Types of Cement and Their Characteristics

Cement is a binding material used in construction and engineering applications. There are different types of cement tailored to meet specific requirements in construction. Understanding the key characteristics and suitable uses of various cement types is essential for engineers.

Ordinary Portland Cement

Ordinary Portland Cement (OPC) is the most common cement used in general concrete construction. It is made by grinding a mixture of limestone and clay to form a clinker, which is then ground with 2-3% gypsum.

• Has a grey color when finely ground
• Initial setting time of 30-90 minutes
• Compressive strength reaches 70-80 MPa in 28 days
• Contain high amounts of C3S and C2S compounds

OPC is suitable for use in general structures, concrete roads, prestressed concrete, and more.

Portland Pozzolana Cement

Portland Pozzolana Cement (PPC) contains 15-30% pozzolanic materials such as fly ash, rice husk ash, or silica fumes. The pozzolanic reaction between the pozzolanic materials and calcium hydroxide enhances durability.

• Improved resistance to alkali-aggregate reaction and sulfate attacks
• Gains strength slowly over time
• Reduces leaching of calcium hydroxide in concrete
• Lower heat of hydration, reducing temperature cracks

PPC is ideal for marine environments and mass concrete structures like dams.

Rapid Hardening Cement

Rapid hardening cement is designed to gain strength quickly. It contains higher C3S content and finer grinding, resulting in faster hydration and set times.

• Achieves high strength within a few days
• Initial and final setting times are faster compared to OPC
• Releases more heat during hydration
• Has shorter curing periods

RHC allows fast formwork removal and is suitable for precast concrete construction.

Sulfate Resisting Cement

Sulfate resisting cement has reduced C3A content (<5%) and a low C3A/C4AF ratio. This improves resistance to damage from sulfate attacks.

• High sulfate resistance
• Slower strength gain rate
• Longer initial and final setting times
• Higher heat requirements during manufacture

SRC is used in seawater environments and where soil or groundwater has high sulfate content.

White Cement

White cement is designed for aesthetics and has a white color. It is made from raw materials with low iron oxide content.

• White color provides high reflectance
• Contain less C4AF compound compared to OPC
• More expensive than grey cement
• Suitable for architectural finishes

White cement is used for decorative works and in combination with pigments to produce colored concrete or mortar finishes.

Low Heat Cement and Its Characteristics

Low heat cement is designed to reduce the heat of hydration in concrete to minimize cracking risks in massive concrete structures. Understanding its composition and properties is key.

Composition

Low heat cement has reduced proportions of C3S and C3A which are responsible for most heat evolution during cement hydration. The C3S content is limited to 35-50% and C3A is kept below 7%.

Higher amounts of C2S and C4AF are present which liberate less heat. The cement also contains pozzolanic materials like fly ash and slag to reduce the heat.

Characteristics

• Reduces temperature rise during hydration by around 80% compared to OPC
• Has a lower rate of strength development
• Increased setting time by 30-60 minutes
• Lower final strength than OPC, around 20% lower at 28 days
• Improves concrete workability due to fine grinding

Applications

Low heat cement is ideal for:

• Mass concrete structures like gravity dams to minimize thermal cracks
• Piling concrete and foundation concrete to reduce cracking
• Concrete in hot climates and tropical regions

It provides dimensional stability in large pours and reduces risks of thermal cracks.

High Alumina Cement

High alumina cement has high aluminum oxide content, providing unique properties and applications in construction.

Composition

High alumina cement (HAC) contains alumina in the range of 35-50%, with lower amounts of silica, lime, and iron oxide. It is manufactured by fusing bauxite and lime.

Special calcium aluminate clinker forms on rapid cooling. Gypsum is added as a retarder.

Characteristics

• Very high early strength, can gain 50 MPa in 24 hours
• Rapid setting time of 2-4 hours
• Withstands sulfates and chlorides compared to OPC
• High refractory properties, resists high temperatures
• Undergoes conversion to lose strength over long term
• More expensive than OPC

Applications

HAC is recommended for:

• Repair applications demanding high early strength
• Refractory concrete subjected to high temperatures
• Marine environments and acidic conditions
• Emergency construction works

It rapidly gains strength even at low temperatures.

Blast Furnace Slag Cement

Blast furnace slag cement utilizes industrial by-product slag, enhancing concrete durability and sustainability.

Composition

Blast furnace slag cement contains 25-65% ground granulated blast furnace slag, a glassy by-product of iron production.

Slag reacts with cement hydration products to improve strength and durability. However, slag is less reactive than clinker.

Characteristics

• Improved workability and ease of placing
• Enhanced long term strength due to continued slag hydration
• Lower heat of hydration reduces cracks
• Increased resistance to alkali-silica reaction
• Reduced permeability improves durability

Applications

Slag cement suits:

• Marine structures due to lower permeability
• Foundations and pavements needing low heat of hydration
• Sustainable construction due to the use of industrial by-product

It enhances durability while reducing cement clinker consumption for a lower carbon footprint.

Oil Well Cement

Oil well cement is designed with specific properties to meet challenges in oil well construction.

Composition

Oil well cement has higher fineness, with over 90% passing 90-micron sieve. Special retarders control thickening time.

Its composition is optimized to prevent strength retrogression at downhole temperatures exceeding 200°C.

Characteristics

• High fluidity to be easily pumpable for deep placements
• Controlled thickening time to prevent premature setting
• Withstands high pressures and temperatures in the well
• Low permeability critical for zonal isolation
• Prevent gas or fluid migration along the wellbore

Applications

Oil well cement is essential to:

• Cement casings in deep wells exceeding 2500 m
• Seal casings exposed to high pressures up to 60 MPa
• Withstand downhole temperatures over 200°C

It provides critical zonal isolation in oil and gas wells throughout their service life.

Expansive Cement

Expansive cement counteracts drying shrinkage effects in concrete through controlled expansion.

Composition

Expansive cement contains additional cementitious materials that contribute to expansion during hydration:

• Calcium aluminate cements
• Calcium sulfoaluminate (CSA) cements
• Ettringite formation induces expansion on hydration

Characteristics

• Undergoes controlled expansion of around 0.2%
• Offsets shrinkage in restrained concrete
• Reduces shrinkage cracks
• Provides good workability
• Moderate heat of hydration

Applications

Expansive cement is used for:

• Bonded concrete overlays to minimize reflective cracking
• Concrete repairs needing low shrinkage
• Minimizing cracks in bridge decks and pavements

It enhances crack resistance in restrained, reinforced concrete elements.

Conclusion

There are different cement varieties available to meet specific requirements in construction based on their composition and characteristics. Understanding the key traits of these cements will help engineers select the appropriate type for their projects.