Damaging buildings from within – Ettringite

What does it look like?

The crystal structure of Ettringite. The big blue atoms are calcium, the red oxygen, the light blue atoms are aluminium, the yellow are sulfur and the dark grey atoms indicate the positions of water molecules. Image generated by the VESTA (Visualisation for Electronic and STructural Analysis) software http://jp-minerals.org/vesta/en/

What is it?

Ettringite is a mineral that is produced as Portland cement dries out.  It is a calcium, aluminium hydrated sulfate silicate, so is a pretty complicated inorganic structure that varies in composition depending on the environment. Though ettringite is present in fresh concrete, it is thought that as the cement ages more ettringite can form and cause damage to the structures from within. There's lots of research looking into stopping this.

Where did the structure come from?

This particular structure of ettringite that we have featured was presented in the journal Nature in 1968, and the atomic parameters for this can be found on the American Mineralogist Crystal Structure Database.

Tags: cement   mineral