Urban mining and circular construction – what, why and how it works

Updated and rewritten on 02/02/2021
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When a building’s life comes to an end most of its materials are sent to landfill, incinerated or downcycled into products of much lower value. This is a major loss of valuable materials. That’s where urban mining can help.

What is urban mining?

Urban mining is the process of recovering and reusing a city’s materials. These materials may come from buildings, infrastructure, or products that have become obsolete. When the functional lifetime of an object is over – the car breaks down, the computer is outdated, the building no longer adheres to safety regulations, or a developer just wants to build a new block of flats where an empty office block used to be –  the object’s materials become available. Urban mining is not new, the metals in cars and electronics are often recycled, but the scale of the climate crisis requires it to be applied more ambitiously and more proactively, treating the whole city as a “mine” and actively prospecting materials to ensure that as much of their value is retained. Identifying usable materials and products (and their financial and environmental value) is known as prospecting the urban mine, and it is essential to help industries have a reliable supply of high quality secondary materials. Amsterdam’s buildings contain tons of steel, copper, aluminum and lead, which could be mined for their metals. The first step in any mining process is physically searching for minerals and precious metals. 

Maps showing the steel and copper concentrations in buildings of Amsterdam. The brighter the color, the higher the concentration.

What materials can be “mined”?

The most common materials in the urban environment are from construction and demolition. We conducted a study of the construction sector in the Netherlands, and found that construction and renovation of buildings in the Netherlands results in an annual demand for 17 million tons of materials, most of which is concrete, followed by steel, bricks and wood. Despite this high demand, only 13% of these input materials are currently coming from secondary and renewable sources. So, what happens when a building is demolished? Luckily, most of what is demolished is recycled (88% of the 7 million tons of construction and demolition waste), but most of this is downcycled, meaning the material loses value and it is primarily used outside the sector. Concrete might find its way into road fillings, but rarely into new buildings. Reusing these millions of tons of materials for new construction projects has many advantages. The materials are already there, in the city, so there would be no need for lengthy supply chains, which in turn would increase resilience. And for all cities with a circular economy strategy, urban mining would maintain as much value as possible from these materials, for as long as possible. After all, why mine, produce, and transport all these materials twice, from mines around the world, when there are abundant sources throughout the city?

Tree map of the waste materials from construction and demolition in Philadelphia, 2019

While construction waste provides by far the highest tonnage in the urban mine, everything in the city can be reused at the end of its useful life. Urban mining can be applied to electronic waste, which contains a wealth of literal gold and other precious metals, as well as to entire products and appliances. Billions of mobile phones are thrown away around the world, many of them perfectly usable, as well as fridges, washing machines, and so much more.

Anything in the city can be part of the urban mine. Amsterdam claimed 69 000 unwanted bicycles in 2018 alone, and fishes 15 000+ bikes out of the canals every year. Each and every one represents valuable metals, but possibly also spare parts, ready-made frames, and other components which could be reused locally or to jump-start new production processes. Cars are also a big source of material value in the urban mine.

However, just as big cities are called the “concrete jungle”, the buildings we see all around us are the biggest and most valuable part of any urban mine. Not just concrete, or the steel that reinforces our modern buildings, but the wood, the glass, the copper pipes, the aluminium facades, the roof tiles, the bricks, even the iron railings on our balconies. All of these are valuable finished products that have already gone through a long supply chain.

Every urban construction project is literally surrounded by useful materials and components.

The idea of mining a city can also be applied to a region. We used our model on a regional scale in the Northern Dutch provinces of Groningen, Drenthe and Friesland and found that more than 2 million tons of secondary building materials will become available during the demolition of buildings until 2030. If they can be reused, those materials represent a lot of value: €136 million in value and a reduction of €4 million in environmental costs. 

The second benefit of urban mining is environmental. Beyond these environmental costs, there is also huge potential to reduce environmental impact.  

Retaining value and reducing environmental impacts by reusing and recycling

Before concrete can be used in a building, stone and sand have to be extracted from somewhere. They are bound with cement, which is made of extracted limestone, silica, clay and more. Concrete is reinforced with steel, the creation of which requires 20 gigajoules of energy and emits 1.83 tons of CO2 per ton of steel, as well as air and water pollution from the mining of iron ore. More complex components are then created from these materials. At each step, there are manufacturing, transportation and labor costs, which takes time, energy, effort, emissions and has an environmental impact. Hence each production step, from extraction to manufacturing and assembly, adds value to a construction product. This added value accumulates in a product that is now in a building slated for demolition, and can be retained when we take the time to disassemble buildings and reuse products for their original (or an even higher value) purpose. A wooden window frame is worth so much more than broken glass and wood chips. In fact, in the Utrecht region alone, we found that about 350,000 tons of materials are slated for demolition over the next five years. Those materials have a potential value of €175 million, if they can be captured and cycled. And if we can reuse components that exist, here and now, in our cities, then fewer components need to be created, and fewer materials extracted.

In a circular economy, a product is preserved as close to its finished state as possible, which preserves as much of its value as possible.

Urban mining in practice: Rotterdam, Amersfoort and the Utrecht region

The municipality of Rotterdam has set ambitious circularity targets for 2030, including reducing the use of primary raw materials by 50%. The city also wants to create 3,500 to 7,000 jobs that contribute directly to the circular economy. Currently, 400,000 tons of waste are discarded every year. This material is a huge opportunity. We’ve identified buildings in the city that are scheduled for demolition, and found that they contain 817,000 tons of materials which will become available to be harvested up to 2030. But with a downcycling rate of 85%, there is a lot of potential to not only recycle but also reuse, which would maintain a lot more value. Indeed, 1% of the waste that could be reused as products account for 8% of the environmental impact and approximately €43 million in value. One potential solution is to create a “hub” focused on reusing and recycling at the highest possible value.

However, in rapidly growing regions, the amount of construction may eclipse the amount of demolition. Working with the U10 – the ten municipalities in the Utrecht region, the city of Amersfoort and the Economic Board of Utrecht –we found that more than 5 million tons of building materials are needed to meet the demands of the U10 between 2018 and 2022. This is 20 times more than the current estimated supply of construction materials from the urban mine in the region. In such cases, the high need for construction materials should make urban mining easier: local raw materials from demolitions and disassembly should be in high demand. The amount of construction also presents an opportunity to plan for the urban mine of the future, by designing for disassembly, implementing materials passports, and facilitating the future recycling of urban materials.

Why is urban mining not more common?

The construction sector is not yet geared to use secondary materials for constructing and maintaining the built environment. The barriers to scaling up urban mining have to do with logistics, the demand for reused materials, and perceived performance. The most important barrier to tackle is the lack of information on what harvestable materials are present and what their value in reuse could be. We collaborated with SGS Search to build a model that predicts the value and opportunities for reuse of the materials and products. The future supply of secondary materials can be predicted by the regional demolition and renovation projects, while the potential demand consists of new construction and renovation projects. This detailed information opens up the conversation on matching demand and supply. Once these insights are made more available, in cities across the world, those on the frontlines (developers, architects, contractors, governments) can be mobilized to seize the circular opportunities in the urban mine. 

A circular future

Our climate is changing, supply chains need to be more resilient, and waste intensive patterns need to be minimized for us to operate within more sustainable boundaries. The built environment, in particular, can become much more sustainable. The good news is, this is already starting to happen: as governments and businesses adopt higher sustainability standards and targets, tender requirements, procurement guidelines, and consumer demands are following suit. The first step for cities and regions is simply mapping all the valuable materials that exist in the area. The urban mine is already here, we just need to dig.

Merlijn Blok_Metabolic

Any questions?

Reach out to our 

Built Environment Consultant,
Merlijn Blok

Learn more about our work in Cities and Regions

Our mission is to transition the economy to a fundamentally sustainable state.

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