Producers use admixtures primarily to reduce the cost of concrete construction; to modify the properties of hardened concrete; to ensure the quality of concrete during mixing, transporting, placing, and curing; and to overcome certain emergencies during concrete operations.

What is the function of admixture?

Admixtures influence the physical, chemical, surface-chemical, and mechanical properties of concrete and its durability. Accelerating admixtures reduce the time of setting and increase the rate at which the strength is developed. They are used in cold weather concreting.

What are the main admixtures used in concrete?

Types of Concrete Admixtures

• air entrainers.
• water reducers.
• set retarders.
• set accelerators.
• superplasticizers.
• specialty admixtures: which include corrosion inhibitors, shrinkage control, alkali-silica reactivity inhibitors, and coloring.

How important is an admixture?

Admixtures reduce the required quantity of cement and make concrete economical. They enhance the workability of concrete. Admixtures imparts early strength in concrete. ... There are concrete admixtures that decrease initial strength, but increase the hardened concrete strength more than the normal concrete strength.

Why admixture is used in mix design?

They can improve the performance of problem concrete by modifying its characteristics and enhancing workability. Admixtures are additions to a concrete mix that can help control the set time and other aspects of fresh concrete.

Admixture used in concrete | Civil Engineering interview questions

25 related questions found

How does admixture affect concrete?

They are called water-reducing retarders. Thus resulting in greater compressive strength due to low water cement ratio. Water reducing admixtures are added to concrete to achieve certain workability (slump) at low water cement ratio. A concrete with specified strength at lower cement content thus saving on the cement.

How does admixture affect workability of concrete?

Uses of Concrete Admixtures:

Air entraining agents creates a large number of very tiny air bubbles. These bubbles get distributed throughout the mass of concrete and act as rollers and increase the workability. Mineral admixtures like Pozzolanic materials are also used to improve the workability of concrete.

What is the necessity for adding concrete chemicals?

Chemical admixture are incorporated to modify the properties of concrete such as heat of hydration, accelerate or retard the setting time, improve workability, help in water reduction ,disperse/deflocculates the cement particles, aid in entrain air and finally improve the impermeability and durability characteristics.

Which disadvantage is related to the admixture process?

The biggest disadvantage with this process is that the resin may cure before vacuum process is applied especially in the complex shaped geometries of the laminates. The advantages would be the vacuum bagging finished part possesses a better strength and the part is lighter.

What is meant by proportioning of concrete?

Proportioning of concrete is the process of selecting quantity of cement, sand, coarse aggregate and water in concrete to obtain desired strength and quality.

Why is superplasticizer added to concrete?

Superplasticizers are used to increase the fluidity of concrete without adding excess water. These molecules physically separate the cement particles by opposing their attractive forces with steric and/or electrostatic forces, as explained in Chapter 11 (Gelardi and Flatt, 2016).

What are water reducing admixtures?

A. Water-reducing admixtures are used to increase the strength and workability of concrete and to reduce cost. They. consist of certain organic compounds or mixtures of organic and inorganic compounds to reduce the water requirement of the mixture for a given slump.

What do you mean by admixtures *?

Explanation: Admixtures are those ingredients in concrete other than Portland cement, water, and aggregates that are added to the mixture immediately before or after the concrete mix.

What is the role of water in concrete?

Water is the key ingredient, which when mixed with cement, forms a paste that binds the aggregate together. The water causes the hardening of concrete through a process called hydration. ... The role of water is important because the water to cement ratio is the most critical factor in the production of "perfect" concrete.

What is the difference between mixture and admixture?

As nouns the difference between mixture and admixture

is that mixture is the act of mixing while admixture is an instance of admixing, a mixing-in of something.

How do you increase slump in concrete?

Adding just 1 gallon of water per cubic yard can: Increase slump 1 inch, decrease compressive strength 150 to 200 psi, waste about 1/4 bag of cement, and increase shrinkage by 10%. But water isn't the only way to adjust slump. Consider adding a superplasticizer at the site to increase slump.

How is concrete admixture calculated?

MIX CALCULATION :

1. Volume of concrete = 1m^3.
2. Volume of cement = (373/3.15)x1/1000 = 0.118 m^3.
3. Volume of water = ( 149/1)x1/1000= 0.149 m^3.
4. Volume of admixture = ( 7.6/1.145)x1/1000 = 0.006.
5. Volume of coarse aggregate and fine aggregate = a – ( b + c + d) = 1-( 0.118 + 0.149 + 0.006 )= 0.727 m^3.

What is high range water reducing admixture?

High range water reducing admixture is used to produce high strength concrete to reduce cross section of compression members in high rise building, improve durability of concrete in aggressive environments, and many more applications.

How do water reducing admixtures work?

Water-reducing admixtures essentially neutralize surface charges on solid particles and cause all surfaces to carry like charges. Since particles with like charges repel each other, they reduce flocculation of the cement particles and allow for better dispersion.

Why is curing needed?

Curing plays an important role on strength development and durability of concrete. ... Properly cured concrete has an adequate amount of moisture for continued hydration and development of strength, volume stability, resistance to freezing and thawing, and abrasion and scaling resistance.

What are admixture what are its beneficial effects it offers to concrete?

Admixtures offer high workability, high compressive strength, durability, watertight, wear resistant, and high finish for the complex modern structures, which is expected to drive the growth of concrete admixture market.

What is segregation and bleeding in concrete?

Bleeding is a form of segregation where some of the water in the concrete tends to rise to the surface of the freshly placed material. Conversely, if evaporation of the surface water is faster than the rate of bleed, plastic shrinkage cracking may occur. ...

Why is pozzolana added to cement?

What does a pozzolan do in the concrete? A. ... Pozzolans reduce bleeding because of fineness; reduce the maximum rise in temperature when used in large amounts (more than 15% by mass of cementitious material) because of the slower rate of chemical reactions; which reduce the rise in temperature.

What is admixture in construction?

An admixture is a substance which can be added to concrete to achieve or modify its properties. Admixtures are added to the concrete, in addition to cement, water and aggregate, typically immediately before or during the mixing process.