of finite natural resources for waste generated in other production processes, preferably available locally. As concluded by Bansal et al. 2014, the use of autoclaved aerated blocks (AAC) instead of burnt clay bricks in the construction of a four storied building proved to be more energy efficient. As per Ortiz et al. 2009, the application of LCA is essential for in building and construction sector and can be utilized as a decision-making tool in the construction sector. As concluded by Takano et al 2015, the life cycle energy efficiency increases as the geometrical factors become better for ex. perimeter to area ratio. They also concluded that life cycle energy efficiency of a building increases as the number of floors and stories increase. As concluded by Takano et al 2015, the energy differences between alternate materials were more prominent in the production stage of the building and also that use of recyclable materials greatly influenced the life cycle energy of the building.
2. Objective of the study
Life cycle accounting of any process or a product is imperative as it addresses the parameters in the process that impact or contributes the most towards environmental deterioration. Given the lack of studies conducted on life cycle accounting in the Indian context, this study aims at setting an illustration for a typical residential building in India. This study also identifies the issues associated with a life cycle study during various phases and the possible alternatives that can be suggested. Finally, the study suggests alternate construction materials that can be used to reduce the net impact during the process. An eight-storey residential apartment building, under its final stage of construction, at the Hyderabad Campus of BITS Pilani was chosen for this study to address the following objectives:
- Characterization and quantification of the environmental impacts of the various construction materials that have been used for the building.
- Identifying the impacts of self-consolidating concrete mixes with waste materials like fly ash and (ground granulated blast furnace) GGBS.
- Suggesting possible alternatives to reduce these impacts to reduce the overall life cycle impact of the overall process.
- Quantify the greenhouse gas (GHG) emissions from construction materials and from the on-site machinery used during the construction phase.
Methodology
As per C.K. Chau et al. 2015, life cycle study comprises of three sub-categories: Life cycle Impact Assessment (LCIA), Life cycle energy assessment (LCEA), and Life cycle carbon emission assessment (LCCO2A). Any life cycle study is carried out for the life time scale of a product, that is, right from its birth to its demolition or dumping phase. The life cycle phases of the building are illustrated in figure 1 (Flow diagram for the entire process). This scale includes the raw materials extraction for the manufacturing of the product, their transportation to the manufacturing plant, the manufacturing of the materials, transportation of the materials to the construction site, the construction phase, the operation or the use phase of the building, maintenance and repair followed by the end-of-life or demolition phase of the building. As there exists uncertainty when it comes to operational phase and maintenance and repair, it becomes difficult to quantify the impacts of these phases. The impacts during these phases highly depend upon the nature of inhabitant. Hence, for this study, only the cradle to gate system boundary has been investigated. This practice of focusing on a particular area instead of the entire boundary system is called streamlined LCA. LCA was conducted as per the framework and the norms laid by the ISO 14040 series and the databases used was the Ecoinvent 3.0, ( United States Environmental Protection Agency) USEPA and the (Inventory of Carbon and Energy) ICE 1.6 from the university of BATH, United Kingdom. SimaPro 8.0 was used as the LCA tool for the study.
Life Cycle Impact Assessment
Life Cycle Impact Assessment is carried out in 4 stages which are Goal and Scope definition, Inventory Assessment, Impact Assessment
and
Interpretation.
• Goal and Scope Definition: Defining the purpose of the study, system and functional boundaries of the study.
• Inventory Analysis: Collection of all the input data related to energy consumption, material usage etc.
• Impact Assessment: Quantification of Environmental impacts and input resources.
• Interpretation: Interpreting the results calculated from assessment stage and recommending suitable improvement measures.
Before carrying out LCIA, it is necessary to define a functional unit. The functional unit considered for this study is cubic meter. This study was carried out for cradle to gate system boundary and it considered the manufacturing of the construction materials and their transportation to the construction site, on-site machinery, and electricity usage during the construction phase of the building. The interpretation stage consists of the following major steps: classification, characterization, normalization, and weighing, of which procedure up-to characterization stage is mandatory and normalization and weighing are optional, per the ISO 14044. The impact of any product or a process is translated into various impact categories. For LCIA, there are two possible approaches for interpretation of results; the mid-point approach and the end-point approach. The mid-point approach classifies impacts via impact categories such as ozone layer depletion, global warming potential, acidification and eutrophication potential which depicts a complete picture of the impacts. The end-point approach distributes the impacts into categories like damages to human systems, eco-systems and resource depletion, which are easier to convey to the society. However, the mid-point approach reveals more accurate and comprehensive results with a lesser set of uncertainties than compared to end-point approach [Curran MA. Encyclopaedia of ecology. Elsevier; 2008.]. Therefore, mid-point approach for interpretation was used for the impact assessment in this study.
Life Cycle Carbon Emission Assessment (LCCO2A)
During the construction process, there is
release
of carbon dioxide gas, methane, nitrogenous oxides and many other gases. Carbon emission accounting quantifies the amount of carbon dioxide gas released during the entire
life cycle
of the product i.e cradle to grave i.e for the initial phase, construction phase, operational phase and the demolition phase(Figure 2 system boundaries). Carbon accounting is a form of impact assessment which takes into account the impacts of climate change due to the construction process. The carbon impacts of the operational and the demolition phases are future impacts and thus can only be projected. It becomes difficult to predict the GHG emissions during the operational phase of the building as it depends upon the amount of electricity and heating services used by the residents, the frequency of repair and maintenance work for the building and even the building architecture. Owing to this difficulty and to avoid assumptions and discrepancies, the study mainly focuses on the initial and the construction phase of the building.
As per the (Intergovernmental Panel for Climate Change) IPCC norms, carbon accounting is carried out by two methods, which are top-down or
long term
approach and bottom-up or
short term
approach. The top-down approach consists of calculating the long life emissions of the product i.e right up to the stage of demolition. Top-down is approach is further classified as the Reference Approach and Sectorial Approach. The
top down
approaches express the impacts to the economy or various economic sectors rather than actual emissions at the plant. As
tis
approach estimates the long life impacts, it highly depends upon the service life of the building, which in most cases for a residential building is more than 50 years. Therefore, for a building during its final stage of construction, it is difficult and involves assumptions to estimate the carbon emissions for its service life.
The bottom-up approach consists of the calculation
for
short term
carbon emissions which are those occurring within twenty years of the fuel use.
Bottom-up approach
takes into account the fuel consumption activities and estimates the amount of carbon dioxide released. It can work effectively if reliable databases are available or relevant data is obtained from the enterprises which consume the fuels. The approach uses the schedule of activities of fuel consuming equipment or the activity level directly correlated with fuel consumption to quantify the carbon emissions. As relevant databases and other datasets are available, the bottom-up approach is used to carry out carbon accounting in this study.
The expression for carbon accounting is given as follows:
Carbon Account = Qi × EF Equation (1)
where
Q
i
:
Quantity of the construction material and EF: Emission Factor.
The amount of carbon dioxide released into the environment represents the respective climate change that occurs. For any process, along with carbon dioxide, there are many gases that are released like methane, nitrogenous oxides like N2O, CFC-11 etc. The impacts of these different gases will vary and hence there is a need to connect these various impacts. Global Warming Potential (GWP) which translates the emissions of a specific gas into its respective carbon dioxide equivalent was used for this study. The Intergovernmental Panel on Climate
Change (IPCC) has developed three sets of GWP to account for the impact of a particular GHG with the same amount of CO2 under the constraint of a set time horizon (TH). Therefore, GWP is the integral of the global warming effect of GHG compared with that of CO2 in the same time interval. Three TH are commonly calculated, namely 20 years, 100 years, and 500 years. IPCC's First Assessment Report (Tegart et al. 1990) quoted an atmospheric life-span of CO2 to be between 50 and 200 years. Therefore, it is common to use the IPCC 100 TH GWP. For methane, the conversion coefficient is 25 and for nitrous oxide is 298. Hence, the amounts of methane and nitrogenous oxides released are then further converted to equivalent kg CO2 by using GWP factor. The equation for the conversion is given as follows:
Account = Qi × EF × GWP Equation (2)
Therefore, the overall carbon emissions for any process or a product is the net summation of carbon emissions from all the contributing elements in the process. The final expression for carbon emissions is
Overall Account =