Cement is the basic ingredient of concrete, mortar and plaster which consists of a mixture of oxides of calcium, silicon and aluminium. This article on Portland Cement discusses its composition, manufacturing process, properties, type, uses, etc.
What is Portland Cement?
Portland cement is a generic term used to describe any type of hydraulic cement that is produced by heating a mixture of limestone and clay or limestone and shale in a kiln to a high temperature of 1,450 °C. Then the resulting clinker is ground to a fine powder which is known as Portland Cement.
The name “Portland” comes from the fact that the cement is made to resemble a type of limestone quarried in Portland, England. It was first patient by Joseph Aspdin British stone mason in 1824 in England. Aspidin burnt finely ground limestone and clay in a kiln at very high temperatures which set and gain strength in coming contact with water. He then named it Portland cement which is a hydraulic property in nature.
Usually, cement is grey, with an average particle size of approximately 45μm (Mehta. p427. 2010). However, other colour variations are also made as White Portland cement, which contains little or no iron or manganese.
Composition of Portland Cement
The major raw material required is clay or shale. Clay consists of the oxides of silicon, aluminium and iron whereas, shale is a highly compressed form of clay. Limestone comprises approximately two-thirds of the raw material required for making cement.
Portland cement consists of four major clinker compounds, Tricalcium Silicate (C3S), Dicalcium Silicate (C2S), Tricalcium Aluminate (C3A), and Tetracalcium Aluminoferrite (C4AF) together with the gypsum added during grinding.
| Sl.No. | Clinker Compound | By Weight |
|---|---|---|
| 1. | Tricalcium Silicate (C3S) | 40% |
| 2. | Dicalcium Silicate (C2S) | 30% |
| 3. | Tricalcium Aluminate (C3A) | 11% |
| 4. | Tetracalcium Aluminoferrite (C4AF) | 11% |
Manufacturing Process of Portland Cement
The process used to manufacture modern Portland cement is essentially identical to the process used by Aspidin, as it involves heating a blend of limestone and clay, which are the same fundamental raw materials.
The manufacturing of cement begins with the quarrying of limestone and crushing it into smaller pieces is the initial stage. Crushed limestone and other fundamental raw materials (clay, sand and iron) are stored in silos which are later processed according to needs. These raw materials are mixed together in the proportion stipulated to gain the desired cement types.
The raw materials are then ground into a fine powder in a grinding mill. The fine powder is taken to a rotatory kiln which is heated at 1450 °C where calcium carbonate is converted to calcium oxide. Later at the end of the rotatory kiln where the temperature is much higher, calcium oxide reacts with other raw materials to form a calcium compound which is partially a molten form. The clinker is cooled and stored in a silo.
The cooled clinker is mixed with a small quantity of gypsum, The clinkers and gypsum are ground and blended into a very fine powder which is called Portland cement. The addition of gypsum will help in controlling the setting time of the cement.
Also, read: Ordinary Portland Cement: Properties, Composition, Manufacturing and Uses
Properties of Portland Cement
- Finenss:
Fineness refers to the sizes of cement particles, influencing both the performance and application of the cement. Cement fineness is measured by either the sieve analysis method or by determining the specific surface area. The sieve analysis method mandates that the residue on the 0.080mm square-hole sieve should not surpass 10%. Specific surface area is computed based on the total surface area of 1 kg of cement (m2/kg). For Portland cement, the specific surface area should be greater than 300 m2/kg.
- The Setting Time:
The setting time of cement includes the initial setting time and the final setting time. The initial time refers to the time that cement turns into a paste by mixing with water and begins to lose its plasticity. The time that cement completely loses its plasticity by mixing with water and begins to have a certain structural strength is known as the final setting time.
The initial setting time of Portland cement should not be earlier than 30 minutes and the final setting time should not be later than 6.5 hours. The setting time of cement is measured by a time determinator. The sample is the standard cement paste of which the temperature is 20°C ± 3°C and humidity is more than 90%.
The initial setting time should not be too fast in order to ensure that there is enough time to complete every process, such as casting, before the initial setting time; and the final setting time should not be too late in order to enable the cement to complete its setting and hardening as soon as possible after pouring and tamping to make the next process occur earlier.
- Soundness:
The cement is said to be unsound if it exhibits volumetric instability after hardening. IS code recommends testing with Le Chatelier mould for testing this property. At the end of the test, the indicator of Le Chatelier mould should not expand by more than 10 mm
- Crushing strength:
For this mortar cubes are made with standard sand and tested in a compression testing machine as per the specification of the IS code. The minimum strength specified is 16 N/mm2 after 3 days and 22 N/mm2 after 7 days of curing
- Alklin Content:
The alkali content in cement is indicated by the presence of Na2O and K2O. The prerequisite for the alkali-aggregate reaction to occur in concrete is that the cement must include alkali. When the active aggregate material is used, the cement with low alkali content should be used. The alkali content in cement should not exceed 0.60% or can be determined by the two sides of supply and demand.
Types of Portland Cement
According to ASTM C150, which is a standard specification for Portland cement, there are five types of Portland cement manufactured that are classified based on their physical and chemical properties which are altered in very small quantities. The main types are:
Type I – This is the most common type of cement and is used for general construction purposes. It is suitable for use in concrete, mortar, and other building applications.
Type II – This type of cement is designed to produce concrete that is more resistant to sulfates and other chemical attacks. It is commonly used in structures that are exposed to soil and water containing sulfates.
Type III – This type of cement is used when a fast-setting time is required, such as in precast concrete applications. It has a higher early strength than Type I or Type II cement.
Type IV – This type of cement is used in massive concrete structures where heat buildup can cause cracking. It generates less heat during hydration than Type I, Type II, or Type III cement.
Type V – This type of cement is used in high-sulfate environments such as seawater and soil with high sulfate concentrations. It has the highest resistance to sulphate attacks among all types of cement.
Also, read: Portland Pozzolana Cement: Properties | Advantages | Uses
Types and Their Uses
| Portland Cement | Uses |
|---|---|
| Type I | General-purpose cement, is used where there is no special requirement |
| Type II | Sulfate-resistant cement is used where high sulfate resistance is required |
| Type III | High-early-strength cement is used in precast elements and where high early strength is required, such as in cold weather |
| Type IV | Low-heat-of-hydration Portland cement, used in massive civil engineering structures |
| Type V | Sulfate-resistant cement is used where high sulfate resistance is required |
Also, read: White Portland Cement: Properties, Applications, Advantages, Disadvantages
FAQs:
Q: What is Portland Cement?
Ans: It is a hydraulic cement which was patented in 1824 by Joseph Aspidin. It is produced by heating a mixture of limestone and clay in a kiln to a high temperature of 1,450 °C. Then the clinker is ground to a fine powder which is known as Portland Cement. It has a wide range of applications in construction work.
Q: What is the difference between Portland Cement and OPC?
Ans: Portland cement is a generic term used to describe hydraulic cement that includes several different types of cement. Whereas, OPC (Ordinary Portland cement) is a type of hydraulic cement or Portland cement that is distinguished by the amount of composition in it.
References:
- Mehta, M., Scarborough, W., & Armpriest, D. (2017). Building constructions: Principles, materials, and systems. Pearson Education, Inc.
- Zhang, H. (Ed.). (2011). Building Materials in Civil Engineering (1st ed.). Woodhead Publishing Limited. https://shop.elsevier.com/books/building-materials-in-civil-engineering/zhang/978-1-84569-955-0
- Portland cement. (2023, March 25). In Wikipedia. https://en.wikipedia.org/wiki/Portland_cement
- Britannica, T. Editors of Encyclopaedia (2023, April 21). portland cement. Encyclopedia Britannica. https://www.britannica.com/technology/portland-cement
- Portland Cement Association. https://www.cement.org/cement-concrete/cement-and-concrete-basics-faqs/lists/cement-concrete-basics-faqs/are-there-different-types-of-portland-cement- Cement & Concrete Basics FAQs.
