Civil Engineering - Building Materials - Discussion

As water is added to cement, it hydrates and forms tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite.

Tricalcium silicate forms immediately after hydration and responsible for early strength.

Dicalcium silicate contributes strength by around after 7 days and it is responsible for ultimate strength.

Tricalcium aluminate took months to impart strength after hydration and tetracalcium aluminoferrite took even years. Both are less significant in contributing to strength.

When water is added to cement, each of the compounds undergoes hydration and contributes to the final concrete product. Only the calcium silicates contribute to strength. Tricalcium silicate is responsible for most of the early strength (first 7 days). Dicalcium silicate, which reacts more slowly, contributes only to the strength at later times. Once set, concrete continues to harden (cure) and become stronger for a long period of time, often up to several years. So Ca2SiO4 gives ultimate strength.

Now let and see:

Portland cement is made up of four main compounds: Tricalcium silicate (3CaO.SiO2), dicalcium silicate (2CaO.SiO2), tricalcium aluminate (3CaO.Al2O3), and a tetra-calcium aluminoferrite (4CaO.Al2O3Fe2O3). In an abbreviated notation differing from the normal atomic symbols.

c3s and c2s are major strength giving component in cement. For same amount of ater added (23%). c2a give more amount of c-s-h gel which bind cement molecule together.

c3a provide early setting characteristics while c2a react slowly but provide strength while hardening process.

Raising of C2S, early strength reduces in comparison to C3S but, increases ultimate strength along with decreasing heat of hydration.

Almost after 1 year, C2S contribute the strength and durability almost equal to the C3S.

C2S imparts resistance to chemical attack.

Basically Silica is an strength parameter and alumina is an setting parameter. If we need our structure to attain quick setting we need to increase the quantity of alumina (tricalcium aluminate and tetracalcium aluminoferrite). Vise versa for silica.

Tricalcium aluminate responsible for initial setting time.
Tricalcium silicate responsible for initial strength.
Di calcium silicate responsible for ultimate strength.
Tetra calcium alumino ferrite responsible for the flash set.

C3S hydrates rapidly generating high heat and develops as an early strength however C2S hydrates slowly and takes longer time to gain strength but strength for C3S and C2S will be same. Answer is C3S.

Plasticity is opposite of elasticity,

Plasticity never regains its original shape after applied load as elasticity do.

Plasticity is a stage between liquid limit and plastic limit of the material.

Tricalcium silicate would contribute more in gaining the early and ultimate strength of the concrete then that of dicalcium silicate. So C3S is the answer.