Concrete?! What is that??

   

Concrete?! What is that??

WHAT IS THAT??!

>>Composite construction material composed primarily of 

aggregate, cement and water. 

Aggregate

Aggregates are added to cement with water to form concrete.  Usually they occupy about 65-80% of the total concrete volume.  

Why do we need aggregate in concrete??

-          they greatly reduce cost

-                    they reduce heat output and therefore reduce thermal stress

-                    they reduce shrinkage of concrete

-                    they help to produce a concrete (when fresh) with satisfactory plastic properties

Desirable properties of aggregates:

-                    they must be sufficiently strong

-                    clean, free from constituents which can react harmfully with cement

-                    have small or no moisture movement

-                    be well graded

-                    right shape and texture so as not to adversely affect the properties of fresh and hardened concrete

-                    low thermal conductivity

Cement

The production process

Chalk & clay reduced to particle sizes ≤ 75 µm

│

Mixed in the required proportion

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Mixture either mixed with water to

form a slurry or dried as powder

                           

Figure 13.1

  Calcining –  base materials are heated to form oxides;

                                      CaO (lime) = C

                                      SiO₂ (silica) = S

                                      Al₂O₃ (alumina) = A

                                      Fe₂O₃ (iron oxide) = F

   Clinkering – oxides at high temperatures combine to form compounds mainly

                    calcium silicates, calcium aluminates and calcium aluminoferrites

The final products of the above processes, in the form of clinkers, are chiefly the calcium silicates and aluminates and smaller amounts of other compounds;

                                    Tricalcium silicate = C₃S

                                    Dicalcium silicate = C₂S

                                    Tricalcium aluminate = C₃A

                                    Tetracalcium aluminoferrite = C₄AF

Each grain of cement consists of a mixture of the above compounds.

After cooling a small amount of gypsum (calcium sulfate dehydrate, CaSO₄.2H₂O) is added to the clinker before the mixture is ground to a fine powder. The purpose of gypsum is to retard the curing process so as to prevent immediate stiffening of the cement paste during hydration.

Portland cement             

Ordinary Portland Cement                

Rapid-Hardening Portland Cement   

Ultra high early strength Portland cementLow-Heat Portland cement

Sulphate resisting Portland cement

White Portland cement

Portland blast-furnace cement

Non Portland cement

High alumina cement

Supersulphated cement

Concrete

How concrete function ?? 

The cement and water combined to form a paste and when hardened, binds the aggregates particles together to form a monolithic whole. The cement and water hardened by a chemical reaction, called hydration. 

Type of Concrete

Reinforced Concrete

Pre-stressed Concrete

Mass Concrete