Ordinary Portland cement is a highly popular type of cement that is widely used for various construction purposes. The name “Portland” was given to this cement by Joseph Aspdin in 1824, as he observed that its color and quality closely resembled that of the white grey limestone found in the island of Portland, Dorset.
This type of cement is known for its unique properties and constituents. Ordinary Portland cement is made from a mixture of raw materials such as limestone, shale, and clay, which are finely ground and then heated at a high temperature to form a clinker. The clinker is then mixed with a small amount of gypsum to produce the final product.
The properties of Ordinary Portland cement make it highly suitable for use in construction projects. It has excellent strength and durability, making it ideal for use in structures that are exposed to harsh weather conditions. Additionally, it has a relatively fast setting time, which makes it convenient for use in projects with tight schedules.
One of the key advantages of Ordinary Portland cement is its versatility. It can be used in a wide range of construction projects, including the construction of buildings, bridges, roads, and other infrastructure. Furthermore, it is a cost-effective option compared to other types of cement, which makes it a popular choice among builders and contractors.
In conclusion, Ordinary Portland cement is a highly useful type of cement that has been widely used for centuries. Its unique properties and constituents make it ideal for a range of construction projects, while its cost-effectiveness and availability have made it a popular choice among builders and contractors.
Constituents of Ordinary Portland Cement
Ordinary Portland Cement is manufactured using two principal raw materials: argillaceous or silicates of alumina in the form of clays and shales, and calcareous or calcium carbonate, in the form of limestone, chalk, and marl which is a mixture of clay and calcium carbonate.
To make the cement, these ingredients are mixed in the proportion of about two parts of calcareous materials to one part of argillaceous materials. The mixture is then crushed and ground in ball mills. This process can be done either in a dry state or a wet state.
The resulting dry powder or wet slurry is then burnt in a rotary kiln at a temperature between 1400 degrees Celsius to 1500 degrees Celsius. This high temperature process causes the mixture to undergo chemical reactions and form clinker.
After the clinker is obtained from the kiln, it is first cooled and then passed on to ball mills where gypsum is added. The mixture is ground to the requisite fineness according to the class of product. This final grinding process prepares the cement for use in construction applications.
The chief chemical constituents of Portland cement are as follows:
| Lime (CaO) | 60 to 67% |
| Silica (SiO2) | 17 to 25% |
| Alumina (Al2O3) | 3 to 8% |
| Iron oxide (Fe2O3) | 0.5 to 6% |
| Magnesia (MgO) | 0.1 to 4% |
| Sulphur trioxide (SO3) | 1 to 3% |
| Soda and/or Potash (Na2O+K2O) | 0.5 to 1.3% |
When the raw materials listed earlier are burned and fused, they undergo chemical reactions that result in the formation of certain compounds known as Bogue compounds.
| Compound | Abbreviated designation |
| Tricalcium silicate (3CaO.SiO2) | C3S |
| Dicalcium silicate (2CaO.SiO2) | C2S |
| Tricalcium aluminate (3CaO.Al2O3) | C3A |
| Tetracalcium aluminoferrite (4CaO.Al2O3.Fe2O3) | C4AF |
Portland cement is composed of four compounds, which are tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium alumino-ferrite. The proportion of these compounds can vary in different types of Portland cement. Among these compounds, tricalcium silicate and dicalcium silicates are the most significant contributors to the strength of the cement. The initial setting of Portland cement is mainly due to tricalcium aluminate. Tricalcium silicate hydrates quickly and contributes more to the early strength, while the contribution of dicalcium silicate takes place after 7 days and may continue for up to 1 year.
Tricalcium aluminate hydrates quickly and generates a lot of heat, but it makes only a small contribution to the strength within the first 24 hours. On the other hand, tetracalcium alumino-ferrite is relatively inactive. All four compounds generate heat when mixed with water, with the aluminate generating the maximum heat and the dicalcium silicate generating the minimum. Due to this, tricalcium aluminate is responsible for most of the undesirable properties of concrete. Portland cement with less tricalcium aluminate will have higher ultimate strength, less generation of heat, and less cracking.
The composition and percentage of the four compounds in normal and rapid hardening and low heat Portland cement can vary. Table below gives the details of the proportion of these compounds. In general, the proportion of tricalcium silicate is higher in rapid hardening cement, while low heat Portland cement has a lower percentage of tricalcium aluminate. The proportion of dicalcium silicate is relatively constant across different types of Portland cement.
Composition and compound content of Portland Cement:
| Portland Cement | Normal | Rapid hardening | Low heat |
| (a) Composition: Percent | |||
| Lime | 63.1 | 64.5 | 60 |
| Silica | 20.6 | 20.7 | 22.5 |
| Alumina | 6.3 | 5.2 | 5.2 |
| Iron Oxide | 3.6 | 2.9 | 4.6 |
| (b) Compound: Percent | |||
| C3S | 40 | 50 | 25 |
| C2S | 30 | 21 | 35 |
| C3A | 11 | 9 | 6 |
| C3A | 12 | 9 | 14 |
Properties of Ordinary Portland Cement
Table 2 : Properties of OPC cement
| Properties | Values |
| Specific Gravity | 3.12 |
| Normal Consistency | 29% |
| Initial Setting time | 65min |
| Final Setting time | 275 min |
| Fineness | 330 kg/m2 |
| Soundness | 2.5mm |
| Bulk Density | 830-1650 kg/m3 |
Manufacture of OPC cement
Majorly there are 5 steps involved in the manufacture of OPC cement,
1. Crushing and grinding of raw material
The initial stage in the production of cement involves crushing and grinding the raw materials into small particles of a suitable size. However, the specific process used for this crushing and grinding varies depending on the type of manufacturing process employed.
There are three main types of manufacturing processes for cement: dry process, wet process, and semi-wet process. In the dry process, the raw materials are dried prior to being crushed and ground. This is in contrast to the wet process, where the raw materials are mixed with water and then crushed and ground.
The semi-wet process falls somewhere in between the dry and wet processes. In this method, the raw materials are partially dried and then mixed with water before being crushed and ground.
Regardless of the manufacturing process used, the first step in cement production remains the same: crushing and grinding the raw materials into small particles that are suitable for further processing.
Fig 1: Flow chart of Manufacture of OPC cement.
2. Mixing or Blending
The raw material, which is limestone, is first ground into a fine powder. This powdered limestone is then blended or mixed with clay in a specific ratio of 75% limestone and 25% clay. To ensure a uniform mix, the compressed air is used to thoroughly combine the materials.
In the dry process, the resulting mixture is stored in silos, while in the wet process, slurry tanks are used to hold the mix. The mixture obtained is known as slurry, which contains approximately 35-40% water. The slurry is used in the production of cement, and its quality and consistency play a crucial role in the final product. Therefore, it is essential to mix the limestone and clay in the appropriate ratio and ensure that the resulting slurry is homogeneous.
3. Heating
OPC cement production involves several important steps, with one of the critical ones being the transfer of the product obtained from the mixing stage to the Kiln via conveyor belts. Once the mixture reaches the Kiln, it undergoes several processes before it becomes OPC cement.
In the first stage, the mixture is preheated to 550C, which causes the moisture content to evaporate, and the clay present in the mixture breaks down into silica, aluminium oxide, and iron oxide. The second stage involves raising the temperature to 1500 degree Celsius, where the oxides present in the mixture form their respective silicate, aluminates, and ferrite. This process is essential to produce the desired cement product.
The final stage involves cooling down the product to 200C, where the end product obtained in the Kiln is known as cement Clinkers. These clinkers are in the form of greenish black or grey colored balls. This final product is the result of several carefully controlled processes, and it forms the basis for the OPC cement manufacturing process.
4. Grinding
During the production of OPC cement, the cement clinkers are mixed with the required amount of gypsum in a specific step. The mixture is then grinded into very fine particles before being stored in silos. Once the cement particles are adequately processed, they are packed into cement bags and distributed for use. It is important to note that OPC cement has a relatively short expiry date of approximately 3 months. Therefore, it is crucial to use the cement within this time frame to ensure maximum effectiveness.
Types of Ordinary Portland Cement
OPC cement is classified differently in various countries, based on their respective codes. This means that the same type of cement can have different names or classifications depending on the country. The codes used to differentiate OPC cement are specific to each nation and are often determined by various factors such as manufacturing processes, raw materials used, and local standards. Therefore, it is important to be aware of the codes used in your country when purchasing OPC cement, to ensure that you are getting the right type of cement for your specific needs.
1. AS per ASTM 150 (American Standards)
Portland cement is a common type of cement used for general purposes, and unless otherwise specified, it is assumed to be Type I. Type II Portland cement provides moderate resistance to sulfate and generates less heat during hydration compared to Type I. Type III Portland cement has relatively high early strength and is similar to Type I, but is ground to a finer consistency. Type IV Portland cement is well-known for its ability to generate low heat during hydration. Lastly, Type V Portland cement is used in applications where sulfate resistance is important. It has a low composition of C3A, which gives it high sulfate resistance.
2. As per EN 197 norm ( European norm)
There are five main types of cement known as CEM I, CEM II, CEM III, CEM IV, and CEM V. CEM I is made up of Portland cement and can contain up to 5% of other minor constituents. CEM II, on the other hand, is also composed of Portland cement, but it can contain up to 35% of other single constituents.
CEM III is made up of Portland cement but has higher percentages of blastfurnace slag compared to CEM I and CEM II. CEM IV, on the other hand, is composed of Portland cement and can contain up to 55% of pozzolanic constituents.
Finally, CEM V is a type of cement that contains Portland cement, blastfurnace slag or fly ash, and pozzolana. These five types of cement have different compositions, and their uses depend on the specific requirements of a construction project.
3. As per CSA A3000-08 ( Canadian standards)
There are several types of cement available in the market, each with its unique properties and applications. One of the most commonly used types is General Use Cement (GU) or Ordinary Portland Cement, which is suitable for a wide range of construction projects. It is a versatile and cost-effective option that can be used in various applications such as concrete, mortar, and plaster.
Another type of cement available is Moderate Sulphate Resistant Cement (MS), which is suitable for structures that are exposed to moderate levels of sulphates. This type of cement provides good resistance against sulphate attack and is often used in the construction of foundations, retaining walls, and sewage systems.
Moderate Heat Cement (MH) and Moderate Heat Low (MHL) Cement are two other types of cement that are suitable for large concrete structures such as dams, bridges, and high-rise buildings. These types of cement generate less heat during the hydration process, which can prevent cracking and other issues in the concrete.
High Early Strength Cement (HE) is a type of cement that is designed to achieve high strength in a short amount of time. It is often used in precast concrete products, such as concrete pipes, where early strength is critical to the success of the project.
Low Heat Cement (LH) and Low Heat Low (LHL) Cement are two other types of cement that generate less heat during the hydration process. This makes them suitable for large concrete structures, such as mass concrete pours and foundations, where the risk of thermal cracking is high.
Finally, High Sulphate Resistant (HS) Cement is a type of cement that provides excellent resistance against sulphate attack. However, it generally develops strength less rapidly than other types of cement and is often used in structures that are exposed to high levels of sulphates, such as marine structures and sewage treatment plants.
Uses of Ordinary Portland Cement
The context provided describes the typical usage of concrete without requiring any special properties, primarily in the construction of reinforced concrete buildings, bridges, pavements, and in areas with normal soil conditions. This type of concrete is commonly utilized for various construction purposes where specific properties are not necessary. Additionally, it is extensively used in the creation of concrete masonry units.
Advantages of Ordinary Portland Cement
The given context mentions both advantages and disadvantages of using Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC) in construction projects.
One advantage of OPC is its high resistance to cracking and shrinkage, making it a durable choice for building structures. However, it has a lower resistance to chemical attacks, which may limit its use in certain environments.
Another advantage of OPC is its faster initial setting time compared to PPC. This makes it suitable for projects where formwork needs to be removed early. Additionally, OPC requires a shorter curing period, which can reduce the overall cost of the project by minimizing the time and resources needed for curing.
However, one disadvantage of OPC is its reduced resistance to chemical attacks, which may limit its use in certain environments. Additionally, the shorter curing period of OPC may not be suitable for projects that require extended curing for optimal strength and durability.
In contrast, PPC has a higher resistance to chemical attacks, making it a more suitable choice for construction projects in harsh environments. However, PPC has a slower initial setting time and longer curing period compared to OPC, which may increase the project timeline and cost.
Disadvantages of Ordinary Portland Cement
When it comes to mass concreting, using Ordinary Portland Cement (OPC) may not be the best option due to its high heat of hydration in comparison to Portland Pozzolana Cement (PPC). This can cause issues such as thermal cracking and can be problematic for large-scale concrete constructions.
In addition, concrete made using OPC tends to have lower durability than concrete made with PPC. This means that the concrete may not last as long and could be more prone to damage or deterioration over time.
Another factor to consider is that OPC produces comparatively less cohesive concrete than PPC. This can make the process of pumping concrete a bit more difficult.
Furthermore, OPC has lower fineness compared to PPC, which can lead to higher permeability and result in lower durability. This makes it more susceptible to damage from environmental factors, which can further reduce its lifespan.
Finally, it is worth noting that OPC is generally more expensive than PPC. This makes it less economical for construction projects that require a large amount of cement.