**1. Introduction**

Much effort has been made to improve environmental regulations in order to properly respond to climate change associated with global warming, both overseas and domestically throughout all industries. In order to prepare for climate change, the governmen<sup>t</sup> has announced a voluntary reduction goal, called the Intended Nationally Determined Contributions (INDC) to reduce domestic greenhouse gases by 37%, compared to Business as Usual (BAU) [1]. Amid this, the construction industry, as a core industry, has caught the attention of many for its potential contribution to the achievement of this domestic greenhouse gas reduction goal. The construction industry is a large-scale consumption industry that is responsible for about 30–40% of the CO2 emissions in all industries [2–4]. We are in a state where technology that can reduce CO2 emissions is becoming a necessity. Technology that could achieve the CO2 emissions reduction goal through a realistic CO2 emissions reduction plan, over the entire life cycle of buildings, is needed. In order to reduce the amount of CO2 emissions that are inevitable over the entire life cycle of buildings, the construction industry is evaluating this via quantitative investigation, and research on methods that could reduce or improve carbon emissions are actively underway [5]. In order to reduce the CO2 emissions that are released over the life cycle

of a building, the CO2 emissions data must first be analyzed for each stage, and then a building's greenhouse gas evaluation must be performed considering its entire life cycle. However, more research is currently being performed on CO2 emissions assessment at the operational stage, where more energy is used. In particular, there is very little research on CO2 emission assessment of construction processes because data analysis is difficult due to the short construction period, and because data is difficult to secure [6,7].

This study focused on the construction stage for the reduction and managemen<sup>t</sup> of CO2 emissions of the apartment housing. The main purpose of this study is to sugges<sup>t</sup> a CO2 emission assessment method for the apartment housing construction process. Another purpose is to analyze the CO2 emissions characteristics for each of the 13 main work types used during construction of the apartment buildings, using CO2 emissions evaluation proposals of apartment housing construction projects, and construction records for actual construction sites.

In this study, apartment buildings construction sites were the subjects and the CO2 emissions characteristics for construction materials and construction equipment were analyzed by the work types that occur in each stage. The following process was used to quantitatively assess the amount of CO2 emissions from apartment housing construction, and reflects actual data [8,9].

First, the life cycle assessment was divided into three stages: transportation, construction, and disposal, to assess the CO2 emissions from the construction site. The assessment subjects, which were construction materials and equipment, were the construction materials and equipment invested into each process.

Second, the amount of CO2 emissions from the transportation stage was limited to the fuel consumption of the transportation vehicles required to transport necessary materials to the construction site. An estimation method was proposed for CO2 emissions that considered the transportation distance, transportation vehicle type and average fuel efficiency, number of transportation vehicles, and load for each construction material.

Third, the amount of CO2 emissions during the construction stage was the total fuel and electricity used by construction machines, transportation equipment, the field office, and other facilities that were used on site during construction. The amount of fuel and electricity used during the construction stage for machine equipment and electricity usage was calculated by analyzing data from standard construction estimates and data from the field office.

Fourth, the amount of CO2 emissions during the disposal stage was estimated by first calculating the amount of construction waste that occurs by work type. This was done by reviewing the construction materials excess, then quantitatively calculating the amount of CO2 emissions according to the method of handling construction waste, based on the statistical research report on the recycling of construction waste. With regard to the carbon emission coefficient in relation to the amount of construction materials used, and the amount of energy consumed in each stage, the emission factor of the Korea National life cycle inventory database (LCI DB) and the Korea National DB construction material environment information were applied. The flow of this study is shown in Figure 1.

An assessment method was created regarding the amount of energy used and the CO2 emissions from construction materials and equipment in relation to 13 main types of construction work. This was done by dividing the construction process into three stages: transportation, construction, and disposal. A database was built for each stage, and the amount of CO2 emissions was estimated using it. The 13 main work types during the apartment construction process were deduced, and an analysis of the CO2 emissions characteristics of each stage was performed.

**Figure 1.** The conceptual flow chart of this study.
