Sand – From linear to circular use

Prof. Dirk E. Hebel

Professorship of Sustainable Construction, Karlsruhe Institute of Technology
When we talk about future urban development and consider the rapid rates of urbanisation in Asia, Africa and South America, the question arises as to whether our current building methods and materials are still viable. In all these areas, gigantic construction tasks of cities with millions of inhabitants are still ahead.
Dirk Hebel
Already today, almost 90% of the world’s cement (and thus twice the amount of sand as concrete aggregate) and 70% of the world’s steel are used in developing areas. But if the most important raw material is missing, what alternatives are left? And what role can research institutes and universities play in exploring such alternatives? To reduce our dependence on sand as a finite resource, the demand can basically only be changed by introducing a true circular economy or by substituting sand as a raw material.
Circular economy: Glass recycling

The recycling of raw materials using (regenerative) energy is certainly one of the most important and promising methods. Glass is basically an excellent example of a material that is extracted from sand and can then actually be infinitely recycled and thus brought into a cycle as often as desired at the same quality level. The company Magna Glaskeramik, for example, offers a whole range of products for façades and interior design that consist of melted glass fragments and thus generate a completely new aesthetic; product names such as “Polar White” or “Ice Cube” bear witness to this. We use used glass batches, which we collect and sort mainly in our glass containers and which are free of contamination or adhesions of other materials. 

MAGNA Glaskeramik
© Rene Müller
MAGNA Glaskeramik © Rene Müller
Since glass consists for the most part of sand, it is possible to obtain a sand-like material from waste glass by crushing and grinding, which has the same material properties as original sand and can be processed in exactly the same way. Large quantities of our waste glass are currently not recycled as glass at the same quality level due to adhesions of foreign materials or insoluble coatings and end up in landfills. In the future, we need to design for sorting without generating this waste. However, the existing, landfilled waste glass resource must be activated. This is technically possible, but the price is still too high to compete with sand. In large-scale field trials, the American state of Florida is trying to replenish beaches that have been washed away with ground glass – with great success, as the new land masses are also accepted by flora and fauna. This is a method that could well be used for land reclamation in other parts of the world. [1]

To reduce our dependence on sand as a finite resource, the demand can basically only be changed by introducing a true circular economy or by substituting sand as a raw material.
Circular economy: Concrete recycling

Likewise, the method of recycling or reprocessing concrete structures is gaining in importance. Recently, a company from Holland has made a name for itself by developing a method for the complete recovery of sand, gravel and even reactive cement from old concrete. Under the name SmartCrusher, the company Koos Schenk has patented this method. What is new here is that the original raw materials can be recovered in their original configuration and quality and not cascaded as recycled concrete. Should this process also become economically viable, it would certainly be an important step towards a true circular economy in the construction industry.

SmartCrusher SC2
© Koos Schenk, SmartCrusher BV
SmartCrusher SC2 © Koos Schenk, SmartCrusher BV

Substitution is a radical approach to ultimately replace sand as a raw material. A number of research approaches worldwide are dealing with the question of alternative aggregates in concrete mixtures, be they organic in nature or even obtained from waste. [2] However, all approaches quickly reveal the limits of what is feasible when comparing the compressive strengths of such mixtures with sand. Newer approaches are found through the use of biological adhesives. Be it bacteria or mycelia, a new biological revolution seems to be on the horizon, which can certainly be compared and combined with the digital revolution, as will become apparent in the other contributions to this science blog

[1] See also: Delestrac, Denis. SAND WARS. Documentary. LA COMPAGNIE DES TAXI-BROUSSE, 2013.
[2] See also: Hebel, Dirk E., Marta Wisniewska and Felix Heisel (2017). Building from Waste, Birkhäuser

In an older version, this article was published in 2014 at ETH Zürich, FCL.

Further information about the author

Prof. Dirk E. Hebel
Professor of Sustainable Construction KIT Karlsruhe and Dean of the Faculty of Architecture KIT