CC Pavements Guidelines Circular 8-8-2013

8/13/2019 CC Pavements Guidelines Circular 8-8-2013

http://slidepdf.com/reader/full/cc-pavements-guidelines-circular-8-8-2013 1/14

GOVERNMENT OF ANDHRA PRADESH

OFFICE OF THE DEPUTY EXECUTIVE ENGINEER (PR)

Vig & QC SUB-DIVISION, NALGONDA.

Circular No. AEE1/CC Roads/VQC Nlg/2013, Dated: 16.08.2013.

Sub:-Planning, Design & Construction of Cement Concrete Pavements with Design Mix

concrete in rural areas - Certain provisions and prescribed standards communicated forguidance of field engineers - Reg.

* * *The PR Dept. is executing huge quantum of CC Roads in every nook & corner of this

district. Every village now has minimum of one CC road being constructed every year. It isobserved during the inspection of the various CC roads by the QC Wing in the district that theField Engineers are paying scant attention to the aspect of Design, Execution, Maintenance of

CC Pavements. The IRC/IS Codal provisions are not known & not followed in many of the CCroads. The knowledge of Design of CC Pavement thickness, Design Mix, procedures ofconstruction,correct proportions of ingredients, admixtures, expansion & contraction

joints,curing, water/cement ratio, proper compaction, quality controlis very meager amongfield engineers. The construction of CC Roads is going toawry, left to the mercy of contractor& meastry. It is unfortunate to see that even though in each mandal Rs.1.00 crore and above

CC roads under MGNREGS Scheme for SC/ST are taking up but it is rather pathetic to seethat the construction of CC roads are going as usual without any latest technical know howbeing implemented, though there are enormous literature , IRC & IS Standard Codesavailable on this subject.

In view of the above, for guidance of field engineers every aspect pertaining to CCRoads as per IRC/IS Codes, other literatures, internet contents etc., are reviewed extensivelyand the following brief provisions are compiled in a nut shell & put up below for guidance &better understanding.

(1) Literature & References :: The following codes may be referred for in-depthknowledge on the subject.

IRC: 15-2002 -"Standard Specifications & Code of Practice for Const. of Concrete Roads".IRC: 43-1986 -"Recommended Practice for Tools, Equipment & Appliances for ConcretePavement Construction".

IRC: 44-1976 -"Guidelines for Cement Concrete Mix Design for Pavements".

IRC: 57-1957-"Recommended Practice for Sealing of joints in Concrete Pavements".IRC: 58-1988 -"Guidelines for the Design of Plain Jointed Rigid Pavements for Highways

IRC: SP-83-2008 - Mtc.,& Repairs of CC PavementsIRC: 59-1976 - Gap Graded Cement Concrete MixesIRC: 61-1976 - CC Pavements in Hot WeatherIRC: 84-1983 - Curing of CC PavementsIRC: SP-62-2004 - CC Pavements for Rural Roads.IRC: SP-69 2011 - Guidelines Specifications for Expansion JointsIS-383-1970 - Specifications for Fine & Coarse AggregatesIS-10262 - 2009 -Concrete mix proportioning-GuidelinesIS-6509-1995 - Installation of Joints in Concrete PavementsIS-SP23-182 - Handbook on Concrete Mixes



Preamble ::Concrete pavements offer an alternative to flexible pavements especially where the soil

strength is poor, the aggregates are costly and drainage conditions are bad (as in portions ofthe roads passing through villages and water-logged area). The choice depends on thesefactors and the life-cycle cost (IRC-SP-62-204). It should be noted that concrete pavementsdemand a high degree of professional expertise at the stages of design, construction andmaintenance.

(2) Preparation of Subgrade & Subbase ::

(i) Preparation of subgrade: The materials and their specifications for base, sub-base and subgrade preparation

shall be as per IRC:15. The camber and super elevation of subgrade shall be same as that ofthe concrete slabs. The thickness of subgrade shall be 150-300 mm. If the k value of thesubgrade tested under wet condition is less than 6 kg/cm^2(Aprox.CBR Value 15%), thecement concrete pavement should not be laid directly over the subgrade. A sub-base layer asper Clause 6.2 may be provided.

(ii) Preparation of sub-base course ::

The sub-base shall be laid over a properly compacted subgrade to give uniform support.The sub-base may be composed of (a) Granular Material (WBM or WMM or GSB ≥ SoakedCBR 20), (b) Stabilised Soil with Lime, (c) Semi-Rigid material (Lean Concrete). The 1st twoshall have a min thickness of 150mm & 3rd shall have 100mm thickness (IRC:63).

Any ruts or soft yielding places on the surface shall be corrected and rolled to getfirmsurface.

Further provide a drainage layer of 150mm thick using granular material in addition tothe base course layer in case of very weak subgrade (CBR≤ 2%).

Note: Advantages of using lean concrete sub-base instead of granular sub-base.

There are several shortcomings of using granular sub-base in concrete carriageway:

(i) Since sub-base is permeable, water can seep through sub-base and soil particles will

be pumped out through contraction/expansion joints when subject to traffic load.Consequently, voids are formed underneath the pavement structure and the concretepavement may crack under severe traffic loading.

(ii) Lean concrete increases the strength and renders the roads capable of carrying heavytraffic loads.

(iii) Due to workmanship problem, the unevenness of sub-base may results in cracking of

concrete carriageway when subject to severe traffic loading.

iii) Methodology of Construction of Pavement Quality Concrete (C.C. Pavement)::

(a) Equipment : Tools, equipments and appliances for concrete pavement construction shallbe as per IRC:43 and IRC:SP:49.

(b) PQC wearing base course: The CC base course shall be laid as per the procedure asmentioned in IRC:I5-2002. In brief the procedure is given here as:

(i) A separation membrane shall be used between the concrete slab and sub-base, havingimpermeable plastic sheeting 125 microns thick laid over without bends, which serves(i) to prevent the loss of water from cement paste (ii) enhances the movement ofconcrete slab relative to sub-base layer and reduces the frictional forces developed attheir interface. (iii) prevents the intermixing of freshly placed concrete with loose

materials on the surface of sub-base. Before placing, the sub-base shall be swept cleanof all the extraneous materials using air compressor.

(ii) Fixing of formwork shall be set to true level and securely fixed in position to preventany subsequent disturbance during compaction.



(iii) The coarse aggregate shall not be dumped in heaps directly on the sub-base/basewithin the area over which Concrete is to be laid.

(iv) The concrete ingredients shall be weighed in a batching plant. Where volume batchingis permitted, every effort should be made to minimise variation in batching. Mixing ofconcrete shall be done in a power driven mixer ensuring a uniform distribution ofmaterials.

(v) Concrete shall be deposited within 20 minutes. Concreting shall not be done when theatmospheric temperature is below 5⁰C and above 40⁰C. No concreting shall be

done when concrete temperature is above 30°C (IRC-15).(vi) Water in the fresh concrete should not be in excess of the stipulated quantity, otherwise

concrete is likely to crack within very short period after drying. After compacting andfinishing with screed, a float and then a broomer is used to finally finish the top surfacewith required texture to avoid skidding. Any depressions or high spots showing

departures from the true surface shall be immediately rectified. High spots shall be cutdown and refinished. Depressions shall be enlarged to about 80-100 mm and refilledwith the same fresh concrete, compacted and finished. All the above operation shall be

completed within 75 minutes in winter or 60 minutes in summer from the time ofadding water into the mix.

(vii) Contraction and expansion joints shall be provided as per the Guidelines mentioned in

IRC:15 or IRC:58 and details are given below.(viii) Adequate compaction of concrete by suitable vibratory (first by needle vibratorspecially at edges and then by screed vibrators) equipment is necessary. Every 1%void remaining in the concrete means a loss of strength of the order of 4-5%.

(ix) The CC layer shall be tested for thickness with wooden blocks.(x) Curing shall commence soon after the finished pavement surface can take the weight of

the wet jute mats as per guidelines of IRC:SP:11. Details are given here under.(xi) There should not be any surface variations more than specified as per Table 13 of IRC-

15.(xii) The strength of concrete shall be ascertained either from cube or beams specimens as

detailed here under.(xiii) The camber in straight section of the CC road for annual rainfall less than 1000mm

shall be maintained at 2% as per Table 2.11 of IRC SP-20.

The sample design of rigid pavement for rural roads is appended to this circular.

iv) Design Mix :: The Basics.

Nominal Mix:Nominal mix is the prescriptive type mix achieved by volume proportioning of

ingredients such as 1:2:4 or 1:1½:3 and not indented or designed to get the desiredcompressive strength of concrete, say M15. These are never denoted as M15 or M20 etc.,

Design Mix:Concrete is an extremely versatile building material because, it can be designed for

strength ranging from M10 to M100 and workability ranging from 0 mm to 150mm slump.Concrete Design Mix is made mandatory for M20 and above grades by IS 456-2000.

Design mix is the process of proportioning by weight of all ingredients by Trial andError with different quantities to arrive exact proportions such that the desired targetmean strength is achieved,say M20, in which the letter M refers to the mix and the number tothe specified 28 day cube strength of mix in N/mm². Thus the M20 grade concrete may notnecessarily be 1:1½:3 proportions of aggregates.

Both IS : 456-2000 as well as IS : 1343-1988 envisage that design of concrete mix bebased on the following factors (a) Grade of concrete (b) Type of cement (c) Maximumnominal size of aggregates (d) Minimum water-cement ratio (e) Workability (f) Minimumcement content.

The concreting shall only be commenced for the required grade based on theDesign mix arrived through the Trial mix of same concrete ingredients prior toconstruction of pavement.

One sample design mix for M20 grade is enclosed to this circular.



v) Ingredients of Concrete::

The Basic Ingredients of Concrete are : -1. Coarse Aggregate- It is the basic building component of concrete.2. Fine Aggregate –It forms mortar grout and fills the voids in the coarse aggregates.3. Cement– It is the basic binding material in concrete.4. Water– It hydrates cement and also makes concrete workable.

5. Admixtures - They enhance certain properties of concrete e.g. gain of strength,workability, setting properties, imperviousness etc.

(i) Coarse Aggregates:-

a) Max.size of coarse aggregate: Maximum size of aggregate is the standard sieve sizethrough which at least 90% will pass. Chances of segregation increases, if maximum sizeof aggregate exceeds 25 mm & affects the workability and strength of concrete.(IRC-15-2002).

b) Shape of coarse aggregate: Rounded aggregates have lower surface area will havelowest water demand and also have lowest mortar paste requirement. Hence they will

result in most economical mixes for concrete grades up to M35. Flaky and elongatedcoarse aggregates not only increase the water demand but also increase the tendency ofsegregation, also reduce the flexural strength of concrete. MoRTH restrict the combinedflakiness and elongation to 30% by weight of coarse aggregates.

c) Grading of coarse aggregate: The grading of coarse aggregates of different sizes isvery important to get cohesive & dense concrete and to minimize the segregation. Thevoids left by larger coarse aggregate particles are filled by smaller aggregate particles andso on. Thus the volume of mortar required to fill the final voids is minimum.

d) Strength of coarse aggregate: Cement concrete in pavements is subjected to highflexural stresses and abrasion. Material strength of coarse aggregate is indicated by

aggregate crushing value, impact value, abrasion value which should not more than 30(IRC-SP-20).

(ii) Fine Aggregates (Sand):-

Generally, when the sand is fine, smaller proportion of it is enough to get a cohesivemix; while coarser the sand, greater has to be its proportion with respect to coarseaggregate.

a) Gradation of fine aggregates: IS classifies fine aggregates in 4 zones starting fromzone I representing coarse sand to zone IV representing the finest sand. The fineness ofsand governs the proportion of sand in concrete. The fineness modulus of sand varies

from 2.0 to 4.0, higher the FM coarser is the sand.

d) Silt Content by weight: This is found by wet-sieving of sand and material passing 75micron sieve is classified as silt and shall not more than 3% by weight. This silt hastremendous water demand, affects the workability of concrete resulting in higherwater/cement ratio and lower strength.

e) Stone Dust : In case of coarse sand, a part of sand may be replaced by fine sand toincrease the missing fines in concrete. In case fine sand is not available stone dust (600 µ

passing more than 60 % and 150 µ passing not more than 20%) may be used to replacea part of sand. Such stone dust should not replace more than 15 Kg of sand under normal

circumstances. Stone dust reduces the workability, hence, the water cement ratio islikely to increases.Further, if the sand received at site is finer than the one considered in mix design,

the excess surface area created by the fines will increase the water demand.



in moisture and temperature. Although irregular cracks are unsightly and difficult to maintain,they generally do not affect the integrity of the concrete. Cracks in concrete can be controlledand minimized by properly designed joints. The below two types of joints are commonly usedin concrete pavement.

Expansion Joints:Such joints provides the space in pavement which can expand, relieving compressive

stresses due to expansion and inhibiting any tendency towards buckling of concrete slabs.

Not providing such joints will restrict free expansion, then the structure is subject to an axialstress of 6.21MPa. If the structure is very slender like concrete carriageway, buckling mayoccur.

The compressible fibre board/synthetic board (Mastic pads) with dowel joints shall beprovided in a pavement at suitable intervals. The joint filler shall extend to the entire width ofthe pavement and from the sub-base to 25 to 30 mm below the surface of the pavement.

Different components of a typical expansion joint.In a typical expansion joint, it normally contains the following components: Bitumen

primer, Bitumen sealant, Mastic pad, dowel bar, PVC dowel sleeve, Polythene sheathings(covers) etc.,

Bitumen Primer: The primer is used to improve the adhesive bond between sealingcompound and concrete, to penetrate the pores of the concrete and to coat it with a thin filmof a viscous, sticky material. MORD Data specifies usage of Bitumen primer @ 200 ml per joint. Bituminous sealant: it seals the joint width and prevents water and dirt from entering the joint and causing dowel bar corrosion and unexpected joint stress resulting from restrainedmovement. MORD Data specifies usage of Bitumen sealant @ 800 ml per joint. The sealingcompound shall conform to Grade A for normal pavement constructions (IRC-57-1957).

Mastic Pad 25mm: it is compressible so that the joint can expand freely without constraint& serves the purpose of space occupation such that dirt and rubbish are not intruded in the

joint.These shall be of 20-25mm thickness within a tolerance of ±1.5 mm and of acompressible synthetic material and having compressibility more than 25% IS:1838. It shallprovided 25mm less in depth than the thickness of the slab within a tolerance of ± 3 mm andprovided to the full width between the side forms. Holes to accommodate dowel bars shall beaccurately bored or punched out to give a sliding fit on the dowel bars.

Dowel bar: It serves to guide the direction of movement of concrete expansion and arerequired to transfer wheel loads to the adjacent slab. Therefore, incorrect direction ofplacement of dowel bar will induce un necessary stresses in the joint during thermalexpansion. The mis-alignment of dowels can induce a crack away from a expansion joint, ifthe dowels physically lock two slabs together and restrain their contraction. The dowel barsshall be held accurately in position during the placement, compaction and finishing of

concrete at the expansion joint by dowel chair assembly (IRC-15).However for slabs of thickness less than 150mm no dowel bars required (IS:6509-1972).

RECOMMENDED REQUIREMENT OF DOWEL BARS IN CC PAVEMENTS.(IS-6509-1995)

Pavement thickness Dowel Dia. Dowel Length Dowel Spacing

150 25 500 200200 25 500 300

250 32 500 300

PVC dowel sleeve(pipe): It serves to facilitate the movement of dowel bar. On one side ofthe joint, the dowel bar is encased in concrete. On the other side, the PVC dowel sleeve isbonded directly to concrete so that movement of dowel bar can take place.



Polythene sheaths: The polythene sheaths (covers) of 125 micron thick shall be sheathedto dowel bar for 2/3rd length to segregate the dowel from directly contact with concrete.



EXPANSION JOINTS

Notes: If the construction of concrete carriageway is carried out in summer,can expansion joints be omitted?

If the construction of concrete carriageway is carried out in summer, expansion jointsmay not be necessary. Expansion of concrete carriageway is mainly due to seasonalchanges with an increase in temperature from that during construction to the ambienttemperature (i.e. the temperature in summer). However, if the construction of concretecarriageway takes place in summer, the concrete carriageway will undergo contraction in thefollowing winter, thus the space available in contraction joints can accommodate the futureexpansion in the next summer.

Contraction Joints: These purposely made joints relieves tensile stresses in the concrete and prevents

formation of irregular cracks due to restraint in free contraction of concrete caused by thecement hydration process, traffic loadings and the environment. It provide a suitable plane of

weakness through concrete slab along which the concrete may crack when contraction orshrinkage takes place.Procedure::

Contraction Joints are spaced at 4.50m c/c for slabs 100mm to 250mm thick (IRC-15).These joints are to be sawn 4 hours after compacting concrete and should be completedwithin 12 hours of concrete placement, before it attains the compressive strength of 7 MPa(IRC-SP-83-2008). They shall be constructed by forming in the surface of the slab, a slot notless than 3mm wide and having a depth equal 1/3rd to1/4th the depth of the pavement by aconcrete joint cutting machine OR by pushing into the concrete a flat metal bar or plastic stripor the web of a "T" bar held on its edges by guides, removing the bar subsequently, andkeeping the slot open. The metal bar shall be withdrawn as soon as the concrete has setsufficiently so as not to flow back into the groove. This groove is subsequently widened to 10to 12mm thick , 25mm deep by wooden planks before final setting of cement to seal withsealant later on.

Shallow depth sawing will lead to random cracking and too late sawing leads to uncontrolled/random full depth cracking. Good design and maintenance of contraction joints

have virtually eliminate the need for expansion joints, except at fixed objects such asstructures.Sealing ::

After the curing period is over and before the pavement is opened to traffic, the intrudedmaterials in all joints shall be removed completely and the contact faces of joints shall beprimed with a thin bituminous paint which shall be allowed to dry before the sealingcompound is applied. Bituminous emulsions shall not be used as primers (IS-6509-1995).

Sealing of top grooved surface of 10mm wide x 25mm deep shall be done by a hot appliedrubberised bituminous sealant of approve type poured from a kettle having a spout.



RECOMMENDED SPACING OF EXPANSION & CONTRACTION JOINTS ( IS-6509-1995)

Thickness of Slab 100mm 150mm 200mm & above

Expansion Joints 27m 27m 36mContraction Joints 4.50m 4.50m 4.50m

vii) Admixtures:

Admixtures conforming to 18:6925 and IS:9103 may be used. Now days, admixturesare considered as the 5th ingredient of concrete. The admixtures can change the properties ofconcrete.Commonly used admixtures are as follows:i. Plasticisers & super plasticisers, ii. Retarders, iii. Accelerators, iv. Air entraining agents,

v. Shrinkage compensating admixtures, vi. Water proofing admixtures, vii. Recron fibre.

In CC Roads, generally, the following products are recommended by MORD.

i. Plasticisers & super plasticisers Plasticizers are also called water reducing admixtures. Ordinary water reducing

plasticizers enables upto 15% of water reduction. High range water reducing superplasticizersenables upto 30% of water reduction. Plasticisers helps in increasing the workability ofconcrete i.e., to get lower water/cement ratio without reducing the workability at the same

cement content. Use of plasticisers is economical as the cost incurred on them is less thanthe cost of cement saved. Compatibility of plasticizers with cement should be ascertained



before use in concrete. MORD data recommends usage of superplasticisers @ 0.50% by wt.of cement

ii. Recron3S fibre:Called Secondary Reinforcement, the dosages of 0.25% (125gm per 50 Kg) cement

bag or 0.9Kg per cubic meter of CC may be used. The Reliance industry claimed the followingadvantages. 1. Thermal shrinkage cracks ::Significant reduction.

2. Water penetration ::Significant reduction3. Abrasion Resistance ::Over 40% Improvement over normal concrete4. Impact strength ::Improves significantly5. Flexural & Compressive strength ::10-30% increase over normal concrete.

iii. Curing Compound : Not necessary.

viii) Compaction:

Compaction is the process which expels entrapped air from freshly placed concrete andpacks the aggregate particles together so as to achieve max.strength, increase the density,

abrasion resistance and durability of concrete, also decreases the permeability and reductionof honeycombing and blowholes on the surface of concrete, helps to minimise its shrinkage-and-creep characteristics.

Surface vibrators (Double beam Screed Vibrators), Immersion Vibrators (Pin,Needle),Plate Vibrators shall be used for compaction of concrete. It has to be checked that no extrawater or bleeding shall occur on the top surface of concrete. Excessive water at the top willmake the top surface very weak and there will be more abrasion (IRC:SP:20-2002). Use ofvibrator near side forms is essential to eliminate honey combing. To effect adequatecompaction, the concrete shall be placed with appropriate surcharge over the final slabthickness. In general, the required surcharge is about 20% of the required slab thickness. Airentrapped in the concrete leaving the mixer typically may vary from 5% to 20% by volume.

The presence of 5% voids in the concrete will reduce the strength compared to the fullycompacted concrete by about 30% and the presence of 10% voids will reduce the strength by60% (IRC-15-2002).

Compaction of concrete slabs upto 125mm thickness may be done by means ofvibrating screed alone, while for thicknesses greater than 125mm both internal vibrators,like, needle and vibrating screeds shall be used. The amplitude of vibration of the screed shallnot be less than 1.5 mm and the speed of travel not more than 0.6 m per minute. The needlevibrator develops about 7000 vibrations per minute. Compaction by screeding shall be carriedon till the mortar in the mix just works up to the surface. At any point tested, the concreteshall not show a departure greater than 3 mm from the true surface (IRC-15).

ix) Vaccum Dewatering Technique ::

Precursor:: This method was extensively used in Nizamabad district for Pmgsy Works. TheNQM’s are also greatly appreciated and recommended to NRRDA for wider adoption.

Procedure::Vacuum dewatering process removes surplus water present in the concrete. This

is done using the Vacuum Equipment comprising of Suction Mat Top Cover, Filter pads andVacuum Pump. The process starts immediately after surface compaction. Filter pads areplaced on the fresh concrete leaving about 4 inches of fresh concrete exposed on all sides.

The Top Cover is then placed on the filter pads and connected to the vacuum pump through asuction hose and the pump is started. Vacuum is created between the filter pads and the top

cover. Atmospheric pressure compresses the concrete and the surplus water is squeezed out.The dewatering operation takes approx.1-2 minutes per cm pavement. The dewateredconcrete is compacted and dried to such an extent that it is possible to walk on it withoutleaving any foot prints. The finishing operations - Floating & Trowelling take place right after

dewatering. Floating operation is done with Floating disc. This ensures further compaction



and closing the pores on the surface & generates skid-free finish. Trowelling is done withTrowelling blades in order to further improve the wear resistance, minimize dusting andobtain smoother finish.

Advantages:: It is stated in literature that this technique will ...

i) Reduction in W/C ratio by 15-25% leads to early setting.ii) Increase in compressive strength of concrete by 40-70%.

iii) Surface hardness of the slab increases by 30%.iv) Water absorption is reduced significantly.v) Minimized crack formation, shrinkage reduced by 50%.vi) Lower curling defect in floors.

TYPICAL PICTURE OF CC PAVEMENT WITH VACCUM DEWATERING SYSTEM

x) Surface texture

After the final finishing of the slab and before the application of the curing membrane,the surface of concrete slab shall be brush-textured in a direction at right angles to thelongitudinal axis of the carriageway. Texture depths shall be in the range of 1.0mm to1.25mm depth (IRC_15-2000).

xi) Removing Forms (Shuttering)::

Forms shall not be removed from freshly placed concrete until it has set, or at least 12hours, which ever is later. After the forms have been removed, the slab edges shall be,

cleaned and any honey-combed areas shall be pointed with 1:2 cement sand mortar, afterwhich the sides of the Slab shall be covered with wet jute mat for curing. Slabs withexcessive honey-combing as a result of inadequate compaction shall be removed between the joints & re-laid (IRC:15).



xii) Curing

Purpose::The purpose of curing is to reduce the rate of heat loss & loss of water from freshly

placed concrete to the atmosphere and to minimize the temperature gradient across concretecross section. Concrete develops strength ONLY in the presence of moisture , therefore it isabsolutely important that it is kept moist after casting. Immediately after finishing, theconcrete surface shall be covered against rapid drying by curing. The potable drinking water

may be used for mixing as well curing of concrete.

Methods::Curing can be done by one of the following two methods:

(i) By application of curing compound twice, in areas where water is extremely scarce.(ii) By manual methods using wet jute mats which is kept moist during curing period or

ponding water.

Procedure::Curing shall commence soon after the finished pavement surface can take the weight of

the wet jute mats normally employed for initial curing, without leaving any marks thereon

(IRC:SP:11). The mats shall extend beyond the pavement edges at least by 0.5 m and beconstantly wetted. Initial curing shall be for 24 hours or till the concrete is hard enough topermit labour operations without damages. Final curing, after removal of the mats after 24hours, shall be carried out by ponding of water. Where water is scarce or pavement is on asteep gradient, impervious membrane curing shall be adopted as per specified standard ofMoRT&H. Pavement can be opened to traffic after 28 days of curing of concrete slabs.

xiii) Quality Control

The finished surface should be checked for line, level, camber, grade and surface finishand irregularities should be corrected.

(b) Sampling and testing of beam, cube & core specimens:

Cubes:: Cement concrete cubes 15x15x15 cm and beams 15x15x70 cm (6 No. each) shall becast daily to check 7 and 28 days strength as per IRC:SP:11. They shall be tested in lab forend results and shall not be less than the minimum specified compressive strength. Adequatequality control should be exercised at all stages of construction by suitable trained staff as perguidelines given in IRC:15. The flexural strength of concrete obtained in the field shall not beless than 40 kg/cm².

Cores: Where the quality of the concrete or its compaction is suspect, the actual strength ofthe concrete in the slab shall be ascertained by carrying out tests on cores cut from thehardened concrete at such locations. The cores shall be cut at the rate of 2 cores for every

150 cum of concrete. The results of crushing strength of tests on these cores shall not be Jessthan 0.8 times the corresponding crushing strength of cubes, where the H/D ratio of the coreis two. A core specimen for the determination of pavement thickness shall have a diameter ofat least 10 cm. The H/D ratio when capped, nearly twice its diameter (IS-1199,Cl.4.30).

If, however, the tests on cores also confirm that the concrete is not satisfying thestrength requirements, then the concrete corresponding to the area from which the cores

were cut should be replaced, i.e., at least over an area extending between two construction joints where the defects could be isolated.

Hence it is advised to the field engineers that to record the measurement on each days

work length on day to day basis or joint to joint spacing or 30m interval so as to avoidrejection of entire length of concrete.

(b)Pavement thicknessIn the stretch where deficiency of average thickness is more than 25mm, the panel shall

be rejected and re-laid.



PAYMENT ADJUSTMENT FOR DEFICIENCY IN THICKNESS (IRC-15)

Deficiency in average thickness Per cent contract unit price payable

Upto 5mm 100

5-10 mm 87

10-15 mm 81

15 to 20 mm 75

20 to 25 mm 70

© Surface levels:The measurements of the surface levels shall be taken on a grid of points placed at 6.25

m longitudinally and 3.5 m transversely should not exceed the tolerance as below.Surface Tolerance in CC Pavement is +5mm to -6mm.

(d) Surface regularityThe maximum permitted number of surface irregularities shall be as per Table 13 of

IRC-15.i) permitted number of 4mm thick surface irregularities in 300m length – 40 Nosii) permitted number of 4mm thick surface irregularities in 75m length – 18 Nos

iii) permitted number of 7mm thick surface irregularities in 300m length – 4 Nosiv) permitted number of 7mm thick surface irregularities in 75m length – 2 Nos

(e) Horizontal alignmentThe horizontal alignment shall be checked with respect to the centre line of the

carriageway. The edges ofthe carriageway as constructed shall be corrected within a

tolerance of ±10 mm there from.

(f) Acceptance criteria for Cracks (As per IRC-SP-62-2004)

Concrete slabs may develop cracks of minor to serious nature unless appropriateprecautions are taken to prevent their occurrence either during the construction phase or

postconstruction period.

Cracks can appear generally due to the following reasons:(a) Plastic shrinkage of concrete surface due to rapid loss of moisture.(b) Drying shrinkage.(c) High wind velocity associated with low humidity.(d) High ambient temperature.(e) Delayed sawing of Joints.(f) Rough and uneven surface of the base on which concrete slabs are constructed.

The slabs with full depth cracks are totally un acceptable as it amounts to structuralfailure. Besides, other cracks which are deep and are likely to progress in depth with time are

also to be considered as serious in nature.

The cracks in concrete slabs can be accepted in the following situations:

(a) Plastic shrinkage cracks- The discrete crack which is less than 500mm length and itsdepth of penetration less than half the thickness of the slab and which does not

intersect with a longitudinal edge or formed Joint. The cumulative length of such cracksin each slab shall not be more than 1.0 m length.

(b) Fine hairline crazy cracks.

The concrete slabs are to be rejected when:

(i) Slabs with cracks running transversely or longitudinally penetrating to full depth andlength of the slab.

(ii) Slabs with cracks which are penetrating to more than half the depth.

(iii) Discrete crack which is more than 500 mm length although its depth of penetration isless than half of the depth.



(iv) When the total length of all discrete cracks is > 1.0 m whose depth of penetration is lessthan half the depth.(Refer IRC-SP-83-2008 for Common Defects, Distresses, Causes in Concrete

Pavements).

The above guidelines are prepared after a strenuous study of various literatures fordays together and compiled to guide & aware the field engineers executing the CC roads in

rural areas.

The Field engineers are requested to go through the above exhaustive circular in depthand come up with corrections, suggestions, improvements, doubts and clarifications. It is alsorequested to contact this office for IRC/IS codes, other technical books, technical Internetcontent, drawings etc.,

The Executive Engineers are requested to kindly communicate this circular to all theDeputy Executive Engineer/ Asst.Executive Engineers under their control and ensure the strictadherence to standards of codal provisions in respect of construction of all type of CC Roadsin ODR/VR roads irrespective of whether they are sanctioned under PMGSY,Nabard,MGNREGS

or other grants.

Dy. Executive Engineer(PR) Vig& QC Sub-Division, Nalgonda.

Encl:-1) Sample Concrete Mix Design for M20 Grade Concrete.

2) Sample Rigid Pavement Design.3) Typical drawings of Expansion/Contraction Joints.

To,

The Executive Engineer (PR) PIU Division Nalgonda, PRI Division Nalgonda & Miryalaguda.Copy to all DyEE’s /AEE’s through EE’s concerned. C/S to the Executive Engineer (PR) Vig& QC Divn.Hyderabad for favour of information.

CC Pavements Guidelines Circular 8-8-2013

Documents

Transcript of CC Pavements Guidelines Circular 8-8-2013