Bogue’s Compounds and the Properties

The identification of the major compounds is largely based on R.H. Bogue’s work and hence it is called “Bogue’s Compounds”. The four compounds usually regarded as major compounds are listed in table 1.

Table 1: Bogue’s Compounds
Name of Compound
Formula
Abbreviated Formula
Percentage (%)
Tricalcium silicate
3 CaO.SiO₂
C₃S
30-50
Dicalcium silicate
2 CaO.SiO₂
C₂S
20-45
Tricalcium aluminate
3 CaO.Al₂O₃
C₃A
08-12
Tetracalcium aluminoferrite
4 CaO.Al₂O₃.Fe₂O₃
C₄AF
06-10

It is to be noted that for simplicity’s sake abbreviated notations are used. C stands for CaO, S stands for SiO2, A for Al2O3, F for Fe2O3 and H for H2O.

The equations suggested by Bogue for calculating the percentages of major compounds
are given below.
C₃S = 4.07 (CaO) – 7.60 (SiO₂) – 6.72 (Al₂O₃) – 1.43 (Fe₂O₃) – 2.85 (SO₃)
C₂S = 2.87 (SiO₂) – 0.754 (3CaO.SiO₂)
C₃A = 2.65 (Al₂O₃) – 1.69 (Fe₂O₃)
C₄AF= 3.04 (Fe₂O₃)

Properties of Bogue’s Compounds

Each Bogue’s compounds behaves in different way, Properties of Bogue’s compounds  are as follows:

C₃S

Tricalcium silicate  responsible for early strength and ultimate strength of the cement. First 7 days strength is due to C₃S. C₃S Produces more amount of heat during hydration process.  A cement with more C₃S content is suitable  for cold weather concreting.

C₂S

The hydration of C₂S starts after 7 days. Hence, it gives strength after a duration of 7 days. C₂S hydrates and hardens slowly and provides much of the ultimate strength. It produces less heat of hydration. It is responsible for the later strength of concrete.

C₃A

Sets instantaneously in presence of water. Cement’s internal strength is mainly because of this. The reaction of C₃A with water is very fast and may lead to an immediate stiffening of paste, and this process is termed as flash set.  To prevent this flash set, 2 to 3 % gypsum is added at the time of grinding the cement clinkers.

C₄AF

Acts as a flux during manufacturing. Contributes to the color effects that makes cement gray. Tetracalcium aluminoferrite sets but not fast as Tricalcium aluminate. It does not contribute to the strength of concrete. The hydrates of C₄AF show a comparatively higher resistance to sulphate attack than the hydrates of C₃A. 

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