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IRC:15-1981

STANDARD SPECIFICATIONS

AND

CODE OF PRACTICE

FOR

CONSTRUCTION OE

CONCRETE ROADS

(Second Revision)

/

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IRC: 15-1981

STANDARD SPECIFICATIONSAND

CODE OF PRACTICEFOR

CONSTRUCTION OFCONCRETE ROADS

(Second Revision)

s 1

PublishedbyTHE iNDIAN ROADS CONGRESS

Jamnagar House, Shabjahan Road,

New Deihi-ilOOll1981

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IRC: 15-1981

First published July, 1965

First Revision, December 1970

Second Revision, July, 1981

(Rights ofPublication and ofTranslation are reserved)

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IR C 15-1981

CONTENTS

Page

INTRODUCTION ... 1

2. SCOPE 2

3. MATERIALS ... 2

3.1. Cement ... 2

3.2. Aggregates ... 3

3.3. Water .. 5

3.4. Reinforcement .,. 53.5. Dowel and Tie Bars .. 5

3.6. Premoulded Joint Filler ... 5

3.7. Joint Sealing Compound ... 5

3.8. Quality Control Tests on Materials ... 6

4. PROPORTIONING OF CONCRETE . 7

4.1. Proportioning on the Basis of Strength ... 7

4,2. Approximate Proportions ... 8

4.3. Field Mix ... S

4.4. Water Content and Workability ... 9

5. TOOLS, EQUIPMENT, AND APPLIANCES ... 9

5.1. General ... 9

5.2. List ofTools, Equipment and Appliances ... 9

6. PREPARATION OF SUBGRADE AND

SUB-BASE ... 1 1

6.1. General ... 1 1

6.2. Sebgrade .,, II

6.3. Sub-base ... 12

6.4. Capillary Cut-off ... 1 3

6 5 Frost Affected Areas 15

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Page

7. FORMS ... 17

7.1. Steel Forms ... 177.2. Wooden Forms ... 17

7.3. Setting ofForms ... 18

8. JOINTS .., 18

8.1. General +., 188.2. Types ofJoints ... 18

8.3. Transverse Joints ... 198.4. Longitudinal Joints ... 21

9. CONSTRUCTION ... 21

9.1. Storage and Handling of Cement ... 21

9.2. Storage and Handling of Aggregates ... 22

9.3, Batching of Materials ,,, 22

9.4. Mixing ... 23

9.5. Control ofWorkability and Strength ... 24

9.6. Transporting and Placing ofConcrete ... 25

9.7. Water-proof Paper 26

9.8. Placement ofSteel ... 26

9.9. Compaction and Finishing ... 28

9.10. Curing ofConcrete ... 31

9.11. Final Surface Test ... 339.12. Removing Forms .. 34

9.13. Concreting during Monsoon Months ... 34

9.14. Concreting in Hot Weather ... 34

9.15. Concreting in Cold Weather .. 35

9.16. Work on Gradients ... 36

917. Protection of Concrete ... 36

9.18. Sealing ofJoints ... 369. 19. Opening to Traffic . ~. 38

10. BASIS OF PAYMENT ,.. 38

10.1. Tolerance in Pavement Thickness ,.. 38

10 2 Determination of Concrete Strength 39

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Page

SUPPLEMENTARY NOTES

N. 1 . CONCRETE ... 42

N. 1.1. Desirable Properties of Pavement

Concrete ... 42

N. 1.2. Workability .,. 42N. 1.3. Strength ... 42

N. 1.4, Degree ofCompaction ... 43N. 1.5. Durability ... 44

N. 1.6. Resistance to Abrasion 44

N. 1.7. Riding Quality ... 45

N. 1.8. Surface Texture ,.. 45

N. 1.9. Use ofAdmixtures ,.. 45

N. 1.10. Computation ofConcrete Strength ... 46

N. 1.11. Correction ofthe Strength of

Cubes for Ages Greater than 28 days ... 49

N. 2 . ARRANGEMENT OF JOiNTS ... 50

N. 2.1. Staggered Joints .,, s oN. 2.2. Skew Joints ,,. 50N. 2.3. Acute-angled Corners ... 50

N. 2.4. Spacing ofJoints ... 50

N. 3. REINFORCEMENT ,.. 52

N. 3.1. Basis ofDesign ,,, 52N. 3.2. Types ofReinforcement ... 53

N. 3.3. Location of Reinforcement ,,. 53

N. 4. LOAD TRANSFER DEVICES ... 54

N. 4.1. General .., 54

N. 4.2. Dowel Bars ... 54

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Page

N. 6 . CONCRETING IN COLD WEATHER .. 57

N. 6.1. General .., 57N. 6.2. Preparation for Concreting ... 58

N. 6.3. Placement Temperatures ... 58

N. 6.4. Safe Temperatures .. 58

N. 6.5. Protection ,,. 59

N. 6.6. Heating of Materials ... 59N. 6.7. Accelerators and Anti-freeze

Compounds ... 59

APPENDICES

A. List ofI.R.C. Standards Referred to inthe Text ... 60

B . Details ofJoints ... 62

C. Direct Field Adjustment Chart forConcrete Mixes to Counteract Variations in

Compressive Strength Due to Use ofDifferent Quality Cements and Other Factors 64

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1 . INTRODUCTION

1 . 1 . The First revision of the standard was brought out in1970. Since that time, a number of new standards relating to

different aspects of cement concrete road construction have beenpublished by the Indian Roads Congress based on drafts preparedby the Cement Concrete Road Surfacing Committee (present list ofpersonnel given below), processed further by the Specifications andStandards Committee (list of members given on inside of front andback cover).

1.2. A need was felt to update IRC 15 in the light ofabove

referred new standards. This task was carried out jointly by Dr.R.K. Ghosh, Member-Secretary, Cement Concrete Road SurfacingCommittee, R.P. Sikka, Member-Secretary, Specifications andStandards Committee; Y.R. Phull and M. Dinakaran, Scientists,Central Road Reserch Institute; and K. Arunachalam, ExecutiveEngineer, Ministry of Shipping and Transport (Roads Wing),Government of India.

STANDARD SPECIFICATIONS AND CODEOF PRACTICE FOR CONSTRUCTION OF

CONCRETE ROADS(SecondRevision)

K. K, Nambir

Dr. R. K. Ghosh

Ma). Get S. S. AbluwaliaCol. Avtar Siagh

Dr. K.L. BhanotU.S. Bhatia

D.C. ChaturvediMG. DandavateDr. M.P. DhirP.K. Issac

P.J. JagusMa). Gen. R.K. KairaDr. S. K. KhannaD.N. KhuranaP.J. Mehta

Y.K. Mehta

,Convenor

Meinher-Secretary

N. V. MeraniY.R. PhullG.S. RaoM.M.D. SethAmarjit SinghN. Sivaguru

P.V. SomashekharS.D. Vidyarthi

Director General

CementResearch Instt. ofIndiaCity Engineer,

Municipal Corporation of

BombayDirector (Civil Engineering),

Indian Standards Institution

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IRC: 15-1981

2 . S C O P E

2.1. The Code of Practice is intended to indicate what is con-sidered to be good practice for the construction of cement con-crete road pavements, including preparation of the subgrade and

sub-base underneath these pavements. This does not however coverthe requirements offully mechanised constructions.

2.2. The Code deals with various aspects ofcement concreteroad construction like materials, equipment, proportioning, measure-ment, handling of materials, and mixing, subgrade and sub-basepreparation, forniwork, joints, reinforcement, of concrete placing,finishing, curing etc. For greater elucidation of certain aspectssuch as properties and tests for concrete, arrangement ofjoints,

reinforcement, load transfer devices, tie bars, and concreting undercold weather supplementary notes have been added to this Code,vide paras N. I to N. 6. Provisions ofthis Code shall apply unlessrequired to be modified by special circumstances to take intoaccount unusual conditions oftraffic, subgrade, etc.

2.3. Some of the aspects ofcement concrete roads are dealtwith in greater detail in separate standards of IRC, vide fist atAppendix-A. Reference to these standards is drawn in the textwhere relevant.

3. MATERIALS

3.1. Cement

3.1 .1 . Ordinary an d high strength Ordinary portland cement:This should comply with the requirements of IS 269-1976 Speci-fication for Ordinary and Low-Heat Portland Cement (Third Revi-

sion), or ofIS 8112 -1976 Specification for High Strength Ordi-nary Portland Cement. Ordinary Portland Cement and HighStrength Ordinary Portland Cement are most widely used forconcrete pavements.

3.1.2. Rapid hardening portland cement This should com-ply with the requirement ofIS:8041E-l976 Emergency Specificationfor Rapid Hardening Portland Cement. E n general, this cementwould be used only where time is a critical factor and the road is

required to be opened to traffic at an earlier date than would bepossible if Ordinary Portland Cement or High Strength OrdinaryPortland Cement is used.

3.1.3. Portland blastfurnace slag cement: This should complywith the requirement of IS 455-1967 Specification for PortlandBlastfurnace Slag Cement (Second Revision).

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3.1.4. Port land pozzolana cement: This should comply withthe requirements of15: 1489-1976 Specification for Portland Poz-zolana Cement (Second Revision).

3.2. Aggregates3.2.1. General: Aggregates should comply with E S : 383-1970

Specification for Coarse and Fine Aggregates from Natural Sourcesfor Concrete (Second Revision) with special reference to the addi-tional requirements stipulated for use in road works excepting inthe case of Los Angeles Abrasion Test limit. lhe Los AngelesAbrasion Test limits shall be not more than 35 per cent and 50 percent for concrete wearing course and sub-base course respectively.

In addition, the limits of deleterious material shall not exceed therequirements set out in IS : 515-1959 ~Specificationfor Natural andManufactured Aggregates for Use in Mass Concrete. Weatheredrock should not be used.

In order to make good concrete, it is important to avoidcrushed aggregate ofpoor shape. Very angular, flaky, elongated orsplintery aggregates give a harsh mix oflow workability.

Maximum size of aggregate should not exceed 1/4th ofthe

pavement slab thickness, in case of pavements having reinforce-ment, maximum size of aggregate should also not exceed 1/4th ofminimum clear spacing between reinforcing bars.

3.2.2. Coarse aggregates

Continuous grading: Continuously graded coarse aggregateshould be furnished in at least two separate sizes with separationat 20 mm i.S. sieve when combined material graded from 40 to 4.75

mm is specified, and at 25 mm I.S. sieve when combined materialgraded from 50 to 4.75 mm is specified, and at 25 mm~ I.S. sievewhen combined material graded from 50 to 4.75 mm is specified.

Ga p grading : Gap graded or single-sized coarse aggregate maybe used, as an alternate aggregate to the continuously graded aggre-gate particularly where the grading offine aggregate is fine to veryfine, as stipulated in IRC : 59-1976 Tentative Guidelines for Designof Gap Graded Cement Concrete Mixes for Road Pavements. Gap-

grading may also become necessary when it is not economical toobtain materials to get continuously graded coarse aggregate as perstandard or when it is found that omission of certain intermediatesizes is generally beneficial leading to easy admittance ofthe finerparticles into coarser fractions through reduction in interferenceamong the particles. Thus in some cases e~~p..paox1y.grade4nrtd~anbe utilised by making adjustment in (be cparspaggregategr*qaqiojto

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accommodate the available sand grading without particle inter-ference. In such cases the combination ofcoarse and fine aggre-gates suggested in Table 1 may be adopted

TABLE I. SUGGESTEDCOMPATIRLE GRADATION

O E C O A 1 E S E AND FINEAGGREGATES F O R T H E PURPOSE OF GAP-GRADING

Coarse aggregate Number of(Single sized) g ~

(mm)

I. 6350

2 . 5040

23

2

201010- 4 + 7 5

II or L I !III or IV

10 4.75 III or IV

3 loril

2 lorli

3

Ilorli!

For more details regarding design of gap graded cement concretemixes, reference may be made to IRC : 59-1976.

3.2.3. Fine aggregate Fine aggregate shall preferably benatural sand. Crushed stone sand may also be used satisfactorilyin concrete. The fine aggregate shall conform to IS : 383-1970excepting that in Grading Zone IV, the permissible percentagepassing limits on 300 and 150-micron sieves shall be 15-55 percent and 0.20 per cent respectively instead of 15-50 per centand 0-15 per cent as stipulated in IS Specification. Curshed

sand is usually more angular in shape than naturally occurringsand, and for this reason may tend to make the mix a little moreharsh. in some cases, it may prove advantageous to use a mixtureofnaturally occurring sand and crushed stone sand if the former isnot obtained in adequate supply or where its grading is poor. Bulk-ing due to presence of moisture in the fine aggregate should beaccounted for when volumetric batching is employed.

Smaller sizecoarse aggregate

(Single sized)(mm)

Fine aggregate(as per IS: 383-1970,

para 2.2,3.)Sand Zones

3. 4020

4 . 2010 2 IlorlIl

3 IIIorIV

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3.3. Water

Water used in niixing or curing of concrete shall be clean andfree from injurious amounts of oil, salt, acid, vegetable matter or

other substances harmful to the finished concrete. It shall meet therequirements stipulated in clause 4.3. of IS : 456-1978 Code ofPractice for Plain and~Reinforced Concrete (Second Revision).Potable waters are generally considered satisfactory for mixing orcuring.

3.4. Reinforcement

3.4.1. Steel wire fabric This shall conform to the require-ments ofIS: 1566-1967 Specification for Hard-drawn Steel WireFabric for Concrete Reinforcement.

3.4.2. B a r mats : The steel in bar mats shall conform to therequirement of IS : 432-1966 Specification for Mild Steel andMedium Tensile Steel Bars and Hard-drawn Steel Wire for Con-crete Reinforcement.~ The bars shall be ofthe size and spacingshown on the plans. All junctions of longitudinal and transversebars shall be securely tied or welded together.

3.5. Dowel an d Tie Bars

Dowel and tie bars shall be plain round steel bars conform-ing to the requirements of IS : 432-1966.

3.6. Prenioulded Joint Filler

Premoulded joint filler shall be ofthe thickness shown on thedrawings within a tolerance of :~1.5 mm. It shall be 25 mm lessin depth than the thickness ofthe slab, within a tolerance of+ 3mm and of the full width between road forms. Holes to accommo-date dowel bars shall be accurately bored or punched out.

The joint filler shall comply with the requirements of IS1838-1961 Specification for Preformed Fillers for Expansion Joint inConcrete, Non-extruding and Resilient Type (Bitumen-impregnated

Fibre).

3.7. Joint Sealing Compound

The sealing compound shall comply with the requirements ofthe IS : 1834-196 1 Specification for Hot Applied Sealing Com-pounds for Joints in Concrete.

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3.8. Quality Control Tests on Materials

The quality control tests on the materials and the frequencyof tests are given in IRC: Special Publication No. 1 1 Handbook of

Quality Control for Construction of Roads and Runways (FirstRevision). These are reproduced in Table 2 for ready reference

TABLE-2 Q U A L I T Y CoFrrRoL T E S T S O N M A T E R I A L S

1 . Cement Physical and chemi-cal tests

ii) Deleteriousconstituents

iii) Moisture Content

i i i ) A l k a l i - a g g r e g a t ereactivity

4. Water Chemical test

Test Method Minimum desirablefrequencies

IS: 269/445/ Once for each source1489/8112 ofsupply and occa-

sionally when calledfor in case of longand/or improperstorage

IS :2386/Pt. (I) One test for 1 5 m ofeach fraction ofcoarse and fineaggre-gate

-do-

Regularly as requiredsubject to a mini-mum ofone test perday for coarse aggre-gate and tw o tests perday for fine aggregate

-do- Once for each sourcefor deriving themoisture content

bulking relationshipOnce for each sourceof supply and subse-quently when war-ranted by changes inthe quality of aggre-g a t e

IS : 2 3 86 / As required(Pt. V )

IS : 2386/ -do-(Pt. VII)

IS : 4 5 6 Once for approval ofsource of supplysubsequently only incase of doubt

M a t e r i a l Te st

i) Gradation2 . Coarseandfineaggre-gates

3 . Coarseaggre-gate

IS: 2386/ P t . ( I I )I S : 2 3 8 6 /P t . ( I I I )

iv ) Bulking of finea g g r e g a t e ( f o rvolume h a t c h i n g )

i) L o s Angelesabrasion valuejAggregate impacttest

i i ) S o u n d n e s s

IS : 2386/ (Pt. IV)

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4 , PROPORTIONING O F CONCRETE

4.1. Proportioning on the Basis ofStrength

4.1.1. As the stresses induced in concrete pavements aremainly fiexural, it is desirable that their design is based on thefiexural strength of concrete. For economical design, the designvalue adopted for fiexural strength of pavement concrete shall notbe less than 40 kg/sq. cm at 28 days. The mix shall be so designedas to ensure the minimum structural strength in the field with thedesired tolerance level. To achieve the desired minimum strengthin the field, the mix in the laboratory shall be designed for some-what higher strength, making due allowance for the type and ex-

tent ofquality control feasible in the field.

With S = minimum strength ofconcrete in the field at 2 8 days,S == average strength ofconcrete at 28 days for which the mix

shall be designed in the laboratory,

== dimensionless factor for the desired tolerance level, and

v = expected co-efficient of variation (per cent) offield testsamples, based on a knowledge of the type ofcontrol v i z ~ .

very good, good or fair, feasible at site,

S= ___

The values oftolerance level factor t, and coefficient of varia-tion for normal paving concrete are given in Table 3 for differentdegrees of quality control for genera! guidance in concrete mix

design.

T A B L E 3 . VALUES OF TOLERANCE LEVEL FACTOR t AND COEFFICIENT 01VARIATION V FOR DIFFERENT DEGREE C O F Q U A L i T Y C O N T R O L

Degree ofqualitycontrol

Premissibletolerance

Tolerancefactor

t

Coefficientofvariation

V

Very Good I in iS 1,50 7%

~_

Good 1 iii 15 1.50 10%

Fair 1 in 1 0 1.28 15%

Note : Very Good quality conira! :Control with weigh-batching, use ofgraded aggregates, moisture determination ofaggregates etc. Rigid

b h li l

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Good quality control: C o n t r o l w i t h w e i g h - b a t c h i n g , u s e o f gradeda g g r e g a t e s m o i s t u r e d e t e r m i n a t i o n of a g g r e g a t e s e t c . c on st a n t s u p e r .v i s i o n b y t h e quality control team,

Fair quality control: Control w i t h volume-batching for aggregates.Occasional checking of aggregate moisture. Occasional supervision

by the quality control team.

4.1.2. The paving concrete mix should preferably be design-ed in the laboratory and controlled in the field on the basis ofitsfiexural strength. Where this is not possible, correlation betweenflexural and compressive strengths should first be established onthe basis ofactual tests on additional samples made for the purposeat the time ofdesigning the mix in the laboratory and quality controlthen exercised on the ba3is ofcompressive strength, so long as the

materials and mix proportions remain substantially unaltered.

4.1.3. For design of cement concrete mixes guidance may behad from IRC : 44-1976 Tentative Guidelines for Cement ConcreteMix Design for Road Pavements and IRC : 59-1976 TentativeGuidelines for Design of Gap-graded Cement Concrete Mixes forRoad Pavements.

4. 1 .4. Where a heavy duty Wear-resistant concrete pavement

is desired, such as for manouvering and storage areas of trackedvehicles or for anticipated concentrations of steel tyred traffic,concrete with minimum field compressive strength of450 kg/cm

2 at28 days, shall be adopted for wearing course, the 28 days minimumfiexural strength requirement in the field remaining 50 kg/sq, cm.

4.1.5. The minimum cement content for the mix correspond-ing to 40 kg/cm2 flexural strength in the field at 28 days shall not,however, be less than 350 kg per m8 of concrete and for mix corres-

ponding to 450 kg/cm2 compressive strength in the field at 28 daysshall be minimum of400 kg per m3 ofconcrete.

4.2. Approximate Proportions

The approximate proportions by weight (or by volume, onlyi n unaviodable cases) necessary to produce concrete satisfyingtheabove c o n di t i o n s using aggregates from the sources designated maybe furnished in the tender documents, for guidance only, it being

expressly understood that this information is only for the conven-ience ofthe bidder,

4.3. Field Mix

After the award of the contract, the proportions, that is, thefield mix, determined by the laboratory for the particular aggregates

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approved by the engineer shall govern. These proportions will becorrected and adjusted by the engineer to compensate for moisturecontent in the aggregates or fluctuations in the grading of coarse andfine aggregates at the time ofuse.

Where fine aggregate is permitted to be measured volumetri-cally, due allowance should be made for its bulking.

4.4. Water Content and Workability

The water content per batch of concrete should be maintainedconstantly except for suitable allowances to be made for free

moisture and absorption by aggregates determined from time totime during construction. Adjustments for workability shall be madeby variations in the ratio of the coarse to fine aggregate or improv-ing upon their grading without change in cement content or water-cement ratio. The slump of the concrete mix for pavements com-pacted by vibration should not be more than 25 mm, preferably bet-ween 0 and 12 mm, and that by manual compaction not more than50 mm. No price adjustment would be permissible for variations inthe gradations of the aggregates or in the ratio ofcoarse to fine

aggregates necessitated from adjustment at site.

4.5. More information about the desirable properties ofpaving concrete is given in Supplementary Notes, para N. I.

5 . TOOLS, EQUIPMENT AND APPLIANCES

5.1. General

All tools, equipment and appliances necessary for properpreparation of subgrade, laying of sub-base and batching, mixing,placing, finishing and curing of concrete shall be at the project sitein good working condition and shall have been inspected by theEngineer-in-charge before the paving operations are permitted tostart. Throughout the construction ofthe project, the constructionagency shall maintain all necessary tools, equipment and appliancesin first class working condition to ensure proper execution of thework. Arrangements shall also be made for requisite number ofstand-by units in the event of break-downs during construction.

5.2. List ofTools, Equipment and Appliances

5.2.1. A list oftools, equipment and appliances required forth diff t h f t d t ti i i b l

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This list pertains to semi-mechanised type of construction only, as

practised most in this country.

(a) Subgrade and Sub-base Compaction

(i) Compaction equipment (three wheeled or tandem roller,pneumatic roller, vibratory roller or sheep-foot roller)

(ii) Watering devices (water lorries, bhisties/water carriers or

watering cans),

(b) Preparation ofSub-base for Concreting and Formwork

( i ) Scratch templates or strike boards

(ii) Bulk-heads( i i i ) P i c k a x e s , s h o v e l s a n d s p a d e s

( i v ) Formwork a n d i r o n s t a k e s

(c) Concrete Manufacture

(i) S h o v e l s a n d s p a d e s(ii) S i e v i n g s c r e e n s

(iii) W e i g h b a t c h e r(iv) Aggregate measuring boxes (only where volume batching of

aggregates is permitted as a special case)

( v ) W a t e r pump

( v i ) Water measures

(vii) Concrete mixer

( d ) T r a n s p o r t a t i o n , L a y i n g a n d C o m p a c t i o n o f Concrete:

( i ) W h e e l b a r r o w s/ i r o n pa n s

(ii) Wooden bridges(iii) Spades(iv) Concrete vibrators (both internal and screed board types)

(v) Wooden hand tampers

(e) Finishing Operations : Surface and Joints

( i ) Wooden b r i d g e s

(ii) Floats (longitudinal and long-handled wooden floats)( i i i ) Templates

(iv) Three-metre long straight edges including one master straightedge

(v) Graduated wedge gauges( v i ) M i l d s t e e l s e c t i o n s a n d b l o c k s f o r m a k i n g j o i n t grooves

(vii) Edging tools including double-edging tools( v i i i ) C a n v a s b e l t s

( i x ) Long h a n dl e d b r o o m s

( x ) Diamond c u t t e r ( w h e n m a k i n g s a w - c u t j o i n t s )( x i ) Grinder (for grinding local high spots)

(1 ) Curing

(i) Hessian cloth burlap or polyethylene sheeting

( i i ) W a t e r i n g d e v i c e s a s i n a ( i i ) ( f o r p o n d i n g o p e r a t i o n )

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( g ) C l e a n i n g a n d S e a l i n g of J o i n t s

( i ) l r o n r a k e r

(ii) Coir brush(iii) C y c l e pu m pf pn e u m a t i c a i r blower( i v ) Kerosene st ov e( v ) T h e r m o m e t e r

( v i ) T r a n s f e r r i n g p o t

( v i i ) P a i n t e r s b r u s h

(viii) Pouring kettle(ix) Scraper

5.2.2. Specifications for different tools, equipment andappliances are given in IRC 43-1972 Recommended Practicefor Tools, Equipment and Appliances for Concrete PavementConstruction, This ~document also gives a list of other snialltools, equipment and appliances ; minimum balanced set of tools,equipment and appliances ; their routine maintenance and upkeep;and details of field laboratory equipment.

6 . PREPARATION OF SUBGRADE AND SUB-BASE

6.1. General.

The suhgrade or sub-base for laying ofpaving concrete slabsshall comply with the following requirements

(1) that no soft spots are present in the subgrade or sub~base

(2) that the uniformly compacted subgrade or sub-base extends atleast 300 mm on either side ofthe width to be concreted

(3) that the subgrade is properly drained

(4) that the minimum modulus ofsubgrade reaction obtained with a

p l a t e b e a r i n g t e s t s h a l l be 5.5 k g j c m .

The manner ofachieving these requirements shall be deter-mined depending upon the type of subgrade or sub-base on whichconcrete is to be laid, and the following requirements in respect oft h e v a r i o u s types s h a l l be s a t i s f a c t o r i l y m e t . The c o n s t r u c t i o nprocedures for subgrade and sub-bases should follow relevantiRC specifications, and quality control should be exercised as laiddown in ERC SP- 11.

6.2. Subgrade

6.2.1 - Where the type ofsoil in the formation of the road isof a quality to ensure the r e q u i r e m e n t s i n t h e aforementioned p a r a ,no intermediate s b base need be sed The t 150 mm l of

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the formation shall be compacted at or slightly above the optimummoisture content to the exact profile shown in the drawing. Itshall be checked for trueness by means ofa scratch template (see.IRC 43-1972 for details) resting on the side forms and s e t t o t h eexact profile ofthe base course, The template shall be drawn alongthe forms at right angles to the centre line of the road. Uneven-ness of the surface as indicated by the scratch points shall notcxceed 12 mm in 3 m. The surface irregularities in excess of thisshaU be properly rectified and the surface rolled or tamped until itis smooth and firm. The subgrade shall be prepared and checkedat least two days in advance of concreting.

6.2.2. Where no sub-base is considered necessary and con-crete is laid directly on the prepared subgrade, the subgrade shallbe in moist condition at the time the concrete is placed. Ifneces-sary, it should be saturated with water not less than 6 hours normore than 20 hours in advance ofplacing concrete. Ifit becomesd r y prior t o t h e a c t ua l placing ofthe concrete, it shall be sprinkledwith water taking care to see that no pools ofwater or soft patchesare formed on the surface. It is desirable to lay a layer of water-proofpaper whenever concrete is laid directly over soil subgrade.

Where s u c h a layer of waterproof paper is proposed to be placedbetween c o n c r e t e and t h e s u b g r a d e , the moistening of t h e subgradeprior to placing of the concrete shall be omitted.

6.3. Sub-base

6.3.1. Where the subgrade is of a type not satisfying therequirements of pam 6.1, a sub-base layer should be providedbefore laying the concrete. The sub-base may be of granularmaterial, stabilised soil or semi-rigid material as listed below

(a) Graim!ar nrate~ lal

(i) one layer flat bricksoling having joints filledwith sand under onelayer ofwaterbound macadam conforming to IRC: 19-1977.

(ii) Two layers ofwater bound macadam,(iii) Well-graded granular materials like natural gravel, crushed

slag, crushed concrete, brick metal, laterite, kankar etc. con-forming to IRC: 63-1976.

(iv) Well-graded soil aggregate mixtures conforming toIRC: 63-1976.

(b) Stabilised soilL o c a l s o i l or moorum s t a b i l i s e d w i t h l i m e or l i m e - f l y a sh orcement, as appropriate to give a minimum soaked CBR of, 50a f t e r 7 d a y s c u r i n g . F or g u i d a n c e a s r e g a r d s design of mixesw i t h l i m e o r cement, r e f e r e n c e ma y b e made t o IRC: 51 and 50

i l

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(C) Sem i rigid urn teria?

(i) Lime-burnt clay puzzolana concrete. The lime-puzzolanamixture should conform to LP. 40 or L.P. 20 of IS : 4098-1967.The 28 day compressive strength ofthe concrete should be in

the range of 40-60 km/cm2.(ii) Lime-fly ash concrete conforming to IRC : 60-1976.

(iii) Lean cement c on c r e t e or lean cement-fly ash concrete conform-

ing to IRC: 74-1979,

6.3.2. Thickness of sub-base should be 15 cm when thematerial used is ofany ofthe types listed in paras .6.3.1 - (a) and (b).This may, however, be reduced to 10 cm for semi-rigid materials

in para 6.3.1. (c). The sub-base should be constructed in accor-dance with the respective specification and the surface finished tothe required lines, levels and cross-section.

6.3.3. Where the suhgrade consists of heavy clay (L.L.>50)such as black cotton soil, the sub-base should be laid over a 15 cmthick blanket course consisting ofnon-plastic granular material likelocal sand, gravel, kankar, etc. or local soil stabilised withI i i n c .

6.3.4. In water-logged areas and where the sub-grade soilis impregnated with deleterious salts such as sodium sulphate etc.in injurious anlotlnts** a capillary cut-off should be provided beforeconstructing the sub-base, vide details given in para 6.4.

6.3.5. The sub-base or blanket course, as the case may be,shall be laid over a properly compacted subgrade to give uniformsupport.

6.3.6. The sub-base shall he in moist condition at the timethe concrete is placed. There shall, however, be no pools of wateror soft patches formed on the sub-base surface. In case where asand layer is placed between the sub-base and pavement concrete,a layer of water-proof paper shall be laid over the sand layer.No moistening of the sub-base shall be done in this case.

6.4. Capillary Cut-off6.4.1. As a result ofmigration of water by capillarity from

the high water table, the soil immediately below the pavement getsmore and more wet and this leads to gradual loss in its bearing

* * S u l p h a t e c o n c e n t r a t i on ( a s s u l p h u r t r i o x i d e ) more than 0.2% in s u b g r a d esoil and more than 0.3% in ground water.

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value besides unequal support. Several measures such as depres-sing the sub-soil water table by drainage measures, raising oftheembankment and provision of a capillary cut-off are available formitigating this deficiency and should be investigated for arriving atthe optimum solution. However, where deleterious salts in excessof the safe limits are present in the subgrade soil, a capillary cut-offshould be provided in addition to other measures.

6.4,2. The capillary cut-off may be a layer of coarse or finesand, graded gravel, bituminised material, or an impermeablemenibrane. Layer thicknesses recommended for different situationsare given in Table 4,

TABLE 4. RECOMMENDED THIcKNEss OF SAND/GRADED GRAVEL LAYER FO RCAPILLARY Cut-on

Thickness of layercm

SI. Situation Coarse sand Fine sand Graded gravelNo. (mean dia (mean dia (4 0 mm and

0.64 mm) 0.18 mm) down without

F f i n e s )

I, Water t a b l e a t t h e s a m e l e v e l 1 5 4 5 1 5as the subgrade surface

2. Embankment about 0.61.0 m 12 35 1 1h i g h

3. Embankment about 0.61.0 m high 10 30 8

but with the top 15 em subgradelayer being ofsandy soil havingP1 of5 or less and sand contentnot less than 50 per cent

6.4.3. Cut-off with bituminised or other materials my beprovided in any ofthe following ways

(i) Bituminous impregnation using primer treatment

50 per cent straight run bitumen (80-100) with 50 per cent highs p e e d d i e s e l o i l or i t s e q u i v a l e n t i n t w o a p p l i c a t i o n s of 1 kg s q . n i .e a c h , a l l o w i n g t h e f i r s t a p p l i c a t i o n t o p e n e t r a t e b e f o r e a p p l y i n g t h esecond one,. These applications should b e g i v e n under t h e roadbedas well as onto the sides.

(ii) Heavy-duty tar feltEnveloping s i d e s a n d b o t t o m o f the roadbed with heavy-duty tar

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(iii) Poly ethylene envelopeEnveloping sides and bottom of the roadbed with polyethylenesheets ofat least 400 gauge.

(iv) Bituminous stab ilised soilProviding bituminous stabilised soil in a thickness of at least4 cm.

Note: E x p e r i e n c e on t h e successful use of the above capillary cut-oilsis, however, limited.

6.4.4. For more details about mitigating the adverse effectsof high water table, reference may be made to IRC:34-1970

Recommendations for Road Construction in Waterlogged Areas.

6.5, Frost Affected Areas

6.5.1. In frost affected areas, the sub-base may consist ofanyofthe specifications given in 6.3.1. (a), (b) or (c) excepting that inthe case of the items 6.3.1. (b) and 6.3,1. (c), the compressivestrength ofthe stabilised or semi-rigid material cured in wet condi-tion shall be at least 35 kg/cm

2 at 7 days. For moderate condi-tions, such as those prevailing in areas at an altitude of3,000 mand below, the thickness of frost affected depth will be about45 cm. For protection against frost, the balance between the frostdepth (45 cm) and total: pavement thickness should be made up withnon-frost susceptible material.

6.5.2. For extreme conditions, such as those prevailing inareas above an altitude of3,000 m, the foundation may be designedindividually for every location after determining the depth of

frost.

6.5.3. The suggested criteria for the selection of non-frostsusceptible materials are as follows

(i) Graded gravel : Not more than 8 per cent passing 75 micron sieve.Plasticity index not more than 6 . Liquid limit not more than 2 5 .

(ii) Poorly graded sands, generally 1 0 0 per cent passing 4.75 mms i e v e

Max. 10 per cent passing 75 micron sieveMax. 5 per cent passing 50 micron sieve

(iii) Fine uniform sand, generally 100 per cent passing 425 microns i e v e

~ 1 8 per cent passing 7 5 micron sieveMax. 8 per cent passing 50 micron sieve

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6.6. Existing Macadam Sub-base

6.6.1. When concrete pavement is laid over existing waterbound macadam road, it shall be ensured that the existing macadani

road constituting the sub-base extends over the required width andhas a minimum thickness of 150 mm. Where the general uneven-ness of the surface varies by more than 25 mm from the requiredcross-section, the surface can be reconditioned after scarifying andadding suitable quantities ofmetal over the entire area includingadditional metal for correcting the camber and grade as required.Alternatively, depressions in the surface may be levelled up byusing lean cement concrete or lime-pozzolana concrete or lime-fly ash concrete or lean cement-fly ash concrete as per para 6.3.1

(c), properly compacted prior to laying of the concrete pavementslab, in addition to the depth that may be required for correction ofthe camber,

Where the width of the existing water bound macadamsurface falls short of the width to be concreted by not more than300 mm on either side and the condition of the surface is soundenough for receiving the paving concrete, the extra width may be

made up by placing at least 100 mm depth oflean cement concreteor lime-puzzoinna concrete or lime-fly ash concrete or lean cement-fly ash concrete as per para 6.3.1. (c) in trenches ofrequired widthat the sides ofthe existing metalling after taking care to see that thebottom ofsuch trenches is well compacted by suitable tampersbefore placing ofthe new sub-base material. The correction to theunevenness ofthe surface and for camber shall follow the samelines as in the preceding paragraph.

Where the existing water bound macadam surface falls shortofthe width proposed to be concreted by more than 300 mm oneither side, the sub-base shall be reconstructed by removing theentire material ofthe macadam and forming a fresh macadamsurface of the required width by excavation and addition of newmetal to the extent necessary over the entire width satisfying therequirements stated earlier.

6.7. Existiug Black-topped Surface

Where concrete slabs are to be laid over existing black-toppedsurfaces, no special treatment is necessary where the surfaceextends over the required width and is worn uniformly under traffic.Otherwise, steps suggested in para 6.6. should be followed.Concrete shall not be laid on black-topped surfaces having soft

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spots caused by excessive bitumen or where thick premixed carpetshave been rutted under traffic. In such cases the entire bituminoussurfacing material shall be removed up to the top ofthe compactedmacadam surface and the surface shall be prepared as detailed inpara 6.6.

7 . FORMS

7 . 1 . Steel Forms

All side forms shall be of mild steel unless use of woodensections is specially permitted. The steel forms shall be mild steel

channel sections ofdepth equal to the thickness ofthe pavement.

The sections shall have a length ofat least 3 m except oncurves of less than 45 m radius, where shorter sections may beused. When set to grade and staked in place, the maximumdeviation ofthe top surface ofany section from a straight line shallnot exceed 3 mm in the vertical plane and 5 mm in the horizontalplane. The method ofconnection between sections shall be suchthat the joint formed shall be free from difference in level, play or

movement in any direction. The use ofbent, twisted or worn-outforms will not be permitted. At least three stake pockets for bracingpins or stakes shall be provided for each 3 m ofform and the brac-ing and support must be ample to prevent springing ofthe formsunder the pressure of concrete or the weight or thrust of machineryoperating on the forms.

The supply offorms shall be sufficient to permit their remain-

ing in place for 12 hours after the concrete has been placed, orlonger ifnecessary in the opinion of the Engineer-in-charge.

7.2. Woodeu Forms

Wooden forms may be used only when specifically permittedin the drawing with the exception that their use is herein approvedfor all curves having radii of less than 45 m. Wooden formsshall be dressed on one side. They shalt have minimum base width

of 100 mm for slab thickness upto 200 mm and & minimum basewidth of 15 0 tnm for stabs over 200 mm thick. Their depth shallbe equal to the thickness of the pavement. These forms whenused on straights shall have a minimum length of 3 m. Formsshall be held by stakes set at intervals not exceeding 2 in, Twostakes, one on each side, shalt be placed at eachjoj~(. The forms

halI hc firmly nailed or secused to the side stakes and scutely

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braced at joints, where necessary, so that no movement will resultfrom the pressure of the concrete or the impact ofthe tamper andduring finishing work. Wooden forms shall be capped along theinside upper edge with 50 mm angle iron, well recessed and keptflush with the face ofthe wooden forms. The maximum deviationofthe top surface of any section from a straight line shall notexceed the~~stip~~latk~nslaid down in para 7.1.

7.3. Setting of Forms

The forms shalt be jointed neatly and shall be set with exact-ness to the required grade and alignment. Both before a n d after

the forms are placed and set, the subgrade or sub-base under theforms shall be thoroughly tamped in an approved manner. Suffi-cient rigidity shall be obtained to support the forms in such aposition that during the entire operation of compacting and finish-ing ofconcrete they shall not at any time deviate more than 3 mmfrom a straight edge 3 m in length. Forms which show a varia-tion from the required rigidity or alignment and levels shown in thedrawing, shall he reset or removed, as directed. The length andnuniber ofstakes shall be such as to maintain the forms at the

correct line and grade. All forms shall be cleaned and oiled eachtime before they are used. Forms shall be set for about 200 mahead ofthe actual placing of concrete.

8 . JO1NTS

8.1. General

The location and type ofjoints shall be as shown in the draw-ing. The edge ofthe slab at all joints shall be rounded offwith anedging tool having a radius of 6 ~ 1 mm. The concrete along theface of all joints and around alt tie bars and dowels shall be com-pacted with an internal vibrator inserted in the concrete andworked along the joint and around all tie bars and dowels to ensurea concrete free from honeycombing.

8.2. Types of Joints

There are three general types of joints. These are

(i) Expansionfeb11. Such joint provides the space into which pave-ment can expand thus relieving compressive stresses due to expan-sion and inhibiting any tendency towards buckling of concretes l a b s .

(ii) Contraction foul. S u c h joint relieves tensile stresses in the con-crete d t formation of irreg lar cracks d to restraint in

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free contraction of concrete. Contraction joints also relieve stressesdue to warping.

(iii) Warpingjoint. Such joint relieves stresses due to warping. Theseare commonly used for longitudinal joints dividing the pavement

into lanes.

In addition, construction joints are provided whenever cons-truction operations require them. These are full depth joints andmay belong to any of the above types.

All joints shalt be carefully installed in accordance with thelocation and details given on the plans. The details of differenttypes ofjoints are shown in Appendix-B.

&3. Transverse Joints

8.3. 1 . General : Transverse joints can he expansion, contrac-tion or construction joints and shalt be placed as indicated on thedrawing. They shall make a right angle with the centre line of thepavement and surface of the sub-basefsubgrade. Contractionand expansion joints shall be continuous from edge to edge ofthe pavement through all lanes constructed at the same or differentt i rues.

8.3.2. Transverse expansion joints: These shall extend overthe entire width ofthe pavement. They shall be ofthe dimensionsand spacing as shown on t h e d r a w i n g .

Dowel b a r s ( s e e Supplementary Note N. 4) as per dimensions,location and spacing shown on the drawing are required at expan-

sion joints to transfer wheel loads to the adjacent slab. For slabsofthickness less than ISO mm no dowel bars may be provided(IS: 6509-1972). The premoulded expansion joint filter, a com-pressible material used to flit the gap between adjacent slabs atexpansion joint shall conform to IS: 1838-1961. The height ofthefiller board shall be such that its top is 25 mm below the surface ofthe pavement. The dowel bars shall be held accurately in posi-tion during the placement, compaction and finishing of concreteat and near the expansion joint. This and the protection ofthe

joint groove during construction may be achieved by means ofsufficiently strong bulkheads (as per IRC: 43-1972) with holes drill-ed along the centre tine to accommodate the dowel bars and a mildsteel section (as per IRC: 43-1972) respectively. The tatter shalL beoiled or greased before placing in position to avoid bonding withconcrete. The top and bottom edges of the bulkheads and mildsteel section shall be shaped to correspond to the camber of the

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pavement at the joint. If considered convenient, two-piece splitbulkheads may a l s o be used. When dowel bars are provided,bulkheads shalt be uscd in pairs, one at the joint location, and theother some distance away to hold the projecting ends ofthe dowel

bars to maintain their alignment.

For cases where dowel bars are not provided, one singlebulkhead without holes will be adequate.

The bulkheads shalt be securely staked in place at righta n g l e s t o t h e c e n t r e l i n e and s u r f a c e of t h e pavement with sufficientstakes to hold them in the specified position.

After the concrete has sufficiently hardened, the mild steelmetal section shall be removed carefully without disturbing theedges, The edges shalt then be rounded with an edging tool. Forf a c i l i t a t i n g removal of t h e mild s t e e l s e c t i o n a s well as e d g i n g

operation, t h e t o p of t h e section may be f l a r e d on both s i d e s w i t h

the required curvature ofa rounded edge.

Under no circumstances shall any concrete be left above theexpansion joint filter or across the joint at any point. Any con-

crete spanning the ends ofthe joint next to the forms shall be care-fully cut away after the forms are removed.

8.3.3. Transverse contraction joints: These shall be placedas shown on the drawing and shalt be ofthe weakened plane ordummy groove type. They shall be constructed by forming inthe surface of the stab, a slot not less than 6 mm wide and havinga depth equal to one-third to one-fourth the depth ofthe pavementat the thinnest part of its section. This slot may be formed in a

manner approved by the Engineer-in-charge such as by pushinginto the the concrete a fiat bar or the web ofa T bar using asuitable vibratory device, removing the bar, and keeping the slotopen. It shall he ensured that no spalling of concrete occurs whileremoving the bar. The edges ofthe joint shall be rounded with anedging tool before the concrete hardens.

8.3.4. Transverse construction joints: These shall be placedwhenever placing of concrete is suspended for more than 30

minutes. Excepting in the case of emergency, construction shallalways be suspended at the regular site ofexpansion or contractionj o i nt s . I f t h e c o n s t r u c t i o n j o i n t is located at the site of an expan-sion joint, regular expansion joint shall be provided; ifat the site ofa c o n t r a c t i o n j o i n t or o t he rw i s e, t h e c on s t r uc t i on joint shalt be ofbutt type with dowels. Procedure of construction of butt typejoint is given in para 8 4 and details in Appendix B

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At alt construction joints, bulkhead shall be used to retain theconcrete and care shall be taken in striking offand finishing thesurface to the top face of the bulkhead. When work is resumed,the surface of concrete laid subsequently, shall conform to thegrade and cross-section of previously laid pavement, and a straightedge 3 in in length shall be used parallel to the centre line, tocheck any deviation in the surface ofthe two sections. Any devia-tion from the general surface in excess of3 mm shall be corrected.

8.4. Longitudinal Joints

8.4.1. These shall be of the plain butt type and shall belormed by placing the concrete against the face of the slab con-creted earlier. The face of the slab concreted earlier, shall bepainted with bitumen before placing offresh concrete.

8.4.2. Tie bars shalt be used at longitudinal joints and theyshalt be ofthe dimensions and at spacings shown on the drawing.Tie bars shall be supported so as not to be displaced during con-struction operations, Tie bars shall be bonded in the slabs acrosslogitudinal joints, and whilst casting the first slabs, they may bebent so that one end of them lies along the forms. After removalof the forms, bars shall be straightened so that they extend into theconcrete placed on the other side ofthe joint.

8.5. For details about arrangement ofthe different types of

joints, see Supplementary Note, N. 2.

9, CONSTRUCTION

9.1. Storage and Handling of Cement9.1.1. Cement shall not he stored for a long time and should

be used normally within six months of its date ofreceipt. Evenduring this period ofstorage it is essential that cement shalt beprotected from moisture by storing it in suitable sheds. A storageshed with a concrete floor laid on a well-drained foundation maybe satisfactory. Cement in bags shall be stored on boards raisedabove the floor level for the purpose of ventitation, and the bagsshall not touch the walls of the shed. Different consignmentsshould be separately stacked and used in order in which they havebeen received. When bulk supply cement is used, special storagefacilities such as covered hopper bins will be required.

9.1.2. Supply ofcement should be co-ordinated with its con-sumption so that it is not stored right through the rainy season, when

ll ti i di ti d C t h i l hi h

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have been caused due to improper storage or by pressure due toover-loading ofbags shall not be considered for use unless theselumps can be easily powdered with pressure between fingers.Before such cement is used, representative sample containing also

the lumps in fair proportion shall be taken and tested as perIS:269-t976, 8112-1976, 1489-1976, 455-1967 or 8041 E-1976 asthe case my he, to fulfil the minimum requirements.

9.1.3. Owing to the slightly detiquescent nature of rapid-hard ening cement special care should be taken in its storage and,in any case, it should not be stored for longer than three months.

9.2. Storage and Handling ofAggregates

9.2.1. The location and preparation of sites, minimum sizeofstackand the methods adopted for dumping and stacking toprevent segregation of coarse and fine material shall be subject tothe approval of the Engineer. Aggregates from different sourcesand/or of different gradings shall not be stacked together. Eachseparate size of coarse aggregate shall be stacked separately. Thestoring ofaggregates upon the carriageway or shoulders shalt notbe permitted.

9.2.2. Ifaggregates are stored in conical stacks, segregationwill be increased by the rolling ofthe coarser particles down thesides of the stacks. To avoid this, stacks should be built up inapproximately horizontal layers. Dry fine aggregate segregates andgets blown away easily ; it may be helpful to moisten it .

9.2.3. To assist in controlling the water/cement ratio, largefluctuations in the moisture content ofaggregates may be reduced by

storing the bulk ofthe material well in advance of use. For thispurpose, all washed aggregates shalt be stacked for draining atleast 12 hours before being batched. It is also a good practice toreserve the bottom 150-300 mm or so ofthe stacks as a drainagelayer. Where this cannot be done, the aggregates should not beplaced on the ground. In such case, somewhat raised planks,metal sheets or concrete bnse should be provided and laid to slopes.

9.2.4. The aggregates shalt be handled from the stacks and

fed into the mixer in such a manner as to secure the stipulatedgrading of the inateriat. Aggregates that have become mixedwith earth or other foreign material shall not be used. They shallbe washed clean before use.

9.3. Batching of Materials

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d e t e r m i n i n g t h e p r o p o r t i o n of i n g r e d i e n t s for the f i e l d m i x , t h e fineaggregate and each separated size of coarse aggregate shall beproportioned by weight in an approved weigh-batching plant andplaced into the hopper of the mixer along with the necessary

quantity ofcement. Cement shall be measured either by weightor by the bag as packed by the manufacturer. Where cement ismeasured by t h e b a g , i t would be n e c e s s a r y t o sample-check t h e

weight of the bags occasionally. Al! materials other than cementshall be calculated on the basis of one or more whole bags ofcement taking the weight of cement as 1440 kg/rn

3. The Engineermay pe r m i t t h e u s e of f r a c t i o n a l bags of cement provided they areaccurately weighed and are handled in a manner meeting with hisapprovat. Water may be measured by volume. Where it is

u n a v o i d a b l e , volume batching of aggregates may be permitted as aspecial case. It shoutd, however, be borne in mind that weigh-b a t c h i n g i s d e f i n i t e l y much more de s i r a b l e t h a n volume b a t c h i n g .

9.3.2. Ifbatching by volume is permitted, as a special case,separate measuring boxes shall be provided for the different aggre-gates. The boxes shallbe ofstrong construction provided with handlesfor convenient lifting and loading into the mixer. They shalt be ofs u c h s i z e t h a t it should be possible to measure out the r e q u i s i t e

quantity ofaggregate per batch in whole box or by multiples thereofand capable of being lifted by two men. Each box shall beprovided with a straight edge of required length for striking offa f t e r f i l l i n g . I f so di r e c t e d by the Engineer, improved facilities suchas tipping boxes of accurate capacity working on run-out railsarranged for direct delivery into the hopper of the mixer shalt beprovided by the construction agency. In volume batching, suitableallowance shall be made for the bulking of fine aggregate due tothe presence of water. For this purpose the bulking shalt bedetermined as per relevant Indian Standard Specification.

9.4. Mixing

9.4.1. General : The mixing of concrete shall be done in abatch mixer ofapproved type which will ensure a uniform distribu-tion of materials throughout the mass so that the mix is uniformin colour and homogeneous. All concrete shall be mixed in

quantities for immediate use.

The mixer shall be equipped with an approved water measur.ing device capable of accurate measurement ofwater required perbatch. The mixer shall preferably be equipped with a mechanicallyoperated pump for filling the mixer tank.

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The mixer, if so specified, shall be equipped with an approvedtiming device which will automatically lock the discharge leverd u r i n g t h e f u l l t i m e of mixing a n d r e l e a s e i t a t t h e en d o f t h emixing period ; the device shall also be equipped with a bell,

adjusted to ring each time the lock is released. Ifthe timing deviceg e t s br o k e n o r o u l o f o r d e r , t h e mixer w i l l b e permitted t o b e usedwhile the same is being repaired, provided an approved time-pieceequipped with minute and second hands is provided. Each batchshall be mixed for at least one and a halfminutes.

Spilling of the materials at either end of the mixer shalt becorrected by reducing the size ofthe batch and in no case shall thevolume of the mixed material per batch exceed the manufacturers

guaranteed capacity ofthe mixer. The type, size and number ofmixers shall be so chosen as to provide the required output withoutoverloading.

The mixing speed of the drum shall not be less than 15r e v o l u t i o n s per mi n ut e n or the peripheral speed ofthe drum greaterthan 60. m per minute.

The batch of cement, fine aggregate and coarse aggregate

shall be fed into the mixer simultaneously with the water beingintroduced either at the same time or before the dry materials.The entire contents of the drum shall be discharged before anym a t e r i a l s a r e placed t h e r e i n f o r t h e succeeding b a t c h .

The skip shalt be so maintained and operated that each batchwill be completely discharged into the mixing drum at the loadingo f t h e m i xe r . The mixer s h a l l b e cleaned a t s u i t a b l e i n t e r v a l s

while in use.

Pick-up and throw-over blades in the drum ofthe mixer whichare worn down 20 mm or more in depth shall be replaced with newblades.

9.4.2. Time of mixing : The mixing of each batch wiltcontinue not less than one and half minute after all the materialsare discharged into the mixer.

9.4.3. Retempering The r e t e m p e r i n g o f c o n c r e t e i . e .remixing with or without additional cement, aggregate or watershall not be permitted.

9 . 5 . Control ofWorkability an d Strength

9.5.1. Workability ofconcrete: The workability ofconcreteh l l b h k d b f i l t t t i f t

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test in accordance with IS I 199-1959 Method of Sampling andAnalysis ofConcrete. The frequency oftesting shall be one testper 10 m

3 of concrete and the permissible tolerances from thespecified value for workability shall be

Slump :E 12 mm

Compacting factor 0.03

Where variations beyond the permitted tolerances areobserved, necessary adjustment shalt be made keeping the water-

cement ratio same.

9.5.2. Strength ofconcrete: The strength of concrete shall

be determined either by compressive or fiexurat strength tests(preferably the latter, since concrete pavements are designed ont h e b a s i s of f i e x u r a l s t r e n g t h o f c o n c r e t e ) depending on t h e f a c i t i t i e savailable, For this purpose, during the progress of the work,cubebeam samples s h a l t b e c a s t f o r t e s t i n g a t 7 and 2 8 da ys .Sampling and testing shall be done in accordance with IS: 1199-1959Method of Sampling and Analysis ofConcrete and IS: 516-1959Method of Test for Strength of Concrete respectively. Theminimum frequency o f samples s h a l l b e 3 c u b e / b e a m samples f o r

each age of7 and 28 days for every 30 m3 ofconcrete. For d e t a i l sabout determination of concrete strength, reference may be madeto para 10.2.

On a paving job, the strength ofconcrete should be continu-ously monitored to ensure that the design strength is achieved. Incertain cases, because ofchange in the source ofcement or controlor climatic factors, the strength may show some variations whichwould require re-designing of the mix. However, where the

variations are not large, the mix proportions could be adjusted int h e f i e l d t h r o u g h a s i m p l e procedure explained in Appendix-Co b v i a t i n g t h e n e e d for r e d e s i g n i n g .

9.6. Transporting an d Placing ofConcre te

The concrete shall be mixed in quantities required for imme-d i a t e u s e a n d s h a l l b e d e p o s i t e d o n t h e s u b g r a d e / s u b - b a s e t o th erequired depth and width of the pavement section, in successive

b a t c h e s and i n continuous o p e r a t i o n w i t h o u t t h e us e o f i n t e r m e d i a t eforms or bulk-heads between joints. Care shalt be taken to see thatno segregation ofmaterials results whilst the concrete is being trans-ported from the mixer to the place where it is deposited. The usualmethod of transport of concrete in India is in pans as head loadsor in small wheel barrows. The spreading shall be as uniform aspossible to avoid rehandling of the concrete. Where, however, a

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certain amount ofre-distribution is necessary, it shall be done withs h ov e l s a n d n o t w i t h r a k e s . W h i l e b e i n g p l a c e d, t h e c o n c r e t eshall be rodded with suitable tools for slab thicknesses of 12.5 cmand less, so that formation ofvoids or honeycomb pockets is pre-vented. The concrete shall be particularty well placed and tappedagainst the forms and along all joints. For higher thicknesses aninternal vibrator shall be employed in lieu ofrodding of the con-crete. To effect adequate compaction, the concrete shall be placedwith appropriate surcharge over the final slab thickness. Theamount of surcharge will depend on the mode ofplacement ofc o n c r e t e a n d s h a l l b e d et er mi n ed b y t ri a l . In g e n e r a l , t h e r e q u i r e dsurcha rge is about 20 per cent ofthe required slab thickness. Anyp o r t i o n o f t h e b a t c h o f c o n c r e t e t h a t b e c o m e s s e g r e g a t e d w h i t edepositing it on subgrade shalt be thoroughly mixed with the mainbody of the batch during the process ofspreading. In case ofun-avoidable interruption, a full depth transverse joint shall be madeat the point of stoppage of work provided the section on which thework has been suspended is about 2 to 3 m tong.

In placing of concrete for two course construction, necessi-tated by either positioning of the reinforcement, a richer mix forthe wearing surface, or when thickness ofthe concrete is beyond20 cm, the bottom layer of concrete shall be struck offto therequired levels by a vibrating screed working on the side formswith n o t c h e s corresponding t o t h e depth o f t h e t o p c o u r s e o f con-crete. The vibrating screed should have a vibrating unit mountedon it similar to that ofthe screed used for compaction ofthe finalsurface of concrete. The time lag between laying ofthe two coursesshall not exceed the initial setting time ofcement.

9.7. Water-proof Paper

The water-proof paper, when necessary (see para 6.2.) shallbe laid by unrolling the roll prior to the placement of concrete.The paper shall be unrolled with an overlap ofnot less than10 cm,

9.8. Placement of Steel

9.8.1. Reinforcement: Reinforcing steel shatl be free fromdirt, scale or other foreign matter and rust of such degreeor development as to impair bond of the steel with theconcrete. The width of fabric sheets or bar mats shallb e such t h a t when p r op e r l y placed i n t o t h e work t h e

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extreme longitudinal bars or wires of the sheets or mats wilt belocated not tess than 50 nim and not more than tO O mm from theedges ofthe slab. Except for dummy joints, the length of fabric

sheets or bar mats shall be such that when properly placed intothe work, the reinforcement wilt be clear oftransverse joints bynot less than 50 mm and not more than 100 mm as measured fromthe centre ofthe joint to the ends oflongitudinal bars or wires ofthe sheet or mat.

W h i l e o v e r l a p p i n g t h e s h e e t s o r m a t s i n e i t h e r d i r e c t i o n , t h eo v e r l a p s h a l l b e a t l e a s t e q u a l t o the spacing between the bars or

wires in the respective direction or 40 times the diameter of thebar or wire, whichever is more.

Whilst using reinforcement in one layer, the concrete shall beplaced in two stages. The initial layer shall be uniformly struckoff to a depth corresponding to the reinforcement shown in thedrawings and lightly compacted by a screed to obtain uniformlevels. The reinforcing fabric sheet or bar mat shall then be placedon t h e c o m p a c t e d l a y e r o f c o n c r e t e a n d r e ma i n i n g d ep t h s h a l l b e

f i l l e d i n w i t h c o n c r e t e t h e r e a f t e r .

In doing this operation, the initial layer of concrete shall bestruck offto the entire width ofthe slabs and ofsufficient length topermit sheet or mat of reinforcement to be laid full length withoutfurther manipulations of the reinforcement. Displacement ofther e i n f o r c e m e n t d u r i n g c o n c r e t i n g o p e r a t i o n s s h a l l b e p r e v e n t e d .

Details about the types, design and location ofreinforcementare given in Supplementary Note, N. 3.

9.8.2. Load transfer devicesdowels: Transverse expansionjoints shall be equipped with dowels of the dimension and at thespacing and location indicated on the drawing. They shall befirmly supported in place, accurately aligned parallel to thesubgrade/sub-base, parallel to each other and parallel to thecentre line of the pavement, by means of appropriate dowel

supports. The dowel supports shall ensure that the dowels arenot displaced during construction. The permissible tolerancesin dowel bar alignment in both vertical a n d h o r i z o n t a l d i r e c-tions shall be1 mm in 100 mm for dowels of 20 mm ands m a l l e r diameters a n d :1: 0.5mm in 100mm for dowels ofdia-meter greater than 20 mm. One-half of each dowel shall bepainted with a thin film of bitumen and equipped with a tight

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provide space for the dowel when pavement expands and the jointcloses. This sleeve shalt be partly filled with cotton waste toprevent it being pushed too far on the dowel during construction.

h e s e s l e e v e s a r e not required on dowels, if used, in dummy con-raction or construction joints.

Design of dowels is discussed in Supplementary Note, N. 4.

9.8.3. T ie bars: Tie bars provided in longitudinal joints ofplain butt type to prevent opening ofsuch joints shall be bondedo the adjacent slabs on both sides of the longitudinal joint.

They are installed by providing appropriate (drilled) holes in theide forms depending on the size and spacing ofbars. They are

bent aside temporarily to avoid obstruction to construction trafficand straightened later at the time oflaying ofslab in the adjacentlane.

Design oftie bars is explained in Supplementary Note, N. 5 .

9 .9 . C o m p a ctio nan d Finishing

9.9.1. Compact ion: The pavement shall be compacted eitherby means of a power-driven paver-cum-finisher or by a vibratingscreed along with internal vibrators where the slab thickness ismore than 12.5 cm. For lesser thicknesses vibrating screed may besupplemented with manual rodding. For areas where the width ofhe slab is very small as at the corner of street junctions, etc. com-paction with wooden hand tampers may be adopted subject to theapproval of the Engineer-in-charge. In no case, however, handcompaction shalt be permitted for slab thicknesses beyond 10 cm.All compaction shall be done in accordance with the followingrequirem ents:

(i) Paver-cam-finisher of standard make or standard vibrating screedand internal vibrators shall be used for compaction. The vibratingscreed shall rest on side forms. it shall be lowered vertically on totheconcrete surface, evenly spread to the appropriate level abovethe base to provide the required surcharge for compaction; allowedto remain in position for a few seconds until compaction is com-

plete, then lifted vertically and lowered on to theadjacent strip ofuncompacted concrete. The amplitude ofvibration ofthe screedshati not be less than 1.5 mm and the speed of travel not morethan 0,6 m per minute. lhe screed shall again be taken slowlyover the surface, sliding with its axis slightly tilted away from thedirection ofsliding and the operation repeated until the requireddense, close knit textured surface is obtained, Compaction ofconcrete slabs upto 12.5 cm thickness may be done by means of

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in the case ofslabs of lower t h i c kn e s s , i n t e rn a l v i b r a t o r s ma y b eused with advantage for compacting the slab corners aad edges.The working ofthe vibrators shall be regularly checked and stand-byes shall always be maintained for emergency use.

(ii) Where hand tamp:op is permitted as a special case:

(a) Concrete with surcharge, as soon as placed, shall be struckoffu n i f o r n i l y a n d s c r e e d e d , t o s u c h l e v e l above the base that whencompacted and finished, the pavement shall conform to thegrade and cross-section indicated by the plans. the entiresurface shall then be tamped and the tamping operation con-tinued until a close knit dense surface is obtained.

(h) The tamper shall rest on the side forms and shall be drawnahead with a sawing motion, in combination with a series oflifts and drops alternating with lateralshifts, the aim of this

operation being compaction andscreeding

tothe

approximatel e v e l r e q u i r e d . S u b s e q u e n t t a n p i n g s h o u l d a d v a n c e a b o u t7 5 mm at a time in the direction in which the work is proceed-ing, and in the final stages tamping should be closer, about12 mm at a time until a level and dense surface is obtained.

(iii) Segregated particles of coarse aggregate which collect in front ofthe tamper or screed shall be thrown outside the forms or thoro-ughly mixed by hand with the uncompacted mass of concretealready placed. Under no circumstances shall such segregateparticles be carried forward and pushed on to the base in front of

the mass,(iv) Compaction by taniping or screeding shall be carried on till the

mortar in the mix just works up to the surface. Care shall beexercised and the operation of tamping so controlled as to preventan excess ofmortar and water from being worked on to the top.Repeated operation other than to secure the necessary compactionand to eliminate voids shall be avoided,

(v) Immediately after the tamping or screeding has been completed andbefore the concrete has hardened, i.e. whilethe concrete is still in a

plastic stage, the surface shall be inspected for irregularities with aprotile checking template and any needed correction made byadding or removing concrete followed by further compaction andfinishing.

9.9.2. Floating: As soon as practicabte after the concrete hasbeen compacted, its surface shall be smoothened by means ofalongitudinal float, operated from a foot-bridge. The longitudinal floatshall be worked with a sawing motion, while held in a floating posi-tion parallel to the carriageway centre line and passed graduallyfrom one side of the pavement to the other. Movements aheadalong the centre line of the carriageway shall be in successiveadvances ofnot more than one halfthe length ofthe float.

9.9.3. Straight-edging: After the longitudinal floating hasbeen completed, and excess water has disappeared, but while the

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oncrete is still plastic, the stab surface shall be tested for truenessith a 3 m straight edge. The straight edge shall be held in suc-

essive positions parallel to the road centre line in contact with theurface and the whole area gone over from one side of the slab

the other. Advance along the road shall be in successive stages of

ot more than one-halflength ofthe straight edge. Any area ofdep-ssion found shall be scooped to a depth of4-5 cm, filled immediate-with freshly mixed concrete, struck, compacted, and refinished.igh areas shall be cut down and refinished. The straight edging andfloating shall continue until the entire surface is found to be freeom observable departures from the straight edge and the slab has

he required grade and camber.

The slab surface shall be retested for trueness, before the con-

rete begins to set, with the 3 m long master straight edge and theraduated wedge gauge.

The straight edge shalt be placed on the surface in successiveositions, parallel to the carriageway centre line. Irregularities shalle measured with the help ofthe wedge gauge moved transverselyt various poitits until it touches both the straight edge and the con-rete surface.

At any point tested, the concrete shall not show a departurereater than 3 mm from the true surface. Ifat any place the depar-re exceeds this value, not more than 3 passes of the vibrating

creed shall be allowed and the surface tested again in the specifiedmanner. If the irregularity still exceeds the limit aforesaid, the

oncrete shall be removed to a depth of 50 mm or upto the top sur-ace of the reinforcement, if any. The area of concrete to beemoved shall be demarcated by the length ofthe straight edge inhe position ofmeasurement acrossthe full width ofthestab. Where

he point ofmeasurement in default is tess than 4.5 m from theearest transverse expansion joint, the whole area upto the jointhall be removed to the required depth. The concrete so removedhall not be re-used in the carriageway. Fresh concrete shall belaced, compacted and finished in the manner already described

n these specifications and shalt again be subject to test for accuracyffinish.

The foregoing procedure shall be adopted at each shifting of

he straight edge and the whole area shall be gone over from onede ofthe stab to the other. The straight edge shall advance longi-udinally in successive stages of not more than one-half the lengthfthe straight edge.

No extra payment shatl be made for the removal of theejected concrete and or laying fresh concrete.

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Although the concrete may be removed immediately followingmeasurement of the irregularity and while it is still wet, this shaltnot mean any waiver from complying with the requirements ofthisclause, if for any reason the concrete to be removed has already

hardened.

After straight edging ofthe surface, it shall be finished by bett-ing and brooming in the manner described in para 9.9.4. and 9.95.

9.9.4. Belting: Just before the concrete becomes non-plastic,the surface shall be belted with a two-ply canvas bett having suit-able handles to permit controlted uniform manipulation. The beltconforming to the stipulations laid down in IRC : 43-1972 shall be

operated with short strokes transverse to the carriageway centreline and with a rapid advance parallel to the centre line,

9.9.5. Brooming : After belting and as soon as surplus wateri f any, has risen to the surface, the pavement shall be given a broomfinish with an approved tong handled steel or fibre broom conform-ing to the stipulations laid down in IRC : 43-1972. The brooms h a l l b e putted gently over the surface ofthe pavement from edgeto edge. Adjacent strokes shalt be slightly overlapped. Broomingshall be perpendicular to the centre line of the pavement and soexecuted that the corrugations thus produced will be uniform incharacter and width, and about 1.5 mm deep. Brooming shall becompleted before the concrete reaches such a stage that the surfacei s l i ke l y t o b e t o r n o r u n du l y r oug h en ed b y t h e o p e r a t i o n . Thebroomed surface shalt be free from porous or rough spots, irregu-larities

1 depressions and small pockets, such as may be caused byaccidentally disturbing the particles of coarse aggregate embedded

near the surface.

9.9.6. Edging: After belting and/or brooming have been com-pleted, but before the concrete has taken its initial set, the edgesof the slab shall be carefully finished with an edging tool of 6 mmradius and conforming to the requirements laid down in IRC : 43-1972 so as to leave the pavement edges smooth and true to tine.

9.10. Cnring ofConcrete

Immediately after the finishing operations have been complet-ed, the entire surface ofthe newly laid concrete shall be coveredagainst rapid drying, and cured, Failure to provide sufficient covermaterial ofthe stipulated type, or inadequate supplies of water forcuring shall be adequate cause for immediate suspension of concret-

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9.10.1. Initial curing : After completion of the finishingopcrations, the surface of the pavement shall be entirely coveredwith wet hessian cloth, burlap or jute mats. The coverings usedshall be of such length (or width) that when laid wilt extend at

teast 500 mm beyond the edges ofthe slab, shall be so placed thatthe entire surface and both the edges of the stab are coniptetelycovered. They shall be placed as soon as the concrete has setsufficiently to prevent marring ofthe surface. Prior to their being

placed, the coverings shall be thoroughly wetted with water andplaced with the wettest side down, They shall be so weigheddown as to cause them to remain in intimate contact with thesurface covered. They shall be maintained fully wetted and inposition for 24 hours after the concrete has been placed, or untit

the concrete is sufficiently hard to be walked upon without suffer-ing any damage. To maintain the coverings wet, water shall begently sprayed so as to avoid damage to the fresh concrete. Ifit becomes necessary to remove the coverings for any reason, theconcrete stab shall not be kept exposed for a period of more thanhalfan hour.

Worn coverings or coverings with holes shalt not be permitted.Coverings reclaimed from previous use other than curing concrete

shall be thoroughly washed prior to use for curing purposes. Ifthec o v e r i n g i s f u r n i s h e d i n s t r i p s , t h e s t r i p s s h a l l b e l a i d t o o v e r l a p a tleast 15 0 mm.

Covering shall be placed from suitable wooden bridges (IRC:43-1972). Watking on freshly laid concrete to facilitate placingcoverings will not be permitted.

9.10.2. Final cnring: Upon the removal of the covering theslab shalt be thoroughly wetted and then cured by one ofthe follow-ing methods offinal curing

(a) Curing with wetearth: Exposed edges of the slab shall be bankedwith a substantial berm ofearth, Upon the slab shalt then be laid asystem of transverse and longitudinal dykes o f clay about 50 mmh i g h , c o v e r e d w i t h a blanket of sandy soil free from stones to pre-vent the drying up and cracking of clay. The rest ofthe slab shallthen be covered with sufficient sandy soil so as to produce a blanketofearth not less than 40 mm de p t h a f t e r w e t t i n g . Th e earth cover-

ing shall be thoroughly wetted white it is being placed on the surfaceand against the sides of the slab and kept thoroughly saturatedwith water for 14 days and thoroughly wetted down during themorn-ing ofthe 15th day and shall thereafter remain in place until theconcrete has attained the required strength and permission is givento open thepavement to traffic. When such permission is granted,the covering shall be removed and the pavement swept clean. Iftheearth covering becomes displaced during thecuring period, it shallb l d t th i i l d th d t t d

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(Ii) Impervious membrane method: The membrane shall consist ofa practically colourless impervious liquid ofa type approved by theEngineer-in-charge. The use of any membrane material whichwould impart a slippery surface to the pavement or alter its natural

colourwill

not be permitted. Liquid shall be applied under pres-sure with a spray nozzle in such a manner as to cover the entiresurface with a uniform film, and shall be of such character that itwill harden within 30 minutes after application. The amount ofliquid applied shall be ample to seal the surface ofthe pavementthoroughly. The liquid shall be applied immediately after the finish-ing ofthe surface and before the cement has set, or, ifthe pavementis first covered with burlap or hessian cloth or the like, it m ay beapplied upon their removal.

The impervious coating used for membrane curing shalt be

such that when applied to the surface oftest slabs made ofcementsand mortar in the manner prescribed for the use ofthe materials inthe field, the mortar shalt retain at least 90 per cent ofthe mixing

water when exposed for 14 4 hours to temperatures between 32 to38Cat a relative humidity of30 per cent to 50 per cent,

The mortar test slab used shall be composed of one partcement, 1.71 parts fine aggregate and 0.346 parts ofwater, byweight. The stab shall be cast in a non-absorbent watertight

mould, and shall remain in the mould throughout the test. Theslab shalt be approximately 400 mm long by 400 mm wide by50 mn-i deep. The coating shalt be applied to the exposed surfaceofthe slab within 2 hours ofthe time the slab is cast.

Materials for use as impervious coatings will be approved bythe Engineer-in-charge on the basis oftests outlined above. Therate of application of such coatings will be prescribed by theE n g i n e e r - i n - c h a r g e on t h e b a s i s o f t h e s a m e t e s t s .

This method ofcuring may he found suitable in locationswhere there is scarcity ofwater and in ghat sections.

9.11. Final Surface Test

The final surface test shall be made after the curing periodand after the removal ofthe material used for curing. The surface

shalt be of correct alignment, grade and contour specified. Anyspots higher than 3 mm and not higher than 6 mm above thecorrect surface, as shown by the 3.0 m straight edge and the wedgegauge, used in the manner prescribed above, shall be ground downwith an approved grinding tool to the required level. Whendeviation exceeds the foregoing limits, the slab shall be removed tothe full depth and replaced. The area ofpavement to he removed

d l d h ll b h d b h

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oints, adjacent to the deviation, across th Q full width of thestab.

9.12. Removing Forms

Forms shall not be removed from freshly placed concreteuntil it has set, or at least 12 hours, whichever is later. They shaltbe carefully removed in such a manner that no damage is done tothe edges ofthe pavement. After the forms have been removed,Ime slab edges shall be cleaned and any limited honey-combed

areas pointed up with 1:2 cement sand mortar, after which thesides ofthe slab shall be covered with earth to the level of thetop of the stab for final curing (para 9.10,2). Slabs with excessive

honey-combing as a result of inadequate compaction shalt ber enwved between nearest transverse joints.

9.13. Concre t ing during Monsoon Months

When concrete is being placed during monsoon months andwhen it may be expected to rain, sufficient supply oftarpaulins orother waterproof cloth shalt he provided along the line of work.Any time when it rains, alt freshly laid concrete which has not beencovered for curing purposes shall be adequately protected by meansoftarpaulins or other waterproof cloth. Any concrete damaged byrain shall be removed and replaced.

9.14. Concreting in Hot Weather

As placing of concrete in air temperatures above 40C, orabove 35~Ccombined with relative humidity below 25 per cent andor wind velocity higher than 10 km/hour, is attended with defectslike toss of workability throtigh accelerated setting, formation ofplastic shrinkage cracks, etc., it is recommended that unlessadequate p r e c a ut i on s a r e t a k e n , no concreting shall be done inconditions more severe than the above. The procedures recom-mended for adoption in case ofhot weather concreting are givenin 1RC : 61-1976 Tentative Guidelines for the Construction ofCement Concrete Pavements in Hot Weather. Briefdetails oftheprocedure are given below

Aggregates, cement and water shall be protected from the direct sun

and mixing operations shall also be carried out in shade. In additionportable shelters shall be provided to protect the concrete during placingand finishing operations. This may be in the form ofgable frames tocover thefull length ofthe concrete pavement laid in a day. The surfacesofthe formworkand subgrade coming in contact with concrete shall bemoistened prior to placing of the concrete to prevent absorption ofmixing water. Since the setting time of concrete is considerablyreduced under such temperatures, labour force shall be reinforced to

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protective cover shalt be adequate to exclude exposure of the concretedirectly to thc sun and also eliminate contact with drying winds. Priorto removal ofthe portable shelters, the hardened concrete shall becovered with wet hessian or burlap or the like followed by one oftheusual methods ofcuring like ponding, etc. In addition, the moist curing

period shall be extended to 4 weeks.

For further details reference may be made to IRC 1976.

9.15. Concreting in Cold Weather

Except by specific written authorisation from the Engineer-ia-charge, concreting shall not be continued when a descending airtemperature i n t h e s h a d e a n d away f r o m a rt i f i c i a l h e a t drops below4C,nor shall concreting be resumed until an ascending air temper-

ature in the shade and away from artificial heat reaches 4C.

When specific written authorisation is granted to permit con-creting at temperatures below those specified above, equipment toheat the aggregates and water shall have to be provided. Inaddition, use of calcium chloride as an accelerator when soindicated may be permitted. The amount of calcium chloridesolution used shall not exceed about 2.3 litres per bag (50 kg nett)of cement and this solution shall be considered as a part of themixing water. This solution shalt be prepared by dissolving 45 kgofgranulated or flaked calcium chloride in about 95 litres of water.Normally ordinary Portland cement as per iS : 269-1976 alone shallbe used when calcium chloride is employed as an additive. Alsoit is recommended that when calcium chloride is proposed tobe used, there should be no steel reinforcement in the concretepavement.

Concrete heating equipment capable of producing concretethat will have temperature ofat least 15Cand not exceeding 32Cat the time of placing it between the forms shalt be provided. Theaggregates shalt be heated prior to being loaded into the concretemixer. The equipment used shall heat the mass uniformly andshall preclude the possible occurrence of overheated 2ones whichniight affect the concrete properties. Water used for mixing shallnot be heated beyond 66C. Material containing frost, ice, snowor lumps ofhardened mass shall not be used. Heating methods

which alter or prevent the entrainment ofthe required amount ofa i r i n t h e c o n c r e t e s h a l l n o t b e a d o p t e d . D ur i n g pl a c e m e n t o fc o n c r e t e , t a r p a u l i n c ov e r s o r other readily removable coveringsshould closely follow the placing of concrete, so that only a fewmetres of the finished slab are exposed to the outside air at any onetime. The coverings may be so arranged that heated air, whereprovided could be freely circulated on top of the pavement The

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coverings may be further covered by layers of straw or otherinsulating materials, no sooner the wet concrete is strong enough totake their load,

When concrete is being placed in cold weather and the airtemperature is expected to fall below 2C,the air surrounding theconcrete shall be maintained at a temperature of15Cfor at least 3days and not less than 4Cfor a period ofnot less than 7 days.

Any concrete damaged by frost action shall be removed andreplaced.

Under no circumstances shall the concreting operationscontinue when the air temperature is less than 7C.

For more details about concreting in cold weather, seeSupplementary Note, N.6.

9.16. Work on Gradients

The progress on gradient of all operations of placing, com-pacting and finishing of concrete should proceed from the lower tothe higher rcaches. The concrete mix shall be stiff