Expansive cement, also known as shrinkage-compensating cement, is a special type of cement that undergoes controlled expansion after setting. This unique property makes it ideal for use in construction projects where minimizing shrinkage cracks is essential. In this article, we’ll delve deeper into the manufacture, properties, types, and uses of expansive cement.
Manufacture of Expansive Cement Expansive cement is produced by adding certain materials to ordinary Portland cement during the manufacturing process. These materials include calcium sulfate, magnesium oxide, and calcium oxide. The resulting cement has the ability to expand during the early stages of hydration.
Properties of Expansive Cement Expansive cement has a number of properties that make it ideal for use in certain construction applications. Some of these properties include:
- Controlled Expansion: Expansive cement undergoes controlled expansion after setting, which helps to compensate for shrinkage losses.
- High Strength: Expansive cement has a higher strength than ordinary Portland cement, making it ideal for use in applications where high strength is required.
- Durability: Expansive cement has good durability, making it resistant to water, frost, and chemicals.
- Low Heat of Hydration: Expansive cement generates less heat during the hydration process, which reduces the risk of thermal cracking.
Types of Expansive Cement There are two main types of expansive cement: Type K and Type M.
Type K expansive cement is made from a mixture of Portland cement, anhydrous tetracalcium trialuminate sulfate, and calcium sulfate. Type K expansive cement has a slower rate of expansion than Type M cement.
Type M expansive cement is made from a mixture of Portland cement, anhydrous tetracalcium trialuminate sulfate, and calcium sulfate, with the addition of magnesium oxide. Type M expansive cement has a higher rate of expansion than Type K cement.
Uses of Expansive Cement Expansive cement is primarily used in applications where minimizing shrinkage cracks is essential. Some common uses of expansive cement include:
- Bridge Decks: Expansive cement is used to construct bridge decks, where minimizing shrinkage cracks is essential to ensure the long-term durability of the structure.
- Concrete Pavements: Expansive cement is used in the construction of concrete pavements, where minimizing shrinkage cracks is important to maintain a smooth surface.
- Precast Concrete: Expansive cement is used in the production of precast concrete products, where minimizing shrinkage cracks is essential to ensure the structural integrity of the product.
Conclusion Expansive cement is a special type of cement that undergoes controlled expansion after setting. This unique property makes it ideal for use in construction projects where minimizing shrinkage cracks is essential. With its high strength, durability, and low heat of hydration, expansive cement is a versatile material that can be used in a wide range of construction applications.
Manufacture of Expansive Cement
Expansive cement is manufactured using a process similar to that of Portland cement. However, the raw materials used for the formation of clinkers are different. To create expansive cement, limestone and clay are heated together to form clinkers at a temperature of about 2,600 degrees Fahrenheit. In the next batch, limestone, calcium sulphate, and bauxite are combined at a temperature of around 2,300 degrees Fahrenheit to form sulfoaluminate clinkers. These two types of clinkers are then ground together to produce expansive cement.
When exposed or mixed with water, sulfoaluminate in the expansive cement expands in volume. There are two main types of expansive cement, namely Type K and Type M. Type K expansive cement is made using calcium sulfate and an aluminate compound, while Type M expansive cement is produced using calcium sulfate, calcium aluminate, and calcium oxide.
Expansive cement is useful for a variety of applications in the construction industry. It can be used for repairing cracked concrete structures and for grouting joints in precast concrete elements such as bridges and tunnels. Expansive cement can also be used to compensate for shrinkage in concrete due to drying, in mass concrete structures, and for stabilizing soil, especially in areas with expansive soils that are prone to swelling and shrinking. Overall, expansive cement is a versatile material that can help solve various problems in concrete structures.
Fig 1: Use of expansive cement mortar in grouting of anchor bolts.
Physical properties of Expansive Cement
Table 1: Properties of expansive cement
| Properties | Value |
| Setting Time | 75 min |
| Air Conctent | 12 % |
| 7 Days expansion | |
| Min | 0.04 % |
| Max | 0.10 % |
| Compressive Strength | |
| 7 Days | 14.7 Mpa |
| 28 Days | 24.5 MPa |
Types of Expansive Cement
Expansive cement is a type of cement that undergoes a controlled expansion after setting. This expansion is caused by the presence of certain expansive compounds in the cement mixture. Depending upon the type of expansive compound used in the cement, expansive cement can be divided into three types.
The first type of expansive cement is based on the use of calcium sulfate compounds, such as gypsum. When calcium sulfate is added to the cement mixture, it reacts with water to form calcium sulfate dihydrate crystals. As these crystals grow and expand, they cause the cement to also expand. This type of expansive cement is commonly known as gypsum-based expansive cement.
The second type of expansive cement is based on the use of calcium aluminate compounds. When calcium aluminate is added to the cement mixture, it reacts with water to form calcium aluminate hydrates, which cause the cement to expand. This type of expansive cement is commonly known as calcium aluminate-based expansive cement.
The third type of expansive cement is based on the use of calcium sulfoaluminate compounds. When calcium sulfoaluminate is added to the cement mixture, it reacts with water to form ettringite crystals, which cause the cement to expand. This type of expansive cement is commonly known as calcium sulfoaluminate-based expansive cement.
In summary, expansive cement is a specialized type of cement that can undergo controlled expansion after setting. The type of expansive compound used in the cement mixture determines the specific type of expansive cement. Gypsum-based expansive cement, calcium aluminate-based expansive cement, and calcium sulfoaluminate-based expansive cement are the three main types of expansive cement.
1. K Type expansive cement
Expansive cement is created from a mixture of raw materials including portland cement, anhydrous tetracalcium trialuminate sulfate (C4A3S), calcium sulfate (CaSO4), and lime (CaO). To make this type of cement, these ingredients are ground together until they form a fine powder. The resulting product is an expansive cement that has a variety of applications.
2. M Type expansive cement
Portland cement clinkers undergo a grinding process with calcium sulfate. During this process, the clinkers are crushed and pulverized until they are reduced to a fine powder. The addition of calcium sulfate helps to regulate the setting time of the cement, ensuring that it sets properly and hardens over time. This process is essential for creating a strong and durable cement that can withstand the demands of construction and engineering projects. By grinding the clinkers with calcium sulfate, the resulting cement mixture can be used in a variety of applications, from building foundations to roadways and bridges.
3. S Type expansive cement
Expansive cement is a type of cement that differs from traditional Portland cement in its composition. It contains a higher amount of computed tricalcium aluminate (C3A) and calcium sulfate than what is typically found in Portland cement. The presence of these components gives the cement its unique properties that allow it to expand after it sets and hardens.
The higher C3A content in expansive cement allows for more rapid hydration, which leads to an increase in early strength development. However, this rapid hydration also causes the cement to produce more heat during the setting process, which can result in cracking and other structural issues if not managed properly. The additional calcium sulfate in the mixture helps to control the heat of hydration, allowing the cement to expand without causing damage.
Overall, the unique composition of expansive cement makes it a useful material in construction applications where controlled expansion is desired, such as in the production of precast concrete elements or in repair work where a tight fit is required.
Uses of Expansive Cement
A specialized type of cement is utilized for constructing massive, seamless floor slabs without any joints. Additionally, this cement is also effective in filling gaps in foundations and creating self-stressed concrete, which is stronger than traditional portland cement concrete. The material is particularly employed in the production of pre-stressed concrete components for bridges and buildings. It is also utilized in the construction of water-retaining structures and for repairing damaged concrete surfaces. Moreover, the cement is used in grouting of anchor bolts.