CHEMICAL &

MINERAL ADMIXTURES IN
CONCRETE
 CONCRE
Basic Definition: TE

• Concrete is a composite material that essentially consists of a

binding medium embedded with Fine-Aggregate (typically sand)
and Coarse Aggregate (typically gravel), water with or without
chemical and mineral admixture and filler.

• Concrete is a highly heterogeneous material on a macroscopic

scale, as it can be made up from an infinite combination of
suitable materials and its final properties are dependent on the
treatment it gets while production, placing, during curing and
exposure conditions during its service life.

• The effectiveness of production( selection of combination of suitable

materials, mixing etc.)
, placing (consolidation) and curing procedures are critical for
attaining full properties of a concrete mixture.
 CONCRETE
Admixtures are material other than cement, aggregates &
ADMIXTURES
water that are added to concrete either before or during
mixing to alter its properties & performance in fresh
(workability, setting time etc) and hardened state
(strength, durability etc.)
Concrete admixtures are generally divided into 2 types
1. Chemical admixture
2. Mineral admixture
• Mineral and 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.
 CONCRETE
ADMIXTURES
Typically incorporated to improve the following concrete properties

• Protect Against Freeze Thaw Cycles –Improve Durability

• Mid- Range water reducers
• High-Range water reducers – superplasticizers
• High Strength Concrete
• Corrosion Protection
• Set Acceleration
• Strength Enhancement
• Set Retardation
• Crack Control (shrinkage reduction)
• Flowability
• Self levelling
• Finish Enhancement
 CHEMICAL
ADMIXTURES
• Chemical admixtures are used to improve the quality of
concrete during mixing, transporting, placement and
curing. They 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.

• They are basically chemical compounds. Dosage

ranges from 0.2% to 2% by weight of cement.
 CHEMICAL
ADMIXTURES
Chemical admixtures fall into the following categories:

• Air entrainers
• Water reducers
• Set retarders
• Set accelerators
• Superplasticizers
• Specialty admixtures: which include corrosion
inhibitors, shrinkage control, alkali-silica reactivity
inhibitors, and coloring.
 CHEMICAL
ADMIXTURES
• Air entraining agent:
Air-entraining agents entrain small air bubbles in the concrete.
The major benefit of this is enhanced durability in freeze-thaw
cycles, especially relevant in cold climates.
• Retarding Admixtures:
Retarding admixtures slow down the hydration of cement,
lengthening set time. Retarders are beneficially used in hot
weather conditions in order to overcome accelerating effects of
higher temperatures and large masses of concrete on concrete
setting time
• Accelerating admixture :
Accelerators shorten the set time of concrete, allowing a
cold-weather pour, early removal of forms, early surface
finishing, and in some cases, early load application.
 CHEMICAL
• Water Reducing Admixtures :
ADMIXTURES
Water reducing admixtures require less water to make a
concrete of equal slump, or increase the slump of
concrete at the same water content. Typical water
reduction is the range of 10 – 15%.
• Superplasticizers :
High range water reducers are admixtures that allow
large water reduction or greater flowability (as defined
by the manufacturers, concrete suppliers and industry
standards) without substantially slowing set time or
increasing air entrainment.
• Specialty admixtures:
Include corrosion inhibitors, shrinkage control, alkali-
silica reactivity inhibitors, and coloring.
 WATER REDUCING ADMIXTURES
(Normal/High
Range)
Reasons for Using a Water Reducer: Option 1
• To get a stronger and more durable concrete from a given
amount of cement by allowing reduction of water-
cement ratio
• Most regular water reducers will permit 5-15% reduction
water
→ Example
• Original mix:
330 kg cement, 181.5 kg water, w/c = 0.55
→strength at 28 days = 30 MPa
• Mix with water reducer
330 kg cement, 165 kg water, w/c = 0.5
→strength at 28 days = 36 MPa
 WATER REDUCING
ADMIXTURES
(Normal & High Range)
Reasons for Using a Water Reducer: Option 2

• For a given w/c a mix may turn out to be unworkable

• Add water reducer to increase slump without making

adjustment to mix proportions.

• Results in better compactibility of the mix and strength increase

slightly
 WATER REDUCING
ADMIXTURES
(Normal & High Range)
Reasons for Using a Water Reducers: Options 3

• Economy: a concrete with the same w/c and same strength can
be produced with less
cement.
• Normally the extra cost for the water reducer is more than offset
by savings in cement.
• Example
→Original Mix
330 kg cement, 165 kg water, w/c =0.5
→Mix with WR (10% water reduction)
150 kg water, For w/c = 0.5
cement required = 300 kg. ÎSave 30 kg cement/m 3)
 CHEMICAL
ADMIXTURES
Terms associated with the interaction of chemical admixture and
cementitious system.
• Saturation point :Saturation dosage of a given HRWRA (High Range
water reducing admixture) exists for each cementitious system.
Beyond this dosage any additional increase does not generate any
increase in fluidity of the cement paste and the increase slump of
concrete.
• Incompatibility : A rapid loss is sometime observed in
superplasticized concrete, although the saturation dosage has
been used, in this case the cement and HRWRA are said to be
incompatible.
• Compatibility : When a high slump can be maintained for a longer
period of time, without any significant segregation and bleeding,
the HRWRA are said to be compatible.
• Robustness: When a little variation in the composition of one of
the ingredient of the mix does not lead to a big variation of the
properties of the concrete.
 CHEMICAL
Issues relatedADMIXTURES
to incorporation of chemical admixtures in
concrete.
Compatibility and Robustness :
Compatibility and robustness are the two main issues
governing the choice of chemical admixture in
cementitious systems, to achieve the intended concrete
properties.
• Simple tests on grouts, such as Marsh Cone test or Mini-
slump cone test can give a fair idea of compatibility
between chemical admixture and cementitious system.
• Fewer trials concrete mixture may be needed to obtain
an optimized concrete mixture, once above test on
grouts are performed.
 CHEMICAL
ADMIXTURES
Key Factors governing chemical admixture and
cementitious system compatibility.
• Chemical & phase compositions of cement
especially C3A & alikali.
• Cement fineness.
• Amount and type of Gypsum
• Chemical & Average molecular weight of admixture.
• Dosage of Admixture & addition method.
• Degree of sulphonation, purity.
• Type and quantity of mineral admixture present in
the concrete.
MARSH
CONE
MARSH CONE
TEST
 MINERAL ADMIXTURES
•Mineral admixtures affect the nature of the hardened
concrete through hydraulic or pozzolanic activity. Pozzolans
are cementitious materials and include natural pozzolans
(such as the volcanic ash used in Roman concrete), fly ash,
Silica Fume, Metakaolin, Rice Husk Ash, GGBFS.

•Mineral admixtures make mixtures more economical

(enables reduction in total cement content), reduce
permeability, increase strength, and influence other
concrete properties.

•They can be used with Portland cement, or blended

cement either individually or in combinations.
 DIFFERENT TYPES OF MINERAL ADMIXTURES
Fly Ash (By product of Thermal Power Plant) :
• Derived from burning coal, fly ash is a valuable additive that makes
concrete stronger, more durable and easier to work with.
•Fly ash aids the formation of cementitious compounds to
enhance the strength, impermeability and durability of
concrete.
Two main classes of fly ash are used in concrete, Class F, and
Class C.
Class F
•The burning of harder, older anthracite and bituminous coal
typically produces Class F fly ash. This fly ash is pozzolanic in
nature, and contains less than 7% lime (CaO). requires a
cementing agent

•Reduces bleeding and segregation in plastic concrete. In hardened

concrete, increases ultimate strength, reduces drying shrinkage and
Class C (Fly ash produced from the burning of younger
lignite or sub-bituminous coal, in addition to having
pozzolanic properties, also has some self-cementing
properties.)
Provides unique self-hardening characteristics and improves
permeability. Especially useful in pre-stressed concrete and
other applications where high early strengths are required

Unlike Class F, self-cementing Class C fly ash does not

require an activator. Alkali and sulfate (SO4) contents are
generally higher in Class C fly ashes.
DIFFERENT TYPES OF MINERAL ADMIXTURES
Fly Ash (By product of Thermal Power Plant) :
•In addition to economic and ecological benefits, the use
of fly ash in concrete improves its workability, reduces
segregation, bleeding, heat evolution and permeability,
inhibits alkali-aggregate reaction, and enhances sulfate
resistance.
•Even though the use of fly ash in concrete has
increased in the last 20 years, less than 20% of the fly
ash collected was used in the cement and concrete
industries
•One of the most important fields of application for fly
ash is PCC pavement, where a large quantity of
concrete is used and economy is an important factor in
concrete pavement construction.
DIFFERENT TYPES OF MINERAL ADMIXTURES
Silica Fume (By product of Silicon and Ferro-Silicon Alloy) :
•particles are approximately 100 times smaller than the average
cement particle. Because of its extreme fineness and high silica
content, Silica Fume is a highly effective pozzolanic material
•Silica fume can make a significant contribution to early-age
strength of concrete. One kg of silica fume produces about the
same amount of heat as a kg of portland cement, and yields
about three to five times as much compressive strength.
•Silica fume improves concrete in two ways – the basic
pozzolanic reaction, and a microfiller effect. Addition of silica fume
improves bonding within the concrete and helps reduce
permeability, it also combines with the calcium hydroxide produced
in the hydration of portland cement to improve concrete
durability.
DIFFERENT TYPES OF MINERAL ADMIXTURES
Silica Fume (By product of Silicon and Ferro-Silicon Alloy) :
•As a microfiller, the extreme fineness of the silica fume allows it
to fill the microscopic voids between cement particles. This
greatly reduces permeability and improves the paste-to-
aggregate bond of the resulting concrete compared to
conventional concrete.
•It has been found that Silica Fume improves compressive
strength, bond strength, and abrasion resistance; reduces
permeability; and therefore helps in protecting reinforcing steel
from corrosion.
Caution:
The higher percentage of silica fume used, the higher the
amount of super plasticizer needed - but mix can become
"sticky".
 DIFFERENT TYPES OF MINERAL ADMIXTURES
Ground Granulated Blast Furnace Slag (By product of Iron Industries)
•Ground granulated blast-furnace slag is the granular
material formed when molten iron blast furnace slag is
rapidly chilled (quenched) by immersion in water. It is a
granular product with very limited crystal formation, is
highly cementitious in nature and, ground to cement
fineness, hydrates like Portland cement.
•Concrete containing GGBFS as a partial cement
replacement has longer-lasting workability
and low slump loss during hot weather construction.
 DIFFERENT TYPES OF MINERAL
ADMIXTURES
•Concrete containing GGBFS exhibits a lower heat of
hydration than conventional Portland cement concrete.
•The use of GGBFS as a partial replacement for Portland
cement can reduce available alkalies and can reduce the
reaction between certain siliceous components of concrete
aggregates and the alkalies in the concrete
•Use of GGBFS as a partial cement replacement gives
concrete moderate resistance to sulfate attack
 DIFFERENT TYPES OF MINERAL ADMIXTURES
Metakaolin:
•Calcination of Kaolin (a fine, white clay mineral), results a highly
pozzolanic material called matakaolin.
Rice Husk Ash :
•Rice milling generates a by product know as husk . This surrounds
the paddy grain. During milling of paddy about 78 % of weight is
received as rice , broken rice and bran .Rest 22 % of the weight of
paddy is received as husk . This husk is used as fuel in the rice mills to
generate steam for the parboiling process .
•This husk contains about 75 % organic volatile matter and the balance
25 % of the weight of this husk is converted into ash during the firing
process , is known as rice husk ash ( RHA ). This RHA in turn contains
around 85 % - 90 % amorphous silica.
• Mineral and Chemical Admixture play a very important role in concrete, its judicious
selection improves its fresh and hardened concrete properties & enhances its long terms
performance.

• New age concrete like Self Compacting Concrete, High Volume Fly Ash Concrete, High
Performance Concrete etc, would not have been realized without the availability /
incorporation of mineral and chemical admixture.

• Mandatory use of mineral and chemical admixture should be encouraged in order to

attain true sustainable development.
THANK YOU