A Study on Life Cycle CO 2 Emissions of Low-Carbon Building in South Korea

There have been much interest and many efforts to control global warming and reduce greenhouse gas (GHG) emissions throughout the world. Recently, the Republic of Korea has also increased its GHG reduction goal and searched for an implementation plan. In buildings, for example, there have been technology developments and deployment policies to reduce GHG emissions from a life cycle perspective, covering construction materials, building construction, use of buildings and waste disposal. In particular, Korea’s Green Standard for Energy and Environmental Design is a certification of environmentally-friendly buildings for their energy saving and reduction of environmental pollution throughout their lives. In fact, the demand and adoption of the certification are rising every year. In construction materials and buildings, as a result, an environmentally-friendly aspect has become crucial. The importance of construction material and building development technologies that can reduce environmental load by diminishing GHG emissions in buildings has emerged. Moreover, there has been a rising necessity to verify the GHG reduction effects of buildings. To assess the reduction of carbon emissions in the buildings built with low-carbon construction technologies and materials, therefore, this study estimated life cycle carbon emissions in reference buildings in which general construction materials are used and in low-carbon buildings. For this, the carbon emissions and their reduction from construction materials (especially concrete) between conventional products and low-carbon materials were estimated, using Life Cycle Assessment (LCA). After estimating carbon emissions from a building life cycle perspective, their reduction in low-carbon buildings compared to the reference buildings was reviewed. The results found that compared to conventional buildings, low-carbon buildings revealed a 25% decrease in carbon emissions in terms of the reduction of Life Cycle CO2 (LCCO2) per unit area. If diverse production technologies and sales routes are further developed for low-carbon construction materials, carbon emission reduction effects would considerably increase.


Introduction
At the recent 2015 United Nations Climate Change Conference (COP 21), which was held in Paris, France, the 'Paris Agreement', a new framework convention on climate change, was adopted.It is the first consensus that is more binding than the Kyoto Protocol, keeping the efforts of advanced and developing countries.Therefore, there has been a rising interest in it for a proper response to a post-2020 climate framework around the world.
The Republic of Korea also announced a voluntary action plan to reduce greenhouse gas emissions by 37% from the business-as-usual (BAU) level of 851 million by 2030 [1].For this, there have been many efforts to reduce GHG emissions throughout the industries.Businesses have operated a "GHG and energy target management system" and cap-and-trade to control GHG emissions.From a product standpoint, the product carbon footprint labeling has been run to encourage the use of low-carbon products.In buildings, the Green Standard for Energy and Environmental Design (G-SEED) has been applied to find ways for reducing GHG emissions considering the life cycle of the green buildings that have reduced GHG emissions with the use of environmental load-reduced materials.
In particular, Korea's construction industry accounts for 48% of the total material consumption and 40% of the national energy consumption.In terms of CO 2 emissions during the production of construction materials, in addition, the construction sector accounts for about 25% [2].Therefore, there have been many efforts to develop and commercialize low-carbon construction materials that can satisfy the demand for environmentally-friendly buildings.As a result, there has been a rising necessity for the assessment of environmental loads by the life cycle of construction materials and environmental assessment and continuous management throughout the life of buildings.
Therefore, this study analyzed carbon emissions and reduction against the buildings built with low-carbon construction materials after reflecting the government's movement to reduce GHG emissions.For this, an assessment technique that can quantitatively assess carbon emissions in construction materials and buildings was chosen.Depending on the building life cycle, data by GHG the emission factor were collected.Then, Life Cycle CO 2 (LCCO 2 ) emissions were assessed according to the useful life of a building.As a result, GHG emission reduction key technologies were derived from construction materials and buildings.It appears that the study results would be useful data in developing a roadmap and implementation plan for the reduction of GHG emissions from a long-term perspective for low-carbon buildings.

Previous Studies Regarding Environmental Impact Assessment on Buildings Using LCA
According to previous studies, the environmental impact of buildings has been assessed in a more objective and quantitative manner, using LCA, which unveils environmental impact substances throughout the product and service processes and assesses environmental impact [3].
According to studies on energy consumption and carbon emissions throughout a building life cycle, in foreign countries, the environmental impact of energy consumption and greenhouse gas emissions was assessed.In particular, there have been studies targeted to analyze energy consumption patterns by building type in the operation phase [4], to design an energy-saving building and to develop an energy-saving solution through the analysis of diverse cases in foreign countries [5].In terms of the characteristics of a building's operation phase, it accounted for up to 85% of total carbon emissions by building type due to the use of heating and cooling energy and electrical facilities [6,7].
In the study abroad, Wang et al. had found suggestions on improving the green building rating tools to encourage the GHG emission reduction performance of green buildings [8].Additionally, Liu et al. reviewed the existing research and implementation examples to understand the development of carbon labeling [9].Furthermore, Rogers et al. took an integrated analysis approach to explore the options available for a U.K. homeowner to reduce their domestic emissions [10].Mahapatra analyzed the energy use of the buildings fulfilling the requirements of the Swedish building code and compared the primary energy use and CO 2 emissions from the operation of the building [11].
In other research work, some studies on green building certification, building materials and building life cycle greenhouse gas emissions were released [12,13].Additionally, the renewable energy research, such as solar and biomass energy, were conducted [14][15][16][17].
Zhang et al. conducted the life cycle assessment of the air emissions by using a particular case to examine emissions during the construction stage [18].Additionally, Baek et al. performed a study to identify the requisites for an LCCO 2 assessment program that can be used in the schematic design phase [19].Furthermore, Bribián et al. presented the state-of-the-art regarding the application of life cycle assessment in the building sector [20].Additionally, Verbeeck et al. outlined the goal and scope of the LCI and introduced several calculation methods for LCI of building.Then, they presented the results of a contribution analysis of the life cycle inventory of four typical Belgian residential buildings [21,22].
Furthermore, the paper did research about the status of low-carbon technologies in the building area and discussed the necessity and importance of reducing carbon emissions in the full life cycle of buildings [23].
In the Republic of Korea, there have been many environmental impact assessments on buildings using LCA.These studies can be divided into two categories: those [24][25][26][27] that suggested a method to assess the environmental impact using LCA and case studies on the building environment [28][29][30].In addition, BIM template development studies [31] for the implementation of LCA on environmentally-friendly buildings and Life Cycle Inventory (LCI) DB development studies on construction materials have been very active [32].
Even though there have been many LCAs and studies on buildings, those that reflect the environmental impact of the latest low-carbon construction materials have not been enough.
Therefore, this study has derived the results that would be useful in estimating and analyzing the carbon emissions and reduction of low-carbon construction materials by carrying out environmental impact assessment on buildings using LCA.

The Status of the Development of Low-Carbon Construction Materials
The product carbon footprint labeling in the Republic of Korea issues measured carbon levels and low-carbon certification on all products and services.In particular, there has been a rising demand for certification on carbon emissions and reduction in construction materials and inventories [33].At the same time, the development of carbon reduction technologies has been active, and diverse low-carbon products have been produced [34].
In terms of key technologies to reduce carbon emissions at a construction material production stage, it would be able to enhance the efficiency of input management and production processes by reducing the amount of input, using industrial byproducts or applying new materials and reducing carbon emissions during production through fuel switching [2].In particular, regarding concrete, which is the most widely used for structures among construction materials, the products made of these latest carbon reduction technologies were chosen, and carbon emissions and reduction were measured.In terms of the selection of products, those that are same as conventional products in terms of specification, strength, physical property and test items were chosen, and same functions and functional units were applied [2].
Table 1 states the properties of low-carbon concrete products, while Table 2 reveals the reduction of carbon emissions in each product, compared to conventional products.Among the nine products for which carbon emission reduction and reduction rates were compared in Table 2, those with the same functions and functional units are alphabetically listed in Table 1.

Research Methods
Among the assessment methods mostly used during LCA to assess the LCCO 2 emissions of buildings, process analysis [35] was adopted.A building is a composite structure comprised of construction materials.In addition, input and output data, which are produced through its life cycle are very complicated.Therefore, it was believed that the limitation on the scope of data collection considering the characteristics of a building's life cycle would derive the carbon emissions and reduction of a building in a clear manner.

System Boundary
In general, a building consumes energy and resources and produces a variety of wastes through its life cycle, which include the design, production of construction materials, construction, building use and maintenance, demolition and recycling and reconstruction.
As shown in Figure 1, therefore, this study divided building life cycle stages and set the system boundary to define the scope of data collection in each stage and to perform LCCO 2 assessment.
considering the characteristics of a building's life cycle would derive the carbon emissions and reduction of a building in a clear manner.

System Boundary
In general, a building consumes energy and resources and produces a variety of wastes through its life cycle, which include the design, production of construction materials, construction, building use and maintenance, demolition and recycling and reconstruction.
As shown in Figure 1, therefore, this study divided building life cycle stages and set the system boundary to define the scope of data collection in each stage and to perform LCCO₂ assessment.

Environmental Load Assessment Plan by Life Cycle
Considering a building's life cycle, the scope of data collection was divided into four stages: construction material production (manufacture) phase, construction phase, operation and maintenance phase and demolition phase.
Table 3 states the matters that should be considered at LCA depending on a building's life cycle phase.

Construction material production
The process of the manufacturing and processing of raw materials; the building materials to be charged into the building consume resources and the energy required for production, such as the production of products

Material transport
The process of transporting the material to be put into the building from the dealer or store to construction sites

Construction activities
The transported material on site, using a variety of construction equipment; the process of applying the building

Use
The process that residents maintain a comfortable life by using various equipment during their life time

Environmental Load Assessment Plan by Life Cycle
Considering a building's life cycle, the scope of data collection was divided into four stages: construction material production (manufacture) phase, construction phase, operation and maintenance phase and demolition phase.
Table 3 states the matters that should be considered at LCA depending on a building's life cycle phase.
Table 3. Description of the unit process for the building LCCO 2 assessment.

Construction material production
The process of the manufacturing and processing of raw materials; the building materials to be charged into the building consume resources and the energy required for production, such as the production of products

Material transport
The process of transporting the material to be put into the building from the dealer or store to construction sites

Construction activities
The transported material on site, using a variety of construction equipment; the process of applying the building Table 3. Cont.

Unit process Description
Operation and maintenance phase

Use
The process that residents maintain a comfortable life by using various equipment during their life time

Maintenance
The process of maintaining the building as the initial conditions by repairing works Demolition phase

Destruction
The process of the building by using the construction machinery demolition

Waste material transport
The process of transporting the waste materials to a treatment plant in accordance with the disposal method after the destruction process

Recycling
The process of converting recyclable waste materials to new raw materials or manufacturing new products through crushing and screening work

Waste landfill/incineration
The process of burying or burning the non-reusable residue waste

Utilization of the LCI Database of the Construction Materials
The environmental information of the construction materials that can be used to perform LCA on the environmental impact of buildings was collected.For this, the results of national LCI DB and conventional LCI DB development-related studies were referenced.In case of construction materials in which KLCI DB [36,37] is not found, a foreign LCI DB [38] was used or LCI results were calculated in person in accordance with international standards (See Table 4.).

Assumptions and Restrictions
To analyze subjects with many variables, it is needed to restrict the subjects and scope of data collection to permit LCA based on process analysis.Therefore, the factors having considerable environmental impact by the life cycle of buildings were extracted and used in preparing a data collection scenario and setting assumptions.
At the operation and maintenance and demolition phases, it is able to estimate environmental load by assuming the factors with significant environmental impact and setting a scenario depending on certain conditions.

Overview of LCA-Targeted Building
The target building is a building aimed to verify the effects through the development of carbon-reduction construction materials.It features a PR (publicrelations) hall on the first floor, a monitoring space on the second floor and empirical and reference spaces on the third and fourth floors.As a result, the area apart from the empirical and reference spaces was set as a "common space" and divided into common space, empirical house and reference house for building analysis.
As indicated in Table 5, among the gross floor area (1078 m 2 ), the common space accounted for 738 m 2 , while empirical and reference houses were 170 m 2 each (85 m 2 /floor).

Assumptions and Restrictions
To analyze subjects with many variables, it is needed to restrict the subjects and scope of data collection to permit LCA based on process analysis.Therefore, the factors having considerable environmental impact by the life cycle of buildings were extracted and used in preparing a data collection scenario and setting assumptions.
At the operation and maintenance and demolition phases, it is able to estimate environmental load by assuming the factors with significant environmental impact and setting a scenario depending on certain conditions.

Overview of LCA-Targeted Building
The target building is a building aimed to verify the effects through the development of carbon-reduction construction materials.It features a PR (publicrelations) hall on the first floor, a monitoring space on the second floor and empirical and reference spaces on the third and fourth floors.As a result, the area apart from the empirical and reference spaces was set as a "common space" and divided into common space, empirical house and reference house for building analysis.
As indicated in Table 5, among the gross floor area (1078 m 2 ), the common space accounted for 738 m 2 , while empirical and reference houses were 170 m 2 each (85 m 2 /floor).As shown in Table 6, for the evaluation of building LCCO₂, a building was divided into office and residential spaces by reflecting the target building's spatial characteristics, and functional units were selected.In terms of service life setting for a building, 30 years were set for a reinforced concrete structure in accordance with the Corporate Tax Act (No. 40 of the References).

Function
The function of the support for a variety of business activities The function of household-dwelling

Functional unit
The office building for 30 years A residential building for one household during 30 years

Reference flow
Resources and energy, which are put into the office buildings for 30 years

Resources and energy input to a building for a household during 30 years
Reference flow unit kgCO₂ eq./m 2 .30years

Material Production Phase
This phase includes the processes from the collection of raw materials needed to manufacture construction materials to their production.
The total mass of inventories used for the construction of the target building was 3172 tons (2.9 tons/unit area).Considering the characteristics of a reinforced concrete structure, ready-mixed concrete, sand and gravel, cement and precast concrete accounted for about 95% of the total input.
In this study, 99.7% of the cumulative contribution was applied for the "cut-off" based on the total construction material input, including the common area of the building and empirical and reference houses (See Table 7 and Figure 2.).As shown in Table 6, for the evaluation of building LCCO 2 , a building was divided into office and residential spaces by reflecting the target building's spatial characteristics, and functional units were selected.In terms of service life setting for a building, 30 years were set for a reinforced concrete structure in accordance with the Corporate Tax Act (No. 40 of the References).

Material Production Phase
This phase includes the processes from the collection of raw materials needed to manufacture construction materials to their production.
The total mass of inventories used for the construction of the target building was 3172 tons (2.9 tons/unit area).Considering the characteristics of a reinforced concrete structure, ready-mixed concrete, sand and gravel, cement and precast concrete accounted for about 95% of the total input.
In this study, 99.7% of the cumulative contribution was applied for the "cut-off" based on the total construction material input, including the common area of the building and empirical and reference houses (See Table 7 and Figure 2.).

Construction Phase
The construction phase refers to the stage in which a building is being built with various equipment and facilities, since the transportation stage is where construction materials are brought to the construction site.
In this phase, CO₂ is mostly emitted by construction machines and equipment and transportation vehicles.Therefore, the data on these transportation vehicles and transportation distance are collected.Furthermore, this is calculated based on fuel and power consumption at the construction site.In the building, the construction equipment was mostly used for earthwork, reinforced concrete work and plaster work.

Operation and Maintenance Phase
This phase is to use and repair and manage the building until it is demolished.Among energy consumption and building maintenance, in this study, the former was only considered for carbon emissions.Based on previous studies on building energy consumption [31], annual power

Construction Phase
The construction phase refers to the stage in which a building is being built with various equipment and facilities, since the transportation stage is where construction materials are brought to the construction site.
In this phase, CO 2 is mostly emitted by construction machines and equipment and transportation vehicles.Therefore, the data on these transportation vehicles and transportation distance are collected.Furthermore, this is calculated based on fuel and power consumption at the construction site.In the building, the construction equipment was mostly used for earthwork, reinforced concrete work and plaster work.

Operation and Maintenance Phase
This phase is to use and repair and manage the building until it is demolished.Among energy consumption and building maintenance, in this study, the former was only considered for carbon emissions.Based on previous studies on building energy consumption [31], annual power consumption (41.7 kwh/m 2 ) and annual city gas consumption (16.1 Nm 3 /m 2 ) were considered.In terms of the useful life of the building, 30 years [39,40] were set according to a standard repair cycle.

Demolition Phase
This phase is to deconstruct a building and dispose of or recycle the materials when it becomes useless after the expiry of its social and physical lives.
This study did not consider CO 2 emissions, which occur during the demolition of the low-carbon building or transportation of the wastes, because assessment was conducted, focusing on CO 2 emissions among total construction material input.In addition, CO 2 emissions were considered according to the waste estimation and disposal methods.Depending on the treatment method by the type of construction wastes, therefore, 97.5% of recycling rates, 1.8% of landfill and 0.7% of incineration were applied, using statistical values [37].

Material Production Phase
As shown in Table 8 and Figure 3, the CO 2 emissions of input materials were 495,802 kg CO 2 eq.Regarding environmental impact by the construction material, ready-mixed concrete was the highest with 72.7%, followed by reinforcing bar and steel bar (10.1%) and cement (8.6%) in terms of CO 2 emissions.The CO₂ emissions by common area, residential house and empirical house are estimated as shown in Table 9 and Figure 4.The CO 2 emissions by common area, residential house and empirical house are estimated as shown in Table 9 and Figure 4.Among total input for the building, the largest amount of construction materials was used during the foundation and frame works for the common space.Therefore, CO 2 emissions were the greatest in the common space.In addition, even though reference and empirical houses were the same in terms of area, there was a difference in the amount of input to the empirical house because of the use of low-carbon ready-mixed concrete, PC panel and insulated products.Among total input for the building, the largest amount of construction materials was used during the foundation and frame works for the common space.Therefore, CO₂ emissions were the greatest in the common space.In addition, even though reference and empirical houses were the same in terms of area, there was a difference in the amount of input to the empirical house because of the use of low-carbon ready-mixed concrete, PC panel and insulated products.

Construction Phase
In this phase, CO₂ emissions were assessed by classifying emission effects by the transportation of construction materials and construction.In terms of CO₂ emissions generated in transporting construction materials to a construction site, ready-mixed concrete was 67.3%, while other materials were 32.7% (See Table 10.).As indicated in Table 11, in terms of CO₂ emissions generated by the use of construction equipment, the use of diesel oil during earthwork and concrete pouring was 68.1%, while power consumption for other works, such as plaster work, was 31.4%.

Construction Phase
In this phase, CO 2 emissions were assessed by classifying emission effects by the transportation of construction materials and construction.In terms of CO 2 emissions generated in transporting construction materials to a construction site, ready-mixed concrete was 67.3%, while other materials were 32.7% (See Table 10.).As indicated in Table 11, in terms of CO 2 emissions generated by the use of construction equipment, the use of diesel oil during earthwork and concrete pouring was 68.1%, while power consumption for other works, such as plaster work, was 31.4%.The CO 2 emissions generated during the construction phase were 11,353.1 kg CO 2 eq.Among them, 92.7% was created during transportation, while 7.3% was generated by construction.In terms of CO 2 emissions during transportation, ready-mixed concrete was the highest with 62.4%, while other materials were 30.3%.

Operation and Maintenance Phase
In this phase, assessment is conducted based on the energy consumption [31] of apartment houses.For the consumption of heating energy by empirical houses (third floor and fourth floor: one apartment unit each), the simulation data from the manufacturer of input materials were used.
For the two apartment units, 170 m 2 (85 m 2 /unit) was applied.For reference and common spaces, in contrast, 908 m 2 was adopted.Then, LCA was performed with the assumption that the building's useful life was 30 years.
As shown in Table 12, the total CO 2 emissions for 30 years are 1,890,282 kg CO 2 eq.In the case of the empirical houses (third floor and fourth floor: one apartment unit each), which were built with low-carbon ready-mixed concrete and concrete products, it was able to reduce heating energy consumption by 37%.

Demolition Phase
In this phase, CO 2 emissions were analyzed from waste concrete, waste metal, waste wood and waste glass.The disposal method was classified into recycling, burying and incineration steps.Assessment was performed after applying the three methods as follows: recycling (97.5%), landfill (1.8%) and incineration (0.7%) [35].
The CO 2 emissions generated during the demolition phase are 33,412 kg CO 2 eq.In particular, waste concrete accounts for 96.7% with 32,311 kg CO 2 eq (See Table 13.).According to estimation on the LCCO 2 emissions of the building, a total of 595 tons CO 2 eq./m 2 is produced annually.As shown in Table 14 and Figure 5, in terms of CO 2 emissions by life cycle, the material production (manufacture) phase (81.8%) was the highest, followed by the construction phase (1.9%), the operation maintenance phase (10.6%) and the demolition phase (5.7%).

The Results of the LCCO₂ Assessment of the Low-Carbon Building
According to estimation on the LCCO₂ emissions of the building, a total of 595 tons CO₂ eq./m 2 is produced annually.As shown in Table 14 and Figure 5, in terms of CO₂ emissions by life cycle, the material production (manufacture) phase (81.8%) was the highest, followed by the construction phase (1.9%), the operation and maintenance phase (10.6%) and the demolition phase (5.7%).In particular, as shown in Figure 6, empirical houses revealed a decrease in CO₂ emissions by 141.8 kg CO₂ eq./m 2 annually, compared to the common and reference spaces.Furthermore, the sources of CO₂ emissions in each stage were as follows: ready-mixed concrete (manufacture phase), transportation of ready-mixed concrete (construction phase), consumption of heating energy (LNG) (operation and maintenance phase) and concrete disposal (demolition phase).In particular, as shown in Figure 6, empirical houses revealed a decrease in CO 2 emissions by 141.8 kg CO 2 eq./m 2 annually, compared to the common and reference spaces.Furthermore, the sources of CO 2 emissions in each stage were as follows: ready-mixed concrete (manufacture phase), transportation of ready-mixed concrete (construction phase), consumption of heating energy (LNG) (operation and maintenance phase) and concrete disposal (demolition phase).

The Results of the LCCO₂ Assessment of the Low-Carbon Building
According to estimation on the LCCO₂ emissions of the building, a total of 595 tons CO₂ eq./m 2 is produced annually.As shown in Table 14 and Figure 5, in terms of CO₂ emissions by life cycle, the material production (manufacture) phase (81.8%) was the highest, followed by the construction phase (1.9%), the operation and maintenance phase (10.6%) and the demolition phase (5.7%).In particular, as shown in Figure 6, empirical houses revealed a decrease in CO₂ emissions by 141.8 kg CO₂ eq./m 2 annually, compared to the common and reference spaces.Furthermore, the sources of CO₂ emissions in each stage were as follows: ready-mixed concrete (manufacture phase), transportation of ready-mixed concrete (construction phase), consumption of heating energy (LNG) (operation and maintenance phase) and concrete disposal (demolition phase).

Discussion and Limitation
This study aimed to comparatively analyze the effects of the construction materials (concrete, cement, etc.) manufactured with carbon emission reduction technology on the carbon emissions of a reinforced concrete structure throughout its life cycle.
For this, car emissions and the reduction amount by construction material were estimated, and the results were applied to the target building.Then, its life cycle carbon emissions were estimated.
There are two types of products: a product that reduced carbon emissions during the production of construction materials; and an insulated product that reduces energy consumption during the operation of a building.Therefore, the reduction of energy consumption in the operation phase was expected.
However, no effective values on energy simulation in the target building were applied.In addition, there were limitations in individually analyzing the LCCO 2 emissions of the various concrete products that were applied to each building area.
Hence, it is needed to improve the carbon emission estimation results by energy resumption after monitoring energy consumption at the operation phase.Furthermore, there should be studies to analyze the effects of CO 2 reduction in each construction material on a building through diverse influential factors, for example, input of construction materials, life cycle, energy source, etc.

Conclusions
This study estimated LCCO 2 emissions against the buildings built with low-carbon concrete and energy-saving materials, using Korea's LCI DB for construction materials.The LCCO 2 assessment and analysis on low-carbon construction materials and buildings found the following: (1) The carbon-reduction technologies for construction materials include: the reduction of resource consumption by using recycled materials or industrial byproducts (manufacture phase); the decrease in CO 2 emissions by shortening the production processes or changing fuels; the decrease in resource consumption throughout the life of buildings by reducing the consumption of materials for repair with construction materials that reduce energy consumption and have a long lifespan (operation and maintenance phase).(2) A low-carbon building refers to one built with low-carbon construction materials and conventional ones.A total of 3115 tons of construction materials were added.Among them, those for a building frame (ex: ready-mixed concrete, sand and gravel, reinforcing bar, pipe, etc.) accounted for over 80%.(3) According to the analysis on CO 2 emissions by input material, ready-mixed concrete, wood, reinforcing bar and cement were the major sources of CO 2 emissions.They accounted for 92.8% of total annual CO 2 emissions.(4) Total CO 2 emissions generated throughout the life (30 years) of low-carbon buildings are 2,423,004 kg CO 2 eq.In terms of CO 2 emissions by stage, the operation and maintenance phase (78.0%) was the highest, followed by the manufacture phase (20.1%), the demolition phase (1.4%) and the construction phase (0.5%).When compared to the studies (domestic papers) under simulation conditions [41], the results were similar to this study in terms of emission ratio in the order of operation stage (81.39%-86.45%),production stage (11.66%-15.85%),construction stage (1.49%-2.15%)and disposal stage (0.4%-0.61%).In overseas studies, as well [42], the operation stage (77%-85%) was the highest, followed by the production and construction stages (14%-21%) in terms of emission ratio.These results reveal that energy-saving and carbon emission reduction effects would increase during building maintenance.(5) Regarding LCCO 2 emissions, carbon emissions were the highest in the manufacture of ready-mixed concrete for which heating energy, electricity and input materials were mostly used.This kind of result stems from the input of the materials for low-carbon concrete and energy-saving ones.
(6) Compared to common and reference areas, empirical houses reduced CO 2 emissions by about 25% (141.8 kg CO 2 eq./m 2 per year).(7) To reduce CO 2 emissions throughout the life of buildings, it is needed to consider the embodied energy of construction materials and embodied CO 2 emissions at the construction material manufacture phase, as well as at the operation and maintenance phase.There should be an in-depth study on carbon-reduction of construction materials in empirical houses.

Figure 1 .
Figure 1.System boundary for LCCO₂ assessment of a building.

Figure 1 .
Figure 1.System boundary for LCCO 2 assessment of a building.

Figure 2 .
Figure 2. The cumulative mass contribution of input materials.

Figure 2 .
Figure 2. The cumulative mass contribution of input materials.

Figure 3 .
Figure 3. CO₂ emission distribution of the whole building during the material production phase

Figure 3 .
Figure 3. CO 2 emission distribution of the whole building during the material production phase

Figure 4 .
Figure 4. CO₂ emissions by construction material input in the building sectors.

Figure 4 .
Figure 4. CO 2 emissions by construction material input in the building sectors.

Table 1 .
Properties of low-carbon construction materials (ready-mixed concrete).

Table 2 .
CO 2 emissions and reduction amounts of low-carbon products as compared to the baseline product (unit: kg CO 2 eq./unit).

Table 3 .
Description of the unit process for the building LCCO₂ assessment.

Table 4 .
List of LCI DB for construction materials.

Table 5 .
Overview of the building.
GWP: Global Warming Potential.Resources: (1) KLCI DB: Korea life cycle inventory database, (2) CFF: Carbon Emission Factor in the development of carbon reducing concrete structural materials and energy-saving building materials.

Table 5 .
Overview of the building.

Table 6 .
Overview of the LCCO₂ assessment.

2nd Floor Common Space 3rd, 4th Floor Reference House 3rd, 4th Floor Empirical House (Low-Carbon Materials)
SpatialResources and energy, which is input and output into the building life cycle (production of building materials, construction, use, disposal)

Table 7 .
The cumulative mass contribution analysis.

Table 6 .
Overview of the LCCO 2 assessment.

Table 7 .
The cumulative mass contribution analysis.

Table 8 .
CO 2 emissions by input material during the material production phase.

Table 9 .
Material inputs and CO 2 emissions by building sector.

Table 11 .
CO₂ emissions by construction activity.

Table 10 .
CO 2 emissions by material transport.

Table 11 .
CO 2 emissions by construction activity.

Table 12 .
CO 2 emissions during the operation and maintenance phase.

Table 13 .
CO 2 emissions by demolishing the building.