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Monday, 12 December 2016

CEMENT AND ITS TYPES

We were discussing “Cushioning hydraulic cylinder working principle” and various other “hydraulic actuators” in our previous posts. Today we are going to start here one very important topic i.e. Cement technology. We will understand the various terminologies and engineering concepts used in cement technology with the help of this category.

Let us first see here one very brief introduction of cement, as we must understand that what we are going to read in this section and hence first we will briefly introduce the term cement and after that we will classify the cements in to its various types with the help of this post.

Further we will go for  discussion of raw material, preprocessing, chemistry of cement, hydration of cement, properties of cement compounds, selection of the process, process technology, burning technology, firing technology, clinker cooling and grinding, cement packing and dispatch, pollution control and much more facts about cement technology in our next post in this category of cement technology.

Cement

Cement is a finely ground hydraulic binding medium for mortar and concrete, consisting substantially of compounds of CaO with SiO2, Al2O3, Fe2O3, which have been formed by sintering or fusion. When mixed with water, cement hardens both in air and under water and retains its strength under water. It has to possess constancy of volume and attain a compressive strength of at least 25 N/mm2 at the end of 28 days.

Classifications of cement

There are various types of cement used differing in their cementing properties on account of the differences in the types of additives or the proportions in which they are used.

Ordinary portland cement

This is the ordinary cement used in the industry possessing high strength and great durability. On setting, it liberates 90 cal. /g of heat of hydration.

Low Heat Portland cement
This type of cement liberates only 70 cal./g of heat of hydration; therefore where great masses of concrete are involved, risk of expansion and shrinkage cracks arising from thermal stresses created by dissipation of heat of hydration is reduced. However, its rate of strength development is lower than that of OPC.

Rapid Hardening Portland cement
This cement is ground finer and has slightly altered composition as compared to OPC. It has a similar setting time but develops high strength at an early stage.

White Cement
This is ordinary cement but having a low proportion of iron oxide and hence has white color. It can be colored to any desirable shade by adding pigments. It is used for tiles, terrazzo, artistic decoration, etc.

Hydrophobic Cement
This cement has a water- repellent coating of fatty acids and hence can be stored for long periods, in humid conditions. The coating is, however, lost by abrasion when mixed with sand and aggregates. This cement has improved workability and density, reduced bleeding and decreased water absorption of hardened concrete.

Oil - well cement 

This is special-purpose cement used for cementing steel casings of oil and gas wells. It is more coarsely ground than OPC. By adding retarders like starches, sugars etc. the oil-well cement grout is maintained as a fluid for enough time at high temperature and pressure to allow placement. It develops its strength in a very short time.

Portland blast furnace slag cement

This is also special-purpose cement made by grinding ordinary clinker with granulated rapidly cooled blast furnace slag and gypsum. Thus it helps conserve limestone and allows good use of waste products. It is resistant to acids, sulphates and alkalis.

Pozzolana Portland cement

This cement is prepared by adding 10-25% of pozzolanic material to clinker and gypsum. Pozzolanic material is capable of reacting with lime in presence of water to produce cementitous product. This cement has better cohesiveness, improved workability, less segregation and better resistance to alkalis and sulphates.

Hi - alumina cement

This is manufactured by heating until molten, a mixture of limestone and bauxite. The product is cooled and finely ground. It is characterized by a very rapid rate of strength development and approaches its final gauge strength within 24 hours

Masonry cement

This group of cements consists of materials intended for use in mortars. Their purpose is to provide cement which gives more plastic mortar than OPC. They are produced by grinding a mixture of portland cement and limestone with a plasticiser that entrains air.

Sorrel cement

Mag. Oxy-chloride or Sorrel cement is the product obtained when magnesia and a solution of MgCl2 react together. Magnesite is calcined to give a lightly burned reactive product and the finely ground material mixed as required with a strong solution of MgCl2, resulting in the formation of Mag. oxy-chloride --- 3 MgO.MgCl2.11H2O

It is mainly used as a flooring material with an inert filler and a pigment to color it. The surface is protected against water by polishing with wax and turpentine.

Gypsum plaster

There are a number of cementing materials consisting essentially of cal. sulphate CaSO4.2H2O that are produced by partial or complete dehydration of gypsum. Gypsum produced as a byproduct in the production of phosphate fertilizers is used to make hemi-hydrate gypsum plastics whereas anhydrous gypsum formed as a byproduct in the manufacture of HF is used with an accelerator to form flooring plaster.

Do you have any suggestions? Please write in comment box.

We will see other topic i.e. raw materials for the production of cement in our next post in the category of Steel and cement technology.

I am very thankful to Mr. Subrata Bhaumik, Independent cement consultant, for providing such beautiful information and contents about cement technology.

Mr. Subrata Bhaumik has more than 50 (Fifty) Years (1965 - 2016) of Experience in Cement and other related Industry covering more than 100 assignments in cement plants with capacities ranging from 100 tpd to 10,000 tpd in India and abroad involving visit to 25 countries overseas in connection with work.

For more detailed information about the original Author of this content, please click the Author profile link below.


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