British Method of Mix Proportioning_g2

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BRITISH METHOD OF MIX

PROPORTIONING

Presented byGroup 2

Yogesh Kumar Kumawat

Suman Meena

Shereena O A

Presented on

26thAugust 2011

Modified on

09thSeptember 2011


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Introduction

Current method is that revised by Dept. of

environment (UK) in 1988

Recognizes the durability requirements of mix

selection

Applicable to normal weight concrete made

with Portland Cement only or Blast furnace

slag/fly ash


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The Method Consists of Five steps


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Step 1Determination of free w/c ratio in relation tocompressive strength

Target Mean Strength = Characteristic

Strength + Margin

Margin = k * s

where k A value appropriate to the defect

percentage permitted below the characteristicstrength. [ k = 1.64 for 5 % defect ]

s The standard deviation


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From table 1, find the appropriate value of

strength say f1(at a water-cement ratio of 0.5)

corresponding to

a) type of cement

b)type of aggregate

c)age


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Table 1approx. comp. strengths at free w/c ratio =0.5


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Fig.1 Relation between

compressive strength and

free water cement ratio

mark a point corresponding tostrength f1, at water cement ratio

0.5.

draw a curve parallel to the

nearest curve, through this point

Using the new curve,

Read off ( abscissa) the watercement ratio

corresponding to the target mean

strength (ordinate)

Free water-cement ratio


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Step 2

Determination of water content


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Table 2. Approximate Free

water contents required to

give various levels of

workability

Quantity of water contentdepends on

workability

Maximum size of aggregate

Type of aggregate (crushed

/Uncrushed)


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Step 3

Determination of Cement content

Cement content =

Arrived water content(step 2)arrived free water cement ratio(step1)


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Step 4

Determination of Total Aggregate

content


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Fig.2 Estimated wet

density of fully compacted

concrete

read off Fresh density from fig 2

Total Aggregate content = Fresh

densitywater contentcement

content


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Step 5

Fine and Coarse Aggregate Content


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Proportion of Fine aggregate in total aggregate

Governing factors

Max. size of aggregate

The level of workability

The w/c ratio

The percentage of fine aggregate passing 600micron

sieve

Read off from fig. 3,

Corresponding to the above factors


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Fine aggregate content = total aggregate

content x proportion of fine aggregate

Coarse aggregate content = Total aggregate

contentfine aggregate content


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Based on the above calculations, trial mixes

are made


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Limitations

This method is based on the characteristics of

the materials available in UK.

Hence it may not be applicable to other parts

of the world


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British Method of Mix Proportioning_g2

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