Current construction and demolition waste management strategies for Philippine construction sector – A systematic literature review

2.1. Construction and Demolition Waste

Construction and demolition wastes (CDW) are the most significant wastes generated by the construction sectors, and they are classified into two types. Construction waste is generally defined as relatively clean and heterogeneous wastes generated from various construction activities, while demolition waste is defined similarly to construction waste but with different materials resulting from the demolition action [11]. Construction waste can be generated from six different sources [12], which are as follows: design source, procurement source, handling of materials source, operation source, residual source, and additional sources.

Figure 1. Timeline of CDW related policies in the Philippines.

2.2. Philippines CDWM Initiatives

Several legislations have been created to combat the issues of climate change and pollution. Policies related to CDW and waste management started as early as 1978 and continuously evolved to address the problems on solid waste management better. This study discussed five initiatives by the Philippine government related to CDW management and waste minimization. A timeline is presented in Figure 1, showing the CDW-related policies. 2.2.1. Philippine Environmental Code (PD 1152) PD 1152 stated the creation of waste management guidelines, including promoting technological and education efforts to prevent environmental damage. The code requires all local government units (LGUs) to prepare and implement waste management programs. It is also stated the methods of proper solid waste disposal. A policy on managing and conserving natural resources includes managing mineral resources [13]. 2.2.2. Ecological Solid Waste Management Act of 2000 (RA 9003) RA 9003 declared the State's policy to implement a systematic, comprehensive, and ecological solid waste management (ESWM) program. The ESWM policy related to CDW includes solid waste avoidance and waste minimization, proper waste segregation, promotion of research and development, private sector participation, and integration of ESWM into academic curricula. The ESWM policy related to CDW includes: (1) solid waste avoidance and reducing waste volume through source reduction and waste minimization techniques, (2) proper segregation, collection, transport, storage, treatment, and disposal of solid waste excluding incineration, (3) promotion of national research and development (R&D) programs to improve solid waste management, and conservation of resources, (4) encouragement for private sector participation, (5) encourage cooperation and self-regulation among waste generators and (6) integration of ESWM and resource conservation in academic curricula to promote environmental awareness. The implementing rules and regulations of RA 9003 relevant to CDW that are mandated include the establishment of an SWM Board, submission of a 10-year SWM plan, the estab-

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Government funding for CDWM research and recycling businesses

New South Wales (NSW) Environmental Protection Agency (EPA) Specifications for

Supply of Recycled Materials for Pavement, Earthworks, and Drainage

NSW Road & Maritime Services Technical Guide for Management of Road Construction & Maintenance Wastes

CDWM: Construction and demolition waste management; CE: Circular economy; EU: Europe Union; USA: United States of America.

lishment of material recovery facilities (MRFs), closure of open dumpsites and conversion into controlled dumpsites by 2004 and banning of controlled dumpsites by 2006 [14]. 2.2.3. National Solid Waste Management Framework (NSWMF) The NSWMF is a framework built along the three main dimensions: (a) the scope of waste management activities, (b) critical actors and partners in implementing the activities, and the means for achieving the SWM objectives. The scope of the NSWMF is anchored on sections 15 and 16 of RA 9003, which includes: planning and management, waste generation, and waste handling and transport [15]. 2.2.4. National Solid Waste Management Strategy (NSWMS) It is a medium-term plan designed to address critical issues, gaps, and barriers encountered by SWM implementers and demonstrate the path for full implementation of RA 9003. It consists of eight strategic components, which include: (1) bridging policy gaps and harmonizing policies, (2) capacity development, social marketing, and advocacy, (3) sustainable SWM financing mechanisms, (4) creating economic opportunities, (5) supporting for knowledge management on technology, innovation, and research, (6) organizational development and enhancing inter-agency collaboration, (7) compliance monitoring, enforcement and recognition and (8) cross-cutting issues: good SWM governance, caring for vulnerable groups, reducing disaster and climate change risks [16].

2.2.5. Recycle Construction Materials Act (HB No. 7044) It is a proposed legislation submitted to the House of Representatives on June 30, 2022. The proposed law shall declare a policy of the State to adopt measures in providing economic incentives and assistance for individuals and entities to establish facilities that recycle CDW as components for building or construction materials. It also aims to reduce CDW through granting of the following incentives: import tax exemptions for equipment used in recycling CDW, tax credits in purchasing CDW recycling equipment, tax exemptions on donations to people and entities involved in recycling CDW, directing of government-owned banks in financing businesses related to CDW recycling and giving financial grants to LGUs with approved programs for CDW recycling [17].

2.3. Recent Global CDWM Policies

The issue of CDW is a common problem across the globe. Most developed countries realized the severity of CDW and have advocated for more sustainable construction and waste minimization in the industry. Some of the best policies implemented recently to combat the issue of CDW are presented in Table 1.

3.1. SLR Search Strategy

As recommended by Kitchenham and Charters, multiple electronic sources were used to search for relevant primary publications [25]. The search strategy was conducted on reputable journals related to CDWM published by Science Direct, Taylor and Francis, Emerald Insight, and ASCE Library. The keywords used in the preliminary search stage include construction waste, waste management, and demolition waste. There will be no time boundary restraint for the publication dates of related research. The review will focus only on research articles and exclude gray literature such as conference proceedings, thesis, and books.

3.2. SLR Selection Criteria

Following the preliminary search stage, there will be a filtering process to select relevant articles based on their titles and abstracts. Kitchenham and Charters outline the inclusion/exclusion criteria and quality assessment [25]. The filtering process began with the title and abstract of the articles. The quality evaluation included a full-text content and relevance check. The final selection includes only articles on the English language for practical reasons.

3.3. Data Extraction and Synthesis

After the final article sample was completed, the author read each article, and the contents relevant to emerging CDW management strategies were coded to establish a systematic classification. This approach established the main themes of the existing literature relevant to CDW management.

4.1. Information Technology Based

With the increasing technological advancement, CDWM can benefit from the recent advances, particularly in the digitalization of the construction process. Emerging IT-based processes and methods such as building information modeling (BIM), simulation techniques, and big data (BD) provides evidence in CDW minimization and management.

Figure 5. Conceptual framework of CDWM strategies. Construction waste generation must be accurately quantified before implementing waste management strategies. BIM is a new technology that has sparked widespread interest and has emerged as a critical solution in CDWM [32]. BIM has been considered a front-runner tool in CDW estimation and quantification [29]. CDW estimation capabilities based on BIM guide CDWM, particularly in disposal scheduling, cost estimation, on-site reuse, and waste bin allocation [26]. An information management system on CDW can also be generated using BIM to harmonize CDW data, such as quantification and source identification. Decision-makers can benefit from information on regional waste generation in developing more realistic policies, determining the location of new waste facilities, and allocating labor and tracking resources. Quantification at the project level refers to forecasting the production of construction waste in a specific project. It can assist project managers in adjusting the material purchase schedule, arranging proper on-site stockpiling, and determining the potential waste recycling benefit and disposal cost to the client [29]. Another IT-based strategy uses simulation modeling techniques such as Systems Dynamics to perform what-if scenarios regarding CDW policies to aid decision-making [33, 63]. On-site waste management is difficult and time-consuming. The simulation model was developed using system dynamics, a comprehensive approach. It has been demonstrated that simulation modeling can identify complex scenarios' effects and ultimately indicates that increasing on-site sorting positively impacts public filling [31]. Construction site methods can also be simulated to analyze waste generation and prevent CDW-generating activities [30].

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Table 2. Classification of CDWM strategies from SLR data synthesis Classification

BIM-based CDW information management system, CDW quantification, CDW estimation to streamline decision making, planning of concrete and drywall waste reuse and recycling throughout construction projects, CDW disposal planning & scheduling, disposal cost estimation planning, BIM-enabled building waste analysis (BWA) Big data-assisted CDW quantification and source identification Simulation-based methods for prevention/reduction of CDW generation and CDW management policies Policy-based Building Waste Assessment Score (BWAS) Construction Waste Disposal Charging Scheme (CWDCS) Legislation to penalize or incentivize CDW initiatives Establishment of product standards for recycled CDW Site Waste Management Plan (SWMP) Environmental Management Systems (EMS) and Green Building Standards (GBS) Design based Promotion of the usage of durable materials Use of modular/prefabrication/off-site/IBS construction Design for deconstruction/disassembly Design for the use of recycled CDW Design optimization to minimize material consumption Life Cycle Assessment (LCA), Life Cycle Costing (LCC) Operations based Application of lean construction principles Application of Circular Economy (CE) principles Utilization of Reverse Logistics (RL) Off-site CDW sorting On-site CDW sorting Knowledge-based Increase CDW awareness and promotion Establishment of CDW research center for CDW technology initiatives Training of personnel to ensure quality and eliminate reworks and CDW Procurement based Green procurement Contractual provisions for CWD management Construction project bidding agency qualification measures

CDWM: Construction and demolition waste management; CDW: Construction and demolition waste; BWA: BIM-enabled building waste analysis.

Most research about CDW mentions the problems of the lack of CDW data. Waste forecasting is a complex learning process involving objective and subjective data interpretation. Nonetheless, it is necessary to forecast CDW quantities on-site using an up-to-date method [31]. Big data is a technology used to analyze massive amounts of data generated by CDW to resolve management issues. It can be used to establish a CDW database to aid CDW initiatives such as CDW quantification and CDW source identification. These data can then be used in performing advanced analysis such as Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) in the design stage to optimize the design and help in minimizing the generated CDW [32].

4.2. Policy Based

Several countries have initiated government-led policies regarding CDW including China and the USA. These policies involve legislation and standards related to CDW. Legislations are further divided into penalty-based and incentive-based policies. Many countries have widely adopted the Polluter-Pays-Principle (PPP) enacted under environmental law, which holds polluters accountable for adverse environmental impacts. In the construction industry, the PPP puts economic restraints on contractors to implement waste-reduction measures such as recycling and waste segregation as part of the

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construction processes [38]. One policy is the Construction Waste Disposal Charging Scheme (CWDCS) implemented in Hong Kong. CWDCS encourages waste generators to optimize the 3Rs practices over disposal. Upon implementation, the amount of CDW disposed of in landfills decreased by approximately 40% from 6600 tpd in 2005 to around 4000 tpd in 2006 [38]. However, strict implementation should be used and safeguarded due to the risk of illegal CDW dumping to avoid paying discharge fees [34]. The implementation of mandatory policies related to construction, such as EMS [40], strict implementation of SWMP [42], and a building requirement for BWAS [35], helped to implement agencies monitoring construction activities in regulating CDW generation and compliance. Among the ISO 14001 EMS requirements is the monitoring and control of consequential impacts of the construction process and the fulfillment of lawful accountability concerning environmental aspects of such activities [27]. SWMP encourages contractors to effectively manage construction waste on construction sites through adequate waste planning, monitoring, and reporting and reduce illegal construction waste transportation and disposal. This instrument is used in several countries/regions, including the UK, Hong Kong, Australia, the USA, Japan, and Singapore [37]. Green building standards (GBS) frequently include CDWM provisions, promoting CDW reduction and recovery. Criteria points can be obtained by achieving the prescribed CDW parameters and targets using recycled CDW. Cities in China have started implementing GBS to regulate the capacity of landfills by mandating the use of recycled CDW and promoting CDW segregation [40]. Establishing approved product standards in the use of recycled CDW fostered the increased marketability of CDW as alternative building materials, and some countries increased the tax on raw materials to promote the use of recycled CDW. The recycling product certification label can boost consumer confidence, increase recycled product sales, and ensure the recycling industry chain runs smoothly. Contractors are also more willing to use certified recycled products. The European Commission has created a technical specification called EN 12620:20 02 + A1:2008 to encourage using secondary recycled materials as aggregates. Japan devised a set of standards for using recovered and recycled aggregate as filler construction material, which led to an increase in the recycling rate of more than 97% [40].

4.3. Design Based

Many researchers have argued that much construction waste is generated due to poor design considerations [35]. CDW reduction during the pre-construction phase reduces CDW generation during the construction phase by optimizing the design through innovative technologies and sustainable construction materials, resulting in decreased resource consumption and more empowered environmental protection.

The construction industry continues to rely heavily on traditional building technologies such as cast-in-situ, timber formwork, plastering, and painting. As a result, the construction process is highly labor intensive. This, combined with poor quality and the overuse of multi-layered subcontractors, impedes management control and results in excessive waste from construction activities. Specifying innovative technologies and methodologies in the design will aid in reducing CDW generation. Modern Methods of Construction (MMC), such as prefabrication and IBS, are some innovative methods the designer can specify. Plastering waste can be reduced by up to 100% using prefabrication methods. Timber formwork has the potential to reduce waste by 73.91% to 86.87%. Concrete waste can be reduced by approximately 51.47% to 60%. Steel bar waste can be reduced from 35% to 55.52% [49]. An Industrial Building System (IBS) can reduce the waste generation rate (WGR) from 4.8 tons/100sq.m to 1.55 tons/sqm compared to the conventional cast in-situ methodologies [47]. Deconstruction is the process of fully or partially separating the building parts to facilitate the reuse and recycling of materials. The design for the deconstruction method anticipates producing the least waste at the end of each building's lifespan [55]. Designing for flexibility and adaptability reduces the risk of CDW generation. Buildings should be designed to optimize the geographical location and design flexibility to accommodate interior space reconstruction and disassembly. This further suggests that proper documentation's role in the design stage should include provisions for deconstruction plans [45]. The consideration during design for deconstruction/disassembly using offsite methods yielded favorable results to minimize demolition wastes [50]. Material optimization during design to reduce resource consumption. This includes optimizing design sections and rebar usage in terms of length, weight, quantity, and cutting using BIM-based methods [30]. Substandard materials can easily break away during construction, necessitating replacement, which may often necessitate the destruction of other parts of the structure. The use of approved materials can reduce wastage due to cutting. Similarly, choosing resistant materials will eliminate repairs and replacement [45].

4.4. Operations Based

The construction stage includes construction execution, material deliveries, site management, and logistics management. CDW is generated due to errors in these processes and poor communication and execution. Many process improvement techniques are available for construction implementation. Lean construction is a technique for reducing waste and increasing productivity in the construction industry. Researchers believe adopting leanbased methodologies and tools will reduce all forms of CDW because lean entails refocusing on the construction process and creating value through process improvement [54].

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The lean concept of Just-In-Time (JIT) in material handling and delivery reduces the risk of material wastage during operations [52]. In the modular construction industry, value stream mapping is used to identify waste. To improve the identified waste-generating processes, lean principles in the form of the 5S (sort, straighten, shine, standardize, and sustain) were applied [53]. The establishment of sorting facilities for CDW improved the flow of waste management. Launching off-site CDW facilities in Hong Kong for separating and sorting construction waste before final disposal significantly reduces the depreciation of existing landfills for receiving and processing construction waste [59]. CDW segregation is a crucial part of project site management practice for reducing CDW. Recycling, as a waste-management strategy, necessitates the separation of recyclable and non-recyclable waste during the construction stage [60]. Site sorting has received much attention in the UK because it simplifies recycling operations and accurately separates inert and non-inert materials. There is a chance that the materials will be reused on-site in waste skips or for other projects if these practices are followed [50]. On-site CDW sorting could boost reuse and recycling rates while significantly lowering construction waste transportation and disposal costs. Construction waste sorting can potentially extend the life of landfills designed for or receiving non-inert CDW [60]. The concept of circular economy (CE) involves resource consumption. Infrastructure and construction projects are the primary end-users of this consumption [56]. CE aims to reduce resource consumption, pollution emissions, CDW generation, and environmental impacts and provide social benefits [55]. Most mineral resources are consumed during construction activities, and most are discarded as CDW during end-of-life. The transition to a more circular economy, where output flows can be reintegrated as secondary resources, appears to be a promising solution for the construction industry [34]. CE concepts such as disassembly, reuse, and flexibility are critical components of circular construction. Suppliers manufacture these parts precisely to order specifications, minimizing material and waste on the construction site. This involves promoting secondary materials from recycled and recovered CDW as materials for new construction by increasing its competitive value and quality to compete with raw materials [56]. Reverse Logistics (RL) is the method of organising, integrating, and monitoring the continuous flow of generated waste from the point of generation to final disposal to recapture value (RL). As a result, selecting an RL method is an essential part of an action strategy for effective CDWM [57]. RL can drive sustainable performance in the construction industries (CI) by guaranteeing the adequate supply of raw materials, warehouse processing, finished inventory, and related information needed for recapturing or creating value, as well as proper waste disposal [58]. RL can help with waste management, selective demolition, and using recovered materials in construction, reinforcing responsible and sustainable behavior [57].

4.5. Knowledge-Based

The lack of proper knowledge and awareness of the effects of CDW remains a significant concern in the industry. The Chinese government in Shenzhen realized that raising awareness about CWM is one of the keys to waste reduction. Since 2007, the government has launched a set of promotional activities for the general public and stakeholders, training for construction professionals and the workforce to raise awareness and establishing awards to encourage active participation from both the public and private sectors [61]. The lack of public awareness in the recycling industry is also a challenge. Increasing public perception towards CDWM and recycling can be enhanced through demonstrations and publicity measures. Using recycled aggregate in three road projects in Belgium helped boost consumer confidence in recycled products. Shenzhen conducted 14 project expositions in China that extensively utilized recycled CDW products as the primary material in pavement constructions and drainage applications [40]. CDW can be generated due to a lack of proper training for construction workers regarding waste generation and resource consumption resulting in collective massive waste generation, particularly in concrete, masonry, and steel works. Introducing proper training and awareness programs will help develop a zero CDW attitude throughout the construction cycle [54, 40]. Another effective way to reduce waste generation is through education and training. The effectiveness of CDWM strategies can be increased by educating construction professionals about CDW minimization strategies, emphasizing the benefits of profit maximization, and instilling in all employees that CDWM is as important as time, cost, quality, and safety issues in construction projects [54]. A CDWM and recycling information platform can help to reduce misinformation and knowledge gaps between the recycling industry and construction stakeholders. To promote CDW reuse as renewable materials, Japan launched an information platform that has provided information about CDW and building aggregates [40]. According to a study, lacking training is a significant barrier to effective waste minimization. In professional development, waste minimization strategies should be included to improve the knowledge base, particularly in CDW innovation and technology [45]. Establishing a research center focused on CDW management, including developing recycled CDW as construction materials, segregation and sorting methods, and CDW quantifications and source identifications will initiate collective efforts in combating CDW generation and improving CDW minimization [61]. Since 2007, there has been a significant increase in CDWM research funding in China. The study covers various subject matters, including using recycled materials from CDW, Shenzhen CDWM guidelines, and Shenzhen clay waste landfill strategic planning [61].

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4.6. Procurement Based

CDW generation can occur during the construction project procurement (bidding process) and material procurement. Implementing a more innovative procurement process is a step toward a circular economy. China began implementing innovative procurement through a relational contract that included mechanisms to protect both parties' interests and a transparent information-sharing platform. Including CDW management contractual provisions as a requirement for prospective bidders can aid in strict compliance and implementing CDW minimization policies [55]. Adding compliance to EMS for contractors will provide a positive view on implementing CDW management policies during execution [22]. Contract revisions which include a compulsory site waste management plan (SWMP), incentives for effective implementation of SWMP, penalties for violations, mandatory application of Green Building Index (GBI), and scrutiny of sub-contractors in managing waste effectively, can be adopted to promote CDW management during procurement process [36]. The Netherlands started to apply green procurement, also known as sustainable procurement, by acknowledging the utilization of secondary materials as a point of evaluation during the procurement process's initial planning stages. During the award of the construction project, the core sustainable public procurement criteria require the contractor to apply appropriate waste reduction and recovery initiatives [51, 64].

ditionally, it is recommended that further research is needed in terms of studies targeting the possible adoption of any of these current CDW management strategies in the Philippine context to identify the compatibility, facilitators, and barriers that will affect the adoption of the said strategies.