a model for estimating construction waste generation index for building project in china
TRANSCRIPT
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Resources, Conservation and Recycling 74 (2013) 20– 26
Contents lists available at SciVerse ScienceDirect
Resources, Conservation and Recycling
journa l h om epa ge: www.elsev ier .com/ locate / resconrec
model for estimating construction waste generation indexor building project in China
ingru Li ∗, Zhikun Ding, Xuming Mi, Jiayuan Wangollege of Civil Engineering, Shenzhen University, Shenzhen 518060, China
r t i c l e i n f o
rticle history:eceived 7 October 2012eceived in revised form 17 February 2013ccepted 20 February 2013
eywords:aste generation per gross floor area
WGA)he amount of construction waste
a b s t r a c t
The increasing construction and demolition (C&D) waste causes both cost inefficiency and environmentalpollution. Many countries have developed regulations to minimize C&D waste. Implementation of theseregulations requires an understanding of the magnitude and material composition of waste stream. Con-struction waste generation index is a useful tool for estimating the amount of construction waste andcan be used as a benchmark to enhance the sustainable performance of construction industry. This paperpresents a model for quantifying waste generation per gross floor area (WGA) based on mass balanceprinciple for building construction in China. WGAs for major types of material are estimated using pur-chased amount of major materials and their material waste rate (MWR). The WGA for minor quantities
aterial waste rate (MWR)uildinghina
of materials is estimated together as a percentage of total construction waste. The model is applied toa newly constructed residential building in Shenzhen city of South China. The WGA of this project is40.7 kg/m2, and concrete waste is the largest contributor to the index. Comparisons with transportationrecords in site, empirical index in China and data in other economies reveal that the proposed model isvalid and practical. The proposed model can be used to setup a benchmark WGA for Chinese construction
large-
industry by carrying out. Introduction
Construction and demolition (C&D) waste has become an impor-ant issue not only from the perspective of cost efficiency butlso due to its adverse effect on the environment. In an attempto protect the environment and to improve sustainability of theonstruction industry, many countries and regions have devel-ped various regulations and initiatives to minimize C&D waste.n the United Kingdom, the Code for Sustainable Homes makes on-ite waste minimization, sorting and recycling obligatory (Unitedingdom Government – Department for communities and Localovernment, 2006). Several regulations have existed to control&D waste in Hong Kong (Tam and Tam, 2008a). As an exam-le, waste management plan is compulsory for all constructionrojects in Hong Kong since 2003 (Tam, 2008b). The Brazilian Envi-onmental Protection Agency published Resolution 307 in 2002,hich requires all local authorities to prepare and execute plans for
he sustainable management of C&D waste (Brazilian Government-nvironmental Protection Agency, 2002). In mainland China, the
dministration of Urban Construction Garbage was promulgatedn 2005 to promote a series of local regulations on C&D waste
∗ Corresponding author. Tel.: +86 755 26732840; fax: +86 755 26732850.E-mail address: [email protected] (J. Li).
921-3449/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.resconrec.2013.02.015
scale investigations in the future.© 2013 Elsevier B.V. All rights reserved.
management (Ministry of Housing and Urban-Rural Developmentof the People’s Republic of China, 2005).
However, implementation of these provisions requires anunderstanding of the magnitude and material composition of thewaste stream (Cochran and Townsend, 2010). A construction wastemanagement plan, for example, requires contractors to estimatethe quantity of total construction waste and its main componentsat the planning phase, which will facilitate waste reduction, reusingand recycling during the construction process.
A number of researchers were aware of this situation and con-centrated on quantification of C&D waste in various countries(Llatas, 2011). These studies can be divided into two categories:studies that determine an overall C&D waste generation amountin a region (e.g. Bergsdal et al., 2007; Cochran et al., 2007;Franklin Associates, 1998; Kofoworola and Gheewala, 2009; Yostand Halstead, 1996) and those that measure C&D waste generationindex at project sites (e.g. Bossink and Brouwers, 1996; Formosoet al., 2002; Poon et al., 2004a; Skoyles, 1976). In the secondcategory, most of researchers discussed the construction wastegeneration index as estimation of this index is more difficult thandemolition waste generation index.
The construction waste generation index is identified as a mean-
ingful tool to promote construction waste management. It can beapplied to predict the amount of construction waste generated in aproject, which will assist project stakeholders to prepare appro-priate waste management plans. Comparing the index between
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ifferent projects can help project stakeholders to gain more insightbout their construction waste management performance and toeview the effectiveness of construction waste management prac-ices. Moreover, the amount of construction waste generated in aegion or a country can also be estimated by employing the indexnd construction area (Cochran et al., 2007).
However, the consideration on construction waste manage-ent is fairly negligible in mainland China. Low awareness of
ustainable construction accounts for the deficiency of data abouthe amount of construction waste either at a macroscopic levelr a microscopic level. A widely cited construction waste gener-tion index, 50–60 kg/m2, was provided by Lu (1999) based onmpirical estimation without detailed interpretation. However, theaste generation index will vary in a wide range with construc-
ion technology, structure type, building occupancy, and especiallyanagement level (Li et al., 2010). The above empirical index
eveals limited information for project stakeholders for under-tanding the magnitude and composition of construction waste andreparing an appropriate construction waste management plan. Inarticular, the culture and common practices of the construction
ndustry in China may not be entirely similar to other economies.hus, an approach to the measurement of a construction wasteeneration index for the Chinese construction industry should benvestigated.
Given the situation, the objective of this research is to present aractical and simple model for measuring the construction wasteeneration index for building projects in China. The study is struc-ured in four parts. The first part includes a literature review on theuantification of construction waste. The second section describeshe approach to measuring the waste generation index for buildingonstruction. Then, the method is illustrated using a newly con-tructed residential building project in Shenzhen, China. Finally, allhe findings are discussed in detail and conclusions are drawn.
. Reviews
.1. Main construction waste generation indexes
Amounts of construction waste generation have received sig-ificant attention because this information is a prerequisite toeveloping appropriate solutions for managing waste. A varietyf researchers have developed different methodologies to quan-ify construction waste. As mentioned above, these studies cane divided into two categories: studies that determine an overallaste generation amount in a region and those that measure theaste generation index at a project site.
Of the second category, some studies investigated materialaste rates (MWR), which are the percentages of waste material tourchased material or required by the design, to indicate the wasteeneration level of construction projects. For an example, Skoyles1976) measured the MWR of major materials in UK and found theercentages of waste materials ranged from 2 to 15%, on averageouble the losses generally assumed. Enshassi (1996) found from
study in the Gaza strip that the materials loss was approximately.6–11%. Formoso et al. (2002) indicated that the waste rate ofaterials in the Brazilian building industry was fairly high and var-
ed widely across different projects. Bossink and Brouwers (1996)evealed that approximately 1–10% of the purchased constructionaterials (by weight) was left as waste. In Hong Kong, Poon et al.
2004b) identified the material waste levels of various trades forublic housing and private residential buildings. Tam et al. (2007)
nvestigated waste levels of five major types of construction mate-ial in terms of subcontracting arrangements and project types.
Other studies derived a waste generation index using the vol-me or quantity of waste generated per gross floor area (WGA).
and Recycling 74 (2013) 20– 26 21
Poon et al. (2004a) calculated the WGAs for two public housingconstruction sites as 0.14 m3/m2 and 0.21 m3/m2. In China, Lu et al.(2011) performed a total of five measurement exercises to inves-tigate the WGAs of four typical trades. Llatas (2011) developed amodel to estimate WGA and applied to a dwelling project in Spain.A WGA of 0.1388 m3/m2 was obtained from the case study. Anotherstudy in Spain derived a WGA as 0.1075 m3/m2 from a newlyconstructed residential building that generated waste of approx-imately 172.2 m3 on a total of 1600 m2 floor area (Solís-Guzmúnet al., 2009).
2.2. Measurement method of these construction waste generationindexes
In addition to different units of measure, the above studies alsoadopted varied approaches to measuring construction waste gener-ation indexes. They reached their objectives using three differentapproaches: (1) field monitoring; (2) interviews and (3) materialbalance.
The first approach collects data by conducting field monitoringbecause direct records of construction waste amounts are generallyunavailable at sites. Skoyles (1976) and Enshassi (1996) measuredthe MWR by comparing contractors’ records of delivery with mea-surements of finished work. Formoso et al. (2002) investigated theoccurrence of material waste in Brazil by direct observation of sites.Bossink and Brouwers (1996) sorted and weighed all constructionwaste materials at five housing construction sites. This method wasalso adopted by Lu et al. (2011). Poon et al. (2004a) conductedregular site observations at construction sites and collected databy visual inspection, tape measurements and truck load records.The quantities of waste were calculated by multiplying the truckvolume and the total number of trucks used for waste disposal.
Apart from this type of ‘hard’ method for measuring waste, ‘soft’methods, such as questionnaire surveys and interviews, have alsobeen adopted (Lu et al., 2011). For example, Poon et al. (2004b)identified the waste levels of various trades based on site observa-tions and interviews with professionals. Tam et al. (2007) collectedthe waste levels of five major types of construction material frominterviews with project managers.
Another approach quantifies the construction waste generationindex based on the material balance principle. This approach con-siders the fact that after the building materials are delivered tothe site, part of the materials are incorporated into the buildingstructure during construction, and the remainder is discarded aswreckage waste or package waste on site (Cochran and Townsend,2010). Solís-Guzmún et al. (2009) identified three categories ofwaste in the construction process: demolished, wreckage andpackage waste. They quantified these three types of waste by mul-tiplying the quantities of material used in structural elements withthe corresponding transformation coefficients. The material usedin each structural elements is obtained from the budget document.These coefficients were estimated from the Andalusian Construc-tion Costs Database and the guidelines of an expert team. Llatas(2011) further applied the approach to quantify the amount ofwaste expected in each building element according to the EuropeanWaste List.
To quantify construction waste by carrying out field observa-tion, on-site sorting, weighing and monitoring related documentsis a relatively accurate method but requires a great deal of timeand human resources. This approach requires field monitoring tocontinue until the end of construction activity in order to obtainthe total quantity of waste generated on the site. This require-
ment is one key reason that only a few sample construction siteswere investigated in previous researches (Bossink and Brouwers,1996; Poon et al., 2004a). Furthermore, our previous experimentalresearch also found that on-site sorting and weighing occupy too
2 ation and Recycling 74 (2013) 20– 26
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Table 1The major materials using in building construction projects.
No. Material Note
1 Concrete The major material of concrete work2 Steel bar The major material of concrete work3 Brick and block The major material of masonry work4 Timber formwork The major material of concrete work
2 J. Li et al. / Resources, Conserv
uch space and manpower and thus would encounter difficultiesor bulky waste streams on large construction sites (Lu et al., 2011).
easuring waste as the difference between the amount of materialsffectively purchased and the actual quantities used in building isdopted by Skoyles (1976) and Enshassi (1996). However, Skoyles1976) also pointed out that bills of quantities in tendering doc-ments only provided basic measurements of a project and theeasurement had to be repeated between 15 and 20 times during
he building process. The repeated measurements greatly increasehe difficulty in monitoring waste by comparing contractors’ deliv-ry records with measurements of finished work.
By contrast, quantifying the construction waste based on theaterial balance principle is a more practical substitute for large
onstruction sites. In particular, this method can estimate the gen-ration index for each waste component, in addition to total waste,hich facilitates stakeholders to develop their waste reuse or
ecycling plans. However, the process of gaining reasonable trans-ormation coefficients such as those in Solís-Guzmún’s study is aritical problem. In the next section, the details of our approachill be presented.
. Methodology
This section presents a new model to quantifying WGA for build-ng construction based on the mass balance principle. The modelosts less time and manpower to collect data than many exist-ng methods, which makes it suitable to be used in conductingarge scale statistical investigations. The application of the modelncludes five phases:
1) Listing the major types of construction material;2) Investigating the purchased amount of these major materials;3) Investigating the actual MWR of each type of material listed in
phase 1;4) Estimation of the percentage of the remaining wastes;5) Calculating the total WGA and the WGA for each type of mate-
rial.
The first thing to notice is that this study will measure the WGAy weight, although the majority of the aforementioned studiesalculated WGA by volume (Llatas, 2011; Poon et al., 2004a; Solís-uzmún et al., 2009). Poon et al. (2004a) collected data by visual
nspection, which is more convenient to calculate the quantitiesf waste by volume. Llatas (2011) stated that volume is a valuableatum that facilitates estimation of the size and numbers of con-ainers. However, the density of the mixed waste may vary broadlyith various compositions, which will cause difficulty in comparing
he waste generation levels between different projects. Moreover,he landfill fee in China is applied by weight using weight machinest landfills. Thus, WGA by weight is considered in this study.
.1. Listing the major types of construction material
Although buildings across the world is varied in buildingtructure and construction techniques, typical construction wasteomponents include concrete, brick and block, steel reinforcement,imber, cement and mortar, ceramic tile, plastic and cardboardackaging materials, etc. (Bossink and Brouwers, 1996; Formosot al., 2002; Poon et al., 2004b; Tam et al., 2012). However, theroportions of these components may vary within a large range inifferent countries and regions.
In China, multilayer or high-rise buildings comprise the majorityf newly constructed buildings due to the high population densitiesf cities. The reinforced concrete structure is most popular in theseuildings. Thus, waste material is mainly sourced from concrete
5 Mortar The major material of wet trades of finishing work6 Tile The major material of wet trades of finishing work
work, masonry work, timber formwork, and the wet trades of fin-ishing work, such as screeding, plastering and tile laying (Poon et al.,2004b). Other small amounts of waste come from water and wirepipes, packaging material and other small goods. It is obvious thatthe major types of construction materials, such as concrete, timberformwork and steel bar, are the major source of construction waste(Li et al., 2010).
For the popular reinforced concrete framework buildings inChina, the major materials consist of concrete, steel bar, brick andblock, timber formwork, mortar and tile, as listed in Table 1.
3.2. Investigating purchased amounts of major materials
The amount of material purchased can be collected from the pur-chasing records of finished projects or from the budget documentsof ongoing projects. The amount in the budget document gener-ally includes normal material loss during construction and thus isclose to the actual purchased amount. Because most types of mate-rial are purchased batch by batch in China, a situation in whichthe purchased material will significantly exceed the demand willrarely occur. Even if this situation occurs, the extra amount can bereturned to the supplier. Thus, this situation is not considered inthis study.
3.3. Investigating actual MWR
MWR is measured by dividing the amount of waste by eitherthe amount of purchased material (Bossink and Brouwers, 1996;Enshassi, 1996; Poon et al., 2004a; Skoyles, 1976; Tam et al., 2007)or the amount of material required by the design (Formoso et al.,2002). The two possible rates will differ to a very small extentunless the rate is quite huge, for example, 73.7% for cement in Brazil(Formoso et al., 2002). To facilitate the intuitive understanding andestimation of project stakeholders, MWR is evaluated as the ratioof waste material to purchased material expressed as a percentagein this study.
As mentioned in Section 2.2, two different methods have beenadopted to measure MWR: “hard” methods, such as field monitor-ing (Bossink and Brouwers, 1996; Enshassi, 1996; Formoso et al.,2002; Poon et al., 2004a; Skoyles, 1976), and “soft” methods, suchas interviews (Poon et al., 2004b; Tam et al., 2007). In this study,the MWR on each site is obtained from the project manager’sestimation. In China, the project manager is the core person ofa construction project, who is fully responsible for project cost,schedule and quality. Thus, project manager’s estimation is gen-erally believable. In addition, there are other benefits to obtain anestimation of the MWR from the project manager.
(1) It can minimize time and cost involvement of investigation. Asdiscussed above, field monitoring takes a great deal of time andhuman resources and therefore encounters difficulties for bulky
waste streams on large construction sites, such as multilayer orhigh-rise buildings in China. In contrast, interviews with projectmanagers and related managers have been verified as a valid
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alternative approach (Poon et al., 2004b; Tam et al., 2007), andcan be used to collect data during a short time period.
2) Actual MWR instead of normal MWR is obtained. Although thenormal MWR can be acquired from the Construction Norm (Luet al., 2011), our previous study revealed that MWRs in actualconstruction practice significantly differ with that in the Con-struction Norm (Li et al., 2010). Thus, usage of the actual MWR ismore accurate for estimating the construction waste generationindex.
.4. Estimation of the percentage of remaining wastes
In addition to the waste generated from the major materi-ls listed in first phase, there are also numerous types of smalluantities of waste, such as cardboard packaging, plastic pile, ironire, and so on. These remaining wastes include numerous cate-
ories, but comprise only a small part of the total waste by weight.mong them, a small part of valuable waste, such as cardboardackaging, may be voluntarily collected by site workers and resoldo secondhand buyers. Other remaining wastes may generally be
ixed together and are difficult to reuse or recycle on-site. Thus,stimation of the remaining wastes by category is time- and cost-onsuming and unworthy.
In this study, these remaining wastes are estimated together byhe project manager. It is assumed to be a certain percentage of theotal waste. Our previous study revealed that the waste generatedrom major materials accounts for nearly 90% of the total construc-ion waste (Li et al., 2010). Bossink and Brouwers (1996) echo thestimation that the majority of construction waste, excluding pack-ng waste and small fractions waste, weighs nearly 90% of the totalmount of construction waste in the Netherlands. It can be deducedhat in this situation these remaining wastes occupy approximately0% of the total waste.
.5. Calculation of WGA
In the first step, the total construction waste generated on sites calculated using Eq. (1):
G =n∑
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here WG refers to the total construction waste generated from theroject by weight (kg), Mi means the purchased amount of majoraterial i in the identified list by weight (kg); ri is the MWR ofajor material i; W0 is the remaining waste; n is the number ofajor material types.In the second step, the total WGA is calculated using Eq. (2):
GA = WGGFA
(2)
here GFA means the gross floor area of the building project (m2).For the third step, the WGA for major material i is calculated
sing Eq. (3):
GAi = (Mi × ri)GFA
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. Case study
The method presented in the above section is applied to a newlyonstructed building project in Shenzhen, a metropolis in South
hina. The project is a residential building with reinforced concreteramework. The detailed characteristics are illustrated in Table 2.To collect related data, our research team visited the con-
truction site twice during March 2009. On the first visit, a short
and Recycling 74 (2013) 20– 26 23
interview was carried out with the project manager and site man-agers. The objective of the interview was to introduce our researchand to explain the data we needed. We explained the implica-tions of these data and then discussed the availability of these datawith the managers. One week later, our research team returnedwith a questionnaire and collected all the required data from theproject manager. The project manager first confirmed that themajor materials on this project included the six types of mate-rials as listed in Table 1. He provided the purchased amount ofthese major materials from procurement records and estimated theMWR for each major material. He also agreed that the remainingwastes accounted for approximately 10% of the total waste. Table 2presents the data collected.
It should be noted that the amounts of purchased material(shown in the third column) are measured in different units; forexample, concrete is measured in cubic meters (m3) and form-work in square meters (m2). These measurements are original datadrawn from procurement records. To calculate the mass of WG, theamount is uniformly transformed into tons using the density andthickness of each material, if necessary.
Our research team calculated the total WGA and the WGA foreach major material (illustrated in Table 2) and then discussed theresults with the project manager. The project manager verified thatthe method is easy to understand and implete in site.
It can be noted from Table 2 that the total WGA is 40.7 kg/m2.Concrete is a major contributor to total WGA, accounting for 43.5%of the total WGA. The second major generator is timber formwork,at 7.6 kg/m2, followed by steel, brick and block and mortar. WGAfor tile is least at only 0.5 kg/m2.
5. Discussion
5.1. WMR and WGA for each major material
Concreting is a major building construction process. Shenzhenrequires the use of ready-mixed concrete in the entire constructionprojects. Concrete waste is mainly sourced from excessive order-ing, overfilling the formwork, broken formwork and redoing dueto poor quality. It is estimated that the WMR of concrete on thissite is only 1%, far lower than the 3% in Netherlands (Bossink andBrouwers, 1996) and 3–5% in Hong Kong (Poon et al., 2004b). How-ever, the amount of purchased concrete accounts for 85% of thetotal amount of purchased material by weight. Due to this, con-crete waste generated per gross floor area occupies nearly half ofthe total WGA.
Due to inexpensive, lightweight and easy to cut, timber form-work is widely used in construction projects in China. Timberformwork is a type of revolving material, which will not be incor-porated into the building during the construction process. It willbe discarded as waste, generally after being revolved five to tentimes. Thus, its waste material amount is quite large. In addition,the WGA for timber formwork is in direct relation to the number ofreuses times. If the timber formwork revolves only five times dueto low durability, then it will generate twice the amount of wasteas it revolved ten times. In this project, the timber formwork wasrevolved an average of seven times. However, approximately 20%of the timber formwork revolved only 3–4 times and was reused inother projects after finishing concrete work. The MWR is estimatedas 80%.
Steel reinforcement bars are one of the principle materials inbuilding construction. Steel bar waste is mainly generated from
on-site cutting. A small amount results from abortive work. In thisproject, the MWR of steel bar was 3.0%, slightly lower than the3–5% in Hong Kong (Poon et al., 2004b). The project manager alsoasserted that the MWR was at a relatively low level in China. The
24 J. Li et al. / Resources, Conservation and Recycling 74 (2013) 20– 26
Table 2WGA for a residential building in Shenzhen.
General information Building occupancy: residential buildingStructure form: reinforced concrete frameworkUnderground/aboveground floors: 2/32Gross floor area (GFA): 76117.7 m2
Commencement date/investigation date: May 2007/March 2009
Project progress Foundation: finished Building structure: finishedMasonry: finished Plastering: finishedTiling: ongoing
Material MWR (%) Amount purchased Amount purchased (t) WG (t) WGA (kg/m2)
Concrete 1.0 56,011 m3 134426.4 1344.2 17.7 43.5%Steel bar 3.0 10,204 t 10204.0 306.1 4.0 9.8%Brick and block 5.0 6511 m3 5208.8 260.4 3.4 8.4%Timber formwork 80.0 60,020 m2 720.2 576.1 7.6 18.7%Mortar 4.0 6500 t 6500.0 260.0 3.4 8.4%Tile 4.0 45,568 m2 1002.5 40.1 0.5 1.2%
� 2786.9 36.6 90.0%309.7 4.1 10.0%
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Table 3Actual amount of waste material from records.
Material Amountrecorded
Amountrecorded (t)
WGA(kg/m2)
Steel bar 390 t 390 5.1
W0
Total WGA
ow MWR of steel bar leads to a low WGA, although its purchasedmount is the second largest. Its WGA is 4.0 kg/m2, only half of theGA for timber formwork.Brick and block are mainly used in masonry work. A combination
f causes can lead to the waste of brick and block. Most loss hap-ens during delivery, handling, and transportation, such as damageuring loading and unloading, broken brick and block due to over-tacking, cutting due to lack of modular coordination, over-orderingrick and block leftover as waste. The MWR for brick and block canary within a wide range depending on the skill and responsibil-ty of the workers. On the investigated site, the MWR is 5.0%, farigher than 2.0% from the Shenzhen Construction Norm. Althoughhe site managers required the subcontractor workers to save as
uch material as possible, the workers still paid little attention toheir performance. The low price of the material and low awarenessbout the environmental management are two critical reasons forhis apathy.
Controlling the use of mortar on site is relatively difficultecause this material is used in several processes, for example,asonry work, plastering and floor rendering. In situ production
f mortar commonly exceeds the demand because it is difficult toccurately estimate the amount needed by each work team. Theurplus mortar will become waste. Waste is also generated whenortar overflows the wheelbarrow during transportation. Droppedortar during masonry and plastering will also be wasted if not
eclaimed in time. In this site, the MWR of mortar was 4.0% at aver-ge, similar to that in Hong Kong (Poon et al., 2004b) and the UKSkoyles, 1976). Fortunately, the construction industry in Shenzhenas begun using ready-to-use mortar as required since 2011, whichill help to reduce mortar waste.
In China, residential buildings are commonly sold without finendoor finishing. Tile is applied only in public spaces, such as cor-idors and stairways. Tile waste is mainly sourced from cutting tot the building modular. The MWR in this project was estimatedt 4.0%, lower than the 6–8% in Hong Kong (Poon et al., 2004b).ccording to the managers, many irregular spaces and a variety ofaving patterns caused the high waste level, though the WGA forile was considerably smaller.
Of the six major materials, concrete, brick and block, mortar andile are inert materials, which are suitable for producing recycledonstruction materials, such as recycled brick, recycled aggregate,
ecycled concrete, and so on. Their generation accumulates up to0% of the total waste in this project. However, this type of wastes commonly deposited in public landfills in China. On one hand,he original material is dissipating, coupled with the extensive
Timber formwork 42,000 m2 504 6.6Mixed waste 260 m3 390 5.1
development and redevelopment of the city. On the other hand,there is not yet enough capacity to recycle such a large quantity ofinert construction waste. More effort has to be devoted to fill thisgap in China.
Wasted steel bar and large panel timber formwork will be col-lected and resold to secondhand buyers or recycling companies.Waste steel bar generally costs half of the original material. Becauseof its high value, more than 90% of waste steel bar is elaboratelyrecycled.
5.2. Comparison with transportation records in the project
The selected building project was at a finishing stage duringthe investigation. Masonry and plastering work had been finished,and 90% of the tiling work had been completed. As the majority ofthe construction work was finished, our research team reviewedthe resale and transportation records to find the actual amounts ofwaste material and the data are illustrated in Table 3. To measureby weight, the amount is uniformly transformed into tons using thedensity and thickness of each material, if necessary. The density ofmixed waste is assumed to be 1.5 ton/m3.
The recorded amount of steel is 390 ton and it is higher thanthe 306 ton estimated by our method. This deviation derives fromthe slight underestimation of the MWR by the project manager.The actual MWR deduced from the records is up to 3.8%. However,the difference between the two WGAs is only 1.1 kg/m2, whichaccounts for 2–3% of the total WGA. This deviation has a limitedeffect on the total WGA. As mentioned above, it is difficult to find anextremely accurate waste rate unless the entire work is monitoredup to the end and all related documents are collected. Estimationof MWR by project manager is not very precise but is a practicalalternative.
The amount of timber formwork in the record is approximately504 ton, lower than our estimate of 576 ton. Two reasons maycause this difference. First, our estimation includes all timber form-work waste, such as deteriorated large panels and cutting margins.
J. Li et al. / Resources, Conservation
Table 4Calculation of normal WGA.
Material NormalMWRa (%)
The amountpurchased (t)
WG (t) WGA(kg/m2)
Concrete 1.5 134426.4 2016.4 26.5Steel bar 4.5 10204.0 459.2 6.0Brick and block 2.0 5208.8 104.2 1.4Timber formwork 100 720.2 720.2 9.5Mortar 2.0 6500.0 130 1.7Tile 2.0 1002.5 20.0 0.3
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owever, only large panels of timber formwork are sold andecorded. The off-cut scrap is commonly collected and transportedogether with other mixed waste without records. In addition, themount of resold timber formwork is derived from approximatetatistics, as this material is usually sold in bulk.
The mixed waste in this project includes waste concrete, brokenrick and block, off-cut tile, waste mortar, timber scrap, packag-
ng waste and plastics. The recorded amount is far lower thanhe estimated amount. The total estimated amount of concrete,rick and block, mortar and tile is close to 2000 ton. After discus-ion with the project manager and site visits, the possible reasonsor this discrepancy are summarized. First, waste concrete fromxcessive ordering is usually poured out around the constructionite. Other concrete from overfilling or broken formwork is cleareds backfill material, although this practice is prohibited by Con-truction Specifications in China. Similarly, surplus mortar andropped waste mortar are also collected as backfill. A small quan-ity of broken brick and block is used to backfill the foundation.he majority of these types of waste are illicitly reclaimed on site.his situation demonstrates that the estimation of constructionaste by reviewing related records is not a feasible approach inhina.
.3. Comparison with empirical data in China
As mentioned above, a popular empirical WGA in China is0–60 kg/m2, given by Lu (1999). The WGA in this case is lowerhan the empirical data. Although Lu (1999) did not mention the
easurement method of the empirical data, it is found that theata is close to the normal WGA. It can be seen from Table 4 thathe normal WGA is 50.4 kg/m2, which is calculated using the normal
WRs from the Shenzhen Construction Norm.Compared with Table 2, it is obvious that the normal MWRs for
oncrete and steel are higher than the actual MWRs of the surveyed
ite. A main reason is that these two types of materials are relativelyxpensive and also account for a large part of purchased material.hus, enormous attention is paid to reducing waste from deliverynd handling. The WGA for concrete in Table 2 is only 17.7 kg/m2,able 5GAs of residential buildings in other countries or regions.
Countries Total WGA (kg/m2) WGAi (kg/m2)
Concrete Brick
Americaa 43.7 22.9 –
Norwayb 30.7 19.11
Koreac 47.8 15.87 4.53
a Data sources: Cochran et al. (2007).b Data sources: Bergsdal et al. (2007), including office buildings and apartment buildinc Data sources: Seo and Hwang (1999), including concrete frame buildings, but not lim
and Recycling 74 (2013) 20– 26 25
8.8 kg/m2 less than that in Table 4. Similarly, WGA for steel bar inTable 2 decreases by 2.0 kg/m2. Moreover, as 20% of timber form-work is reused in other projects, the WGA for timber formworkin this case also decreases by 1.9 kg/m2 from normal estimation.Although the actual MWRs for brick and block, mortar and tileare higher than the normal MWR, the increase in WGA is fairlysmall. As a whole, the actual WGA is 20% lower than the normalWGA.
5.4. Comparison with research data in other economies
Comparison between countries can help with benchmarkingand identifying good waste management practices (Lu et al., 2011).However, comparing the WGA of different economies is difficultdue to the different construction technologies and work proce-dures involved and because distinct measurement approacheswere adopted in each of them (Formoso et al., 2002). Despitethe lack of comparability between most of the WGAs in variouscountries, comparison between the indexes with certain similaritystill can bring some enlightenment.
For this purpose, several WGAs in different economies are care-fully selected by reviewing previous studies, as shown in Table 5.All these three WGAs are obtained from concrete framework res-idential buildings and measured with the same units. The WGAsin America and Norway result from previous empirical survey ofwaste composition and generation. Seo and Hwang (1999) calcu-lated WGA in Korea using a similar method with our approach.
In our case, the total WGA is slightly lower than that in Americaand Korea but is higher than Norway. Because the building struc-tures and occupancies are similar, the deviation of total WGA maybe contributed to different construction practices and managementlevel. Table 5 further compares the WGA for each material in dif-ferent countries and regions. Obviously, the WGAs for concreteand brick in each economy are similar, but the WGAs for steeland timber vary significantly. As mentioned above, timber form-work is more popular than metal formwork in China. The timberwaste will decrease if the former can be widely substituted by thelatter. This may be the reason that timber waste in Norway is dis-tinctly lower than in other countries. Steel waste is mainly sourcedfrom cutting steel bar on-site. If preassembled steel reinforcementis applied, steel waste may be drastically reduced. This practicemay contribute to the remarkably low WGA for steel in Americaand Norway.
In summary, comparisons with transportation records revealthat the method presented in this study is valid and practical toestimate the actual WGA. At the same time, comparisons betweenempirical data in China and WGA in other economies indicate thatthe waste generation level in China is decreasing as more atten-
tion being devoted to preventing the production of waste material.But the WGA in China can still be improved by adopting low-wastetechnologies (Poon et al., 2003) or incentive system (Tam and Tam,2008a).Steel Timber Mortar Tile
0.9 6.4 – –0.48 2.75 – –5.17 3.84 0.35 0.33
gs.ited to residential buildings.
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. Conclusions
This research proposes a model for quantifying WGA for build-ng construction in China. Purchased amount and actual MWRs of
ajor material are used to estimate total WGA and WGA for eachajor component. The WGA for other minor quantities of material
s estimated together to simplify the estimation approach. A newlyonstructed residential building in Shenzhen is used as case studyo illustrate the model, and the WGA of this case is 40.7 kg/m2. Ofhat amount, concrete represented 43.5%, timber formwork 18.7%,teel bar 9.8%, brick and block 8.4%, mortar 8.4% and tile 1.2%. Theata are compared with on-site transportation records, empiricalata in China, and data in other economies. Comparisons with theseata reveal that the method is valid and practical for estimating thectual WGA.
The proposed method is particularly suitable to be used foronducting large-scale statistical investigations, as the model isimple and related data is easy to obtain. By conducting statisticalnvestigation on a regional or a national scale, abundant knowl-dge about construction waste magnitude and composition can bebtained and used to develop appropriate waste management pol-cy. Based on the investigation result, a benchmark WGA, which
ill guide construction industry in taking more effective waste-eduction practices, can be set up. It is the objective of our futureesearch.
A limitation of the proposed method is that the reliability ofGA mainly relies on the accuracy of WMR provided by projectanager. Requiring the project managers to explain their data in
etail may be a feasible solution to avoid significant deviation.oreover, the model only provides a rough estimation of construc-
ion waste generation and composition. If accurate estimation isequired, material should be further subdivided in term of buildinglements or other characteristics like Llatas’ research. Of course,he requirement will increase the complexity of this model.
cknowledgments
The authors are very grateful for the constructive commentsrovided by the two anonymous reviewers. The present study isart of the Humanities and Social Sciences research project entitled
Construction project stakeholders’ attitude and behavior towardonstruction waste minimization and transformation mechanism’11YJAZH047) funded by the Ministry of Education of the People’sepublic of China.
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