making of concrete

8/4/2019 Making of Concrete

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Cement



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The cement used in this study is 53 Grade, Ordinary Portland cement. Theraw materials used for the manufacturing of Portland cement consistmainly of lime, silica, alumina and iron oxide. Four compounds areregarded as the major constituents of cement. They are Tricalcium Silicate

(CзS), Dicalcium Silicate (C2S), Tricalcium Acuminate (CзA), and TetraCalcium Aluminate Ferrate (C4AF). The silicates (CзS and C2S) are theimportant compounds which are responsible for the strength of hydratedcement paste. The presence of CзA is undesirable.However, CзA is beneficial in the manufacture of cement that facilitates

the combination of lime and silica. C4AF is also present in smallquantities. It reacts with gypsum to form Calcium Sulphoferrite and its

presence may accelerate the hydration of silicates.When water is added, the silicates and aluminates of Portland cementform products of hydrates, which in turns produce firm and hard mass.

The amount of CзA in most cement is comparatively small.



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For manufacture of thecube ,the design used is M60.The following are thematerials used for the

design .

CementAggregateFine aggregateWaterPlasticizerFly ash



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Specifications of the cube

• Size of the cubes: 150x150x150mm• Materials to be used: Cement, Fine Aggregate, Coarse Aggregate• Admixture: micro air-720

• curing period: Curing period of 7 days• Number of samples made : 2• Symbol imprinted on the cubes: H10

DESIGN STIPULATION:-

Target strength = 60MpaMax size of aggregate used = 12.5 mmSpecific gravity of cement = 3.15Specific gravity of fine aggregate (F.A) = 2.6

Specific gravity of Coarse aggregate (C.A) = 2.64Dry Rodded Bulk Density of fine aggregate = 1726 Kg/m3Dry Rodded Bulk Density of coarse aggregate = 1638 Kg/m3



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Water



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Water is an important ingredient of concrete as itactively participates in the chemical reaction withcement. Since it helps to form the strength givingcement gel, the quantity and quality of water isrequired to be looked very carefully. Theexcessive may affect not only the strength but

also setting time. As a rule, water unsuitable for drinking may not necessarily be unfit for mixingconcrete. Seawater which contains about

35,000ppm dissolved salts is not harmful to thestrength.



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Plasticizer



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Micro Air-720MICRO-AIR 720 is an air-entraining

admixture which creates ultra stableair bubbles that are strong, smalland closely spaced; and alsoresults in reducing segregation andbleeding.



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Typical properties of Micro Air-720

Color : Pink free flowing liquid



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Direction for use of MICRO-AIR 720MICRO-AIR 720 is a ready-to-use liquid which is dispensed into the concrete together with the mixing water. Theplasticizing effect and water reduction are higher if the admixture is added to the damp concrete after 50 to 70% of the mixing water has been added. The addition of MICRO-AIR 720 to dry aggregate or cement is not recommended.

DosageOptimum dosage of MICRO-AIR 720 should be determined in trial mixes. As a guide, a dosage range of 1% to 2% byweight of binder is recommended.

Usage GuideIt should be stirred well before use and introduce along with gauging water at the last to the mixer for best result,always use measured quantities.

Storage and Shelf lifeMICRO-AIR 720 must be stored where temperatures do not drop below +5°C. If product has frozen, thaw at +5°C orabove and completely reconstitute using mild mechanical agitation. Shelf life is at least 12 months when stored asabove.



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Advantages Improved ability to entrain and retain air in concrete•Improved air-void system in harden concrete•Reduced permeability - increased water tightness.•Improved plasticity and workability.•Reduced segregation and bleeding.



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Flyash



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Fly ash is a powdery substance obtained from thedust collectors in the electrical power plants thatuse coal as fuel. From the cement point of view

the mineralogy of fly ash is important. It startsout as impurities in coal- mostly clays, shale,limestone & dolomite. They cannot be burned sothey turn up as ash. The fly ash mixtures reached

similar to higher long term compressivestrengths, due to the pozzolanic properties of thefly ash and the lower w/c ratios. The setting timesfor the fly ash mixtures were approximately two

hours longer. The fly ash mixtures comparablecosts, increased compressive strengths, andenhanced durability properties.



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Components % Composition

Silicon Dioxide 49.82

Aluminum Oxide 19.24

Iron Oxide 19.09

Calcium Oxide 4.94

Magnesium Oxide 0.97

Sulfur Trioxide 1.15

Sodium Oxide 0.64

Loss of Ignition 0.56

Chemical composition of Flyash

E i i P i f Fl h



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Engineering Properties of Fly ashFineness: Fineness is the primary physical Characteristic of fly ash that relates to pozzolanicactivity. As the fineness increases, the pozzolanic activity can be expected to increase. Pozzolanic Activity: Pozzolanic Activity refers to the ability of the silica and aluminacomponents of fly ash to react with available calcium or magnesium from the hydration products of Portland cement.

Loss of ignition: Fly ashes must have a low enough loss of ignition to satisfy ready mix concrete producers, who are concerned about product quality and the control of Air Entraining Admixtures.Workability: At a given water content ratio, the spherical shape of fly ash particles greater workability than with conventional concrete mixes. When fly ash is used, the absolute volume of fly ash usually exceeds that of cement in conventional concrete mixes. The increased ratio of solidsvolume to water volume produces a paste with improved plasticity and more cohesiveness.

Time of Setting: When replacing up to 25 percent of the Portland cement inconcrete, all fly ashes and most fly ashes increase the time of setting.However, some fly ashes may have little effect on, or possibly even thedecrease, time of setting. Delays in setting time will probably be morepronounced, compared with conventional concrete mixes, during the cooleror colder months.



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Fine Aggregate

ll A il bl i d i d i h i l d



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Locally Available river sand is used in the experimental study.Sand is generally considered to have a lower size limit of about1.18mm or a little less. The process of dividing a sample of aggregate into fraction of particle size is known as sieveanalysis and its purposes are to determine the grading or sizedistribution.



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Compressive strength of

concrete

The strength of the material is defined as the ability to resist stresses



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The strength of the material is defined as the ability to resist stresseswithout failure. The compressive strength of the material is theresistance offered by the material against the compressive force.Compressive strength is the measure of ability of cement concretespecimens to withstand the compressive load. This test is final check

on the compressive strength becomes the important strength criteriato analyze the concrete.

To determine the compressive strength of various types of concrete,test specimen of 100mm x 100mm x 100mm size were cast andstored in room temperature. After 24 hours the specimens are

demoulded and cured in the water tanks. At the end of curing periodthe cubes are taken out of the tanks and the cubes are Air dried andtests are carried out at 7th day & 28th day.

The compressive strength is calculated from the formulae give below

Load (N)

Compressive Strength = ___________________ Area of cube (mm²)



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making of concrete

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