Improving cement with bauxite residue

By David Ariño Montoya

Cement is everywhere in our societies. It is hidden behind the wall of your house, under the roads you take every day or underneath the streets of our cities. The uses of cement have been different through the ages and understanding its history can give us hints to improve it in the future. In previous posts we saw the history of alumina [1] but now is time to see: the history of cement!

Cement in Ancient History

In ancient times, construction materials were limited to those that could be easily collected from the environment. For example, gypsum was commonly used in Egypt to raise the Pyramids. Not very far from the coasts of Egypt, across the Mediterranean Sea, lime was a common material to build walls and structures in the Roman Empire. It happened that in the locality of Puzzuoli, workers started mixing lime with the ashes from the volcano in its vicinity. Workers became aware that when the lime was blended with the ashes of the volcano the resulting material had better properties: higher strength and the capability to set under sea water. [2]

This observations were collected in the 1st century BCE by the Roman architect and engineer Marcus Vitruvius Pollio in his “Ten books of architecture”. He wrote: “There is also a kind of powder from which natural causes produces astonishing results. This substance, when mixed with lime and rubble, not only lends strength to buildings of other kinds, but even when piers are constructed of it in the sea, they set hard under water”.[3]

Cement in Modern Times

Nowadays, when a material is blended with cement to improve its final properties is called pozzolanic (remember that those volcano ashes came from Puzzuoli). But unlike in ancient times we are not limited to make use of the materials laying in the environment. Thanks to the study of chemistry and materials it is possible to assess the wastes from different industrial sectors and optimise the final properties of the cement that we want to design.

As a matter of fact, on a daily basis, several by-products are being used by the cement industry. Take for example the European standard for cement production: wastes catalogued as silica fume, fly ash, burnt shale and blast-furnace slag are highly valuable materials for cement production.

Cement in the future

Trends show that demand for cement will increase in the next decades. In the future, bauxite residue can be of great help to make construction materials. Not only for the introduction of new building materials such as inorganic polymers.[4] With the necessary studies and research, bauxite residue can be blended with cement to improve its final properties and produce new varieties of cement as it is done with other materials in the present day.