Admixture are the materials used in the cement to modify one or more of its properties in the plastic or hardened state of concrete.
Instead of using special cement for a particular purpose it is beneficial to use admixture in an ordinary portland cement for achieving the desired effect.
Thus use of admixture in concrete construction is to achieve economical constructionis is firstly.
The effect and results of using admixture depends on the properties of concrete is firstly. Sometimes it is difficult to predict effect and result because of change in increment brand, aggregate grading, mix proportion using rich mix.
Function of Admixture:
- Firstly to increase slump and workability
- They reduce or accelerate initial setting
- To increase the strength
- It is reduce or prevent shrinkage
- To accelerate the rate of strength development at an early stage.’
- Increase bonding between concrete and steel
- Decreases permeability of concrete
- Thus to produced colored concrete
- To reduce or avoids the corrosion of reinforced steel
- It is increase the band between existing concrete and new concrete.
- To improve the impact and abrasion resistanceis lastly.
Firstly chemicals which are mixed with concrete ingredients and spread throughout the surface of concrete to improve the moulding and setting properties of the concrete mix are called chemical admixtures.
It reduces the cost of construction, modifies the properties of concrete and improves the quality of concrete during mixing, transportation, Placing and curing.
Types of chemical admixture
- Water reducing admixture
- Super plasticizer
- Air entraining admixture
2. Mineral admixture or pozzolana
Mineral admixtures are finely divided into siliceous material added to concrete either as filler or to improve durability of concrete. They have fine size particles which are either natural material or by product of industries such as fly ash. They have fine size particles which are either natural material or by product of industries such as fly ash.
Types of mineral or pozzolanic
- Natural pozzolana
- Artificial pozzolana