DEPARTMENT OT' CryIL ENGINEERING

. Fineness
"r o,
reducing friction between aggregates.
Unit - 3 Proportioning Of Concrete Mix IIax. Nominal size of aggregates:
Mix Design: o In general, larger the maximum size of
o It is defined as the appropriate selection and aggregate, smaller is the cement requirement for
proportioning of constituents to produce a a particular water-cement ratio, because the
concrete with pre - defined characteristics in the workability of concrete increases with increase
fresh and hardened states. in maximum size of the aggregate.
c This mixes are designed in order to achieve a c However, the compressive strength tends to
defined workability, strength and durability. increase with the decrease in size of aggregate.
f,'actors to be considered for proportioning of NIini. Cement content:
materials: . The cement content itself would not have a
o Structuralrequirement. direct role on the strength of concrete; if cement
o Environmental conditions. content is required to increase the workability of
o Site coriditions, especially the methods of concrete mix for a given water-cement ratio,
concrete- then the compressive strength may increase with
l) Production the richness of the mix.
ii) Transport o Sufficient volume of cement paste to overhll the
iii) Placement voids in the compacted aggregates.
iv) Compaction o Concrete mixes having high cement content may
v) Finishing give rise to shrinkage, cracking and creep of
o Avarllable of raw materials concrete also increases with the cement paste
Principles of concrete mix design: content.
Estinding the required batch weights for the NIax. \Y/C ratio:
concrete invotves a sequence oflogical straight forward The water-cement ratio is the ratio of the
steps wh&hsed on a series of rial mixes, computer weight of water to the weight of cement used in a
simulations, sormd nrle of thumb advice or combination concrete mix and has an important influence on the
of all thre- quality of concrete produced.
The following data are required for mix
proportioniry of concrete : . A lower water-cement ratio leads to higher
r Gra&designation strength and durability, but may make the mix
. T}?eofcement more difficult to place.
o Max. nominal size of aggregates . Placement difficulties can be resolved by using
o Mini. Cement content plasticizers or super-plasticizers.
. Man.WC ratio.
. Wortability
. Maximum 0.50 water-to-cement ratio (l:2)
o Exposureconditions.
when concrete is exposed to freezing and

. TlTeof aggregates.
thawing in a moist condition or to de-icing
. Type of admixture used.
chemicals, and a maximum 0.45 water to
o Method of transporting and placing. cement ratio for concrete in severe or very

Gnade designation: severe sulphate conditions.

o It gives characteristics compressive sffength
Properties of concrete related to mix design:
requirements of the concrete.
o The following' characteristics are the most
lt'smajor factor influencing mix design.
important properties of concrete:
Type of cement:
r . Workability
Chofoe of cement depends upon the o Durability
rsquiremerts at hand.
o For very high compressive strength of port land
r Strength

ceineatgrades 43 and 53 used.

. Volume change
. When early strength rap.ld hardening cement is
o Air entrainment
used-
. Density
 or&aUruty: factors that contibute to density for all types ofconcrete
The workability of the concrete for satisfactory are:
placing and compaction is controlled by: . Use of well - graded aggregate of the largest
o Size and shape of the section possible maximum size.
o Quantity and spacing of reinforcement. . Minimum water content consistent with good
. Method of employed for transporting and workability.
placing and compacting. o Minimum air content consistent with adequate
Durability: durability.
. Durability of concrete is the resistance to . Thorough consolidation during placement
deteriorating influences which may reside Physical properties of materials required for mix
inside the concrete itself, or to the design:
aggressive environments. o Cement
o Durability is achieved by restricting the r Stength/grade of cement
minimum water cement content and the . Initial and final setting time of cement
ma:<imum water cement ratio and the type o Fineaggregate
of cement. . Graduation of fine aggregrte
Strength: r Specific gravity if fine aggregate
o It is one of the most important properties of o Coarseaggregate
concrete and influences many other describable . Sizeofcoaxseaggregate
properties of the hardened concrete. r &ading of coarse aggregate
. The mean compressive sftength required at a . Sh4eof ooarse aggreg;ate
specific age, usually 28 days, determines the . Strength ofooarse aggrefgate
nominal water-cement ratio of the mix. o AggFegate absorption
. The other factor affecting the strength of o Water
concrete at a given age and cured at a prescribed NOMINAL MD( AI$D DESIGN MIX:
temperature is the degree of compaction. Mix design is a process of selecting suitable
Volume change: ingredients and determining their relative proportions
. Volume change is the most detrimental with the objective of producing concrete having certain
of concrete, which affect the long -
properties minimum workability, strength and durability as
term strength and durability. economically as possible.
. The aspect of volume change in concrete is A mix design can be designed in trvo ways as
important form the point of view that it cause's explainedbelow:
unsightly cracks in concrete. o
NominalMix
. The effect of volume change due to thermal .
DesignMix
properties of aggregate and concrete, due to Nominal Mix:
alkali/aggregate reaction, due to sulphate action. o It is used for relatively unimportant and simpler
. This type of volume change in concrete is called concrete works.
shrinkage. . In this type of mix, all the ingredients are
Air entrainment: prescribed and their proportions are specified.
. Air entrained concrete is made by mixing a o Therefore there is no scope for any deviation by
small quantity of air entraining agent or by using
the designer.
air entraining cement. o Nominal mix concrete may be used for concrete
. This air entraining agent incorporate millions of ofM20 or lower.
non-coalescing air bubbles, which will act as
Design Mix:
flexible ball bearings and will modify the o It is performance based mix where choice of
properties of plastic concrete regarding
ingredients and proportioning are left to the
workability, segregation, bleeding and finishing
designer to be decided.
quality of concrete.
o Jt is . The user has to specify only the requirements of
modifies the properties of hardened
concrete in fresh as well as hardened state.
concrete.
. The requirement in fresh concrete are
Densitv:
The value of density was addressed indirectly in
workability and finishing characteristics,
rrherecc in hqrrlcne.l annnreta tl.-ca aro mqi-I.,
 luences the concrete mix design: Maximum water content per m' of concrete for
o WC ratio nominal maximum size of aggregate
o Cement content Nominal maximum size Maximum water content
o Relative proportion of fine and coarse aggregate of assresate (mm) (ke) per m3
o Use of admixture
l0 208
20 186
Objective of mix design:
40 165
o The basic objective of concrete mix design is to
find the most economical proportions. Step 3: Selection ofn'ater and sand content:
o To achieve the desired and result strength, For the desire workability, the quantity of
cohesion, workability, and durability. mixing water per unit volume of concrete and the ratio
Factor affecting the properties of concrete: of frne aggregate to total aggregate by absolute volume
o The qualrty and quantity of cement water and are to be estimated from below table
aggregates Clatg is Cn{*ioa Adjrdr,eet Rcqailul in
I Rf Tal,b 6)
o Batching -------*
WrterContcnt Pcrccttagc
Pcneot SrndinTotrl
o Transporting Aggtcgat.
o placing Fot dccrcar in wrtcr-..Eqnt tado 0 -2'0
by (0'60- 0'$ ) thrt L 0l
. Compacting Fol lncrcgc la complcdog frcror +r 0

o ( 0'9
- 0'8 ) tbet L 0'10
Curing For rmd conforrniag to Zooc III of 0 -15
Basic steps in mix design: Teblc { of IS: 383-1970
Totlt *9prctat -3'5
a Find the target mean strength. .t
ltcreforq rcquircd lad cootcot Pclccntagc of total aggrcg*e by
a Determine the curve of cement based on its abrrolutc roluoc - 35 - l't - 3l'5 pctccnt

strength. Rcquircd ratcr @itcot - 1S6 + lT# = 186 + 5'58 - 19l'6 llot
a Dete,rrrine water cement ratio. Step 4: Selection of Cement content:
a Determine cement content. Water
o Determine of fine aggregate proportions. Cement:
r Determine of coarse ag$egate proportions. Water ce,ment ratio
. Mix proportions Step 4: Iletermination of fine and coarse aggregate
BIS METHODS OT'MIX DESIGN: content:
The proportioning is carried out to achieve
specified characteristics at specified age, workability of
,:[,*t -i.*] x afo,una

fresh concrete and durability requirements. This standard r=[n,+$++. J;]- *r-
is applicable for ordinary and standard concrete grades wherc

only. f = abolutc volumc o[ frah oncrctc, nhich b cqual to gros

volumc ( Bt ) rniilr the volumc ofcntrappcd rirr'
Step by step procedure:
l/ = ma$ ofwatcr ( tg ) pcr m! of coacrctc,
Step 1: Target mean strength for mix design: C = rus of emcnt ( lg ) pcr dof con*cte,
fe,: fck+ 1.65 ^S
Jo = lpccifc grrvitY of ccmeot,
Where, l = ratio of 6nc eggrcgatc to toal lggrcgatc by absolutc
f.1 :
votuoe,
target mean compressive strength
irrr - total qasgolBnc rggregaic ald corrcc aggrcgatc ( Lg )
at 28 days in N/mm2. per m! ofcoucrcte rerpcctivrly, aod
f"r, : characteristic compressive strength S6, ,$s1 o spccifc gravitio ofsaturatcd lnfaec dry 6oe aggrcgatc and
coarc aggrcgatc rapctivcly,
at 28 days in N/mm2
S : standard deviation N/mm2
Step 5: Mix proportion:
Step 2: Selection of water cement ratio:

i:S
& rsc
WC ratio Cement
Fine
aggregate
Coarse
agqreqate

&