The document discusses concrete admixtures, which are materials added to concrete to modify its properties for specific applications. It outlines their functions, types (chemical and mineral admixtures), and advantages such as improved workability, reduced cost, and enhanced durability. Different chemical admixtures like air entrainers, water reducers, set retarders, accelerators, and superplasticizers, along with mineral admixtures like fly ash, silica fume, and GGBS, are detailed for their roles in improving concrete quality.

1. MATERIAL TESTING AND EVALUTION
TOPIC
ADMIXTURE
PREPARED
BY
ER.SANJEEVSINGH
SNJV432@GMAIL.COM
MODULE-IV

2. CONTENTS
 Introduction of admixture
 Function of admixture
 Types of admixture
 Advantages of admixture

3. INTRODUCTION OF ADMIXTURE
 Admixture is defined as a material other than cement, aggregate and
water used as an ingredient of concrete, added to the batch
immediately before or during mixing, to modify the properties of
ordinary concrete to make it more suitable for required situation.
 Producers use a admixture 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,
curing and to overcome certain emergencies during concrete
operations.

4. FUNCTION OF ADMIXTURE
 Increase workability without increasing water content or decrease
the water content at the same workability.
 Retard or accelerate time of initial setting;
 Reduce or prevent shrinkage.
 Modify the rate or capacity for bleeding.
 Reduce segregation;
 Retard or reduce heat evolution during early hardening;
 Accelerate the rate of strength development at early ages.
 Decrease permeability of concrete.
 Increase bond of concrete to steel reinforcement.

5. TYPES OF ADMIXTURE
CHEMICAL
ADMIXTURES MINERAL
ADMIXTURES

6. CHEMICAL ADMIXTURE
 Chemical admixtures reduce the cost of construction, modify properties of
hardened concrete, ensure quality of concrete during
mixing/transporting/placing/curing, and overcome certain emergencies
during concrete operations.
 Chemical admixtures are used to improve the quality of concrete during
mixing, transporting, placement and curing.
 Types of chemical admixture
 air entrainers
 water reducers
 set retarders
 set accelerators
 superplasticizers

7. AIR ENTRAINERS
 Air entrainment is the intentional creation of tiny air bubbles in concrete.
 A concrete maker introduces the bubbles by adding to the mix an air
entraining agent, such as wood resins, vegetable fats and oil.
 The air bubbles are created during mixing of the plastic (easy flowing, not
hardened) concrete, and most of them survive to be part of the hardened
concrete
 The primary purpose of air entrainment is to increase the durability of the
hardened concrete, especially in climates subject to freeze-thaw; the
secondary purpose is to increase workability of the concrete while in a plastic
state in concrete.

8. WATER REDUCERS
 Water reducers are special chemical products added to a concrete mixture
before it is poured.
 Water reducers offer several advantages in their use, listed below:
 reduces the water content by 5-10%
 decreases the concrete porosity
 increases the concrete strength by up to 25% (as less water is required for
the concrete mixture to remain workable)
 increases the workability (assuming the amount of free water remains
constant)
 reduces the water permeability (due to less water being used)
 gives a better finish to surfaces (due to all of the above)

9. SET RETARDERS
 This type of chemical admixture decrease the initial rate of reaction between
cement and water and there by retards the setting of cement.
 It function by coating the surface of C3S { tri calcium silicate ) components,
thus delaying this reaction with the water.
 Reaction products are slow to form as such the setting and hardening of
concrete.
 Retardation in setting time up to 8-10 hours is possible by suitable use of
retarders.
 Example of retarders such as ligno sulphonic acids and their salts, hydro-
carboxylic acids, carbohydrates including sugar.

10. SET ACCELERATORS
 A cement accelerator is an admixture for the use in concrete mortar
rendering or screeds.
 The addition of an accelerator speeds the setting time and thus cure
time starts earlier.
 This allows concrete to be placed in winter with reduced risk of frost
damage.
 Concrete is damaged if it does not reach a strength of 500 pounds per
square inch (3.4 MPa) before freezing.
 Accelerators such as calcium nitrate, calcium formate, calcium chloride etc.

11. SUPERPLASTICIZERS
 The admixture capable of reducing water content by about 30% are known as
super plasticizer.
 heir addition to concrete or mortar allows the reduction of the water to cement
ratio without negatively affecting the workability of the mixture, and high
performance concrete.
 The strength of concrete increases when the water to cement ratio decreases.
 Superplasticizers are melamine formaldehyde condensates, modified lingo
sulfonates etc.

12. MINERAL ADMIXTURES
 Mineral admixtures make mixtures more economical, reduce permeability,
increase strength, and influence other concrete properties
 Mineral admixtures {fly ash, silica fumes, slags} are usually added to
concrete in larger amounts to enhance the workability of fresh concrete ; to
improve resistance of concrete to thermal cracking, alkali aggregates
expansion, and sulfate attack: and to enable a reduction in cement content.
 Fly ash
 Silica fume
 Ground granulated blast furnace slag.

13. FLY ASH
 Fly ash produced in small dark flecks by the burning of powdered coal and
transported by the flue gases and collected by electrostatic precipitator.
 The importance of fly ash in concrete has grown so much because a
common ingredient in concrete , specially for making high strength and
high durable concrete.
 The use of fly ash as concrete admixture not only extends technical
advantages to the properties of concrete but also contributes to the
environmental pollution control.
 Use of right quality fly ash result in reduction of water demand for desired
slump.
 As the reduction of water content, bleeding and drying shrinkage will also
be reduce.

14. SILICA FUME
 Silica fume is a byproduct of producing silicon metal or ferrosilicon alloys.
 Silica fumes rises as an oxidized vapour, it cools, condenses, and collected in
cloth bags.
 It should be in premium white and standard grey colors.
 Particle size is less than 1 micron with average dia of 0.1 micron.
 The shape of the particle is spherical.
 Silica fumes reduce the workability of concrete.
 Water demand increases in proportion to silica fume added.
 Water demand is 1% for every 1% of replacement of cement.
 Bleeding is reduced as silica fumes particles find their way between two
cement grains.
 Concrete containing silica fumes show outstanding performance in
development of strength.

15. GROUND-GRANULATED
BLAST-FURNACE SLAG (GGBS )
 Ground-granulated blast-furnace slag (GGBS ) is obtained by quenching molten
iron slag (a by-product of iron and steel-making) from a blast furnace in water or
steam, to produce a glassy, granular product that is then dried and ground into a fine
powder.
 The replacement of cement with GGBS will reduce the unit water content necessary to
obtain the same slump.
 This reduction of unit water content will be more pronounced with increase content
and also on the fineness of slag. This is because of the surfaced configuration and
particle shape of slag being different than cement particle.
 In addition, water used for mixing in not immediately lost, as the surface hydration of
slag is slightly slower then that of cement.
 Reduced heat of hydration.
 Refine of pore structures.
 Reduced permeability to the external agencies.
 Increased resistance to chemical attack

16. ADVANTAGES OF ADMIXTURE
 Admixtures reduce the required quantity of cement and make concrete
economical.
 They enhance the workability of concrete.
 Admixtures imparts early strength in concrete.
 Admixtures reduce the early heat of hydration and overcome thermal cracking
problem in concrete. If there is a more heat of hydration then cracks can
propagate in fresh concrete.
 Admixtures improve the resistance against freeze-thaw effect on concrete.
 Concrete admixtures maximize the sustainability by bringing waste products in
use.
 Concrete admixtures can accelerate the setting time as well as there are
admixtures that decelerate concrete setting time
 There are some admixtures that act as anti-bacterial agents.
 There are concrete admixtures that decrease initial strength, but increase the
hardened concrete strength more than the normal concrete strength.

17. THANKS