Schneier on Security

Clive Robinson • November 24, 2019 3:00 PM

@ Tatütata,

On the background issue, there is a looming global sand shortage…

Yes there is but it’s kind of hidden in “plain sight” so we tend not to think of it, the same with the limestone, aggregates, carbon footprint, and pottable water issues of construction concretes as well.

There are various mixes of concretes made from mixes of cement[1], sand and aggregate.

Cement is made by effectively “crushing and burning limestone rock”, sand is the result of millions of years of erosion and aggregate some what less time of erosion.

One of the things that makes sand important not just for building is that it is mainly silica or silicon dioxide (SiO2). This is usually in the form of quartz, which, because it is fairly chemicaly inert, is a very good insulator, and has considerable hardness makes it usefull in many applications. The reason non-organic sand is silica based is that quartz is the most common mineral resistant to erosion or weathering. Thus as softer rocks weather comparatively faster down to silt, that then get washed out by suspendion in water the still larger silica remains behind as a sand.

This weathering process is actually increadibly energy intensive and takes considerable time to erode rocks to stones, then pebbles, then gravel, then sand, then silt for it to be washed away to form sedimentry rocks that then get subducted to eventualy become magma and the cycle continue.

This cycle being a primary geological process takes times longer than the human race has been in existance. Therfore in human terms sand and limestone and the aggrigates used to make concretes we use for construction are “Non renewable resources of finite availability”…

Thus the question arises as to “recycling”[2]. Currently most construction concretes have a comparitively short life (40years on average) before being broken up. Due to the finite availability of iron it’s common to extract the rebar as scrap and recycle it. The remaining concrete “rubble” tends to be used as a form of “hard core” in some foundations and the like or as a form of land erosion prevention, with still large quantities going to landfill at considerable financial and environmental expense. Which is obviously not the best use that could be made of it, hence the increase in recent times of turning it into low quality aggregate on site. Part of this is due to the large amounts of energy required to do the transportation off to landfill and obtaining gravel aggrigates thus recycling can reduce construction costs. Energy is another environmental issue with the making of concrete, it has a very high carbon footprint as well as using very large quantities of often potable water which it’s self has a quite non-negligible carbon footprint.

In short “Concrete is a major disaster area” in the making for mankind and the rest of the planet and we need to address all it’s issurs as a matter of high priority. But politically that is highly unlikely as concreate is seen as a primary economic enabler…

[1] Many people call the result of making concrete “cement” which after a moments thought can be seen to be wrong. Cement is actually a “binder” for the strong sand and aggregates, the result is quite durable if brittle even though the cement it’s self is actually quite a weak material. There are two types of cement the second –hydrous / Portland– is made from the first –non-hydrous / Lime– which is made by crushing and burning limestone in a high energy process. As with sand limestone is also being used at a prodigeous rate and this as well is of great environmental concern.

[2] https://en.m.wikipedia.org/wiki/Concrete_recycling