Case Study on Carbon Footprint Life-Cycle Assessment for Construction Delivery Stage in China

Abstract

The construction industry’s high energy consumption and carbon emissions significantly burden the ecological environment. Thus, it is necessary to study measures and strategies for emissions reduction during construction for an improved, safe and sustainable environment. Using the life-cycle assessment method, this study aims to investigate construction-building outcomes and their carbon footprint during the construction delivery stage. This work used a compiled database of carbon-emission factors per unit for concrete and mortar with different densities and 16 building-project case studies in Fujian Province to verify the empirical findings. The results show that general civil engineering works produce more carbon emissions than decoration engineering. Furthermore, cement’s average proportion of carbon emissions relative to total carbon emissions is the largest at 30.26%. Our findings also show a strong linear relationship between the total carbon emissions, eaves height, project cost, and building area during the building construction. The findings in this paper promote the conversion of buildings from high-energy consumption to multi-carbon reduction. The concept of this research contributes to the existing knowledge by proposing a carbon-footprint calculation method and establishing the trend of carbon emissions in building construction.

1. Introduction

Numerous solid wastes and greenhouse gases (GHG) are generated as high-energy-consuming and high-emission products during the construction process. Thirty percent of China’s total energy consumption comes from construction projects [1]. Construction activities account for around 40% of the total natural resources and energy consumed by human beings, representing approximately 40% of total solid waste [2]. Most previous studies regarding building carbon footprints focused on the operation stage of the building rather than the construction delivery stage [3]. The accuracy and completeness of calculations at each stage need further improvement [4]. The construction delivery stage uses various materials, construction machinery, and transportation equipment, resulting in a large amount of carbon dioxide (CO₂) [5]. The energy and materials used during the delivery stage of construction exhibit the characteristics of concentrated and absolute emissions [6]. Many studies have been carried out abroad to evaluate the life cycle of buildings, and a large amount of primary data have been accumulated; however, the research level in this area is still in the early stage and lacks not only a unified standard database but also evaluation models.

On the other hand, the extreme difference in energy composition between China and foreign countries also makes the primary data available abroad but not directly usable in China. Nowadays, research on low-carbon cities and buildings is relatively extensive; it has gained massive attention and attraction. For example, domestic and foreign research results show that the construction delivery stage consumes less fuel than the material-production, operation, and demolition stages; however, many studies ignore this fact. In addition, researchers report that energy consumption during the construction process exhibits short time and concentrated emissions characteristics. The absolute amount of carbon emissions is significant, offering excellent potential for carbon reduction [7].

Nowadays, the carbon footprint of building engineering projects involves other stages based on their life cycles [8]. However, the study of carbon footprints for a construction project during the construction delivery stage is rarely discussed because the materials and tools used in the project’s construction delivery stage can be very complex, and few carbon-emission analyses account for the construction delivery stage [9]. Although these factors need to be considered, the accuracy and integrity of their results on carbon-footprint analysis should be further improved.

This study aims to enhance the knowledge of carbon footprints in building-construction projects. The objectives of this study are to quantify carbon footprints generated during the construction process of a project and to achieve calculation and empirical analysis for actual cases by establishing a carbon-emission calculation model based on life-cycle assessment (LCA). Firstly, a brief literature review considering building carbon footprint is analyzed using LCA in this research work. Secondly, building products that are often used in the construction delivery stage for projects are selected, and the limits of the construction process are clarified. Thirdly, the effects and amounts of buildings’ carbon footprints in the construction delivery stage are estimated. Furthermore, analysis results from 16 building projects, refereed as case studies in Fujian Province, China, are presented to understand carbon emissions better and identify carbon-emission trends.

2. Literature Review

2.1. Carbon Emissions from Construction

Many studies on carbon emission from construction projects have been conducted, but mostly in foreign countries. Research related to carbon emission from construction projects in China is relatively scarce; simultaneously, a unified and standardized database, evaluation model, and accounting model have not yet been well developed. Thus, the present study intends to investigate buildings’ carbon footprints by referring to the literature.

Several calculation methods are usually used for carbon-emission calculation, where the measurement method uses specific, approved standards or instruments to measure the concentration, flow rate, and footprint path. The inputs and outputs must be comprehensively analyzed [10], and such a work process is complex and time-consuming [11]. The emission-coefficient method calculates the total footprints based on the average value of the quantity of emitted gas [12]. The carbon-emission coefficient method is relatively simple, straightforward, and easy to understand; it is based on activity data and carbon-emission coefficients. However, it is also relatively extensive when compared with other methods. Therefore, the carbon-emission coefficient method was selected to calculate the carbon emissions during the building phase.

Several studies combining carbon footprints have also already been conducted. In this context, case studies determine the boundary range of carbon footprints and the correlation between energy and carbon share embodied in different levels of building energy efficiency [2]. Moreover, these case studies can correlate building energy consumption and carbon emissions [13] and verify reductions in building energy consumption and carbon emissions using a scientific construction-management system [14]. Different structural methods calculate energy consumption and carbon emissions, such as LCA [15]. A carbon-emission calculation model [16] has been established, and identification shows that energy, building materials, and machinery are the primary carbon-emission sources [17]. A carbon-emission law is established and analyzed according to the influence of base cost on carbon emissions [1]. Energy consumption and carbon emission for different building materials can be analyzed in building components in the production, transportation, and installation phases [18]. Authors [1,19] proposed an accurate calculation of the carbon emissions from precast concrete piles during their construction process using the LCA theory combined with an energy-analysis tool. At present, the analysis methods for determining the factors influencing building carbon emissions include ecological emission [20], the logarithmic mean divisia index decomposition method [21], and emission intensity [22]. Research indicates that emission intensity is the largest share of carbon-emission factors in the construction industry.

Research on carbon footprints in the construction field is mainly based on data from international organizations or foreign institutions. Buildings are divided into detailed stages, and their total carbon footprints are obtained using the carbon-emission calculation method. However, a construction period of two to five years for projects can be regarded as a micro life cycle [23], and studying the carbon footprint in detail is extremely necessary. Previous studies generally considered that the construction-operation phase caused many emissions, and the construction-operation period occupied most of its entire life cycle [24]. Therefore, the evaluation period significantly affected the evaluation results. The literature mentioned above did not consider emission reduction in the construction process due to construction scale, design period, and construction period. On the other hand, it calculated carbon emissions per unit construction area per year. As a result, it obtained comparable calculation results, which guided the optimization of the construction-material production process, transportation, construction, and waste disposal during the construction delivery stage.

2.2. Basic Issues of Carbon Footprints during Construction

2.2.1. Types of GHG and Their Measurement Units

GHG in the atmosphere mainly include CO₂, water vapor, methane (CH₄), nitrous oxide (N₂O), ozone (O₃), fluorochlorocarbons (CFC_S), hydrofluorocarbons (HFC_s), perfluorocarbons (PFC_s), hydrochlorofluorocarbons (HCFC_s), and sulfur hexafluoride (SF₆) [25]. The sources of GHG emissions can be divided into natural sources (including gases such as CO₂, CH₄, N₂O, and O₃) and anthropogenic sources (including CFC_s, HFC_s, PFC_s, and SF₆) [26]. According to the decision at the Montreal Convention, chlorofluorocarbons (CFC_s) have been banned, while CO₂, N₂O, CH₄ have been left and kept as the main three gases from GHG that cause increased temperature; this is presented in the Intergovernmental Panel on Climate Change (IPCC) evaluation report.

Global warming potential (GWP) is a unit of measurement that assesses the degree of the effects that GHG have on global warming, i.e., a certain period in which the degree of a certain GHG affects global warming per unit mass is converted into an equivalent effect caused by the same quality of CO₂ using a relevant conversion value [27]. Following the IPCC inventory guidelines for GWP, CO₂ GWP is set to a standard value of one, and those for other GHG are obtained differently [1]. The same conversion rules can be used to obtain the CO₂ equivalent to other GHG, as listed and shown in

Table 1. GWP of GHG.

GHG	GWP for Each Time Span
	20 a	100 a	500 a
CO2	1	1	1
CH4	82.5 ± 25.8	29.8 ± 11	10.0 ± 3.8
N2O	273 ± 118	273 ± 130	130 ± 64

.

2.2.2. International Carbon-Emission Accounting Standards

At the accounting level, the PAS 2050 specification is suitable for calculating CO₂ emissions from different life-cycle periods at different stages. Therefore, this study refers to the PAS 2050 specification to define carbon emission limits, determine the source of carbon emissions, and develop an accounting model. The PAS 2050 specification clearly defines the system limits of carbon emissions, carbon sources related to products within the system limits, information, and accounting methods required to perform accounting. The calculation system determines that activity-level data and emission factors are two types of information necessary to calculate carbon emissions. The formula provided by IPCC to calculate the amount of carbon emissions is the same. The system limits are divided into nine parts: energy, raw materials, use, facility operation, transportation, storage, asset commodities, manufacturing and service provision, and final disposal [28].

2.3. Determination of Carbon-Emission Factors for Building Materials

2.3.1. Semifinished Materials

(a)

Sand and gravel.

Sand and gravel are basic materials used in building construction. A study of the literature reveals that different scholars have calculated sand and gravel carbon emission factors in different ways [29,30]. In the present work, when the carbon-emission factors of sand and gravel are studied, the data on the energy consumption of sand and gravel obtained by scholars are used. The carbon-emission factors of sand and gravel are then calculated. A literature search found that the average electricity consumption per cubic meter of sand is 1.32 kW·h, and fuel oil is 0.76 kg [29]. The packing density of sand is 1450 kg/m³, and gravel is 1560 kg/m³ [12]. Subsequently, the sand and gravel carbon-emission factor is computed by combining the carbon-emission factor of electricity and fuel oil. The calculation formula is expressed as sand carbon emissions: 1.32 × 1.01 + 0.76 × 3.9 = 4.297 (kg/m³); sand: (1.32 × 1.01 + 0.76 × 3.90)/1.45 = 2.964 (kg/t); and stone: (1.32 × 1.01 + 0.76 × 3.90)/1.56 = 2.755 (kg/t).

(b)

Concrete.

The consumption ratio of various concrete materials with various strengths is determined according to the budget quota data of Fujian Province. Among these materials, the cement grade for concrete C10 is 32.5, the crushed stone is 40 mm, and the slump is 10–30 mm. For 42.5, the crushed stone is 40 mm and the slump is 30–50 mm. In addition, non-pumped commercial concrete cement with various strengths is included, the grade of which is 42.5, and the crushed stone is 31.5 mm. Pumped commercial concrete cement with various strengths is also added with a grade of 42.5, crushed stone with 20 mm, and a slump degree of ≤160 mm. The impermeability label of onsite-mixed waterproof impervious concrete with various strengths is P6, the cement strength is 42.5, the crushed stone is 20 mm, and the slump is 30–50 mm. The impervious label of pumped waterproof impervious concrete with various strengths is P8, the cement grade is 42.5, the crushed stone is 20 mm, and the slump is ≤160 mm. The carbon emissions from the pumping agent of the pumped concrete are ignored. According to the mixing ratio of the concrete material composition obtained by this research, the carbon-emission factors for ordinary concrete with different strengths and those with waterproof, impervious, pumped, and non-pumped commercial concrete are calculated. The results are listed and shown in

Table 2. Carbon-emission coefficient of ordinary concrete.

Material (m3)		Mix Ratio				Carbon-Emission Factor (kgCO2/m3)
		Cement (kg)	Crushed Stone (m3)	Medium Sand (m3)	Water (m3)
Ordinary concrete	C10	192	0.875	0.522	0.165	173.193
	C15	257	0.869	0.474	0.175	229.520
	C20	263	0.854	0.465	0.175	234.637
	C25	276	0.886	0.441	0.175	245.981
	C30	316	0.881	0.418	0.175	280.661
	C35	369	0.857	0.407	0.175	326.621
	C40	411	0.85	0.384	0.175	363.032
	C45	453	0.83	0.375	0.175	399.447

Note: The carbon-emission coefficient of ordinary and Portland cement is 0.87 kgCO₂/m³, and that of sand and gravel is 4.297 kgCO₂/m³.

.

(c)

Mortar.

The material consumption of mortar represents the amount of cement labeled as 32.5, and the carbon-emission factor of mortar is determined according to the calculation method of concrete. Their results are listed and shown in Table 3.

Table 3. Mortar carbon-emission coefficient.

Material (m3)		Mix Ratio				Carbon-Emission Factor (kgCO2/m3)
		Cement (kg)	Medium Sand (m3)	Lime (m3)	Water (m3)
Masonry cement mortar	M2.5	202	1.02	-	0.3	180.396
	M5	222	1.02	-	0.3	197.796
	M7.5	242	1.02	-	0.3	215.196
	M10	283	1.02	-	0.3	250.866
	M15	313	1.02	-	0.3	276.966
	M20	364	1.02	-	0.3	321.336
Masonry mixed mortar	M2.5	164	1.02	0.095	0.25	166.638
	M5	190	1.02	0.08	0.25	186.203
	M7.5	216	1.02	0.066	0.25	205.972
	M10	242	1.02	0.051	0.25	225.537
	M15	295	1.02	0.022	0.25	265.741
Cement mortar	1:1	758	0.64	-	0.3	662.483
	1:1.5	638	0.81	-	0.3	558.814
	1:2	550	0.93	-	0.3	482.769
	1:2.5	485	1.02	-	0.3	426.606
	1:3	404	1.02	-	0.3	356.136
Mixed mortar	1:2:8	129	0.98	0.32	0.6	182.157
	1:3:9	152	1.02	0.26	0.6	190.12
	1:0.5:3	368	0.93	0.15	0.6	355.251
	1:0.3:3	391	0.99	0.1	0.6	365.336
	1:0.2:2	504	0.85	0.08	0.6	458.971
Plain cement slurry		1502	-	-	0.3	1307.013
Lime mortar	1:3	-	1.02	0.34	0.6	74.172
	1:4	-	1.02	0.25	0.6	55.8429

Note: The clay paste in the masonry mixed mortar is replaced by lime paste. The density of lime is 1320 kg/m³, and the lime required to produce 1 m³ of lime paste is 400 kg. Therefore, the carbon-emission factor of lime is 0.509 kgCO₂/m³, and the emission coefficient is 203.656 kgCO₂/m³. According to the calculation and analysis of international experts and scholars, the obtained carbon-emission coefficients of the most commonly used building materials are collected and summarized in Table 4, which provide data support for quantifying carbon emission in construction projects.

Table 3. Mortar carbon-emission coefficient.

Material (m3)		Mix Ratio				Carbon-Emission Factor (kgCO2/m3)
		Cement (kg)	Medium Sand (m3)	Lime (m3)	Water (m3)
Masonry cement mortar	M2.5	202	1.02	-	0.3	180.396
	M5	222	1.02	-	0.3	197.796
	M7.5	242	1.02	-	0.3	215.196
	M10	283	1.02	-	0.3	250.866
	M15	313	1.02	-	0.3	276.966
	M20	364	1.02	-	0.3	321.336
Masonry mixed mortar	M2.5	164	1.02	0.095	0.25	166.638
	M5	190	1.02	0.08	0.25	186.203
	M7.5	216	1.02	0.066	0.25	205.972
	M10	242	1.02	0.051	0.25	225.537
	M15	295	1.02	0.022	0.25	265.741
Cement mortar	1:1	758	0.64	-	0.3	662.483
	1:1.5	638	0.81	-	0.3	558.814
	1:2	550	0.93	-	0.3	482.769
	1:2.5	485	1.02	-	0.3	426.606
	1:3	404	1.02	-	0.3	356.136
Mixed mortar	1:2:8	129	0.98	0.32	0.6	182.157
	1:3:9	152	1.02	0.26	0.6	190.12
	1:0.5:3	368	0.93	0.15	0.6	355.251
	1:0.3:3	391	0.99	0.1	0.6	365.336
	1:0.2:2	504	0.85	0.08	0.6	458.971
Plain cement slurry		1502	-	-	0.3	1307.013
Lime mortar	1:3	-	1.02	0.34	0.6	74.172
	1:4	-	1.02	0.25	0.6	55.8429

Note: The clay paste in the masonry mixed mortar is replaced by lime paste. The density of lime is 1320 kg/m³, and the lime required to produce 1 m³ of lime paste is 400 kg. Therefore, the carbon-emission factor of lime is 0.509 kgCO₂/m³, and the emission coefficient is 203.656 kgCO₂/m³. According to the calculation and analysis of international experts and scholars, the obtained carbon-emission coefficients of the most commonly used building materials are collected and summarized in Table 4, which provide data support for quantifying carbon emission in construction projects.

Table 4. Carbon-emission factors of common building materials.

Building Material Name	Unit	Carbon Emission Factor (kgCO2/unit)	Cited Literature
Ordinary Portland cement	kg	0.87	[30]
plaster	kg	0.21	[31]
Lime	kg	1.2	[32]
		0.509	[3]
Limestone	kg	0.785	[33]
Iron	kg	1.01	[34]
Aluminum	kg	1.02

Table 4. Carbon-emission factors of common building materials.

Building Material Name	Unit	Carbon Emission Factor (kgCO2/unit)	Cited Literature
Ordinary Portland cement	kg	0.87	[30]
plaster	kg	0.21	[31]
Lime	kg	1.2	[32]
		0.509	[3]
Limestone	kg	0.785	[33]
Iron	kg	1.01	[34]
Aluminum	kg	1.02

2.3.2. Steel

Steel is an indispensable main building material used in construction projects. The amount of carbon emission from steel exhibits a clear relationship with manufacturing technology. Most of the CO₂ emitted during steel production is from fuel and energy usage. Although the carbon-emission coefficient of steel in all construction materials is high, steel should be considered for recovery. However, steel recovery in reinforced concrete is relatively difficult, and the recovery rate is only 0.5. Therefore, a higher recovery rate of 0.9 is chosen for steel molds and section steel.

Table 5. Steel carbon-emission coefficients under different recycling conditions (kgCO₂/kg).

Recovery Rate	Large-Scale Steel	Small- and Medium-Sized Steel	Hot-Rolled Steel Bar	Cold-Rolled Steel Bar
0	3.744	3.003	3.154	3.938
10%	3.519	2.823	2.965	3.702
20%	3.295	2.643	2.766	3.465
30%	3.07	2.462	2.586	3.229
40%	2.845	2.282	2.397	2.993
50%	2.621	2.102	2.208	2.757
60%	2.396	1.922	2.019	2.52
70%	2.172	1.742	1.829	2.284
80%	1.947	1.562	1.64	2.048
90%	1.722	1.381	1.451	1.811
100%	1.498	1.201	1.262	1.575

and

Table 6. Carbon-emission factors of four types of steel.

Building Material Name	Unit	Carbon-Emission Factor kgCO2/kg			Scope of Application
		90%	50%	0%
Large steel	kg	1.722	-	3.744	Section steel
Small and medium steel	kg	1.382	-	3.003	Angle steel, flat steel, steel formwork, Steel bracket, etc.
Hot-rolled strip	kg	-	2.757	3.154	Cold drawn steel wire
Cold-rolled strip	kg	-	2.208	3.938	Rebar, round steel

list the carbon-emission factors of various types of steel under different recovery rates.

Concerning the emission coefficients of the welding core and electrode, the carbon-emission coefficient value of steel materials was used [35].

2.4. Carbon-Emission Factors of Some Decoration Materials

Construction projects use many construction and decoration materials. The amount of different materials varies greatly during the construction process, as projects require different land and numerous construction and decoration materials. For the carbon-emission factors of other construction materials used in decoration projects, existing research results from other scholars are used.

2.4.1. Water-Discharge Factor

The average water resource allocated to most people is 2300 m³, which is only approximately one-fourth of the global per capita level. These data show that, relatively speaking, China lacks water resources. Construction projects consume a large amount of water during the delivery stage. The production and preparation of tap water consumes less energy, and most of the energy is consumed in transporting water. According to research [4,15], the value of the water-discharge factor is 0.91 kg/m³.

2.4.2. Wood

Wood is a green and environmentally friendly material with carbon fixation. Some countries combine the carbon sequestration function of wood. Thus, the calculated carbon-emission coefficient is negative. Considering the actual situation, in which the ecological value of wood has not been reasonably utilized because of the random logging of forest resources in China, the situation is most unfavorable when the carbon fixation function of wood is considered [30]. The carbon-emission factor of wood is 73.9 kgCO₂/m³.

2.5. Carbon-Emission Factors of Construction Machinery

The carbon-emission factor of mechanical equipment during the construction delivery stage can be obtained by calculating the amount of fuel consumed by the construction machinery unit and the carbon-emission factor of the fuel at this stage [36]. Electricity is the main energy used by construction machinery and equipment. The carbon emission of fuel is combined with the emissions of the three stages of production, transportation, and combustion [32]. The formula for calculating the carbon-emission factor of mechanical equipment is

$$C=3.99\times M_{\alpha }+3.94\times M_{\beta }+1.01\times M_{\gamma }$$

(1)

where $M_{\alpha }$, $M_{\beta }$, and $M_{\gamma }$ are the mechanical equipment’s diesel, gasoline, and electricity consumed during the construction process.

3. Materials and Methods

Interventional studies involving animals or humans, and other studies that require ethical approval, must list the authority that provided approval and the corresponding ethical approval code. This study presents a theoretical reference to promote the conversion of buildings from high energy consumption to multi-carbon reduction and to provide data support to improve carbon emissions in China being “traded” on the market.

To fill the gap in the existing literature, this study considers the carbon footprint of building products. Carbon-emission factors are analyzed, and their accounting-system model for construction products is established. A unit quota carbon-emission coefficient database is developed, considering CO₂ as a measurement standard. Carbon footprints during the construction delivery stage are calculated, and the carbon-emission trend of building construction is verified using engineering examples. The main contributions of this study are the investigation of the construction quantity list for construction sub-items as a unit and the calculation of the unit carbon-emission coefficient in each quota. The framework of this paper is shown in Figure 1.

This case study selected 16 buildings in Nanping, Longyan, Quanzhou, and Fuzhou, Fujian Province, China, and the essential selection criteria are summarized in

Table 7. Summary of the construction-project cases.

Case Label	Case Project Name	Structure Type	Total Cost (Ten Thousand Yuan)	Building Area (m2)	Eaves Height (m)
1	Public rental house	Reinforced concrete frame shear wall construction	101.92	1157.89	20.25
2	Tax office	Reinforced concrete frame shear wall construction	332.94	1676.00	19.65
3	Building #3	Assembled monolithic frame shear wall construction	3359.22	21,281.97	69.00
4	Building #5	Assembled monolithic frame shear wall construction	4255.09	25,843.56	81.00
5	Building #8	Assembled monolithic frame shear wall construction	1344.84	8432.30	55.20
6	Building #9A, resettlement building	Shear wall construction	1727.62	10,694.66	72.00
7	Building #9B, resettlement	Shear wall construction	1379.72	8433.87	57.00
8	Building #10	Assembled monolithic frame shear wall construction	2221.28	13,981.87	84.00
9	Building #4 in a Taiwanese business community	Reinforced concrete frame shear wall construction	3374.98	21,388.88	69.00
10	Building #6 in a Taiwanese business community	Reinforced concrete frame shear wall construction	4252.72	26,196.43	81.00
11	Building #7 in an investment community	Reinforced concrete frame shear wall construction	1549.46	9878.34	55.20
12	Building #11 in an investment community	Reinforced concrete frame shear wall construction	2213.54	13,954.99	84.00
13	Apartment buildings 1 and 2	Assembled monolithic frame shear wall construction	3220.82	22,995.98	63.40
14	Middle-school dormitory	Reinforced concrete frame shear wall construction	205.24	1819.66	14.85
15	Building #2	Assembled monolithic frame shear wall construction	497.82	3598.44	18.30
16	Building #1 in a garden district	Assembled monolithic frame shear wall construction	1799.29	10,730.30	64.20

. There was variability in the type of structure in these 16 cases.

3.1. Building Carbon-Footprint Calculation Model

Accounting Process Based on PAS 2050 Specification

The evaluation standard of carbon footprints can provide reference for the calculation method of carbon footprints. PAS 2050 (PAS 2050: 2008 Specification for Greenhouse Gas Emission Assessment of Goods and Services in Life Cycle) is the first standard for the carbon footprint of products in the world. It is a standard for evaluating greenhouse gas emissions in the life cycle of products and services based on the life cycle assessment (LCA) method. The calculation process in this study refers to the calculation process of the PAS2050 specification, which includes four factors: setting targets, defining scope, carbon-source analysis, and carbon-emission accounting for building carbon emissions. Figure 2 presents the carbon-footprint accounting system in construction engineering based on PAS 2050 specifications.

(a)

Target determination

By calculating carbon emissions during the construction delivery stage of construction projects, quantitative indicators of the construction products are obtained, quantitative data and results are analyzed, and the patterns of carbon emissions are summarized, thus providing data support and a theoretical basis.

(b)

Determination of carbon-emission limit

The carbon-emission limit defines the scope of carbon-emission calculations for products, divided into building-material production and transportation, building construction, use, and waste recycling. This work mainly studies the amount of carbon emitted during building construction. For construction projects, the scope and emission path are relatively straightforward. According to the construction-quantity calculation software commonly used in construction costs in Fujian Province, the construction of a project is based on the construction sub-item project, quantity list, and construction process. The stage is divided into four parts, namely: earthwork, pile foundation, general civil engineering, and decoration works, which are defined here as a four-stage discharge. Each stage is again subdivided into different small parts based on the amount of work covered by each small part. The carbon emissions of the four subsection projects are obtained by accumulating the carbon emissions of the project-quantity list. As a result, the total carbon emissions include four subsection projects, as shown in Figure 3.

(c)

Classification of carbon-footprint sources

The carbon footprint source for each subproject is mainly the carbon emissions from the use of building materials and energy from mechanical and electrical equipment. According to the defined carbon-emission accounting scope, we determined the work content of each sub-item project one-by-one and clarify the materials and machinery used in each project list, as well as the GHG emissions from “material” and “machine usages”. We then perform accounting to understand the overall status of carbon emissions for construction projects during the construction delivery stage. A schematic diagram of the carbon-footprint sources for a project is illustrated in Figure 4.

3.2. Calculation of Carbon Footprint during Construction

Calculating a carbon footprint during the construction of a single building essentially means accounting for the CO₂ emissions of the building from scratch. Raw materials are mined using different methods and processes, such as machine operation and crushing. The fuel and electricity consumed during these processes produce carbon emissions. The raw materials include sand, ore, limestone, clay, wood, and other materials. In the mining phase of raw materials, no accurate statistical data are currently compiled because of a chemical reaction series that needs to be carried out during the mining process. The processing and manufacturing of raw materials into building materials and the building components used in the construction delivery stage consume fuel energy and electricity, and they emit a large amount of CO₂. The construction of a building can be divided into many subprojects. The carbon emissions of these subprojects are gradually calculated to accumulate carbon footprints during the building-construction process, and more related, detailed calculations are expressed in Equations (2)–(7).

$$W=W_1+W_2+W_3+W_4$$

(2)

where W represents the carbon emission during the building stage and $W_1$, $W_2$, $W_3$, and $W_4$ are the carbon footprints from the four subprojects of earthwork, pile foundation, general civil engineering, and decoration, respectively.

$$W_1={\displaystyle \sum _{i=1}^m{L}_i}$$

(3)

$$L_i={\displaystyle \sum _{j=1}^n{G}_j\times Q_j}$$

(4)

Similarly, the calculation formulas of $W_2$, $W_3$, and W₄ can be obtained, where $L_{\mathrm{i}}$ is the carbon emissions from the ith list ($i$ = 1, 2, …, m) during the construction delivery stage, $G_j$ is the engineering quantity calculated from the jth quota ($j$ = 1, 2, …, n) in the ith list during the construction delivery stage, and $Q_j$ is the carbon emission per unit in the jth quota.

$$Q_j=M_j+E_j$$

(5)

$$M_j={\displaystyle \sum _{x=1}^m{M}_{jx}\times (1-s)\times GW{P}_x}$$

(6)

$$E_j={\displaystyle \sum _{y=1}^n{E}_{jy}\times GW{P}_y}$$

(7)

where: M_j—jth quota ($j$ = 1, 2, …, n) of carbon emissions from consumable materials; $E_{ij}$—Carbon emissions from the jth quota ($j$ = 1, 2, …, n) from the use of mechanical equipment; $M_{jx}$—Quality of x-type building materials used in the quota ($x$ = 1, 2, …, m); $GW{P}_x$—Carbon-emission factor of the xth material; $E_{jy}$—Number of shifts performed by the yth machine in the quota ($y$ = 1, 2, …, n); $GW{P}_y$—Carbon-emission factor of the yth mechanical equipment shift; $S$—Recycling coefficient of category x building materials. Note: Carbon-emission factor $GW{P}_x$ of the materials is divided into considered and not-considered recovery rates. In the calculation, the carbon-emission factor that considers the recovery rate is substituted into the calculation formula to replace recovery factor S of the building material.

3.3. Calculation of Carbon-Emission Coefficient

3.3.1. Determination of Basic Data

The carbon-emission factors of building materials used in this study are mainly obtained from domestic and foreign literature. In contrast, the carbon-emission coefficients of semifinished materials are based on the unit material consumption and literature review obtained from the fixed consumption in the engineering-quantity calculation software. The carbon-emission factors of water, cement, lime, and other materials are further calculated. The carbon-emission factors for mechanical shifts are mainly calculated by searching the energy consumption of construction-machinery shifts and the carbon-emission factors of diesel, gasoline, and electricity. The carbon-emission factors of fuel are currently available in data published by some international organizations and official agencies, and individual experts and scholars can summarize the carbon-emission factors for construction materials in individual studies.

3.3.2. Determination of the Unit Carbon-Emission Coefficient

Considering the calculation results in relevant engineering-quantity calculation software, we search for the type and quantity of building materials used per unit of quota included in the project list, model specifications, and amount of mechanical equipment used during construction. We also searched existing literature to obtain the carbon emissions of building materials and machinery. We determine carbon emission factors to calculate the unit carbon emissions according to the calculation model, summarize the unit quota carbon-emission database, use the calculation results of engineering quantity, and finally obtain the total carbon emissions. The carbon emission per unit $Q_{ij}$ of the jth quota in the ith list is expressed as shown in Equation (8):

$$Q_{ij}={\displaystyle \sum _{x=1}^p(M_{jx}\times (1-s)\times GW{P}_x)}+{\displaystyle \sum _{y=1}^q(E_{jy}\times GW{P}_y)}$$

(8)

According to the unit fixed-consumption material and type of machinery used by the software that calculates engineering quantity, we refer to the fixed unit price calculation method in the software that calculates the engineering quantity. We then converted the unit price of the building materials and construction machinery in the fixed amount into a mechanical table shift and construction material carbon-emission factor. Subsequently, the fixed unit carbon emission is calculated. The carbon emissions of a building are measured. Building structure, building area, story height, building material, construction machinery, construction technology, environmental effect, and other conditions make each construction project different. Therefore, accounting for the carbon emissions of each construction project is necessary. The fixed carbon-emission coefficient of the engineering quantity calculated in this study is included in the project construction process engineering-quantity estimation, design estimate, construction drawing budget, and completion settlement.

3.4. Carbon-Footprint Assessment on Construction Projects

3.4.1. Project Unit Carbon Emissions

According to the carbon-footprint indicators of actual engineering projects, the area and output carbon-emission intensity of engineering projects are defined as the ratio of CO₂ emissions during the project’s construction to their unit construction area and unit project cost. Therefore, we assumed that the cost and building area of an i project to be Pi and $A_i$, respectively, and the calculation formulas of the carbon-emission intensity per unit area and carbon-emission intensity per unit cost in case $i$ are expressed in Equations (9) and (10), respectively.

$$U{A}_i=\frac{W_i}{A_i}$$

(9)

$$U{P}_i=\frac{W_i}{P_i}$$

(10)

The calculation formulas of the area intensity for the average carbon emission and the intensity of the output value of average carbon emission in 16 cases are expressed in Equations (11) and (12), respectively.

$$AUA={\displaystyle \sum _{i=1}^{16}{W}_i}/{\displaystyle \sum _{i=1}^{16}{A}_i}$$

(11)

$$AUP={\displaystyle \sum _{i=1}^{16}{W}_i}/{\displaystyle \sum _{i=1}^{16}{P}_i}$$

(12)

Let $X$ be $P$ and $A$ respectively. Then, the relative carbon-emission intensity for case i is expressed in Equation (13).

$${DUX}_i=U{X}_i/AU{X}_i$$

(13)

The relative value of the intensity is divided into five levels: “extremely high”, “higher”, “normal”, “lower”, and “low”. If $DU{X}_i$ ≥ 2, the intensity is extremely high. If 1 ≤ $DU{X}_i$ < 2, it is higher. If 0.8 ≤ $DU{X}_i$ < 1, it is normal. If 0.5 ≤ $DU{X}_i$ < 0.8, it is lower. If $DU{X}_i$ < 0.5, it is low.

3.4.2. Comprehensive Carbon-Emission Factor of the Inventory

According to the calculation principle of the comprehensive unit price of the inventory, the fixed project amount is multiplied by the unit’s fixed carbon-emission factor, and the total is divided by the inventory project amount. The calculation formula for the comprehensive carbon emission factor of the inventory is expressed as follows:

$$C_i=\frac{L_i}{L{G}_i}=\frac{{\displaystyle \sum _{j=1}^n{G}_j\times Q_j}}{L{G}_i}$$

(14)

where $C_i$ is the comprehensive carbon-emission coefficient of the ith list, and $L{G}_i$ is the quantity of the ith inventory. A carbon-emission model for the construction delivery stage of a project is established. The construction of the model enables the relevant construction authorities to use the preliminary engineering design and construction plan before project activity starts. From the “material consumption”, two aspects of “machine use” are used to account for the GHG emissions and understand the overall status of GHG emissions during the construction delivery stage of the project, from both the macro and micro perspectives. At the same time, this work also provides a basic method for calculating GHG emissions in different projects and even in the construction industry. According to the established carbon-emission calculation formula, we calculate the project unit quantity carbon-emission coefficient of the project, introduce the calculation result of the construction project quantity, summarize the carbon emissions of the project during the construction delivery stage, and analyze the carbon-emission effects of each subproject in the construction delivery stage. We then propose the corresponding emission-reduction measures.

4. Case Study Analysis and Results

4.1. Demonstration of the Calculation of Carbon Emissions during Construction

According to the LCA-based carbon-emission calculation model, the obtained unit quota carbon-emission factor database is incorporated into the project-quantity activity data obtained in the 16 cases to investigate the project, various engineering construction delivery stages, and obtain the mechanical-equipment carbon-emission inventory data. For the case study calculation, according to the carbon-emission calculation model, the total carbon emission for the building in Case 1 is 471,742.79 kgCO₂, and the carbon emission per square area of the building is 407.42 kgCO₂/m². According to the assumed construction time, if it is evenly distributed over the design life cycle, the carbon emission per square area is 8.15 kgCO₂/m²·year. The annual carbon emissions per square meter during the construction period is 433.05 kgCO₂/m²·year (the construction time is one year). The construction unit project is divided into four subprojects, and the proportion of carbon emissions for each subproject in Case 1 is shown in Figure 5.

The four subprojects (general civil engineering, pile foundation, earthwork, and decoration engineering) are further subdivided, and the calculation is summarized as follows:

(a)

Earthwork

According to the calculation results, the total carbon emission of the earthwork project is 176.14 kgCO₂. However, according to the engineering-quantity list, the carbon emission of the earthwork project is divided between excavation foundation earthwork and earth (stone) backfilling, which account for only a tiny percentage of 0.91%.

(b)

Pile-foundation engineering

The total carbon emission of the pile-foundation project is 41,326.48 kgCO₂. The carbon emission of the pile-foundation project is divided into concrete cast-in-place piles and reinforced cages. The basic project accounts for more than two-thirds of carbon emissions, and the carbon emission for the steel cage is less than one-third, which is 23.42%.

(c)

General civil engineering

The total carbon emission of the civil-engineering project is 353,646.32 kgCO₂. According to the engineering-quantity list, the carbon emissions for the general civil-engineering projects are divided into concrete engineering, brick and masonry engineering, roofing engineering, steel-reinforcement engineering, formwork scaffolding, and others. The carbon emissions and proportions of various subprojects are shown in Figure 6.

(d)

Decoration project

The total carbon emission for the decoration works is 76,593.85 kgCO₂. Carbon emissions for the decoration works are divided into the door carbon emissions, window installation, floor, wall pillars, external wall decoration, and others according to the list of works, as shown in Figure 7.

To further analyze the carbon emissions of buildings, we obtain the carbon-emission data of buildings with high credibility, especially those of various subprojects and projects that use different types of materials. The case data are processed following the same rules as those in Case 1. Because of limited space in this paper and a large amount of data in the case calculation results, the calculation data of all cases cannot all be individually presented. Therefore, only the summary of the calculation results of the carbon emissions of the 16 projects is listed in

Table 8. Summary of the calculation results of carbon emissions for all cases (kgCO₂).

Case	Total Carbon Emissions		Total Carbon Emissions (Considering Recycling)
	Considered Recycling	Did Not Consider Recycling	Earthwork Engineering	Pile Foundation Engineering	General Civil Engineering	Decoration Engineering
Case 1	471,742.79	601,309.75	176.14	41,326.48	353,646.32	76,593.85
Case 2	1,149,465.01	1,406,398.39	1231.35	83,118.27	676,426.20	388,689.19
Case 3	12,852,651.16	16,707,112.96	2159.59	1,503,021.83	9,241,614.56	2,105,855.18
Case 4	17,511,172.73	22,163,188.85	2622.48	1,833,381.59	11,658,984.64	4,016,184.02
Case 5	5,413,604.84	6,880,834.81	855.67	572,423.03	3,448,074.07	1,392,252.07
Case 6	7,185,594.66	9,188,095.23	1085.24	736,267.67	4,724,363.15	1,723,878.61
Case 7	5,876,481.28	7,418,507.70	15,986.86	572,536.73	3,792,397.62	1,495,560.07
Case 8	8,926,066.37	11,319,321.65	26,503.40	974,333.99	5,591,756.65	2,333,472.33
Case 9	12,956,501.70	16,814,151.49	2170.43	1,510,764.47	9,315,070.47	2,128,496.34
Case 10	17,606,912.11	22,244,521.30	2658.28	1,858,936.85	11,623,529.11	4,121,787.86
Case 11	6,582,313.43	8,216,793.79	1002.40	677,148.14	4,301,621.85	1,602,541.04
Case 12	8,867,731.43	11,254,182.67	26,452.44	972,387.29	5,566,688.13	2,302,203.57
Case 13	14,464,624.27	18,419,516.11	43,590.09	1,627,153.86	9,756,116.05	3,037,764.26
Case 14	987,703.31	1,188,404.50	599.32	99,380.58	717,715.53	170,007.87
Case 15	2,874,895.49	3,422,078.09	1064.52	220,757.72	1,508,706.60	1,144,366.65
Case 16	7,554,129.73	9,207,247.92	1651.52	738,848.79	4,203,490.43	2,610,138.99

Note: Considering recycling of carbon emissions means that the project considers the recycling of steel materials in calculating carbon emissions.

.

According to the division of material consumption in the engineering-quantity calculation software, material consumption is divided into building materials, semifinished products, and machinery shift. The emission data are listed and shown in

Table 9. Calculation results of the proportion of carbon emissions from the consumed building materials (kgCO₂).

Case	Material Carbon Emissions					Semifinished Product Carbon Emission	Machinery Carbon Emission	Other Carbon Emissions
	Cement	Steel	Wood	Sandstone	Brick Block
1	158,692.25	91,287.20	1543.97	3237.81	37,169.38	162,985.31	31,134.16	148,678.03
2	436,721.35	213,170.12	9389.36	17,068.43	49,283.98	441,362.22	47,748.21	292,965.27
3	3,408,673.00	2,892,946.87	35,716.82	51,375.14	963,986.38	3,915,249.19	508,146.99	3,488,784.13
4	4,304,399.55	3,573,951.28	41,841.27	64,603.26	1,257,062.07	5,057,750.57	605,657.88	5,830,275.84
5	1,301,984.30	1,156,640.82	12,834.70	19,677.70	340,058.00	1,540,862.28	265,060.43	1,744,925.85
6	1,814,637.76	1,572,176.72	17,143.40	26,380.50	506,357.20	2,080,403.30	258,856.81	2,253,774.61
7	1,499,924.50	1,159,668.15	14,334.20	21,756.69	422,831.41	1,755,369.48	201,532.52	1,983,897.07
8	2,268,375.45	1,832,100.67	20,785.27	33,162.64	564,880.18	2,606,456.08	418,237.53	2,814,190.65
9	3,433,619.99	2,902,321.15	35,665.89	51,798.64	973,795.83	3,960,586.53	510,414.69	3,538,121.04
10	4,440,304.25	3,525,209.75	42,299.72	67,384.62	1,286,170.04	5,207,078.47	605,104.47	5,781,502.41
11	1,649,034.80	1,185,840.93	16,053.42	25,138.49	417,743.72	1,905,146.75	287,851.56	2,323,502.37
12	2,263,906.84	1,830,253.90	20,750.36	33,104.48	553,498.04	2,598,285.71	294,625.35	2,899,205.18
13	3,510,981.13	2,689,276.96	35,934.15	53,391.73	1,326,798.86	3,789,644.69	500,769.87	4,720,317.70
14	459,772.24	253,422.05	2992.10	7822.09	144,687.30	412,022.65	31,264.09	136,048.24
15	738,855.40	421,213.08	6619.70	13,128.81	162,377.91	774,610.17	52,603.70	1,480,096.89
16	1,909,559.35	1,249,720.08	19,395.77	28,434.55	112,051.85	2,163,265.46	331,180.97	3,164,938.37

Note: In carbon emissions from material consumption, the carbon emission factor of steel materials (round steel, etc.) is applied in considering material recycling.

.

Considering that the cement, sand, and gravel in construction materials already include the consumption of cement, sand, and other materials in the semifinished products, the carbon emissions of the semifinished products are not included in the total carbon emissions.

4.2. Carbon-Footprint Analysis

According to the abovementioned building carbon-emission data, this study analyzes the building carbon-emission trend from the overall construction and subprojects. Firstly, the proportion effect for each part on the carbon emissions is calculated by analyzing: the overall carbon emissions for the project, the contribution of different construction materials used in the project, and the construction machinery’s contribution to carbon emissions. Secondly, according to survey data and calculations of building area and project cost, each case’s unit carbon emission and average carbon emission are obtained. The relative carbon-emission intensity in each case is analyzed. Finally, from three dimensions of “building height”, “building area”, and “building cost”, the regression-analysis method is implemented to obtain a one-to-one correspondence scatter plot between carbon emissions and building area, eaves height, and project cost. The characteristics and regularity of the graph are studied to explore the linear relationship.

4.3. Carbon-Emission Characteristics

According to the calculation results for the 16 cases, the average carbon emission of the earthwork project accounts for about 0.1% of the total carbon emissions for the entire project and, respectively, 10.12% for the pile-foundation project. The average proportion of emissions is 65.86%, and the average percentage of the decoration projects for total carbon emissions is 24.99%. More details are shown in Figure 8 and Figure 9.

Among the 16 actual projects, the earthwork projects’ carbon emissions are within 0.1% of the total carbon emissions, and the pile-foundation project accounts for approximately 10%. The general civil-engineering projects have the most significant carbon emissions, which reach 60–75%, followed by decoration engineering at 15–40%.

4.3.1. Carbon-Emission Sources Analysis

The materials used in each of the 16 case projects are summarized and divided into building materials, machinery shift, and semifinished products. Then, the percentage of material consumption in the three parts of the project is calculated. All materials and semifinished products are divided into cement, steel bars, bricks, sand, wood, and other materials. The steel bars include threaded-steel, round, and cold-drawn low-carbon steel bars and the semifinished products include ordinary concrete and cement mortar. More details are shown in Figure 10 and Figure 11.

From the 16 cases, project carbon emissions are divided into: cement, steel, wood, sand, bricks, machinery, and other factors. The cement carbon emissions account for 25.7–44.38% of the total project carbon emissions. The average ratio is 30.26%, and the carbon emissions of steel account for 14.65–25.49%; the average ratio is 21.89%. The carbon emissions of bricks account for 5.65–13.97%, and the average ratio is 7.58%. The mechanical carbon emissions account for 1.83–6.60%, and the average ratio is 4.28%. The average proportions of carbon emissions from sand and wood are 0.54% and 0.32%, respectively. Finally, we divide the project’s carbon emissions into steel, bricks, semifinished products, machinery, etc. The semifinished products account for 26.94–41.39% of the project carbon emissions, averaging 33.34%.

4.3.2. Carbon-Emission Intensity Analysis

According to the calculation formulas of carbon emission and relative intensities, the distribution of carbon intensity (area and production) of CO₂ emissions during the construction of the 16 projects is calculated; more details are shown in Figure 12.

4.4. Overall Trend of Carbon Emissions

To further explore the effect of building area, building eaves height, and building cost on the total carbon emissions for the project in the construction process, this study analyzes the trend and characteristics from a two-dimensional rectangular coordinate diagram based on three pairs of relationships and one-to-one corresponding points. The results are shown in Figure 13.

The R² at 0.9916 (Figure 13a) indicates that carbon emission in the construction delivery stage are related to building area. The correlation analysis yields a significance value at 0.000 < 0.05 to indicate a significant relationship (

Table 10. ANOVA significance analysis of carbon emission and building area.

Model a	Square Sum	Degree of Freedom	MSM	F	Significance
Regression	4.628 × 1014	1	4.628 × 1014	1652.514	0.000 b
Residual	3.921 × 1012	14	2.801 × 1011
Total	4.667 × 1014	15

^a Dependent variable: carbon emission; ^b Predictive variable; (constant): building area.

).

The R² at 0.6586 (Figure 13b) indicates a strong relationship. The correlation analysis yields a significance value at 0.000 < 0.05 to indicate a significant relationship (

Table 11. ANOVA significance analysis of carbon emission and building eaves height.

Model a	Square Sum	Degree of Freedom	MSM	F	Significance
Regression	3.074 × 1014	1	3.074 × 1014	27.007	0.000 b
Residual	1.593 × 1014	14	1.138 × 1013
Total	4.667 × 1014	15

^a Dependent variable: carbon emission; ^b Predictive variable; (constant): building eaves height.

).

The R² at 0.9913 (Figure 13c) indicates a strong relationship. The correlation analysis yields a significance value at 0.000 < 0.05 to indicate a significant relationship (

Table 12. ANOVA significance analysis of carbon emission and building cost.

Model a	Square Sum	Degree of Freedom	MSM	F	Significance
Regression	4.626 × 1014	1	4.626 × 1014	1593.065	0.000 b
Residual	4.066 × 1012	14	2.904 × 1011
Total	4.667 × 1014	15

^a Dependent variable: carbon emission; ^b Predictive variable; (constant): building cost.

).

The Pearson correlation coefficient for building area, building eaves height, and building cost > 0.7 signifies a robust linear relationship as shown in

Table 13. Correlation analysis of carbon emission with building area, building eaves height and building cost.

	Building Area	Building Eaves Height	Building Cost
Carbon emission	0.996 **	0.812 **	0.996 **

** Value is significant.

.

The results, as mentioned earlier, show that the relationship model between carbon emission and building area, building eaves height, and building cost can be used to estimate carbon emission during the building-construction delivery stage, which provides a theoretical basis for a construction enterprise to quantify the carbon emission of a project.

4.5. Comprehensive Assessment of Carbon Footprint Based on LCA

The comprehensive carbon-emission coefficients of the inventory are investigated. Different engineering projects contain different quantities of inventory, and the same inventory includes different project quotas, which result in the calculation of a comprehensive carbon-emission inventory coefficient. The same list for the same project may also contain multiple comprehensive carbon-emission factors.

The summarized list shows that the minimum value for the comprehensive emission coefficient of the in situ-cast concrete reinforcement is 2300.59 kgCO₂, and the maximum value is 24,278.15 kgCO₂. This is followed by the roof reinforced concrete water tank, exhaust duct (pipe), roof-roll waterproofing, and roof split. The comprehensive carbon emissions of the grid slits and stone steps exceed 1000 kgCO₂ and should be used as a key emission-reduction factor. The comprehensive carbon emissions are also significant and can be used as an important factor. In addition, a comprehensive list of beam slabs, beamless slabs, rectangular beams, fire shutter doors, railings, ring beams, stone floor, awnings, balcony slabs, independent foundations, gutters, cornices, and pile cap foundations is available. The carbon-emission factor value also exceeds 300 kgCO₂ and should be seriously considered.

5. Discussion

Compared to the operation phase, CO₂ generated during the construction process is mainly concentrated in large-unit carbon emissions and the effect on climate, which is vital in controlling carbon emissions and cannot be ignored.

This study calculates a project’s unit quota carbon-emission factor database using LCA. In this database, using search and comparison, the commonly used carbon emission in a project is more significant, such as that of the unit carbon-emission factor of reinforced-concrete, rectangular-roof water tank quota, which is 6900.97 kgCO₂/set. It is 3091.14 kgCO₂/t for cold-drawn, low-carbon steel-bar production and installation. Its levels are 2328.69, 2292.41, 2278.83, and 1541.57 kgCO₂/t, respectively, for steel-bar cage production and installation, round-steel bar production and installation, threaded steel-bar production and installation, and embedded iron-part installation. Secondly, manual digging and pouring of concrete piles, C30 non-pumped independent foundation concrete, C30 topped concrete, pumped-awning concrete, C30 pumped-column concrete, C30 pumped-wall concrete, C30 pumped beamless slab, and C30 pumped independent are performed. The carbon emissions from the concrete foundation of the pile caps are all between 300 and 400 kgCO₂/m³.

From the carbon-emission ratio on subprojects, the general civil-engineering projects have the most significant carbon emissions, which account for 65.86% of the project’s total carbon emissions; thus, they have the most significant potential for emission reduction, followed by decoration projects. The average ratio is 24.99%. In addition, the project carbon-emission intensity indicators show large fluctuations. For example, the area carbon-emission intensity is between 400 and 800 kgCO₂/m², and the average area carbon emission of the building is 647.99 kgCO₂/m² compared to other research results for emissions around 412.87 kgCO₂/m² [37]. However, it increased by 235.12 kgCO₂/m³, equivalent to 36.28%, mainly because of different construction materials. The output value of carbon intensity is between 3400 and 5800 kgCO₂/million, and the average output value of carbon-emission intensity is 4197.66 kgCO₂/ten thousand yuan. Further optimizing the choice of building materials will greatly reduce carbon emissions per unit area.

From the emission-source perspective, according to the summary analysis of project carbon emissions by materials, the average proportion of carbon emissions from cement accounts for 30.26% of total project carbon emissions. The average carbon emissions from steel are 21.89%, and the carbon emissions from bricks are 5.65~13.97%. The average ratio is 7.58%. The average ratio of mechanical carbon emissions is 4.28%, and those for sand and wood are 0.54% and 0.32%, respectively. By dividing project carbon emissions into steel, bricks, semifinished products, machinery, and others, the average proportion of semifinished products in project carbon emissions is 33.34%.

In the divisional projects in each case, this work investigates the effect of building area, building eaves height, and project cost on the total carbon emissions. The calculation results show that the regularity of carbon emissions during the construction process is relatively strong. Furthermore, through regression analysis, the formula for estimating carbon emissions in the building-construction process uses area, eaves height, and project cost as independent variables. Therefore, carbon emissions are obtained as the dependent variable, and this provides a theoretical basis for quantifying the amount of carbon emitted by construction projects.

By analyzing the carbon-emission characteristics in the presented cases, an emission-reduction strategy is proposed from the perspectives of the overall carbon emission of the building and that of the subprojects, and the selection of building materials, construction machinery, and construction technology is further refined. Furthermore, the formulation of emission-reduction policy systems can actively encourage enterprises to participate in voluntary emission-reduction work.

Through comparison with other study cases, the trend of total carbon emissions from buildings can be obtained. According to carbon-emission evaluation, the standard measurement method for a building’s energy, building materials, and GHG emissions is obtained. From the carbon-emission evaluation results and distribution rules for buildings, effective carbon-reduction measures can be formulated to reduce GHG emissions during the construction delivery stage to realize emission-reduction goals set by China, which provide a reference for calculating the carbon emissions in similar types of building constructions.

6. Conclusions

Considering that carbon emissions during construction delivery stages have attracted interest from the industry, this study focuses on analyzing the activity characteristics during a building-construction delivery stage to quantify the carbon footprint in the construction delivery stage of buildings. Furthermore, by implementing LCA, developing a carbon-emission calculation model enhances the previous carbon-emission calculation model. As a result, we obtain the carbon-emission factor database of each unit of concrete, mortar, and other factors, as well as the Fujian construction project quota carbon-emission factor database.

According to the principle of calculating the total construction cost of a project based on the set price of the project quantity, the unit price is replaced by the carbon-emission coefficient of the unit quota to calculate the total carbon emission of the project. A calculation formula is developed to quantify the amount of CO₂ footprint during a project’s construction process. Carbon emissions from four subprojects are analyzed, including general civil, decoration, pile-foundation, and earthwork engineering subprojects. Among the carbon footprints of building materials used in a project, the average proportion of carbon emission for cement is the largest, representing 30.26% of the total carbon emission for a project. According to the regression analysis, the total carbon emission is a dependent variable, and the building area, eaves height, and project cost are considered independent variables. The results show a strong linear relationship between the eaves height, building area, project cost, and carbon emission.

This research contributes to the literature by obtaining carbon-emission trends and adjusting carbon emission values. Furthermore, the results of this research encourage a construction unit to work out its enterprise quota according to its technical level and to obtain calculation results of carbon emissions that are closer to the actual carbon emission of a construction project, which can provide references for the promotion or application of emission-reduction policies during the building-construction delivery stage.

Although the goal of this study has been achieved, there are still some limitations, for example: (a) basic data on domestic carbon-emission factors are not sufficient, which cannot provide accurate requirements; in addition, the employed data for carbon-emission factors of building materials are only from foreign institution publications; (b), this study is based on a case study in Fujian Province, China; therefore, we suggest future studies consider the carbon footprint of buildings in other areas and establish an accurate carbon-footprint calculation system for the unit-fixed carbon-emission coefficient database, which can contribute to establishing a more authoritative and unified emission-coefficient database.