aluminous cement is a type of cement in the manufacture of which limestone and bauxite are used, heating up to 1800 °C (liquid state), cooling quickly and going through a grinding process.

Before hydration, aluminous cement is composed of alumina (AlO) and lime (CaO), both at 40%. They combine to give hydrated calcium aluminate.

They pose problems because the ACH (hexagonal) is unstable and transforms into CAH (cubic) which reduces volume, losing strength. This transformation begins after 28 days and in one year it has almost completely occurred. It has a very high hydration speed, sets in 1-2 hours and acquires full resistance after 24 hours. They produce a high heat of hydration.

It is used in ovens (withstands up to 1800 °C), refractory concrete, precast concrete and water seals due to its rapid setting and high resistance to aggressive water. It should not be used in structures.

The incorrect use of aluminous cements has led to construction problems, especially during the third quarter of the century, when this type of cement was used for its rapid hardening properties. After several years, some of the buildings and structures collapsed or had to be demolished due to the degradation of the cement. Heat and humidity accelerate the degradation process called "conversion." A swimming pool roof was one of the first structures to collapse in the United Kingdom.[1]​.

In Madrid, a large housing block nicknamed Corea (as it was built by the Americans during the Korean War 1951-1954) had to be demolished in 2006. Also in Madrid, the Vicente Calderón football stadium was affected and had to be completely rebuilt and reinforced.[2]​.

Due to its loss of alkalinity, the concrete expands, breaking and exposing the reinforcement, which corrodes.