Advances in Building Technology, Volume 2 M. Anson, J.M. Ko and E.S.S. Lam (Eds.) © 2002 Elsevier Science Ltd. All rights reserved
1431
BALANCE THEORY FOR RECYCLING OF CONSTRUCTION AND DEMOLITION WASTES E.O.W. Wong and R.C.P. Yip School of Professional and Continuing Education, The University of Hong Kong, Pokfulam Road, Hong Kong
ABSTRACT The key to reduce construction and demolition wastes (C&D wastes) lies in finding a way to make them valuable. Recycling of C&D wastes into profitable commodities is one of the effective means. Balance of the supply of C&D wastes and the demand of recycled C&D waste products (Balance Theory) is recommended in new developments. The maturity of Balance Theory requires gradual estabhshment of recycling facilities. These facilities are capable to accept and handle not only inert materials but also other C&D wastes like wood and wood products, cardboard, metal, plastics etc. The Balance Theory rouses construction workers to adopt the idea of reduction of wastes. They are educated to clean their working places constantly and collect all construction wastes they generated into separate collection spots within the construction site. The site management personnel is required to establish site facilities and set up conditions in employment contracts and subcontracts for workers and subcontractors to follow. The culture of separating wastes at sources must be established and widely adopted so that Balance Theory could be realised. All in all. Balance Theory advocates the amount of wastes generated from a construction project and sent for recycling process must be equivalent (or proportional) to the amount of the recycled C&D products imported and used as construction materials for that project. Evaluation of the Balance Theory can be extended to a group of developments within a district or even augmented to a city as a whole. Zero C&D wastes sent to landfill may be too idealistic, however, minimisation of C&D wastes could be realised if Balance Theory is enforced. Appropriate actions taken by the Government may be needed to encourage the execution of the Balance Theory when recycling facilities and the green working culture of construction participants are well developed. Balance Theory can be first carried out in government projects as pilot scheme. The proportion of imported and exported amount of C&D wastes be reviewed and adjusted to suit the adoption and development of the Balance Theory.
1432 KEYWORDS Recycling, Sustainable Development, Construction & Demolition Waste, Balance Theory, Waste Management, Material Management.
BACKGROUND Since 1987, the notion of "Sustainable development" was introduced in the Brundtland Report. Sustainable development or sustainability is generally defined as a constraint on present consumption to ensure that future generations will inherit a resource base no less than the previous generation inherited, hi meeting this intergenerational goal, sustainability is concerned with two types of limits the environment imposes on growth or development - source limits and sink limits. Source limits refer to the environment's finite capacity to provide resources - both renewable and nonrenewable, and both mere production inputs and essential, non-substitutable "natural" services. The sink limit refers to the environment's capacity to assimilate the wastes that economic growth and development cause. Environmental Protection Department of the Hong Kong Special Administrative Region (EPD 1998) defined construction and demolition (C&D) materials as a mixture of surplus materials arising from any excavation, civiL1)uilding construction, site clearance, demolition activities, road works and building renovation. Statistical information fi-om the EPD 2000 showed that the average daily C&D materials produced was 4 times as much as that of municipal solid waste. This reflected that the construction industry generated a substantial high proportion of solid waste in Hong Kong. The aim of this article is to arouse the significance of sustainable development in the culture of the construction industry. On national level, sustainability is a resource management and pollution control problem. On the global level, sustainability is concerned with intragenerational equity, crossboundary pollution, the loss of biodiversity, and the aesthetic value of nature. Although definitions of sustainability vary, there are some important common themes: a concern for the environment, an appreciation of the crucial difference between development and growth, and most importantly, a concern for both inter- and intra-generational equity, hi order to achieve the global aim, there are several ways that have to be achieved in the construction industry: • • •
to minimise the amount of construction & demolition wastes through better planning and design; to recover those unavoidable C&D wastes into secondary material; to employ the secondary materials in construction projects.
ESTABLISHMENT OF BALANCE THEORY The composition of C&D waste materials disposed at landfill sites in Hong Kong in 1995 is shown in Table 1 (Source: EPD 1995). It is noted that the asterisked inert materials can be easily recyclable into secondary materials if they are properly sorted and re-employed in construction site as temporary works and permanent works. The other C&D waste, except the ferrous metals, being sent to landfills can also be re-used if they are properly handled through recycling processes. Recent research indicated that the recycled inert materials of the C&D wastes were largely re-used for reclamation, road sub-base, bituminous macadam, and concrete of lower structural grade. Demolished ferrous metal can be sent to steel mill for processing as recycled steel. The scrap metal market in Hong Kong has successfully collected and recovered over 90% of ferrous metal wastes
1433 from construction site. This scrap metal was largely shipped aboard for reproduction as other metal products and partially recycled locally as reinforcement bar, and in turn being used in local construction projects. Wood wastes in construction site include wood products, bamboo, trees and vegetation (mainly obtain from over-site activities in civil engineering works). If wood wastes are properly handled, the recycled products are basically cellulose products in chip and powder form. These recycled products can be used as raw material for chipboard, paper pulp, daily cover in landfill and mulch for moisture retention in landscaping works. Hence, though the construction industry produces quite significant amount of C&D wastes, we could recover them and re-use them into construction projects and benefit the community as a whole. TABLE 1 COMPOSITION OF CONSTRUCTION & DEMOLITION WASTE DISPOSED OF AT LANDFILLS IN 1995 (SOURCE: EPD 1995)
Component Soil/Sand* Concrete/Mortar* Rock/Rubble* Reinforced concrete*
Composition of each category of construction & demolition waste received at landfill sites (% by weight) Road work Excavated Demolition Renovation Site material soil waste Clearance Waste 23.0 73.8 21.5 19.4 33.0 1.2 16.9 10.8 7.4 4.6 14.4 14.2
12.5 0.4
27.7 5.8 12.1
Brick/Tiles*
0.8
0.4
Sub-total Slurry & mud
693 1.8
88J 9.7
77.9
Asphalt
24.7
0.0 3.2
1.5
15.0 0.9
38.8 7.0
1.4
9.6
54.9 1.0
82.2
0.2
0.0
3.1
Cement contaminated
1.7
0.0 0.4
15.6
3.3
Wood
0.6
0.9
10.5
13.3
7.1
Ferrous metals Non-ferrous metals
0.5
0.0 0.0
0.6 0.7
1.0 0.2
1.3 0.1
0.7
5.6
13.8
2.9
100.0 59.4
100.0 8.5
100.0 14.6
100.0 12.3
Others (include bamboo, trees, glass, plastics, bulky wastes /fixtures, organics & garbage Total Percentage of total quantity of C&D waste landfiUed
0.0 1.4
100.0 5.2
Note: * Inert materials which are considered suitable for public filling areas The above figures are estimated by visual inspection of 3060 trucks loads delivering construction & demolition waste in 1995. They should be regarded as indicative only rather than actual composition of construction & demolition waste during the year.
The basic principle of Balance Theory is to acquire the equilibrium between the supply of the C&D wastes and the demand of the recycled C&D secondary materials. The Theory requires gradual achievement in Balance Ratio as defined: C&D Secondary Materials Employed (by weight) Balance Ratio (BR) = C&D Wastes Produced (by weight)
1434 If a construction project acquires a high Balance Ratio (BR), that means it does not produce too much C&D wastes. Even if it produces much wastes, it is able to absorb quite a high proportion of the secondary materials. From Table 1, it reflects that quite a high amount of C&D materials can be re-used or recycled into construction secondary materials even in different natures of projects. Hence, if a project can achieve 70% BR, it arrives a satisfactory level. If a project can achieve 80% or higher, it acquires at commentary level.
PLANNING & DESIGN Balance Theory advocates that the amount of C&D wastes generated from a construction project is equivalent (or proportional) to the use of recycled C&D products. In order to obtain a commentary level, reduction of wastage is a fundamental step to achieve this purpose. Waste minimisation can be greatly achieved at design stage. A good design saves considerable amount of wastages. Considerations of the dimension in design approach in one way complies with the fimctional requirements and on the other way focuses on minimising the cutting wastage of materials. Minimisation of discrepancies in construction information by carefiil coordination of all design components enables reduction of unnecessary abortive and redundant works. Standardisation of building elements allows repeated use of standard components such as system formwork, prefabricated units and precast units. Selection of environmental friendly materials and environmental friendly construction methods will be determinants of sustainability. Largely adoption of recycled materials in temporary works and permanent works is another essential step to increase the balance ratio. EPD 2000 revealed that 80% of C&D inert materials were sent to public filling area as reclamation material. However, if better sorting process is undertaken, some of these materials could be retrieved to re-use or recycle as usable materials for construction aspects. It is, for instance, concrete fragments of smaller size in C&D wastes are treated by crushing and sieving processes. They can be used as aggregate in road formation, bituminous macadam, concrete blocks or lower structural grade concrete (RILEM recommendation 1992). The other 20% of C&D wastes which were sent to landfill can also be retrieved to a large extent by better sorting process for re-use through recycling. Wood waste can be re-used in producing wood chip products and paper pulp products. Gypsum board wastes can be reproduced as gypsum board or other gypsum products. Plastic wastes can be turned out as plastic raw materials. Consideration should be given to the cost, energy consumption and waste generation during the process of sorting, retrieval and recycling of these wastes. Cost-benefit analysis approach to evaluate the actual financial and environmental benefits must be taken into account. Selection of recycled materials in the design of temporary and permanent works enhances the achievement of a higher Balance Ratio. Preference should be given to recycled materials in design stage to ensure a certain amount of recycled materials is used in the proposed project. When new materials must be used, consideration should be given to the selection of material that is recyclable and re-usable after demolition.
WASTE MANAGEMENT AT WORK Recent study of construction wastes (Poon et al 2001) revealed that pubHc housing projects generated less construction wastes when compared to private residential projects. Table 2 shows the significance of wastes by trade in these two categories of projects.
1435 From the figures, it reflected that standardised public housing project, due to its repetitive nature, provides better condition for site management which enhances reduction of construction wastes. It is evident that the design and conscious waste reduction implementation affects greatly the outcome of waste management. Other than the nature of project, adoption of a stringent waste management plan on site will greatly reduce the level of wastage and in turn reduces the resources require to handle the wasted materials. TABLE 2 WASTE PERCENTAGE IN DIFFERENT TRADES FOR PUBLIC HOUSING PROJECT VS. PRIVATE RESIDENTIAL PROJECT
Trade
Public Housing Project
Private Residential Project
Material
Percentage Wastage
Percentage Wastage 4-5%
Concrete
Concrete
3-5%
Formwork
Timber board
5%
15%
Reinforcement
Steel bars
3-5%
1-8%
Masonry
Brick & Block
6%
4-8%
Dry wall
Fine aggregates
5%
6-10%
Wall screeding
Ready mixed concrete
7%
4-20%
Floor screeding
Ready mixed concrete
1%
4-20%
Wall plastering
Plaster
2%
4-20%
Ceiling plastering
Plaster
2%
4-20%
Floor tiling
Tiles
6%
4-10%
Wall tiling
Tiles
8%
4-10%
Installation of bathroom fittings
Sanitary fittings
2%
1-5%
Installation of kitchen fittings
Kitchen fittings
1%
1-5%
Waste Management Plan can be categorised into three assertions: a) Waste Preventive and Reduction Action at Design Stage i)
Coordinate with designer to ensure dimension of material is well considered to avoid cutting wastage; ii) Adoption of pre-fabricated precast building components; iii) Design to suit system formwork or large panel formwork to reduce the use of timber formwork; iv) Designer and specification writer to willfully adopt recycled secondary materials in new development.
1436 b)
Waste Preventive and Reduction Action during Site Operations This plays an important role to minimise unnecessary waste and fulfill recycling. It requires full devotion of site management and supervisory staff to propel all kind of waste preventive and reduction plans to push workers and subcontractors to implement. These plans are not limited to: i) ii) iii) iv)
c)
carefully plan ahead of all works to avoid mistakes, abortive works and double handling; establish site facilities for collection and sorting of C&D wastes; centralise material cutting and storage areas so that reusable pieces can be easily located; educate workers to be "green" construction consciousness by reducing unnecessary cutting of materials, cleaning working spots constantly, collect and sort all their construction wastes into the designated collection spots;
Material Management to Avoid Unnecessary Wastage Material management to avoid unnecessary wastage should be the joint effort of site management and head office policy. i)
Adopt just-in-time material ordering and consumption system to manage material to avoid unnecessary wastage due to stockpile and transportation damage within site areas; ii) Consider environmental friendly alternatives like cut-to-size, and/or pre-mixed materials to avoid in-situ cutting and mixing; iii) Adopt to use as much recycled materials when condition permits; iv) Establish corporate policy to enforce waste management plan and enforce its implementation by means of incentive or penalty system.
CULTURE AND EDUCATION The strategy in setting up a successful waste management plan to achieve high Balance Ratio, relies much on the partnership between government, industry and consumers and on shared responsibilities among the main actors. Economic constraints, lacking technical specifications for the recycled materials as well as unclear legislation with respect to secondary materials constitute obvious barriers in the development of the use of recycled materials. Hence, specific actions have to be undertaken in order to give the evident opportunities a chance: Liformation and sensibilisation of all the parties involved is a necessary. Responsibilities have to be refined. On site, the site manager is "a king" who also decides whether the waste is separated or not. Up to now, even the economical benefits have not made them start separation and few even consider starting it for environmental reasons. To start source separation on a large scale seems to require an order from waste officials. Economic bottle necks have to be relaxed. Indeed, how strong the social concern about the environment may ever be, the final motivation for using recycled materials will always stay an economic one. As long as there is no real economic interest in using recycled materials instead of virgin raw materials the use of the former will last marginal. The sustainability paradigm presents challenges as well as opportunities for the construction industry. It will mean higher costs for polluting materials, disposal methods, and processes. It will put a
1437 premium on recycling. Sustainability also opens up new markets for those firms willing to take the initiative and gain the expertise. As business becomes aware that reducing waste and pollution means more profits, new markets are created for the industry. These opportunities include: installing more efficient, less polluting energy systems in power plants; providing environmental upgrades for existing factories; incorporating new more efficient, less polluting technologies into new facilities; and making buildings more energy efficient. Firms with this expertise, particularly those emphasising at the source reduction, will be in demand. Specifications which reUed thus far for a great extent on past experience with virgin materials of well known geological origin have to be reviewed and adapted. Moreover, the standard forms of building contracts are recommended to be revised to address environmental issues and that building professionals need to become aware of the importance of sustainable construction and tailor their professional services accordingly.
GOVERNMENT ENACTMENT AND ENCOURAGEMENT Support and encouragement from the Government is essential to stimulate a new industry sustainability development. There are mainly twofold of functions that the Government should play for the initiation and the subsequent growing industry. First and most essential encouragement the Government could give is to provide project funding in developing recycling facilities and the employment of the recycled secondary materials. Bonus can be awarded to those projects achieving commentary or even satisfactory level of the Balance Ratio. It could support private enterprises to enter into the recycling businesses like sorting, classification of wastes, processing and transportation. On the other fold, the Government can legitimate more stringent rules to enforce the use of recycled materials as well as set up codes of practice for construction participants to carry out the Environmental Management Systems (EMS). Li Ontario, the new waste management regulation enforces source separation to be part of the demolition projects over 2000 square metres. The EMS aims to provide a comprehensive framework for achieving sustainability during the construction stage of projects. Similar codes are pubhshed by the South African Bureau of Standards (SABS 1993). In the preface to this Code of Practice, the SABS acknowledges the valuable assistance derived from "Specification for Environmental Management Systems", published by the British Standard Institution (BSI1992). In South Africa, most formal EMS have been implemented by large industrial and business organisations. It provides a comprehensive checklist which should improve the practice of environmental management of construction.
CONCLUSION Construction industry must inevitably change its historic methods of operating with little regard for environmental impacts to a new mode that makes environmental concerns a centerpiece of its efforts. A proactive, involved industry that addresses environmental effects squarely will have a far better chance of addressing issues and finding solutions prior to government involvement on a scale that has negative consequences for the industry. The Balance Theory as well as the proposed Balance Ratio can be used as a means for establishing the goals of sustainable or green construction. The era of sustainability, perhaps more than anything else, is establishing that we need to synthesize and integrate information to provide future generations with their own sustainable environment.
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