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Mix Design For Concrete Roads As Per IRC:15-2011

By

Kaushal Kishore, Materials Engineer, Roorkee

ABSTRACT:

The stresses induced in concrete pavements are mainly f lexural. Therefo re f lexural st rength is more o f ten

specif ied than compressive st rength in the design of concrete mixes f or pavement construction. A simple

method o f concrete mix design based on f lexural strength f or no rmal weight concrete mixes is described in

the paper.

INTRODUCTION:

Usual criterion f or t he strength of concrete in the building indust ry is the compressive strength, which is

cons idered as a measure of quality concrete. However, in pavement const ructions, such as highway and

airport runway, the f lexural strength of concrete is considered more important, as the stresses induced in

concrete pavements are mainly f lexural. Therefo re, f lexural strength is more o f ten specif ied thancompress ive strength in the design of concrete mixes f or pavement construction. It is not perfectly reliable

to predict f lexural st rength f rom compressive strength. Further, various codes o f the world specif ied that

the paving concrete mixes should pref erably be designed in the laboratory and contro lled in the f ield on the

basis of its f lexural st rength. Therefore, there is a need to design concrete mixes based on f lexural

strength.

The type of aggregate can have a predominant ef f ect, crushed rock aggregate resulting in concrete with

higher f lexural strength than uncrushed (gravel) aggregates f or comparable mixes, assuming that sound

materials are used. The strength o f cement inf luences the compressive and flexural st rength of concrete

i.e. with the same water- cement rat io, higher strength cement will produce concrete of higher compressiveand f lexural strength.

MIX DESIGN DETAILS

IRC: 15-2011 specif ied that f or concrete roads OPC sho uld be used. This code also allowed PPC as per IS:

1489 (Part-1) with f lyash content not more t han 20 percent by weight o f PPC. Accordingly OPC + f ly ash

may be used in concrete roads. Flyash shall be not more than 20 percent by weight of cementit ious

material. However, IS: 456-2000 specif ied that f ly ash conf orming to grade-1 of IS 3812 may be used as

part replacement o f OPC provided unifo rm blended with cement is essent ial. The const ruction sites where

batching plants are used this may be practicable. In ordinary sites where mixer or hand mixing are done

unifo rm blending of f ly ash with cement is not practicable. At such construction sites, PPC may be used.

PPC should be used with caution where rapid construction methods like slip f orm is being used. Joints

cutting also need early st rength.

1 CharacteristicFlexuralStrength at28 days

: 4.5 N/mm2

2 Cement : Three mixes are to be designed

MIX-A

With PPC (Flyash 18 percent based) conf orming to IS:1489-part - I-1991. 7 days

st rength 37.5 N/mm2. Specif ic Gravity : 3.00

MIX-B
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With OPC-43- Grade conf orming to IS: 8112-1989. 7 days st rength 40.5 n/mm2.Specif ic Gravity : 3.15

MIX-C

With OPC of Mix-B and Fly ash conf orming to IS:3812 (Part- I)-2003 Specif icGravity : 2.20

Note:Requirements of all the three mixes are the same. Fine Aggregate, Coarse

Aggregate and Retarder Super plasticizer are the same for all the three mixes.

3 Fly ashreplacement

: 20% Fly ash is required to be replaced with the to tal cementitious materials.

4 Maximumnominal sizeofaggregates

: 31.5 mm Crushed aggregate

5 Fineaggregateand coarseaggregategrading

: Given in Table 1

6 Minimumcementcontent fo r4.5 N/mm2characteristicf lexuralstrength:

: (a) OPC shall not be less than 360 kg/m3.

(b) PPC shall not be less t han 425 kg/m3. Fly ash in it 20% maximum by weight ofto tal cementitious materials

(c) OPC + Fly ash mix OPC shall not be less t han 340 kg/m3. Fly ash 20%maximum by weight of cementat ions material

7 Maximum f reeW/C Ratio

: (a) For OPC 0.45

(b) For PPC 0.50

8 Workability : 40 mm slump at pour the concrete will be transported from central batching plantthro ugh transit mixer, at a dist ance of 15 Km during June, July months . The

average temperature last year during these months was 300C.

9 Exposurecondition

: Moderate

10 Method of placing

: Fully mechanised construction

11 Degree o f supervision

: Good

12 Maximum ofcementcontent

: (a) OPC 425 kg/m3

(b) PPC 425 kg/m3

13 Chemicaladmixture

: Retarder Super plasticizer conforming to IS:9103-1999. With the givenrequirements and materials, the manufacturer of Retarder Super plasticizerrecommends dosages of 1% bw of OPC, which will reduce 15% of water withoutloss of workability. For f ly ash included cement dosages will be required to be

adjusted by experience/ trials.2% maximum by weight o f cementit ious material

14 Values of Z x(for NationalHighway)

: 1.96 x 0.40


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TEST DATA FOR MATERIALS AND OTHER DETAILS

1. The grading of f ine aggregate, 1 & 2 aggregates are as given in Table. 1.

2. Properties of aggregates

Tests Fine aggregate Aggregate 1 Aggregate 2

Specif ic Gravity 2.65 2.65 2.65

Water Absorption % 0.8 0.5 0.5

3. Target average f lexural strength f or all A, B and C mixes

S = S+ Zq

=4.5 + 1.96 x 0.40

= 5.3 N/mm2at 28 days age

4. For Mix A, B and C free W/C ratio with crushed aggregate and required average f lexural target s trength o f

5.3 N/mm2at 28 days f rom Fig. 1 Curve D f ound to be 0.42. This is lower than specif ied maximum W/C ratio

value of 0.45 f or OPC and 0.50 for PPC.

Note:In absence of cement s trength, but cement conf orming to IS Codes, assume f rom Fig. 1

Curve C and D f or OPC 43 Grade

Take curves C and D f or PPC, as PPC is being manufactured in minimum of 43 Grade of st rength.

5. Other datas: The Mixes are to be designed on the basis of saturated and surface dry aggregates. At the

time of concreting, moist ure content of site aggregates are to be determine. If it carries surface moisture

this is to be deducted f rom the mixing water and if it is dry add in mixing water the quantity o f water

required for absorpt ion. The weight of aggregates are also adjusted accordingly.

DESIGN OF MIX-A WITH PPC

a) Free W/C ratio f or the target f lexural strength of 5.3 N/mm2as worked out is 0.42 fo r f irst trial.

b) Free water f or 40 mm slump from Table 2 for 31.5 mm maximum size of aggregate.

2/3170 + 1/3200= 180 kg/m3

From trials it is f ound that Retarder Super plast icizer at a dosages of 1.3% bw of PPC may reduce 15%

water without loss of workability

Then water = 180 (180 x 0.15) = 153 kg/m3

c) PPC = 153/0.42 = 364 kg/m3(Required minimum PPC is 425 kg/m3)

d) Formula f or calculation o f f resh concrete weight in kg/m3

Um= 10 x Ga(100 A) + Cm(1 Ga/Gc) Wm(Ga 1)

Where,

Um=Weight of f resh concrete kg/m3

Ga=Weighted average specif ic gravity of combined f ine and coarse aggregate bulk, SSD

Gc=Specif ic gravity o f cement. Determine actual value, in absence assume 3.15 f or OPC and 3.00 f or PPC

(Fly ash based)

A=Air content , percent . Assume for t rial ent rapped air 1.5%


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For 31.5 mm maximum size of aggregate

There is always entrapped air in concrete. Theref ore ignoring entrapped air value as NIL will lead the

calculation of higher value of density. Take exact value of air as obtained in the test

Wm=Mixing water required in kg/m3

Cm=Cement required, kg/m3

Note:- T he exact density may be obtained by f illing and f ully compacting constant volume suitable metal

container f rom the trial batches o f calculated design mixes. The mix be altered with the actual obtained

density of the mix.

Um=10 x Ga(100 A) + Cm(1 Ga/Gc) Wm(Ga 1)

=10 x 2.65 (100 1.5) + 425(1- 2.65/3.00) 153 (2.65 -1)

=2409 kg/m3

e) Aggregates = 2409 425 153 = 1831 kg/m3

f ) Fine aggregate = 1831 x 0.45 = 824 kg/m3

Aggregate 1 = 1831 x 0.29 = 531 kg/m3

Aggregate 2 = 1831 x 0.26 = 476 kg/m3

g) Thus f or 4.5 N/mm2 f lexural strength quantity of materials per cu.m. of concrete on the basis of

saturated and surf ace dry aggregates:

Wate r = 153 kg/m3

PPC = 425 kg/m3

Fine Aggregate (sand) = 824 kg/m3

Aggregate (1) = 531 kg/m3


Retarder Super Plasticizer 1.3% bw of PPC = 5.525 kg/m3

MIX- B WITH OPC

a) Water = 180 (180 x 0.15) = 153 kg/m3

b) OPC = 153/0.42 = 364 kg/m3

c) Density: 10 x 2.65 (100 1.5) + 364 (1 2.65/3.15) 153 (2.65 1)= 2416 kg/m3

d) Total Aggregates = 2416 364 153 = 1899 kg/m3

Aggregate 1 = 1899 x 0.29 = 551 kg/m3

Aggregate 2 = 1899 x 0.26 = 494 kg/m3

Fine Aggregate = 1899 x 0.45 = 854 kg/m3

e) Thus f or 4.5 N/mm2f lexural st rength quantity of materials per cu.m of concrete on the basis of SSD

aggregates are given below:

Wate r = 153 kg/m3

OPC = 364 kg/m3

Fine Aggregate (sand) = 854 kg/m3



Retarder Super Plasticizer 1% bw OPC = 3.640 kg/m3


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MIX-C WITH OPC + FLY ASH

With a total cementitious material of 430 kg/m3,

OPC = 430 x 0.80 = 344 kg/m3

Fly ash = 430 x 0.20 = 86 kg/m3

Mix on t he basis o f SSD Aggregates,

(1) Water as worked out earlier = 153 kg/m3

(2) OPC = 344 kg/m3

(3) Fly ash = 86 kg/m3Density = 10 x 2.65 (100 1.5) + 430 (1 2.65/3.00) 153 (2.65 1) = 2410 kg/m3

Total Aggregates = 2410 153 344 86 = 1827 kg/m3

(4) Fine aggregate 0.45 x 1827 = 822 kg/m3

(5) Aggregate (1) 0.29 x 1827 = 530 kg/m3

(6) Aggregate (2) 0.26 x 1827 = 475 kg/m3

(7) Retarder super plasticizer 1.5% bw of cementit ious material = 6.450 kg/m3

Note:

(1) Cementitious material worked out as per IRC : 15-2011, which specif ied: In case f ly ash (as per IS: 3912Part 1) is blended at site, the quantity of f ly ash shall be rest ricted to 20 percent by weight of cementitious

material and the quantity of OPC in such a blend shall not be less t han 340 kg/m3.

(2) Af ter t he f irst trial mix, its actual density is to be determined, as specif ied elase where in this paper. The

mix proport ions shall then be worked out accordingly including the water content, the dosages o f Retarder

SP f or required workability keeping the f ree w/c rat io with in the permiss ible limits and adjust ing it according

to the required f lexural st rength.

(3) The mix proport ions given in this paper are f or f irst t rial and to be adjusted as per actual site materials,

conditions and requirements.

For 4.5 N/mm2flexural strength quantity of material per cu.m of concrete on the basis of saturated

and surface dry aggregate s of Mix A, B and c are given below:

Materials MIX. A with PPC Mix. B with OPC Mix. C with OPC+Flyash

Water kg/m3 153 153 153

PPC kg/m3 425

OPC kg/m3 364 344

Flyash kg/m3 86

Fine Agg. kg/m3 824 854 822

Agg. (1) kg/m3 531 551 530

Agg. (2) kg/m3 476 494 475

Retarder Super- plasticizer kg/m3 5.525 3.640 6.450

W/ Cementitious rat io 0.36 0.42 0.356


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Note:-

1. For exact W/C ratio t he water in admixture should also be taken into account.

2. PPC reduces 5% water demand. If this is f ound by trial then take reduce water f or calculation.

3. If the t rial mixes does not gives the required properties of the mix, it is then required to be altered

accordingly. However, when the experiences grows with the particular set o f materials and site condit ions

very few trials will be required, and a expert o f such site very rarely will be required a 2nd trial.

CONCLUSION

1. For 4.5 N/mm2f lexural st rength concrete having same material and requirement, but without water

reducer, the OPC required will be 180/0.42 = 429 kg/m3

2. With the use of superplasticizer the saving in OPC is 65 kg/m3and water 27 lit/m3.

3. In the f inancial year 2009-2010 India has produces 200 million to nnes o f cement. In India one kg of

cement pro duce emitted 0.93 kg of CO2. Thus the production o f 200 million to nnes of cement had emitted

200 x 0.93 = 186 million tonnes of CO2to the atmosphere.

4. If 50 million tonnes cement in making concrete uses Water Reducers 7500000 tonnes of cement can be

saved. 3750000 KL of potable water will be saved and the saving of Rs. 3300 crores per year to theconst ruction Industry. 6975000 tonnes of CO2will be prevented to be emitted to the atmosphere. The

benef its in the uses of water reducers not limited to this. When water reduces shrinkage and porosity o f

concrete are reduces which provides the durability to concrete st ructures.

5. India is f acing serious air, water, soil, food and noise pollution problems. Every ef f ort s therefo re are

necessary to prevent pollution on top priority basis.

6. As the st ress induced in concrete pavements are mainly f lexural, it is desirable that their design is based

on the f lexural strength of concrete. The quality of concrete is normally assessed by measuring its

compress ive strength. For pavings, however, it is the f lexural strength rather than the compression

st rength of concrete which determine the degree of cracking and thus the performance of road, and it isimperative to contro l the quality on the basis o f f lexural st rength.

7. As per IRC: 15-2011, in case of small size projects, where f acilities f or testing beams with three print

loading are not available, in such cases, the mix design may be carried out by using compressive strength

values and there af ter f lexural strength will be determined as per correlation between f lexural strength with

compress ive strength given the f ollowing equation.

Where f cr is the f lexural strength in MPa or N/mm2and fck is t he characteristic compressive st rength in

MPa or N/mm2as per IS: 456-2000.

REFERENCES:

1 IS : 383-1970

Specifications f or coarse and f ine aggregates f rom natural sources f or concrete(second revision) BIS, New Delhi

2 IS: 456-2000

Code of practice f or plain and reinforced concrete (f ourth revision), BIS, NewDelhi

3 IS: 9103-1999

Specif ication f or admixtures f or concrete (f irst revision) BIS, New Delhi

4 IS: 8112-1989 Specif ications f or 43 Grade ordinary port land cement (f irst revision) BIS, NewDelhi

5 IS: 2386(Part-III)1963

method o f test f or aggregate f or concrete. Specif ic gravity, density, voids,absorption and bulking, BIS, New Delhi


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6 IS: 3812(Part-I)2003

Specif ication f or pulverized f uel ash: Part- I f or use as pozzo lana in cement,cement mort ar and concrete (second revision) BIS, New Delhi

7 IS: 1489-Part-I 1991

Specif ications f or po rtland pozzolana cement (Part- I) Flyash based. (Thirdrevision), BIS, New Delhi

8 IRC: 15-2011 Standard specif ications and code of practice for construction of concrete road(Fourth revision)

9 Kishore Kaushal, Concrete Mix Design Based on Flexural strength fo r Air-Entrained Concrete,

Proceeding of 13thConf erence on o ur World in Concrete and Structures, 25-26, August, 1988,Singapore.

10 Kishore Kaushal, Method of Concrete Mix Design Based on Flexural Strength, Proceeding of theInternat ional Conf erence on Road and Road Transport Problems ICORT, 12-15 December, 1988,New Delhi, pp. 296-305.

11 Kishore Kaushal, Mix Design Based on Flexural Strength of Air-Entrained Concrete. The IndianConcrete Journal, February, 1989, pp. 93-97.

12 Kishore Kaushal, Concrete Mix Design Containing Chemical Admixtures, Journal of the NationalBuilding Organization, April, 1990, pp. 1-12.

13 Kishore Kaushal, Concrete Mix Design f or Road Bridges, INDIAN HIGHWAYS, Vol. 19, No. 11,November, 1991, pp. 31-37

14 Kishore Kaushal, Mix Design f or Pumped Concrete, Journal of Central Board of Irrigation andPower, Vol. 49, No.2, April, 1992, pp. 81-92

15 Kishore Kaushal, Concrete Mix Design with Fly Ash, Indian Const ruction, January, 1995, pp. 16-17

16 Kishore Kaushal, High-Strength Concrete, Bulletin of Indian Concrete Institute No. 51, April-June,

1995, pp. 29-31

17 Kishore Kaushal, Concrete Mix Design Simplified, Indian Concrete Institute Bulletin No. 56, July-September, 1996, pp.25-30.

18 Kishore Kaushal, Concrete Mix Design with Fly Ash & Superplasticizer, ICI Bulletin No. 59, April-June 1997, pp. 29-30

19 Kishore Kaushal. Mix Design f or Pumped Concrete, CE & CR October, 2006, pp. 44-50.

Table. 1: Grading of Aggregate s

IS SieveDesignation

Percentage of passing by mass

Fineaggregatef rom river

45%

Crushedaggregate

Combinedgrading ofmix

IRC: 15-2011 recommended grading o f combinedaggregates f or pavement quality concrete (PQC)

(1)

29%

(2)

26%

31.50 mm 100 100 100 100 100

26.50 mm 100 100 98 99 85 95

19.0 mm 100 100 25 81 68 88

9.50 mm 100 46 0 58 45 65

4.75 mm 94 5 44 30 55


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600 micron 42 0 19 8 30

150 micron 10 5 5 15

75 micron 2 1 0 5

Table. 2: Approximate fre e-water content (kg/m3) required t o give various levels of workability for

non-air-entrained (with normal entrapped air) concrete.

Maximum size of aggregate (mm) Type of aggregate Slump (mm) 25 + 10 40 + 1031.5

Uncrushed

Crushed

160

190

170

200

Note:- When coarse and f ine aggregate of diff erent types are used, the f ree water content is est imated by

the expression.

2/3Wf+1/3Wc

Where,Wfsub>= Free water content appropriate to type o f fine AggregateAnd Wc= Free water content appropriate to type of coarse aggregate.


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We at engineeringcivil.com are thankful to Er. Kaushal Kishorefor submitting the revised mix design as per

IRC:15-2011. This will be of great help to all civil engineering students and faculty who are seeking information

on mix design based on revised IRC.

engineeringcivil.com-mix design for concrete roads as per irc152011

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