Blended cement can be defined as uniform mix of ordinary Portland cement (OPC) and blending materials such as silica fumes, fly ash, limestone and slag to enhance its properties for different uses. Blended cement can improve workability, strength, durability and chemical resistance of concrete.
In this article we discuss about characteristics, types, advantages and uses of blended cements.
Characteristics of Blended CementThe enhanced properties that are obtained due to blending of cement with different materials are,
- Improved workability and pumpability.
- Reduced water demand
- Enhanced bleed control
- Lower drying shrinkage and creep
- Improved resistance to sulphate attack and chloride penetration
- Reduced potential for Alkali Aggregate Reaction
Types of Blended CementThe classification of blended cement is based in the type of blending material used in the cement. As per American Society for Testing and Materials (ASTM) specification, blended cement are classified in to 4 types,
1. Type IS (X), Portland-Slag CementBlends containing up to 70% slag cement are used for general construction.
2. Type IP (X), Portland-Pozzolan CementUsed for general construction, this blend can contain up to 50% pozzolan. Fly ash is the most common pozzolan used in blended cement.
3. Type IL (X), Portland-Limestone CementRelatively new to the U.S. market, portland-limestone cement contains between 5% and 15% percent interground limestone.
4. Type IT, Ternary Blended CementTernary cements are blends two complementary supplementary materials such as fly ash, slag cement or silica fume. Note:
- The highest amount of material in the blend determines its type. For example, if fly ash were the highest component, it would be considered Type IP.
- The "(X)" in the designation refers to the percentage of the ingredient included in the blended cement. The remainder is portland cement. For example, Type IL (10), portland-limestone cement, contains 10% limestone and 90% portland cement.
Advantages of Blended Cement
- It provides a finer texture than OPC when mixed and placed. So it can be used for finishing and elevation works.
- Water consumption is less which makes it easy to work with and shape.
- The strength gained after 28 days is significantly stronger than OPC, in both compressive and flexural stress.
- The permeability of blended concrete is low, due to which the life of concrete is extended by reducing penetration of aggressive water run-off compounds such as sulfates and chlorides when compared to ordinary cement.
- Cracks occurred due to thermal stress by variation of temperature is reduced by the use of blended cement.
- Reduced problems realted to Alkali-Silica Reaction by using a mix of blended cement as either silica fume and slag, or silica fume and fly ash.
- Blending material used are industrial by products, the used of these industrial by product reduces the use of natural resources such as limestone, silica and clay.
Uses of Blended CementBlended cement makes it an ideal choice for a wide range of applications such as,
- Domestic construction
- Major engineering project.
- Pre-cast concrete where high durability and off-form finish are required
- Stabilisation including pavement recycling for road construction
- Mining applications
- Specialist formulations such as adhesives, renders, mortars and grouts.