Fineness,Soundness,Initial and final setting time,Setting and hardening of cement|Industries Extension officer Notes
Basic Civil engineering|Industries Extension officer
Fineness of cement
Fineness is the measure of the size of the cement particles.
It is measured by sieve test or r permeability apparatus test.
Fineness obtained by sieve expressed in percentage.
For good quality cement this should not be more than 10%.
Fineness is also expressed in specific surface, which is a me
It is measured by sieve test or r permeability apparatus test.
Fineness obtained by sieve expressed in percentage.
For good quality cement this should not be more than 10%.
Fineness is also expressed in specific surface, which is a me
of degree of grinding.
Specific surface is found by permeability apparatus test and it should be more than 2250 cm/gm.
Specific surface is found by permeability apparatus test and it should be more than 2250 cm/gm.
Soundness of cement
The property of cement, which is a measure of resistance against the large volumetric change after setting, is called soundness of cement.
Free lime and manganese, which is present in extra, causes this volume change.
Free lime and manganese, which is present in extra, causes this volume change.
This can be measured by Le Chatelier Test and expressed in millimeters.
For ordinary cement, the expansion for Le Chatelier Test should not be more than 10 mm.
For ordinary cement, the expansion for Le Chatelier Test should not be more than 10 mm.
Initial and final setting time
The process of changing the cement paste to hard solid mass is known as setting of cement and time taken for this is called as setting time of cement.
The stage of setting of cement at which any crack that only appears, does not reunite, is called initial setting.
The period from which the water is added till initial setting takes place is called initial setting time.
For ordinary Portland cement it is not less than 30 minutes.
The period from which the water is added till initial setting takes place is called initial setting time.
For ordinary Portland cement it is not less than 30 minutes.
The stage of setting of cement at which plastic cement becomes a hard solid mass is called final setting and time taken for this is called final setting time.
For ordinary Portland cement it is around 10 hours.
For ordinary Portland cement it is around 10 hours.
Setting and hardening of cement
Though the setting and hardening of cement take place simultaneously these are two distinct processes.
Setting of the cement is changing the plastic state of cement to solid state.
Hardening of cement is gaining of strength. This is proportional to the hydration of cement.
Hardening of cement is gaining of strength. This is proportional to the hydration of cement.
In rotary kiln, oxides present in the raw materials of cement when
subjected to high temperature combine with each other to form complex compounds.
These are called Bogue's compounds. Those are given below.
These are called Bogue's compounds. Those are given below.
Name of the compound -Formula -Abbreviation
Tricalcium Silicate -3 CaO.SiO2 - C3S
Dicalcium Silicate- 2 CaO.SiO2 - C2S
Tricalcium Aluminate- 3 CaO.Al2 O3- C3A
Tetracalcium Aluminoferrite -4 Cao.Al2 O3 Fe2O3 - C4AF
C =Ca O,Lime stone
S = SiO2 Clay
A= Al2 O3 ,Bauxite
F = Fe2 O3 Hematite
When water is added to cement, C3A will get hydrated first, which is responsible for early setting of cement.
This generates considerable amount of heat. C3A does not contribute any strength.
This generates considerable amount of heat. C3A does not contribute any strength.
Tricalcium Silicate (C3S) hydrates after C3A.
This imparts initial strength to the cement.
Dicalcium Silicate (C2S) gets hydrated next which is responsible for the development of strength in later stages.
Tetracalcium aluminoferrite (C4AF) has no role in setting and hardening of cement.
In general, the hydration of these Bogue's compounds is responsible for setting and hardening of cement.
This imparts initial strength to the cement.
Dicalcium Silicate (C2S) gets hydrated next which is responsible for the development of strength in later stages.
Tetracalcium aluminoferrite (C4AF) has no role in setting and hardening of cement.
In general, the hydration of these Bogue's compounds is responsible for setting and hardening of cement.
0 Comments