WHAT IS THIS?

ASR – alkali-silica reaction – makes concrete crack. ASR, which is also known as concrete cancer, is seen here through an electron microscope in the lab.

Concrete is made up of cement, gravel, and water and contains alkali ions – such as sodium hydroxide and potassium hydroxide – that originate from the cement.

If the gravel of the concrete also contains the silicon mineral, also known as silicon dioxide, it reacts with the alkali ions to produce a thick alkalisilica gel.

If water enters the concrete, it is absorbed by the alkali-silica gel, which swells, making the concrete bubble and crack.