concrete admixtures

a simple presentation on admixtures

1. CONCRETE ADMIXTURES PRESENTED BY: YALLA ADINARAYANA ROLL NO:1117242 GEOTECHNICAL ENGINEERING

2. INTRODUCTION HISTORY NEED OF ADMIXTURES TYPES OF ADMIXTURES CONCLUSION REFERENCES CONTENTS

3. Admixture is define as a material other than cement, aggregate, water used in concrete. This is added to the batch immediately before or during the mixing. INTRODUCTION

4. History of admixtures is as old as the history of concrete Specially developed in Japan and Germany around 1970 Later on they were popular in USA and E urope even in middle east and far east. Unfortunately the use of plasticizers and super-plasticizers have not become popular in India till recently. The use of admixtures non popular in India because 90% of concrete works are in hands of common builders or Government departments who do not generally accept something new. HISTORY

5. Plasticizes were not manufacture in India and they were imported, so it is costly. Later international companies collaborated with Indian companies and have started manufacturing chemical admixtures in India. In India have also started using higher strength of concrete for high rise buildings and bridges. Use of Ready mix concrete (RMC) has really promoted the use of admixtures in India.

6. To modify properties of fresh and hardened concrete. To ensure the quality of concrete during the mixing, transporting, placing, and curing. To overcome certain unexpected emergencies during concrete operations by using admixtures and etc… NEED OF ADMIXTURES

7. Admixtures Plasticizers Super Plasticizers Retarding admixtures Accelerating admixtures Air-entraining admixtures Mineral admixtures Damp proof and Water-proofing admixture Grouting admixture Corrosion inhibiting admixtures Coloring admixtures and etc.., TYPES OF ADMIXTURES

8. The organic substances or combination of organic and inorganic substances which allow a reduction of water content for the given workability or give high workability at the same water content are termed as plasticizing admixtures. Plasticizers are used in the water content of 0.1% to 0.4% by weight of cement. Advantages are High strength of concrete and more workable. The mechanism involved in plasticizer as follows PLASTICIZERS

9. Super plasticizers constitute a relative new category and improved version of plasticizers. They are chemically different from plasticizers. They permits the reduction of water to the extent up to 30% without reducing workability. SUPER PLASTICIZERS

10. It is possible to use of w/c ratio as low as 0.25 by using these admixtures and achieve up to a strength of 120Mpa . They produce more workable concrete and high strength of concrete They are also know as High Rang Water Reducers.

11. The admixture that slows down the chemical process of hydration. The mechanism involves large admixture anions and molecules are absorbed on the surface of cement particles, which hinders further reactions between cement and water. RETARDERS

12. The commonly known retards are Calcium Ligno sulphonates and   Carbohydrates derivatives. These are helpful for concrete that has to be transported to long distance, and helpful in placing the concrete at high temperatures. Sugar is most effective retarding agent without effecting ultimate strength.

13. Accelerating admixture are added to the concrete to shorten the setting time and increase the rate of early strength. In past Calcium chloride is used. But it is harmful for reinforcement concrete. ACCELERATORS

14. These can be used for earlier removal of formwork, reduce the required period of curing and emergency repair work. By using these cement set hardly 5 minutes. So it is used in underwater construction and basement of water proofing operation.

15. Air-entraining admixtures are used to introduce and stabilize microscopic air bubbles in concrete. These bubbles are introduced by an air entraining agent, a type of chemical that includes detergents. AIR-ENTRAINING ADMIXTURES

16. In cold weather, water in concrete converts into ice. As ice occupies more volume than liquid water so it exerts stress on surrounding concrete as a result concrete might crack . But air bubbles inside the concrete provide space for the enhanced volume of ice and prevents cracks in the concrete.

17. Plasticizers , super plasticizers and air entraining admixtures is mostly used. Super plasticizers is widely used all over the world . India is catching u with the use of super plasticizers in the constructions of high raise building , long span bridges because It reduced cement content ,increased workability and strength. CONCLUSION

18. Concrete technology –MS Shetty www.aboutcivil.com www.pdhengineer.com REFERENCES

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