Cement Manufacturing Functions, Composing Properties Application & Characteristics

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Cement, one of the most important building materials, is a binding agent that sets and hardens to adhere to building units and made up of limestone(calcium), sand or clay, bauxite (aluminum) and iron ore, and may include shells, chalk, marl, shale, clay, blast furnace slag or slate.

Cement Powder

Function of Cement

To bind the sand and coarse aggregate together to fill voids in between sand and coarse aggregate particle to form a compact mass.

Composition of Cement

For understanding cement composition, one must know the functionality of cement ingredients.
By altering the amount of an ingredient during cement production, one can achieve the desired cement quality.

Ingredients of Cement

There are eight major ingredients of cement. The general percentage of these ingredients in cement is given below:

Sr.No.	Ingredient	Percentage in cement(%)	Function
1.	Lime (CaO)	60-65	Deficiency in lime causes cement to set quickly. Excessive presence of lime causes cement to expand and disintegrate.
2.	Silica(SiO₂)	17-25	Silica imparts strength to cement.
3.	Alumina(Al₂O₃)	3-8	Alumina imparts quick setting property to the cement. Excess alumina weakens the cement.
4.	CalciumSulphate(CaSO₄)	1-3	It slows down or retards the setting action of cement.
5.	Ironoxide(Fe₂O₃)	0.5-6	Iron oxide imparts colour to cement.
6.	Magnesiaoxide(MgO)	0.1-0.5	Excess magnesia will reduce the strength of the cement.
7.	SulphurTrioxide(SO₃)	1-3	Excess Sulphur Trioxide causes cement to unsound.
8.	Alkalis(K₂O, Na₂O)	0-1	Excess Alkaline matter causes efflorescence.

Manufacturing of Cement

Manufacturing Process of Cement

Stage of Cement Manufacture

There are six main stages of cement manufacturing process:

Stage 1: Raw Material Extraction/Quarry

The raw cement ingredients needed for cement production are limestone (calcium), sand, clay, etc.
The raw materials are blasted from the quarry.

Stage 2: Crushing

The raw ingredients are quarried and crushed to smaller pieces.

Stage 3: Raw Grinding

The crushed raw ingredients are then combined them with additives and grinding them to ensure a fine homogenous mixture.
It can be done through 2 process: a. Dry Process (modern technology) b. Wet Process (old technology)

Flow diagram of Dry process and Wet process

Stage 4: Burning

The raw mix is pre-heated before it goes to the kiln, which is heated by a flame that can be as hot as 2000° C.
The raw mix burns at 1500° C producing Clinker.

Stage 5: Grinding

The Clinker and the Gypsum are very finely ground giving pure Cement.
Other secondary additives and material can also be added to make a blended cement.

Stage 6: Storage, Packing and Dispatch

Cement is conveyed from grinding mills to silos (large storage tanks) where it is packed in 20-40 kg bags.
Most of the product is shipped in bulk quantities by trucks, trains or ships.

Characteristics of Good Cement

1. The color of cement should be uniformly grey with greenish shade. It gives an indication of excess of lime or clay and the degree of burning.

2. It should feel smooth when touched or rubbed in between fingers.

3. If hand is inserted in a bag of cement or in a heap of cement, it should feel cool and not warm.

4.It should be free from any hard lumps.

5. Excess amount of clay and silt in cement gives earthy cement.

Physical Properties of Cement

Fineness of Cement

The size of the particles of the cement is its fineness.
It is an important factor to decide the rate of gain of strength and uniformity. In general, finer the grains higher the surface area.
Test: Sieve Test

Soundness of Cement

Soundness refers to the ability of cement to not shrink upon hardening.
Good quality cement retains its volume after setting without delayed expansion, which is caused by excessive free lime and magnesia.
Test: Le Chatelier Test

Consistency of Cement

The ability of cement paste to flow is consistency.
Test: Vicat Test

Strength of Cement

Three types of strength of cement are measured : compressive, tensile and flexural.
Various factors affect the strength, such as water-cement ratio, cement-fine aggregate ratio, curing conditions, size and shape of a specimen, the manner of molding and mixing, loading conditions and age.
Tests: AASHTO T 106, ASTM C 348

Typical Cement Fineness and Compressive Strength

Setting Time of Cement

Cement sets and hardens when water is added.
This setting time can vary depending on multiple factors, such as fineness of cement, cement-water ratio, chemical content, and admixtures.
Tests: AASHTO T 131 , ASTM C 191

Heat of Hydration

When water is added to cement, the reaction that takes place is called hydration.
Hydration generates heat, which can affect the quality of the cement and also be beneficial in maintaining curing temperature during cold weather.
Test: ASTM C 186

Loss of Ignition

Heating a cement sample at 900° – 1000° C (that is, until a constant weight is obtained) causes weight loss.
This loss of weight upon heating is calculated as loss of ignition.
Test: AASHTO T 105 , ASTM C 114

Bulk density

When cement is mixed with water, the water replaces areas where there would normally be air. Because of that, the bulk density of cement is not very important.
The density of cement may be from 62-78 pounds per cubic foot.

Specific Gravity (Relative Density)

Specific gravity is generally used in mixture proportioning calculations.
Test: AASHTO T 133, ASTM C 18

Chemical Properties of Cement

Sr.No.	Ingredients	Percentage (%)
1.	Alumina : Iron Oxide	> 0.66
2.	Lime: AluminaLime: IronOxideLime: Silica	> 0.66 or < 1.02
3.	Loss of Ignition	< 4
4.	Sulphur Content	< 2.75
5.	Weight of insolublere side	< 1.50
6.	Weight of magnesia reside	< 5

Common Applications of Cement

1. Construction

It is used in mortar for plastering, masonry work, pointing, etc.
It is used in concrete for laying floors, roofs and constructing lintels, beams, stairs, pillars etc.

Cement used for roof construction

2. Transport

It is used in the construction of roads, pathways, crossings, bridges, tunnels, parking, sleepers, and runways etc

Cement used in driveway

3. Hydrophilic Construction

It is used in the construction of important engineering structures such as pipes, culverts, drains, canals, dams, weirs, reservoir, tanks and pools etc.

Cement used in drainage pipes

4. Miscellaneous

It is used for constructing piers, docks, retaining wall and breast wall etc.

Cement used in construction of retaining walls

Types of Cement

Sr.No.	Types of Cement	Reference Indian grades	Application
1.	Ordinary Portland cement	Grade 33-IS: 269 Grade 43-IS: 8112 Grade 53-IS: 12269	Widely used in residential construction where special type of cement properties is not required.
2.	Portland Blast furnace Slag cement	IS:455	It is better suited for use in marine structures as docks, harbors, and jetties. It is also used in road construction in marshy and alkaline soils
3.	Portland Pozzolana cement	IS:1489	It is mainly used in building construction where strength required with age.
4.	Rapid Hardening cement	IS:8041	It is used in road pavement works. It is also used for precast concrete casting(Beams, Columns etc)
5.	Extra Rapid Hardening cement		It is used for very high early strength concrete.
6.	Acid Resistant cement		It is used for acid resistance and heat resistance coatings of installations for chemical industry
7.	Sulphate resisting cement	IS:12330	It is used for pile foundation. It is used in sewage and water treatment plants.
8.	Low heat cement	IS:12600	It is used in mass construction (dams,marine constructions). It is also used in retaining wall construction.
9.	Hydrophobic cement	IS:8043	It is useful where cement is stored for longer duration in wet climatic conditions.
10.	Quick setting cement	–	It is used in underwater constructions. It is also used in places where cold and rainy conditions persist.
11.	Air entering cement	–	It is used in frost resistance concrete (frost also makes gap in concrete like water).
12.	Masonry cement	IS:3466	It is used as masonry mortar for use in brick,block, and stone masonry construction. It is also used to produces tucco.
13.	High alumina cement	IS:6452	It is commonly used in construction work near and along sea-shore. It is also used in works where concrete is subjected to high temperatures, frost, and acidic action.
14.	Expanding Cement	–	It is used for construction of water retaining structures. It is also used for repairing the damaged concrete surfaces.
15.	Oil well cement	IS:8229	It is used for cementing work in the drilling of oil wells where they are subject to high temperatures and pressures.
16.	Coloured cement	–	It is used for floor finishing.
17.	White cement	IS:8042	It is used as a base coat before painting. It is also used to cover the hairline cracks on concrete surface to give smooth finish.