USE OF CHEMICAL AND MINERAL ADMIXTURE IN CONCRETE

Presenting by U13CE030 Hardik Visapara U13CE003 Chirag Mandaviya

INTER COLLEGE POWER POINT PRESENTATION CONTESTULTRATECH – SPARKLING STARS

Content:

Basic of Admixture Need of Admixture Types of admixture Various chemical admixtures Various mineral admixtures Conclusion

What is ADMIXTURE and Why it is used ? A material other than water, aggregates, or cement that is used as an

ingredient of concrete or mortar to control setting and early hardening, workability, or to provide additional cementing properties is called as Admixture.

Admixtures are added in small quantity either in powder or liquid form Combination of various admixtures are to be used where more than one

property is to be altered

Need of Admixture:

Purpose: To modify the fresh property;

Increase the workability without increasing the water cement ratio or decrease the water content at the same workability.

Retard or accelerate the time of initial setting. Reduce or prevent the settlement or create slight expansion. Modify the rate or capacity of bleeding.

Need of Admixture:

Purpose: To modify harden property;

Reduce the heat of evolution. Accelerate the rate of strength development at early stages. Increase the durability. Decrease the permeability of concrete.

Types of Admixtures

Chemical admixtures : Accelerators, Retarders, Water-reducing agents, Super plasticizers, Air entraining agents etc.

Mineral admixtures : Fly-ash Blast-furnace slag, Silica fume etc.

Chemical Admixtures

Accelerator: An admixture which, when added to concrete, increases the rate of hydration

of hydraulic cement, shortens the time of set in concrete, or increases the rate of hardening or strength development.

Set Accelerating Admixtures: Reduce the time for the mix to change from the plastic to the hardened state. Set

accelerators have relatively limited use, mainly to produce an early set. Calcium chloride in 1 to 2 % w/w used as accelerators

Chemical Admixtures

Accelerator: Applications:

Used in repair works Used in cold weathers For early removal of formworks

Chemical Admixtures

Retarders: The function of retarder is to delay or extend the setting time of cement paste

in concrete. Retarding admixtures delay the end of the dormant period and the start of

setting and hardening. The mechanism of set retards is based on absorption. The large admixture

anions and molecules are absorbed on the surface of cement particles, which hinders further reactions between cement and water i.e. retards setting.

The commonly known retards are Soluble Zinc salts, Soluble Borates and Carbohydrates derivatives used in fraction of percent by weight of cement.

Chemical Admixtures

Retarders: Applications:

For concreting in hot weather. For preventing formation of cold joints. Ready mixed concrete (RMC).

Chemical Admixtures

Water Reducing Admixtures (Plasticizers): Purpose:

To achieve a higher strength by decreasing the water cement ratio at the same workability as an admixture free mix.

To achieve the same workability by decreasing the cement content so as to reduce the heat of hydration in mass concrete.

To increase the workability so as to ease placing in accessible locations. Water reduction is more than 5% but less than 12% The commonly used admixtures are Lignosulphonic acid and

hydrocarbolic acids etc.

Chemical Admixtures

Water Reducing Admixtures: Applications:

For Improving workability without altering w/c ratio. High strength and high performance concrete. Good finishing of concrete surface.

Chemical Admixtures

Super plasticizers: It is also called as High range water reducing admixtures. They are improved version of plasticizer. They permits water reduction up to 30% without loss of workability. Commonly used super plasticizers are Modified lignosulphonates, Acrylic

polymer, Polycarboxylate ethers, Multicarboxylate ethers, etc.

Chemical Admixtures

Super plasticizers: Applications:

Very high workability. Self compacting concrete. Self leveling concrete. High strength and High performance concrete.

Chemical Admixtures

Air Entraining Admixtures: Air is intentionally in corporated in form of minute spherical bubbles of 5

micron to 80 micron distributed evenly in entire mass of concrete. Various admixtures used as air entertainer:

Natural wood resins. Animal and vegetable fats. Olive oil and fatty acid. Wetting agents such as sulphonated organic compounds. Water soluble soaps.

Chemical Admixtures

Air Entraining Admixtures: Functions:

Improves workability. Reduce segregation and bleeding. Better finishing due to plasticity. Improves resistance to frost action.

Chemical Admixtures

Corrosion inhibitors: Corrosion-inhibiting admixtures can significantly reduce maintenance costs of

reinforced concrete structures throughout a typical service life of 30 to 40 years. Although corrosion-inhibitors can raise the corrosion threshold, they are not an alternative to impermeable durable concrete.

Colouring admixtures: To give shade to the concrete.

Bonding admixtures: Increases Bonding Strength between concrete and reinforcement

Mineral Admixtures

Admixtures like fly ash, silicate fume, slag comes in the category of mineral admixtures.

To enhance the workability Improve resistance to thermal cracking and alkali–aggregate reaction To enable reduction in cement content Reduces segregation, bleeding and heat of hydration

Mineral Admixtures

Fly ash: Fly ash is fine residue left after combustion of ground or powdered coal. They are all generally finer than cement. Consist mainly of glassy–spherical particles as well as residues of hematite

and magnetite. The use of fly ash in concrete makes the mix economical, improves the

workability, reduces segregation, bleeding and heat of hydration.

Mineral Admixtures

Silica fume (Micro silica): It is obtained as a byproduct during the production of silicon and

ferrosilicon alloys The particle size of silica fume is 100 times smaller than cement

particles i.e. its fine as cigarette smoke Improves compressive strength, bond strength, abrasion resistance It makes the concrete dense that results in protection of reinforcement

against corrosion

Conclusion

Admixture are essential to obtain concrete with certain desired characteristics such as high compressive strength, high workability, and high performance and durability parameters to meet the requirement of complexity of modern structures.

They reduce cost of concrete construction and helps in achieving specific concrete properties more effectively.

Admixtures ensure quality of concrete during mixing, transporting, placing, and curing in adverse weather condition.