Introduction
Concrete is mixture of cement, water, Find Aggregates (Sand), and Coarse Aggregates (crushed rocks or gravel) in which cement and water are harden by chemical reaction which is called Hydration to bind non-reacting component ( Aggregates).

Concrete, Ingredients of Concrete & Their Function
basic Ingredients pf concrete
Basic Ingredients of Concrete:-
1.       Cement
2.       Aggregates
3.       Water
4     Admixture
 Cement:-  Cement is binding material in the cement concrete. It is used for different works where strength and durability are of prime importance.
Function of Cement:-
· It fills up voids existing in the fine aggregate and makes the concrete impermeable
· It provides strength to concrete on setting and hardening.
· It binds the aggregate into a solid mass by virtue of its setting and hardening properties when mixed with water.
Aggregates:- Aggregates are classified in Two Groups to provide good quality of Concrete

1.      1)  Coarse Aggregates Particle size greater than 4.75 mm

2.      2)  Fine Aggregates (Sand) Particle size less than 4.75 mm

Fine Aggregates (sand) :-  Sand consists of small angular or rounded grains of silica. It is commonly used as the fine aggregate in cement concrete. Both natural and artificial sands are used for this purpose.

Function Of sand:-
1. It fills the voids existing in the coarse aggregate.
2. It reduces shrinkage and cracking of concrete.
3. By varying the proportion of sand concrete can be prepared economically for any
Required strength
4. It helps in hardening of cement by allowing the water through its voids.
5. To form hard mass of silicates as it is believed that some chemical reaction takes place
Between silica of sand and constituents of cement.

Requirements For Good Sand:-
1. Fine aggregate should consist of coarse angular sharp and hard grains.
2. It must be free from coatings of clay and silt.
3. It should not contain any organic matter.
4. It should be free from hygroscopic salt.
5. It should be strong and durable and chemical inert.
6. The size of sand grains should pass through 4.75mm sieve and should be entirely
Retained on 75 micron sieve.


Coarse aggregates:-  It Consist of gravel more than 4.75mm in size which is crushed by stone crusher.

Function of Coarse Aggregates:-
1. Coarse aggregate makes solid and hard mass of concrete with cement and sand.
2. It increases the crushing strength of concrete.
3. It reduces the cost of concrete, since it occupies major volume.

Requirements For Coarse Aggregates:-
1. Coarse aggregate used may be crushed stone, gravel and broken bricks.
2. Crushed stone: It is an excellent coarse aggregate provided. It is obtained by crushing
Granite, sandstone and close grained limestone.
3. Crushed granite chips are commonly and advantageously used in reinforced cement
Concrete.
4. Broken bricks well burnt and over burnt bricks are broken into suitable size and used as
Aggregate. It should be well watered before its use. Broken bricks are used as
Aggregate for concrete in foundations and under floors.
5. But generally crushed stone is only used as coarse aggregate.

Water:- The water is used in concrete plays an important part in the mixing, laying compaction setting and hardening of concrete. The strength of concrete directly depends on the quantity and quality of water is used in the mix.

Function f water:-
1. Water is only the ingredient that reacts chemically with cement and thus setting and
Hardening takes place.
2. Water acts as a lubricant for the aggregate and makes the concrete workable.
3. It facilitates the spreading of cement over the fine aggregate.

Admixture:- Concrete admixtures are added to change the properties of concrete to make it function as required. Admixtures are used to modify properties of both fresh and hardened concrete.

Function of admixture to modify the property of fresh concrete:-
a) To increase work ability without increasing water content or to decrease the water content at
the same work ability.
b) To retard or accelerate both initial and final setting times.
c) To reduce or prevent settlement.
d) To create slight expansion in concrete and mortar.
e) To modify the rate or capacity for bleeding or both.
f) To reduce segregation of concrete, mortars and grouts.
g) To improve penetration and or pump ability of concrete, mortars and grouts.
h) To reduce rate of slump loss.

Function Of Admixture to modify harden property of concrete:-
a) To retard or reduce heat generation during early hardening.
b) To accelerate the rate of strength development.
c) To increase the strength of concrete or mortar (Compressive, tensile or flexural).
d) To increase the durability or resistance to severe conditions of exposure including the
Application de-icing salts.
e) To decrease the capillary flow of water.
f) To decrease the permeability to liquids.
g) To control the expansion caused by the reaction of alkalis with certain aggregate constituents.
h) To produce cellular concrete.
i) To increase the bond of concrete to steel reinforcement.
j) To increase the bond between old and new concrete.
k) To improve impact resistance and abrasion resistance.
l) To inhibit the corrosion of embedded metal.
m) To produce colored concrete or mortar.

Concrete Admixture can be classified as Follows:-
1. Set-Retarding:
Set retarding concrete admixtures are used to delay the chemical reaction that takes place when the concrete starts the setting process.
2. Air-Entrainment:
Air entrained concrete can increase the freeze-thaw durability of concrete. Other benefits from this
admixture are:
• High resistance to cycles of wetting and drying
• High degree of workability
• High degree of durability
The entrained air bubbles act as a physical buffer against the cracking caused by the stresses due to
water volume augmentation in freezing temperatures. Air entrainers are compatible with almost all
the concrete admixtures. Typically for every 1% of entrained air, compressive strength will be reduced
by about 5%.
3. Water-Reducing:
Water-reducing admixtures are chemical products that when added to concrete can create a desired slump at a lower water cement ration than what is normally designed. Water-reducing admixtures are used to obtain specific concrete strength using lower cement content.
4. Accelerating:
Accelerating concrete admixtures are used to increase the rate of concrete strength development, or to reduce concrete setting time. Calcium chloride could be names as the most common accelerator component; however, it could promote corrosion activity of steel reinforcement. Accelerating admixtures are especially useful for modifying the properties of concrete in cold weather.
5. Shrinkage Reducing:
Shrinkage reducing concrete admixtures are added to concrete during initial mixing. This type of
admixture could reduce early and long term drying shrinkage.
6. Super plasticizers:
The main purpose of using super plasticizers is to produce flowing concrete with very high slump in
the range of 200 - 250 mm to be used in heavily reinforced structures and in placements where
adequate consolidation by vibration cannot be readily achieved. The other major application is the
production of high-strength concrete at w/c’s ranging from 0.3 to 0.4. High workability concrete
containing super plasticizer can be made with a high freeze-thaw resistance, but air content must be increased relative to concrete without super plasticizer.
7. Corrosion-Inhibiting:
Corrosion-inhibiting admixtures fall into the specialty admixture category and are used to slow
corrosion of reinforcing steel in concrete. Corrosion inhibitors can significantly reduce maintenance
costs of reinforced concrete structures throughout a typical service life of 30 – 40 years.