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Authors: LY Shen1, VWY Tam2, CM Tam3, S Ho4 Address: 1 Department of Building & Real Estate, The Hong Kong

Polytechnic University, Hong Kong 2 Department of Building & Construction City University of Hong Kong 83, Tat Chee Avenue, Kowloon, Hong Kong

E-mail address: 1tam.vivian@student.cityu.edu.hk Keywords: construction, construction waste, waste management,

project types, Hong Kong

ABSTRACT

Construction wastes have become the major source of solid wastes in Hong Kong where construction and demolition activities generate thousands of tonnes of solid wastes every year. The increasing generation of construction wastes has caused significant impacts to the environment and aroused growing public concern in the local community. Thus, the minimization of construction wastes has become a pressing issue. This paper investigates the profile of waste generation from applying different types of building materials to different types of construction projects. It is considered that the application of various building materials to different types of projects has different impacts to the size of waste generation. Therefore, the paper attempts to identify the relations between waste generation and the application of building materials to different types of projects. Following this identification, proper methods are proposed to mitigate the generation of wastes by adopting proper construction and management methods, which allow the waste reduction from using building materials. Data from the construction industry of Hong Kong are used for the analysis.

INTRODUCTION

Waste management for construction activities has been promoted with the aim of protecting the environment and the recognition that wastes from construction and demolition works contribute significantly to the polluted environment (Shen et al., 2002). The construction industry plays a vital role in meeting the needs of society and enhancing the quality of life (Tse, 2001; Shen and Tam, 2002). However, the responsibility for ensuring the construction activities and products in consistent with environmental policies needs to be defined and good environmental practices through reduction of wastes need to be improved (EPD, 2002). Normally, the best way to deal with material wastes is not to create it in the first place (Snook et al., 1995; Gavilan and Bernold, 1994; EPD, 2002). The environmental situation resulted from construction in Hong Kong has become a pressing issue. According to the Environment Protection Department (EPD) (Chung, 2000), the construction industry generated about 32,710 tonnes of construction wastes per year in 1998, nearly 15% above the figure in 1997. Figure 1 shows the quantities of construction wastes disposed of from 1991 to 2001. To manage such a huge quantity of construction wastes, the Hong Kong government adopts a policy of disposing the waste to either land reclamation or landfills. For decades, landfill has provided a convenient and cost-effective solution to the wasteful practices of the industry (Mills et al., 1999). Ferguson et al. (1995) found that more than 50% of the wastes deposited in a typical landfill in UK come from construction wastes. According to Rogoff and Williams (1994), 29% of the solid-wastes in the USA are construction wastes. Wong and Tanner (1997) pointed out that the landfills, originally expected to last 40 to 50 years, would be filled up by 2010, even if there are adequate outlets for construction materials. All these investigations demonstrate that construction business is a large contributor to waste generation and that there is significant potential for protecting the environment through managing construction wastes properly. The paper targets for exploring the prevailing types of construction projects in Hong Kong and investigating their relationship with the generation of construction wastes; and suggesting recommendations in improving contractors’ waste management based on the above findings.

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0 5000 10000 15000

Yea

r

Quantity (x 1,000 tonnes)

C&D material reused for landreclamation

C&D waste disposed of atlandfills

Figure 1: Quantities of construction waste reused in reclamation and disposed of landfills from 1991 to 2001 (Source: EPD, 2002)

INVESTIGATION OF WASTE MANAGEMENT IN CONSTRUCTION PRACTICE

Building material wastages can be defined as the difference between the value of materials delivered and accepted on site and those properly used as specified and accurately measured in the work, after deducting the cost saving of substituted materials transferred elsewhere, in which unnecessary cost and time may be incurred by materials wastage. Generally, wastages of building materials can be divided into two types (Skoyles and Skoyles, 1987); one is direct waste and the other is indirect waste. Skoyles and Skoyles (1987) defined direct waste as the loss of those materials, which were damaged and could not be repaired and subsequently used, or which were lost during the building process; indirect waste was distinguished from direct waste because it normally represented only a monetary loss and the materials were not lost physically. Such losses arise principally from substitution of materials, from use of materials in excess of quantities allowable under the contract, and from errors. The failure to recognise and record waste from these causes makes accounting for materials meaningless. Therefore, a simple measure of waste on site would be the difference between that used as specified and the quantity of material delivered to site as a percentage of such deliveries. The economic and environmental benefits to be gained from waste minimisation and recycling are enormous (Guthrie et al., 1999), since it will benefit both the environment and the construction firms in terms of cost reduction. The economic benefits of waste minimisation and recycling include the possibilities of selling specific waste materials and the removal from site of other wastes at no charge or reduced cost, with a subsequent reduction in materials going to landfill at a higher cost (Snook et al., 1995). Therefore, it can increase contractors’ competitiveness through lower production costs and a better public image. However, very few contractors have spent efforts in considering the environment and developing the concept of recycling building materials (Lam, 1997). Because contractors rank timing as their top priority, their effort is always focused on completing the project in the shortest time, rather than the environment (Poon et al., 2001b). Their account books cannot reveal the potential savings resulted from reduction in construction wastes. Managing building material waste can in fact achieve higher construction productivity, save in time and improvement in safety (Chan and Ma, 1998; Gavilan and Bernold, 1994; Skoyles and Skoyles, 1987) while extra wastes take extra time and resources for disposal that may slow down the construction progress. The major causes of material wastage including concrete, steel reinforcement, formwork and brick/block, are tabulated in Table 1 based on a survey to construction participants.

20012000199919981997199619951994199319921991

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Table 1: Causes of material wastage Construction Material Causes Specification

Over-order Exact quantity of concrete required is unknown per pour due to deficiency in planning

Concrete

Loss during concreting Methods of placing; use of aged timber board

Steel Reinforcement Cutting Use of steel bars that size does not fit

Formwork Cutting Use of timber boards that size does not fit

Cutting Use of products that size does not fit

Brick / Block

Damaged during transportation

Unpacked supply

Concrete

Concrete is the most widely used material both for substructure and superstructure of buildings. The wastage is mainly resulted from the mismatch between the quantity of concrete ordered and that required in the case of ready mix concrete supply. The contractor may not know the exact quantity because of imperfect planning, leading to over-ordering. Wastes are also resulted project delays and unnecessary waste handling processes.

Reinforcement

Steel reinforcement bars are also common materials used. The main cause of wastage is resulted from cutting. Damages during storage and rusting also form a major part of wastage. Pre-bending in the factory could reduce cutting waste.

Formwork

Another major material used is timber board. The main causes of wastage are the natural deterioration resulted from usage and cutting waste. Both are difficult to avoid. Among the projects surveyed by the authors (see the following section), there is one construction site bearing wastage of 20% in timber used for foundation works.

Brick and block

Bricks and blocks are the most common walling material. The main cause of waste is cutting. Unpacked supply may increase wastage of broken damage because of the fragile nature of the materials. Unused bricks left on site may end up in the trash skip ultimately.

RESEARCH METHODOLOGY

A survey was conducted in October 2001 to April 2002 to collect the material wastage information in relation to different types of projects. Seventeen contractors have been interviewed with the details summarized in Table 2.

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Table 2: Details of the interviewed contractors Company Trades of

materials Project types Construction stage Contract

sum C R F B PBH PH CM CP I M S Sub Super 1 √ √ √ √ 150

millions (M)

2 √ √ √ √ √ 119M 3 √ √ √ √ √ 5M 4 √ √ √ √ √ 470M 5 √ √ √ √ √ √ √ 600M 6 √ √ √ √ 10M 7 √ √ √ √ √ 418M 8 √ √ √ √ √ 142M 9 √ √ √ √ √ 43M 10 √ √ √ √ √ √ 306M 11 √ √ √ √ √ √ √ 260M 12 √ √ √ √ √ 213M 13 √ √ √ √ √ √ √ 63M 14 √ √ √ √ √ √ 5M 15 √ √ √ √ √ 90M 16 √ √ √ √ √ √ 90M 17 √ √ √ √ √ 18M Notes: Trades of materials – Concrete (C); Reinforcement (R); Formwork (F); Brick/block (B) Project types – Public housing (PBH); Private housing (PH); Commercial project (CM); Composite building projects (CP); Industrial (I); Monastery (M); School (S) Construction stage – Substructure (Sub); Superstructure (Super)

From the seventeen contractors’ information, seven types of projects: public housing projects (11.8%), private housing projects (52.8%), commercial projects (11.8%), composite building projects (5.9%), industrial projects (5.9%), monastery projects (5.9%) and school projects (5.9%) are identified. Four types of materials, namely, concrete, reinforcement, formwork, and brick/block, varies with types of projects are considered. The survey response of the trades of material wastages with types of projects are shown in Table 3. Both substructure (42.3%) and superstructure (57.7%) construction are considered in this survey. All contracts belong to building construction with contract sums ranging from 5 to 418 millions.

Table 3: Material wastages and types of projects Public

housing Private housing

Commercial Composite building

Industrial Monastery School

Concrete 11.8% 52.8% 11.8% 5.9% 5.9% 5.9% 5.9% Reinforcement 12.5% 56.1% 12.5% 6.3% 6.3% 6.3% - Formwork - 66.6% 16.7% - - 16.7% - Brick/block - 55.5% 11.1% 11.1% 11.1% - 11.1%

MATERIAL WASTAGE AMONG PROJECT TYPES

Table 4 and Table 5 summarize findings of the survey, which studying the material wastage levels of various types of projects, the maximum and minimum levels of material wastage and average levels of material wastage vary with different types of projects respectively. However, no matter which types of projects it is, there is some unavoidable wastage, which are called as ‘natural wastage’, such as cutting and so minimum wastage levels for materials need to be set.

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Table 4: Maximum and minimum wastes among different types of projects Concrete Reinforcement Formwork Brick/Block

Project Min. %

Max. %

Max-Min %

Min. %

Max. %

Max-Min %

Min. %

Max. %

Max-Min %

Min. %

Max. %

Max-Min %

Public housing 3.49 13.56 10.08 2.96 5.45 2.48 - - - - - - Private housing 1.13 9.00 7.88 1.81 10.96 9.15 1.79 20.00 18.21 1.66 6.67 5.01 Private Commercial 4.35 4.98 0.64 3.09 5.00 1.91 5.00 5.13 0.13 5.02 5.02 0.00 Composite Bldg 6.67 6.94 0.28 5.00 5.11 0.11 - - - 6.92 6.92 0.00 Industrial 2.00 2.00 0.00 3.00 3.00 0.00 - - - 3.00 3.00 0.00 Monastery 5.00 5.00 0.00 4.29 5.00 0.71 10.00 15.00 5.00 - - - School 8.70 8.70 0.00 - - - - - - 3.33 3.33 0.00

Table 5: Average material wastage among different types of projects

Types of projects Trades Public

Housing %

Private Housing

%

Private Commercial

%

Composite Building

% Industrial

% Monastery

% School

% Concrete 5.99 3.37 4.96 6.84 2.00 5.00 8.70 Reinforcement 3.95 5.32 3.94 5.07 3.00 4.37 - Formwork - 4.01 5.00 - - 11.11 - Brick/ Block - 4.45 5.02 6.92 3.00 - 3.33

Table 4 shows the lowest level of wastage in reinforcement bar is 1.91% in private commercial projects, which indicates that it can hardly be further reduced and the value can be set as a natural wastage for that particular item. For items with higher wastage levels than the natural wastage, for examples, 18.21% of formwork wastage in private housing projects, there should be more ‘room’ to reduce the wastage levels. These items are called as potential wastage items, which are expressed as the following formula: Potential wastage items: Max. – Min. wastage The survey results show that a very high mean wastage level is noted for concrete, especially for projects of public housing, composite building and school as shown in Table 5. The promotion of using prefabrication can effectively reduce the wastage in concrete. The result also shows that the wastage levels vary with different types of projects. For example, the standardized designs of industrial building can reduce the wastage levels. The private housing projects generate the highest wastage levels especially for steel reinforcement, which may reflect the non-standardized building structures resulting in different sizes of formwork, reinforcement, and brick/block-work that generate higher levels of material wastage. Poon et al. (2001a) addressed the different wastages of materials in the trades of concrete, reinforcement, formwork and masonry for private and public housing projects as shown in Table 6. The table shows that the wastage in formwork for private housing projects is much higher than that for public housing projects. Table 6: Percentage wastage of materials for various trades for private and public housing projects

(Source: Poon et al., 2001a) Trade Material Percentage wastage in private

housing %

Percentage wastage in public housing

% Concrete Concrete 4-5 3-5 Reinforcement Steel bars 1-8 1-8 Formwork Timber broad 15 5 Masonry Brick and block 4-8 6

Skoyles and Skoyles (1987) pointed out a problem that the natural level of material wastage depends on the cost effectiveness of the approaches used to control it. Therefore, the cost of reducing wastage directly related to the values of material saved; however, this relationship is no longer linear. It shows that higher cost effectiveness can only be achieved at the initial stage, and lower cost effectiveness happens at the later stages. Thus, the optimum level of material saved should be identified before projects start. The optimum level should be the small improvement cost in reducing wastage that brings about a large impact on materials saved and

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increase in profits. It seems to be more effective to reduce the wastage for items bearing higher levels of wastage, which have relatively larger room for wastage reduction. This approach is important in determining where attention should be focused to maximize saving in material wastage.

CONCLUSION AND RECOMMENDATIONS

This paper demonstrates that the waste generation has direct link with subcontracting arrangements. The survey results demonstrate that different types of construction projects have different levels of waste generation. Private housing projects are found generating the highest wastage levels when compared with other types of projects. The reason may be resulted from the fact that the private housing projects normally are of non-standardized building structures. As a result, different sizes and shapes of building components such as formwork, reinforcement and brickwork are required that results in higher wastage levels. Wastage minimization should be integrated into the construction processes and planned at the tender stage. The selection of sub-contractors needs to consider their wastage reduction plan as part of assessment criteria. Provision of waste reduction training to on-site staff is also considered important in raising environmental awareness and helping site staff generating a better working procedure to reduce generation of materials wastage. A waste control system is suggested as part of site management functions, which collects waste generation data, identifies the major areas of waste generation, analyses the causes for the waste generation, produces solutions for mitigating waste and feedbacks the decision-making to the working staff who work on those key areas. The waste control system can also present dynamic information to the senior management who can coordinate among various subcontractors and departments for implementing the system effectively.

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