Cement

Introduction

- cement generally refers to adhesive and cohesive material which are capable of bonding together particles of solid material into a compact durable mass.
- mass of calcalerous cement containing compound of lime as it chief constituent
- primary function of cement is binding fine and coarse aggregate together.

Classification of cement

.'. Hydraulic cement:- which sets and hardens in water such cement consist portland cement among others.

.'. Non-hydraulic cement:- is the one that does set and harden in water example of such cement is Plaster Of Paris (POP) cement among others.

Sources of cement

Cement can be manufactured from either natural cement stone or artificially by using calcareous and argillaceous materials.

¤ Natural cement consist of roman cement, puzzolana cement, medina cement.
¤ Artificial cement consist of portland and special cement.

Uses of cement

1. For its high strength; cement are used in bridge piers, light house lofty towers.

2. For large structures; cement can be used in bridge construction, silos, and chimney among others.

3. For structures exposed to action of water; cement can be used in reservoirs, dams, dock yards among other thing.

Manufacture of Cement

Calcareous and argillaceous raw materials are used in the manufacture of portland cement.

Calcareous; this contains cement rock, marl, chalk, marine shell.

Argillaceous; this contains silicates of alumina-clay, shale, slate, blast furnace slag.

Cement is manufactured by dry or wet process

Dry process

Limestone and clay are ground to a fine powder separately and are mixed. Water is added to make a thick paste (slurry). The cakes of the paste are dried and charged into a rotary kiln. The kiln dries out as it flows, the water being evaporated first and then it reaches its maximum of 1500c thereby fusing the material into clinker. The clinker is cooled and ground to fine powder. A small amount of gypsum is added to retard the setting cement. As been described below
CHALK (CaCo3)+CLAY=>ground with H2O=> SLURRY=>SIEVING=>ROTATING KILN=>GRIND CLINKER+GYPSUM=>Bagged as CEMENT.

Wet process

crushed raw materials are field into a ball mill and a little water is added. When the mills is operated, it pulverizes the materials to form slurry with water.

The slurry is passed to silos where its is adjusted to desirable chemical composition.

The corrected slurry is then fed into a kiln where it loses moisture and forms lumps or noodles.

They are finally burned at1500c into a clinker. The clinker is then ground, and gypsum added.

CHALK(CaCO3)+CLAY=>GROUND WITH H2O=>SLURRY=>SILOS(Where chemical composition is adjusted)=>ROTATING KILN=>CLINKER=>GRIND CLINKER+GYPSUM=>Bagged as CEMENT.

Setting and hardening of cement

Cement set when mixed with water by way of a complex series of chemical reactions. The different constituents slowly crystallize and the interlocking of their crystal give cements its strength. Gypsum is added to retard the setting of cement.

Types of Cement

1. Rapid hardening portland cement.
2. High alumina cement.
3. Super sulphated portland cement.
4. Sulphated resisting portland cement.
5. Portland slag cement.
6. Low heat portland cement.
7. Portland puzzolano cement.
8. Masonry cement.
9. Air entraining cement.
10. Water repellant.

Link to www.wikipedia/cement.com for more info about cement