Improved cement properties

Improved cement properties

Even though concrete and its major component cement are generally traditional materials, their properties can still be improved.

The Faculty of Chemistry at the Brno University of Technology is a domestic workplace of scientists and teachers who have been looking into the issue of concretes for a long time. One of a number of their discoveries and inventions is a method of heat generation control when hydrating aluminous cement by adding strontium aluminous cement.

The method of manufacturing aluminous cement was patented in France in 1908. Due to its high costs, the use of this cement is limited to the sectors in which its properties bring significant benefits. These include, in particular:

  • civil engineering – fast setting to high strength, mainly at low temperatures
  • civil engineering – high chemical resistance
  • refractory materials – high resistance at high temperatures
  • component in cement mixtures – allows some important properties to be modified (e.g. setting speed, volume change, etc.)

Its advantages, particularly the fast setting of concrete mixtures, led to a relatively wide use of aluminous cement in civil engineering in the 1950s to 1970s, but in inappropriate applications. A number of structures had to be then expensively reconstructed or prematurely demolished because the material used had degraded. One such case was the functional department store Jepa in Svobody Square Brno, which was damaged by bombs and a subsequent fire in 1944 and, after the end of the war, it was repaired using this technology along with other things. Under the name Furniture House it had to be demolished in 1988 because of poor statics and today the Omega Palace stands in its place.

This gradual loss of strength, which is caused by the conversion of the hexagonal products of hydration, greatly depends on the temperature at which hydration takes place. With these properties, i.e. the great dependence of the formed hydration products on temperature and the continuous transformation of hydration products, calcium-aluminous cement differs significantly from Portland cement.

The subject of the invention is controlling the speed of hydration heat release from aluminous cement (hydration kinetics) and control of the length of the induction period (workability extension) of aluminous cement based concretes and mortars by adding strontium aluminous cement. The effect increases with the quantity of added SrAC, so it is easy to control. By spreading the heat generation intensity over a longer period of time overheating of concrete structures can be avoided. As the overall released heat remains unchanged, but is released over a longer period of time, the properties of the binder are not adversely affected by adding SrAC. This invention is patent protected.

Author of the paper: author collective from the Faculty of Chemistry

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