Evaluation of the CO2 emissions of an innovative composite precast concrete structure building frame

Journal of Cleaner Production 242 (2020) 118567

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Evaluation of the CO2 emissions of an innovative composite precast concrete structure building frame Haider Hamad Ghayeb*, Hashim Abdul Razak, N.H. Ramli Sulong** Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603, Kuala Lumpur, Malaysia

a r t i c l e i n f o

a b s t r a c t

Article history: Received 14 August 2018 Received in revised form 7 September 2019 Accepted 22 September 2019 Available online 24 September 2019

The type of frame system, materials, and power consumption used for the construction of new buildings cause environmental issues because of the production of carbon dioxide (CO2) emissions. Therefore, a new type of sustainable precast concrete structural system called SMART frame has been introduced to reduce the CO2 emissions during the construction of buildings. To determine the effectiveness of the CO2 emission reduction based on the new SMART frame, a similar frame configuration based on reinforced concrete (RC) was used. The SMART and RC building frames consisted of 12 storeys with similar floor areas and were designed under similar conditions. The CO2 emissions based on the material resources and construction methods used for the two building models were analysed. Additionally, the power consumption associated with the use of electricity and fuels for the devices and equipment was considered in the analysis of the total CO2 emissions. The total CO2 emissions of the SMART and RC frame buildings in kilograms (kg) per square meter (m2) are 455.94 and 516.12 kg CO2/m2, respectively. Thus, the total amount of CO2 emission reduction achieved in this study is 60.18 kg CO2/m2. In terms of the individual effects of materials and power consumption, the SMART building has a larger contribution, accounting for a 12.42% and 8.12% decrease in the CO2 emissions, respectively, compared with the RC building. Overall, based on the materials and power consumption used during the construction stage of the SMART frame building, the total CO2 emissions decreased by 11.66% compared with the RC building. Therefore, the SMART frame can be adopted as a sustainable frame alternative to the RC frame system. © 2019 Elsevier Ltd. All rights reserved.

Handling Editor: Baoshan Huang Keywords: Composite precast concrete CO2 emission Precast building Reinforced concrete frame SMART frame

1. Introduction The effect of global warming on the world climate has worsened due to carbon dioxide (CO2) emissions into the atmosphere (Gattuso et al., 2015; Smith and Wigley, 2000). Global CO2 emissions represent 65% of the total gas emission ratio, making this environmental issue a crucial one to be addressed (Wiedmann and Minx, 2008). Policy makers are facing new challenges with respect to the evaluation of environmentally beneficial development and economic methods (Zhao et al., 2017). However, an innovative approach was proposed to analyse the industrial contributions to CO2 emissions (Ali et al., 2017). The construction industry has caused significant environmental issues, which are mainly based on CO2 emissions (Chou and Yeh,

* Corresponding author. Fax: þ603 79675318. ** Corresponding author. E-mail addresses: [email protected], [email protected] (H.H. Ghayeb), hafi[email protected] (N.H.R. Sulong). https://doi.org/10.1016/j.jclepro.2019.118567 0959-6526/© 2019 Elsevier Ltd. All rights reserved.

2015). The CO2 is generated during construction, that is, during the manufacturing, transportation, production, and installation of the building members, which are used to construct new buildings (Ramesh et al., 2010). Modern construction of green buildings aims to reduce the greenhouse gases that are produced throughout the process (Giesekam et al., 2014; Sartori and Hestnes, 2007). Furthermore, due to the increasing development of commercial and residential buildings, research studies have focused on the reduction of CO2 emissions generated during the energy usage and construction phases of special buildings such as single family rezhouses (Castellano et al., 2015; Hirano and Fujita, 2016; Pe García et al., 2014; Rey et al., 2007; Ürge-Vorsatz et al., 2007). Construction materials play a significant role in the energy usage within the construction phase. Thus, a large amount of CO2 emissions is due to the used materials (Li et al., 2014; Nadoushani and Akbarnezhad, 2015; Oh et al., 2016; Park et al., 2014). The percentage differences in the CO2 emissions for concrete and steel, that is, two typical building materials, are 267% and 863%, respectively (Oh et al., 2017). These results indicate that increasing the cross-

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sectional area of the steel section is more advantageous for the reduction of CO2 emissions than increasing the cross-sectional area of concrete for composite structures subjected to high axial loads in high-rise buildings (Choi et al., 2016). The use of fly ash (FA), silica fume (SF) and granulated-blast furnace slag (GBFS) as an alternative materials to partially replace cement is a sustainable approach to reducing CO2 emissions (Peng et al., 2018; Song et al., 2019; Song and Yin, 2016; Wu et al., 2016). In addition, waste material such as palm oil clinker (POC) serves as an eco-friendly material in the mix proportion of concrete for reducing CO2 emissions in construction (Abutaha et al., 2018). Therefore, the construction of new buildings has significantly influenced the environment due to the emissions of CO2 based on the used materials and construction method. Based on construction methods utilising sustainable structural frames for buildings, the CO2 emissions can be reduced because less materials are used in the construction phase. In this study, an innovative composite precast concrete structure (ICPCS) called SMART frame (SF) is proposed and its CO2 emission is compared with that of a similar RC frame used for a 12-storey building. The scope of this paper is to evaluate the CO2 emissions due to material usage and power consumption during the construction phase. The CO2 emissions based on the material usage, that is, concrete, reinforcement bars, steel sections, steel couplers, bolts, and formwork, as well as the power consumption were computed independently and in combination to examine the overall CO2 emissions by the two types of building systems. Because the material amount used significantly reduces the CO2 emissions, the construction phase was considered when evaluating the amount of CO2 emissions and power consumption based on materials used during the construction phase. However, the improved ICPCS technique provided extra capacity to carry heavy loads and was applied to the long span in the building. Thus, the reduction of the amount of material used during the construction phase is a result of decreasing the number of beams and columns used for the SMART building. Hence, the CO2 emissions decreased. Therefore, the use of the SF in the construction of sustainable buildings is an environment-friendly alternative to the conventional RC frame. 2. Advantages of using composite precast concrete structures Past studies have indicated that adopting composite precast concrete (CPC) members in the construction phase of apartment buildings is a typical method for reducing CO2 emissions. The emissions can be reduced by 75%e80% compared with conventional buildings due to the decreased amount of reinforced concrete bars in the building (Hong et al., 2010b). It is possible to achieve a 10% CO2 emission reduction during construction by using a Modularised Hybrid System (MHS) for precast apartment buildings (Hong et al., 2010a). Furthermore, the use of CPC members reduces the CO2 emissions by decreasing the amount of used materials while ensuring structural stability (Gaidu cis et al., 2009; Hong et al., 2010b; Lee et al., 2011; Yoon et al., 2010). The concept of applying a green frame was proposed to decrease the CO2 emissions (Hong et al., 2010b) by utilising CPC members. This method reduces the CO2 emissions by 18%e23% compared with conventional RC construction methods (Hong et al., 2010b). (Lee et al., 2012) improved the composite beam and column system proposed by (Hong et al., 2010b); the CO2 emissions were reduced by 2.8%. Therefore, the use of structural buildings employing CPC members is increasing; this novel concept is also known as new precast frame (Lee et al., 2012). Studies on residential buildings have indicated that the use of composite precast frames reduces the construction costs and total CO2 emissions during construction (Lee et al., 2016).

3. Characteristics of innovative composite precast concrete structures The proposed composite precast structural system called SMART green frame used for the construction precast concrete (PC) buildings is depicted in Fig. 1. The SMART green frame consists of CPC columns and beams. The columns are at least 12 m long and suitable for the installation in a 3-storey building. This system has the capability to quicken the erecting process associated with precast building systems. The composite precast columns and beams are connected using steel joints during the installation. The composite members can be fast and accurately installed in the precast structural building. However, the beams must be erected after the columns have been installed. The SF columns have three levels, where each level is equivalent to the storey height of the building (Fig. 1). Once the composite elements of the PC columns and beams are completely installed, a hollow core slab (HCS) with a thickness of 150 mm is installed in each floor. The reinforced concrete slabs with a layer thickness of 75 mm are then cast in situ to secure the structural integrity. The steel reinforcement bar of this concrete layer has a diameter (Db) of 12 mm. The slab in a PC building consists of an HCS with a solid slab layer thickness of 75 mm. The use of the SMART green frame reduces the construction duration and improves the constructability based on the application of the composite joint method and HCS (Schaufelberger and Holm, 2017). The CPC is utilised for the units of a housing apartment, where the floor height must be the same as that used for conventional structural wall systems and must be maintained during the operation of these housing units (Park et al., 2014). The CPC members were produced and lifted during the installation using tower cranes. The elimination of most of the formworks of the composite PC columns, beams, and HCS units resulted in saving construction costs and time, whereas a steel mould was used to produce the CPC members. Wet construction using in situ casting of concrete for the conventional RC frame system increases the construction costs and time because of the utilisation of temporary formwork. Therefore, the PC system has the potential of saving construction time compared with the conventional method (RC), which uses in situ casting of concrete wall members (Luthra et al., 2017). The flange was terminated at the top or bottom of the steel section; however, this flange can only resist a small bending moment. Thus, removing the flange will decrease the amount of steel used for the CPC beams, which will increase the efficiency of the structural members (Hong et al., 2010b). The utilisation of composite precast concrete beams is an excellent method that can be used to decrease the amount of materials, construction costs, and CO2 emissions (Hong et al., 2010b). Such a composite beam can also be used to connect the steel and RC columns (Lee et al., 2011). (Lee et al., 2011) used a T-shape steel plate, which was fixed to the beam end, while (Choi et al., 2013) used double steel plates for the vertical axis of the PC beam. The length of the steel plate used in the study was 1/4 of the beam length (Choi et al., 2013) (Ghayeb et al., 2017). used a single plate embedded in a beam steel cage at 1/3 of the beam length. In this study, single plates were cast within PC beams and the embedded length was 33.33% of the beam length. 4. Details about the SMART frame used in this study The SF structure was developed based on the current ICPCS, as depicted in Figs. 1 and 2. In this study, a novel CPC frame was used to enhance the efficiencies of the structural members. Based on the use of the novel frame, the amounts of steel and concrete materials used for the construction of the PC building could be decreased. The

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Fig. 1. The PC columns and beams of the SMART green frame. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2. Beamecolumn connection concept in the SMART frame.

constructability of the composite members was upgraded and the construction time was reduced. The ICPCS was analysed along the long and short spans of the structural buildings. The material reduction is a result of decreasing the number of beams and columns used for the PC building. The SF was applied to the long span due to the composite action of steel sections and concrete, which increased the moment capacity in the middle and the end of the beams, respectively. Fig. 2 depicts the combination of the SF steel section structure and concrete reinforcement bars. The steel sections were applied to the SF elements. The steel sections and bars reinforced the concrete beams and columns. The use of steel sections for the composite PC members improved the buildability. A protruding steel plate was also embedded in the steel cage of the beams at 1/3 of the beam length and was connected to

the columns with two orthogonal plates using bolt systems. The steel tubes were embedded into the steel cage of the lower and upper portions of the precast columns, as shown in Fig. 2. The protruding tubes of the lower and upper columns in each floor have orthogonal slots, which are used to fix the orthogonal plates. The outer diameter of the lower tube in the upper column is smaller than the inner diameter of the upper tube in the lower column, leading to an easier installation during erecting. Thus, the utilisation of steel sections in the SF with reinforced concrete sections increased the resistance to tension and compression forces by the steel sections. The small tube of the upper column is fixed to the top tube of the lower column and all tubes are connected using bolts, as shown in Figs. 1 and 2, Figs. S1, and S2. For fast and safe connections between beams and columns, the orthogonal plates were slid and set into the connection zone and the plate beam was then connected to the orthogonal plates using backing plates and steel bolts (see Figs. 1 and 2, Figs. S1, and S2). The reinforced bars of the lower columns installed every three floors are connected to the steel bars of the upper column using steel couplers to ensure that the steel bars continue through the column sections, as shown in Figs. 1 and 2, Figs. S1, and S2. The SF members can be easily prepared and assembled on site. Hence, the costs of transportation of the frame members can be reduced. The composite beam and column elements of the SF can be quickly and accurately installed using steel connections. Similarly, the HCS units were fixed on the beams in each floor. The voids in the HCS units significantly decreased the steel and concrete quantities as well as the weight of the slabs. It is known that decreasing the material quantities of the input resource decreases the CO2 emissions (Gaidu cis et al., 2009; Hong et al., 2010b; Lee et al., 2011; Yoon et al., 2010). The joints between the beam and column act as composite because of the steel sections of the joints. Thus, increasing the section stiffness of the beams and columns reduces the necessity to increase the number of steel bars in that section. Consequently, the

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use of reinforced bars can be decreased. The ICPCS frame has a high constructability with respect to the composite RC sections in the structure and the connection process is similar to that used for steel buildings, which contain the simplest connection elements. The steel sections are embedded in the steel cage of the beams and columns and each member includes protruding steel sections, as suggested by (Ghayeb et al., 2017). The embedded length of the steel plate is related to the beam length (lb) and applied load on the beam (Oh et al., 2016). The structural stability of the beam with a length span of 7.5 m is satisfactory for a steel section length of 1/ 5e2/13 of the beam length. The rebar of the beams of the external connection was fixed with a headed anchor (steel coupler; Fig. S1). The headed anchor end of the steel coupler had an adequate lap length, which provided a safe transfer of the load and satisfactory length development of the steel bars in the end section. Because the steel bars using the headed anchors were shorter than those used in the conventional anchorage method, the 90 bend used in the conventional method increases the length of the steel bars (Lee et al., 2016). Decreasing the length of the steel bars reduces the amount of steel, leading to the reduction of input resource materials used for the project. The development prefabricated composite PC columns increased the efficiency ratio, as shown in Fig. S2. The steel tubes in the joints have strong compression strengths; thus, the columns are not easily damaged when moved during the installation. Furthermore, the CO2 emission can be reduced based on the reduction of the materials. 5. Case study of the energy and CO2 emissions associated with PC and RC buildings 5.1. Project description The RC and PC buildings consisted of two blocks of 12-storey buildings, including the ground floor (Fig. 3). The area of each

building in this project was 4190 m2 and the total area of all floors was 17303.20 m2 (Fig. S3). The buildings were initially designed with RC and PC frames. However, a CPC frame was utilised to enhance the structural efficiency of the building and reduce the CO2 emissions. Previous CPC frame structure analyses were used (Gaidu cis et al., 2009; Ghayeb et al., 2017; Hong et al., 2010b; Lee et al., 2011; Yoon et al., 2010) and CPC was applied in the short span. Consequently, a new design was required for the 7.5 m long span. The application of a SF in a PC building is also beneficial when analysing the effects of CO2 emission reduction. The RC and the SF buildings were designed under the same load conditions in this study. The span lengths of the RC and PC buildings are illustrated in Fig. S3. The span of the PC building helped to decrease the number of column and beam members due to the combined action of steel sections and reinforced concrete in the structural members to increase the stiffness. In addition, the composite members have a higher capacity to carry external moments. The SF was applied in the structural PC building to improve the seismic performance and reduce the CO2 emissions. Table S1 documents the strength of the materials. The RC and SMART frame models were designed using the same material strengths. The concrete strength (fck) was 50 MPa and the tensile strength of the rebar (fyk) was 540 MPa for (diameter of bar, Db  16 mm) and 515 MPa for (Db  20 mm). Two different materials were used for the steel sections: S355JR, fyk ¼ 417 MPa, was used for the steel plates and the steel tube material was A106 grade B, fyk ¼ 325 MPa. Furthermore, high-tension bolts and typical bolts with tensile strengths of 900 MPa and 650 MPa, respectively, were used. The properties of the steel couplers are also listed in Table S1. Table S2 presents the design loads of the RC and PC buildings. The building was subjected to a wind velocity of 33.5 m/s, a seismic load (S) of 0.18, and ultimate design loads of the floors of 22 kN/m2. The ETABS 2016 and Midas SDS 2017 programs were used to analyse the RC and SMART buildings. The beam and column

Fig. 3. Three-dimensional view of the finalised PC building.

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sections of the RC and PC buildings are depicted in detail in Figs. S4 and S5, respectively. The top and bottom bars of the beams were arranged in two rows to achieve structural stability (see Fig. S4). The columns were classified into three types, that is, external, internal, and corner columns (Figs. S3 and S5). The beams and columns in the PC model were designed as composite structural members. Each composite PC member was combined with a reinforced concrete section including steel section and steel rebar (Figs. S4c and d and S5b). The embedded steel sections decreased the number of steel bars. The design of the composite PC frame considered the structural stability and space efficiency of the steel sections and bars. Based on the application of the steel sections to the structural members of the PC building, a portion of the load could be carried and the reinforced efficiency of the concrete sections could be increased. Therefore, the amount of reinforcement steel bars in the sections of the structural members was reduced. A solid slab was applied in the RC building, while a HCS unit was used for the PC building. The slab thickness and details of the RC and PC buildings are illustrated in Figs. S4a and b and Figs. S4c and d, respectively. Finally, the foundation and shear walls of the RC and PC buildings were identical and thus excluded from the CO2 emission analysis. As presented in Table 1, the RC structural members were designed using 864 columns and 1464 beams, representing a total of 2328 structural members. However, 468 main columns and 756 beams were applied and specifically designed for the sections of the SMART structure building. The ratio of the total members used for the SF to that used for the RC frame (SF/RC) was 52.58%, as presented in Table 1. The beam and column members were designed based on the original RC and PC plans (Figs. S3, S4, and S5). Nevertheless, it was expected that an adequate CO2 reduction can be accomplished based on the reduced number of structural members.

5.2. Material consumption The material quantities used for the RC and SF buildings are presented in Table 2. The total concrete quantity of each floor of the RC and SF buildings includes the columns, beams, and slabs. The concrete quantity of the structural members of the RC frame is 5633.09 m3, while the concrete quantity for the SF is 4382.29 m3 (Table 2). The concrete quantity of the SF includes all in situ- and precast members. The RC concrete quantity is higher than that of

Table 1 RC and SMART frame (SF) member efficiency ratio. Floor No.

A Total structural members of the RC frame

B

Total structural members of the SMART frame (SF)

Ratio ¼ B/A (%)

Columns

Beams

Columns

Beams

GF-F1 F1-F2 F2-F3 F3-F4 F4-F5 F5-F6 F6-F7 F7-F8 F8-F9 F9-F10 F10-F11 F11-Roof (RF)

72 72 72 72 72 72 72 72 72 72 72 72

122 122 122 122 122 122 122 122 122 122 122 122

39 39 39 39 39 39 39 39 39 39 39 39

63 63 63 63 63 63 63 63 63 63 63 63

52.58 52.58 52.58 52.58 52.58 52.58 52.58 52.58 52.58 52.58 52.58 52.58

Total

864

1464

468

756

52.58

A: total amount of structural members of the RC frame; B: total amount of the structural members of the SF; Fi: floor number; GF: ground floor.

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Table 2 Total amount of temporary formwork and concrete used for each floor in the RC and SMART frame buildings. Floor number

Total floor area (m2)

RC frame

SF

RC frame

SF

F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12

1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93

469.424 469.424 469.424 469.424 469.424 469.424 469.424 469.424 469.424 469.424 469.424 469.424

365.191 365.191 365.191 365.191 365.191 365.191 365.191 365.191 365.191 365.191 365.191 365.191

2632 2632 2632 2632 2632 2632 2632 2632 2632 2632 2632 2632

1150 1150 1150 1150 1150 1150 1150 1150 1150 1150 1150 1150

Total

17303.20

5633.09

4382.29

31584

13800

Concrete quantity (m3)

Formwork amount (m2)

the SF (by 1250.80 m3). The difference in the concrete quantity between the RC and SMART structures is due to the decreased number of structural members. The voids inside each HCS unit also decrease the amount of the concrete in each floor by 66.52 m3. The composite action of the steel sections and RC in the SF increases the stiffness of the beams and columns compared with that of the RC members. Therefore, the span length of each panel increases. Based on the difference in the span between the columns, the number of columns and beams decreases. The decrease in the structural frame elements led to a reduced amount of concrete used for the SF building. In addition, the CO2 emissions were reduced based on the reduced concrete usage. An increase in the efficiency ratio was achieved based on the formworks of the SF, with formworks equivalent to 13800 m2. The efficiency ratio of the RC frame significantly decreased (total amount of formwork of 31584 m2). The SF required 17784 m2 less formworks than the RC frame because of the higher efficiency of the SF building, whereas most of the formworks were eliminated from the PC members because each member was precast. Additionally, the application of HCS units eliminated the use of formworks for the floor slabs. The total weight of the reinforcement bars or steel tendons was estimated per bar or tendon diameter. The total weight was calculated based on the volume and weight of each bar or tendon per diameter used in the buildings. The total weight of the steel tendons was added including the total weight of the steel bars used for each floor. Additionally, the total weight of the steel sections was estimated based on the cross section and density of each section. The weight of the steel couplers was calculated based on the density and cross section of each coupler. The amounts of steel used for the RC and SMART frames are presented in Table 3. The SF required 907.05 t of reinforcement bars, while 1403.69 t of steel rebar were used for the RC frame. The steel bars and sections are complementary with respect to the reinforcement of structural members. Thus, the SFs were reinforced using steel sections and the total amount of steel bars was reduced by 496.64 t. Steel sections, couplers, tendons, or bolts were not used for the RC building. The SF building used 64.62% of the steel bars applied for the RC building. In addition, 350.30 t of steel sections and 15552 nuts and bolts were used for the SF building, as shown in Table 3. The total numbers of the steel couplers used for the SF building were arranged according to their bar diameter to simplify the calculation of the coupler amount. In total, 5208 steel couplers were used for all the levels of the SF; 504, 1752, 336, 1944, and 672 couplers had a bar diameter of 12 mm, 16 mm, 20 mm, 25 mm, and

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Table 3 Total amount of steel used for the RC and SMART frame buildings. Floor number

Total area (m2)

Rebar quantity (ton)

Steel quantity Steel sections (ton)

Couplers (EA) SF

Bolts and nuts (EA)

RC

SF

RC

SF

RC

RC

SF

1 2 3 4 5 6 7 8 9 10 11 12

1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93 1441.93

135.78 124.56 124.56 124.56 119.11 119.11 119.11 119.11 111.53 111.53 111.53 83.19

81.87 79.49 79.49 79.49 77.73 77.73 77.28 77.28 75.01 75.01 75.01 51.66

0 0 0 0 0 0 0 0 0 0 0 0

30.19 30.19 30.19 30.19 30.19 30.19 30.19 30.19 30.19 30.19 30.19 18.20

0 0 0 0 0 0 0 0 0 0 0 0

*504 (12), 1752 (16), 336 (20), 1944 (25), and 672 (32)

0 0 0 0 0 0 0 0 0 0 0 0

1296 1296 1296 1296 1296 1296 1296 1296 1296 1296 1296 1296

Total

17303.2

1403.69

907.05

0

350.30

0

5208

0

15552

EA: Each piece; 1.0 ton ¼ 1000 kg; *the number of the couplers used in the SF (bar diameter) i.e. 504 (12).

32 mm, respectively (see Table 3). 5.3. CO2 emissions from the materials The CO2 emissions were estimated based on the production of materials in the construction phase. For instance, the CO2 emissions due to the production of one cubic metre (1 m3) of concrete were estimated from the processes involved in both concrete production and casting as well as the energy consumed. Hence, to determine the CO2 emissions associated with a process, the energy consumption per unit of material produced had to be audited (Table 4, Figs. 4 and 5). Thus, the CO2 emissions based on the material consumption were estimated using Eqs. (1) and (2).

Production CO2 ¼

n X ðQi

 CO2em Þ

(1)

i¼1

Installation CO2 ¼ S (Eci  CO2Ei),

(2)

where Qi is the quantity of the resource material such as formwork, rebar, and concrete; CO2-em is the CO2 emission rate, as shown in Table 4; Eci is the quantity of energy used; and CO2Ei is the CO2 emission rate associated with the energy use. The CO2 emissions of a building can be evaluated using the CO2 emissions per material amount. The CO2 emissions in the construction building phase were estimated based on the used materials. In previous studies, rules regarding the evaluation of the amount of CO2 emissions for each material in the construction phase were adopted and a reduction in the CO2 emissions was achieved (Hong et al., 2010a, 2010b; Lee et al., 2011, 2016). The evaluation of the energy usage was based on the consumption of raw materials. The processing of these materials for the use in the construction is presented in Fig. 6. This estimation may is the best reasonable way to evaluate the CO2 emissions from materials in the construction phase. Therefore, these data were applied in the analysis and estimation of the CO2 emissions in this study. Based on the literature, Table 4 presents the CO2 emissions for every unit of significant materials used in the construction phase. In this study, the CO2 emissions of SF and RC buildings were verified and compared. The amount of CO2 emissions was based on the quantities of the materials that were used during the construction. Steel section materials present higher CO2 emissions than other materials such as rebar, concrete, couplers, and bolts (Table 4). The CO2 emissions

of rebar and steel sections were 3505 and 4166 kg CO2-e/t, respectively. The CO2 emissions associated with the concrete production were 451.0 kg CO2-e/m3 for in situ- and precast members, that is, much lower than those of steel bars and sections. In a separate study, the CO2 emissions from concrete were evaluated based on the in situ cast surface area. The CO2 emissions recorded for concrete and steel bars were 550 and 620 kg CO2-e/m2, respectively (Guggemos and Horvath, 2005). Therefore, the quantity of steel significantly influences the CO2 emissions. The average units shown in Table 4 were applied in this study. In addition, the basic unit for the steel sections was utilised for the steel plates (Hong et al., 2010b). The total amount of nuts and bolts was calculated as the basic unit of bolts in the case of high-tensile strength (Hong et al., 2010b). The total CO2 emissions determined in this project are presented in Table 5. The CO2 emissions from the resource materials used in the construction were estimated based on the average basic units of the CO2 emissions shown in Table 4. The quantities in Tables 2 and 3 were calculated based on the design drawings of the two buildings. Table 5 shows that the total amount of CO2 emissions from concrete in the RC and SF buildings is 2540.52 and 1976.41 t, respectively. Hence, the SF structure eliminated 564.11 t of the total CO2 emission compared with the RC structural frame. Thus, the total CO2 emissions were reduced by 22.20% due to the use of concrete in the SF. In addition, the steel reinforcement bars emit 4919.93 and 3179.20 t of CO2 in the RC and SF buildings, respectively. Therefore, based on the use of steel bars in SF structure, the CO2 emissions were reduced by 35.38% compared with the RC building. The reduction of the CO2 emissions from the formwork was 153.48 t in the SF compared with the RC frame. This corresponds to a reduction in the CO2 emissions of 56.31% in the SF compared with the RC frame. In the SF, higher CO2 emissions were generated from the steel sections, couplers, and bolts compared with the RC frame due to an increase in the amount of steel sections. The total CO2 emissions based on the amount of steel materials used in the SF were reduced by 4.94%. Finally, the total CO2 emissions from all materials in the construction phase of the SMART and RC frames were 6772.44 and 7733.02 t CO2, respectively. Therefore, in the SF system, the CO2 emissions were decreased by 12.42% compared with the RC frame system based on the materials used for the construction. In summary, based on the materials of the precast buildings using an SF, the CO2 emissions were reduced by 22.20%, 4.94%, and 56.31% for concrete, steel materials, and formworks, respectively, compared

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Table 4 Basic units and factors of materials for the conversion to CO2 emissions. Description

CO2 emissions

Author/s

Average CO2 emissions used in this study

Production cement

(700e1000) kg CO2-e/t 927 kg CO2-e/t 820 kg CO2-e/t 900 kg CO2-e/t 45.9 kg CO2-e/t 40.8 kg CO2-e/t 56.0 kg CO2-e/t

(Gartner, 2004; Josa et al., 2004)

874.25 kg CO2-e/t

Production coarse aggregate

Production fine aggregate

13.9 kg CO2-e/t

0.1 MJ CO2-e/t 0.42 kg CO2-e/m3 5.2  103 kg CO2-e/L Batching plant 3.3 kg CO2-e/m3 Electricity factor (0.52114 e0.74884) kg CO2-e/kWh Production steel bar (3500e3510) kg CO2-e/t Production steel sections 4166.00 kg CO2e/t Production high-tensile 13.5  102 kg CO2-e/bolt and bolts; nut a Steel Coupler Db ¼ 12 mm Db ¼ 16 mm Db ¼ 20 mm Db ¼ 25 mm Db ¼ 32 mm Production plywood 8.11e9.15 kg (Formwork) CO2-e/m2 Transportation of cement By Road: 10 kg CO2-e/t By Rail: 17 kg CO2-e/t By Water: 31 kg CO2-e/t Concrete transport 9.4 kg CO2-e/t Fuel use of car 0.242 kg CO2-e/ Diesel car (large) km Petrol car (large) 0.298 kg CO2-e/ km Onsite placement activities 9.0 kg CO2-e/m3 (fuel, Pumping, vibration) Production of 1 m3 concrete 290 kg CO2-e/m3 (fck ¼ 25 MPa) 340 kg CO2-e/m3 (fck ¼ 32 MPa) Production of 1 m3 concrete 140.43 kg CO2-e/ (fck ¼ 24 MPa) m2 b b Production of 1 m3 451.0 kg CO2-e/ concrete (fck ¼ 50 MPa) m3 Production water Super plasticiser (SP)

Marceau et al. (2006) Flower and Sanjayan (2007) (Benhelal et al., 2013; Hasanbeigi et al., 2010) Flower and Sanjayan (2007) Turner and Collins (2013) (Basbagill et al., 2013; Chau et al., 2015; Hammond and Jones, 2011; Hammond et al., 2008; Jeong et al., 2012) (Basbagill et al., 2013; Chau et al., 2015; Flower and Sanjayan, 2007; Hammond and Jones, 2011; Hammond et al., 2008; Jeong et al., 2012) (Baird et al., 1997; Lensink, 2005) Hong et al. (2015) Flower and Sanjayan (2007)

47.57 kg CO2-e/t

13.9 kg CO2-e/t 0.1 MJ CO2-e/t 0.42 kg CO2-e/m3 5.2  103 kg CO2-e/L

Flower and Sanjayan (2007) (Brander et al., 2011; Statistics, 2011)

3.3 kg CO2-e/m3 0.6350 kg CO2-e/kWh0.6350 kg CO2-e/kWh

(Basbagill et al., 2013; Chau et al., 2015; Hammond and Jones, 2011; Hammond et al., 2008; Hong et al., 2010a; Jeong et al., 2012; Lee et al., 2011, 2016; Yoon et al., 2010) (Hong et al., 2010b; Kim et al., 2004)

3505 kg CO2-e/t

(Hong et al., 2010b; Kim et al., 2004)

13.5  102 kg CO2-e/bolt and nut

1.91 kg CO2-EA 3.33 kg CO2-EA 4.69 kg CO2-EA 8.60 kg CO2-EA 19.49 kg CO2-EA (Basbagill et al., 2013; Chau et al., 2015; Hammond and Jones, 2011; Hammond et al., 2008; Jeong et al., 2012) Clear et al. (2009)

Production CO2 (kg CO2EA) ¼ Ac  Lc  steel density  4.166

4166.00 kg CO2-e/t

8.63 kg CO2-e/m2 11 kg CO2-e/t

Flower and Sanjayan (2007) Hill et al. (2011)

9.4 kg CO2-e/t 0.242 kg CO2-e/km

Consultancy (2010)

0.298 kg CO2-e/km

Flower and Sanjayan (2007)

9.0 kg CO2-e/m3

Flower and Sanjayan (2007)

290 kg CO2-e/m3 340 kg CO2-e/m3

(Hong et al., 2010a; Lee et al., 2011, 2016; Yoon et al., 2010)

140.43 kg CO2-e/m2

b

b

Calculated as mixed design materials of concrete (Ghayeb et al., 2019)

451.0 kg CO2-e/m3

a Specific data to compute the CO2 emissions of couplers were not available; therefore they were calculated based on the weight of each coupler piece and CO2 emissions of the steel section; EA: Each piece; litre: L; ton: t. b [(Cement: Gravel: Sand: Water: SP) (kg/m3] ¼ [450:1014:670:171: 4.5]; Concrete density ¼ 2400 kg/m3.

with the RC frame building (Fig. 7).

5.4. CO2 emissions associated with the power and energy consumptions The devices and equipment used during the construction phase also emit a certain amount of CO2 because they use oil and electric power during the construction of the building. In addition to the CO2 emissions from materials, the energy production associated with oil and electric power is also expected to cause CO2 emissions (Kim et al., 2004). With respect to the analysis of 28 apartment

building units by (Kim et al., 2004) using life cycle assessment (LCA), deterioration equations were proposed for the CO2 emissions in the construction phase (Kim et al., 2004). The equations were used in this study to estimate CO2 emissions generated from oil and power consumption. The consumption of energy for the oil production was estimated using Eq. (3). In addition, Eq. (4) was used to calculate the CO2 emissions (Kim et al., 2004). Eco ¼ 0.0017  Af þ 37.5 QCO2

o

¼ Eco  3.06,

(3) (4)

8

H.H. Ghayeb et al. / Journal of Cleaner Production 242 (2020) 118567

use of electric power, Ece, was calculated to be 55.06 TOE based on Eq. (5). The total amount of CO2 emissions was calculated using Eq. (6): Ece ¼ 0.0247  Af

0.79

QCO2 e ¼ Ece  1.64,

Fig. 4. Assessment model and process to evaluate the CO2 emissions during building construction.

where Eco is the consumption of oil energy during the construction in tons of oil equivalent (TOE), Af is the total floor area (m2), and QCO2 o is the total amount of CO2 emissions based on the oil usage (t CO2). The total floor area of each building was calculated to be 17303.2 m2; thus, the energy consumption (Eco) was 66.92 TOE. The total CO2 emissions based on the oil usage were 204.78 t CO2, as shown in Table 6. The energy consumption depending on the electric power consumption in the construction phase was estimated using Eq. (5), while Eq. (6) was used to calculate the CO2 emissions (Kim et al., 2004). The power consumption based on the

(5) (6)

where Ece is the total amount of power consumption due to electricity usage in the construction phase [TOE], and QCO2e is the total amount of CO2 emissions depending on the total power (electricity) consumption at the same phase (Ton-CO2), that is, 90.30 t CO2. Three tower cranes were used during the SF construction, as depicted in Fig. 8. However, two tower cranes were needed for the RC frame construction (Fig. 8). To cover the entire area of the SMART building and decrease the time required to lift the precast members, three tower cranes were used in the construction of the SMART building. Therefore, the construction time decreased. A typical electrical tower crane consumes 800 A (244 kW, 208 V) and an energy equivalent to 8  244 ¼ 1952 kWh, assuming 8 h of operation per day. However, the total operation time of the tower crane is 8.5 and 14 months for the PC and RC buildings, respectively. Thus, the estimation of the total power consumed for the use of the tower cranes is 431392 kWh based on Eq. (7). The average conversion factor of 0.6350 kg CO2/kWh was applied to obtain the total CO2 emissions. Therefore, the total CO2 emissions for each tower crane in the SF are 273.93 t CO2 based on Eq. (8). The usage of three tower cranes in the SMART building saves time and thus the total days required to complete the construction decreases. At least 14 months are required to complete the RC building construction. Therefore, the total consumption energy of a tower crane is 710528 kWh. The corresponding energy-generated CO2 emissions of each tower crane are 451.19 t CO2. The two tower cranes used for the construction of the RC building produce 902.38 t CO2, while the three tower cranes in the SMART building produce 821.79 t CO2, as calculated using Eq. (8). Although three tower cranes are used for the precast building, the CO2 emissions are smaller than those of the RC building. The SF CO2 emissions produced by the tower cranes are 91.07% of those of the RC building. Furthermore, the duration of the construction of the PC building was shortened. Therefore, the usage of an additional tower crane saves time and

Fig. 5. CO2 emission system for the production of 1 m3 of concrete.

H.H. Ghayeb et al. / Journal of Cleaner Production 242 (2020) 118567

9

Fig. 6. CO2 emissions during the construction phase of RC and PC buildings.

reduces the total cost of the project.

Total QCO2ete ¼ QCO2e þ (QCO2et  number of tower cranes)

Total energy (Et) ¼ total power  total working days/month  total working months (7)

5.5. Total CO2 emissions from materials and power consumption

QCO2et ¼ Et  0.6350

(8)

where QCO2et is the total amount of CO2 emissions produced by the electricity usage of the tower crane during the construction phase (t CO2). The CO2 conversion factor is equal to 0.6350 kg CO2/kWh. The total CO2 emissions produced by the electricity usage of the tower cranes and electricity (QCO2ete) in the construction phase (t CO2) were estimated using Eq. (9).

(9)

The reduction ratio of the CO2 emissions based on the materials in the SF building was 12.42% compared with RC frame building. The reduction in CO2 emissions was the result of the resource input due to the use of the SF. A CO2 reduction of 8.12% was also obtained based on the power consumption in the SF building. Table 6 presents the total CO2 emissions from the materials used and consumption of energy. The total CO2 emissions for each unit area in the RC and SF buildings are 516.12 and 455.94 kg CO2/m2,

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Table 5 CO2 emissions based on the material usage in the construction phase of RC and SMART frame buildings. Total CO2 emission (t CO2)

Classification material Process

Description

a

Concrete Reinforcement

Rebar Steel sections Steel coupler PC installation High-tensile bolt b Total (Rebar þ Steel sections þ Bolts) c Formworks Total(aþbþc)

CO2 emission per unit area (kg CO2/m2)

Emission ratio (%)

RC

SF

RC

SF

SF/RC

2540.52 4919.93 0.00 0.00 0.00 4919.93 272.57 7733.02

1976.41 3179.20 1459.35 38.18 0.21 4676.94 119.09 6772.44

146.82 284.34 0.00 0.00 0.00 284.34 15.75 446.91

114.22 183.74 84.34 2.21 0.01 270.29 6.88 391.40

77.80 64.62 e e e 95.06 43.69 87.58

a: Concrete material; b: Steel material; c: Formworks materials and works.

Fig. 7. Reduction ratios of the CO2 emissions based on the materials used in SMART frame buildings compared with RC buildings.

Table 6 Overall CO2 emissions based on the materials and power consumption. CO2 emission unit area (kg CO2/m2)

Emission ratio (%)

Resource item

CO2 emission (t CO2) RC

SF

RC

SF

SF/RC

Materials Oil Electric power Total CO2 emissions

7733.02 204.78 992.68 8930.48

6772.44 204.78 912.09 7889.31

446.91 11.84 57.37 516.12

391.40 11.84 52.71 455.94

87.58 100.00 91.88 88.34

respectively. Therefore, a total reduction of 60.18 kg CO2/m2 corresponding to a reduction ratio of 11.66% was realised in the SF building. Higher CO2 emissions were recorded for the RC frame building compared with the SF (by a factor of 1.132). 6. Conclusions The construction of new buildings leads to crucial environmental issues due to the CO2 emissions produced by the use of construction materials, design and construction frames, and power consumption. Therefore, an innovative CPC structure called SF was proposed in this study and the associated CO2 emissions were compared with those of a RC building. The total amount of construction materials, such as formworks, steel bars, and concrete, was decreased in the SF building, which reduced the construction time compared with that of the conventional RC system. The decrease in the construction materials resulted in a greater efficiency and promoted the sustainable construction of the SF

Fig. 8. Arrangement of the tower cranes.

building. Hence, the CO2 emissions were reduced. In addition, the composite action of the steel sections and reinforced concrete increased the moment capacity and stiffness of the PC members and decreased the number of PC building members. Thus, the usage of steel sections reduced the reinforcement bars in the PC members. The elimination of most of the formworks for the composite PC building members also reduced the construction cost and time. This resulted in a higher efficiency of the PC building due to the SF usage during the construction. Therefore, SF utilisation promoted the sustainability, characterised by less materials and time required for the construction phase. The construction materials used for the SF were decreased by 1250.80 m3 and 17784 m2 for concrete and formworks, respectively, compared with the RC building. The reduced CO2 emissions ratios of the SF building based on the utilisation of formworks, steel bars, and concrete were 56.31%, 35.38%, and 22.20%, respectively, compared with those of the RC system. Although the steel sections, couplers, and bolts amounts were higher in the SF, the total amount of steel materials of the SF was smaller than that of the RC frame (by 242.99 t). The smaller amount of steel materials of the SF used in the precast building led to a 4.94% reduction of the total CO2 emissions compared with the RC building. The total CO2 emissions per square metre produced by the usage of materials in the construction phase were 446.91 kg CO2/m2 for the RC building and

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391.40 kg CO2/m2 for the SF precast building. The CO2 emissions associated with the SF building were reduced by 55.51 kg CO2/m2 based on the material usage. This corresponds to a 12.42% decrease in the CO2 emissions based on the use of a SF as an alternative to the RC frame. However, increasing the number of tower cranes during the construction increases the energy consumption and CO2 emissions. Based on this study, the project timeline should be carefully followed to decrease the construction time of the precast building compared with the conventional RC building. The construction times required for the RC and PC buildings were 14 and 8.5 months, respectively. The composite members of the precast structural building were quickly installed. The SF usage therefore decreased the construction time and thus the cost. Consequently, the time saved by using tower cranes for the construction and proper management led to the reduction of the total amount of CO2 emissions. The CO2 emissions ratio from the power consumption based on the use of three tower cranes for the construction of the SF building was reduced compared with the use of two tower cranes for the construction of the RC building. The CO2 emissions produced by the tower cranes in the SF were 91.07% of those of the RC building, which decreased by 80.59 t CO2. Overall, the total CO2 emissions per square metre based on the material usage and electric power consumption in the construction phase were 516.12 kg CO2/m2 for the RC building and 455.94 kg CO2/m2 for the SF precast building. The reduction of the CO2 emissions in the PC building was 60.18 kg CO2/m2, due to the use of materials and electric power in the construction phase compared with the RC building. Therefore, the precast building using the SF led to a 11.66% CO2 emission reduction compared with the RC building based on material usage and consumption of energy in the construction phase. Finally, future directions based on this study include the use of sustainable material, such as a geopolymer concrete, instead of normal concrete to reduce the CO2 emissions of precast buildings. The CO2 emission analysis associated with the materials used for the building construction can be useful in the building design, that is, suitable materials can be chosen to decrease the CO2 production. In addition, the analysis of the CO2 emissions based on the energy usage of the buildings is also important for the evaluation of the CO2 emissions during the occupancy phase. Acknowledgements The authors would like to thank the University of Malaya and Ministry of Higher Education, Malaysia, for the support provided in form of a Postgraduate Research Grant (PPP-Project No. PG1992015B) and Fundamental Research Grant Scheme (FP050-2017A). The authors would also like to thank the Faculty of Engineering, University of Malaya, Malaysia, for the support provided for the research project No. GPF071A-2018. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jclepro.2019.118567. References Abutaha, F., Razak, H.A., Ibrahim, H.A., Ghayeb, H.H., 2018. Adopting particlepacking method to develop high strength palm oil clinker concrete. Resour. Conserv. Recycl. 131, 247e258. https://doi.org/10.1016/j.resconrec.2017.11.031. Ali, Y., Ciaschini, M., Socci, C., Pretaroli, R., Severini, F., 2017. An analysis of CO2 emissions in Italy through the Macro Multiplier (MM) approach. J. Clean. Prod. 149, 238e250. https://doi.org/10.1016/j.jclepro.2017.02.094.

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