CO₂ Emission Calculation Method during Construction Process for Developing BIM-Based Performance Evaluation System

Abstract

Nowadays, global warming is a big challenge for human beings; since the Kyoto Protocol became effective, greenhouse gas emissions have been an important environmental evaluation index in all industries. Construction is a big contributor to greenhouse gas emissions. The greenhouse gas emissions in the construction stage are mainly from the construction materials and the construction activities. The purpose of this paper is to quantitatively calculate the carbon dioxide emissions in the construction process, and provide a method of controlling the CO₂ emissions effectively by converting into cost. In this study, the authors selected the tunnel construction as the research object, and chose the primary greenhouse gas-CO₂ to estimate emissions. The authors did a research based on BIM (Building Information Modeling) technology, to calculate CO₂ emission during the construction process. It considered the CO₂ emissions from main materials and equipment. Finally, the authors used the recent carbon emission trading price to convert the CO₂ emission into cost, and did the economic analysis. The method proposed in this paper can effectively evaluate the CO₂ emissions in the construction process; it has a good reference significance for the selection of low-carbon emission materials in the design process, and it provides a case reference and direction for research of low-carbon equipment. By using the EU emissions trading system, the economic conversion of CO₂ emissions will provide an economic evaluation index for the CO₂ emissions of tunnel construction activities. Meanwhile, based on the method of this study, a BIM-based automated performance evaluation system could be developed.

1. Introduction

According to the United Nations Framework Convention on Climate Change (UNFCCC), industrialized countries must reduce their greenhouse gas emissions (GHG) [1]. South 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 [2]. Therefore, all industries should join efforts to lower their greenhouse gas emissions. Energy is needed to manufacture construction products, and is “invested” in the construction, modernization and renewal measures of new buildings. Energy consumption occurs in the process of transportation and construction, as well as in the demolition and disposal of buildings and materials [3]. Construction is a significant sector for emitting greenhouse gas [4]. In particular, South Korea’s construction industry accounts for about 48% of the national material consumption, and 40% of the national energy consumption [5,6]. In order to reduce the GHG emissions of construction, at first we need to know exactly how much is being emitted. The purpose of this paper is to quantitatively calculate the CO₂ emissions during the construction process and to provide a method of controlling the CO₂ emissions effectively by converting them into cost. There are several phases during a building’s lifecycle that emit greenhouse gas, including materials production, construction, use, maintenance, and the end of life [5,7]. As the materials production stage and construction stage are directly related to the construction process, this study selected the first two stages as study stages. It mainly considered GHG emissions from the main materials and equipment. Meanwhile, the building information modeling (BIM) technology has been gaining more and more attention in the Architecture, Engineering and Construction (AEC) industry. One of the main advantages of BIM is its ability for the user to quickly get relevant information about materials and parts which have already been created in the modelling phase [8]. Depending on the stage of the project and the complexity of the model, estimates can be made from details stored in the model. This study made full use of the quantity take-offs function of Revit (a BIM software).

Almost 80% of global warming gas emissions by volume are carbon dioxide (CO₂). Of that 80%, approximately a third arises from sectors relevant to tunneling, including transport, cement and steel manufacture and commercial energy consumption [9]. So, this study selected a tunnel as a study object. It used BIM to calculate the CO₂ emission during the tunnel construction process, including CO₂ emission caused by tunnel materials and construction activities. It aimed to make the tunnel environmental assessment work simpler, and to offer a good basis for developing BIM-based automated performance evaluation system in the future.

2. Literature Review

2.1. Related Research

J. Kim [10] did a study of reliability-based quantity estimation error analysis, applying for a road BIM project. It showed the detailed method of how to use the Revit structure to make a 3D tunnel model and proved that the BIM based design is becoming more useful, because of a more exact quantity estimation, considering effects of vertical curve and superelevation. In the construction industry, various efforts have been made to evaluate environmental impacts; M. Yang [11] suggested a methodology to calculate the CO₂ emission quantity from major construction materials of a steel box girder railway bridge project, along with a system to calculate it automatically. B. Kim et al. [4] presented a comparative analysis on how much greenhouse gas is generated by various equipment types are used in different construction activities. It showed a detailed method of how to calculate the fuel consumption of equipment. M. Oh et al. [12] did a study to evaluate CO₂ of a building in the early design stage, as well as to assess its impacts on the environment. J. Araujo et al. [7] analyzed the importance of the use phase of a road in the LCA of different paving alternatives, namely by evaluating energy consumption and gaseous emissions throughout the road pavement’s life. K. Jun et al. [13] did a study on the CO₂ emission cost for different kinds of tile work types in the construction phase. Y. Lee et al. [14] did a study to develop a system for the BIM-based estimation of CO₂ emissions, for apartments utilizing Autodesk Revit, by using the national Life Cycle Inventory Database (LCI DB). Through the above investigation, we can see that BIM has the advantage of accurate evaluation in quantity estimation. Meanwhile, in order to evaluate the environmental impact in the field of construction, a variety of studies have been carried out. Some studies calculate CO₂ emission from construction material, while others calculate the CO₂ emissions associated with various equipment in different construction activities. At the same time, there are also studies on the calculation of CO₂ emission costs related to various types of work during the construction process. However, there is a lack of comprehensive evaluation on the cost of CO₂ emissions associated with various influencing factors in construction activities, which comes both from materials and equipment. In this search, based on previous studies’ use of BIM for quantity estimates and CO₂ emissions calculation, the authors propose a method to convert CO₂ estimates to an economic indicator, by using EU emission trading system.

2.2. LCA (Life-Cycle Assessment)

Life-cycle assessment (LCA) is a technique to assess the environmental impacts associated with all the stages of a product’s life from-cradle-to-grave (i.e., from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling) [5,15].

For LCA CO₂ emission evaluation of tunnel project, the authors divided the life cycle of tunnel into four stages. (Materials production; construction; use and maintenance; and end of life), each of which consists of the following:

(1)

Materials production: this phase includes 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 [5].

(2)

Construction: this phase includes all the activities necessary for tunnel construction, such as earthworks, concrete pouring, material transport etc.

(3)

Use and maintenance: this phase includes the operation for using, repairing and manage the tunnel project until it is demolished, such as, repairment of tunnel road pavement, maintenance of lighting and ventilation condition inside the tunnel, etc.

(4)

End of life: the last phase occurs when the tunnel reaches the end of its useful life. According to the tunnel management strategy, the tunnel may be recovered or demolished, and removed materials may be recycled or left in the field, increasing the burden on the environment [7].

The life-cycle assessment (LCA) of tunnel CO₂ emission includes four stages, as shown in Figure 1.

In this study, the authors selected stage 1 and stage 2 as the research scope, which are directly related with construction process.

3. Research Scope and Method

This research attempts to find the CO₂ emission calculation method during the tunnel construction process, and takes a 10-m tunnel section as an analysis object (While only one of the cross sections is selected for research, there could be many different cross sections in the tunnel project. This study mainly focuses on the research of calculation method and used the calculated amount of 10-m tunnel section as a representative case study), and other necessary research data was based on assumption similar to the actual project. The process of this study is as follows:

(1)

In the aspect of BIM model, the authors used CAD to draw the tunnel cross section, then imported it to the Revit, and used the Revit family to create the 3D model of each part, then gave material information to each part, and finally combined them together.

(2)

With respect to tunnel materials, the authors investigated the related CO₂ emission factors, and did a survey about the main engineering equipment used in the construction process.

(3)

The authors inputted the CO₂ emission factors to the Revit, and set the calculated value formula for the CO₂ emission. Finally, through the function of Revit, the authors could derive the quantity of each part of the tunnel and calculate the related CO₂ emission automatically.

(4)

With regard to the quantity derived from the Revit, and referring to the national standard estimating reference, published by the Korea Institute of Construction Technology (KICT), the authors calculated the fuel consumption for the main construction equipment, and then multiplied it by the CO₂ emission factors. The authors obtained the CO₂ emission for the main equipment in the process of tunnel construction.

(5)

The authors analyzed the CO₂ emission during the tunnel construction process, including the CO₂ emission from the material, and the CO₂ emission produced by the main equipment used in the construction process. By using the EU emissions trading system, the authors calculated the CO₂ emission cost, and economic analysis was also carried out.

4. CO₂ Emission Calculation for a Tunnel Project

4.1. Creating the 3D Tunnel Section by BIM Tool

Project A is a highway tunnel project located in South Korea, of which the overall length is 1477.6 m, as shown in Figure 2. It was designed as four lanes and built by NATM (New Austrian Tunnelling method).

In order to find a method to calculate the CO₂ emissions from the tunnel project, the authors selected a 2D tunnel cross section drawing, and assumed the length of the tunnel section to be 10-m as an analysis object, as shown in Figure 3.

The process of creating the 3D tunnel section is shown in Figure 4.

4.2. Survey for CO₂ Emission Factor and Main Equipment

4.2.1. Survey for CO₂ Emission Factor

The authors investigated the CO₂ emission factors of materials from different resources. The result is listed in

Table 1. CO₂ emission factors of materials.

Name of the Material	CO2 Emission Factor	Unit	Resources
Ready mixed concrete25-240-15	420	CO2 kg/m3	MOTIE of Korea [16]
Ready-mixed concrete25-210-12	400	CO2 kg/m3	MOTIE of Korea [16]
General concrete (ready-mixed concrete)	346	CO2 kg/m3	KEITI of Korea [17]
PVC	1265	CO2 kg/t	MOTIE of Korea [18]
Cement	1050	CO2 kg/t	ME of Korea [16]
Stainless steel	2800	CO2 kg/t	ME of Korea [19]
Carbon steel	2165	CO2 kg/t	ME of Korea [19]
Rubble	11.33	CO2 kg/m3	Intergovernmental Panel on Climate Change (IPCC1996) [20]

.

Because the quantity derived from the Revit exists as volume form, so some units above need to be changed. The changed CO₂ emission factors are listed in

Table 2. The changed CO₂ emission factors.

Name of the Material	CO2 Emission Factor (Before)	Material Reference Density	CO2 Emission Factor (Changed)
PVC	1265 kg/t	1280 kg/m3	1619 kg/m3
Cement	1050 kg/t	3150 kg/m3	3308 kg/m3
Stainless steel	2800 kg/t	2700 kg/m3	7560 kg/m3
Carbon steel	2165 kg/t	2700 kg/m3	5846 kg/m3

.

4.2.2. Survey for Main Equipment

As the objective of the research was to develop a method to quantify the impact of CO₂ emissions as an economic cost, the complexity of the actual construction process was simplified. In this study, the primary excavation method used was blasting, but the scope of the analysis was limited to the primary construction equipment used, listed in

Table 3. Main construction equipment research scope.

Work Type	Main Equipment
Earthwork	Dump truck
	Wheel loader
Concrete work	Mixer-truck
Cement work	Mixer-truck

.

4.3. Extracting Materials Quantity and Calculating CO₂ Emission

The process of calculating CO₂ emission is as follows:

Step 1: Editing parameter of CO₂ emission factor

As there is no input parameter related with CO₂ in Revit, we edited the shared parameters and made a new input parameter of CO₂ emission factor named “CO₂ emission [kg per m³]”, as shown in Figure 5.

Step 2: Selecting parameter we needed

The next step was to select the parameters we needed from the Revit.

Step 3: Making CO₂ emission computing formula

The authors used the calculated value function of Revit. Through making a computing formula (CO₂ emission [kg per m³]*Material: Volume), it was possible to calculate the CO₂ emission by Revit itself, without any plugin, as shown in Figure 6.

Step 4: Inputting CO₂ emission factor

The authors specified CO₂ emission factors to each part of the tunnel.

Step 5: Extracting materials quantity and CO₂ emission

After selecting the needed parameters, materials quantity and CO₂ emission can be automatically extracted, as shown in Figure 7.

4.4. CO₂ Emission Calculation of the Main Equipment

4.4.1. The Process of Calculating CO₂ Emission for the Main Equipment is Illustrated for the Wheel Loader Used for Earthwork Below

Step 1: Getting the earthwork quantity

The authors used Revit to draw the excavation scope to get earthwork quantity; the volume from the Revit is 748.4 m³, as shown in Figure 8.

Step 2: Calculating the CO₂ emission of the wheel loader

Referring to the national standard estimating reference by the Korea Institute of Construction Technology (KICT), and assuming the necessary data, which is listed in

Table 4. Wheel loader variable data.

Equipment Variable	Data
q (bucket capacity)	1.72 m3
k (bucket coefficient)	1.0
f (soil conversion factor)	77%
e (production efficiency)	60%
m (reciprocal of the velocity)	1.8(s/m)
l (average distance)	8.0 m
t1 (load time)	6 s
t2 (idle time)	14 s

, the authors can calculate the fuel consumption for wheel loader.

Productivity per hour (Wheel loader): Q = 3600·q·k·f·e/(m·l + t1 + t2) (m³/h)

(1)

To better understand the calculation process, consider the following situation. A hauling activity requires a volume of 748.4 m³ of earthwork. A wheel loader with a bucket capacity of 1.72 m³ loads the earth into a dump truck. Authors suppose that the bucket coefficient is 100%. That is, the loader has an output of 1.72 cubic meters of the earth per cycle. Meanwhile, it has a total cycle time for the activity, as follows: m × L + t1 + t2 = 1.8(s/m) × 8.0(m) + 6(s) + 14(s) = 34.4 s, where m (second per meter) is the reciprocal of the velocity of the wheel loader, L (meter) is the average distance, and t1 (second) and t2 (second) are load time and idle time, respectively. Cycles of equipment per hour are calculated as 3600(s)/34.40(s) = 104.65 cycles per hour. The soil conversion factor (f) and production efficiency (e) are assumed as 77% and 60%, respectively. Such values are applied to Equation (1), resulting in the working hours of the loader for the hauling activity [4].

So, the hours of the work are: 748.4/(1.72 × 104.65 × 0.77 × 0.60) = 9 h.

The fuel consumption is: 9.8 L/h × 9 h = 88.2 L

Referring to the LCI DB, the CO₂ emission factor is 2.6 kg/L, The CO₂ emission of the wheel loader is: 2.6 kg/L ×88.2 L = 229.32 kg

4.4.2. Calculating the CO₂ Emission for Other Equipment

Finding the volume needed from the materials quantity extracted by Revit, as shown in

Table 5. Quantity of work.

Work Type	Section	Volume(m3)
Earthwork	Excavation scope	748.4
Concrete work	Drainage way	19.95
	Concrete lining	62.61
	Shotcrete	11.45
	Concrete slab (30 cm)	22.5
Cement work	Cement treated base	11.25

, and referring to the national standard estimating reference by KICT, and assuming the necessary data, it can calculate the fuel consumption for the dump truck and mixer-truck. The equipment CO₂ emission of mixer-truck and dump truck is calculated shown as follows:

Calculation for CO₂ emission of mixer-truck:

Productivity per hour (mixer-truck): Q = 60·w·e/[t1 + 60·(l/v1 + l/v2) + t3 + t4]
(m³/h)

(2)

Applying variable data in

Table 6. Mixer-truck variable data.

Equipment Variable	Data
w (carrying capacity)	6 m3
e (production efficiency)	95%
t1 (loading time)	4.5 min
t3 (unloading time)	3 min
t4 (waiting time)	8 min
l (average distance)	3 km
v1 (travel speed with loading)	15 km/h
v2 (travel speed without loading)	20 km/h

Note: For concrete lining, pumping time is considered, t3 is assumed as 24 min. For shot concrete, shotcrete time is considered, t3 is assumed as 45 min.

to Equation (2); Q(Mixer-truck) = 9.37 m³/h, Q(Mixer-truck for concrete lining) = 5.95 m³/h, Q(Mixer-truck for shot concrete) = 4.36 m³/h.

So, the hours of the work are: (19.95 + 22.5 + 11.25)/9.37 + 62.61/5.95 + 11.45/4.36 = 18.88 h.

The fuel consumption is: 13 L/h × 18.88 h = 245.44 L.

Referring to the LCI DB, the CO₂ emission factor is 2.6 kg/L, the CO₂ emission of the mixer-truck is: 2.6 kg/L × 245.44 L = 638.14 kg.

Calculation for CO₂ emission of dump truck:

Productivity per hour (dump truck): Q = 60(T/rt·L) f·E/[Cms·T·L/(60·Es·q·k·rt) +
(l/v1 + l/v2)·60 + t3 + t4 + t5)] (m³/h)

(3)

Applying variable data in

Table 7. Dump truck variable data.

Equipment Variable	Data
T (carrying capacity)	15 t
rt (density in natural stage)	1.9 t/m3
L (volume conversion rate)	1.25
f (soil conversion factor)	77%
E (production efficiency of dump truck)	90%
Cms (cycle time for loading by loader)	34.4 s
q (bucket capacity)	1.72 m3
k (bucket coefficient)	1.0
Es (production efficiency of loader)	60%
t3 (unloading time)	0.8 min
t4 (waiting time for loading)	0.42 min
t5 (automatic cover installation and dismantling time)	0.5 min
l (average distance)	6 km
v1 (travel speed with loading)	15 km/h
v2 (travel speed without loading)	20 km/h

to Equation (3); Q (Dump truck) = 8.34 m³/h.

So, the hours of the work are: 748.4/8.34 = 89.74 h.

The fuel consumption is: 15.9 L/h × 89.74 h = 1426.87 L.

Referring to the LCI DB, the CO₂ emission factor is 2.6 kg/L, the CO₂ emission of the dump truck is: 2.6 kg/L × 1426.87 L = 3709.86 kg.

5. The Result Analysis

5.1. CO₂ Emission Factors of Materials and the Proportion of Quantity of Each Section in Tunnel

From the CO₂ emission factors of materials, as shown in Figure 9, it can be seen that different materials have different CO₂ emission factors, therefore, during the design process, we could choose the materials with lower CO₂ emissions, according to needs.

From the circle graph, as shown in Figure 10, it can be seen that the proportion of quantity of each section in tunnel, concrete lining, concrete slab (30 cm) and drainage way account for a large proportion; the three sections take over 76 percent.

5.2. Economic Analysis of CO₂ Emission during the Tunnel Construction Process

In order to convert the CO₂ emission into cost, this study used the recent carbon emission trading price. The main developed countries are trying to reduce the emission of atmospheric pollutants, and they have established a variety of trading systems for carbon emissions exchange. In this study, we used the global trading system named EU ETS (EU emissions trading system) [21]. The EU ETS is a cornerstone of the European Union’s policy to combat climate change, and its key tool for reducing industrial greenhouse gas emissions cost-effectively. The study used EU Allowances—carbon credits used in the EU ETS.

Based on the calculation of CO₂ European emission allowances, historical prices provided by ‘Makers Insider’, the average price in 2019 is 0.02472 eur/kg [22]. In addition, as the unit provided by ‘Markets Insider’ is in Euros, according to the 2019 average exchange rate of Euro to KRW (Korean Won) 1305.86 [23], the unit is subject to be changed. The calculation formula of the CO₂ emission fee is as follows:

CO₂ emission fee (KRW) [13] = CO₂ emission (kg) × Average price of CO₂ emission (eur/kg) × Annual average exchange Rate

According to the formula above, the calculation process for project A is shown in

Table 8. Calculation process of CO₂ emission fee during tunnel construction process for Project A.

Category	Division	10 m Section CO2 Emission (kg)	Project A CO2 Emission (kg) (1477.6 m)	Average Price of CO2 Emission (eur/kg)	Annual Average Exchange Rate	Project A CO2 Emission Fee (won)
Tunnel material	Drainage way	7978.07	1,178,840	0.02472	1305.86	38,053,956
	Cement treated base	37,226.64	550,060.8			177,564,363
	Common ditch cover	240	35,462.4			1,144,757
	Ditch cover	5103	754,019.3			24,340,390
	Concrete lining	26,298.03	3,885,797			125,436,863
	Drainage pipe filling	85.15	12,581.76			406,150
	Drainpipe	294.99	43,587.72			1,407,049
	Rock bolt	3684.49	544,420.2			17,574,353
	Shotcrete	3960.21	585,160.6			18,889,488
	Steel pipe	266.29	39,347.01			1,270,155
	Waterproofing sheet	501.46	74,095.73			2,391,874
	Concrete slab (30 cm)	7784.96	1,150,306			37,132,856
Main equipment	Dump truck	3709.86	548,169			17,695,364
	Mixer-truck	638.14	94,291.6			3,043,813
	Wheel loader	229.32	33,884.3			1,093,815

(The CO₂ emission of project A was estimated approximately by using the calculated amount of 10-m tunnel section as the average value in this study).

5.3. Results and Discussion

(1)

From the results in

Table 9. Proportion of CO₂ emission fee during the construction process of project A.

Category	Division	CO2 Emission Fee (Won)	Total Fee (Won)
Tunnel material	Drainage way	38,053,956	445,612,254 (95.32%)
	Cement treated base	177,564,363
	Common ditch cover	1,144,757
	Ditch cover	24,340,390
	Concrete lining	125,436,863
	Drainage pipe filling	406,150
	Drainpipe	1,407,049
	Rock bolt	17,574,353
	Shotcrete	18,889,488
	Steel pipe	1,270,155
	Waterproofing sheet	2,391,874
	Concrete slab (30 cm)	37,132,856
Main equipment	Dump truck	17,695,364	21,832,991 (4.67%)
	Mixer-truck	3,043,813
	Wheel loader	1,093,815
Total	-	-	467,445,245 (100%)

, we can see that the CO₂ emission fee of tunnel material is 467,445,245 won, and the CO₂ emission fee of main equipment is 21,832,991 won. The tunnel material takes over 95.32% of the total CO₂ emission fee; in order to reduce the tunnel CO₂ emission cost, the researchers should focus on the development of low carbon materials.

(2)

For the tunnel material, the CO₂ emission fee of cement treated base, concrete lining, drainage way and concrete slab (30 cm) is very high. Four of them take over 84.9% of the tunnel material CO₂ emission fee. Areas for further research would be to reduce the CO₂ emission factor of cement and concrete, for example, by developing new types of cement and concrete, or using a replacement with lower CO₂ emission factor.

(3)

Even though, compared with the tunnel material, the CO₂ emission fee of the main equipment is not very high, it is a large expense for the whole tunnel project. According to the results, we can see that most of the CO₂ emission fee comes from the dump truck. During the tunnel construction, the quantity of earthwork is very high, so there is more use of the dump truck. As a consequence, we should take the reduction of earthwork as an important consideration in the tunnel design. We can also design a reasonable construction route to reduce the transportation distance and improve the equipment, to reduce the fuel consumption of the dump truck.

6. Conclusions

In order to reduce the CO₂ emission in the construction area, it is necessary to estimate the emission first. In this paper, taking a tunnel project as an example, combined with the BIM software’s automated calculation function, the CO₂ emission of tunnel material and the main equipment during the construction process were calculated. The economic calculation was also carried out through using the EU emissions trading system.

Through the analysis of the tunnel material’s CO₂ emission calculation, it has a good reference significance for the selection of low-carbon emission materials in the design process, and it could play a practical role in guiding the research direction of developing low-carbon materials.

Through the calculation of equipment’s CO₂ emission and the analysis of the results, it shows a clear calculation example for calculating CO₂ emission from the equipment, and it provides a case reference and the direction for low-carbon equipment research.

Through using EU emissions trading system, the economic conversion CO₂ emissions will provide an economic evaluation index for the CO₂ emissions of tunnel construction activities. By linking with cost, it can provide an environment-friendly guidance for selecting the construction material and construction equipment.

However, because this paper mainly focuses on the research for methodology, a tunnel section and related main equipment which are powered by fuel are selected as the research object, some of the necessary research data was assumed. The calculation results could not accurately reflect the actual situation of tunnel construction, but the calculation and analysis methodology mentioned in this paper could be referred to.

In this research, we added CO₂ emission factors into the BIM models as a field; the EU ETS related values could also be added as field and internal calculations could be made within Revit. Based on the calculation process provided in this paper, BIM-based automated calculation system of CO₂ emissions during tunnel construction process can be further developed. It can contribute to the expansion of BIM technology in the field of civil engineering. Meanwhile, there are various performance evaluation indexes in the field of AEC, many of which are related to quantity calculation. The methodology mentioned in this paper can also provide a good reference role for developing related evaluation systems based on BIM. It can make evaluation work simpler and more efficient.