The most sustainable source of natural resources lies not under the ground, but within our buildings. Urban mining — the process of recovering and reusing a city’s materials — allows us to tap into the resource mines of existing buildings for new construction rather than extracting materials from virgin sources. In this article, we explore the benefits of urban mining, how it can be harnessed for buildings, and the challenges cities face in adopting and implementing urban mining at scale.
“Future cities will become huge, rich and diverse raw materials mines. These mines will differ from any now to be found because they will become richer the longer they are exploited; new veins, formerly overlooked, will be continually opened.”
-Jane Jacobs, "The Economy of Cities" (1969)
Let us explore two scenarios of constructing buildings from scratch.
In the first scenario, materials for the building’s components are extracted from virgin sources. Metals are mined and transported to steel, copper, and aluminium plants, where they are processed and then converted into windows and structural elements. They are then transported again to construction sites, across cities, countries, and continents, where they are assembled to form a building’s structure.
However, a closer look at each of these steps will reveal hidden implications. Virgin reserves of building materials are depleting at a rapid rate, which means that raw material extraction is further straining limited sources. Moreover, geological mining is associated with several unethical practices, human rights violations, and environmental issues, and relying solely on naturally-mined resources for building construction perpetuates these cycles of environmental damage and social injustice.
The biggest problem, however, is the massive energy consumption and carbon footprint of creating building materials from scratch. In China, for example, aluminium extraction and production accounted for 17,000 kg of greenhouse gases (GHG) per ton in 2008 [1]. Transporting these materials across production and construction sites further increases carbon emissions, not to mention the energy-intensive machinery used to assemble these building components.
Now let’s set aside this climate anxiety-inducing, not-so-hypothetical scenario, and think of an alternate model.
Here, the raw materials for a new building’s construction are “mined” from other buildings which are unfit for further use. This preserves virgin mines in their pristine states, quelling the environmental and social damages caused by their extracting industries. More importantly, this effectively eliminates the energy consumption and carbon emissions caused by processing and transporting new building materials. An added benefit of this model is the reuse of old building materials, which would have otherwise been demolished or discarded at landfills.
This is the model proposed by urban mining — tapping into buildings as sources of raw materials after their functional lifetime — and it is a model with significant benefits for building industries, economies, and the environment.
Simply put, urban mining is the process of recovering and reusing a city’s materials, which may include anything from buildings and infrastructure to discarded products. Once their functional lifetimes come to an end — buildings fall into disrepair, cars break down, phones become unusable — the materials of these objects become available for reuse.
The term ‘urban mine’ first came into circulation in 1988, when Japanese professor Randolph Nanjo used it to refer to sites where materials were accumulated in urban systems.
While the term ‘mining’ brings negative connotations to mind, it involves a systematic approach of prospecting, exploration, development, and exploitation, which helps assess the economic feasibility and ROI of the material extraction process well before the first hole is dug. The same approach is adopted in urban mining, which commences with prospecting — researching areas with urban mines to identify usable materials and products. The next step, exploration, entails quantifying the stock of usable materials. This informs the third step — determining the feasibility of extraction.
Urban mining is prevalent in the electronics and car industries as discarded cars and electronic products are key sources of metals that can be fully recycled, especially precious metals such as gold, silver, and palladium. However, the amount of useful materials held within buildings and the scale of the climate crisis is prompting the use of urban mining processes in the building industry as well, catalysing a shift from geological material sourcing.
By giving used materials and products a second life, urban mining eliminates the energy consumption and carbon emissions associated with creating new products and materials from scratch — essentially making do with one product instead of two. This reduces unnecessary production and encourages the efficient use of existing materials and products, which helps projects save costs and time.
Therefore, implementing urban mining at a large scale can drastically decrease emissions from production cycles and reduce the unrestrained consumption of resources.
When a building is made from materials sourced from urban mines, its embodied carbon is reduced; on the other hand, when materials are recovered from an unfit building, its embodied carbon is reclaimed instead of being released into the atmosphere.
Using local buildings and urban infrastructure as material sources have other benefits. Closed-loop, decentralised systems of material recovery provide local sources of secondary materials, which reduces the costs and carbon emissions caused by transporting materials from other places. Creating local ecosystems of material recovery and resale also reduces the project region’s reliance on external imports. This is especially important considering the renewed focus of countries on self-reliance after the pandemic when supply chain and logistical disruptions upended entire industries.
Building projects that use secondary materials have several additional advantages, apart from those listed above. Green certifications like GRIHA and LEED award points to building projects that include a significant percentage of recycled materials as part of the building’s specifications. Green labels lead to more economic benefits for building owners in the long run, as buildings with green labels are shown to have higher occupancy rates, higher selling prices, and greater occupant satisfaction [4]. Governments in several regions also offer tax rebates and other incentives to green label-certified buildings.
Buildings are the largest urban mine compared to other anthropogenic stocks, accounting for more than 50 per cent of all extracted metals [5], and hence serve as great sources of secondary materials. These can include anything from concrete, steel, and bricks, to the wood, glass, metal pipes, aluminium facades, roof tiles, and railings used in buildings, as they are all valuable finished products. Resources can be extracted from buildings even before they are considered unfit for use, especially when functional changes convert building components, like HVAC systems, from in-use to end-of-life products.
Metals are some of the most sought-after materials from the urban mining of buildings.
The combination of high prices for metals, their theoretically limitless recyclability and lifecycles, and their high efficiency of separation make them ideal for recovery. The global construction and demolition waste industry targets 100% recycling of all metals, with 90% of those embedded in concrete expected to be recovered [5].
While demolition is adopted by most urban mining efforts to quickly recover materials from unused buildings, it makes the separation of material streams difficult and doesn’t allow the salvage of whole building components. Deconstruction is a more efficient alternative that retains the original value of building components, as it involves the selective dismantling and removal of materials from buildings. This allows building components to be preserved as close to their finished state as possible, which is in keeping with circular economy principles.
Using buildings as urban mines requires efforts from all stakeholders in the building industry, especially architects, contractors, and manufacturers. To facilitate easy deconstruction, architects need to design buildings using modular components and detachable connections. Along with building owners, they must maintain accurate material passports for their buildings — digital data sets that record exactly what materials, products, and components go into a structure. This makes it much easier to recover everything of value from a building after its lifetime.
Additionally, manufacturers need to be responsible for recovering and reusing their products after their functional lifetimes, especially for lighting, flooring, partitioning and ceiling products. Waste management entities need to recover and reuse building waste as much as possible, connecting with marketplaces and wholesale buyers of recycled products to integrate recovered materials into the market.
With resource consumption rapidly increasing in India due to population growth, rapid urbanisation, economic and industrial growth, and rising incomes, primary material sources will soon not be enough to satisfy the resource needs of our future [7]. Urban mining of dominant waste streams like electronic waste, end-of-life vehicles and construction and demolition waste can provide an alternate source of materials, especially because the formal and informal sectors are currently operational in such material recovery.
India’s renewed focus on sustainability and circular economy principles also make the adoption of urban mining more relevant and crucial, helping the country meet its carbon and pollution-reduction targets.
Apart from its economic benefits, exploring urban mining in India as an alternative to geological mining helps avoid several environmental and social issues. In the past, many serious conflicts have emerged from the environmental damage and loss of livelihoods and habitat caused by mining expansion, as many mineral reserves in the country are located in areas rich in biodiversity and inhabited by indigenous people, like forests and watersheds.
India currently has several environmental policies and regulations centred around the Environment Protection Act (1986) as an umbrella act that addresses hazardous levels of pollution and environmental damage. Moreover, the country also has an extensive network of regulatory bodies at various levels of government to help implement these policies. Recently, the Indian government shifted its focus on waste management regulations from the “Polluter Pays Principle” to “Extended Producer Responsibility”, which makes the producer responsible for the entire lifecycle of the product and creates closed-loop systems that ensure recovery of end-of-life products to foster urban mining.
India has also formed and launched the Indian Resource Panel (InRP), a committee of 10 environmental experts developing a framework for resource efficiency and secondary resource utilisation.
The committee’s efforts will also include drawing lessons from other countries to create business models that support resource efficiency and urban mining.
Construction and demolition waste (CDW) is one of India’s biggest municipal waste streams, estimated to be around 500 million tons in total [7]. This waste consists of soil, sand and gravel; bricks and masonry; concrete; and other miscellaneous materials; however, building components of value such as metal fittings and wooden frames are already removed from the waste stream at demolition sites by the informal sector. Currently, a small portion of this waste is used as fill material for low-lying areas, while the rest is dumped at garbage sites and landfills, or illegally in open areas and along roadsides.
However, all of the three main materials found in CDW can be re-integrated into the construction sector.
Soil, sand, and gravel can be used as fill material in earthworks, while concrete and bricks can be converted into aggregates and further building materials like ready-mix concrete, paving blocks, etc. While pilot programmes for collecting, segregating, and converting C&D waste into building materials are already in progress in Delhi and Ahmedabad, they need to be scaled and implemented to other urban regions, especially those that produce high amounts of CDW.
While the urban mining of buildings has immense potential for application in India, several challenges exist in implementation and resource recovery. In most Indian cities, urban local bodies (ULBs) and city planning authorities have limited capacities and resources to collect, sort, and process waste, with a lack of space being a major constraint.
Public support for facilities that manage building waste is also low, because of unsanitary conditions created by such facilities in the past [7].
ULBs and city departments also lack the technical expertise required to develop and implement a well-planned resource recovery system based on sound assessments of resource availability and recovery potential.
The domination of resource recovery from buildings by the informal sector also poses a significant challenge to the adoption of urban mining methods, along with unique opportunities. While informal workers are able to efficiently recover materials of high value from CDW with minimal investment and equipment, they carry out exploration and recovery processes in unsanitary conditions that negatively affect their health. After objects of value are extracted, the remainder of the waste is discarded like any other CDW in India — openly dumped or burned down. Also, informal workers only extract the materials that they deem valuable and can reprocess with their rudimentary technology. This leads to some important fractions of waste going unprocessed or unrecovered.
By combining the informal sector’s expertise in the collection, segregation and dismantling and the formal sector’s technological tools for recovery of materials and disposal, cooperative models of urban mining can be formed.
This can also help mainstream the informal sector and their grassroots innovations. Moreover, involving them in ethical and safe urban mining processes and upgrading their facilities maintains the livelihoods of nearly 100,000 people employed in this sector [7].
