IRC: 59.

1976

TENTATIVE GUIDELINES
FOR
DESIGN OF GAP GRADED
CEMENT CONCRETE MIXES
FOR ROAD PAVEMENTS

THE INDIAN ROADS CONGRESS

<<
 IRC: 59-1976 “Tentative Guidelines for the Design of Gap Graded Cement Concrete
Mlxe~for Road Pavements”

Reference Existing Version Revised Version

!RC : 59-1976
Page 3, Table I Max. size Single size Max~size of Max. size Single size Max. Size of
of aggre- coarse compatible of aggregate coarse aggregate compatible
gate (mm) aggregate fine aggregate (mm) (mm) finer
(mm) — - aggregate
Small size
coarse aggre-
gate (mm)

63 63-50 20 10
- 63 63-53 22.4-11-2
10 -4.75 11.2-5.6
50 50-40 10 -4.75 53 53-45 11.2-5.6
40 40-20 45 45-22.4
20 20-10 22.4 22.4-11.2

Page 9-Fig. 2
—————40 mm Crushed Stone ————45 mm Crushed Stone
——-—-—40 mm Natural Gravel 45 mm Natural Gravel

Page 11, Table 4 Size of aggregate Bulk density kg/rn3 Size of aggregate Bulk density kg/rn3
coarse aggregate coarse aggregate
63-50 mm 63-53 mm
50-40 mm 53-45 mm
40-20 mm 45-22.4 mm
20-10mm 1520 22.4-i 1.2 1560
10-4 75 mm — 1520 11.2-5.6 mm 1540

<<
 • I _••__ ..• ••_ — — •_.~.. ~ — . .- •.

Eziating weraiou Revised version

line aggregate Fine aggregate

Coarse sand 14’O Coarse sand 1460
(Zone I & II) (Zone 1 & 11)
Page 13, Table 5 Max. size 10 20 40 50 Maa. size of Il 2 22.4 45 53
of aggregate aggregate (mm)
(mm)
P~gr15, Appendix
(A) Design Max. size of 40 mm Max. size of 45 nun
Stipulations aggregate (Single size aggregate (singe size
(~i) rounded rrunded aggregate)
aggreRate)
39.0 x0.89 K .460 . -
Ws —~-~———— =514 ~ Kg
Page 16, (0) 396x0.89x1450
(ui’( 3rd line 100 511 Kg.
Since na—(l—-1460,’li)00X2.65)X 100—44.9 per
(iv) 2nd line Since n,”(l—!450/l000) x 2.65) cent
x 100—45.3 per cent 1000 K 3.15 39.6x44,9 xO,89’
1+05x3.l5 0 0 + I0000)
3rd line w = 000 x 3.15

10 4’ ~‘~:42s
45.3 X 0.89)
L 10000 315.9 Kg
= 317.7 Kg
—0.5x3t5.9 — 57kg
(v) 2nd line =1,05 X 317.7 158.85 kg Mix proportions
‘lvi) Mix proportions Coarse Water Cement Fine Coarse
Water1) (Kg/rn’)
Cement Aggregate
Fine Aggregate (Kg/rn~) 1Kg/rn5) Aggregate Aggregate
(Kg/rn (Kg/rn2) (Kg/rn’) (Kg/m5) (Kg/rn’)
158.85 317.7 511.0 1424.0 ‘ ‘157.95 315.9 514.5 1424 0
or 0.5 1 1.608 448, ‘ 0.5 1 t 1.629 4.508

Existing versIon Revised versJo~

(i) For cement.t50 kg, net quantities Ci) For cement —50 kg, net quantities of
of materiaja are fine aggregate= materials are fine aggregate 8 1,45 kg
80.40kg, coarse aggregate = 224.0 kg coarse aggregate==7 225.4 kg and water
and water 25 0 kg~25.Olitre. 25.0 kg -“25.0 litre.
(i) Extra water to be added to cater for (ii) Extra water to be added to cater for
absorption by coarse aggregate~= absorption by coarse aggregate=n5 4x
224x0.4/lOo — 0.896 kg — 0.896 0.4/100=0.901 kg—0,90t litre water to be
litre,, Water to be deducted for free deducted for free moisture present in fine
moisture present in fine aggregate= aggregate=81,45~2/
80.40 x 2/100—1.608 kg— 1.608 litre, 1~iJ,~,1629kg— 1.629
Actual quantity of water to be litre. Actual quantity of water to be added
added is therefore is therefore=25,00 +0.901 —1.629 =24,272
25.000+0.896—l,6cjg “24 288 litre.
— litre.
liii) Actual quantity of fine aggregate
required 80.400+1,60882 008 kg.
(iii) Actual quantity of fine aggregate requir-
(iv) Actual quantity of coarse aggregate ed—8I,45+l 629—83 079
required 224.000—0,g963 104 kg.
(iv) Actual quantity of coarse aggregate requir-
Therefore, the actual quantities of the ed~—225.4-0.901—224.499 kg.
different constituents per bag of
cement are Therefore, the actual quantities of diffe-
rent constituents per bag of centent are
Cement—So kg Sand’—82.oog kg
Water=24.288 C~oarseaggr,— ~~Censent~5okg Sand=83079 kg
<< litre 223.104 kg.
Water—24.272 litre Coarse Aggregate
‘224.499 kg.
 IRC: 59-1976

TENTATIVE GUIDELINES
FOR
DESIGN OF GAP GRADED
CEMENT CONCRETE MIXES
FOR ROAD PAVEMENTS

Published by
THE INDIAN ROADS CONGRESS
Jamnagar House, Shahjahan Road
New Delhi-i10011
1976
Price Rs t$4 24
(plus Packing & Postage)
<<
IRC 59~l976

First published : Mi’trch I 976

( Rig/t is of’ Publication and of Translation arc reserved)

Printed nt Printnid, New Delhi- 110024

<<
 IRC: 59-1976

TENTATIVE GUIDELINES FOR DESiGN OF

GAP GRADED CEMENT CONCRETE MIXES
FOR ROAD PAVEMENTS

1. INTRODUCTION
These guidelines were approved by the Cement Concrete
Road Surfacing Committee (Personnel given below) in their meeting
held at Chandigarh on the 1st March, 1975.
K.K. Nambiar —C2mvenor
Dr. R .K. Gh ash —-itfember-Secretary

Aiembers
D.C. Chaturvedi K.C. Mital
Dr. M.P. Dhir NI. Patel
Brig. Gobindar Singh P.S. Sandhawalia
C.L.N. Iyengar AR. Satyanarayana Rao
P.J. Jagus S.B.P. Sinlia
M.D. Kale N. Sivaguru
Brig. R.K. Kalra Dr. ftC. Visvesvaraya
Dr. S.K. Khanna Director Genera I (Road
Deve Iopm ent)—ex—offido
CS. Padmanabhan (Co-opted)
These were processed by the Specifications & Standards Com-
mittee in their meeting held on the 12th and 13th December, 1975
and approved by the Executive Committee and the Council in their
meetings held on the 22nd December, 1975 and 3rd January, 1976
respectively.
1.2. General
1,2.1. A significant criterion in designing cement concrete
mixes is to ensure that the voids in the compacted coarse aggregate
get tilled with compacted fine aggregate and the resid ual voids in
the total compacted aggregate structure with the cement paste of a
given water-cement ratio to meet the strength requirement, Depen-
ding on the workability needed for a particular construction, it will
be necessary to increase the amount of’ cement paste appropriately
over that required to fill the residual voids, One way of achieving
this desideratum is through gap—grading of aggregates with permissi-
ble maximum size of coarse aggregate followed by admissible
maximum size of finer coarse aggregate or fine aggregate, as the
case may be, The relationship between the permissible and

I
<<
IRC: 59-1976

admissible sizes constitutes the basis for compatible gradation

required in the design of gap-graded concrete mixes.
1.2,2. The principle of gap-gradation of aggregates is that the
voids in the larger aggregate particles are big enough to adniit
particles of the selected lower size withottt causing any interference
to the larger particles or dilation thereof. The flow of concrete
results from easy admittance of the finer fractions into the voids of
coarser fractions, This may be explained as follows:
Assuming the maximum size of single-size coarse aggregates as
I), the largest voids in the packing thereof will be able to accorn Ito-
date smaller aggregates of size 0.414 D, which in turn will accom-
modate still smaller aggregates of size 0.225 D, all aggregates
idealised as spheres. The residual voids can be geometrically filled
with further smaller aggregates of size 0.155 D. This theoretical geo-
metrical model can go on down to the extreme fines. Such, arrange-
ment is, however, possible only through very careful hand-packing,
and in practice, the aggregates of sizes 0.414 D and 0.225 D cannot
easily enter the side interstices after the single-size coarse aggregates
of size D have been closely packed. Aggregates of size 0.155 D
and lower alone can possibly slip into such side interstices without
difficulty. Forcing any intermediate size of aggregate smaller than
I) but greater than 0.155 D with the aid of vibration, may result in
wedging out the coarse aggregates of size D from~~contacting each
other and thereby requiring considerably more quantity of mortar
and hence more cement and water for any stipulated water-cement
ratio, Properly designed gape-graded concrete mixes are, therefore,
likely to require less quantity of cement for the same water-cement
ratio and workability,
1.2.3. In general, if the requirements of gap-graded concrete
are to be satisfactorily met from the practical point, it is necessary
to eliminate from the continuous grading range, aggregates of at
least two and at best three successive sizes, depending upon the
shape, size and type of the coarse aggregates used. The suggested
ranges of single-size coarse aggregates and aggregates of selected
lower size for different maximum sizes of aggregates with a view to
achieving compatible gradation as envisaged in gap-gradation are
given in Table I.
1.2.4. IRC: 15-1970 “Standard Specifications and Code of
Practice for Construction of Concrete Roads” stipulates collection
of coarse aggregates for paving concrete in.different sizes. These
are then combined in suitable proportions to obtain the stipulated
continuous grading. In India, by and large, such continuous grad-
ings are not produced from crushing operations. The elimination of
a particular size front the grading range of coarse aggregate to

2
<<
 IRC: 59-1976
TABLE I SUGGESTED Cor%sPATmLE GRADATION OF COARSE AND FINER
AGGREGATES FOR THE PURPOSE OF GAP-GRADING

Max. size Single size Number Max. size of compatible

of aggre~ coarse of gaps finer aggregate
gate aggregate
(mm) (mm) ~‘“

Small size coarse aggregate Sand zonesS

(mm) (IS: 383-1970)

63 63-50 2 20-10 It or lit

3 10.4.75 Itt or 1V

50 50-40 2 10-4.75 ill or IV

3 — brIE

40 40-20 2 — brIE

3 — ttorilt

20 20-10 11 or Hi

3 iii or IV

* Foot Note : Fineness modulus of sand Zone i-4.00 to 2.71

Zone 11-3.35 to 2.11
Zone 111-2.75 to 1.71
Zone IV-2.25 to 1.35

obtain gap-grading should, therefore, pose no problem. Since finer

fractions of coarse aggregates are costlier than their coarser counter-
parts, such elimination may turn out to be cheaper from the point
of material costs also. Where, however, the all-in aggregates from
the crushers provide the stipulated continuous grading, purposely
eliminating a fraction therefrom by sieving to produce gap-graded
aggregate may be uneconomical. For the same reason, fine aggre-
gate should not be screened to obtain the desired fractions Ibr gap-
grading. In many parts of the country, however, fine aggregates of
different granulometry are available and those with finer granulo-
3
<<
IRC : 59-1967

metry generally cost less, It is, thereibre, imperative that before

choosing between the continuous and gap-grading, the above
aspects should be carefully considered and comparative economics
of the two types of mixes worked out.
1.2.5. For gap-graded concrete mixes, the workability is
required to be low from the point of segregation. It is desirable to
specify a. slump of 0-12 mm fhr gap-graded paving concrete mixes.
(lap-graded concrete mixes should be compacted only through
vibrato.ry effort. Manual compaction should not be permitted.

2. GUIDELINES

2.1. The following are required to be specified in the design

of a cement concrete nux:
(a) Minimum cornpressivejtlexural strength of concrete in the field at
2$ days.
(b) Maximum size of coarse aggregate to be used and its type.
(c) Degree of workability, related to the nature of construction and
compaction equipment available.
(d) Degree of quality control expected to he exercised—’very good’,
‘good’ or ~faii: and permissible co-efficient of variation or
standard deviation.
(e) Accepted tolerance level.
The stipulations in respect of the above items shall generally
conform to the requirements laid down in IRC: 15—1970,, where the
work pertains to concrete pavement. For other works, relevant
standard specification may he consulted.

2.2. Tests for Materials

The. materials used should conform to the relevant standard
specihcalions. For mix design, it will he ne.cessary to know the
results of’ the ibllowing tests:
(a) Cement: (it Compressive strength at 7 (lays (IS: 269—I 967**)
(ii) Specific gravity (IS: 269_l967*~
(A value of 3,15 may be assumed, if test cannot
be conducted).
(h) Aggregate:
ii) Specific gravity (IS: 2386 Part Ill—I 963@)

~ Specifications for Ordinary, Rapid Hardening and L.ow Heat

Portland Cements.
@ Methods of Test for Aggregates for Concrete — Pt. ill, Specific
Gravity, Density, Voids, Absorption and Bulk ing.

4
<<
 1RC : 59-1976
(ii) Bulk density of saturated surface-dry samples
(IS: 23$6’Part Ill l963lLt4.
(iii) Per cent water absorption (IS: 2386 Part 1963@)
(iv) Sieve analysis (iS: 2386 Part I—1963@ i’)

2.3. Aggregate Gradhig

2.3.1 As stated earlier, single-size coarse aggregate shotild he
chosen as far as possible, (Table I.) If this size is large and after
allowing for 2 or 3 gaps still a. fraction of finer coarse aggregate is
required as the next compatible size, then as per gap-grading princi-
ple a second set of 2 or 3 gaps are required to be provided between
the finer coarse aggrega.te and the fine aggregate. (sand). However,
since the second set of gaps will result in eliminating alniost~~all the
coarser fractions of fine aggrega..te and only fine to very fine sand
will he left in most cases, this may not be desirable from the point
of water demand and shrinkage. Under such circumstances., the
number of gaps in th,e second set may be reduced from 2 or 3 to I
or even 0.
2.3.2. Fine aggregate should preferably be natural sand con-
forming to iS: 383— 1 97Q*, although crushed stone sand may also he
used. in the latter case, the fine aggregate should conform to
iS: 383-1970, excepting that in Grading Zone IV, the perniissihle
percentage pas.sing, liniits on 300 -, and 150 micron siev!es should he
15-55 per cent and 0-20 per cent respectively as per I RC: I 5-i 970
in stead oi’i 5-50 per cent and 0—1 5 per cent as stipulated in IS
Specification. As far as possible, the size of the fine agg,regate
(Zone 1, H, III or 1V) shotild be as stipulated in Table 1. Where.
there is pr ‘a. tic ii dtfflc nIt ‘~ in ~L t t ing ft n c. aggregate con to tin tng to
the stipulated Zone, the. next coarser Zone might he adopted.
There is no need of sieving the fine aggregate to obtain th.e desired
Zone.
2.4. l)esign ~trength of Concrete
2.4.1. As in continuously graded concrete, so also in gap—
graded concrete the strength varies with the water-cement ratio.
Higher the water-cement ratio, lower is th..e strength of gap-graded
concrete. Studies have shown that for the same water-cen.. ent
ratio, both continuously graded and gap-graded concrete mixes yield
similar strengths for workable mixes.
Methods of Test for Aggregates for Concrete—Pt. EEl, Specific
Gravity, Density, voids, Absorption and Bulking.
0 ~u Same is U~ Pt I P irtiele Size tnd Sli ipe
* Spec ifications for Coarse and Fine Aggregates from Natural Sources
for Concrete

5
<<
IRC : 59-i976

2.4.2. In order to get the specified minimum compressive or

flexural strength in the field, the concrete mix has to be designed
for somewhat higher average compressive or fle,xural strength
depending on the degree of quality control (denoted through per-
missible co-efficient of variation or standard deviation) and the
tolerance level. The average strength (S) at 28 days for which the
mix should be designed is given by the equation:

S 1
l-t,vf 100
where, ~ = minimum compressive or fiexural strength (Kg/cm2) in
the field at 28 days,
t factor (dimensionless) depending on specified tolerance
level, and
v co-efficient of variation (per cent) specified.
2.4.3. The values oft in eqn. (1) for different tolerance level
are given in Table 2.

TA1SLE 2: VALuES OF ToLERANCE FACTOR (t)

i~oiera nce~
level
untO IinlS lin2D lin4O IinIOO

Number of
samples

10 1.37 1.65 1.81 2.23 2.76

20 1.32 1.58 1.72 2.09 2.53
30 1.31 1.54 1.70 2.04 2.46
~ (infinite) 1.28 1.50 1.64 1.96 2.33

2.4.4. The average design compressive strengths of concrete

for different combinations of specified minimum strength, tolerance
level and coefficient of variation corresponding to an infinite num-
ber of samples have been worked out and are shown in Table 3. On
smaller jobs where a finite number of samples is to be tested, the
corresponding average design strengths could be obtained by
application of appropriate tolerance factor in eqn. (1).

6
<<
 TAaLE 3: AVERAGE DESIGN STRENGTHS OF CONCRETE FOR DIFFERENT DEGREES OF
QUALITY CONTROL AND TOLERANCE LEVEL

Mm. Specified concrete strength (Kg/cm!) at 28 days

8 Compressive Strength~275 kg/cm2 Compressive Strength 350 Kg/cm8

Compressive Strength 200 Kg/cm Flexural Strength 35 Kg/cm2
Degree Flexural Strength = 20 kg/cm2 Flexural Strength = 28 Kg/cm2

Quality
Control Toler- Coef, of Av. Av. Toler- Cod. Av. Av. Toler- Coef. Av, Av,
ance variat- design design ance of design design ance of design design
level ion compr. flex. level van- compr, flex. level Vani~ conapr. flex,
str. str. ation str. str. ation str. str.
(Kg/cm8) (Kg/em2j~ (Kg/cm2) (Kg/cm2)~ (Kg/cm2 (Kg/cm2)

Very

good I in 15 10 235 23.5 1 in 15 7 310 31.3 1 in 20 7 400 40.0

Good 1 in 10 15 250 25.0 1 in 15 10 325 32,9 1 in 15 10 415 41,5

Fair linlO 20 270 27,0 linlO 15 340 34.7 —

C)

‘P
‘0
‘—8
0~
<<
IRC 59-1916
2,4,5. According to IRC: 15-1970, the permissible tolerance
level and coefficient of variation for concrete road pavements are
I in 15 (i.e., t=l.5 for infinite number of samples) and 10 per cent
respectively.

2.5. Selection of Water-Cement Ratio

As the compressive strength of ordinary portland cements
available in India varies considerably from factory to factory, it is
not possible to have a single curve of correlation between water—
cement ratio and compressive strength of concrete. A set of such
curves with 7 days compressive strength of cement as the third
parameter is given in IRC: 44-i972~* and is reproduced here in
Fig. 1 for the purpose of guidance. For a particifiar cement, know-
ing its compressive strength at 7 days, the water-cement ratio for
the average compressive strength of concrete can be selected from

£
U,
I-, _____
tn — 1
7-Days Coiv~ProSh~Q Straft;tb C~rv~low
2}
U) 5n~Ia(~fct W~t~
of Cesont
WitA Pivsdod Coi~crt(t
Staid Standird Sjand~rd Sand Mn
Sand(I5 Z6~ (IS650-~966) DmS~$n

350 440 A
U SrS 39~ e
2*0 352 C
245 30$ D
>- 20 264 E
75 2W F

01

0-4 0.6 0.6 1.0

~kThB-cEMENT RATIO BY Wt
Fig. 1.. Design curve for cement Concrete mixes in relation to 7~days
compressive strength of cement
~* Tentative Guidelines for Cement Concrete Mix Design for Road
Pavements

8
<<
 LRC :59-1976

40

C,
x
I~J

>

300 ~

200s~
N

0.40 0.~

WATER-CEMENT RATIO (BY WT)

5vers’ Iaw~to “low’ wo~¼ab1Ilty correspor~dis~
(For
to a sl~~p0-25 n~u~)
Fig. 2. Chart for assessment of flexural strength of concrete from
its cube compressive strength

9
<<
IRC : 59-1976

the curve as stated above. Where design is based on flexural

strength of concrete, the approximate relationship between com-
pressive and fiexural strength of concrete may be obtained from
Fig. 2.
2.6. Selection of Water Sand and Content
2.6.1 The principle of mix design for gap-graded concrete is
.

radically different from that for continuously graded concrete. The

basis of such design, as stated earlier, is that the voids in the coni—
pacted single-size coarse aggregates will be filled by the selected
easily admissible finer aggregates (in most cases sand), meaning
thereby that the compacted bulk volume of the latter will be equal
to the voids in the former, In the same way, the voids in the
compacted, easily admissible finer aggregates (in most cases sand)
will he filled by the cement paste having the stipulated water-
cement ratio.
2.6.2. i’he void content in aggregate can be easily calculated
from its bulk density and specific gravity determined through tests,
If the bulk density and specific gravity of aggregate are d (kg(m~)
and s (gm/cma) respectively, then the void con tent n is

(1-.- I~s ) 100% (2)

‘l’he approximate values of specific gravity, bulk density and

void content in different single-sized coarse aggregates and coarse
(Zone I and Ii.) and line (Zone III and IV) sands are given in Table
4. These values are meant for guidance only.

2.7. Mix Proportioning by Optimum Void-Filling Principle

2.3.1. The mix proportions of gap-graded concrete can be
calculated in the following manner
Let
(i) V (in ii~) . gross volume of single sized coarse aggregate
= gross volume (V== 1 m’) of wet mix minus the
volume (v5) of entrapped air minus the volume
(v’p) of “extra” cement paste required to provide
the desired workability.
(ii) v. (in ma) gross volume of next compatible size of fine
aggregate (in most cases sand)
== volume of voids in the single-size coarse
aggregate

10
<<
 IRC: 59-1976

with ni denoting per cent of voids in

single-size coarse aggregate,
and (iii)~ (in m3) = volume of cement paste required to fill the
voids in finer aggregate
= volume of voids in finer aggregate

• with n2 denoting per cent of voids in

finer aggregate
-— n
1 .n2. V
10000
The total voiLime of cement paste is therefore V’p Vp r

Knowing and water—cement ratio (r) by weight, the quantities of

Vp

cement and water t. an be easily calculated.

TAnLE 4. APPaoxistATr VALUEs or Sprciric GRAvITy, BULK Drxsrrv

ANt) Volt) CONTENTS OF Cos 5SF AND FINE Acosroans

Size of aggregate SpecifIc gravity 3)

Bulk density (%) void
Per cent
(gjcm’) (kg m

Coarse aggregate*
63—50 mm 2,65 1650 37,7
50—40 mm 2.65 1620 38.6
40—20 mm 265 1600 39,6
20—10 mm 2.65 1520 42.6
10—4.75 nm 2.65 1520 42,6

Fine aggregate
Coarse sand
(Zone I & II) 2.65 1450 45,3

Fine sand
(Zone I P1 & iS’) 2.63 1350 48.7

~P%’o!e The above, values are average for both angular (manufactured) and
rounded (natural) coarse aggregates.

11

<<
IRC :59-1976

2.7.2. The mix proportions by weight per m~gross volume

of wet concrete therefore are

Water Cement Compatible finer Coarse aggregate

aggregate (in most
cases sand)

(kg/m3) kglm~ kg/rn3

kg/ms

where
(i) W,, —

(1 -v,-v’p) d~ (3)
(ii) 1+,

~o ~ ~ ~ (4)
1000 v~.s~
(in) W, ——
I r.s,
1000 s,, r Fit
~)J
,

.
~ ~ ~ (l-v~-v (5~
a rid (iv) W~, .= r.
lOO() r,s, r , n
‘1
.~.... -
1 112
(I ~
,
~)J (6)
8) of entrapped air in 1m3 gross volume
with == volume
of wet concrete
(m (see para 2.7.3.)
volume (m3) of “extra” cement paste required for
desired workability in 1m3 gross volume of wet con-
crete (see para 2.7.4),
Per cent of voids in single-size coarse aggregate,
pi~zz~ Per cent of voids in finer aggregate,
= hulk density (Kg/rn3) of coarse aggregate,
— bulk density (Kg/rn3) of finer aggregate (in most cases
.-

sand),
specific gravity of cement, and
r water-cement ratio by weight.

12

<<
 mc 59-1976
2.7.3. Approximate quantities (i~)of entrapped air in wet
concrete mixes having different maximum sizes of coarse aggregate
are shown in Table S.

Tans 5. A~noxasnAuouwr os Eina*nuo Am IN NON

AISRAW5D ~ONOUfl

Msx.slzeofaureaate 10 20 40 50 63
(mm)

Entrauoed air
4%) 3 2 1.0 0.5 04

Volume of aIr per

1 m’ gross 0.03 0.02 0.01 0.005 0.004
volume of wet
concrete (&)

2.7.4. The amount (9,) of“extra” cement paste required in

the concrete mix will depend on the degree of workability desired,
which in turn will depend on the compactive effort Intended to be
applied and the amount of reinforcement proposed in the struct-
ure. In India, most concrete pavements are built without any
reinforcement excepting dowel bars at expansion joints and some-
times dc-bars at longitudinal joints. The dump stipulated in IRC:
15-1970 is very low to low (0 to 25 mm) for paving concrete mixes
when compacted by vibration. Since gap-graded concrete mixes
should be dry to prevent segregation, the slump shall not be more
than 12 mm. For this degree of workability, the amount (if,) of
“extra” cement paste may be taken as equal to about 11 per cent of
the gross volume (‘F) of wet concrete on average basis. The
quantity of “extra” cement paste will in reality depend on the
shape and size of coarse aggregate as weli as the grading offine
aggregate. Therefore, if greater refinement is desired, the volume
of “extra” cement paste may be increased or decreased by 1 per
cent (making it 12 per cent or 10 per cent of!) depending on
whether the coarse aggregate is angular (e.F., crushed stone) or
rounded (e.g., gravel). Similarly, if sand available is such that the
number ofgaps between the lowest coarse aggregate fraction and
the fine aggregate is required to be reduced to 1-2 or 0-1 instead of
2-3 (see pare 2.3.1), the volume of“extra” cement paste may be
reduced by 1 and 2 per cent (making it 10 and 9 per cent of F) when
the number ofgaps is 1-2 and 0-1 respectively.
13
<<
IRC 59~l976

3. WORKED OUT EXAMPLE ON MIX DESIGN

An example illustrating the mix d.esign procedure is worked
out in Appendix.
4. TRIAL MIX
4.1. With mix proportions obtained from para 2.7.2. the m.ix
is prepared and the workability measured. If the workability
measured is different from the stipulated value, the “extra’’ cement
l)aste (Vp) shall be adjusted. To obtain maximum benefit from
gap-graded concrete, the water-cement ratio of the mixes is kept low,
usually between 0.40 and 0.60. For this range of water-cement ratio,
for each. 12 mm increase or decrease in observed slump, the amount
of “extra” cement paste3niay be reduced or increased respectively
by S per cent. For 1 m gross volume of wet mix, (V) this reduct-
ion or increase in “extra’’ cement paste (v’p = 0.1 V=0.l m3) would
irnean an alteration by p t).05 V’p = p 0.005 m3 for each 12 mm
ncrease or decrease in the observed slump value.
4.2. The mix proportions are thereafter recalculated with
the adjusted cement paste as per procedure given above for three
water-cement ratios comprising the pre-selected water-cement-ratio
and two other values, one higher and the other lower than
the pre.-selected ratio by 0.05. The strength of concrete with
the three svater-cement ratios is then determined in accord-
ance with 1S: 5l6~1969**. The values of strength obtained are
then plotted against water-cement ratios and the appropriate
water-cement ratio for the required strength chosen from the plot.
The final mix proportions are then recalculated for this water-
cement ratio, other parameters remaining the same.
** Methods of Test for Strength of Concrete

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 t,RC : 59-1976
Appendix

WORKED OUT EXAMPLE FOR CEMENT CONCRETE MIX DESIGN

(A) i)esign Stipulations

(i) Minimum compressive strength 260 Kg/cm2
required in the field at 28-days
40 mm (single-size,
(ii) Maximum size of aggregate rounded aggregate)
12 mm (extra cement
(iii) Degree of workability paste, v’p=O.l tnt/ma)
Good (co-efficient of
(iv) Degree ol’ quality control variation 10%)
linlS
(v) Accepted tolerance level
(major work involving testing
of a large number of samples
i.e., t from Table 2=1.50)
0.01 m’jm3
(vi) Entrapped air, v~,

(B) Test Data for Materials:

(i) Compressive strength of cement 308 Kg/cm2
at 7 days (15,: 269-1967)
3.15
(ii) Specific gravity of cement
(iii) Specific gravity of coarse aggregate 2.65
and fine aggregate
(iv) Water absorption: 0.4%
(a) Coarse aggregate 0.6%
(b) Fine aggregate
(v) Free (Surface) moisture: nil
(a) Coarse aggregate 2%
(h) Fine aggregate
(vi) Bulk density of saturated surface—dry
coarse aggregate (4): 1600 kg/m’ (Table 4)
(vii) Bulk density of saturated surface-dry
3 (Table 4)
fine aggregate (4): 1450 kg/rn
(C) I)esign Strength of Concrete. (5)
260 10 ,..260 260
—
— 1—1.5 ~ ~-~ç3o6 kLc.m
1 ~ 100
=say, 310 kg/cm2

(D) Selection of Water-Cement Ratio:

From Fig. 1. corresponding to 7-days cement strength of 308 kg/cm2
and design strength of concrete of 310 kg/cm2, water-
cement ratio required =0.50.

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1RC : 59-1976
2 of Wet Concrete
(E) Calculation of Mix Proportions per I in
0) V=l in’
Therefore V=V—vC v’p= 1.00 0.01—0.10=0.89 in2

(ii) W~
2—Vda=0.89x 1600=1424 Kg

(iii) W~= !fi~..d~.

Since n1=(l — 1600/1000x2.65)x 100=39.6 per cent

39.6x0.89x1450
______ =511 Kg
1000 a2 ( ~ii,ll~

(iv) l3~= Tn0V’~--iooo~ (/

Since ,u=(1—1450/1000x2,65) x 100=45.3 per cent

—1000x3.15
—. ,~ o
.10+ 39,6x45.3x0.89
=317.7 Kg
(v) W0=r, W0
=0.5x317.7=158.85 kg
(vi) Mix proportions
Water2) (Kg/ni2)
Cement (Kg/rn’)
Fine Aggregate (Kg/m3)
Coarse Aggregate
(Kg/rn
158.85 317.7 511.0 1424.0
or 0.5 : I : 1.608 : 4.48
(F) Actual Quantities required for the mix per 50 kg bag of cement
(i) For eement=50 kg, net quantities of materials are: fine aggregate
=80.40 kg, coarse aggregate=224.0 kg and water 25.0 kg=25.0
litre.
(ii) Extra water to be added to cater for absorption by coarse aggre-
gate=224x0.4/lOO=0.896 kg=0.896 litre. Water to be deducted for
free moisture present in fine aggregate= 80.40 x 2/100=1.608 kg
=1.608 litre. Actual quantity of water to be added is therefore
r.:::25,000 +0.896—1.608=24.288 litre.
(iii) Actual quantity of fine aggregate required=::8tL400~i~ 1.608=
82.008 kg.
(iv) Actual quantity of coarse aggregate required=224.000---0.896=
223.104 kg.
Therefore, the actual quantities of the different constituents pci
hag of cement are:
Cement=50 kg Sand=82.008 kg
Water =24.288 litre Coarse aggr.=223.104 kg,

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