Estimate Construction Waste China

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Resources, Conservation and Recycling 74 (2013) 2026

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Resources, Conservation and Recycling

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A model for estimating construction waste generation indexfor building project in China

Jingru Li, Zhikun Ding, Xuming Mi,Jiayuan Wang

College of Civil Engineering, Shenzhen University, Shenzhen 518060, China

a r t i c l e i n f o

Article history:

Received 7 October 2012

Received in revised form 17 February 2013Accepted 20 February 2013

Keywords:

Waste generation pergross floor area

(WGA)

Theamount of constructionwaste

Material waste rate (MWR)

Building

China

a b s t r a c t

The increasing construction and demolition (C&D) waste causes both cost inefficiency and environmental

pollution. Many countries have developed regulations to minimize C&D waste. Implementation ofthese

regulations requires an understanding ofthe magnitude and material composition ofwaste stream. Con-

struction waste generation index is a useful tool for estimating the amount of construction waste and

can be used as a benchmark to enhance the sustainable performance ofconstruction industry. This paper

presents a model for quantifying waste generation per gross floor area (WGA) based on mass balance

principle for building construction in China. WGAs for major types ofmaterial are estimated using pur-

chased amount ofmajor materials and their material waste rate (MWR). The WGA for minor quantities

of materials is estimated together as a percentage of total construction waste. The model is applied to

a newly constructed residential building in Shenzhen city of South China. The WGA of this project is

40.7 kg/m2 , and concrete waste is the largest contributor to the index. Comparisons with transportation

records in site, empirical index in China and data in other economies reveal that the proposed model is

valid and practical. The proposed model can be used to setup a benchmark WGA for Chinese construction

industry by carrying out large-scale investigations in the future.

2013 Elsevier B.V. All rights reserved.

1. Introduction

Constructionand demolition (C&D) waste hasbecome an impor-

tant issue not only from the perspective of cost efficiency but

also due to its adverse effect on the environment. In an attempt

to protect the environment and to improve sustainability of the

construction industry, many countries and regions have devel-

oped various regulations and initiatives to minimize C&D waste.

In the United Kingdom, the Code for Sustainable Homes makes on-

site waste minimization, sorting and recycling obligatory (United

Kingdom Government Department for communities and Local

Government, 2006). Several regulations have existed to control

C&D waste in Hong Kong (Tam and Tam, 2008a). As an exam-

ple, waste management plan is compulsory for all construction

projects in Hong Kong since 2003 (Tam, 2008b). The Brazilian Envi-

ronmental Protection Agency published Resolution 307 in 2002,

whichrequires alllocal authorities to prepare andexecute plans for

the sustainablemanagementof C&Dwaste (Brazilian Government-

Environmental Protection Agency, 2002). In mainland China, the

Administration of Urban Construction Garbage was promulgated

in 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).

management (Ministry of Housing and Urban-Rural Development

of the Peoples Republic of China, 2005).

However, implementation of these provisions requires an

understanding of the magnitude and material composition of the

waste stream(Cochran and Townsend,2010). A constructionwaste

management plan, for example, requires contractors to estimate

the quantity of total construction waste and its main components

at the planningphase, which willfacilitate waste reduction, reusing

and 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 amount

in a region (e.g. Bergsdal et al., 2007; Cochran et al., 2007;

Franklin Associates, 1998; Kofoworola and Gheewala, 2009; Yost

and Halstead, 1996) and those that measure C&Dwaste generation

index at project sites (e.g. Bossink and Brouwers, 1996; Formoso

et al., 2002; Poon et al., 2004a; Skoyles, 1976). In the second

category, most of researchers discussed the construction waste

generation index as estimation of this index is more difficult than

demolition waste generation index.

The constructionwaste generationindex is identifiedas a mean-

ingful tool to promote construction waste management. It can be

applied to predict the amount of construction waste generated in a

project, which will assist project stakeholders to prepare appro-

priate waste management plans. Comparing the index between

0921-3449/$ seefrontmatter 2013 Elsevier B.V. All rights reserved.

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J. Li et al. / Resources, Conservation and Recycling74 (2013) 2026 21

differentprojects canhelp project stakeholders to gainmore insight

about their construction waste management performance and to

review the effectiveness of construction waste management prac-

tices. Moreover, the amount of construction waste generated in a

region or a country can also be estimated by employing the index

and construction area (Cochran et al., 2007).

However, the consideration on construction waste manage-

ment is fairly negligible in mainland China. Low awareness of

sustainable construction accounts for the deficiency of data about

the amount of construction waste either at a macroscopic level

or a microscopic level. A widely cited construction waste gener-

ation index, 5060 kg/m2, was provided by Lu (1999) based on

empirical estimationwithout detailed interpretation. However, the

waste generation index will vary in a wide range with construc-

tion technology, structure type, building occupancy, and especially

management level (Li et al., 2010). The above empirical index

reveals limited information for project stakeholders for under-

standingthe magnitudeand compositionof constructionwaste and

preparing an appropriate construction waste management plan. In

particular, the culture and common practices of the construction

industry in China may not be entirely similar to other economies.

Thus, an approach to the measurement of a construction waste

generation index for the Chinese construction industry should be

investigated.Given the situation, the objective of this research is to present a

practical and simple model for measuring the construction waste

generation index for building projects in China. The study is struc-

tured in four parts. The first part includes a literature reviewon the

quantification of construction waste. The second section describes

the approach to measuringthe waste generation index for building

construction. Then, the method is illustrated using a newly con-

structed residential building project in Shenzhen, China. Finally, all

the findings are discussed in detail and conclusions are drawn.

2. Reviews

2.1. Main constructionwaste generation indexes

Amounts of construction waste generation have received sig-

nificant attention because this information is a prerequisite to

developing appropriate solutions for managing waste. A variety

of researchers have developed different methodologies to quan-

tify construction waste. As mentioned above, these studies can

be divided into two categories: studies that determine an overall

waste generation amount in a region and those that measure the

waste generation index at a project site.

Of the second category, some studies investigated material

waste rates (MWR),which are thepercentages of waste materialto

purchased material or required by the design, to indicate thewaste

generation level of construction projects. For an example, Skoyles

(1976) measured the MWRof major materials in UK and found thepercentages of waste materials ranged from 2 to 15%, on average

double the losses generally assumed. Enshassi (1996) found from

a study in the Gaza strip that the materials loss was approximately

3.611%. Formoso et al. (2002) indicated that the waste rate of

materials in theBrazilian building industry was fairlyhigh and var-

ied widely across different projects. Bossink and Brouwers (1996)

revealed that approximately 110% of the purchased construction

materials (by weight) was left as waste. In Hong Kong, Poon et al.

(2004b) identified the material waste levels of various trades for

public housing and private residential buildings. Tam et al. (2007)

investigated waste levels of five major types of construction mate-

rial in terms of subcontracting arrangements and project types.

Other studies derived a waste generation index using the vol-

ume or quantity of waste generated per gross floor area (WGA).

Poon et al. (2004a) calculated the WGAs for two public housing

construction sites as 0.14 m3/m2 and 0.21m3/m2. In China, Luet al.

(2011) performed a total of five measurement exercises to inves-

tigate the WGAs of four typical trades. Llatas (2011) developed a

model to estimate WGA and applied to a dwelling project in Spain.

A WGA of 0.1388 m3/m2 was obtainedfrom the case study. Another

study in Spain derived a WGA as 0.1075m3/m2 from a newly

constructed residential building that generated waste of approx-

imately 172.2m3 on a total of 1600m2 floor area (Sols-Guzmn

et al., 2009).

2.2. Measurementmethod of these constructionwaste generation

indexes

In addition to different units of measure, the above studies also

adopted varied approaches to measuringconstruction waste gener-

ation indexes. They reached their objectives using three different

approaches: (1) field monitoring; (2) interviews and (3) material

balance.

The first approach collects data by conducting field monitoring

because direct records of constructionwaste amounts are generally

unavailable at sites. Skoyles (1976) and Enshassi (1996) measured

the MWRby 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 construction

waste materials at five housing constructionsites. This method was

also adopted by Lu et al. (2011). Poon et al. (2004a) conducted

regular site observations at construction sites and collected data

by visual inspection, tape measurements and truck load records.

The quantities of waste were calculated by multiplying the truck

volume and the total number of trucks used for waste disposal.

Apart from this type of hard methodfor measuringwaste, soft

methods, such as questionnaire surveys and interviews, have also

been 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) collected

the waste levels of five major types of construction material frominterviews with project managers.

Another approach quantifies the construction waste generation

index based on the material balance principle. This approach con-

siders the fact that after the building materials are delivered to

the site, part of the materials are incorporated into the building

structure during construction, and the remainder is discarded as

wreckage waste or package waste on site (Cochran and Townsend,

2010). Sols-Guzmn et al. (2009) identified three categories of

waste in the construction process: demolished, wreckage and

package waste. They quantified these three types of waste by mul-

tiplying the quantities of material used in structural elements with

the corresponding transformation coefficients. The material used

in 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 of

waste expected in eachbuilding element according to the European

Waste List.

To quantify construction waste by carrying out field observa-

tion, on-site sorting, weighing and monitoring related documents

is a relatively accurate method but requires a great deal of time

and human resources. This approach requires field monitoring to

continue until the end of construction activity in order to obtain

the total quantity of waste generated on the site. This require-

ment is one key reason that only a few sample construction sites

were investigated in previous researches (Bossink and Brouwers,

1996; Poon et al., 2004a). Furthermore, our previous experimental

research also found that on-site sorting and weighing occupy too


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22 J. Li et al. / Resources, Conservationand Recycling74 (2013) 2026

much space and manpower and thus would encounter difficulties

forbulky waste streams on large constructionsites (Lu etal.,2011).

Measuringwasteas thedifference between theamountof materials

effectively purchased and the actual quantities used in building is

adopted by Skoyles (1976) and Enshassi (1996). However, Skoyles

(1976) also pointed out that bills of quantities in tendering doc-

uments only provided basic measurements of a project and the

measurement had to be repeated between 15 and 20 times during

the building process. The repeated measurements greatly increase

the difficulty in monitoring waste by comparing contractors deliv-

ery records with measurements of finished work.

By contrast, quantifying the construction waste based on the

material balance principle is a more practical substitute for large

construction sites. In particular, this method can estimate the gen-

eration index for each waste component, in additionto total waste,

which facilitates stakeholders to develop their waste reuse or

recycling plans. However, the process of gaining reasonable trans-

formation coefficients such as those in Sols-Guzmns study is a

critical problem. In the next section, the details of our approach

will be presented.

3. Methodology

Thissectionpresentsa newmodel to quantifyingWGA for build-

ing construction based on the mass balance principle. The model

costs less time and manpower to collect data than many exist-

ing methods, which makes it suitable to be used in conducting

large scale statistical investigations. The application of the model

includes five phases:

(1) Listing the major types of construction material;

(2) Investigating the purchased amount of these major materials;

(3) Investigating the actual MWRof 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 WGA

by weight, although the majority of the aforementioned studies

calculated WGA by volume (Llatas, 2011; Poon et al., 2004a; Sols-

Guzmn et al., 2009). Poon et al. (2004a) collected data by visual

inspection, which is more convenient to calculate the quantities

of waste by volume. Llatas (2011) stated that volume is a valuable

datum that facilitates estimation of the size and numbers of con-

tainers. However, the density of the mixed waste may vary broadly

withvarious compositions,whichwill cause difficulty in comparing

the waste generation levels between different projects. Moreover,

the landfill fee in Chinais applied by weight using weight machines

at landfills. Thus, WGA by weight is considered in this study.

3.1. Listing the major types of constructionmaterial

Although buildings across the world is varied in building

structure and construction techniques, typical construction waste

components include concrete, brick and block, steel reinforcement,

timber, cement and mortar, ceramic tile, plastic and cardboard

packaging materials, etc. (Bossink and Brouwers, 1996; Formoso

et al., 2002; Poon et al., 2004b; Tam et al., 2012). However, the

proportions of these components may vary within a large range in

different countries and regions.

In China, multilayer or high-risebuildings comprisethe majority

of newly constructed buildings due to the highpopulation densities

of cities. The reinforced concrete structure is most popular in these

buildings. Thus, waste material is mainly sourced from concrete

Table 1

The major materials using in building construction projects.

No. Material Note

1 Concrete The major material of concrete work

2 Steel bar The major material of concrete work

3 B rick and block The m ajor mater ialo f m aso nr y work

4 Timber formwork The major material ofconcrete work

5 Mortar The major material of w et trades of finishing w ork

6 Tile The major material of wet trades of finishing work

work, masonry work, timber formwork, and the wet trades of fin-

ishing work, suchas screeding, plastering andtile laying (Poonetal.,

2004b). Other small amounts of waste come from water and wire

pipes, packaging material and other small goods. It is obvious that

the major types of construction materials, such as concrete, timber

formworkand steel bar, are the major source of constructionwaste

(Li et al., 2010).

For the popular reinforced concrete framework buildings in

China, the major materials consist of concrete, steel bar, brick and

block, timber formwork, mortar and tile, as listed in Table 1.

3.2. Investigating purchased amounts of major materials

Theamountof materialpurchased canbe collected fromthe pur-

chasing records of finished projects or from the budget documents

of ongoing projects. The amount in the budget document gener-

ally includes normal material loss during construction and thus is

close to the actual purchased amount. Because most types of mate-

rial are purchased batch by batch in China, a situation in which

the purchased material will significantly exceed the demand will

rarely occur. Even if this situation occurs, the extra amount can be

returned to the supplier. Thus, this situation is not considered in

this study.

3.3. Investigating actual MWR

MWR is measured by dividing the amount of waste by either

the 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 extent

unlessthe rate is quite huge, forexample,73.7% forcement in Brazil

(Formoso et al., 2002). To facilitate the intuitive understanding and

estimation of project stakeholders, MWRis evaluated as the ratio

of waste material to purchased material expressed as a percentage

in this study.

As mentioned in Section 2.2, two different methods have been

adopted 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 managers

estimation. In China, the project manager is the core person of

a construction project, who is fully responsible for project cost,

schedule and quality. Thus, project managers estimation is gen-

erally believable. In addition, there are other benefits to obtain an

estimation of the MWRfrom the project manager.

(1) It can minimize time and cost involvement of investigation. As

discussed above,field monitoring takes a great deal of time and

human resourcesand thereforeencounters difficulties for bulky

waste streams on large construction sites, such as multilayer or

high-risebuildings in China. In contrast, interviews withproject

managers and related managers have been verified as a valid


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alternative approach (Poon et al., 2004b; Tam et al., 2007), and

can be used to collect data during a short time period.

(2) Actual MWRinstead of normal MWRis obtained. Although the

normal MWRcan be acquired from the Construction Norm (Lu

et al., 2011), our previous study revealed that MWRs in actual

construction practice significantly differ with that in the Con-

structionNorm (Lietal.,2010). Thus, usage ofthe actualMWRis

moreaccurate for estimating theconstructionwaste generation

index.

3.4. Estimation of the percentage of remaining wastes

In addition to the waste generated from the major materi-

als listed in first phase, there are also numerous types of small

quantities of waste, such as cardboard packaging, plastic pile, iron

wire, and so on. These remaining wastes include numerous cate-

gories, but comprise only a small part of the total waste by weight.

Among them, a small part of valuable waste, such as cardboard

packaging, may be voluntarily collected by site workers and resold

to secondhand buyers. Other remaining wastes may generally be

mixed together and are difficult to reuse or recycle on-site. Thus,

estimation of the remaining wastes by category is time- and cost-

consuming and unworthy.

In this study, these remaining wastes are estimated together by

the project manager. It is assumed to be a certain percentage of the

total waste. Our previous study revealed that the waste generated

from major materials accounts for nearly 90% of the total construc-

tion waste (Li et al., 2010). Bossink and Brouwers (1996) echo the

estimationthat the majorityof constructionwaste, excludingpack-

ing waste and small fractions waste, weighs nearly 90% of the total

amount of constructionwaste in the Netherlands. It canbe deduced

thatin thissituation these remaining wastes occupy approximately

10% of the total waste.

3.5. Calculation of WGA

In the first step, the total construction waste generated on site

is calculated using Eq. (1):

WG =

n

i=1

Mi ri +W0 (1)

where WG refers to thetotal constructionwaste generated fromthe

project by weight (kg), Mi means the purchased amount of major

material i in the identified list by weight (kg); ri i s the MWR of

major material i; W0 is the remaining waste; n is the number of

major material types.

In the second step, the total WGA is calculated using Eq. (2):

WGA =WG

GFA (2)

where GFA means the gross floor area of the building project (m2).

For the third step, the WGA for major material i is calculated

using Eq. (3):

WGAi =(Mi ri)

GFA (3)

4. Case study

Themethod presentedin the above section is applied to a newly

constructed building project in Shenzhen, a metropolis in South

China. The project is a residential building withreinforced concrete

framework. The detailed characteristics are illustrated in Table 2.

To collect related data, our research team visited the con-

struction site twice during March 2009. On the first visit, a short

interview was carried out with the project manager and site man-

agers. The objective of the interview was to introduce our research

and to explain the data we needed. We explained the implica-

tions of these data and then discussed the availability of these data

with the managers. One week later, our research team returned

with a questionnaire and collected all the required data from the

project manager. The project manager first confirmed that the

major materials on this project included the six types of mate-

rials as listed in Table 1. He provided the purchased amount of

thesemajor materialsfrom procurement records andestimatedthe

MWR for each major material. He also agreed that the remaining

wastes accounted for approximately 10%of the total waste. Table 2

presents the data collected.

It should be noted that the amounts of purchased material

(shown in the third column) are measured in different units; for

example, concrete is measured in cubic meters (m3) and form-

work in square meters (m2). These measurements are original data

drawn from procurement records. To calculatethe mass of WG, the

amount is uniformly transformed into tons using the density and

thickness of each material, if necessary.

Our research team calculated the total WGA and the WGA for

each major material (illustrated in Table 2) and then discussed the

results withthe project manager. The project manager verified that

the method is easy to understand and implete in site.It can be noted from Table 2 that the total WGA is 40.7kg/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. WGA

for tile is least at only 0.5 kg/m2.

5. Discussion

5.1. WMR and WGAfor each major material

Concreting is a major building construction process. Shenzhen

requires theuse of ready-mixed concrete in the entireconstruction

projects. Concrete waste is mainly sourced from excessive order-ing, overfilling the formwork, broken formwork and redoing due

to poor quality. It is estimated that the WMRof concrete on this

site is only 1%, far lower than the 3% in Netherlands (Bossink and

Brouwers, 1996) and 35%in HongKong(Poon et al., 2004b). How-

ever, the amount of purchased concrete accounts for 85% of the

total amount of purchased material by weight. Due to this, con-

crete waste generated per gross floor area occupies nearly half of

the total WGA.

Due to inexpensive, lightweight and easy to cut, timber form-

work is widely used in construction projects in China. Timber

formwork is a type of revolving material, which will not be incor-

porated into the building during the construction process. It will

be discarded as waste, generally after being revolved five to ten

times. Thus, its waste material amount is quite large. In addition,the WGA for timber formwork is in directrelationto the number of

reuses times. If the timber formwork revolves only five times due

to low durability, then it will generate twice the amount of waste

as it revolved ten times. In this project, the timber formwork was

revolved an average of seven times. However, approximately 20%

of the timber formwork revolved only 34times andwas reused in

other projects after finishing concrete work. The MWRis estimated

as 80%.

Steel reinforcement bars are one of the principle materials in

building construction. Steel bar waste is mainly generated from

on-site cutting. A small amount results from abortive work. In this

project, the MWR of steel bar was 3.0%, slightly lower than the

35% in Hong Kong (Poon et al., 2004b). The project manager also

asserted that the MWRwas at a relatively low level in China. The


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Table 2

WGA fora residential building in Shenzhen.

General information Building occupancy: residential building

Structure form: reinforced concrete framework

Underground/aboveground floors: 2/32

Gross floor area (GFA): 76117.7 m2

Commencement date/investigation date: May 2007/March 2009

Project progress Foundation: finished Building structure: finished

Masonry: finished Plastering: finished

Tiling: 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%

W0 309.7 4.1 10.0%

Total WGA 3096.5 40.7 100.0%

low MWRof steel bar leads to a low WGA, although its purchased

amount is the second largest. Its WGA is 4.0 kg/m2, only half of the

WGA for timber formwork.Brickand block aremainly usedin masonrywork. A combination

of causes can lead to the waste of brick and block. Most loss hap-

pens during delivery, handling, and transportation, suchas damage

during loading and unloading, broken brick and block due to over-

stacking, cuttingdue to lackof modularcoordination, over-ordering

brick and block leftover as waste. The MWRfor brick and block can

vary within a wide range depending on the skill and responsibil-

ity of the workers. On the investigated site, the MWRis 5.0%, far

higher than 2.0% from the Shenzhen Construction Norm. Although

the site managers required the subcontractor workers to save as

much material as possible, the workers still paid little attention to

theirperformance. Thelow price of thematerial andlow awareness

about the environmental management are two critical reasons for

this apathy.Controlling the use of mortar on site is relatively difficult

because this material is used in several processes, for example,

masonry work, plastering and floor rendering. In situ production

of mortar commonly exceeds the demand because it is difficult to

accurately estimate the amount needed by each work team. The

surplus mortar will become waste. Waste is also generated when

mortar overflowsthe wheelbarrow during transportation. Dropped

mortar during masonry and plastering will also be wasted if not

reclaimedin time. In this site, the MWRof mortarwas 4.0% at aver-

age, similar to that in Hong Kong (Poon et al., 2004b) and the UK

(Skoyles, 1976). Fortunately, the constructionindustryin Shenzhen

has begun usingready-to-use mortar as required since 2011, which

will help to reduce mortar waste.

In China, residential buildings are commonly sold without fineindoor finishing. Tile is applied only in public spaces, such as cor-

ridors and stairways. Tile waste is mainly sourced from cutting to

fit the building modular. The MWRin this project was estimated

at 4.0%, lower than the 68% in Hong Kong (Poon et al., 2004b).

According to the managers, many irregular spaces and a variety of

paving patterns caused the high waste level, though the WGA for

tile was considerably smaller.

Of thesix major materials, concrete, brick andblock, mortarand

tile are inert materials, which are suitable for producing recycled

construction materials, such as recycled brick, recycled aggregate,

recycled concrete, and so on. Their generation accumulates up to

60% of the total waste in this project. However, this type of waste

is commonly deposited in public landfills in China. On one hand,

the original material is dissipating, coupled with the extensive

Table 3

Actual amount of waste material from records.

Material Amount

recorded

Amount

recorded (t)

WGA

(kg/m2)

Steel bar 390 t 390 5.1

Timber formwork 42,000 m2 504 6.6

Mixed 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 of

inert construction waste. More effort has to be devoted to fill this

gap in China.

Wasted steel bar and large panel timber formwork will be col-

lected and resold to secondhand buyers or recycling companies.

Wastesteel bar generallycosts halfof the originalmaterial. Because

of 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 during

the investigation. Masonry and plastering work had been finished,

and 90% of the tiling work had been completed. As the majority of

the construction work was finished, our research team reviewed

the resale and transportation records to find the actual amounts of

waste material and the data are illustrated in Table 3. To measure

by weight, the amount is uniformly transformed into tons using the

density and thickness of each material, if necessary. The density of

mixed 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 from

the slight underestimation of the MWR by the project manager.

The actual MWRdeduced from the records is up to 3.8%. However,

the difference between the two WGAs is only 1.1kg/m2, which

accounts for 23% of the total WGA. This deviation has a limited

effecton the total WGA. As mentionedabove, it is difficultto find an

extremely accurate waste rate unless the entire work is monitored

up to the end and all related documents are collected. Estimation

of MWRby project manager is not very precise but is a practical

alternative.

The amount of timber formwork in the record is approximately

504 ton, lower than our estimate of 576 ton. Two reasons may

causethis difference. First, our estimationincludes all timber form-

work waste, such as deteriorated large panels and cutting margins.


6/7


Table 4

Calculation of normal WGA.

Material Normal

MWRa (%)

The amount

purchased (t)

WG (t) WGA

(kg/m2)

Concrete 1.5 134426.4 2016.4 26.5

Steel bar 4.5 10204.0 459.2 6.0

Brick and block 2.0 5208.8 104.2 1.4

Timber formwork 100 720.2 720.2 9.5

Mortar 2.0 6500.0 130 1.7

Tile 2.0 1002.5 20.0 0.3

45.4

W0 5.0

Total WGA 50.4

a Data source: Shenzhen Construction Norm.

However, only large panels of timber formwork are sold and

recorded. The off-cut scrap is commonly collected and transported

together with other mixed waste without records. In addition, the

amount of resold timber formwork is derived from approximate

statistics, as this material is usually sold in bulk.

Themixedwastein this project includes wasteconcrete, broken

brick and block, off-cut tile, waste mortar, timber scrap, packag-

ing waste and plastics. The recorded amount is far lower than

the estimated amount. The total estimated amount of concrete,brick and block, mortar and tile is close to 2000 ton. After discus-

sion with the project manager and site visits, the possible reasons

for this discrepancy are summarized. First, waste concrete from

excessive ordering is usually poured out around the construction

site. Other concrete from overfilling or broken formwork is cleared

as backfill material, although this practice is prohibited by Con-

struction Specifications in China. Similarly, surplus mortar and

dropped waste mortar are also collected as backfill. A small quan-

tity of broken brick and block is used to backfill the foundation.

The majority of these types of waste are illicitly reclaimed on site.

This situation demonstrates that the estimation of construction

waste by reviewing related records is not a feasible approach in

China.

5.3. Comparisonwith empirical data in China

As mentioned above, a popular empirical WGA in China is

5060 kg/m2, given by Lu (1999). The WGA in this case is lower

than the empirical data. Although Lu (1999) did not mention the

measurement method of the empirical data, it is found that the

data is close to the normal WGA. It can be seen from Table 4 that

thenormalWGA is50.4kg/m2, which is calculated usingthe normal

MWRs from the Shenzhen Construction Norm.

Compared with Table 2, it is obvious that the normal MWRs for

concrete andsteelare higherthanthe actualMWRs of the surveyed

site. A main reasonis thatthesetwo types of materials arerelatively

expensive and also account for a large part of purchased material.

Thus, enormous attention is paid to reducing waste from deliveryand handling. The WGA for concrete in Table 2 is only 17.7kg/m2,

8.8 kg/m2 less than that in Table 4. Similarly, WGA for steel bar in

Table 2 decreases by 2.0 kg/m2. Moreover, as 20% of timber form-

work is reused in other projects, the WGA for timber formwork

in this case also decreases by 1.9kg/m2 from normal estimation.

Although the actual MWRs for brick and block, mortar and tile

are higher than the normal MWR, the increase in WGA is fairly

small. As a whole, the actual WGA is 20% lower than the normal

WGA.

5.4. Comparisonwith research data in other economies

Comparison between countries can help with benchmarking

and identifying good waste management practices (Lu et al., 2011).

However, comparing the WGA of different economies is difficult

due to the different construction technologies and work proce-

dures involved and because distinct measurement approaches

were adopted in each of them (Formoso et al., 2002). Despite

the lack of comparability between most of the WGAs in various

countries, comparison between the indexes with certain similarity

still 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 WGAs

in America and Norway result from previous empirical survey of

waste 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 America

and Korea but is higher than Norway. Because the building struc-

tures and occupancies are similar, the deviation of total WGA may

be contributed to differentconstruction practices and management

level. Table 5 further compares the WGA for each material in dif-

ferent countries and regions. Obviously, the WGAs for concrete

and brick in each economy are similar, but the WGAs for steel

and timber vary significantly. As mentioned above, timber form-

work is more popular than metal formwork in China. The timber

waste 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 mainlysourced

from cutting steel bar on-site. If preassembled steel reinforcement

is applied, steel waste may be drastically reduced. This practice

may contribute to the remarkably low WGA for steel in America

and Norway.

In summary, comparisons with transportation records reveal

that the method presented in this study is valid and practical to

estimate the actual WGA. At the same time, comparisons between

empirical data in China and WGA in other economies indicate that

the 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 canstill be improved by adopting low-waste

technologies (Poon et al., 2003) or incentive system (Tam and Tam,

2008a).

Table 5

WGAs of residential buildings in other countriesor regions.

Countries Total WGA (kg/m2) WGAi(kg/m2)

Concrete Brick Steel Timber Mortar Tile

Americaa 43.7 22.9 0.9 6.4

Norwayb 30.7 19.11 0.48 2.75

Koreac 47.8 15.87 4.53 5.17 3.84 0.35 0.33

a Data sources: Cochran et al. (2007).b Data sources: Bergsdal et al. (2007), including office buildings and apartment buildings.c

Data sources: Seoand Hwang (1999), including concrete frame buildings, but notlimited to residential buildings.


7/7


6. Conclusions

This research proposes a model for quantifying WGA for build-

ing construction in China. Purchased amount and actual MWRs of

major material are used to estimate total WGA and WGA for each

major component. The WGA for other minor quantities of material

is estimated together to simplify the estimation approach. A newly

constructed residential building in Shenzhen is used as case study

to illustrate the model, and the WGA of this case is 40.7kg/m2. Of

that amount, concrete represented 43.5%, timber formwork 18.7%,

steel bar 9.8%, brick and block 8.4%, mortar 8.4% and tile 1.2%. The

data are compared with on-site transportation records, empirical

datain China, and datain othereconomies. Comparisons withthese

data revealthat the methodis valid andpractical forestimating the

actual WGA.

The proposed method is particularly suitable to be used for

conducting large-scale statistical investigations, as the model is

simple and related data is easy to obtain. By conducting statistical

investigation on a regional or a national scale, abundant knowl-

edge about construction waste magnitude and composition can be

obtained and used to develop appropriate waste management pol-

icy. Based on the investigation result, a benchmark WGA, which

will guide construction industry in taking more effective waste-

reduction practices, can be set up. It is the objective of our futureresearch.

A limitation of the proposed method is that the reliability of

WGA mainly relies on the accuracy of WMRprovided by project

manager. Requiring the project managers to explain their data in

detail may be a feasible solution to avoid significant deviation.

Moreover, themodelonly provides a rough estimation of construc-

tion waste generation and composition. If accurate estimation is

required, material should be further subdivided in term of building

elements or other characteristics like Llatas research. Of course,

the requirement will increase the complexity of this model.

Acknowledgments

The authors are very grateful for the constructive commentsprovided by the two anonymous reviewers. The present study is

partof the Humanities and Social Sciences research project entitled

Construction project stakeholders attitude and behavior toward

construction waste minimization and transformation mechanism

(11YJAZH047) funded by the Ministry of Education of the Peoples

Republic of China.

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