5. Cement in Civil Engineering

 

Cement in Civil Engineering

Cement is the primary binding material in modern construction, acting as a glue that holds aggregates together in concrete and mortar. The most common type is Portland Cement, invented in 1824, known for its hydraulic properties—it sets and hardens by reacting with water (hydration), even underwater.

Chemical Composition of Ordinary Portland Cement (OPC)

Typical compounds (Bogue's compounds):

Chemical components of ordinary Portland cement (type 1 ...

• Tricalcium Silicate (C₃S): 40–60% (early strength).
• Dicalcium Silicate (C₂S): 15–30% (long-term strength).
• Tricalcium Aluminate (C₃A): 5–12% (quick setting, heat evolution).
• Tetracalcium Aluminoferrite (C₄AF): 5–10% (color, minor strength).

Manufacturing Process

Main steps (Dry Process is most common):

1. Raw material extraction (limestone, clay).
2. Crushing and proportioning.
3. Grinding to raw meal.
4. Heating in kiln (1450°C) → Clinker formation.
5. Cooling and grinding clinker with gypsum → Cement powder.

Types of Cement

Common types used in civil engineering:

Type	Description	Grades (Compressive Strength at 28 days)	Common Uses	Key Properties
Ordinary Portland Cement (OPC)	Basic Portland cement; no additives.	33, 43, 53 MPa	General construction, RCC, prestressed concrete	High early strength, versatile
Portland Pozzolana Cement (PPC)	OPC + Pozzolana (fly ash 15–35%).	Similar to OPC but slower initial	Mass concrete, dams, marine structures	Durable, resistant to chemicals
Portland Slag Cement (PSC)	OPC + Blast furnace slag (25–70%).	Similar to OPC	Coastal/marine works, sewage	Excellent sulfate resistance
Rapid Hardening Cement	Higher C₃S content; finer grinding.	Higher than OPC	Road repairs, cold weather	Very quick setting
Sulfate Resisting Cement (SRC)	Low C₃A (<5%).	Similar to OPC	Foundations in sulfate soils	Resists chemical attack
Low Heat Cement	Low C₃S and C₃A.	Lower heat evolution	Mass concrete (dams)	Minimizes cracking from heat

Common grades comparison:

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Hydration Process

Cement + Water → Calcium Silicate Hydrate (C-S-H gel) + Calcium Hydroxide + Heat.

Stages: Initial (minutes), Dormant (hours), Acceleration (strength gain), Deceleration.

Uses in Construction

• Concrete: Cement + Sand + Aggregates + Water (for beams, slabs, columns).

• Mortar: For plastering, masonry.
• Precast elements, roads, bridges.

Cement provides high compressive strength, durability, and versatility but generates significant CO₂ during production—modern blends like PPC/PSC are more sustainable. Proper curing is essential for optimal strength development.