Concrete 3g

UHPC is based—like its quotidian cousins—on sand and cement. In addition, though, it is doped with powdered quartz the pure stuff, rather than the tainted variety that makes up most sand and various reinforcing metals and fibres.UHPC can withstand more compression than other forms of concrete. Ductal, a French version of the material which is commercially available, can withstand pressure many times higher than normal concrete can. UHPC is also more flexible and durable than conventional concrete. It can therefore be used to make lighter and more slender structures.

For this reason, Iranian civil engineers are interested in using it in structures as diverse as dams and sewage pipes and are working on improving it. Mahmoud Nili of Bu-Ali Sina University in Hamadan for example, is using polypropylene fibres and quartz flour, known as fume, in his mix. It has the flexibility to absorb far heavier blows than regular concrete. Rouhollah Alizadeh may do better still.

Dr Alizadeh, a graduate of the University of Tehran, is currently working at Ottawa University in Canada on the molecular structure of cement. Once again, this research is for civilian purposes and could pave the way for a new generation of UHPC with precisely engineered properties and outstanding performance.One way to tamper with the internal structure of concrete is to use nanoparticles. Ali Nazari and his colleagues at Islamic Azad University in Saveh have published several papers on how to do that with different types of metal-oxide nanoparticles. They have worked with oxides of iron, aluminium, zirconium, titanium and copper. At the nanoscale materials can take on extraordinary properties. Although it has been demonstrated only in small samples, it might be possible, using such nanoparticles, to produce concrete that is four times stronger than Ductal.All of which is fine and dandy for safer dams and better sewers, which threaten no one. But UHPC’s potential military applications are more intriguing—and for many, more worrying.

A study published by the University of Tehran in 2008 looked at the ability of UHPC to withstand the impact of steel projectiles. These are not normally a problem during earthquakes. This study found that concrete which contained a high proportion of long steel fibres in its structure worked best. Another study, published back in 1995, showed that although the compressive strength of concrete was enhanced only slightly by the addition of polymer fibres, its impact resistance improved sevenfold.Western countries, too, have been looking at the military uses of UHPC. An Australian study carried out between 2004 and 2006 confirmed that UHPC resists blasts as well as direct hits. The tests, carried out at Woomera once the British empire’s equivalent of Cape Canaveral, involved a charge equivalent to six tonnes of TNT. This fractured panels made of UHPC, but did not shatter them. Nor did it shake free and throw out fragments, as would have happened had the test been carried out on normal concrete. In a military context, such shards flying around inside a bunker are a definite plus from the attackers’ point of view, but obviously not from the defenders’.

via Bunker-busting: Smart concrete | The Economist.


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