HYDRATION OF CEMENT
Reaction between cement compounds and water due to which different structures ( C-S-H, ca(oH)2, ettrigite, monosulphate ) are formed in the cement / concrete and heat is extract from it is known as heat of hydration .This is extothermic reaction.
Here we discuss about different bogues compouds and reaction of these products with water .
In cement bogues comounds are :
Reaction between cement compounds and water due to which different structures ( C-S-H, ca(oH)2, ettrigite, monosulphate ) are formed in the cement / concrete and heat is extract from it is known as heat of hydration .This is extothermic reaction.
Here we discuss about different bogues compouds and reaction of these products with water .
In cement bogues comounds are :
- C3S - Tri calcium silicate
- C2S - Di calcium silicate
- C3A - Tri calcium Alumiate
- C4AF - Tetra calcium Alumino ferrite
When water intracts with cement it first reacts with Aluminate compound which reaction is give below:
Tricalcium aluminate reacts with water in presense of gypsum and make calcium aluminate trisulphate hydrate which is known as ettrigite and librate heat, ettrigite which is form above is stable only in solution of gypsum but due to deficiency of gypsum its reacts( ettrigite) reacts with balance C3A ad make calcium alumiate monosulphate hydrate, this monosulpahe is stable only in presence of deficiency of sulphate but monosulphate reacts with sulphate present in water and soil and again convert in to trisulphate hydrate which moleucule size is 2.5 to 3 times more than monosulphate structure due to which cracks are appears in concrete.
After this ferrite reacts with water in presence of gypsum and make calcium aluminate trisulphate hydrate( ettrigite) , aluminium hydroxide and lime in concrete.
Ettrigite futher reacts with ferrite and make garnets in concrete which do not contribute any strength in concrete.
After this water reacts with C3S in cement and make calcium silicate hydrate and calcium hydroxide and liberate more amount of heat.
After reaction with C3S water reacts with C2S and make same calcium silicate hydrate and calcium hydroxide and librate heat.
In above reactions C-S-H is only responsible for strength in concrete/cement which is formed in the case of C3S and C2S .
In the case of C3S reaction more amount of calcium hydroxide form in comparison of C2S , calcium hydroxide is harmful for cement which reacts with sulphate from water and soil and make calcium sulphate which cause deterioration of concrete and cause lack of durability of concrete.
Only one benefit of calcium hydroxide is it maintain PH VALUE of concrete alkaline and reduce the corrosion of reinforcement.
C3A and C4AF is responsible for initial set of concrete.
C3S is responsible for high early strength in concrete.
C2S is responsible for strength in concrete in later stage.
C-S-H which is produce during reaction of C2S with water is more than the quantity of C-S-H produce by C3S and also quantity of calcium hydroxide is low in case of C2S . C-S-H which is produce by C2S is good quality than C-S-H produce by C3S and also density of C-S-H produce by C2S is high.
No comments:
Post a Comment