What Is Cement?
Cement, one of the most important building materials, is a binding agent that sets and hardens to adhere to building units such as stones, bricks, tiles, etc. Cement generally refers to a very fine powdery substance chiefly made up of limestone (calcium), sand or clay (silicon), bauxite (aluminum), and iron ore, and may include shells, chalk, marl, shale, clay, blast furnace slag, slate. The raw ingredients are processed in cement manufacturing plants and heated to form a rock-hard substance, which is then ground into a fine powder to be sold. Cement mixed with water causes a chemical reaction and forms a paste that sets and hardens to bind individual structures of building materials.
Evidence of the use of cement is believed to have been found in the hidden civilization of Mohenjodaro dating back 5000 years. The ancient Greeks used some form of mortar, but it remained for the Romans to develop and use cement. Cement is a substance that is used in a soft or plastic state, which then hardens to make things stick together.
It can thus be regarded as a binder, glue, or adhesive, which in its hardened state binds aggregate particles to form a strong, rigid composite. Remember, the mixture of cement, sand, stone, and water is referred to as concrete. There are various substances that can act like cement, but we will be concentrating on the specific types used for concrete within the building and construction industry.
Cement for construction is based on Portland cement and is supplied in powder form (either in bags or bulk) and, if mixed with water, will set and develop strength. Such cement is used extensively in most parts of the world because the raw materials are available in most regions. Also, these cement are relatively cheap and versatile as setting takes place at normal temperature and pressure, and can be used underwater and result in a strong and durable concrete.
How is Cement Made?
- Rock quarries are blasted with explosives to get limestone (calcium carbonate) and clay. These raw materials are transported to crushing units to be crushed into smaller particles.
- Various types of grinding mills are used to ground the above mixture into a homogenous mixture.
- The above raw material is then mixed with additional components like silica, iron ore, etc., to make the required cement type.
- This mixture is fed into a kiln that burns it at extremely high temperatures. A process known as sintering converts the mixture into clinker. The clinker resembles marble-sized pebbles.
- Next, the clinker is cooled down and stored in silos and later ground into a fine powder (cement) with grinding mills.
- The cement is packed into different types of packaging and shipped.
OPC Cement.
- OPC (Ordinary Portland Cement) is one of the most popular construction building materials used all across the globe.
- This name ‘Portland’ was given by the British cement manufacturer Joseph Aspdin at 1824 because of its strong resemblance to Portland Stone, a type of white-grey limestone found at this isle of Portland, Dorset at England.
- Joseph Aspdin is also credited to have patented this first true artificial cement, which he named as the Portland cement.
Uses of Ordinary Portland Cement (OPC):
- It is used for general construction purposes where special properties aren’t required.
- This is normally used for the reinforced concrete buildings, pavements, bridges, and where soil conditions are normal.
- It is also used for most concrete masonry units and for all uses where the concrete isn’t subject to special sulfate hazard or where the heat generated by this hydration of cement isn’t objectionable.
- It has great resistance to shrinkage and cracking but has less resistance to chemical attacks.
Specifications OPC Cement
| Parameter | OPC Cement | IS:12269 | |
| Sp. Surface (m2/kg.) | 340 ± 10 | 225 m2/kg. minimum | |
|
Setting Time (in minutes)
|
Initial | 100 ± 5 | 30 minutes minimum |
| Final | 150 ± 5 | 600 minutes maximum | |
|
Expansion
|
Le-Chatelier Expansion (in mm) | 1.5 mm max. | 10 mm maximum |
| Autoclave Expansion (in %) | 0.17% | 0.8% maximum | |
|
Compressive Strength (MPa)
|
3 Days | 40 ± 2 | 27 MPa minimum |
| 7 Days | 50 ± 2 | 37 MPa minimum | |
| 28 Days | 61 ± 2 | 53 MPa minimum | |
PPC Cement
- Portland-pozzolana cement (PPC) is produced by grinding together Portland cement clinker and artificial pozzolana (Fly ash) with this addition of gypsum or calcium sulfate.
- Fly ash is a very fine material produced as a residue precipitated electro-statically or mechanically from the exhaust gases of a coal-fired thermal power station.
- Generally, 15-25% fly ash is mixed and ground together with 65-75% Portland clinker and 3-6% gypsum
Uses of Portland Pozzolana Cement (PPC):
- This Cement is Flyash based cement recommended for brick masonry, plastering, tiling, and waterproofing work.
- In these works, strength isn’t the major criterion.
- PPC has an edge on OPC as PPC has a slower rate of the heat of hydration.
- Thereby PPC is prone to educe shrinkage & less cracks ), better workability, and finishing.
Specifications PPC Cement
| Parameter | OPC Cement | Requirement as per lS1489 (Part-1) : 1991 | |
| Sp. Surface (m2/kg.) | 340 ± 10 | 300 m2/kg. minimum | |
|
Setting Time (in minutes)
|
Initial | 160 ± 5 | 30 minutes minimum |
| Final | 270 ± 5 | 600 minutes maximum | |
|
Expansion
|
Le-Chatelier Expansion (in mm) | 1.5 mm max. | 10 mm maximum |
| Autoclave Expansion (in %) | 0.17% | 0.8% maximum | |
|
Compressive Strength (MPa)
|
3 Days | 72 ±1 | 16 MPa minimum |
| 7 Days | 168 ± 2 | 22 MPa minimum | |
| 28 Days | 672 ±4 | 33 MPa minimum | |
Difference Between OPC and PPC
| Sr.NO. | OPC Cement | PPC Cement |
| 1 | Definition: A mixture of limestone and other raw materials like argillaceous, calcareous, gypsum is prepared and then grinded to prepare OPC. | Definition: PPC is prepared by adding Pozzolanic materials to OPC. So, the main components are OPC clinker, gypsum, and pozzolanic materials (15~35%), which include calcined clay, volcanic ash, fly ash, or silica fumes. |
| 2 | Strength: Initial strength is higher than PPC. | Strength: PPC has a higher strength than OPC over a longer period of time |
| 3 | Heat of hydration: Generates more heat than PPC in hydration reaction which makes it less suitable for mass casting. | Heat of hydration: It has a slow hydration process and thus generates less heat than OPC. |
| 4 | Durability: Less durable in aggressive weather. | Durability: More durable in aggressive weather. |
| 5 | Cost: Costlier than PPC. | Cost: Cheaper than OPC. |
| 6 | Environmental Impact: Emits CO2 during the manufacturing process. | Environmental Impact: It constitutes industrial and natural waste which makes it eco-friendly. |
| 7 | Application: It is suitable where fast construction is required but not suitable for mass concreting due to heat issue as mentioned above. | Application: It is suitable for all types of construction work. For example RCC casting of buildings, mass concreting for bridges and even plastering and other non-structural works. |
| 8 | Setting Time: Lower than PPC. Its initial setting time is 30 minutes and final setting time is 280 minutes. Its faster setting time helps faster construction. | Setting Time: Setting time of PPC us higher than OPC. Its initial setting time is 30 minutes and the final setting time is 600 minutes. Its slower setting time helps to get better finishing. |
| 9 | Fineness: OPC has finiteness of 225 sq.m/kg. It has lower fineness than PPC. So, it has higher permeability resulting lower durability. | Fineness: OPC has finiteness of 300 sq.m/kg. It has higher fineness than OPC. So, it has lower permeability resulting in higher durability. |
| 10 | Grades available: 33 Grade, 43 Grade, and 53 Grade OPC cement are available | Grades available: No specified grade of PPC cement is available. |
| 11 | Workability: Lower than PPC. | Workability: Higher than OPC. |
| 12 | Resistance against chemical attack: It has lower resistance against alkalis, sulphates, chlorides etc. | Resistance against chemical attack: It has higher resistance against alkalis, sulfates, chlorides, etc. |
Frequently Asked Questions about Cement:
What is cement?
Cement is a binding agent that sets and hardens to adhere to building units such as stones, bricks, tiles, etc. It is primarily composed of limestone, sand or clay, bauxite, and iron ore, processed into a fine powder form.
How is cement made?
Cement is made by crushing limestone and clay, grinding them into a fine powder, mixing with additional components like silica and iron ore, and then heating this mixture in a kiln at high temperatures. The resulting product, called clinker, is cooled, ground into a fine powder, and packaged for use.
What is Ordinary Portland Cement (OPC)?
OPC is one of the most commonly used types of cement in construction. It is suitable for general construction purposes where special properties aren’t required. OPC sets and develops strength when mixed with water and is widely used in reinforced concrete buildings, pavements, bridges, and more.
What is Portland Pozzolana Cement (PPC)?
PPC is produced by grinding together Portland cement clinker and artificial pozzolana, such as fly ash, with the addition of gypsum. It is recommended for brick masonry, plastering, tiling, and waterproofing work, offering slower hydration, better workability, and finishing compared to OPC.
What are the key differences between OPC and PPC?
OPC typically has higher initial strength, faster setting time, and lower cost compared to PPC. However, PPC offers higher strength over a longer period, slower heat of hydration, better durability in aggressive weather, and is more environmentally friendly due to its use of industrial waste materials.
