How not to pound sand


Sand. How in the world can we be running out of sand? The world seems full of it, right? River-beds, oceans and deserts are full of sand.  Yet according to a number of recent articles, certain types of sand are being depleted so rapidly that some countries are putting bans on exporting it.  Such bans have given rise to sand mafias in some parts of the world.  Such sand mafias, which could have been called  Sandinistas if the name hadn’t already been taken, clandestinely mine river-beds and vacuum ocean floors to sell this finite resource to voracious buyers both far and near, leaving behind devastated eco-systems and sandless beaches.

To what end you ask? Our insatiable appetite for concrete is largely to blame; more specifically for the construction of housing, offices, factories, in fact brand new cities that spring up practically overnight in some parts of the world.  One kilometer of road requires 30,000 tons of sand and a single house can quickly use up to 200 tons (more details here). Concrete accounts for 80% of mined sand usage. Depending on the specific end use for concrete, up to 3 times the amount of sand will be required for every part of cement. Its role is to fill in the spaces of larger aggregates (e.g. stone). Both fine and course sand are used in cement with varying impacts on comprehensive strength, flex strength, permeability, durability, shrinkage, cracking, etc. Desert sand, due to its smoother and rounder geometry, doesn’t work as well as river and ocean sand so it is largely ignored.

Given that I blog about all things biochar, where does biochar come in to play on this most recent tragedy of the commons (i.e. disappearing sand)?  It is no secret that biochar is being tested and used in concrete recipes (see here, here, and here).  To date, however, the motivation for including biochar in concrete has focused on carbon sequestration or to lighten up the weight of concrete.  But perhaps displacing the use of sand with biochar in concrete should focus more on the ecological benefit of saving our rivers, oceans and related flora & fauna from utter devastation.

But since eco-system services is often a tough sell, especially without regulations to control those that feel no shame in ruining the environment, economic impact must be addressed.  Sand is still shockingly cheap (roughly $6/ton) given that it is the most in demand natural resource after water.  At that rate, biochar is unlikely to compete purely on price for a very long time.  However this recent paper suggests the biochar added to cement can help reduce cracking and improve flexural strength as compared to using just sand for the fine aggregate. This same research claims that biochars ‘jagged and irregular shape provides a snug fit to cement paste’.  Earlier research out of Korea showed that certain types of biochar ‘reduces water evaporation from concrete which reduces both the plastic shrinkage and drying shrinkage’.  Thus improving concrete through the use of biochar could potentially reduce liabilities related to concrete failure, or reduce curing time which means faster building, or could provide better insulation which will reduce building operating costs.  If we start to approach the use of biochar in buildings through this lens, it just might attract more interest than focusing on its carbon sequestration potential.  Future research would be well served to use a Triple Bottom Line approach to using biochar in building materials.

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