Unit:2

1. CONCRETE TECHNOLOGY
Dr. S. GOPIKUMAR Ph.D. Associate Professor
gopikumar@scadengineering.ac.in
Department of Civil Engineering
SCAD College of Engineering and Technology

2. UNIT II
CHEMICAL AND MINERAL ADMIXTURES (9)
Course Outcomes
CO2 - At the end of this unit, students will have the knowledge on chemical and mineral admixtures.

3. Admixtures is defined as a material, other than,
Cement
Water
Aggregate
used as an ingredient of concrete
added to the batch immediately before or during mixing.
Admixtures are used to modify the properties of ordinary concrete so as to make it more
suitable for any situation.
History of admixtures is as old as the history of concrete.
1. Plasticizers and superplasticizers, are of recent interest. Specially developed in Japan &
Germany around 1970.
2. Later on they were made popular in USA and Europe.
3. Use of Plasticizers and Superplasticizers have not become popular in India till recently
(1985).
Introduction

4. 1. To modify properties of fresh & hardened concrete
2. To ensure the quality of concrete during mixing, transporting, placing & curing
3. To overcome certain unexpected emergencies during concrete operations (ie, set
retarders)
4. Increase slump and workability
5. Retard or accelerate initial setting
6. Reduce or prevent shrinkage
7. Modify the rate or capacity for bleeding
8. Reduce segregation
9. Retard or reduce heat evolution during early hardening
10. Increase strength (compressive, tensile, or flexural)
11. Decrease permeability of concrete
12. Increase bond of concrete to steel reinforcement
13. Increase bond between existing and new concrete
14. Improve impact and abrasion resistance (hardness)
15. Inhibit corrosion of embedded metal
16. Anti-washout & Produce colored concrete.
Need for the study

5. Chemical admixtures
Improve the quality of concrete during mixing, transporting, placement
and curing.
Reduce the cost of construction, modify properties of hardened concrete and
overcome certain emergencies during concrete operations.
Basically chemical compounds.
Dosage ranges from 0.2% to 2% by weight of cement.
Chemical Admixture

6. Accelerating admixture:
 Accelerating admixtures are added to concrete to increase the rate of early strength
development.
 Accelerators shorten the set time of concrete.
• Permit earlier removal of formwork
• Reduce the required period of curing
• Advance the time that a structure can be placed in service
• Partially compensate for the retarding effect (slow down) of low temperature during cold
weather concreting
Commonly used materials as an accelerator:
• Calcium chloride
• Some of the soluble carbonates
• Silicates fluosilicates
• Some of the organic compounds such as triethenolamine
Chemical Admixtures
– Accelerators – their effects on concrete properties

9. Retarders
 Retarder is an admixture that slows down the chemical process of hydration
 Concrete remains as a plastic
 Workable for a longer time
1. Retarders are used to overcome the accelerating effect of high temperature on setting
properties of concrete in hot weather concreting.
2. Very useful when concrete has to be place in very difficult conditions and delay may
occur in transporting and placing.
3. Gypsum and Calcium Sulphate are well known retarders.
4. Other examples are: starches, cellulose products, sugars, acids or salts of Acids
Chemical Admixtures
– Retarders –their effects on concrete properties

11. Retarders
 Gypsum, Sodium citrate, Sodium gluconate, Borax
 Setting and hardening behaviors of dehydrated cement paste (DCP)
 DCRCM Dehydrated Cement paste composite Reactivated Cementitious Materials.

12. Plasticizers (Water Reducers)
 Combinations of organic and inorganic substances
 Allows a reduction in water content
 Higher workability at the same water content
The basic products constituting plasticizers:
1. Anionic surfactants such as lignosulphonates and their modifications and derivatives,
salts of sulphonates hydrocarbons.
2. Non ionic surfactants, such as polyglycol esters, acid of hydroxylated carboxylic acids and
their modifications and derivatives.
3. Other products, carbohydrates.
Chemical Admixtures
– Plasticisers – their effects on concrete properties

15. Superplasticizers (High Range Water Reducers)
Improved version of plasticizer
Developed in Japan and Germany during 1960 and 1970.
Chemically different from normal plasticisers
 Allow large water reduction
 Greater flowability
 Without substantially slowing set time
 Increasing air entrainment.
Classification of Superplasticizers:
• Sulphonated malanie-formaldehyde condensates (SMF)
• Sulphonated naphthalene-formaldehyde condensates (SNF)
• Modified lignosulphonates (MLS)
Chemical Admixtures
– Super plasticizers – their effects on concrete properties

18. Waterproofing admixture
Impervious (resistant) to water under two conditions
 Firstly, when subjected to pressure of water on one side.
 Secondly, to the absorption of surface water by capillary action.
Available in powder, paste or liquid form
Consist of pore filling or water repellent materials.
Chemically active pore filling materials:
Silicate of soda
Aluminium/zinc sulphates
Aluminium/calcium chloride.
Chemically inactive filling material:
Chalk,
Fullers earth
Talc
Chemical Admixtures
– Water proofers – their effects on concrete properties

21. Mineral admixtures
 Economical (permit reduction in total cement content),
 Reduce permeability, increase strength, and influence other concrete properties.
 Used with Portland cement, or blended cement either individually or in combinations.
Pozzolanic materials
• Siliceous or siliceous-aluminous materials,
• Little or no cementitious value,
• In finely divided form and in the presence of moisture,
• Chemically react with calcium hydroxide liberated on hydration, at ordinary temperature,
to form compounds, possessing cementitious properties.
Qualities
• Lower the heat of hydration and thermal shrinkage
• Increase the water tightness
• Reduce the alkali-aggregate reaction
• Improve resistance to attack by sulphate soils and sea water
• Improve extensibility
• Lower susceptibility to dissolution and leaching
• Improve workability
• Lower costs
Mineral Admixture

22. Fly Ash (By product of Thermal Power Plant):
1. Derived from burning coal
2. Valuable additive that makes concrete stronger
3. More durable and easier to work
4. Enhance the strength, impermeability and durability of concrete.
Class F
 Reduces bleeding and segregation in plastic concrete
 In hardened concrete, increases ultimate strength
 Reduces drying shrinkage and permeability
 Lowers heat of hydration
 Reduces creep
Class C
 Provides unique self-hardening characteristics and improves permeability.
 Useful in pre-stressed concrete and applications where high early strengths are required.
 Useful in soil stabilization.
Mineral Admixtures
– Fly ash – their effects on concrete properties

23. Fly Ash (By product of Thermal Power Plant):
1. Economic and Ecological benefits
2. Improves workability
3. Reduces segregation, bleeding.
4. Inhibits alkali-aggregate reaction
5. Enhances sulfate resistance.
6. Use of fly ash in concrete has increased in the last 20 years.
7. Less than 20% of the fly ash collected was used in the cement and concrete industries.
8. 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.

26. Silica Fume (By product of Silicon and Ferro-Silicon Alloy)
1. Microfiller (fill the microscopic voids between cement particles).
2. Greatly reduces permeability and improves the paste-to-aggregate bond of the resulting
concrete compared to conventional concrete.
3. Improves compressive strength, bond strength, and abrasion resistance
4. Reduces permeability and 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".
Mineral Admixtures
– Silica Fume – their effects on concrete properties

28. High performance concrete (HPC)
Self consolidating concrete (SCC)
Self consolidating high performance concrete (SCHPC)
.

29. Ground Granulated Blast Furnace Slag (By product of Iron Industries)
1. 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.
2. Concrete containing GGBFS as a partial cement replacement has longer-lasting
workability and low slump loss during hot weather construction.
3. Concrete containing GGBFS exhibits a lower heat of hydration than conventional Portland
cement concrete.
4. 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.
5. Use of GGBFS as a partial cement replacement gives concrete moderate resistance to
sulfate attack.
Mineral Admixtures
– Ground granulated blast furnace slag
– their effects on concrete properties

32. Metakaolin:
 Calcination of Kaolin (a fine, white clay mineral), results a highly pozzolanic material.
Mineral Admixtures
– Metakaoline – their effects on concrete properties

35. 1. 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.
2. 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.
3. Mandatory use of mineral and chemical admixture should be encouraged in order to
attain true sustainable development.
Conclusion

36. THANK YOU