As cities continue to grow rapidly and multiply across developed and emerging markets, managing their use of materials becomes a task of vital importance for civilization. Cities are no longer built ‘for eternity’ like Rome, not even for centuries, and even landmark protection centers in many places on just a few prewar legacies. Most other urban structures existing today may be expected to have a useful life cycle of 50 to 100 years, trending downward. Rising price levels for land in highly developed central locations and the stunning opportunity costs of suboptimal use dictate a timely replacement of unproductive real estate in the wake of new technologies, but also to accommodate synergies created by nearby developments or improved transportation infrastructure. Yet, at the same time, only a rapidly dwindling percentage of the debris left by demolition finds its way to out-of-town landfills, and that signals hope: in some environmentally conscious and well-administered cities around the globe, at least half but potentially a lot more of demolition waste can be recycled and finds recurring use in new construction and industrial production. This diagnosis represents a material value of at least six but often seven or even eight figures – per demolished object. With more than half the planet’s population already dwelling in urban habitats, these dimensions are motivation enough to refer to the recovery of such percentages of the ‘gross demolition product’ as ‘urban mining’ and to redefine ‘waste’ as an increasingly precious asset.
So it is appropriate to look at urban real estate as a kind of warehouse of raw materials, containing sand, gravel, concrete, metals, woods and synthetics – all commodities in limited supply. Yes, even wood can be recycled, it happens right here in the U.S., and even for upscale uses such as custom furniture. To carry a ton of concrete to a waste dump may run a tab between $15 and $30 while the same ton may be sold as recycled material for up to $8. Also because of increased public awareness and vocal opposition to environmental toxicity, there is increasing scarcity of landfill acreage in the proximity of major urban settlements. An even more valuable sector of urban debris is e-waste, usually shipped to places like China or India but also to all of West Africa, particularly Liberia, Ghana, Cote d’Ivoire, Benin, Nigeria. Metal deposits in e-waste are up to 40 to 50 times richer in target elements than ore extracted from mines. The novel science of hydrometallurgy now provides advanced technologies for refining pure metal fractions out of mixed raw material resources in relatively simple processes, safely and at comparatively very low cost.
Take urban copper, for example. It is an amazing resource to tap into: an Austrian study showed that electrical household appliances contain 6.4 percent of copper used in the country, cars account for 8.7 percent, but real estate takes up 84 percent of “urban copper.” On average, today’s buildings house seven times more metal as buildings contained a century ago. About half of naturally occurring copper has already been used up in our existing urban structures. Given the speed of urban development, it does not take a mathematician to predict a time when the market price of copper might qualify it as a ‘precious metal.’ Despite recent findings on the Pacific Seabed limiting global dependency on deposits in China, recycling rare earth elements will remain a vital necessity at least until they are obviated by technological innovation. The U.N. Environmental Program estimates that 50 million tons of e-waste are generated annually around the world – a rapidly rising tide. Their StEP initiative (Solving the E-waste Problem) found that the global production of electronic items used 320 tons of gold and more than 7,500 tons of silver annually, amounting to an aggregate value of $21 billion - of which just 15 percent is currently being recycled. Urban mining is arguably the most highly yielding alternative source available to us to reduce reliance on metal imports.
Which begs the question of its practicalities and of forward-looking facilitation.
Building Information Modeling (BIM) is a new planning tool that contains three-dimensional virtual CAD modeling of construction projects from a first sketchy draft to detailed plans to a call for proposals to site inspection to facility management. A unified standard for BIM is expected to be enacted by the European Union by the end of 2015. Singapore has already introduced BIM as a requirement in all plan submissions for projects with gross floor area exceeding 5000 square meters.
No different in a sense than treasure maps of old, only a lot more accurate and reliable, BIM’s importance for urban mining is difficult to overestimate: it can considerably reduce the cost of efficient waste separation. When networked, it is also a potential source for data feeds needed to create a register of “mineable” materials integrated in any existing structure built with BIM. Today, every demolition object has to be evaluated individually – often based on almost unsubstantiated estimates. This relates to the potential of BIM technology like an abacus does to a modern computational device: BIM can provide almost every level of detail required (or justifiable in terms of cost). It is the contracting industry’s functional equivalent of grocer’s “farm-to-fork” databases and increasingly detailed mandated accounting for every step the product takes to its final consumer.
Material recycling also significantly reduces a demolition’s CO2 footprint. For example, recycled concrete consumes substantially less gray energy than the production of primary concrete. Additionally, about two thirds of trucking runs to landfills sites may be saved. An almost trivial cliché says that one man’s trash may be another man’s treasure, but the first part of that equation is no longer sustainable in urban environments expected to house twice the current human population by the end of the 21st century. Turning every increasingly networked and recorded ‘smart city’ into a proverbial perpetuum mobile by tightly integrated, institutionalized urban mining is not only a potential given available data and technology but a vital necessity.