Zero Waste Systems: Barriers and Measures to Recycling of Construction and Demolition Waste

: Urbanization, population growth, increased consumption, infrastructure, and housing needs are some of the factors that result in increased waste. Recycling has been a crucial way to reduce the amount of materials that end up in disposal sites and is how citizens, more aware of the impacts on the environment, participate in some of the schemes to reduce waste. Zero waste is an approach developed to preserve the ﬁnite resources available, but major barriers are hindering its efﬁcient and effective implementation. This study intended to unveil those barriers in the Costa Rican construction sector and to propose measures to increase the recycling rates. In order to achieve the objective, construction companies, cement producers, waste managers, personnel of refuse material facilities, waste transformers, construction material distributors, and a director of the Ministry of Health were interviewed to determine the challenges in the valorization of concrete, wood, metal, and packaging waste materials. This article reports the ﬁndings, which include, among others, the fact that most construction companies dispose the waste without any separation, except for metals. The cement producer companies do not participate in any form of collection system in spite of the available technology and equipment and the absence of innovative technologies for the transformation of materials.


Introduction
Cities around the world are expanding rapidly due to population growth, with the consequence of an increasing consumption of resources and the production of residues. Municipalities, mostly responsible for waste management, face a burden on the municipal budget caused by the high costs associated with its management [1,2].
Different approaches and tools have been proposed in order to reduce waste. In 1979, Dr. Ad Lansink, introduced the Waste Hierarchy as a simple ranking system used for the different waste management options, according to which is the best for the environment. Its objective is to maximize efficiency in the use of natural resources by means of reducing waste at the source, reusing materials, recycling, energy recovery, and landfilling. In spite of criticism, it has been incorporated in the regulations in different parts of the world [3].
Another concept shaped after a conference in Geneva in 2002 is Zero Waste. This is a set of principles proposing the conservation of all resources by means of responsible production, consumption, reuse, and recovery of products, packaging, and materials without burning and with no discharges to land, water, or air that threaten the environment or human health [4].
Both approaches, as well as others proposed, include recycling as one of the means to reduce the loss of materials in the environment. Nevertheless, achieving Zero Waste in Table 1. Barriers for household waste recycling [9,10]. Companies lack knowledge on modern machinery and technologies to improve and increase production processes Workers at recycling related businesses with low skills There are no detailed statistics on available materials, real savings, or ecological footprint due to recycling Materials cannot be transformed in the country

Construction Sector and the Environment
As cities grow, more investments in infrastructure are needed, as well as housing projects to provide shelter and services to the increasing population. This situation has imposed pressure upon the construction sector [11][12][13][14].
This industry is well known as contributing to a significant percentage of the Gross Domestic Product (GDP) in low-and middle-income countries, providing employment to a substantial portion of the working population. Nevertheless, at the same time it is perceived as a major contributor to environmental degradation, due to its high consumption of natural resources, such as water and energy among others, and the generation of, inter alia, greenhouse gases, waste, waste waters, and dust [15][16][17].
Construction and demolition waste (C&DW) is considered the largest waste flow worldwide and has reached to 30-40% of total waste according to Akhtar and Sarmah [18], while some other scholars have reported higher proportions of C&DW disposed in landfills, as presented in Table 2. USA 20-29 [19,23,24] Australia 20-30 [25] Germany 19 [25] Finland 13-15 [26] Japan/Tokyo 57 [27] Worldwide 13-35 [19,28] C&DW has been extensively studied in developed countries, but few reports are from low-and middle-income countries, such as Costa Rica. Therefore, a study was performed in the country with the participation of fifty-two (52) companies: 30 small, 15 medium, and 7 large firms. They were asked, among others, the types of non-hazardous and hazardous waste produced during the development of their projects. Figures 1 and 2 show the percentage of companies that reported the generation of the specific non-hazardous and hazardous waste streams. The most common non-hazardous materials include cement bags (2-layers kraft paper + polypropylene), pieces of polyvinyl chloride (PVC), electric wires, clean wood, and plastic (high and low density) packaging materials [29]. At the time of the study, the insulation materials were considered as non-hazardous, as mentioned by del Río Merino et al. [30]. On the other hand, polyvinyl chloride (PVC) was at the center of a controversial debate, in which a number of diverging scientific, technical, and economic opinions have expressed that it affects human health and the environment.
The most important hazardous materials consist of metallic and plastic paint containers and paint residues in mixing vessels, textiles impregnated with solvents used to clean surfaces before painting, paintbrushes, and gypsum-based materials, all of which are disposed generally in inadequate disposal sites making it a toxic waste. Asbestos was reportedly not present.
Various studies have analyzed the composition (in percentage) of C&DW, which is presented in Table 3. Concrete and related materials, wood, metal, gypsum, and plaster, as well as packaging materials, are the most abundant ones found in those countries. The most important hazardous materials consist of metallic and plastic paint containers and paint residues in mixing vessels, textiles impregnated with solvents used to clean surfaces before painting, paintbrushes, and gypsum-based materials, all of which are disposed generally in inadequate disposal sites making it a toxic waste. Asbestos was reportedly not present.   The most important hazardous materials consist of metallic and plastic paint containers and paint residues in mixing vessels, textiles impregnated with solvents used to clean surfaces before painting, paintbrushes, and gypsum-based materials, all of which are disposed generally in inadequate disposal sites making it a toxic waste. Asbestos was reportedly not present.

Construction and Demolition Waste Recycling
The amount of C&DW generated in Costa Rica by the industry is also increasing at a rapid rate and the proper management of it is a challenge, particularly in developing countries. Recycling is one of the options to obtain a Zero Waste Activity, but the construction industry is far from reaching sustainability. Therefore, a study was done in order to determine the obstacles faced by the Costa Rican construction sector in order to increase recycling rates for concrete, wood, metal, and packaging materials. The barriers studied are presented in Tables 4-8, which are grouped around technical, financial, social, environmental, and legal aspects. Concrete Canada It is not cost effective to deconstruct and reuse concrete [42] Wood Canada Inadequate management of on-site grading, particularly in the case of preserved wood products [42] Wood Canada Lack of knowledge on treatments options enabling the reuse and recycling of preserved wood [42] Wood Canada Absence of infrastructure for the collection, transport, storage, and preparation of preserved or untreated wood [42] Steel Canada Complications of reusing building components in "as is" condition [42] Wood Norway The barrier is related to form, strength, and contaminations [42] Concrete Norway Removal of paint in concrete is costly therefore it is sent to special disposal sites [42] Concrete Norway Construction companies might not have the equipment to separate concrete from the reinforcing bars [42] Concrete Norway New road projects consider recycled concrete to be of low quality, despite evidence showing the contrary [42] Kraft paper packaging N.I. Bags impregnated with cement causes conventional paper recycling to be impossible [43] N.I. not indicated. Table 5. Barriers to recycling of C&DW according to financial aspects.

Concrete European Union
Funding problems for research on alternatives to optimize existing options for recycling [41] Concrete Canada Recycled aggregates are considered of low quality, therefore it should have a lower price [41] General N.I. Lack of funding to implement circular economy in C&DW management [41] General N.I. Construction costs do not reflect environmental costs [42] General N.I. Lack of time for C&DW separation [42] General N.I. Absence of contractual requirements for the reuse and recycling of materials [42] General N.I. Reluctance to segregate for recycling and re-using materials with a low economic value or difficult to reuse [42] General N.I. Perspective that C&DW management are not cost-effective [42] Wood Canada Infrastructure for timber recycling is considered costly [42] Concrete Japan It is more costly and energy-intensive to produce aggregates from recycled concrete than from virgin raw materials [42] Concrete Norway The cost of virgin gravel can be cheaper than recycled aggregate when the transportation and storage costs are added [42] Concrete USA Recycling plants are not always available near demolition sites and sometimes charge a fee to process the demolition waste; it is cheaper to transport waste to the landfills [42] General N.I. Priority is given to economic benefits and not to environmental aspects [42] General N.I. Lack of financial incentives for reduction or recycling of C&DW [42] N.I. not indicated. Table 6. Barriers to recycling of C&DW according to social aspects.

Material Location Barrier Source
General N.I. Attitude of constructors toward C&DW [44][45][46] General N.I. User preference for new over reused or recycled materials [45,47] General N.I. Construction industry culture [44] General N.I. Lack of a well-developed C&DW recycling market [42,48] General N.I. Low customer demand for sustainable buildings [49] General N.I. Difficulty to modify labor practices [48] General N.I. Belief that efforts will not be sufficient to eliminate C&DW completely [12] N.I. not indicated. Table 7. Barriers to recycling of C&DW according to environmental aspects.

Material Location Barrier Source
Concrete European Union Deficiencies in the planning, design, renovation, and deconstruction processes hinder the "zero discharge" target [41] General N.I. Inefficient processes of dismantling, classification, transport, and recovery of C&DW [42,44,50] General N.I. C&DW reduction does not receive sufficient attention in construction planning and design [49,50] General N.I. Limited use of recyclable materials in construction [50] General N.I. Unfriendly methods in the construction and demolition processes [46,47,51,52] General N.I. Landfilling is preferred due to the lack of incentives for other treatments [47,53,54] General N.I. Lack of Extended Producer Responsibility for construction materials [55,56] General N.I. Complexity for the transformation of the sector into a circular economy model of production and consumption [45,46,56] General N.I. Lack of knowledge and awareness related to the management of C&DW [44,47,56] General N.I. No benefits for sorting packaging materials [44] General N.I. Lack of integration of sustainable C&DW management [56] General N.I. Uncertainty in moving toward circular economy in C&DW management [45,56] General N.I. Lack of certainty on the status of the C&DW [42,44] N.I. not indicated. Table 8. Barriers to recycling of C&DW according to legal aspects.

Material Location Barrier Source
Concrete European Union Insufficient regulation support prohibiting the disposal of C&DW in dumps or landfills, so there is less encouragement to recycle it [41] Concrete European Union Deficiencies in certifications demonstrating that recycled concrete complies with standards and can meet the same properties as virgin materials [41] General N.I. Inadequate regulations and enforcement for C&DW [47,48,55,57,58] General N.I. Lack of clear C&DW national goals, objectives, and vision [46,54,59] General N.I. Lack of standardized reporting and accessible data on C&DW reduction [12,46] General N.I. Contractors lacking economic penalizing methods for C&DW management [48] General N.I. Lack of coordination among stakeholders of construction sector [49] General N.I. Inconsistencies between different governmental institutions [49] General N.I. Absence of industry standards or performance standards for C&WM [60] General N.I. Individual responsibilities in terms of waste management are poorly defined [60] General N.I. Lack of enforcement of construction and waste management policies and plans [48] Wood Japan The recycling policy is not complied with, as the preference is to use wood as an energy resource rather than to recycle [42] N.I. not indicated.
This article reports the findings and provides some ideas on how to overcome these barriers.

Materials and Methods
This study had the aim to determine the barriers different stakeholders from the construction sector face in order to reduce C&DW by means of recycling. It also intended to provide some actions that would increase recycling rates. In order to obtain information, the literature provided an overview of the reported barriers affecting household waste recycling as well as C&DW. A questionnaire for different stakeholders of the construction sector was prepared based on the information gathered and sent to thirty contractors (30) of small, middle, and big size construction companies. Another one was planned for the only two (2) cement producers, which are part of multi-national companies from Mexico and Switzerland as well as another one adapted for twenty-five (25) waste managers along with two (2) refuse material facilities, all registered at the Ministry of Health with a permit to manage specific types of waste. Additionally, a survey was prepared to be applied to nine (9) waste transformers utilizing construction waste for recycling purposes, three (3) cement, wood, and metal distributors to determine environmental practices within the company toward recycling and one (1) director of the Ministry of Health to determine the vision and support toward C&DW recycling.
The questionnaire contained questions that covered a number of topics: general information about their business, questions related to the recovery of construction and demolition waste, the technical, financial, social, environmental, and legal barriers faced by their organizations, and ideas on how to overcome them, according to their point of view. Prior to the data collection, the survey instrument was pre-tested for ease of understanding and content validity. Suggestions to improve the tool were included as recommended.
Efforts were made to ensure high response rates from respondents, especially due to the fact that, the research was performed during the COVID-19 pandemic. These included telephone follow-ups, e-mails with reminders, interviews, and site visits (when possible). The responses were obtained from a total of ten (10) construction companies, eleven (11) waste managers (5 related to wood, 3 to metals, and 3 to concrete), two (2) cement-producing companies, six (6) waste transformers, and one (1) material refuse center.
An interview was prepared for the director of the Ministry of Health in which the main topics presented were related to the Costa Rican legislation in regard to waste in general and C&DW, barriers for recycling from the normative point of view, and the support the Ministry provides to enable the environment to increase C&DW recycling rates.

Results and Discussion
The number of responses received does not necessarily allow for generalizations but permits the determination of the challenges different stakeholders face in relation to C&DW recycling toward a Zero Waste System. However, an individual perspective is provided on each of the actors involved.

Construction Companies
Ten construction companies provided information in which most of them dispose wastes without any separation, except for metals, due to their value in the market, especially steel, iron, and aluminum. Four respondents mentioned the separation of concrete waste to be used within the project and half of them reuse wood in the same or other projects as formwork. Packaging materials sometimes are utilized to fill up hollow concrete blocks as a way to reduce the waste sent to the disposal sites.

Cement Producing Companies
Two companies produce cement in Costa Rica. Both stated being aware of the waste produced from their products and having a collection system for their packaging materials; however, the latter functions mainly under contracts between the cement companies and big construction firms. This practice is the result of the obligation, for the contractors, to have a proper waste management system in order to participate in public tenders. The waste collected becomes alternative fuel in the cement kilns. Small and medium companies and hardware shops do not participate in any form of collection system in spite of the available technology and equipment.

Concrete Managers
Three concrete managers responded to the questionnaire. One of the respondents expressed they collected the waste and disposed it in a landfill. Another one indicated they classified the waste into two categories: clean or contaminated. In case of clean material, it was used as covering material in landfills, while the contaminated one was disposed in a fixed place of the landfills. The third company informed the concrete waste was not properly separated because that required more labor, thus increasing construction costs; therefore, they preferred to send it to a landfill.

Wood Managers
Four wood managers provided answers to the questionnaires. Each company, respectively, pointed out the lack of innovative solutions for this type of waste. Efforts have been made to reduce it but the cost to remove nails, concrete, and other materials increases the expenses of the treatment. In some cases, wood is used as fuel for kilns in the cement companies; in others, it is chipped and used as soil amendment or pelleted for fuel.

Metal Managers
Three metal managers reported the collection and separation of copper, bronze, steel, aluminum, and other metal scrap to be exported mainly to Asia and other countries in Europe and America.

Packaging Materials
No organization was found to manage packaging materials from the construction and demolition sector.

Material Transformation Facilities
Material transformation organizations are mainly micro and small enterprises facing many financial, institutional, technical, and socio-cultural challenges. They mentioned the burdens faced in order to transform materials from the construction and demolition sector. Access to credits and modern transformation technology among others are critical barriers to be more effective in recycling those wastes.

Distributors of Construction Materials
Only one company responded to the information requested and indicated that there is no extended responsibility for the materials they bring into the market. As a result, their participation in the management of the associated wastes is null.

Governmental Office
The congress of Costa Rica passed the National Waste Management Law in 2010, but it still lacks specific regulations for C&DW. Therefore, there is no incentive for the companies to implement the efficient use of materials and good treatment practices.

Materials Reused and/or Recycled in Costa Rica
During the study it was found that the only materials reused are clean and painted wood to be used as formwork or scafoldings. The removed soil is used for gardening if it is not polluted.
Most of the metals are exported to Europe, Asia, North America, and some are recycled in the country. A diversity of plastic materials from packaging are transformed as recycled resins. They are mostly High-Density Polyethylene (HDPE), Low-Density Polyethylene (LDPE), and Polypropylene (PP). In less quantities, they are Polyvinyl Chloride (PVC or Vinyl), Polyvinyl Chloride (PVC), and Polystyrene (PS or Styrofoam) on an experimental recycling development stage. Polyethylene Terephthalate (PET or PETE) is mostly exported.

Technical Barriers
It was found that the starting point of the low rate of recycling of C&DW is the fact that the designs of buildings do not consider the end of life. Once the waste is produced, the separation at the source is difficult, costly, and inadequate. There are deficiencies in the research in order to treat and recycle the concrete, wood, and packaging material. Metals are an exception due to the price in the international markets. Additionally, there is an absence of infrastructure and equipment for the separation at the source.

Financial Barriers
The construction companies have the perception that C&DW management is not cost-effective and that priority is given to economic benefits not to environmental aspects. The construction costs do not reflect environmental costs; it is cheaper to transport waste to the landfills. Additionally, funding research on the implementation of circular economy and alternatives to optimize existing options for recycling is difficult. In the country, it is more costly and energy-intensive to produce aggregates from recycled concrete than from virgin raw materials, the cost of virgin gravel can be cheaper than recycled aggregate when the transportation and storage costs are added. The market for recycled materials is not well developed.

Environmental Barriers
The country has promoted the principle of Extended Producer Responsibility for materials declared of special management but not yet to any construction material. The directors of construction companies lack knowledge and awareness related to the management of C&DW. Sustainable construction is still at an initial stage.

Social
Clients do not demand sustainable buildings. The construction industry as a whole has a culture in which they belief that efforts will not be sufficient to eliminate C&DW completely. The workers at the construction sites resist modifying their construction practices.

Legal
There is a national law related to waste in general but there are inadequate regulations and enforcement for C&DW. It is easier to dispose C&DW in dumps or landfills than find opportunities for reuse or recycle. Contractors lack penalizing methods for C&DW management. The country is lacking clear C&DW national goals, objectives, and vision.

Measures Proposed for the Valorization of C&DW
The questionnaire included items in relation to measures the organizations would propose to valorize the waste produced. These are summarized below as technical, fiancial, environmental, social, and legal measures. Update the legal requirements to be more flexible for the collection and processing of waste materials.

•
Propose the inclusion of the informal collection sector into the simplified Tax Regime and eliminate the obligation to pay taxes when the transaction is lower than a threshold.

Conclusions
Zero Waste proposes the conservation of all resources by different means, one of them being the recycling of wasted products. Nevertheless, there are limiting factors and barriers that hinder performance regarding C&DW management. Understanding the barriers that limit the recycling of C&DW can promote the development of solutions that are technically safe, economically viable, environmentally sound, and socially and legally accepted.
The barriers found in Costa Rica have as well been reported by other authors and presented on Tables 4-8. They have been presented to the ministries of Economic Affairs, Health, Finances, Environment, and the construction sector with the objective to determine paths to reduce or eliminate them with the objective to promote circular economy for the sector.
Efforts are being made in the country to start the use of C&DW as base for roads, as well as to increase the recycling rate of materials that can be transformed in the country.
In Costa Rica, the challenges for an efficient and effective C&DW management require the participation of different stakeholders. The construction sector must adopt responsibility for the environmental impact of their processes and materials chosen for their products. The government must provide an enabling environment by promoting legislation and removing the barriers that would cause the activity to have less impact on the environment. The customers must be aware of their responsibility for their choices of materials, construction processes, and the end of life of the waste produced.
Universities and research centers can promote innovation incorporating new ideas for recycled products and processes, which can generate changes. Nevertheless, those products and processes should be developed according to the respective legislation in the country.
Contractors, manufacturers, distributors, and vendors of construction materials and products are not obliged in Costa Rica to adopt any responsibility for the end of life of their products. Extended Producer Responsibility (EPR) could be a policy to encourage the construction sector to reduce the environmental burden of C&DW. At this moment, the country has 14 types of waste under EPR voluntarily agreements, but none correspond to C&DW. Institutional Review Board Statement: During the analysis of proposals, it was determined that the study did not need an Ethics Committee evaluation since the information requested did not involve sensitive data. The questionnaires stated in the introduction of the tools the following: "Your . . . (organization, municipality, institution, company) play an extremely important role in the recycling chain in our country, but at the same time it faces great financial, institutional and technical challenges. These can be seen as barriers to increasing the collection of waste materials. The purpose of the following survey, is to determine the factors or barriers that affect the work your" (organization, municipality, institution, company) do.
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.