What Is Cement?
Cement is a finely grinded power material, which can work as a binder when water is added to it. It is a mixture of different compounds consisting mainly of silicates and aluminates of calcium formed out of silica, calcium oxide, aluminum oxide, and iron oxide.
- It works is same as glue we use for sticking two objects together, but it can bind natural compounds like sand and aggregate.
- When water is added to cement the hydration process starts (hydration is the chemical process between water and cement) and which produces a bond between sand and aggregate.
- In concrete, the material sand and aggregate give the mass or body to the rete, while cement it functions is to bind the two materials together and fill the between them to make hard concrete.
- Nowadays there is various type of cement available in the market. cement type selection depends on the nature of the work.
Application of Cement
Listed Below are Cement Applications in construction,
- Cement is mostly used as mortar and concrete, in which cement is mixed with aggregates to form a specific grade of concrete.
- Mortar is basically mixture of cement and sand (crushedstone) having size less 5mm i.e 0.2 inch.
- On other hand Concrete is also mixture of aggregates and cement, but both coarse and fine aggregates are present in proportions.
- Mortars made of cement are used for binding bricks, blocks, and stone in masonary walls or as surface renderings.
- Concrete has wide range of applications in construction. Mixtures of soil with portland cement are used for construction of base layer of roads.
- Portland cement has applications in the manufacture of bricks, tiles, shingles, pipes, beams, railroad ties, and various extruded construction operations.
History of Cement
As historical research says that people of that time know about the binding property of lime. In the past, people have been using lime for making brick bonds and other work.
The Roman Empire used lime concretes and also developed the pozzolanic cement material of lime and certain volcanic earth.
This concrete and lime mortar continued to be used up to the middle Ages.
- An English engineer Joseph Aspdin from Leeds city – England in 1824, successfully produced a powder made from the calcined mixture of limestone and clay.
- After that, he has patented the material, and the name was given “Portland Cement”, because when it hardened it produced a material similar to stones from the quarries near Portland Island in the UK.
- With time the process of manufacturing cement has changed but the formula and material remain the same.
- Later, Isaac Charles Johnson in 1845 had some experiment. he burnt a mixture of clay and chalk till the clinkering stage to make better cement and established factories in 1851
- In 1877, The German standard specification for Portland cement was drawn.
- In 1904, The British standard specification was first drawn and moreover, The first ASTM specification was issued in 1904.
- In India, it was first manufactured in 1904 near Madras, by the South India Industrial Ltd. But this venture failed.
- The cement manufacturing unit in Turkey was first started in Darica Cement Factory in 1913 with a production capacity of 20,000 tons/year.
Raw Materials of Portland Cement
- Calcareous rocks material (CaCO3 > 75% such as limestone, marl, chalk),
- Argillaceous rocks material (CaCO3 < 40% such as clay and shale),
- Argillocalcareous rocks material (40-75% CaCO3 such as clayey limestone, clayey marl).
- Portland cement can be manufactured from any two groups above. This raw material must be used in proper form and proportions of lime, silica, and alumina.
Manufacture of Cement
There are four stages in the manufacture of portland cement,
- Crushing and Grinding
- Blending the Materials
Crushing and Grinding
Soft materials first crushed, that too in two stages. This Grinding can be done in a wet or dry state, that depends on the process which is in use. However, for grinding in the dry state the raw materials are needed to be dried in cylindrical rotary dryers.
Soft materials are needed to be broken down through vigorous stirring with the water in wash mills, producing a fine slurry, which is later passed through the screens for removal of oversize particles.
The next step involved after crushing and grinding is blending the crushed raw materials. Initially, an approximation of the chemical composition required for a specific cement is obtained through selective quarrying and with control of the raw material fed in the process to the crushing and grinding plant.
In the dry process mixing of the materials in the silos is carried out by agitation and vigorous circulation which include compressed air. While, in the wet process, the slurry tanks are needed to be stirred by the means of mechanical action, using compressed air or both used together.
Bottle kilns ate the traditional types of kilns followed by chamber kilns and then continuous shaft kilns were invented. The shaft kiln is used in many countries in modern days but the dominant means of burning is the rotary kiln.
When the raw material fed to the kiln at the upper end, it slowly moves down the kiln at the firing, end. The fuel used for firing is pulverized coal, oil, or natural gas. The temperature at the firing end could be as equal as in the range of 1,350 to 1,550 °C or 2,460 to 2,820 °F, depending on the type of raw material is being burned.
The burned product comes out from the kiln in the form of small nodules of clinker. These clinkers are then passed into coolers for colling. The colled clinker depending on its properties can be immediately ground to cement or stored in stockpiles for further use.
The clinker and gypsum are ground to form a fine powder in mills similar to those used before for grinding the raw materials brought directly to mills.
Material properly grinned are passed further while the improperly grinned are again taken to grinding. Sometimes it is required to add a small amount of grinding aid to feed material.
Finished cement is stored in bags and packages for distribution.
Tests on Cement
Various tests are performed on cement to know the properties, characteristics, and suitability for use. Some of the tests on cement are discussed below,
- Setting Time
The fineness of the cement can be tested using sieve analysis tests, however, these days more sophisticated methods are now largely used.
A commonly used method to obtain accurate results for both control of the grinding process and testing the finished cement measures the surface area per unit weight of the cement by analyzing the rate of air passage through a bed of the cement.
However other methods for finding the fineness of cement depend on the principle of measuring the particle size distribution by the rate of sedimentation of the cement in kerosene or by elutriation in an airstream.
After setting of Cement, it should not undergo expansion more than appreciable limits, which could cause disruption of mortar or concrete. This occurrence shows the soundness of cement.
The soundness of cement is tested by subjecting the set cement to boiling in water or to high-pressurized steam for a certain period of time. This test shows the presence of free magnesia or hard-burned free lime in cement.
3. Setting Time
The setting of cement along with its hardening are continuous processes, though two points are differentiated for test purposes. The initial setting time of cement is the instance between the mixing of the cement with water and when the mix has lost plasticity, stiffening to a certain amount.
It roughly states the end of the period when the mix is still wet can be molded into a required shape. The final setting time of the cement can be defined as the point at which the cement has acquired a relatively sufficient firmness to resist a certain degree of pressure.
Cement has the capability to withstand the compressive strength however, it is weak in tensile strength. Hence Reinforced Steel is induced in the cement to provide tensile property to concrete.
The American Society for Testing and Materials (ASTM) had specified the requirement of ratio 1:3 i.e. cement-sand mortar in case of tensile strength and compressive tests on that of 1:2.75 mortar.
The strength requirements of cement laid down by various countries in the world are not directly comparable because of the differences in test methods of each country.
Importance of Cement In Construction
- It is a widely used binding material in the construction industry. After its invention Cement become popular among all other building materials.
- It almost absolute the use of other binding material likes clay and lime. We can say that cement is ruling construction for the past hundreds of years.
- It is a major element in concrete and it can hold the structure together for a long time.
Why Cement Is Popular Building Material
- its use is the same form all around the world.
- It can bind other construction material together.
- It is vast application in the construction industry like, for plastering, tiling, finishing, interior, and exterior work finish, etc.
- It is made today modern world possible.
According to the Cement Manufacturers Association, India is the second-largest Cement Industry in the world by consuming 8% of the global cement installed capacity. Also, the Indian cement industry is the largest consumer of fly ash produced by the thermal power plant of India. India almost consumes 100% of slag produced by the steel plant of India.
Read More: House Raw Material Calculator
Types of Cement In India
- Ordinary Portland Cement (OPC)
- Portland Pozzolana Cement (PPC)
- Rapid Hardening Cement
- Extra Rapid Hardening Cement
- Quick Setting Cement
- Low Heat Cement
- Sulphate Resisting Cement
- Portland Slag Cement (PSC)
- High Alumina Cement
- White Cement
- Coloured Cement
- Air Entraining Cement
- Hydrophobic Cement
- Masonry Cement
- Expansive Cement
- Oil Well Cement
Types of Cement In Europe
Classification as per Euro EN 197-1
- CEM I (Portland cement)
- CEM II (Portland-composite cement)
- CEM III (Blast furnace cement)
- CEM IV (Pozzolanic cement)
- CEM V (Composite cement)
Types Available in USA
Classification as per ASTM C150
- Type I (Portland cement)
- Type II (Sulphate Resisting Cement)
- Type III (Rapid Hardening Cement)
- Type IV (Portland Pozzolana Cement (PPC)
- Type V (Hydrophobic Cement)
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