A. Definition Of CementWhat is cement? Cement is a fine mineral powder manufactured with very precise processes. Mixed with water, this powder transforms into a paste that binds and hardens when submerged in water. Because the composition and fineness of the powder may vary, cement has different properties depending upon its makeup. Cement is the main component of concrete. It's an economical, high-quality construction material used in construction projects worldwide.

B. Functions Of CementCement is an essential material and widely used in infrastructure projects in the civil construction sector. If you add water, cement will be become the cement paste. If it is mixed with fine aggregate, cement paste will be the mortar. If it combined with the coarse aggregate will be a mix of fresh concrete and then becomes a hard concrete. The main function is to bind aggregate grains (with water) forms a solid mass and fills the air cavity between the aggregate grains. Although the composition of the cement in concrete is only about 10%, but due to its function as a cement binder, the role becomes important.

C. How To Make CementThe manufacture of cement is a very carefully regulated process comprising the following stages:1. Quarrying a mixture of limestone and clay. 2. Grinding the limestone and clay with water to form a slurry. 3. Burning the slurry to a very high temperature in a kiln, to produce clinker. 4. Grinding the clinker with about 5% gypsum to make cement. 5. Raw Materials Extraction The limestone and clay occur together in our quarries at Cape Foulwind. It is necessary to drill and blast these materials before they are loaded in 70t capacity trucks.The quarry trucks deliver the raw materials to the crusher where the rock is crushed to smaller than 100mm (4 inches). The raw materials are then stored ready for use.

6. Raw Materials Preparation About 80% limestone and 20% clay are ground in ball mills with water, producing very fine, thin, paste called slurry. The chemical composition of the slurry is very carefully controlled by adjusting the relative amount of limestone and clay being used.the slurry is stored in large basins ready for use.

7. Clinker Burning The slurry is fed into the upper end of a rotary kiln, while at the lower end of the kiln, a very intense flame is maintained by blowing in finely ground coal.The slurry slowly moves down the kiln and is dried and heated until it reaches a temperature of almost 1500 degrees Celsius producing "clinker". This temperature completely changes the limestone and clay to produce new minerals which have the property of reacting with water to form a cementitious binder. The hot clinker is used to preheat the air for burning the coal, and the cooled clinker is stored ready for use.

8. Cement Milling The clinker is finely ground with about 5% gypsum in another ball mill, producing cement. (The gypsum regulates the early setting characteristic of cement). The finished cement is stored in silos then carted to our wharf or packing plant facilities.

There are 2 ways to make cement, wet process and dry processa. Wet ProcessWhen chalk is used, it is finely broken up and dispersed in water in a washmill. The clay is also broken up and mixed with water, usually in a similar washmill. The two mixtures are now pumped so as to mix in predetermined proportions and pass through a series of screens. The resulting cement slurry flows into storage tanks. When limestone is used, it has to be blasted, then crushed, usually in two progressively smaller crushers (initial and secondary crushers), and then fed into a ball mill with the clay dispersed in water. The resultant slurry is pumped into storage tanks. From here onwards, the process is the same regardless of the original nature of the raw materials. The slurry is a liquid of creamy consistency, with water content of between 35 and 50%, and only a small fraction of material about 2% - larger than a 90 m (sieve No. 170). The slurry mix mechanically in the storage tanks, and the sedimentation of the suspended solids being prevented by bubbling by compressed air pumped from bottom of the tanks. The slurry analyze chemically to check the achievement of the required chemical composition, and if necessary changing the mix constituents to attain the required chemical composition. Finally, the slurry with the desired lime content passes into the rotary kiln. This is a large, refractory-lined steel cylinder, up to 8 m in diameter, sometimes as long as 230 m, which is slightly inclined to the horizontal.The slurry is fed in at the upper end while pulverized coal (oil or natural gas also might be used as a fuel) is blown in by an air blast at the lower end of the kiln, where the temperature reaches about 1450oC. The slurry, in its movement down the kiln, encounters a progressively higher temperature. At first, the water is driven off and CO 2 is liberated; further on, the dry material undergoes a series of chemical reactions until finally, in the hottest part of the kiln, some 20 to 30% of the material becomes liquid, and lime, silica and alumina recombine. The mass then fuses into balls, 3 to 25 mm in diameter, known as clinker. The clinker drops into coolers

b. Dry ProcessThe raw materials are crushed and fed in the correct proportions into a grinding mill, where they are dried and reduced in size to a fine powder. The dry powder, called raw meal, is then pumped to a blending silo, and final adjustment is now made in the proportions of the materials required for the manufacture of cement. To obtain a uniform mixture, the raw meal is blended in the silo, usually by means of compressed air. The blended meal is sieved and fed into a rotating dish called a granulator, water weighing about 12% of the meal being added at the same time. In this manner, hard pellets about 15 mm in diameter are formed. The pellets are baked hard in a pre-heating grate by means of hot gases from the kiln. The pellets then enter the kiln, and subsequence operations are the same as in the wet process of manufacture.

D. Types Of Cement And The Application The ASTM has designated five types of portland cement, designated Types I-V. Physically and chemically, these cement types differ primarily in their content of C3A and in their fineness. In terms of performance, they differ primarily in the rate of early hydration and in their ability to resist sulfate attack. The general characteristics of these types are listed in Table. The oxide and mineral compositions of a typical Type I portland cement were given in Tables . General features of the main types of portland cement.

a. Types Of CementGeneral features of the main types of portland cement.ClassificationCharacteristicsApplications

Type IGeneral purposeFairly high C3S content for good early strength developmentGeneral construction (most buildings, bridges, pavements, precast units, etc)

Type IIModerate sulfate resistanceLow C3A content (