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Grade of cement; Bogue's compounds

Short answer

G rade is the minimum 28-day compressive strength of 1:3 cement-sand mortar cubes in MPa. B ogue's compounds: C3S gives early strength, C2S later strength, C3A causes flash set and low sulphate resistance, C4AF acts as flux and imparts color.

Define grade of cement. Explain the role of Bogue's compound of cement.

Grade of cement is the minimum compressive strength, in MPa (N/mm2^2), of 70.6 mm mortar cubes (1:3 cement : standard sand, w/c = (P/4 + 3.0)%) at 28 days, tested as per IS 4031 (Part 6). For example, in IS 269:2015, OPC 33 grade means a minimum 28-day strength of 33 MPa, OPC 43 gives 43 MPa and OPC 53 gives 53 MPa. Higher grades are finer and have more C3_3S, giving higher early strength.

Role of Bogue's compounds

CompoundRole
C3_3S (alite, 40-55%)Rapid hydration; gives early strength (7 days) and also strength at 28 days; high heat
C2_2S (belite, 20-30%)Slow hydration; provides later strength (after 28 days); low heat, good chemical resistance
C3_3A (8-12%)Reacts at once (flash set, controlled by gypsum); little strength; high heat; poor sulphate resistance
C4_4AF (8-12%)Little effect on strength; acts as a flux in the kiln and gives colour; slightly sulphate resistant

C3_3S and C2_2S together make about 70-75 per cent of cement and provide the strength through C-S-H gel; C3_3A and C4_4AF mainly influence setting, heat and durability. More C3_3S gives rapid-hardening cement, more C2_2S gives low-heat cement, and low C3_3A gives sulphate-resisting cement.

✓ Answer checked by Claude Opus 5.5 (high effort)

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