Cement

Cement is a binding substance for materials

Constituents of ordinary or Portland cement

 Manufacture of cement

There are 3 main operations involved in the manufacture of cement.

(a) Mixing raw materials.

(b)Burning

(c) Grinding

(a)Mixing of raw materials

>There are 2 methods of mixing raw materials of cement namely dry process and wet process.

>In dry process, calcareous and argillaceous materials are reduced in size and dried.

>The dried materials are grinded in ball mills or tube mills.

>In wet process, calcareous materials are crushed and argillaceous materials such as clay is washed and stored in basins. The materials are ground to form slurry.

(b) Burning

>the burning of dry mixture of slurry is carried out in long rotary kiln.

>The kiln is supported on rollers such that it can rotate about its longitudinal axis at the rate of one revolution per minute.

>refractory lining is provided on inside surface of rotary kiln.

>The slurry is injected at the upper end of kiln. He hot gases or flames are forced through the lower end in kiln.

>Portion near upper end is known as dry zone, where water drom the slurry gets evaporated.

>Dried slurry descends down to burning zone, carbon-dioxide from he slurry is evaporated and it is converted in to small lumps called nodules.

>The nodules roll down ultimately reach burning zone, where temperature is b/w 1500 degree celcius to 17oo degree Celsius.

>lime and clay fuse to form hardballs of Portland cement known as cinders.

(c) Grinding

>the grinding process is done in ball or tube mills.

>A small quantity of gypsum (3 to 4 percentage) is added.

>Gypsum retards the setting time of cement.

Types of cements

(a)Quick setting cement

>It is produced by adding a small percentage of aluminum sulphate.

>It is used to lay concrete under water.

(b)Low Heat Cement

>heat generated during setting time is very less.

(c) High Alumina cement

>It resists the action of acids.

>It attains ultimate strength in a short period.

>used for furnace insulation.

(d) Expending cement

>It expands during curing.

>it is used for repairing concrete surfaces.

(e)Rapid Hardening Cement

>Attains higher strength in short period.

>As it sets rapidly, construction is speedy.

(f)Acid resistant cement

>This is used for acid resistance.

>Heat resistance coating for installation of chemical industry.

(g) Sulphate Resistant Cement

>It has good resisting power again sulphates.

(h)White Cement

>It is free from iron oxide, magnesium oxide etc.

>Used for floor finish, plaster work and ornamental works.

(i) Colored Cement

>Desired cooler is obtained by mixing colorings material with ordinary cement in the specified proportion.

>In floor finishing and plastering walls.

Uses of cement

>It is used for making cement mortar and cement concrete.

>Sulphate resisting cement is used to protect foundations from chemical action.

>Rapid hardening cements have been used in works which need early strength gain like chimneys and under water concreting.

>White and colored cements are used for ornamental plastering.