Abstract
Construction and demolition waste continues to sharply increase in step with the economic growth of less developed countries. Though the construction industry is large, it is composed of small firms with individual waste management practices, often leading to the deleterious environmental outcomes. Quantifying construction and demolition waste generation allows policy makers and stakeholders to understand the true internal and external costs of construction, providing a necessary foundation for waste management planning that may overcome deleterious environmental outcomes and may be both economically and environmentally optimal. This study offers a theoretical method for estimating the construction and demolition project waste generation rate by utilising available data, including waste disposal truck size and number, and waste volume and composition. This method is proposed as a less burdensome and more broadly applicable alternative, in contrast to waste estimation by on-site hand sorting and weighing. The developed method is applied to 11 projects across Malaysia as the case study. This study quantifies waste generation rate and illustrates the construction method in influencing the waste generation rate, estimating that the conventional construction method has a waste generation rate of 9.88 t 100 m−2, the mixed-construction method has a waste generation rate of 3.29 t 100 m−2, and demolition projects have a waste generation rate of 104.28 t 100 m−2.
Keywords
Introduction
In recent years, the construction industry has continued to expand with the global economy. A driving force in the transformational growth into developed economies, the industry has now become a significant consumer of new material and major solid waste contributor. Statistics show that waste generation from the industry has significantly increased. The United States Environmental Protection Agency (USEPA) estimates that 154.2 million tonnes of building-related construction and demolition waste (CDW) materials were generated in 2003 (United States Environmental Protection Agency, 2003). Meanwhile in the European Union, the industry contributed 33% (of 821m t) of the total waste in year 2012 alone (Eurostat, 2015). A total of 50% of the total waste generated in the United Kingdom is CDW, with the discharge amount estimated at 70m t per year (Sealey et al., 2001). In Hong Kong, it is estimated at 23%, which amounts to 20m t (Poon and Chan, 2007). In Malaysia, the CDW accounts for approximately 41% of total solid waste generation (Eusuf et al., 2012). Malaysian CDW is estimated at 161.19 t per day in 2009, increasing to 299.69 t per day in 2015, and is projected to reach 368.31 t per day by 2023 (Fauziah and Agamuthu, 2003). As the rate of CDW is anticipated to continue increasing in Malaysia and globally, it will soon present a greater challenge to the authorities in managing it.
In the view of environmental economists, waste causes negative externalities to the environment, despite the fact that most of the CDW is inert materials (Franklin Associates, 1998) and may not pose as great a threat as hazardous and municipal solid waste (Wang et al., 2004). Nevertheless, CDW depletes finite landfill resources (Marzouk and Azab, 2014), contributes to the increase of energy consumption, increases greenhouse gas emissions, presents public health issues, and otherwise contaminates the environment. In the United Kingdom, the industry emits approximately 250.3m t of CO2 annually (BIS, 2010), and in the USA, it accounts for 39% of the country’s total CO2 emissions, more than any other individual sector (USGBC, 2006). Notwithstanding legislation (Solid Waste and Public Cleansing Management Act 672: National Solid Waste Management Department, 2007) governing solid waste management in Malaysia, CDW attracts significantly less attention than other forms of waste, such as municipal solid waste. CDW, being both produced and managed mostly by the private sector, suffers from weak enforcement provisions. CDW management practices that are dictated by economic incentives likewise have resulted in large-scale landfill dumping practices, illegal dumping, and open burning. In the study by Begum et al. (2009), cost, lack of knowledge, and awareness of waste recovery are the major hindrances against source separation and recycling. Malaysia’s minimal level of CDW recovery is also attributed to a scarcity of reliable CDW data in fostering the growth of CDW recycling facilities.
Background study
Over the past decade, rapid urbanisation and insufficient attention to CDW, particularly in developing countries like Malaysia, have contributed to an urgent need for additional research on the waste generation rate (WGR) (Begum et al., 2007; Wang et al., 2010). To account for externalities and environmental costs, quantitative waste data is fundamentally important (Myers, 2004). Waste minimisation and recycling are difficult to implement when quantitative data regarding waste composition and WGR are not reliably known (Hassan et al., 2000). Quantitative waste data provides measurable indicators to estimate the WGR in a project, serving as a decision-making tool in planning for an efficient waste management plan, and are central to assessing the feasibility of waste recycling. The study by Marzouk and Azab (2014) suggested a savings of 12.3m t in raw materials substitution if recycling is conducted on the same quantity of landfill disposed material. In Australia, studies proved that an effective waste management plan reduced waste generation by 15%, with 43% less waste sent to landfill, and savings of 50% on related waste handling costs (McDonald and Smithers, 1998).
A number of international researchers are aware of this CDW situation and have devoted applicable research to the WGR. These researches (Franklin Associates, 1998; Llatas, 2011; Lu et al., 2011; Marzouk and Azab, 2014; Poon et al., 2004) focused on regional estimations that required large existing databases of information. In Malaysia, there is no official published, reliable CDW data regarding the WGR or CDW material recovery. There do exist a few studies in Malaysia (Lachimpadi et al., 2012; Lau et al., 2008; Lee et al., 2013) that addressed the WGR based on the project basis and discussed the recyclability of CDW material. In these studies, the researchers estimate WGR by using the methodology of on-site hand-sorting or machinery-based-sorting. This methodology is costly and time-consuming, requiring a high degree of manpower and machinery, thus limiting the number of projects involve in the researches.
There are several methods for estimating the WGR or quantifying CDW. Waste can be estimated either by waste generation quantity or by waste disposal quantity (Franklin Associates, 1998). CDW can also be quantified based on secondary records of waste flow and waste disposal (Mahayuddin and Zaharuddin, 2013). Waste estimates may be quantified by volume of waste generated, waste material density, and floor area of construction or demolition project (Kourmpanis et al., 2008). Waste quantity or volume can be obtained by measuring waste truck trips and size of the waste bin (Poon et al., 2004). However, the quantification method must be modified in accordance to the limitations of data quality and availability (Mahayuddin and Zaharuddin, 2013). A universal waste quantification model can rarely be applied, as the nature of CDW data is dependent upon the local economic conditions, weather, disasters, local regulations, availability of technology, labour, and resources (Franklin Associates, 1998).
Furthermore, the WGR will differ greatly according to variation in the following parameters: Construction method used in the project, type of project, project size, and others (Jaillon et al., 2009; Kourmpanis et al., 2008).
Construction method
The Malaysian construction industry is generally considered a late-adopter of relevant technologies owing to the association of new methods with new risk and cost. The majority of the construction in Malaysia is conducted according to the conventional construction method (CCM). The CCM utilises building components that are constructed on-site through the processes of casting with timber and plywood and is regarded as time-consuming, costly, and highly dependent on labour. The labour-intensive nature is a likely influence on the amount of waste generated by the method (Teo and Loosemore, 2001). The Industrial Building System Roadmap, initiated in 2003 by the Malaysia Construction Industry Development Board, has fostered a slow transition from the CCM to the non-conventional or the Industrial Building System method. Transitional efforts are seen in adoption of the cast-in-situ method. The cast-in-situ method uses lightweight prefabricated formworks of steel or aluminium that are easily erected, dismantled, and reused to replace the use of traditional timber and plywood formwork. It has the effect of reducing labour dependency, maximising productivity, and shortening construction periods. The transition effort remains in its infancy, as most construction projects utilising the cast-in-situ method will do so in combination with the CCM. In this study, such combination of both methods is referred to as the ‘mixed-construction method’ (MCM). Owing to the prevalence of the CCM and MCM in the Malaysian construction industry, this study examines projects of both types in influencing the WGR.
Type of development
In recent years, owing to the rapid urban growth and increase in land prices in the urban area, Malaysia’s cities have seen a surge in high-rise mixed-use development (HRMUD). HRMUD, which comprises a combination of residential units, commercial spaces, and multi-story parking area, offers notable living conveniences and has become the new urban growth development paradigm. In Malaysia, despite the land prices, HRMUD is still developing on greenfield land, either new land or agriculture land. Demolition projects are uncommon in Malaysia, comprising only 0.1% of the total value of construction work done, whereas new construction projects comprise 64.4% (Department of Statistic, 2012–2015).
CDW of HRMUD is generated throughout the entire construction period (24–48 months) and the industry does not store waste information without monetary incentives to outweigh the costs of such additional administration, delays, and other effects on the business efficiency. Consequently, a complete and precise WGR quantification is not economically practicable for builders, and thus it is nearly impossible for researcher to obtain such comprehensive data in Malaysia.
The primary purpose of this study is to propose a less burdensome and more broadly applicable alternative to estimate the WGR of construction and demolition projects in Malaysia. Given that HRMUD is still new and lacking in applicable WGR research, this study focuses on investigating the WGR of HRMUD, relative to the construction method employed. This study also investigates the composition of such CDW to identify the percentage of recyclable material.
Methodology
For the reasons mentioned above and to ensure a broader sampling, this study employs the method suggested in Poon et al. (2004), whereby waste generation is estimated as a function of the number of waste truck trips and the size (volume) of the waste bin being sent out of the project site. The estimation of the total number of waste truck trips is illustrates in equation (1), where N is the total number of waste truck trips, Call is the total waste disposal cost, and C is the disposal cost per truck trip:
By doing on-site measurement, waste truck bin sizes are collected. Then, the volume of waste being disposed out of site is estimated with equation (2), where Vall is the total waste disposal volume and V is the size of the waste bin:
With the modification in accordance to Malaysian construction industry, the WGR is estimated through the indicative mathematical model used by Fatta et al. (2003) and Kourmpanis et al. (2008). The WGR of waste category k is defined by:
where FA is the floor area constructed or demolished (m2), ρ(k) is the waste k density (t m−3), Com(k) is the waste (k) composition (%) that is collected through interviews and review of reports.
The WGR estimation is rendered subject to the following assumptions.
All waste generated on-site is transported by waste truck with a waste bin.
The waste bin is fully loaded when it is transported out of site.
No domestic waste in the waste bin (domestic waste is usually disposed separately).
Total input of timber and plywood is equal to total output, regardless of recycling path.
No burning of timber and plywood is conducted on-site.
Plastic, paper, and cardboard are recycled and not part of the waste disposal output.
No consideration is given to the waste generated on-site that is reused or recycled back on-site.
Project selection
A total of 11 projects were selected as case study; 10 construction projects and one demolition project. Of the 10 construction projects, there are six CCM projects and four MCM projects. No demolition waste was derived from existing structures on these 10 projects, as they were the greenfield development. This research limits its study to one demolition project owing to the rarity of such types of projects in HRMUD, Malaysia. The demolition project was the partial demolition of previously abandoned development, and was the only one that fulfilled the project selection parameters stated below.
The projects were selected in accordance with the fulfilment of the following parameters.
Project job-site accessibility.
Project with available secondary data, such as invoices or reports on waste disposal trips or other waste costs.
Project where a waste sub-contractor handles the construction and demolition waste.
The 11 projects selected span a range of project scales comprising small, medium, and large projects; two projects with a floor area exceeding 150,000 m2, two projects between 100,000 m2 and 150,000 m2, five projects between 50,000 m2 and 100,000 m2, and two projects with a floor area of less than 50,000 m2.
Data collection
Data collection is accomplished through the following methods.
Review of existing secondary data, including monthly progress report, waste management plan, contractor claims and invoices, bill of quantities, and tender documents indicating waste disposal cost, waste composition, and frequency of disposal.
Gathering of primary empirical data through periodic site observations conducted throughout the first half of 2015, including sampling and measurement of waste bin size.
Structured interviews and surveys of related personnel, to supplement and qualitatively improve the above-referenced primary and secondary data obtained.
Waste material density (ρ) is obtained from the average of data gathered from Australia, New Zealand, and Japan. With the lack of directly applicable, published CDW data from Malaysia, the average density data provides a reliable, if general, estimate. Owing to waste materials varying in shape and packed volume, total waste amounts are generally described in weight (Table 1).
Waste material density.
Sources: Burton and Friedrich, 2008; JIWIC, 2015; Memon, 2015; NAHB, 1997).
Results and discussion
Waste composition
Table 2 illustrates the basic numerical data of the 11 projects and is used as the basis for the WGR estimation. Projects 1–6 follow the CCM. Projects 7–10 utilise the MCM. Project 11 is a demolition project.
Project information and waste composition.
Table 3 shows the estimation of waste composition by weight. CDW composition information allows developers to strategically act regarding storage planning, waste material trading opportunity, and waste separation. Total waste generation by the six CCM projects is estimated at 52,905 t, with an average of 8817 t per project. While the four MCM projects produce a total of 14,813 t, with an average of 3703 t per project. Total waste generated by a demolition project is estimated at 134,508 t.
Waste composition for projects.
Comp: composition.
Figure 1 illustrates the waste composition resulting from the CCM projects. The concrete/aggregate category represents the highest percentage (23%) of the waste sampled, followed by reinforced concrete (17%). Cement/plaster, sand/soil, and timber/plywood each represent approximately 13% of the waste.
CCM waste composition (t).
Concrete, aggregate, reinforced concrete, and cement are the main materials in building construction. Project contractors often do not know the exact quantity of each material required, relying instead on estimation that is prone to waste of concrete. Concrete production is time-sensitive and must match up with daily work demand, with a tendency to oversupply rather than risk a costly work delay. In HRMUD, concrete is pumped by hose in a liquid state, tending to waste more concrete the higher the floor of construction.
The CCM relies mainly on timber/plywood as the temporary formwork for casting of building structure. The high timber/plywood composition of the waste is correlated to the formwork, which is discarded regardless of its reusability cycle. The interview survey revealed that contractors are inclined to most inexpensively dispose of timber/plywood by on-site burning. Accordingly, the actual amount of wood waste may exceed 13% of total project waste. Tiles and gypsum are generated only at the construction finishing phase, being strongly affected by the handling skill, design, and material quality. While gypsum board is often used for ceilings in commercial developments, builders wishing to reduce costs do not often use this material for HRMUD, thus the lower percentage of waste.
Figure 2 shows the waste composition of the MCM projects. Concrete/aggregate (22%), reinforced concrete (17%), and cement/plaster (10%) still represent the largest category, and 49% of total waste. Timber/plywood waste is substantially lower in the MCM projects. The cast-in-situ system formwork (steel or aluminium) used in MCM projects accounts for the reduction in timber/plywood, concrete/aggregate, and cement/plaster waste. System formwork is only feasible by the economies of scale, when the building’s design is repetitive enough to justify the initial formwork moulding design costs. In MCM projects, system formwork is used in casting of main floors, beams, and columns, but wood is still used for casting internal walls and various differing design features. Sand/soil occupy a larger percentage (19.5%) of total waste, reflecting the greater impact of excavation work done in the earlier construction stages.
MCM waste composition (t).
Figure 3 shows that demolition waste is mainly composed of scrap metal, concrete/aggregate, brick/block, and cement/plaster. The demolition case study waste composition reflects that it was a building project abandoned at the structural stage, resulting in no waste from internal finishes. The demolition project adopted a partial selective demolition method, facilitating on-site waste separation. Crushing machines were utilised to separate metal bars from concrete and aggregate, producing a large amount of scrap metal, accounting for 62% of the total waste sampled. Scrap metal is most readily recyclable, possessing a high secondary market value, which is applied to offset the contractor costs. The remaining 38% of project waste was not recycled and was instead sent to a dump site.
Demolition waste composition (t).
Waste generation rate
Results show that the different construction methods generate waste at different rates (Table 4). The WGR is a useful performance measure in managing waste across a spectrum of project sizes. A higher WGR indicates a less efficient project, generating higher waste per square metre, and vice-versa. On average, the WGR for CCM is estimated at 9.88 t 100 m−2, while the WGR for MCM is estimated at 3.29 t 100 m−2.
WGR and disposal cost.
WGR: waste generation rate; RM: Ringgit Malaysia.
This study finds that the CCM generates more waste per square metre than the MCM, and appears to be less efficient. Even though this study does not provide research on a purely Industrial Building System project, the WGRs estimated may still serve as a useful indicator to the WGR reduction benefits of adopting such a construction method. In the Lachimpadi et al. (2012) study, the CCM was found to generate waste at 4.8 t 100 m−2, and the MCM at 3.02 t 100 m−2. Although the WGRs of both studies are not quite similar, the WGRs from both studies displayed a similar upward pattern that suggests WGR of the CCM is greater than the WGR of the MCM. The most waste is generated from the demolition project, with a WGR of 104.28 t 100 m−2 (Table 4).
CDW material that traditionally yields a high resale value, such as scrap metal, will be recovered at the originating site, regardless of disposal fees (Llatas, 2011). Landfill dumping is the most common practice for discarding other types of CDW material, such as concrete, reinforced concrete, drywall, rubble, roofing, and brick. Accounting for all of the projects studied, a total of 56% or 114,100 t of waste is disposed to landfill, while a total of 88,127 t or 44% of scrap metal is recycled. Scrap metal resale prices could vary on global market price and the volume submitted to the recycler. Scrap metal resale value (approximately RM600 per tonne) is estimated to be around 30%–40% of the current new material price (RM2000 per tonne), possibly yielding up to RM52 million in resale value across the projects.
This study also collected waste disposal cost data to better relate the WGR to waste management policies. The average disposal cost is RM1.81 m−2 for the CCM projects and RM1.29 m−2 for the MCM projects. Disposal costs tend to be higher when the WGR is higher. For a demolition project, the average disposal cost is estimated at RM3.78 m−2 for all (100%) waste. However, accounting for the 62% of scrap metal recycled, the disposal cost for material that is not readily recyclable material (concrete/aggregate, cement/plaster, and brick/block) is further reduced to RM1.44 m−2. Reduction in disposal costs illustrates the benefit of recycling CDW, which (while not entirely absent) is muted in practise by the lack of incentives, enforcement, and supporting infrastructure for builders.
Conclusion and recommendation
The theoretical method presented in this study demonstrates a less burdensome framework for WGR estimation through available secondary data input, interviews with site personnel, and also periodic site observation. Such a method is significantly more practicable than the costly on-site hand-sorting or machinery-sorting method. The findings from this study also demonstrate the role of the construction method in influencing WGR, highlighting the benefits of transitioning from the CCM to the MCM, particularly in respect to reducing WGR on-site.
WGR data obtained through this method may be applied to a broader series of case studies, and may serve as the foundation for a regional CDW database and CDW projections. With pending massive increases in Malaysian housing demand, and the revival of previously abandoned projects, the opportunity for utilising such regional WGR data is clear, especially where such data suggests the potential for future growth in the CDW recycling industry. Where there are available recycling facilities, the economics may shift to justify an increase in recycling CDW.
Building a quantitative WGR database is crucial in measuring the economic and environmental costs of CDW. Informed consideration of a WGR database information may empower stakeholders and government agencies to meaningfully address the business and environmental impact of CDW. Policy makers may benefit from a WGR database in developing appropriate policies to CDW management, planning for cost associated with landfill management, pricing of dumping fees, and assessing the feasibility of CDW recycling facilities.
It should be noted that the waste density data employed in this study was a composite figure sourced from many countries, and is most usefully understood as an approximation. To improve the accuracy of the WGR, the authors suggest utilising the waste density data from the same country and region, where available. Owing to variations across projects, additional studies on waste composition are needed to refine the accuracy of this research result. WGR established from this study cannot be validated for exact accuracy, and represents one important project type, rather than the industry as a whole. Nevertheless, this study and associated methodology may be useful as an expedient, economical, decision-making tool for stakeholders.
Footnotes
Acknowledgements
The authors acknowledge Japanese Science and Technology Agency (JST) and Japan International Cooperation Agency’s (JICA) joint Science and Technology Research Partnership for Sustainable Development (SATREPS), for the funding of this research as part of the ‘Development of Low Carbon Society Scenarios for Asian Regions’ research project.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors acknowledge Japanese Science and Technology Agency (JST) and Japan International Cooperation Agency’s (JICA) joint Science and Technology Research Partnership for Sustainable Development (SATREPS), for the funding of this research as part of the ‘Development of Low Carbon Society Scenarios for Asian Regions’ research project.