*3.1. Overview*

In this study, the construction process of the apartment housing was divided into transportation, construction, and disposal stage for the purpose of analyzing CO2 emission characteristics of the apartment housing construction process in Figure 4.

**Figure 4.** CO2 emission assessment method proposed in construction process.

In order to estimate the amount of energy used in vehicles transporting materials to the apartment housing construction site, the amount of CO2 emissions in the transportation stage was limited to the amount of fuel used by transportation vehicles when transporting materials from the supply location to the construction site. The distance for fuel consumption calculation was estimated based on scenario. Based on previous research, a CO2 emissions-assessment method considering the distance, average fuel efficiency, number of transportation vehicles, and load (depending on the amount of construction materials used) was presented. The amount of CO2 emissions during the construction stage was the total fuel and electricity used by construction machines and equipment, transportation equipment, the field office, and other facilities used for and during construction on site. The amount of fuel and electricity used during the construction stage for machine equipment and electricity usage was calculated by analyzing data from Korean standard construction estimates and from Korea breakdown cost tables. The amount of CO2 emissions during the disposal stage was estimated by first calculating the amount of construction waste that occurred (by work type) based on surcharges on the construction materials, then quantitatively calculating the amount of CO2 emissions according to the method of handling construction waste, based on a statistical research report on the recycling of construction waste. With regard to the CO2 emission factor regarding the amount of construction materials used and the amount of energy consumed in each stage, the Korean National LCI DB and the Korean National DB of the construction-material environmental information was applied [23,24]. In the transportation stage, distance and fuel for transportation equipment for CO2 evaluation were analyzed, and Korean standard product and national LCI DB were applied. In the construction phase, the construction specification, the national LCI DB, and the Korean Standard Specification were applied to analyze the amount of fuel and the amount of power applied to evaluate 13 construction types. In the disposal stage, the national LCI DB and the Korean Standard Package were applied to analyze the distance fuel for the waste transportation equipment.

#### *3.2. Estimation Method in the Transportation Stage*

The main factors that must be considered in order to estimate the amount of CO2 emissions in the transportation stage are mainly the amount of construction materials used, and the equipment used for transportation [25]. Also, it considered the transportation distance and the vehicles used to

load at the supply and construction sites. This data was used to estimate the amount of energy used, which was then converted to an estimate of the amount of CO2 emissions. This calculation method includes use of the amount of materials at the construction site to deduce the number of transportation vehicles used, and fuel consumption was calculated by using the transportation distance and vehicle fuel efficiency. To do this, the distance to the construction site (from the supply sites), type of vehicle and standard fuel efficiency, and the number of vehicles used must be considered. Because the length of time that transportation vehicles used at a site is flexible, it is impossible to quantify work capacity that depends on the type of vehicle [26,27].

In this study, the loads of vehicles listed in standard construction estimates were investigated, along with the main transportation vehicles observed at the actual site, in order to calculate the number of transportation vehicles according to the supply output value of each construction material. The amount of fuel that was consumed during the transportation stage was calculated by multiplying the distance to the site by the average fuel efficiency of each vehicle. The assessment range of the transportation stage was limited to the fuel consumption for one-way transportation of construction materials by the types of vehicles used for each work type.

In this study, the transportation vehicles and transportation distance regarding the materials used were set as shown in Table 2, and the number of transportation vehicles was calculated according to the supply output value for each construction material. Equations (1) and (2) show the calculation formulas for fuel consumption and CO2 emissions, respectively, during the transportation stage [28,29]. The transportation distance was set to 40 km as referenced from the guideline of Korea Ministry of Land, Infrastructure and Transport standard specification for construction [29].

$$DO\_t = \sum \left( \mathcal{U}\_t \times \frac{k}{M\_{\rm f}} \right) \tag{1}$$

*DOt*: Amount of Fuel Consumed in the Transportation Stage (-)

*Ut*: Number of Vehicles Used (n)

*k*: Distance (km)

*Mt*: Transportation Vehicle Fuel Efficiency (km/L)

$$C\_t = \sum (DO\_t \times EF\_t) \tag{2}$$

*Ct*: Amount of CO2 Emissions in the Transportation Stage (kg-CO2) *DOt*: Amount of Fuel Consumed in the Transportation Stage (L) *EFt*: Fuel Emission Factor (kg-CO2/L)



#### *3.3. Estimation Method in the Construction Stage*

In order to estimate the amount of CO2 emission in the construction stage, this study created categories of fuel consumption and electricity consumption amounts, and calculated the total amount of fuel and electricity used for construction machines and equipment, transportation equipment, field office, and other facilities at the construction site, used for constructing buildings. For the amount of fuel consumed, the number of days and time that equipment was used, according to each work type, was calculated by analyzing the equipment usage conditions from the construction report. The fuel efficiency for each kind of equipment was based on the operating expenses estimated

in the standard construction estimate. Electricity consumption was calculated by obtaining the monthly electricity usage statement for the entire construction period, and calculating the electricity consumption according to the duration of each work type based on the progress schedule. If multiple work types proceeded simultaneously, according to the characteristics of the construction process, the relevant electricity consumption was divided up between the number of construction days for the overlapping work types. In this study, for construction processes in which the construction method (including construction conditions by site) and equipment usage differed, data regarding construction machines and equipment, and transportation equipment used at the actual construction site were obtained from the supply output lists from the actual construction site, and from construction reports. Data regarding the amount of fuel used were analyzed. Data were also analyzed regarding electricity consumption from the actual field office. The calculation formula for the amount of CO2 emissions according to fuel and electricity consumption during the construction stage is shown in Equations (3) and (4), respectively [30].

$$C\_{\mathcal{O}^0} = \sum (M\_{\mathcal{E}} \times T\_{\mathcal{E}} \times EF\_{\mathcal{E}} \times \mathcal{U}\_{\mathcal{E}}) \tag{3}$$

*Cco*: Amount of Fuel CO2 Emissions in the Construction Stage

*Mc*: Fuel Efficiency (L/h)

*Tc*: Time (h)

*EFc*: Fuel Emissions Factor (kg-CO2/L)

*Uc*: Work Equipment Qty. (n)

$$\mathbb{C}\_{\mathfrak{C}^{\mathfrak{t}}} = \sum (I\_{\mathfrak{c}} \times EF\_{\mathfrak{c}}) \tag{4}$$

*Cce*: Amount of Electricity CO2 Emissions in the Construction Stage

*Ic*: Electricity Usage Amount (kwh)

*EFc*: Electricity Emissions Factor (kg-CO2/kwh)

#### *3.4. Estimation Method in the Disposal Stage*

In order to estimate the amount of CO2 emissions in the disposal stage, the amount of construction waste that occurs for each work type was estimated, and the amount of CO2 emissions, according to the processing method of each construction waste, was calculated. In order to estimate the amount of construction waste that occurs by work type, the waste generation estimation method based on surcharge was used. In this study, the premium rate was applied as a means to predict waste at the construction site, and the surcharge value that was presented in the standard construction estimate issued in 2012 (by the Korea Institution of Construction Technology and the Ministry of Land). Construction waste was divided into construction demolition waste, combustible waste, and nonflammable waste according to the method of handling construction waste, which are handled through intermediate processing agencies, incinerators, and landfills, respectively. When calculating data regarding intermediate processing agencies, because data differs from different companies, the incineration and landfill rate referred to the present processing conditions of waste for each construction material according to the Korea Waste Statistical Yearbook in 2012. The surcharges, weight conversion factor, landfill, and incineration emissions factor were considered for each construction material according to the amount used, in order to estimate the amount of CO2 emissions that occur in the incineration and landfill process Equation (5). The amount of energy consumed during the construction waste transportation process was calculated using Equations (6) and (7), based on the amount of fuel consumed in the vehicles that transport the waste to landfills and incinerators.

The estimation method for the amount of CO2 emissions in the construction waste transportation stage was identical to that of the construction process above, and it was set as the amount of energy consumed by transportation equipment according to waste volume. In order to do this, the amount of construction equipment, standard fuel efficiency, and the distance to landfills and incinerators were applied to calculate the amount of fuel used during transportation. The assessment scope of the waste

transportation process was limited to the amount of fuel consumed by vehicles providing one-way transportation of construction waste [31,32].

$$\mathbb{C}\_{dl} = \sum (DM\_d \times EF\_{dl} \times L\_d) \tag{5}$$

*Cdl*: Amount of CO2 Emissions in Landfill Process of the Demolition Stage (kg-CO2)

*DMd*: Construction Waste Volume (kg)

*Ld*: Landfill Rate (%)

*EFdl*: Landfill Emissions Factor (kg-CO2/kg)

$$C\_{di} = \sum (DM\_d \times EF\_{di} \times I\_d) \tag{6}$$

*Cdi*: Amount of CO2 Emissions in Incineration Process of the Demolition Stage (kg-CO2) *DMd*: Construction Waste Volume (kg)

*Id*: Incineration Rate (%)

*EFdi*: Incineration Emissions Factor (kg-CO2/kg)

$$DO\_d = \sum \left( \mathcal{U}\_d \times \frac{k}{\mathcal{M}\_d} \right) \tag{7}$$

*DOd*: Amount of Fuel Consumed in the Construction Waste Transportation Stage (L)

*Ud*: Number of Vehicles Used (n)

*k*: Distance (km)

*Md*: Transportation Vehicle Fuel Efficiency (km/L)

$$\mathcal{C}\_d = \sum (TO\_d \times EF\_d) \tag{8}$$

*Cd*: Amount of CO2 Emissions in the Construction Waste Transportation Stage (kg-CO2)

*TOd*: Amount of Fuel Consumed by Transportation Equipment (L)

*EFd*: Fuel Emissions Factor (kg-CO2/L)
