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METAKAOLIN-METAKAOLIN-A SUPPLEMENTARY A SUPPLEMENTARY

CEMENTETIOUS MATERIALCEMENTETIOUS MATERIAL

BY

R.VALLISH

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INTRODUCTION

•A MATERIAL OTHER THAN CEMENT, WATER AND AGGREGATES THAT IS USED AS AN INGREDIENT OF CONCRETE AND IS ADDED TO THE BATCH IMMEDIATELY BEFORE OR DURING MIXING

ADMIXTURE

•USED TO MODIFY THE PROPERTIES OF ORDINARY CONCRETE SO AS TO MAKE IT MORE SUITABLE FOR ANY SITUATION

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POZZOLONA

• ARE THE TYPE OF ADMIXTURE , WHICH POSSESS LITTLE CEMENTISIOUS VALUE.

• IN FINELY DIVIDED FORM AND IN THE PRESENCE OF MOISTURE, CHEMICALLY REACTS WITH CALCIUM HYDROXIDE LIBERATED ON HYDRATION AT ORDINARY TEMPERATURE TO FORM COMPOUNDS POSSESSING CEMENTITIOUS PROPERTIES

• CLASSIFIED INTO NATURAL AND ARTIFICIAL POZZOLONA

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WHAT IS METAKAOLIN ?

• RELATIVELY NEW MINERAL ADMIXTURE

•HIGH REACTIVITY METAKAOLIN IS ONE OF THE RECENTLY DEVELOPED SUPPLEMENTARY CEMENTING MATERIALS FOR HIGH PERFORMANCE CONCRETE.

•PRODUCED BY CALCINING PURIFIED KAOLINITE CLAY AT A SPECIFIC TEMPERATURE RANGE TO DRIVE OFF THE CHEMICALLY BOUND WATER IN THE INTERSTICES OF KAOLINE AND DESTROY THE CRYSTALLINE STRUCTURE

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•PARTICLE SIZE OF THE METAKAOLIN IS LESS THAN 2μM

•IT IS TYPICALLY INCORPORATED INTO CONCRETE TO REPLACE 5 TO 15% BY WEIGHT OF CEMENT

•MIXTURES CONTAINING HIGH-REACTIVITY METAKAOLIN YIELD GOOD RESULTS IN TERMS OF STRENGTH,PERMEABILITY AND DRYING SHRINKAGE RESISTANCE.

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CONCRETE PROPERTIESFRESH CONCRETE

•MK, BEING VERY FINE IN SIZE GENERALLY HAS HIGHER WATER DEMAND FOR WORKABILITY.

•WITH INCREASED ADDITION OF MK WORKABILITY OF CONCRETE REDUCES

• FURTHER ADJUSTMENTS IN FINES OF CONCRETE, RETAINING COHESIVENESS, REDUCES LOSS IN WORKABILITY

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   •BLEEDING WHICH IS A FUNCTION OF SEDIMENTATION DEPENDS UP ON MIX COMPOSITION AND PROPERTIES OF CEMENT FOR A GIVEN COMPOSITION.

•BLEEDING REDUCES WITH INCREASED SPECIFIC SURFACE AREA.

•THUS MK SURROUNDING THE AGGREGATE PARTICLES HELPS IN REDUCING THE BLEEDING.

BLEEDING

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•COMPRESSIVE STRENGTH OF METAKAOLIN CONCRETE CONTINUES TO INCREASE WITH REPLACEMENT LEVELS AT ALL AGES.

•IT COULD BE SEEN THAT THERE IS A SIGNIFICANT IMPROVEMENT IN EARLY AGE STRENGTH OF CONCRETE IN ADDITION TO 28-DAY STRENGTH LEVELS.

HARDENED CONCRETE

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CHEMICAL COMPOSITION OF METAKAOLIN AND CEMENT

CHEMICALS CEMENT METAKAOLIN

SIO2 21.0% 51.2%

Al2O3 5.2% 45.3%

Fe2O3 2.3% 0.60%

MgO 3.9% --

CaO 63.9% 0.05%

Na2O 0.5% 0.16%

K2O 0.5% 0.16%

SO3 2.4% --

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METAKAOLIN AS A CEMENT RELPLACEMENT MATERIAL

•GREATLY REDUCE POROSITY AND PERMIABILITY

•INCREASE COMPRESSIVE STRENGTH

HRM ADDED TO OPC AT 5-15% BY WEIGHT WILL

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•PROVIDE LONG TERM DURABILITY WHERE ASR IS A CONCERN

•REDUCE OCCURANCE OF EFFLORESENCE

•PROVIDE ENHANCED RESISTANCE TO CHEMICAL ATTACK

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PERMEABILITY

• PARTICLE SIZE OF HRM IS LESS THAN 2μm

• IT WILL SERVE TO FILL THE SPACES BETWEEN CEMENT GRAINS, PHYSICALLY TIGHTENING THE PARTICLE ARRAGEMENT

• HRM REACTS WITH CALCIUM HYDROXIDE TO FORM DURABLE BINDING PRODUCT NAMELY CALCIUM SILICATE AND CALCIUM ALUMINATE HYDRATES

•DISTINCT DENSIFICATION WHICH INCLUDE AN INCREASED STRENGHT AND DECREACED PERMIABILITY.

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POROSITY

• THE PORE SIZE DISTRIBUTION IS AFFECTED BY HRM.

•GENERALLY, THE TOTAL PORE VOLUME IS REDUCED AND THE AVERAGE PORE SIZE IS DECREASED

•SIGNIFICANT DECREASE IN THE OCCURANCE OF VERY FINE PORES IN AN HRM PASTE AS COMPARED TO OPC

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ALKALI SILICA REACTION

THE REACTION BETWEEN THE SILICIOUS MINERAL IN THE AGGREGATE AND THE ALKALINE HYDROXIDE DERIVED FROM ALKALIS IN CEMENT

RESULTS IN THE FORMATION OF UNLIMITED SWELLING TYPE

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EFFLORESCENCE

OCCURS WHEN CALCIUM HYDROXIDE(FREE LIME) BY PRODUCT OF HYDRATION OF CEMENT IS CARRIED TO THE SURFACE OF CEMENT BASED PRODUCTS BY MIGRATING WATER.

WHEN EXPOSED TO ATMOSPHERE CALCIUM HYDROXIDE REACTS WITH CARBON DIOXIDE TO FORM CALCIUM CARBONATE WHICH REMAINS AS WHITE STAINS

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ADVANTAGES AND

APPLICATIONS

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METAKAOLIN MODIFIED CONCRETE HAS A CREAMIER TEXTURE, SETS SOME WHAT FASTER, GENERATES LESS BLEED WATER AND HAS A BETTER FINISHABILITY

THE COMPRESSIVE AND FLEXURAL STRENGTH DEVELOPMENTS OF THE METAKAOLIN MIXTURES ARE SIGNIFICANTLY FASTER THAN THOSE OF THE NON POZZOLONIC CONTROL MIXTURE.

LONG TERM DRYING SHRINKAGE OF METAKAOLIN MIXTURE IS LESS THAN THAT OF PLAIN CONCRETE

ADVANTAGES

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      ACCORDING TO ASTM, THE CHLORIDE PERMEABILITY OF METAKAOLIN MIXTURE IS MUCH LOWER THAN THAT OF PLAIN CONCRETE.

      ELIMINATE FREE LIME FROM THE SYSTEM THROUGH RAPID POZZOLONIC REACTION

      INCREASE THE DENSITY AND REDUCE THE POROSITY AND PERMEABILITY OF THE PASTE SYSTEM

      REDUCE THE CEMENT CONTENT WITH POZZOLONA SUBSTITUTION 5-15%

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  HIGH PERFORMANCE, HIGH STRENGTH AND LIGHT WEIGHT CONCRETE.

   PRECAST CONCRETE WORKS

FIBRE CEMENT AND FERRO CEMENT PRODUCTS

MANUFACTURED REPITITIVE CONCRETE PRODUCTS

APPLICATIONS

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CASE STUDY

City college of New York

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•HIGH-REACTIVE METAKAOLIN (HRM) IS BEING USED IN CONCRETE TO RESTORE THE FACADE OF HISTORIC SHEPARD HALL AT THE CITY COLLEGE OF NEW YORK.

•THE DECISION TO USE THE CONCRETE ADDITIVE WAS BASED ON TO MEET THE PERFORMANCE REQUIREMENTS ESTABLISHED FOR THE BUILDING.

•THE PROJECT DRAMATICALLY DEMONSTRATES THE POTENTIAL OF HRM TO ENHANCE THE PERFORMANCE AND APPEARANCE OF CONCRETE.

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CONCLUSIONS

• METAKAOLIN OFFERS BETTER WORKABILITY COMPARED TO OTHER ADMIXTURES.

•STRENGTH OF METAKAOLIN MODIFIED CONCRETE INCREASE AT ALL STAGES.

•DURABILITY AND COMPRESSIVE STRENGTH ARE LIKE TWO LEGS OF HUMAN BEING, THESE TWO PROPERTIES CAN BE ENHANCED BY THE USE OF METAKAOLIN.

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REFERENCES

•A. K. Tiwari & P. Bandhyopadhyay, “Metakaolin for high performance concretes in India”, Indian Concrete Journal, April 2003.

•M. S. Shetty, “Concrete Technology”, 2002, S. Chand & Co. Ltd.

• Neville. A.M. “Properties of Concrete” Fourth Edition Wiley & Sons 1996.

• Jian-Tong Ding and Zongjin Li, “Effects of Metakaolin and Silica Fume on Properties of Concrete”, July-August 2003, pp. 393-398.

 

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