Presented By : : Prajapati Ghanshyam

Ordinary Portland Cement (OPC) &

Rapid Hardening Cement

Concrete Technology

Content

Definition of Cement & its typesBasic composition of ordinary portland

cementProduction & Manufacturing ProcessUses of OPCGrades of OPCRapid Hardening Portland Cement

Cement & its types

Definition : “ It is defined as the bonding material having cohesive and adhesive properties which makes it capable to unite the different construction materials and form the compacted assembly.”

Types of Cement : Ordinary Portland Cement Rapid Hardening Cement Sulphate Resisting Cement Quick Setting Cement Super Sulphated Cement Low Heat Cement Pozzolona Portland Cement Coloured Cement Hydrophobic Cement Expansive Cement

Ordinary Portland Cement

Ordinary Portland Cement is one of the most widely used type of Portland Cement.

The name portland cement was given by Joseph Aspdin in 1824 due to its similarity in colour and its quality when it hardens like Portland stone.

Portland stone is white grey limestone in island of Portland, Dorset.

Composition of OPC : The chief chemical components of ordinary portland cement: 1. Calcium 3. Alumina 2. Silica 4. Iron

Basic composition of OPC

Contents

%

CaO 60-67

SiO2 17-25

Al2O3 3-8

Fe2O3 0.5-6.0

MgO 0.5-4.0

Alkalis 0.3-1.2

SO3 2.0-3.5

The chief compound which usually form in process of mixing :

Contribution of Compounds to Strength

Production & Manufacturing Process

Manufacturing Raw Materials1. Calcareous (material having content of lime)2. Argillaceous (material having content of silica & alumina)3. Gypsum ProcessCement is usually manufactured by two process:4. Wet process5. Dry process

These two process differ in operation but fundamental of both these process are same.

There are five stages in manufacturing of cement by wet process:

I. Crushing and grinding of raw materialsII. Mixing the material in proportionIII. Heating the prepared mixture in rotary kilnIV. Grinding the heated product known as ClinkerV. Mixing and grinding of cement clinker with

gypsum

Crushing And Grinding: In this phase, soft raw materials are first crushed into suitable size. This is done usually in cylindrical balls or tube mills containing the charge of steel balls.

Mixing the material: In this part, the powdered limestone is mixed with the clay paste in proper proportion (75%=limestone; clay=25%) The mixture is then grounded and made homogeneous by mean of compressed gas. The resulting material is known as “Slurry” having 35-40% water.

Heating the slurry in rotary kiln: Slurry is then introduced in rotary kiln with the help of conveyor. The rotary kiln consists of large cylinders 8 to 15 feet in diameter & height of 300-500 feet.

Kiln rotates at the rate of 1-2 revolution per minute. In rotary kiln, slurry passed through different zones of temperature. This whole process in kiln usually covers 2 to 3 hours.

Different temperature zones are as under:i. Preheating Zone : Temperature is kept upto 500

degree celsius.ii. Decomposition Zone : Temperature is raised upto 800

degree celsius.iii. Burning Zone : Temperature is maintained upto 1500

degree celsius.iv. Cooling Zone : This is last stage where the whole

assembly is cooled upto 150 to 200 degree celsius.

Clinker Formation: The product which is obtained from the rotary kiln is known as the “Cement Clinker”. Clinker is usually in the form of greenish black or grey colored balls.

Grinding the clinker with gypsum: The cement clinker is then air cooled. The required amount of gypsum (5%) is ground to fine powder and then mixed with clinker.

Finally, Cement is packed in bags and then transported

to the required site.

Production The manufacture of OPC is decreasing all over the world

in view of popularity of blended cement on account of lower energy consumption, environmental pollution, economic and other technical reasons.

In India for the year 1998-99 out of the total cement production i.e., 79 million tons, the production in OPC in 57.00 million tons i.e., 70%. The production of PPC is 16 million tons i.e., 19% and slag cement is 8 million tons i.e., 10%.

In the coming years, the use of OPC may still come down but it will remain as an important type for general construction.

Uses of OPC

It is normally used for the reinforced concrete buildings, bridges, pavements, and where soil condition are normal.

It is used for general construction purposes where special properties are not required.

It has great resistance to cracking and shrinkage but less resistance to chemical attacks.

It is also used for most of concrete masonry units.

Grades of Cement

For engineering purposes, there are many types of cement but in general, ‘Ordinary Portland Cement’(OPC) which is available in three grades should be used in house construction.

1. 33 Grade OPC2. 43 Grade OPC3. 53 Grade OPC

33 Grade OPC

It is more suitable cement for masonry and general concrete works where the members are not taken to very high stresses.

43 Grade OPC

43 grades of cement are used where high early strength in 1-28 days range is required.

53 Grade OPC

The strength of 53 grade does not much after 28th day because of early gain while 33 grade continues to gain strength after 28th day.

Compressive strength of different brands of cement

Rapid Hardening Portland Cement

Rapid Hardening Portland Cement (RHPC) is similar to ordinary cement but with higher tri-calcium silicate (C3S) content and finer grinding. It gain strength more quickly than OPC, though the final strength is only slightly higher.

This type of cement is also called High Early Strength Portland Cement.

The one day strength of this cement is equal to the three day strength of OPC with the same water-cement ratio.

Uses of RHPC

It is used where formwork has to be removed as early as possible in order to reuse it.

It is used where high early strength is required. it is generally used for constructing road pavements. It is used for cold weather concreting because rapid

evolution of heat during hydration protects the concrete against freezing.

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