Blended cement is a type of cement that is made by mixing ordinary Portland cement (OPC) with various blending materials like silica fumes, fly ash, limestone, and slag. This results in a uniform mixture that can enhance the properties of the cement for different applications. Blended cement has the potential to improve concrete’s workability, strength, durability, and chemical resistance. In this article, we will delve into the features, classifications, benefits, and applications of blended cements.
Characteristics of Blended Cement
Blending cement with different materials can result in several improved properties. For instance, it can improve the workability and pumpability of the cement mixture, which can be beneficial for various construction applications.
Another advantage of blending cement with other materials is that it can help to reduce the water demand of the mixture. This reduction in water demand can lead to several benefits, such as enhanced bleed control, lower drying shrinkage, and reduced creep.
In addition, blending cement with other materials can improve the cement’s resistance to sulphate attack and chloride penetration. This can be particularly useful in areas where the cement will be exposed to harsh environmental conditions, such as coastal regions.
Finally, blending cement with other materials can also help to reduce the potential for Alkali Aggregate Reaction, which is a chemical reaction that can occur between certain types of aggregates and the cement paste. This reaction can lead to the development of cracks in the concrete over time, which can compromise its structural integrity. Therefore, reducing the potential for this reaction can help to ensure the long-term durability and reliability of the concrete structure.
Fig 1: Types of materials used in blended cement.
Types of Blended Cement
Blended cement is a type of cement that is made by blending different materials together. The classification of blended cement is based on the type of blending material used in the cement. The American Society for Testing and Materials (ASTM) specification provides a framework for the classification of blended cement, and according to this specification, there are four types of blended cement.
The ASTM specification is an important standard for blended cement because it provides a consistent and objective way to classify different types of blended cement. By using this standard, manufacturers can ensure that their products meet the required quality standards and are suitable for use in various applications.
The four types of blended cement classified by the ASTM specification are based on the blending material used in the cement. These materials can include fly ash, slag cement, silica fume, and natural pozzolans. Each type of blended cement has different properties and characteristics, which make them suitable for different applications.
Overall, the classification of blended cement is an important consideration for manufacturers, engineers, and builders who are looking to use this type of cement in construction projects. By understanding the different types of blended cement and their properties, it is possible to select the most appropriate material for a given application, which can help to ensure the durability and longevity of the finished structure.
1. Type IS (X), Portland-Slag Cement
Slag cement is commonly used in construction blends, with proportions of up to 70%. These blends are suitable for general construction purposes.
2. Type IP (X), Portland-Pozzolan Cement
Blended cement is a type of construction material that can contain a maximum of 50% pozzolan. Pozzolan refers to any material that, when combined with calcium hydroxide, can create a cementitious compound. The most commonly used pozzolan in blended cement is fly ash.
Blended cement is a popular choice for construction projects due to its ability to improve the properties of concrete. The addition of pozzolan helps to reduce the amount of Portland cement needed, which not only reduces costs but also makes the concrete more sustainable. Fly ash, a byproduct of coal combustion, is a commonly used pozzolan due to its abundance and low cost.
In addition to reducing the amount of Portland cement needed, blended cement can also improve the durability and strength of concrete. The pozzolan in blended cement reacts with calcium hydroxide to form additional cementitious compounds, which can increase the strength and reduce the permeability of the concrete. This makes blended cement an attractive option for a variety of construction projects.
3. Type IL (X), Portland-Limestone Cement
Portland-limestone cement is a type of cement that has recently entered the market in the United States. It is made by adding between 5% and 15% interground limestone to the cement mixture. This addition of limestone helps to reduce the carbon footprint of cement production and also makes the cement more durable. By using Portland-limestone cement, builders and contractors can create structures that are both environmentally friendly and long-lasting.
4. Type IT, Ternary Blended Cement
Ternary cements are created by combining two supplementary materials, such as fly ash, slag cement, or silica fume, with portland cement. The designation of the ternary cement type depends on the material with the highest proportion in the blend. For example, if fly ash is the primary component, the ternary cement would be classified as Type IP.
The composition of the ternary cement is denoted by adding the percentage of the supplementary material in parentheses after the cement type. The remaining portion of the blend is made up of portland cement. To illustrate, Type IL (10), which stands for portland-limestone cement, contains 10% limestone and 90% portland cement.
Advantages of Blended Cement
Blended cement is a type of cement that offers several benefits over ordinary Portland cement (OPC). Firstly, it provides a smoother texture than OPC, making it ideal for finishing and elevation work. Additionally, it has lower water consumption, making it easier to work with and shape.
Another major advantage of blended cement is its strength. After 28 days, it has significantly higher compressive and flexural stress strength than OPC. Additionally, it has low permeability, which can extend the life of concrete by reducing the penetration of aggressive water run-off compounds like sulfates and chlorides.
Blended cement can also reduce the occurrence of cracks due to thermal stress caused by temperature variations. Furthermore, it can reduce issues related to Alkali-Silica Reaction by using a mix of blended cement with either silica fume and slag or silica fume and fly ash.
Finally, blended cement is environmentally friendly because it uses industrial by-products as blending materials, reducing the need for natural resources like limestone, silica, and clay. Overall, blended cement offers several benefits over OPC, making it an attractive option for various construction projects.
Uses of Blended Cement
Blended cement is a versatile material that is suitable for various applications. It is particularly useful in the construction industry, both for domestic construction and major engineering projects. Its high durability and off-form finish also make it an ideal choice for pre-cast concrete applications.
In addition to construction, blended cement is useful in the stabilization of materials, including pavement recycling for road construction. This makes it an excellent choice for infrastructure projects that require sturdy materials.
Blended cement is also widely used in mining applications due to its strength and durability. It can withstand harsh conditions and is ideal for use in mines, where safety is paramount.
Finally, blended cement can be used to create specialist formulations such as adhesives, renders, mortars, and grouts. This versatility makes it an excellent choice for a wide range of applications, including both commercial and domestic projects.