Cement: hydration mechanisms

 

Hydration mechanisms

Necessity of sulfate

Hydration disorders

Hydration energy

 

Hydration mechanisms

Hydration of a clinker particle

o heterogeneous

o multiphase

What happens when mixing water and cement ?

–dissolution in the water.

–nucleation period

–chemical reaction with the H2O molecules to build hydrates. (new crystals contain water in their structure =  crystallized “solid” water)

 

Hydration: Le Châtelier mechanism

• Hydrated calcium aluminates
• Hydrated sulfo-aluminates
• Portlandite

Hydration of silicate phase: Michaelis mechanism

C3S + 3 H >  C1,5SH1,5 + 1,5 Ca(OH)2

C2S + 2 H  > C1,5SH1,5 + 0,5 Ca(OH)2

 

Necessity of sulfate

Let’s play together…

Hydration without sulphate

Hydration with sulphate

After hydration

Hydration without sulphate addition

Hydration with sulphate addition

Why do we add sulfate ?

Hydration 2 types of ettringite

Hydration Sulphate needed

Depends on the contact surface of C3A with water   

– % C3A

 – fineness of clinker

Hydration disorders

Let’s experiment…

Flash setting = aluminate setting

Ettringite false set

Sulphate false set ~ plaster set

Syngenite false setting

Hydration energy

Adequate hydration at 20 °C

Fineness and hydration energy

Hydration Non-blocking ettringite