Keywords

1 Introduction

The global economy is only 7.2% circular due to rising material extraction and use, leaving fewer materials to cycle back into the economy [1]. In the last fifteen years, the annual global extraction of materials grew from 27 to 92 billion tons [2]. 70% of global greenhouse gas (GHG) emissions, over 90% of global biodiversity loss, and water stress are tied to material handling and use [1]. The highlight is in the category of non-metallic minerals, which includes most building materials, such as sand, gravel, and clay. Globally, the construction sector accounts for almost 50% of resource extraction [3], and 40% of global waste generation [4].

The continuous accumulation of materials in cities in the form of built environment stocks has led to the prospects of urban mining for secondary materials that can be looped back into the economy [5]. The concept of circular economy (CE) has shown promise toward resource sustainability while material flow assessment support in estimating the scale at which a circularity potential exists [6, 7]. Using a lifecycle approach, it has been estimated that a 10–20% reduction in GHG emissions could be achieved through waste prevention, landfill mitigation, and other types of solid waste management [4].

Sustainability in the construction industry requires moving beyond waste management and focusing on building components management [8]. Yet, urban mining of the built environment remains less explored, driven by long lifetimes, and bulky and heavy materials of buildings and infrastructures [5]. However, there has been an increase in the studies analyzing material stock and flows and producing insights on the scale of in-use materials and waste outflows [6, 7]. In addition, public authorities’ involvement is seen as an effective mechanism to promote a circular built environment [9]. If materials embodied in demolition waste flows are reused, it can help reduce the environmental pressure related to the extraction of virgin resources, which relies on the proper management of waste flows and supply chains [10].

The European Commission and several national governments have formulated strategies exalting circularity. In Portugal, the regard and protection of historical and artistic glazed tiles (called “azulejo”) became mandatory in Portuguese cities with the Portuguese Law No. 79/2017, representing an advance in terms of the protection of the Portuguese glazed tiles’ heritage [11]. In the city of Porto, for example, the Materials Bank of the Porto City Council (MB) proposes mechanisms to protect the tile heritage in urban operations. The MB is intended for the storage, preservation, restoration, and return of tile items to the city in the rehabilitation of façades of historic buildings [12].

However, the inventory of traditional Portuguese glazed tiles is scarce and not integrated with other heritage inventories [11]. In addition, the resources for carrying out the Bank's activities are restricted, and common citizens and institutions do generally not value artistic glazed tiles [13]. The result is needless glazed tile removal, demolitions of azulejo-covered buildings, vandalism, and glazed tiles conservation needs [11].

This study seeks to analyze how the flow of processes occurs in the MB, with guidance on procedures for the recovery and reuse of historic Porto tiles and other identity elements. The study seeks to clarify how the MB organizes and manages the realization of its value proposition recovering and reusing non-structural demolition waste. For the authors, it is the first time that this type of flow analysis has been carried out, and the research is the first step in mapping what already exists. It also seeks to understand the opportunity to expand the collaboration and scope of the Materials Bank, to optimize a methodology to coordinate and accelerate recovering of traditional glazed tiles, which will enable stakeholders to constructively engage and play their part in enabling the reused of secondary materials and in the preservation of Porto cultural heritage.

2 Background

2.1 Reuse of Buildings’ Materials Stock

Component reuse in buildings is the process where the building parts are dismantled during deconstruction and are reused in new lifecycles and contexts, without any type of requalification or reprocessing operation [14]. Despite environmental superiority, the systemic reuse of building components is still far from reality [7]. Most construction and demolition waste is either recycled off-site, landfilled, or used for road construction, which is more useful than landfilling but has a higher risk of environmental leakage [10]. In this way, urban mining is a strategic component of circularity or sustainability aiming the resource efficiency use [15].

Different approaches and deconstruction processes to recover buildings’ materials and components can be followed in urban mining [16]. Technical, regulatory, and policy considerations, including labor requirements, as well as the market demand needed to be considered in this practice [17]. However, information on deconstruction projects and the own deconstruction process are limited, mainly because is not attractive in terms of cost and time and by the uncertainties surrounding the markets for secondary materials [16]. With the absence of building components reuse and the lack of a building components reuse market, contractors prefer traditional demolition to the deconstruction process [17].

Experimentally, deconstruction costs could be 17–25% higher than demolition costs, considering the prospects of selling salvaged building components, avoided disposal costs, and additional labor costs [18]. Tatiya et al. [19] proposed that lower net deconstruction costs than the costs of demolition could be achieved primarily based on the sale of recovered materials. Arora et al. [7] developed a methodology to estimate the potential of urban mining of public housing developments, evidencing regulatory requirements for deconstruction and the need to accommodate the uprising of circular business models and define old, yet reusable products/materials or building components out of the concept of waste. Yet, the ease of recovering the same building component varies from site to site within a building itself and hence the combined recovery and reuse potential is based on many onsite experimental exercises of urban mining [7].

To minimize costs and time effects on the deconstruction process, it is important to know the number and features of materials that are stocked in buildings. The Urban Mining and Recycling unit project is a temporary storage of materials and a laboratory that monitors and evaluates the circular potential of materials through an online platform [20]. Cai and Waldmann [21] proposed a database/bank of materials and components based on Building Information Modelling (BIM) to promote the reusing and recycling of materials. Although these initiatives, information on the material composition of older construction projects often lacking or incomplete, and those projects were not designed for disassembly [5]. A detailed understanding of the composition, quantity, and spatial distribution of materials stored in buildings in the built environment is required [5].

The development of material passports for information on the type and quantity of materials used in a building aims at increasing the circularity potential of buildings [22]. For historical buildings, it is essential to develop digital inventories to allow the heritage management process, including identification; research and analysis; heritage impact assessment; planning for conservation, and management activities; and providing information to the public, authorities, and decision-makers [11]. However, the existing Portuguese digital heritage inventory has an incomplete database or lacks the georeferenced location of the building or structure where the glazed tiles are applied [11].

2.2 Protection and Safeguarding of Porto Glazed Tile Cultural Heritage

The traditional glazed tile is a secular element of material culture and a heritage rightly considered one of the country’s most distinctive art forms [11, 13]. Introduced by the Arabs to the Iberian Peninsula and in Portugal in the sixteenth century, azulejos can be found on both the interior and exterior of churches, palaces, houses, and bars around Portugal, playing a decorative role, serving to control the temperature, or depicting stories about Portuguese history, religion, and culture [13]. In the nineteenth century, ceramic factories opened in Porto and Lisbon to mass-produce several patterns of glazed tiles [11]

In Portugal started in 2007 the “SOS Azulejo” project mentored by the Portuguese Judiciary Police Museum. The project was created with a global approach and a strategic line for the effective protection of Portuguese historic and artistic glazed tiles, preventing art and antique burglary and trafficking [13]. In 2017, the initiative managed to create the “National Day of Azulejo” to raise awareness of the importance of the Portuguese historical and artistic tile heritage [13].

In 2017, after requests from the “SOS Azulejo” project, Law No. 79/2017 was instituted, which prohibits the demolition of buildings covered with tiles and/or the removal of tiles from the façades. In 2009, based on these movements, the Porto Materials Bank (MB), implemented nearly two decades ago, was restructured, and underwent numerous institutional changes as a public policy to protect the tile heritage of the city of Porto. The MB's principle is to preserve Porto's buildings with their historic tiles—Hispano-Arabic—from patterns from the 17th to the twentieth centuries (Fig. 12.1). Open to the public since 2010, the MB is a pioneer at the national level and has received awards for promoting the safeguarding of materials that characterize the city's image. In addition to tiles, other decorative and constructive elements from buildings in Porto are recovered, including wooden artifacts, iron, and stonework [12].

Fig. 12.1
2 photos. a. A building alongside a street. b. Roof tiles are arranged over a shelf.

Source Authors, 2023

a Façade with stonework, iron, wood, and toponymic plaques on a public road in the city of Porto; b building artifacts shelves—tiles and roof tiles.

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The importance of protecting and restoring Porto's tile heritage was emphasized by changes to the Municipality's Urbanization and Building Legal Regime, with emphasis on Service Order No. I/194083/19/CMP, which determines the obligation to include in the licensing of urban operations with demolition work to descriptive memory, photographic record, architectural survey, or any other method that allows identifying the framework of the demolition proposal [23]. Projects that provide for the demolition of buildings with façades covered in tiles require a technical assessment to grant or reject the demolition and assess the pertinence of removing the tiles for the MB of the demolished building elements [23]. Law No. 79/2017 states that urban operations where the removal of tiles is carried out only for restoration and/or cleaning, and subsequent replacement, will not require a license [24]. Compliance with this law implies, however, the existence of technical teams, protocols, and an integrated national heritage inventory system, which does not exist yet [11].

3 Research Strategy

This study has a qualitative-descriptive approach and uses the case study as a strategy, with bibliographic and documentary research techniques, interviews, and on-site visits. Case studies allow the researcher to develop an in-depth analysis of a case, with a variety of data collection procedures over an extended period [25]. On-site data collection started in August 2022. The case study was carried out at the Materials Bank of the city of Porto, located in the palace of the Viscondes de Balsemão, De Carlos Alberto square, Porto, Portugal. The interviewees were carried out in a non-structured way in the search to know the processes and activities carried out by the unit. Qualitative interviews are intended to elicit views and opinions from the participants [25].

The study aims to analyze how the flow of processes and policy considerations can leverage urban mining in historical buildings/cities. Mapping a process flow can identify activities that need to be improved, deleted, or added, in addition to serving as a parameter for the creation of other banks of recovered materials. The MB is, hierarchically, subordinate to the Municipal Department of Cultural Heritage Management of the city of Porto. The unit has a physical space like an open museum and shares with other chamber units spaces for storing its collection of recovered building materials.

4 Process Flow in the Operation of the Porto Materials Bank

The flow of information for approval of a building rehabilitation project considers Decree-Law No. 555/1999, which provides for the Legal Regime for Urbanization and Building, with amendments to Laws No. 79/2017 and No. 118/2019 that act on “legal regimes for the municipal licensing of urban subdivisions and urbanization works and private works […]” in the search to meet the requirements of safeguarding the public interest with the administrative efficiency to which citizens legitimately aspire [26].

Figure 12.2 presents the process flowchart for the recovery of tiles from urban demolition works used by the MB in Porto. The flowchart was developed according to the information obtained from the MB, following current legislation. The recovery processes of historic artifacts are concentrated in three main agents: (1) the client, a representative of the historic building; (2) the Municipal Directorate of Urban Development (MDUD), which receives the request for urban intervention; and (3) the MB that is an advisory unit in case there are tiles or other historical artifacts for recovery.

Fig. 12.2
A flowchart in the form of a 2 by 2 matrix with columns labeled, the recovery process of historical elements and construction site or building. Rows labeled as M O U D of the client and Material bank. The process starts from Row 1 Column 1, Row 2 Column 1, Row 1 Column 2, and Row 2 Column 2.

Simplified process flowchart of the Porto Materials Bank for the recovery of tiles from historic buildings

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Normally, the recovery of construction elements occurs when the client requests a license for an urban operation involving demolition services. The license is requested from the Legal Regime for Urbanization and Building, following Service Order No. I/194083/19/CMP. With due, attention to tile façades, it is important to highlight the decision to hire a service to survey the tile values identified in Law No. 79/2017.

The technical opinion issued by the MB will guide decision-makers. In the analysis, it is identified whether the dwelling is among the 2860 buildings mapped since 2007, 623 of which are in the urban perimeter. Next, an analysis of the documentation and attached photographs are carried out to identify the patrimonial value of the constructive elements (catalog of types of ceramics, plaster, wood, paper, metal, and other decorative elements—Table 12.1). In the identification of tiles or other elements related to Porto's historical heritage, a georeferenced mapping of the site is carried out, with a subsequent visit to the site. The visit aims to inspect and characterize the possible recovery and restoration elements. The MB team prepares a technical report that is forwarded to the requesting unit. After analysis of the MDUD, technical guidelines are sent to the customer to proceed with the demolition or recovery of the elements.

Table 12.1 Cataloging of items by material category and registered buildings
Full size table

The recovery of historical artifacts can also occur when a degraded building or one in the process of demolition is reported, an activity carried out in partnership with the civil protection of the municipality. It will be up to the MB to guard, preserve, restore, and return the items to the city in the rehabilitation of façades with the same topology, according to the Architectural Heritage Catalog (Table 12.1).

When donating building materials of historic, patrimonial, and cultural value, the MB team evaluates the item for incorporation into the collection, emphasizing historical aspects and productive elements. Next, the artifact is registered with its characteristics and cataloging, design, photographic record, and a label that provides information recorded in the database. Physically, each tile is stored with its proper identification label in custom-made wooden boxes and organized in chronological order on shelves.

It is a critical part of the process of the amount of building elements to be organized and structured for physical and virtual storage in the database. Database planning allows content management with photographic files of the location of the property and the material with its drawings, among other details for retrieving future information. The historical value and the analysis of the data flow behavior in the rescued pieces indicate the structure to organize the information for the team's decision-making.

In addition, MB operates in other activities such as workshops and support for historic building restoration projects; guidance to architecture and construction engineering professionals; mapping of buildings and works that are part of the city's memory and identity; registration, organization, and archive of the constructive elements that tell the history of the city; between others. It should be added that the MB offers educational workshops for young people and children who visit the site.

5 Discussion

The historical and architectural heritage valued in this study is a public policy associated with the CE. The recovery of materials encourages the dismantling of buildings and structures to store or guide reuse, requalification, remanufacturing, or recycling. The tiled façade with its different details represents a tourist asset that adds economic and environmental value to the buildings. The preservation of the historical heritage of cities is a practice of urban sustainability, reducing the extraction of natural resources, the production of GEE, and construction waste; by improving economic models of recovery and reusing materials, and allowing the salvage of building social–historical values.

The presented flowchart allows the MB process to be constantly revisited, enabling critical analysis, identification of failures, and opportunities for improvement [27]. It is possible to keep it updated and optimized for the reality of the organization. In addition, whenever there is a doubt, it is possible to consult the flowchart, ensuring that this information is not lost, facilitating the understanding and standardization of procedures among those involved in the operations of recovery and storage of historical elements.

In the last 10 years, the requalification of historic buildings has changed the economy and revitalized the city, contributing to the culture of preserving existing buildings, instead of demolition. However, the study found the need to enhance proposed projects with solutions to problems related to the abandonment of buildings with historic potential for the city. Partnerships with public and private institutions that support the generation of circular business and favor the MB's priority activity would be necessary. To this end, the knowledge of Law No. 79/2017 on the corresponding value of the tiled façade elements needs to be communicated to the citizens.

The informational flow of the MB's projects, processes, and interests is inventoried as a set of data, files, documents, photographic records, drawings, and notes that allow for guidance in decision-making in the process of managing the city's assets. The technical and legal information delivered by the MB is a consultative action, but not mandatory in the internal processes of the municipality. As for the educational activities carried out by the technicians, it is the action to promote the principles of the circular economy (reduce, reuse, recycle). Training workshops are offered on the restoration of parts, and services to builders, technicians, engineers, and architects to restore, reuse, or recycle building materials, prospecting for teaching about architectural, historical, cultural, and sustainability heritage.

6 Conclusion

The tile is a distinctive element of Portuguese cultural heritage. The protection and safeguarding of this heritage have gained importance in the country, however, the legislative framework is recent and lacks a more robust structure of resources and operational support. Therefore, municipalities need to play a leading role in the development of tools that allow for recovering and properly storing, both physically and digitally, the recovered elements. This study sought to map a process flowchart of the Porto Materials Bank to generate further discussions and reflections on the adopted process.

The flowchart clarifies the processes and related agents to allow the retrieval and storage of historical artifacts. Good process management depends on how well it is understood and documented. Standard operating procedures will help achieve consistency in operations and the pursuit of continual improvement in MB performance measures such as cost, quality, service, and scale. In addition, they provide the reduction of conflicts between those involved in the processes and the sharing of the process with other organizations.

The MB is a physical platform for safeguarding and protecting heritage, allowing the integration and coordination of different types of information (descriptions, location, areas, dates, photos, among others), different types of materials (tiles, tiles, stucco, iron, among others), and the integration of different purposes, such as the preservation of historical heritage, maintenance of Porto's urban image, diversity of interdisciplinary research, communication, and awareness of citizens, and tourism promotion.

Materials in buildings should sustain their value whereas buildings should function as banks of valuable materials and products. Efficient legislation and public policies that promote the reuse and recycling of construction materials and components are required. The joint action of the stakeholders with the government can further promote the Materials Bank development, strengthening the supervision and implementation of the secondary materials market.

The MB establishes opportunities for the reinsertion or reuse of historic artifacts, even on small residential facades. However, there was no monitoring of the volumes, typology, and quantities of materials that are reinserted in buildings, and that impact the reduction of carbon emissions from the built environment. Future studies should assess the environmental impact of the reinsertion of these secondary materials in the buildings.