presentation of prc 2

8/8/2019 Presentation of Prc 2

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Presented by: Zeeshan Manzoor


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The British method of concrete mix design,popularly referred to as the "DOE method", isused in the United Kingdom and other parts of

the world and has a long established record. Themethod originates from the "Road Note No 4,which was published in Great Britain in 1950. In1975 the note was replaced by the "Design of

Normal Concrete Mixes", published by theBritish Department of the Environment (DOE).In 1988 the "Design of Normal Concrete Mixes"was issued in a revised and updated edition toallow for changes in various British Standards.


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The procedures used by Firstmix are based onthe long established British DOE Method ofconcrete mix design. The method was developed

for use with cements and aggregates, whichconform to the relevant British Standards.However since these Standards lay downrequirements which materials must meet in

order to be suitable for good quality concrete,the procedures of the DOE Method can beapplied to concrete mix design generally, subjectto Firstmix Limitations.


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The DOE method utilizes British test data

obtained at the , and the British Cement

Association. The aggregates used in the testsconformed to BS 882 and the cements to BS

12 or BS 4027 .


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Mixes are specified by the weights of the different

materials contained in a given volume of fullycompacted concrete.

It is assumed that the volume of freshly mixedconcrete equals the sum of the air content and of

the absolute volumes of its constituent materials.The method therefore requires that the absolutedensitiesof the materials be known in order thattheir absolute volumes may be calculated.


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It is assumed that the strength of a concrete mixdepends on:

The Free water/Cement Ratio;

The Coarse Aggregate Type; The Cement Properties


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On the basis of tests the DOE Method provides aTable and a Figure from which one can estimate thefree water/cement ratio, which will provide a given

strength for concrete made from given coarseaggregate and cement types.

It is assumed that the workability of a concrete mixdepends primarily on:

The Free Water Content; The Fine Aggregate Type and, to a lesser degree,

the Coarse Aggregate Type;

The Maximum Size of Coarse Aggregate.


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It is assumed that the workability of a concrete mixdepends secondarily on:

The Percentage of the Fine Aggregate as a proportion ofthe total aggregate content.

The Grading of the Fine Aggregate.

The Free water/Cement Ratio;


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The object of concrete mix design is to find

the proportions in which the concrete

materials - cement, water, fine aggregate andcoarse aggregate - should be combined in

order to provide the specified strength,workability and durability and possibly meet

other requirements, as listed in standardssuch as the British BS 5328.


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Mix Design Stages The mix design is carried out according to the DOE Method in the

following five stages. Stage (I). Determine Free Water/Cement Ratio Required for

Strength Either use a specified margin or calculate a margin for a

given proportion of defectives and statistical standard deviation. Obtain the target mean strength by adding the margin to the

required characteristic strength. Ifair entrainment is specified, calculate an artificially

raised modified target mean strength. Either accept a specified free water/cement ratio or obtain themaximum free water/cement ratio which will provide the targetmean strength for concrete made from the given coarseaggregate type and from cement with the given properties.


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Stage (II). Determine Free Water Content Requiredfor Workability

Either use a specified free water content or obtain the

minimum free water content, which will provide thedesired workability for concrete made with thegiven fine aggregate type, coarse aggregatetypeand maximum size of coarse aggregate.

If the free water content has been determined forworkability, adjust the required free water contentifair entrainment is specified, and adjust further ifa water-reducing admixture is specified.


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Stage (III). Determine Required Cement Content Obtain the minimum cement content, which is required for

strength, by dividing the free water content obtained in Stage (II)by the free water/cement ratio obtained in Stage (I).

Check the minimum cement content, which is required forstrength, against the maximum cement content, which ispermitted, and give a warning if the former exceeds the latter.

Check the minimum cement content, which is required forstrength, against the minimum cement content, which isallowable for durability, and adopt whichever is greater to be the

cement content in the mix. Divide the free water content by the cement content used in themix to obtain a modified free water/cement ratio.


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Stage (IV). Determine Total Aggregate

Content

Obtain a value for the overall aggregate density. Obtain the fractional volume of the aggregate

by subtracting the proportional volumes of the

free water and the cement from a unit volume.

Calculate the total aggregate content bydividing the volume of the aggregate by the

aggregate density.


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Stage (V). Determine Fine Aggregate Content Either use a specified value of the percentage of

fine aggregate, or obtain the percentage of fine

aggregate, which will provide thedesired workability for concrete made with thegiven grading of fine aggregate, maximum sizeof coarse aggregate and the free water/cementratio obtained in Stage (III).

Calculate the fine and coarse aggregatecontents from the total aggregate contentobtained in Stage (IV) and the percentage of fineaggregate.


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