ADMIXTURES

Anish|Ankit|Anurag|Avinav|Bhavika|Debakshi|Deepak|Dorji|Dhruv|Garima

admixtures cannot

compensate for bad practice

and low quality materials

Admixtures

ingredients other

than water,

aggregates,

hydraulic cement,

and fibres that are

added to the

concrete batch

immediately before

or during mixing.

proper use

Effectiveness of admixtures

type and amount of

cement

water content

mixing time

Slump

temperature of concrete

and air

•improved quality

•Change in setting time

•enhanced frost and sulphate

resistance

•control of strength development

•improved workability

•enhanced finishability

be

ne

fic

ial

eff

ec

ts

admixtures

chemical mineral

These

materials

react

chemically

with

calcium

hydroxide

released

from the

hydration of

Portland

cement to

form

cement

compounds

or supplementary cementing materials

added to the concrete mix to improve the properties of concrete.

inorganic

pozzolanic

latent hydraulic

Hydraulic: Moved or operated or effected by liquid

Pozzolana: Variety of volcanic sand with burnt granules resembling powdered brick: is a siliceous or siliceous and aluminous material which, when mixed with hydraulic limes and water, becomes a cement-like compound capable of setting under water.

•more economical •reduce permeability •increase strength

silica

fume

Fly

ash Natural

pozzolans

GGBFS ground

granulated

blast-

furnace slag

Typical

examples

silicious fly ash

pozzolanic

Fly

ash

environmentally friendly

the most commonly used

pozzolan in concrete

by product of coal fired

electric generating plants

improves strength

produced concrete is

denser, results in a

smoother surface with

sharper detail

is an inexpensive replacement

for Portland cement (upto

60%) used in concrete

is also used as an ingredient in

brick, block, paving, and

structural fills.

Action on Concrete

spherical shape of

particles reduces internal

friction

Increases concrete's

consistency and mobility

longer pumping distances

Improved workability

less water

less segregation of mixture

calcareous fly ash

latent hydraulic

Properties depend on type of coal burnt:

GGBFS ground

granulated

blast-

furnace

slag

by product of steel

production (the granular material formed when molten iron blast furnace slag is rapidly chilled by immersion in water)

used to partially

replace Portland

cement (by up to

80% by mass)

has latent hydraulic

properties

improves workability

lower relative density of slag

the increase in paste volume

decreases the water demand

Setting times increases as slag

content increases.

relatively higher fineness of slag

rate and quantity of bleeding is

less than usual

Slag does not contain carbon

may cause instability and air loss

in concrete.

similar to fly ash, but particle size 100

times smaller

higher surface to volume ratio

much faster pozzolanic reaction.

reduces permeability

helps in protecting reinforcing steel

from corrosion.

improves compressive strength, bond

strength, and abrasion resistance

Increased Compressive and Flexural

Strength

Reduced Permeability & Efflorescence

Increased resistance to Chemical

attacks

Reduced Shrinkage

bright white in colour

preferred choice where appearance is

important

silica

fume HRM

High reactivity

Metakaolin

or condensed silica

fume or microsilica

finely divided by-

product of

production of

silicon and

ferrosilicon alloys

Concrete strength and

durability similar to silica

fume concrete

highly processed

reactive alumina-

silicate pozzolan

admixtures

mineral chemical

•corrosion inhibition

•shrinkage reduction

•alkali-silica reactivity reduction

•workability enhancement

•Bonding

•Used in paints to improve

properties

added to the

concrete to

give it certain

characteristics

not obtainable

with plain

concrete mixes

•Reduce cost of

concrete construction

•Modify properties of

hardened concrete

•to ensure the quality

of concrete during

mixing, transporting,

placing, and curing

specialty

category

Accelerating

different types of chemical admixtures as covered in BIS IS 9103 : 1999

Water-

reducing Retarding

Air-

entraining

Super-

plasticizing

Accelerating

admixtures

used to increase

alternatively:

•the rate of concrete setting

•the early strength

development through

accelerated hardening CALCIUM

SULPHOALUMINATE

improves workability

Earlier removal of formworks

reduce potential damage risks

due to freezing

castings in low temperatures

Possibility of earlier finishing of

concrete floor slabs (especially in

low temperatures)

reduced labour costs

Accelerated hydration

increased hydration heat release

earlier strength development

Pure accelerators

either for setting or for hardening of the concrete

Accelerators

/water

reducers-

plasticizers.

examples: Calcium chloride, thiocyanate salts,

alkanolamines, sulfates, nitrates,

formates

Retarding

Admixtures

used in hot weather conditions in order to

overcome accelerating effects of higher

temperatures and large masses of

concrete on concrete setting time

Used to avoid complications when

unavoidable delays between mixing and

placing occur.

prevent prestressed concrete in contact

with the strand from setting before

vibrating operations are completed.

Most retarders also act as water reducers

oxides of lead

and zinc,

phosphates,

magnesium salts,

fluorates and

borates.

inorganic

organic

unrefined calcium,

sodium, NH4, salts of

lignosulfonic acids,

hydrocarboxylic

acids, and

carbohydrates.

delay

hydration of

cement

without

affecting the

long-term

mechanical

properties

the admixture forms a film around the

cement, preventing/ slowing the

reaction with water

thickness of film dictates the rate of

hydration

after a while film breaks down and

normal hydration proceeds

Water

Reducing

/ Plasticizing

Admixtures

USES

1. Added to concrete to

achieve certain workability

(slump) at a lower w/c than that

of control concrete.

2. To obtain specified strength at

lower cement content.

3. They also improve the

properties of concrete

containing marginal- or low-

quality.

COMPOSITION

• salts and modifications of hydroxylized

carboxylic acids.

• modifications of lignosulfonic acids

(lignins).

•polymeric materials.

Deflocculates tied up particles and

releases tied up water.

•Reduces water demand (upto

10%)

•also retards the setting time of the

concrete.

• Increases in compressive strength

are as much as 25%.

• Increases Freeze-thaw resistance

and other durability aspects.

WORKING + EFFECTS

Super-

plasticizing

or high range water reducing admixtures

synthetic, water-soluble organic chemicals that

significantly reduce the amount of water

needed to achieve a given consistence in fresh

concrete.

utilized in two ways:

•To reduce water content

for increased strength and

reduced permeability /

improved durability

•As a cement dispersant at

the same water content to

increase consistence and

workability retention

superplasticizers improves the

workability of concrete

to reduce water requirements 12-

25% without affecting the

workability leads to production of

high-strength concrete and lower

permeability

Use of superplasticizers in air-

entrained concrete can produce

coarser-than-normal air-void

systems

ADVANTAGES

increase in freeze-thaw and scaling resistances

concrete is more workable

reduces bleeding and segregation of fresh concrete.

Air-

entraining

AIR ENTRAINMENT

process whereby many small air bubbles are

incorporated into concrete and become part of

the matrix that binds the aggregate together in the

hardened concrete.

air bubbles dispersed uniformly through the cement

paste increase the freeze-thaw durability of

concrete.

organic additives, which enable the

bubbles to be stabilized or

entrained within the fresh concrete

specialty

category

corrosion

inhibitors

work for many years after concrete has set, increase

corrosion resistance to reduce risk of rusting steel

causing the concrete to crack and scale.

chemical compound, either liquid or

powder, which effectively decreases

or minimizes the corrosion of steel

reinforcement

ACTION

Extend time before corrosion begins

create a protective barrier that stabilizes the rust layer

surrounding steel

Provide thin protective coating that prevents chlorides

from reacting with the steel

provide inhibitors that react with iron to reduce

corrosion by acting as oxygen barrier. Corrosion due to

chloride action

Reduce absorption and water

permeability by acting on the

capillary structure of the cement

paste

Do not reduce water penetrating

through cracks or through poorly

compacted concrete

specialty

category

Water

proofing

or water resisting admixtures

reduce either the surface absorption into the

concrete and / or the passage of water

through the hardened concrete

Bonding

Agents

create a bond

between new/

fresh concrete

with old/ set

concrete

improve pumpability,

thicken the paste, and

reduce separation and

bleeding

Pumping

aids

Pigments used to

change the colour of

concrete Colouring

Agents

accelerators used in

very high doses to

achieve a very fast set-

time

Antifreeze

admixtures

COMMON EXAMPLES:

pozzolan, silica fume, fly

ash, or Metakaolin.

Alkali-silica

reactivity

control

admixtures

The Alkali-Silica Reaction occurs over time in concrete between the highly alkaline cement paste and reactive non-crystalline (amorphous) silica

ASR causes the formation of a swelling gel which increases in volume with water and exerts an expansive pressure inside the material, causing spalling and loss of

strength of the concrete, finally leading to its failure.

prevent the formation of the damaging gel. These

react preferentially with the cement alkalis without

formation of an expansive pressure

Increase cohesion and retard the setting of mortar for

masonry, allowing it to be delivered to a building site by

ready-mix in large volumes that can still be used within its

working life.

Ready-to-

use mortar

admixtures

Recron© 3s is a speciality secondary reinforcement

which Controls Cracking , Reduces Water Permeability,

Reduces Rebound Loss and Brings Direct Saving &

Gain and Increases Flexibility

Recron

3s APPLICATIONS

•PCC & RCC, plastering

•Shotcrete & Ginniting

•Slabs, Footings, foundations, walls and tanks

•Pipes, burial vaults, pre-stressed beams etc

•Concrete blocks, Railway slippers, Manhole covers & tiles etc

•Roads & pavements

•Bridges and dams

Concrete is known to be brittle and weak in tension and develops cracks during curing, due to thermal expansion and contraction over a period of time.

Concrete that is placed under water may be subject to

washout during placing and before it hardens. These

admixtures stabilise the mix, increasing cohesion and

reducing the washout.

Anti-

washout

admixtures

or underwater admixtures

1. A cube of 10x10x10 weighs less than a

kilogram.

2. The constituents are flyash, lime,

gypsum, aluminium powder and

cement.

Preparation.

1. The mixture is put into a mould 9mts

long and is compacted under high

pressure.

2. Bitumen Solution coated steel

reinforcement nets are positioned in

the mould before casting.

3. The Mould is filled to 2/3rd of its height

and after the process it attains the total

height of the mould.

PROPERTIES

lighteweight.

High thermal insulation

Fire resistant

Energy efficient

Low maintainance

Eco-friendly

Lightweight

Concrete