Unit 7 ( CONSTRUCTION OF RIGID/CONCRETE PAVEMENT )

Highway Engineering Engineering

CONSTRUCTION OF RIGID/CONCRETE PAVEMENT

C3010 / UNIT 7

UNIT 7


OBJECTIVES General Objective To understand the general element in constructing rigid/concrete pavement

Specific Objectives At the end of the unit you should be able to:•

identify the structural element of rigid pavement.

•

describe the functions of each layer in the rigid pavement.

•

explain the construction process of the rigid pavement.



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INPUT

7.0

INTRODUCTION

Cement concrete roads are very high standard. They are costliest than all other types of roads. These roads provide excellent riding surface and pleasing appearance. They are called rigid pavements because they do not allow any flexibility.

These roads although require initial heavy expenditure but because of their long span of life, excellent riding surface and negligible maintenance cost, they prove cheaper than bitumen roads. Moreover engineers have more confidence in cement concrete material and they also like to construct these roads.

7.1

ADVA ADVANT NTAG AGES ES AND AND DIS DISAD ADVA VANT NTAG AGES ES OF CONC CONCRE RETE TE ROAD ROADS S

The following are some of the advantages and disadvantages of cement concrete roads:

Advantages

a.

They They prov provid ide e exc excel elle lent nt smoo smooth th surf surfac ace e for for driv drivin ing. g.

b.

They can dea deal wit with h very hea heavy traff raffic ic..

Highway Engineering Engineering c.


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Cons Consid ider erin ing g thei theirr life life spa span, n, mai maint nten enan ance ce cos costt etc, etc, cem cemen entt conc concre rete te roads prove cheaper than bituminous roads.

d.

Maintenance cost is negligible.

e.

Their lilife sp span is is very la large.

f.

Even Even afte afterr the their ir span span of life life,, the they y can can be used used as base base cour course se and and surfacing can be provided of bituminous materials.

g.

Heat Heatin ing g of of agg aggre rega gate tes s and and ceme cement nt is not not to to be be don done. e.

h.

They provide better vi visibility.

i.

Work Workin ing g wit with h cem cemen entt con concr cret ete e is is much much easi easier er and and saf safer er than than with with bituminous materials.

j. j.

Cem Cement ent conc concre rete te road roads s offe offerr comp compar arat ativ ivel ely y less less attr attrac acti tive ve resistance.

k.

In hig high h cla class ss ceme cement nt con concr cret ete e roa roads ds heav heavy y rol rolle lers rs are are not not req requi uire red d for compaction.

l.

Handlin ling of ceme ement is easier ier tha than bitu itumen.

m.

They They perfor perform m quit quite e sati satisf sfact actori orily ly when when laid laid on poor poor types types of sub sub grades.

Disadvantages

a.

They invo involv lve e hea heav vy in initia itiall in inves vestmen tmentt.

b.

Lots Lots of join joints ts are are to to pro provi vide de whic which h pro prove ve addi additi tion onal al plac places es of weakness.

c.

28 days days curi curing ng is requ requir ired ed afte afterr com compl plet etio ion n bef befor ore e the they y can can be opened to traffic.

d.

It is is not not pos possi sibl ble e to adop adoptt stag stage e cons constr truc ucti tion on pro progr gram amme med d in thes these e roads.

e.

Cem Cement ent con concr cret ete e roa road d sur surfa face ce afte afterr som some e tim time e of of use use beco become mes s very smooth and slippery.

f.

It is a noi noisy sy road road,, as as bul bullo lock ck cart carts s or or ste steel el tyre tyred d veh vehic icle les s cau cause se lot lot of noise while moving on them.


7.2 7.2


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CLAS CLASSI SIFI FICA CATI TION ON OF CEME CEMENT NT CONC CONCRE RETE TE ROAD ROADS S

Cement concrete roads can be of following types. Out of all these types, cement concrete slab roads, are most commonly used, and hence construction details of this type of road are discussed in this topic.

a.

Cement concrete slab pavements

b.

Cement gr grouted ma macadam pa pavements

c.

Roller co concrete la layer pa pavements.

d.

Ceme ement-b t-bound mac maca adam dam sandwic wich ty type.

e.

Crete-ways.

a. Cement Concrete Slab Pavements.

In this type of cement concrete roads, cement, sand, coarse aggregate water are premixed in batch mixtures to form cement concrete. Cement concrete so prepared is spread on the prepared sub grade or sub base and consolidated with the help of vibrators or tamper and surface finished smooth.

In this construction, joints at frequent intervals both longitudinally and transversely are provided to nullify the harmful effects of contraction and expansion due to variation in temperature and also during setting.

b. Cement Grouted Macadam Pavements.

In this type of construction, Water Bound Macadam layer or stabilized soil is used as foundation. Existing foundation layer is reconditioned to correct grade and profile and a loose layer of road metal



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or coarse aggregate of 36 to 50 mm size is laid in 125 cm thickness. This coarse aggregate layer is rolled lightly dry to a compacted thickness of about 10 cm. Minimum size of coarse aggregate should not be less than 20 mm as sufficient void spaces are to be deliberately left in this rolled layer. Cement and sand are taken in ration of about 1:2 and grout is prepared by adding sufficient quantity of water in it. Cement-sand mix, having one bag cement, requires about 35 liters water to form a fluid mortar to be used as grout. The grout so prepared is poured over the lightly rolled macadam layer and allowed to seep into the voids deliberately left in the macadam layer.

After grouting, stone chippings of size 5 mm and above, are spread to smoothen the top finished surface and also to help rolling so that grout is further helped in the process of penetration. Finished surface is checked for trueness, camber and profile. The surface is lastly cured as usual. Longitudinal and transverse joints should be provided at suitable interval.

c. Rolled Concrete Pavement

This construction consists of a lean premix of cement concrete which is laid on the prepared sub grade of sub base and rolled with light roller just like Water Bound Macadam Road construction. Rolling operation should be finished before the final setting time of the cement. Curing has to be done for 28 days as usual.

d. Cement Bound Macadam Sandwich Type

In this type of construction, Water Bound Macadam existing layer or stabilized soil base are used as foundation or base. The base layer is reconditioned by carrying out all sorts of repairs. Now take coarse



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aggregate varying in size between 36 mm and 50 mm and spread it on the prepared base. This layer is rolled dry to get a compacted thickness of about 5 cm. Cement and sand are taken ratio of 1:2 and a stiff mortar is made, using appropriate quantity of water (30 liters / cement bags).

This mortar is spread on the rolled surface in about 4 cm thick layer. Now lay an other layer of coarse aggregate of the same size and grading as is used below mortar layer, in a loose thickness of about 6 cm. After spreading the second layer of coarse aggregate over stiff mortar layer, rolling is done using heavy roller about 12 ton. By rolling, the mortar layer is squeezed in to the voids of both the layers of coarse aggregate (one layer above and another below mortar layer) and about 10 cm thick combined layer developed.

Rolling should be stopped as soon as the mortar works up just to the surface. After rolling, the surfacing is finished and checked for camber and profile. Joints are provided at suitable intervals. This type of construction is superior to the grouted macadam roads. These roads exhibit rough texture on the surface and hence are useful in hilly areas, where gradients are steep and other types of roads become slippery and dangerous for use.

e. Crete-ways

Crete ways are track ways made with the help of cement concrete. In village roads there is generally bullock cart traffic. It was originally thought that if only that portion of the road is treated with concrete where wheels of cart are to move lot of savings can be affected because width of treatment to be provided shall be very small. In Crete ways, only 60 – 70 cm wide two parallel concrete strips, at centre to centre spacing of about 1.5 meters are constructed. The space between strips is left untreated or



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may be treated with very inferior type of material. Thickness of strip may vary from 10 – 15 cm.

Crete ways strips may be pre cast and then laid on the prepared sub grade or they may be constructed by laying concrete directly at the site, just in the same way as ordinary cement concrete roads. Crete ways did not become popular due to following reasons:

a. While crossing, crossing, vehicles vehicles coming coming from opposing opposing directions have so get down crete way strips. Getting down and coming up, the crete way is very difficult, since space between strips and out side the strips is soft and bullock carts get entrenched in it. b. During rainy season, season, water may may be held up up in the the kutcha kutcha portion portion between strips. This may affect the foundation of the crete-ways strips and may result is their subsequent settlement. c. In dry weath weather, er, loose loose soil soil from kutcha kutcha space space is is blown blown off and and a trench type hollow space may be formed in between the strips.

In place of track ways of cement concrete, stone slabs covered with bitumen surfacing can also be used. Sometimes, in case of city roads, central part of the road is made from asphalt or bitumen surfacing, for use of motor traffic, and on both of its sides there may be crete ways for carrying bullock carts traffic. Such road in which some width is made from bitumen and remaining from cement concrete, is known as conphalt road.



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INPUT STRUCTURAL PARTS OF CEMENT CONCRETE ROADS AND CONSTRUCTION 7.3 7.3

STRU STRUCT CTUR URE E OF CEME CEMENT NT CONC CONCRE RETE TE ROAD ROADS S

Concrete roads consist of following layers:

Cement concrete pavement

Sub base course

Sub grade

Figure 8.1 Sub grade is concerned its most important property is not the actual strength but uniformity of support. Sub base course of concrete road may be made of Water Bound Macadam, granular material, or stabilized soil. In the case of Water Bound Macadam base, thickness should be at least 15 cm and any new layer of sub base should have been under traffic for some days to get properly compacted.

Construction of cement concrete slab can be done in following two ways: a.

Alternate bay system

b.

Continuous construction.

a. Alte Alterna rnate te Bay Bay Sys Syste tem m



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In this method of laying concrete, width of the road is divided into longitudinal strips. The longitudinal strips are further sub-divided into panels by providing transverse formwork. If the width of the road is just one lane, full width is adopted as one longitudinal strip, but in the case of more than one lane width, each lane is adopted as one longitudinal strip.

In short, the road surface is divided into panels. After this cement concrete is filled in alternative panels or bays both longitudinally and transversely. Size of the bay may be anything like 4 X 4 m, 3.6 X 4.6 m or so. After a lapse of about one weak, remaining left out bays are also filled with cement concrete. The object of adopting alternate bay system of construction is to allow sufficient time to settle and shrink before adjoining bays are filled. The method reduces the possibilities of developing shrinkage base cracks. This system of construction suffers from following draw backs:

i.

A large rge numbe umberr of joi joints nts are deve evelop loped which ich increase the labour cost and also reduce the smooth riding qualities of the resulting surface.

ii. ii.

Duri During ng rain rain,, wate waterr gets gets coll collec ecte ted d in the the unfi unfill lled ed bays bays..

iii. iii.

Work Works s are are not not fin finis ishe hed d at at a stre stretc tch h but but a lar large ge leng length th of the road remains occupied at any moment. If full width is involved, diversions for traffic will have to be provided, thus causing difficulties to traffic and increase in the cost over of all construction.

iv. iv.

Full Fully y mech mechan aniz ized ed cons constr truc ucti tion on is not not poss possib ible le..

v.

Progress of the work is very slow.


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The only advantage of this method of construction is that joints can be easily constructed. Figure 8.2 shows formation of bays on the surface of the road. A, B, C bays are filled first and A’, B’, C’ bays subsequently after a laps of about one week.

Longitudinal Joint

A’

Transverse Joint

B

A

B’

C’ C

C

Figure 8.2

b. Continuous Construction

In this system of construction, continuous longitudinal strips are constructed without any break. Width of the strip is generally kept one lane. This method also helps in marking the traffic lanes after completion, since longitudinal joints will demarcate the limit of each lane. The construction joints are provided at the end of the day’s work. This method of construction is preferred because of the following reasons:

i.

Very few joints will be formed

ii. ii.

In case case of road roads s hav havin ing g mor more e tha than n one one lane lane widt width, h, no diversion is required to be constructed. One lane may


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be adopted for construction at a time and remaining lanes may continue to be used by the traffic. Although traffic will face difficulties but there is no need diversion.

Slab to be laid Laid cement concrete slab Figure 8.3 plan of continuous system.

7.4 7.4

CONS CONSTR TRUC UCTI TION ON STE STEPS PS OF OF CEME CEMENT NT CON CONCR CRET ETE E SLAB SLAB PAVEMENTS.

Construction of cement concrete pavement involves following stages:

a. Prepa Prepara ratio tion n of sub sub grad grade. e. b. Prepa Prepara ratio tion n of sub sub base. base. c. Fixin ixing g of of far farm m. d. Batchin Batching g of materia materials ls and and mixin mixing. g. e. Carrying Carrying and placing placing concrete concrete.. f. Comp Compac acti tion on and and fin finis ishi hing ng.. g. Float Floating ing and and edgin edging. g. h. Belt Beltin ing g and and edgi edging ng.. i.

Curing.

All these operations have been discussed one by one.

a. Preparation Of Sub Grade



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Where formation soil is of very good quality, cement slab may directly be laid over the prepared sub grade. The top 15 cm layer of the sub grade should be compacted and checked for trueness by mean of scratch template. Unevenness of the surface should not exceed 12 mm in 3 m length. Sub grade should be prepared and checked at least two days in advance of concreting. It is desirable to lay a layer of water proofing paper then even concrete can be laid directly over the soil sub grade. Prepared sub grade should complete the following requirements:

i.

There should not be any soft patches on the prepared sub grade.

ii. ii.

Sub Sub gra grade de shou should ld pres prese ent the the un unifor iform m sup suppo port rt to the the concrete slab.

iii.

Should be properly drained.

iv.

Minimum modulus of sub grade reaction obtained with plate bearing test should be 5.5 kg / cm 2.

v.

If wate waterr pro proof of pape paperr is is to to be be lai laid d dir direc ectl tly y ove overr the the sub sub grade, moistening of sub grade prior to placing of the concrete over it, is not required. Moistening is essential in case water proof papers is not used.

b. Preparation Of Sub Grade

When formation soil is very poor quality, or traffic load expected on the pavement is very heavy, a 15 cm thick sub base layer may be used over the prepared sub grade before lying of cement concrete slab. The sub base slab may consist of: i.

One laye layerr of of fla flatt bri brick ck soli soling ng belo below w one one laye layerr of of Wat Water er Bound Macadam.

Highway Engineering Engineering ii. ii.


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Two laye layers rs of Water ater Bound ound Maca Macada dam m may may cons consis ists ts of stone, hard rock, dense blast furnace slag, brick aggregate or any other granular material which is not likely to soften under action of water.

iii. iii.

Well grad graded ed soil gra gravel vel mixt ixture. ure.

iv. iv.

Soil Soil stab stabil iliz ized ed with with 3 – 4 % lim lime e or or cem cemen ent. t.

v.

Lime concrete or lean concrete giving 28 days compressive strength in the field as 40 – 60 kg / cm 2.

vi.

Existing macadam sub base.

vii. vii.

Exis Existi ting ng blac black k top top surf surfac ace e sub sub bas base.

From i to v, all the points are for new constructions and can be adopted as per design requirements. But vi and vii points are for existing sub base and thus have been given in details:

Existing Macadam Sub Base . In case concrete slabs are to be laid on existing Water Bound Macadam roads, it should be seen that Water Bound Macadam should extend at least 30 cm beyond the proposed concrete slab edges. Water Bound Macadam should be at least 15 cm thick. If Water Bound Macadam surface is smaller in width than the proposed width of the concrete slab up to 30 cm on either side, the extra width may be developed by placing 10 cm of 1: 4: 8 lean cement concrete.

Black Topped Surface. Where concrete slab is to be laid over existing black – topped surface no special treatment is necessary. Concrete should not be laid on black topped surfaces having soft spots caused by excessive bitumen or where thick premixed carpets have been rutted badly under traffic. In such cases entire surfacing material should be removed up to the top of compacted macadam and the surface should be prepared as explained in existing Water Bound Macadam surfaces.



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c. Fixing Of Forms.

Forms may be made from mild steel channel sections or wooden planks. Depth of the forms should be equal to the thickness of the slab to be provided. Length of the section for side forms is kept at least 3 m except on curves of less than 45 m radius where shorter lengths Wooden forms should be dress on one side and should have a minimum base width of 10 mm for slab thickness of 20 cm and have a minimum base width of 15 mm for slabs over 20 cm thickness. Deviation of more than 3 mm in a length of 3 m should not occur when forms are filled with concrete. Sufficient number of stakes or pins should be put at the back of the form to impart sufficient support to it.

d. Batching Of Materials And Mixing.

Cement is measured in number of bags. If cement stored in silos is used, its weight is taken as 1440 kg / m 3. Course aggregate and fine aggregates are batched in weigh batching plant and put into the hopper of the mixer along with required quantity of cement. Water is measured by volume. The mixing of each batch should be at least for 1 ½ minutes counted after all the materials have been put into the mixer.

Channel Spike of Needles

A

A

PLAN

Prepared Subgrade

Section at A-A



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e. Carrying And Placing Of Concrete

Prepared premix is carried immediately to the place of actual use by filling into wheel barrows, hand carts or baskets. While concreting, it should be ensured that there is on segregation in the concrete. Concrete put at site is spread uniformly as per requirements of the thickness of the slab. While being placed, the concrete should be rodded so that the formations of voids or honey comb pockets are prevented. The concrete should be particularly well placed and tapped against the forms and along all the joints.

f. Compaction And Finishing

After having uniformly spread, the concrete is compacted either with the help of power-driven finishing machine or by vibrating screed. For constrained areas like corners and junctions, hand compaction can be done using tampers. Hand tamper is also known as hand tamping beam. It consists of a wooden beam 10 cm wide and 25 cm depth. Length of the tamping beam should be equal to the width of the slab plus 30 cm. A steel plate is fixed at the under side of this beam. Tamper is used by placing it on the side forms. Tampers are lifted and dropped to affect compaction. Tamper beam is provided with handles to lift and drop.

g. Floating And Edging

After compaction, with vibrating screed or tamper, the concrete is further compacted and smoothened by means of longitudinal floats. The float is worked longitudinally with sawing motion from one edge of the pavement to the other edge. After this operation, excess water gets



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disappeared but while concrete is still plastic; the surface of the slab should be tested for trueness with the help of 3 m straight edge.

h. Belting and Edging

Just before the concrete becomes non-plastic, the surface should be belted with the help of a two-ply canvas belt which is usually 20 cm wide and at least 1 m longer than the width of the slab. The belt is worked on the surface in transverse direction in short forward and back ward strokes.

After belting and as soon as surplus water disappears from the surface, the pavement is given a broomed finish with an approved steel or fiber broom not less than 45 cm wide. The broom should be pulled gently over the surface of the pavement from edge with each stroke slightly over lapping the adjacent one.

After belting and brooming and before the concrete has taken initial set, the edges of the slab should be carefully finished with an edger of 6 mm radius.

25 CM

ELEVATION

10 CM

PLAN



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i. Curing

Immediately after finishing, the entire surface of the newly laid concrete should be covered against rapid drying with wetted burlap, cotton or jute mat. Covering operation with wet burlap is known as initial curing. Burlap curing is carried out for at least two days. After this, wet burlaps are removed and surface is covered either with damp saturated sand or with free water. Final curing can also be done by applying an impervious membrane which does not impart slipperiness to the pavement. Impervious membrane which is in form of liquid, is applied under pressure, covering the entire surface uniformly. The liquid may be applied immediately after finishing of the surface and before the set of the cement has taken place. If the pavement is first covered with burlap it may be applied upon removal of the burlap. This method of curing can be adopted at places where there is scarcity of water.

k. Final Surface Check

This check is done after curing period when curing sand has been removed from the surface. Undulations in the surface should not exceed 6 mm in length of 3 m.

l. Removing The Forms.

Forms should be removed after a lapse of about 12 hours from placing of concrete. Forms should be removed carefully avoiding any damage to the pavement edges.



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m. Sealing Of The Joints.

After curing period, and before the pavement is opened to traffic, all the joints should be cleared of intruded materials and suitable sealing material put into them.



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INPUT

7.5 7.5

JOIN JOINTS TS IN CEM CEMENT ENT CO CONCRE NCRETE TE ROAD ROADS S

Effective system of joints is essential feature in the successful functioning of the cement concrete roads. Tie bars and dowel bars are provided to maintain the strength of the pavement at the joints and also to act as load transfer devices. Joints in cement concrete pavements can be classified under three headings:

a. Expa Expans nsio ion n joi joint nts s b. Cont Contra ract ctio ion n joint joints s c. Warp Warping ing or hinge hinged d joi joints nts

Expansion joints provide space into which pavement can expand. These joints release compressive stresses developed in the concrete slab. Expansion joints also relieve stresses caused by construction and warping.

Contraction joints relieve tension developed in the concrete due to contraction. They prevent formation of irregular cracks contraction joints also relieve stresses due to warping.

Warping joints relieve stresses due to warping effect develops in the slab. These joints are commonly used for longitudinal joints dividing the pavement into lanes. Warping tendencies are set up in the concrete slab due to temperature difference between top and bottom of the slab. At 12 noon the temperature at the top surface of the slab will be higher than that at the bottom. This causes top fibres of the slab to expand by larger amount than the bottom fibres and slab



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warps down wards at the edges. Similarly at 12 night, the temperature of the bottom of the slab is higher than the temperature at the top of the slab and slab warps upwards at the edges. Weight of the slab tries to prevent this warping of the slab and thus warping stresses are set up. Intensity of warping stress is maximum at the interior and minimum at the edges.

Joints in concrete slab pavement can also be classified according to their direction in relation to the road alignment. Joints constructed in the direction, perpendicular to the alignment of the road are termed as transverse joints. Joints constructed in the direction of alignment known as longitudinal joints.

a. Tranverse Joints

Arrangements of tranverse joints may be staggered, square or skew. All these arrangements are shown in figure below. Out of these arrangements, square arrangement is the best.

Dowel Bars

Tie Bars

Expansion Joints

Contraction Joints

Figure : Square System Of Joints



Dowel Bars

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Staggered Transverse Joints Longitudinal Joints

Cracks

Figure : Staggered System Of Joints

Skew Joints Cracks

Tie Bars

Figure : Skew System Of Joints

In case of staggered arrangement, it is seen that cracks known as sympathetic cracks are developed in the adjoining longitudinal strip just in front of transverse joints already provided skew arrangement should not be adopted because in this case acute corners generally get crushed away. Transverse joints can be further classified as follows:

iv.

i.

expansion joints

ii.

contraction joints

iii.

warping joints

construction joints



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b. Long Longitu itudin dinal al Join Joints. ts.

Spacing of longtudinal joints are determined by the lane widths. If during consruction of the slab, hand tamping or vibrating hand screeds have been used, the spacing should be limited to 4 m. Where machines have been used for all the process involved in concreting and at the time, more than 6 m width is being laid, an intermediate longitudinal joints should be provided either by sawing a dummy joint or inserting a mild steel T-iron to the depth varying from 1/3 to 1/6 of the depth of the slab. These joints may be plain butt type or butt with tie bars in them. Tie bars should be bonded in the slabs across longitudinal joints and whilst casting the first slabs thay may be bent so that one end of them lies along the forms. After removal of the forms, bars should be straightened so that they may extend into the concrete placed on the other side of the joint. Tongued and grooved joints are also sometimes used as the longotidinal joints.

7.6JOINT 7.6 JOINT FILLERS FILLERS AND SEALERS SEALERS

Joints are place where continuity of the concrete slabs is broken. These joints if not filled with proper material and allowed to remain open, grit may be filled in them and subsequently during hot day, the slab may be pushed apart due to expansion in the slab. Expansion not being allow at the joint due to muck filled in it. During rains, water will infiltrate through joints into the soil sub grade thus damaging it. This also results in mud pumping, specially where sub-grade is made of expensive soils.

Due to above mentioned difficulties; the joints must be filled with such a material which is compressible, elastic and durable. A material, which is used for filling the joints, is known as fillers. Some depth at the top of the joints is filled



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with a material which could seal the joints completely against the entrance of water. The material which is used for sealing the joint is known as sealer.

Essential properties for fillers are elasticity, compressibility and durability, where as for sealers adhesion with cement concrete, ductility, resistance to ingress of dust and durability are the desirable properties.

Material most commonly used as fillers are:

a.

cork or cork bound with bitumen

b.

soft wood

c.

impregnated fibre boards

The recommendations has been made that filler is considered satisfactory which can be compressed to 50 % of its original thickness by applying a pressure varying between 7 to 53 kg/cm 2 and material should recover at least 70 % of original thickness after three cycles of applying and removing the load. Also when compressed to 50 % thickness, the free edge of the filler should not extrude by more than 6.5 mm, when all other three edges are restrained.

Bitumen either alone or with mineral filler is mostly used as a sealing compound. Rubber bitumen compound, air blown bitumen’s etc. can also be used.

Highway Engineering Engineering 7.7 7.7

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FUNC FUNCTI TION ONIN ING G OF FILL FILLER ERS S AND AND SEAL SEALER ERS S Sealer

1.

2.

Figure shows the po positions of of the filler and sealer at normal temperature.

Joint Filler

Sealer Oughing Out

During hot day, pavement expands due to rise in temperature and the open gap gets reduced. In this condition, filler gets compressed and sealer compound may spill out of joint. Sealer Broken

3.

During cold night, the edges of the pavements move back due to contraction and open gap will formed.

Similarly, due to increase gap, sealing film will become thin. If sealer material is extensible, it will maintain continuity and if its elongation capacity is poor, it may crack as shown above. So, if defective materials have been used as fillers and sealers, the difficulty shown above may arise and render the joint permeable, through which water or other foreign matter may enter the gap and may affect sub-grade or displace the slabs.



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ACTIVITY 7

TEST YOUR UNDERSTANDING BEFORE YOU CONTINUE WITH THE NEXT INPUT

Question

1.

Stat State e thre three e typ types es of cem cement ent conc concre rete te road roads. s. a. _______ ___________ ________ ________ ________ ________ ______ __ b. _______ ___________ ________ ________ ________ ________ ______ __ c. _______ ___________ ________ ________ ________ ________ ______ __

2.

Stat State e the the stag stages es of ceme cement nt conc concre rete te pave paveme ment nt cons constr truc ucti tion on..



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FEEDBACK ON

Answer

1.

2.

i.

Cement co concrete sl slab pavements

ii.

Cement gr grouted ma macadam pa pavements

iii.

Roller co concrete la layer pa pavements.

Cons Constr truc ucti tion on of of ceme cement nt con concr cret ete e pave paveme ment nt inv invol olve ves s foll follow owin ing g stages:

a.

Preparation of sub grade.

b.

Preparation of sub base.

c.

Fixing of farm.

d.

Batching of materials and mixing.

e.

Carrying and placing concrete.

f.

Compaction and finishing.

g.

Floating and edging.

h.

Belting and edging.

i.

Curing.



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Question 1.

Join Joints ts in in cem cemen entt conc concre rete te pav pavem emen ents ts can can be be clas classi sifi fied ed int into o thre three e categories. Describes them.

2.

Desc Descri ribe be the the pre prepa para rati tion on of subsub-on on a goo good d soi soill for forma mati tion on



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Answer 1.

Expa Expans nsio ion n join joints ts pro provi vide de spa space ce int into o whi which ch pave paveme ment nt can can exp expan and. d. These joints release compressive stresses developed in the concrete slab. Expansion joints also relieve stresses caused by construction and warping.

Contraction joints relieve tension developed in the concrete due to contraction. They prevent formation of irregular cracks contraction joints also relieve stresses due to warping.

Warping joints relieve stresses due to warping effect develops in the slab. These joints are commonly used for longitudinal joints dividing the pavement into lanes. Warping tendencies are set up in the concrete slab due to temperature difference between top and bottom of the slab. At 12 noon the temperature at the top surface of the slab will be higher than that at the bottom. This causes top fibres of the slab to expand by larger amount than the bottom fibres and slab warps down wards at the edges. Similarly at 12 night, the temperature of the bottom of the slab is higher than the temperature at the top of the slab and slab warps upwards at the edges. Weight of the slab tries to prevent this warping of the slab and thus warping stresses are set up. Intensity of warping stress is maximum at the interior and minimum at the edges.

2.

Preparation Of Sub Grade



C3010 / UNIT 7

Where formation soil is of very good quality, cement slab may directly be laid over the prepared sub grade. The top 15 cm layer of the sub grade should be compacted and checked for trueness by mean of scratch template. Unevenness of the surface should not exceed 12 mm in 3 m length. Sub grade should be prepared and checked at least two days in advance of concreting. It is desirable to lay a layer of water proofing paper then even concrete can be laid directly over the soil sub grade. Prepared sub grade should complete the following requirements:

i.

There should not be any soft patches on the prepared sub grade.

ii. ii.

Sub Sub gra grade de shou should ld pres prese ent the the un unifor iform m sup suppo port rt to the the concrete slab.

vi.

Should be properly drained.

vii.

Minimum modulus of sub grade reaction obtained with plate bearing test should be 5.5 kg / cm 2.

viii. viii.

If waterp waterpro roof of pap paper er is to to be be laid laid dire directl ctly y ove overr the the sub sub grade, moistening of sub grade prior to placing of the concrete over it, is not required. Moistening is essential in case waterproof papers are not used.

Unit 7 ( CONSTRUCTION OF RIGID/CONCRETE PAVEMENT )

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