| Unit 19 | Cement |
|---|---|
| 19.1 | Explain introduction and raw materials for cement production. |
| 19.2 | Give main steps in cement production (crushing and grinding, strong heating and final grinding). |
| 19.3 | Explain OPC and PPC cement. |
| 19.4 | Explain Portland cement process with flow-sheet diagram. |
| 19.5 | Explain cement Industry in Nepal. |
Applied Chemistry
Unit 19: Cement
Cements, in general adhesive substance of all kinds but in a narrower sense, the binding materials used in building and civil engineering construction. Cements of this kind are finely Powders that when mixed with Water, set to a hard mass.
- It is usually used to build building, Construction, etc.
Cement is a product obtained by combining materials rich in CaO (lime) with other materials like clay which contains silica (SiO2) along with oxide of Al, Mg and Fe. The average composition of Portland cement is CaO (50-60%), SiO2 (20-25%), Al2O3 (5-10%), MgO (2-3%), Fe2O3 (1-2%), Na 2 O (1%) and SO3(1-2%).
Raw materials for cement production
Basic raw materials for manufacture of cement are
- Calcareous materials (which supply lime (CaO) ): e.g. limestone, cement rock, chalk, clay etc.
- Argillaceous materials (which supply SiO2, Al2O3, Fe2O3 etc.): e.g. clay, shale, blast furnace slag.
- Gypsum CaSO4 .2H2O
Main steps in cement production
There are the following main steps in the manufacture of Portland cement:
- Crusing and Grinding
- Strong Heating
- Final Grinding
- Storing and packing
1. Crusing and Grinding
At first limestones are crushed into fine pieces with the help of crushers installed at the mine sites.
Grinding and blending the materials in the correct proportion:
Crushed limestones are further grinded to provide a fine material for blending step. Thus, obtained grinded material is blended with correct ingredients like clay (CaO), silica (SiO), and iron ore in required proportion and mixed homogeneously to produce clinker of desired composition.
2. Strong heating (Pyro processing)
The blended material is heated at high temperature up to 1300 – 15000C in a rotary kiln to produce clinker.
The kiln is heated with the help of powdered coal or hot gases from lower end of the kiln.
In short, the reactions in kiln may be summarized as,
- Up to 1000C, evaporation of water takes place.
- At 5000C, evolution of combined water from clay starts.
- Between 900 – 12000C, the reaction between lime and silica occurs to form dicalcium silicate and tricalcium silicate.
- Between 1200 – 12500C, liquid formation occurs.
- Between 1200 – 14500C, clinker is formed.
3. Storing clinker and final grinding
The clinker coming from the burning zone is very hot. To bring down the temperature of clinker, the air is admitted in a counter current direction at the base of the rotary kiln. The cooled clinkers are collected in small trolleys and sent to mills. Then the clinkers are grinded into powder in a ball mill along with 2 – 3 % powder gypsum (decrease the setting time) to produce cement.
4. Storing and packing
The grinded cement is store in the silos, from which it is marketed by packing in 50 kg bags.
- Read more: Haloalkanes Notes | Class 12 Chemistry
Types of cement
Mainly, there are two types of cement.
1. Portland cement or Ordinary Portland Cement (OPC)
OPC is most common cement manufactured by grinding a mixture of limestone and other raw materials like calcareous, argillaceous, gypsum to a powder. It has been classified into three grades, namely 33 grade, 43 garde and 53 garde. It is costlier and its initial strength is higher than PPC. It has fast setting property than PPC.
- Uses: It is suitable where fast construction is required For example, for plasters and DHALAN of floors.
2. Pozzolana Portland Cement (PPC)
PPC is variant of OPC obtained by adding a mixture of pozzolana materials namely fly ash and the volcanic ash to the OPC. Pozzolana materials are added the OPC cement in the ratio of 15 – 35 % by weight. The addition of pozzolana improves the strength and durability of the cement and even reduces the costs of concrete production.
- Uses: It is used in construction of dams, building near reservoir, marine construction etc.
Difference between OPC and PPC
| Ordinary Portland Cement (OPC) | Pozzolana Portland Cement (PPC) |
|---|---|
| OPC is most common cement manufactured by grinding a mixture of limestone and other raw materials like calcareous, argillaceous, gypsum to a powder. | PPC is variant of OPC obtained by adding a mixture of pozzolana materials namely fly ash and the volcanic ash to the OPC. |
| It is expensive than PPC. | It is cheaper than OPC. |
| It has better strength than PPC in initial stage. | It has better strength than OPC in long term. |
| It is not favorable in aggressive weather. | It is favorable in aggressive weather. |
| It is available in three grades as 33 grades, 43 grades and 53 grades. | It is available in specific grades. |
| It has high % of chloride, sulphate, alkali etc. in its composition which makes the concrete less durable. | It has low % of chloride, sulphate, alkali etc. in its composition which makes the concrete more durable. |
| It is suitable where fast construction is required For example, for plasters and DHALAN of floors. | It is used in construction of dams, building near reservoir, marine construction etc. |
Manufacture of Portland cement with flow sheet diagram
Manufacture of Portland cement involves the following steps:
Quarrying: Raw materials are extracted from quarries by blasting or by ripping using heavy machinery.
Crushing: Limestones are crushed into fine pieces with the help of crushers installed at the mine sites.
Grinding, blending and homogenization: Crushed limestones are further grinded to provide a fine material for blending step. Thus, obtained grinded material is blended with correct ingredients like clay (CaO), silica (SiO), and iron ore in required proportion and mixed homogeneously to produce clinker of desired composition.
Strong heating (pyro processing): The blended material is heated at high temperature up to 1300 – 15000C in a rotary kiln to produce clinker. The kiln is heated with the help of powdered coal or hot gases from lower end of the kiln.
Storing clinker, grinding and adding gypsum: The clinker coming from the burning zone is very hot. To bring down the temperature of clinker, the air is admitted in a counter current direction at the base of the rotary kiln. The cooled clinkers are collected in small trolleys and sent to mills. Then the clinkers are grinded into powder in a ball mill along with 2 – 3 % powder gypsum (decrease the setting time) to produce cement. The grinded cement is store in the silos, from which it is marketed by packing in 50 kg bags.
Cement industry in Nepal
The use of cement in Nepal begins from 1950’s but supply of cement was diversified in 1965. In 1975, the first cement plant, Himal Cement Company started manufacturing cement of 160 tons per day but it was later shutdown in 2002.
Some cement industries established in the public and private sectors in Nepal are
- Public sectors
- Himal Cement Company Ltd.
- Hetauda Cement Industry Ltd.
- Udayapur Cement Industry Ltd.
- Private sector
- Jagadamba Cement Indusrties Pvt. Ltd.
- Butwal Cement Mills Pvt. Ltd.
- Sagarmatha Cement Udhyog Pvt. Ltd.
- Shivam Cement Pvt. Ltd.
- Koshi Cement Pvt. Ltd.
- Triveni Cement Udhyog
- Clinker based cement industries
- Ambe Cement Pvt. Ltd.
- Bishowkarma Cement Pvt. Ltd.
- Jagadamba Cement Industry Pvt. Ltd.
- Chitwan Cement Udhyog Pvt. Ltd.
Read more:
FAQs
What is cement?
Cements, in general adhesive substance of all kinds but in a narrower sense, the binding materials used in building and civil engineering construction. Cements of this kind are finely Powders that when mixed with Water, set to a hard mass. Read complete cement note
What are the raw materials used in cement?
Calcareous materials (which supply lime (CaO)),Argillaceous materials (which supply SiO2, Al2O3, Fe2O3 etc.), Gypsum etc are the raw materials found in cements.
What are the main steps in cement production?
The main steps in manufacture of cements are:
1. Crushing and Grinding
2. Strong heating (Pyro-processing)
3. Storing clinker and final grinding
4. Storing and packing
What are the types of cement?
Usually, two types of cement are used:
1. Portland cement or Ordinary Portland Cement (OPC)
and 2. Pozzolana Portland Cement (PPC)
Differenciate between OPC and PPC cement?
OPC is most common cement manufactured by grinding a mixture of limestone and other raw materials like calcareous, argillaceous, gypsum to a powder.
PPC is variant of OPC obtained by adding a mixture of pozzolana materials namely fly ash and the volcanic ash to the OPC. Read more
