1. CE 6002 – CONCRETE TECHNOLOGY
SEMBODAI RUKMANI VARATHARAJAN ENGINEERING COLLEGE
SEMBODAI
DEPARTMENT OF CIVIL ENGINEERING
CE 6002 – CONCRETE TECHNOLOGY
UNIT – II
CHEMICAL AND MINERAL ADMIXTURES
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2. What are Admixtures? Admixtures are the material, other than Cement
Water
Aggregates
fiber reinforcement
Which are used as an ingredient of concrete and is added to batch immediately before or during mixing.
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3. Admixtures have long been recognized as important
components of concrete used to improve its performance.
The original use of admixtures in cementitious mixtures is not well documented.
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4. Why admixtures? The major reasons for using admixtures are:
To reduce the cost of concrete construction.
To achieve certain properties in concrete more effectively than by other means.
To maintain the quality of concrete during the stages of mixing, transporting, placing, and curing in ad-verse weather conditions.
To overcome certain emergencies during concreting operations.
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5. Rice Husk Ash Rice husk ash is obtained by
Burning rice husk in a controlled manner without causing environmental pollution.
Material of future as mineral additives.
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6. Rice husk ash Amount used Contains 10% by weight of cement.
It greatly enhances the workability and impermeability of concrete.
Amorphous silica (90% SiO2) in very high proportion when burnt in controlled manner.
5% carbon.
2% K2O.
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7. Rice husk Ash
Effects
Reduces susceptible to acid attack and improves resistance to chloride penetration.
Reduces large pores and porosity resulting very low permeability.
Reduces the free lime present in the cement paste.
Decreases the permeability of the system.
Improves overall resistance to CO2 attack.
Enhances resistance to corrosion of steel in concrete.
Reducing micro cracking and improving freeze-thaw resistance.
Improves capillary suction and accelerated chloride diffusivity.
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8. Blast furnace slag
Blast-furnace slag is a nonmetallic product consisting essentially of silicates and aluminates of calcium and other bases.
The molten slag is rapidly chilled by quenching in water to form a glassy sand like granulated material.
The granulated material when further ground to less than 45 micron will have specific surface of about 400 to 600 m2/ kg (Blaine).
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9. THE END……
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