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The Romans mixed crushed rock with burnt lime and water to build the Pantheon, which still holds the title of the world's largest unreinforced concrete dome. But modern concrete has typically proved miserably inferior and vulnerable to a slow deformation process called "concrete creep."
French researcher Joseph Davidovits uncovered the chemistry of geopolymers, or super-cements. Davidovits also promulgated the theory that the Egyptian pyramids were built using a similar type of geopolymer limestone concrete - an idea supported by X-ray and microscopic study samples.
Recently the US Air Force Research laboratory has backed using geopolymers to build runways, rocket nozzles, and even glue for satellite components. Iran, situated geographically in an earthquake zone has similarly invested in the idea of super-strong concrete, its engineers have developed some of the toughest building materials in the world.
The new super concrete – ultra-high performance concrete (UHPC)
Super concrete is based on the traditional ingredients of sand and cement. But, in addition, pure powdered quartz (rather than the tainted variety that makes up most sand) and various reinforcing metals and fibres are added to it. This is why super concrete can withstand more compression than other forms of concrete. Super concrete is also more flexible and durable than conventional concrete. It can withstand pressure many times higher than normal concrete can and therefore can 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 still further. Researchers in the University of Hamadan in Iran for example, are using polypropylene fibres and quartz flour, known as fume, in their mix. It has the flexibility to absorb far heavier blows than regular concrete. Furthermore researchers at the Ottawa University in Canada are working on enhancing the molecular structure of cement. One way to enhance the internal structure of concrete is to use nanoparticles. For example, using different types of metal-oxide nanoparticles such as 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 the current ultra-high performance concrete.
Uses for both civil and military purposes
Super concrete also has considerable military applications. A study, published 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. Hence super concrete has the potential to withstand the impact of big blasts.
An Australian study carried out between 2004 and 2006 confirmed that super concrete resists blasts as well as direct hits. The tests, carried out in Australia, involved a charge equivalent to six tonnes of TNT. This fractured panels made of super concrete, 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.