What are the two major components in portland cement that co

What are the two major components in portland cement that contribute most to its final strength? What are their hydration products?

Solution

The chief chemical constituents of Portland cement are as follows:

Lime (CaO)

60 to 67%

Silica (SiO2)

17 to 25%

Alumina (Al2O3)

3 to 8%

Iron oxide (Fe2O3)

0.5 to 6%

Magnesia (MgO)

0.1 to 4%

Sulphur trioxide (SO3)

1 to 3%

Soda and/or Potash (Na2O+K2O)

0.5 to 1.3%

The above constituents forming the raw materials undergo chemical reactions during burning and fusion, and combine to form the following compounds called BOGUE COMPOUNDS.

Compound

Abbreviated designation

Tricalcium silicate (3CaO.SiO2)

C3S

Dicalcium silicate (2CaO.SiO2)

C2S

Tricalcium aluminate (3CaO.Al2O3)

C3A

Tetracalcium alumino-ferrite (4CaO.Al2O3.Fe2O3)

C4AF

Tricalcium silicate (C₃S) in cement chemist notation) is typically the most abundant. In Type I, II and III portland cement,C₃S will be more than 50% of the total compounds present. C₃S hydrates and hardens quickly, and consequently, influences concrete\'s setting time and early age strength significantly. Most strength gained from C₃S occurs in the first four weeks

Dicalcium silicate (C₂S), the second most abundant compound in Portland cement, develops strength more slowly than C₃S. Most of its strength is contributed after four weeks.

Tricalcium aluminate (C₃A) plays a major role in the characteristics of fresh concrete. It starts the hydration process quickly upon exposure to water and generates much heat during the first few days. It also contributes to the very early age strength of one to three days

Tetracalcium aluminoferrite (C₄AF) is primarily a result of materials used in the cement manufacturing process to lower the temperatures required in the kilns. C₄AF hydrates rapidly, but contributes little actual strength

Out of these four

1.LIME and SILICA contributes its final strength that is dicalcium silicate

And

2.LIME , ALUMINA and IRON OXIDE are their hydration products