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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