Comment on cements from oxide composition

The compounds are given by Bogue's calculation, so the comparison is made on C$_3$S, C$_2$S, C$_3$A, C$_4$AF and free lime.

Cement-A

• Very high C$_3$S: rapid-hardening, high early strength; quick strength gain at 3 and 7 days, useful for early formwork removal and cold weather.
• High C$_3$A (11.7%) and C$_3$S: very high heat of hydration and quick setting (needs gypsum; SO$_3$ is 2.4%), more shrinkage and thermal cracking, and poor sulphate resistance.
• Free lime of 3.3% is high: excess free lime causes unsoundness, with expansion and cracking later. The high CaO suggests an over-limed cement, which is risky for soundness (IS 269 controls this through the lime saturation factor and the soundness tests).
• Very low C$_4$AF (Fe$_2$O$_3$ only 0.3%), so it is lighter in colour.
• Use: precast work, repairs and emergency works; not for mass concrete or sulphate-bearing soils.

Cement-B

• High C$_2$S (56.6%) and low C$_3$S: slow strength gain, but high long-term strength (after 28 days). This composition is typical of a low-heat cement (e.g. ASTM Type IV, which requires C$_3$S at most 35% and C$_2$S at least 40%).
• Low C$_3$A (5.7%): lower heat, less shrinkage and moderate sulphate resistance. It is just above the 5% limit for a true sulphate-resisting cement (IS 12330), so it is not fully sulphate-resisting. C$_4$AF is moderate (9.1%).
• Low free lime (1.0%): sound cement with a low risk of expansion.
• Use: mass concrete (dams, rafts), hot weather, and moderate sulphate exposure, where thermal cracking must be limited.

Conclusion: Cement-A is a high-early-strength, high-heat cement with a soundness risk; Cement-B is a low-heat, durable, slow-gaining cement with moderate sulphate resistance.