Skip to main content

Bogue's compounds and their role

Short answer

Bogue's compounds are C3S (early strength, high heat), C2S (later strength, low heat), C3A (flash set, very high heat, sulfate attack) and C4AF (flux, little strength). C3S and C2S form C-S-H gel, governing early and long-term strength respectively; C3A is controlled by gypsum.

Explain Bogue's compounds of cement and their role in the properties and strength development of concrete.

Bogue's compounds are the four main compounds formed in the kiln when limestone and clay are burnt to clinker (at about 1450 °C). Their percentages are calculated from the oxide analysis of the cement using Bogue's equations. In cement chemistry notation, C = CaO, S = SiO2_2, A = Al2_2O3_3 and F = Fe2_2O3_3.

CompoundFormulaApprox. %Hydration rateHeat of hydration
Tricalcium silicate (alite)3CaO⋅SiO23CaO\cdot SiO_2 (C3_3S)40-55FastHigh (~500 J/g)
Dicalcium silicate (belite)2CaO⋅SiO22CaO\cdot SiO_2 (C2_2S)20-30SlowLow (~260 J/g)
Tricalcium aluminate (celite)3CaO⋅Al2O33CaO\cdot Al_2O_3 (C3_3A)8-12Very fastVery high (~870 J/g)
Tetracalcium aluminoferrite4CaO⋅Al2O3⋅Fe2O34CaO\cdot Al_2O_3\cdot Fe_2O_3 (C4_4AF)8-12ModerateModerate (~420 J/g)

Role in properties and strength

  • C3_3S: hydrates within hours to days. It gives the early strength (up to 7 days) and much of the 28-day strength, and releases a lot of heat and Ca(OH)2Ca(OH)_2. Cement with more C3_3S is rapid-hardening.
  • C2_2S: hydrates slowly, so it contributes little in the first weeks but provides the strength gained after 28 days (up to about 1 year). It releases little heat and gives better resistance to chemical attack, so low-heat cement is high in C2_2S.
  • C3_3A: reacts instantly with water and causes flash set, so gypsum is added to control it. It adds little to strength (only some at 1 day), liberates a large amount of heat, and is the compound attacked by sulphates (it forms ettringite, which expands). Sulphate-resisting cement keeps it below 5%.
  • C4_4AF: contributes very little to strength; it acts as a flux in the kiln and gives cement its grey colour. It is fairly resistant to sulphates.

Strength development

Early strength is governed by C3_3S and later strength by C2_2S. Together, C3_3S and C2_2S form about 70-80 per cent of the cement and produce the C-S-H gel, which is the main strength-giving product.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Concrete Technology and Masonry Structure chapter 1 questions →