free lime

Hello Maw,

Hard burning of clinker results in large alite and belite crystals which have a lower content of favourable minor element impurities. These impurites are normally in solid solution with the alite & belite and help to destabilise the crystal lattices of the clinker minerals, making the clinker more reactive. Hence harder burned clinker has a lower hydraulic reactivity than softer burned clinker.

Also, hard burned clinker has a low porosity and high density and is therefore harder to grind. This means that there is likely to be more clinker particles in the coarser cement fractions that in the fines. This also contributes to a reduction in cement strength.

The low clinker porosity of hard burned clinker also makes the clinker harder to cool properly. This slow cooling results in large aluminate crystals with reduced impurites, both of which work toward reducing cement strengths.

Regards,

Ted.

thanks alot mrTed,also my laboratory colleages tell me that when LSF is low the amount of C2S will be more or equal to C3S and this creat negative effect to the strength. is it true?

Hello Maw,

Yes, the LSF controls the ratio of C3S to C2S in the clinker, or more correctly, the LSF determines the equilibrium between C3S and C2S by controling the ratio of CaO to SiO2 according to the following system;    2CaO + SiO2 <---> C2S + CaO <----> C3S

So you can see that C3S requires 3 moles of CaO for every mole of SiO2 whereas C2S only requires 2 moles of CaO.

If enough CaO is available in excess of that required to form C2S then C2S can react with the excess CaO to produce C3S. If not, then more C2S will remain in the clinker unable to be converted to C3S, and the final amount of C3S will be proportionately reduced.

Since C3S is by far the predominant strength producing mineral in the clinker, a low C3S results in reduced cement strength development.

Regards,

Ted.