IS 8112 specifies 43-grade OPC — the minimum 28-day standard-mortar compressive strength is 43 N/mm² (IS 4031 on IS 650 sand). It is the general-purpose structural workhorse: adequate for the bulk of M20–M35 work with lower heat and early-shrinkage than OPC 53, and often the better, lower-cracking choice than defaulting to 53. Grade is mortar strength, not concrete grade.
Key Requirements
•OPC 43 = minimum 43 N/mm² 28-day standard-mortar compressive strength (IS 4031 on IS 650 sand)
•Cement grade ≠ concrete grade (OPC 43 ≠ M43) — it is an input to IS 10262 mix design
•General-purpose default for M20–M35; use OPC 53 (IS 12269) only where early strength/high grade governs
•For thick/mass pours prefer PPC (IS 1489) / low-heat — OPC 53 heat is a liability there
•Durability still comes from cover, W/C and curing — not the grade number
Practical Notes
✓OPC 43 is, for most ordinary RCC, the cement that should be the default — reaching for OPC 53 'because stronger' adds heat/cracking risk for strength the structure doesn't need.
✓Reserve OPC 53 for precast/prestressed/fast-cycle/high-grade; use PPC/slag/low-heat where durability or heat governs.
Common Mistakes
⚠Defaulting to OPC 53 everywhere instead of OPC 43 for ordinary work.
⚠Confusing cement grade with concrete grade (OPC 43 ≠ M43).
⚠Using OPC 43 where durability/aggressive exposure needs PPC/slag.