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Singing Concrete

17.01.2003


Physicists from the St. Petersburg State Institute of Technology have invented an unusual method for improving concrete. The researchers believe that the concrete structure will become more uniform, and concrete products will obtain unprecedented durability and water-resistance if, while hardening, concrete is exposed to the influence of electromagnetic field of a strictly determined frequency.



The actual process is as follows: the concrete blocks while they are still in the mould are placed in a kind of metal barrel, which serves as an antenna or resonator. Short pulses of alternating current pass through it. The processing time (a few seconds) and parameters of the electromagnetic field created by the current are strictly determined. As a result, concrete becomes heterogeneous, and with higher quality.

The common problem for cement, concrete and other similar building materials is heterogeneity of structure. The heat inevitably evolved in the course of reaction between sand and cement is carried off slowly and non-uniformly, that is why concrete also hardens non-uniformly. Besides, while concrete is hardening the educed gases form pores and cavities in the body of the products, the pores and cavities being of different size. This results in insufficient durability, sometimes even brittleness of concrete blocks. These drawbacks can be avoided if concrete is stirred up, but this is practically impossible to do. The ’trick’ the Technical University researchers play with concrete resembles stirring to some extent.


When the concrete is exposed to short electromagnetic pulses, which are of low intensity but their parameters are established precisely, alternating currents appear in the thin surface layer of the concrete. Alternating currents, in turn, generate acoustic waves in the overall bulk of the concrete blocks. Figuratively speaking, concrete contained in the steel barrel ’is singing’ under the influence of electric field, but it is ’singing’ in an inaudible way, i.e. in ultrasonic range. This acoustic influence in particular is, in the researchers’ opinion, the regulating factor for the structure of the material.

It is still unclear whether the actual mechanism is like that. The capacity of ultrasound seems to be evidently insufficient to directly stir a large bulk of dense material. Nevertheless, the scientists assume that the moderate directive effect may cause a resonant response from the material, thus causing the structure regulation.

According to Alexei Kolesnikov, one of the inventors, "The process is similar to the railway switch operation - the effort even a child can cope with. However, this relatively minor effort directs to the required track a train weighting a thousand tons and possessing enormous energy."

The physicists have so far failed to prove their hypothesis theoretically, but facts are stubborn things. As a result of such simple processing invented by the scientists, concrete hardens quicker and the blocks made of concrete become more durable and dense. For instance, after undergoing such a ’singing lesson’, the concrete sleepers will be in use much longer and the bearing-wall buildings will not grow damp in cold and rainy weather.

Olga Maksimenko | informnauka

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