4.7 : יציבות הצמנט

Occasionally, after the cement paste sets, the free lime, magnesia, and calcium sulfate may hydrate, causing a destructive expansion in the hardened cement.

Soundness is the ability of the cement paste to resist significant expansion after setting.

Le Chatelier and autoclave accelerated tests are used to determine the soundness of cement.

In a Le Chatelier test, the cement paste is filled in the mold and stored underwater for a specific time.

Afterward, the distance between the indicators is measured. Next, the mold is immersed in water and is boiled for a designated time to accelerate cement hydration.

The setup is then cooled, and the distance between the indicators is measured again to determine the specimen's expansion due to free lime.  

Alternatively, in the autoclave test, a cement paste specimen is prepared and cured in humid air.

The specimen's length is measured before placing it inside the autoclave for high-pressure steam heating.

After heating, the specimen is cooled, and its length is measured to determine its expansion resulting from free lime and magnesia.