The 100 Most Cited Scientific Papers in Construction and Demolition Waste Management

The aim of this study is to identify the 100 most cited papers and their characteristics in the field of Construction and Demolition Waste (CDW) management, which were published in the Web of Knowledge database of the Institute for Science Information (ISI) from the period of 2000 until 28 February 2016. Citation analysis is the identification of literatures from peer-reviewed scholarly community, which is the most common approach in identifying major works. To date, this study is the first of its kind to cite studies related to CDW. This study was carried out by utilizing the Web of Science from the ISI for the most cited studies in each of the related journals in the area of CDW from the Journal Citation Report (JCR). The Cited Reference search tool of the ISI Web of Science database was utilized to analyse the chosen journals and the information was collected from the papers as follows: the type of study as well as the methodology, names and the number of authors and journal names and publication year. The findings from this analysis reveal that the number of citations in the 100 selected articles varies from 8 to 108; these articles have been published in 26 peer-reviewed journals under the classification of CDW. The frequency of citations does not represent the quality of the study; nevertheless, this study provides several guidelines in addressing the topics and authors who have contributed significantly to the body of knowledge in the area of CDW management.


INTRODUCTION
According to Moed (2009), the significance of a journal research paper can be assessed by the number of times it has been cited by other researchers.This research demonstrates how the frequency of citations could project the value of the cited studies in imparting knowledge and prescribing changes in CDW management based on practices, debates, discussions and recommendations for future studies (Lefaivre et al., 2011).However, this approach of utilizing the rate of citations to assess the quality of cited studies or their applicability has been criticized (Cheek et al., 2006).The issue of temporal bias could be present in this type of analysis because some studies might have already been cited repeatedly over time.When the contents of these studies have been integrated into the current body of knowledge, the citation rate could begin to decrease.Newer works, on the other hand, could not have received as many citations.Citation analysis shows that other indices of scientific identification could also be a factor based on particular aspects of knowledge (Garfield, 1993).Thus, this specific resource has been highly acclaimed for the impact of citations of a journal, author, or a nation (Cheek et al., 2006;Basu, 2006;Ohba and Nakao, 2010).
Since 1945, the Institute for Scientific Information (ISI) has aimed to gather and store the most important bibliometric information in terms of scientific publications of peer-reviewed journals.However, it was not until 1962 that a special tool was introduced known as the Science Citation Index, which quantifies the citations.At present, this resource is called the Science Citation Expanded Index, which is the sub-section of the Web of Science.The bibliometric analysis performed on this platform was used to identify the journal papers that were cited the most under the heading of Construction and Demolition Waste (CDW) management.To the best of the researcher's knowledge, such citation analysis has never been performed in the area of CDW management.
Thus, the present study aims to use the bibliometric resource to identify 100 journal papers that have been cited the most in the arena of CDW management published from the year 2000 to February 2016.

CONSTRUCTION AND DEMOLITION WASTE MANAGEMENT
Generally, the term Construction and Demolition Waste (CDW) relates to solid waste generation that is prevalent in the construction and building sector.In particular, CDW refers to the waste derived from activities related to construction, renovation and demolition works such as civil and building constructions, land formation or excavation, site clearances, demolition activities, building renovations and road works (Shen et al., 2004).A considerable amount of CDW is produced worldwide annually.A research by Sandler and Swingle (2006), for example, reports that about 136 million tons of construction and demolition debris is generated annually in the USA and out of this amount only approximately 20-30% of the waste is recycled.Approximately 70 million tons of construction and demolition materials and soil are discarded as waste in the United Kingdom annually (Department of the Environment, Transport and the Regions (DETR), 2000) and the rate of wastage in the construction sector reaches up to 10-15% in the UK (McGrath and Anderson, 2000).In Australia, CDW adds up to almost 16-40% of the total generated solid waste (Bell, 1998).Meanwhile, the Environment Protection Department (EPD) of Hong Kong found that about 2,900 tons of CDW ended up in landfills on a daily basis in 2007 (Poon et al., 2013).China's Municipal Solid Waste (MSW) amounts to about 29% annually and about 40% of this amount is due to activities from the construction sector (Suocheng et al., 2001;Wang et al., 2008).
CDW generation results in multiple adverse impacts such as the utilization of massive land space for the purpose of land fields to contain the waste (Poon et al., 2003), endangerment of the surrounding areas due to toxic pollution (Esin and Cosgun, 2007), as well as natural resources waste.Since it is not possible to stop the generation of CDW and the concept of zero waste is one that is impractical, research into possible solutions that would be able to reduce CDW generation has been ongoing over the past several decades.According to the development of this research, the hierarchy to waste management has been set up, which consists of four strategies as shown in Fig. 1, including reducing waste, reusing, recycling and disposing (Peng et al., 1997).The impact of the utilization of these four strategies is based on an ascending order from low to high.The main principles of this hierarchy involve the minimization of resource usage and the elimination of environmental pollution, which happen to be the two main aspects of a sustainable construction sector (Peng et al., 1997).Reduce, reuse and recycle are the first three strategies in the waste management hierarchy and often called the 3Rs in the management of CDW.These are the fundamental principles in carrying out various programs in the management of CDW.
According to Poon (2007) and Esin and Cosgun (2007), there are two advantages of waste reduction namely minimization of CDW generation and reduction in costs related to the transport, recycling and disposal of waste.The strategy for waste reduction is considered to be the most effective method in reducing the quantity of CDW and eliminating a majority of the challenges linked to the disposal of waste and to the environment (Peng et al., 1997;Esin and Cosgun, 2007).However, CDW cannot be totally eliminated; when CDW is created, strategies dealing with reusing and recycling are optional approaches to lower the volume of CDW that ends up in landfills.Reuse is normally related to utilizing the same materials over again in construction, such as reutilizing the materials for similar functions (e.g., construction sector's timber formwork) as suggested by Ling and Leo (2000) and Duran et al. (2006).Wastes that are no longer fit for reuse are recycled to make new materials for construction or thrown out into the landfill.Following the strategy of reduction, reuse is the next best option as it uses minimum amounts of processes and energy (Peng et al., 1997).The recycling strategy is considered if both prior strategies are not viable.CDW can be formed into new materials using the recycling process.According to Kartam et al. (2004) and Tam (2008), the main advantages of recycling waste include: • Decreasing demand for a new resource • Reducing costs of transport and energy production • Using waste that would otherwise end up in landfill sites • Preserving land areas for urban development in the future • Improving the environment in general In instances where CDW cannot be reused or recycled, it must be disposed in a proper manner in landfills and/or for public filling, to eliminate the problem of polluting the surrounding areas.
Despite the sound strategies developed for the area of CDW management, it is however noted that the implementation of these management approaches is far from perfect in reality (Lingard et al., 2000;Osmani et al., 2006;Kofoworola and Gheewala, 2009).Many past studies have addressed the issues of barriers and complications in applying these approaches.One study reveals that CDW management is not given priority when developing a process design (Osmani et al., 2006).Several studies have pointed out the hindrances caused by using technology with a low-waste count such as prefabrication that is utilized in Hong Kong's construction industry (Tam et al., 2007;Jaillon et al., 2009).Some studies point out that concerns regarding additional costs of recycling and the quality of recycled materials are the main hindrances in promoting the practice of recycling in the construction sector (Tam and Tam, 2006;Tam et al., 2009).These barriers need to be overcome and there is urgent need for solutions.Researchers suggest an international promotion for charging for CDW as carried out by the government of Hong Kong (Tam and Tam, 2006;Hao et al., 2008).The typical reason for the limited success in the management of CDW is due to the differing concerns of the two main stakeholder groups in the process of CDW management.The first stakeholder group consists of authorities, NGOs and the public, who are mainly concerned about reducing the volume of CDW that ends up in landfills.The second group consists of the contractors and subcontractors as well as project clients who are mainly concerned about the profits and advantages of performing CDW management as opposed to how the environment is affected by CDW.
Researchers in the management of CDW have recently pointed out that those in the sector are finding it difficult to promote the efficacy of CDW management.Through a comprehensive and systematic analysis of the CDW management publication in renowned journals, this study could be very timely and helpful for researchers to capture the latest research trends in the field of CDW management.

MATERIALS AND METHODS
The Thomson Reuters Web of Science database was utilized to retrieve the documents to meet this study's objective.The Thomson Reuters Web of Science database is dependent on the online-based SCI-Expanded.This study had extracted documents published with the keywords 'construction and demolition waste management' in the title, abstract, author and keyword-plus search boxes from the year 2000 to February 2016 for the purpose of analysis using the bibliometric approach.The number of papers cited was discovered by utilizing the ISI Web of Knowledge and its search tool, Cited References.Following the identification and selection of the 100 most cited studies, an analysis was conducted to determine the number of citations, the countries and institutions of origin, the publication year, the study topic, design and evidence level.Two independent reviewers carried out the selection of the studies.In cases of disparity, a third reviewer was engaged to reach an agreement.

RESULTS
The amount of citations of the selected 100 papers varied from 8 to 111.Table 1 illustrates that the initial 10 papers had been cited more than 50 times.Although it would not be possible to comment specifically on each of the papers, we will discuss the top three most prominent ones.The paper entitled "Use of Aggregates from Recycled Construction and Demolition Waste in Concrete" had the most citations with 111 noted.This study investigated the many areas of the said issue beginning with a short review of the global condition of  1.This is a comprehensive study on the waste management's copper mass balance in the European region, which include waste from construction and demolitions, electrical and electronic equipments, endof-life vehicles and municipal solid waste.In terms of authors, Yuan Hongping has the most number of papers cited with 8 studies out of the 100 chosen papers.This is followed by Townsend Timothoy and Tam Vivian W. Y. with 7 studies each, Lu  ---------------------------------------------------------------------------------------------------------------------------------------- The chosen 100 papers were found in publications from 27 peer-reviewed journals.The most number of studies cited was from the Journals of 'Resource Conservation and Recycling' as well as 'Waste Management', which had 25 cited studies followed by the Journal of 'Waste Management and Research' with 9 cited studies.According to the 2014 Journal Citation Report, the Impact Factor of each of these journals is 2.564, 3.22 and 1.297 respectively as demonstrated in Table 3.

DISCUSSION
This study as with all other citation analysis studies faced several limitations.The search tool for Cited Reference in the ISI Web of Knowledge caused the most inconvenience, as it does not automatically exclude self-citing (Dumont, 1989).This means that there is a possibility of biasness whereby authors are more likely to cite studies from journals where they can publish their own papers (Seglen, 1997).In addition, citations from books and journals of another language are not included in this database.Other bibliography resources such as Google Scholar have a higher register of captured citations.
Most of the highly cited studies emphasize the areas of general CDW management, recycling of CDW, reduction of CDW and generation of CDW as shown in Table 1.In general, the citations of the papers have been increasing for topics such as recycling of CDW and general CDW management.Studies in the area of general CDW management have the highest representation because this topic encompasses a comparatively wide variety of sub-headings including environment regulations in the management of CDW, cost-benefit analysis and waste management systems and plans.As noted in Table 1, studies in the general topic of CDW have increased from the year 2007.This shows that the areas under the topic of general CDW management will likely become a prominent area of research in the future.The topic of CDW recycling, which is linked to the challenges faced in CDW management from technical and managerial perspectives, is also an area of interest among researchers.It is claimed that this area would continue to receive a lot of attention.Studies in the area of CDW reduction has also witnessed a constant increase with keen attention from researchers; this shows that the reduction of CDW is the best approach in managing CDW by saving resources and eliminating pollution.Furthermore, three other related areas under the topic of CDW generation namely causes of waste, the rate of generating waste and factors that affect the generation of waste, have also received particular interest from researchers.In any related country, the understanding of how CDW is generated is of utmost importance prior to carrying out a thorough study of alternative approaches to waste management.The analysis reveals that developing countries such as Malaysia and China are increasingly focusing on this holistic research area (Yuan and Shen, 2011).It should be noted that overall, these developing countries have also increased their emphasis on the management of CDW.
Surprisingly, studies in the area of reusing CDW have been low as compared to the areas of recycling and reducing waste, although these three dimensions are regarded as the fundamental pillars in the management of CDW.A thorough review of previous literature shows that this is probably due to the existing awareness amongst contractors regarding the benefits of actively re-using waste materials (Yuan and Shen, 2011).

CONCLUSION
To date, based on available resources, this study is the first reportage on the most cited papers dealing with Construction and Demolition waste Management (CDW) in the construction industry.One method of gauging the progress and significant areas of interest in the management of CDW is by identifying the 100 most cited papers in the area of CDW management to investigate the current and future trends of the industry.The evaluation of the most cited studies is important as it acknowledges the quality of the studies that have been carried out thus far, identifies new discoveries and steers CDW management in the right direction based on the findings.
A number of 384 CDW management-related papers from the construction industry published from the year 2000 to February 2016 were evaluated using the Web of Science.Out of this figure, the top 100 most cited papers were chosen according to the JCR Science Edition.Hong Kong as well as the USA ranked number one in terms of quantity of publications.However, the study with the most citations was authored by Rao Akash, Jha Kumar N and MisraSudhir from the Indian Institute of Technology in India.More than half of the 100 cited studies were published in the 'Research Conservation and Recycling' and 'Waste Management' journals.Author, Yuan Hongping of the Hong Kong Polytech University is the first author and the corresponding author of 8 studies, which making him the most active researcher in the top 100 cited studies.

Table 2 :
Authors with the most number of papers included amongst the 100 most cited papers Name Author with more than 3 articles included in the top 100 -

Table 3 :
Journals in which the 100 most cited papers were published