INTRODUTION

MINERAL ADMIXTURES(FLY ASH)PRESENTED BYZUBAIR AHMAD DAR(1EP13CV110)Under the guidance of Mr.VENKATESHA N Asst Professor, Dept of Civil Engineering,East Point College of Engineering & Technology

CONTENTS1.INTRODUCTION2.WHY MINERAL ADDITIVES3.TYPES OF MINERAL ADDITIVES4.FLY ASH AND ITS TYPES5.EFFECT OF FLY ASH ON PROPERTIES OF FRESH CONCRETE6.EFFECT OF FLY ASH ON HEAT OF HYDRATION7.EFFECT OF FLY ASH ON HARDENED CONCRETE8.DURABILITY OF CONCRETE9.CONCLUSION10.REFERENCES

INTRODUTION

Admixtures are ingredients other than basic ingredients cement,water and aggregates that are added to concrete batch immediately before or during mixing to modify one or more of the specific properties of concrete in fresh and hardened state. Added in small quantity either in powder or in liquid form. Combination is used when more than one property to be altered. Admixture is used to modify the properties of ordinary concrete so as to make it more suitable for any situation. Use of Ready mix(RMC)has really promoted the use of admixtures in india,in recent times.

WHY MINERAL ADDITIVESImproves many qualities of concrete,such as:Lower the heat of hydration and thermal shrinkage.Increase the water tightness.Reduce the alkali-aggregate reaction.(gel expansion causes cracking in the concrete)Improve workability.Lower costs.

TYPES OF MINERAL ADMIXTURES

1.Natural PozzolansClay and ShalesOpalinc ChertsDiatomaceous EarthVolcanic Tuffs and Pumicites

2.Artificial PozzolanesFly ashBlast Furnace SlagSilica FumeRice Husk ashGround Granulated Blast Furnace Slag (GGBS)MetakaolineSurkhi

FLY ASH

Fly ash is finely divided residue resulting from the combustion of powdereed coal and transported by the flue gases and collected by electrostatic precipitator .Fly ash is the most widely used pozzolanic material all over the world.In the real world of modern concrete,fly ash is as essential ingredient of the mixture as are portland cement,aggregate,water and chemical admixtures.

In most concretes,fly ash is used in large amounts (by volume) than portland cement,and therefore it is not an admixture i.e, an addition to the mixture.Concrete without fly ash and chemical admixtures should only found in museum showcases.Fly ash was first used in large scale in the construction of Hungry Horse Dam in America in the year 1948 in the approximate amount of 30 percent by weight of cement.In India,fly ash was used in Rihand Dam construction replacing cement upto about 15 percent by weight of cement.

In recent time,the importance and use of fly ash in concrete has grown so much that it has almost become a common ingredient in concrete,particularly for making high strength and high performance concrete.Extensive research has been done all over the world on the benefits that could be accrued in the utilisation of fly ash as a supplementary cementitious material.High volume fly ash concrete is a subject of current interest all over the world.The use of fly ash as concrete admixture not only extends technical advantages to the properties of concrete but also contributes to the environmental pollution control.

Cement is the backbone for global infrastructural development.Production of every tone of cement emits carbon dioxide.Expressing it in another way,it can be said that 7% of the worlds carbon dioxide emission is attributed by portland cement industry as per research done.One of the practical solutions to economise cement is to replace cement with supplementary cementitious materials like fly ash.In India,the total production of fly ash is more than 100 million tons.But our utilisation of fly ash is only about 20% of production.Therefore,the use of fly ash must be popularised for more than one reason.

In india, fly ash was used for the first time in constructoin of Rihand Irrigation Project(fig. below), UP in 1962,replacing cement up to about 15%.

FLY ash images

TYPES OF FLY ASHClass F Fly ash normally produced by burning anthracite or bituminous coal, usually has less than 5% CaO. Class F fly ash has pozzolanic properties only. Class C Fly ash normally produced by burning lignite or sub-bituminous coal. Some class C fly ash may have CaO content in excess of 10%.In addition to pozzalanic properties,class C fly ash also possess cementations properties.

Effect of fly ash on properties of fresh concreteConcrete using fly ash is generally reported to show reduced segregation and bleeding and to be more satisfactory than plain concrete when placed by pumping.

Effect on Heat of Hydration

Replacement of cement by fly ash results in a reduction in the temperature rise in fresh Concrete. This is particular important in mass concrete where cooling,following large temperature rise, can lead to cracking.

Effects of Fly Ash on Hardened Concrete Contributes to the strength of concrete due to its pozzolanic reactivity.Continued pozzolanic reactivity concrete develops greater strength at later age not at initial stage.Contributes to making the texture of concrete dense, resulting in decrease of water permeability and gas permeability.

DURABILITY OF CONCRETE

Concrete containing good quality fly ash shows dense structure which offers high resistivity to the infiltration of deleterious substances. A point for consideration is that the pozzolanic reactivity reduces the calcium hydroxide content, which results in reduction of passivity to the steel reinforcement and at the same time the additional secondary cementitious material formed makes the structure dense, and there by gives more resistance to the corrosion of reinforcement.

It is also recognized that the addition of fly ash contributes to the reduction of the expansion due to alkali-aggregate reaction. In conclusion it may be said that although fly ash is an industrial waste, its use in concrete significantly improve the long term strength and durability and reduce heat of hydration. In other words good fly ash will be an indispensable mineral admixture for high performance Concrete.

USED ATMany high-rise buldingsIndustrial structuresWater front structuresConcrete roadsRoller compacted concrete dams.

MY CONTRIBUTIONMATERIAL:Cement:Ordinary Portland Type-1 cement was used.Fine Aggregate:Manufactured sand.Coarse Aggregate:Lime stone crushed stones of size 12.5mm and 20mm.

REVIEWMineral admixture fly ash was used.M20 grade was used (1:1.5:3).The water cement ratio as 0.55

Fly ash content (%)Fly ash(kg)Cement (kg)Sand(kg)Aggeragate(kg)007.5511.2522.5302.255.2511.2522.5

Table-1:Material Mixing Proportions

Fly Ash Content (%)w/c ratioslump value (mm)compressive strength (Mpa) after 14 days00.555019.21300.556018.95

Table-2: TEST RESULTS

CONCLUSIONCompresive strength of concrete cube of size(150x150x150mm) with zero percent flyash at w/c ratio 0.55 is 19.21 Mpa.Compressive strength of concrete cube of same size and same w/c ratio as mentioned above with 30% of fly ash by weight of cement is 18.95 Mpa.

REFERENCES1.Concrete technology(theory and practice)-MS Shetty 2.P. Chindaprasirt, T. Chareerat, and V. Sirivivatnanon, Workability and strength of coarse high calcium fly ash geopolymer,Cem. Concrete.3.Alaa M Rashad, A brief on high volume fly ash as cement replacement.4.Vanita Aggarwal,S.N.Gupta and S.N.Sachdeva(HIGH VOLUME FLY ASH CONCRETE)5.http://flyash.com