Short panelled Concrete pavement in Built-Up Area

By

Rajib Chattaraj1 and B.B.Pandey2

Abstract

Bituminous roads in built up areas are damaged in monsoon due to poor drainage. Cement concrete pavements become the obvious

choice in such locations. Short panelled Concrete pavements develop much lower wheel load stresses than the conventional ones and

require lower thickness. The paper describes construction of short panelled concrete pavements over stone set pavements in a built up

area in Burdwan district, West Bengal. Stress analysis by Finite Element shows that such a pavement may have a long life due to much

lower stresses. The cost of the pavement is a little higher than the bituminous pavements but far lower than the conventional concrete

pavements whereas the durability is expected to be much higher than bituminous pavement, same as that of conventional concrete

pavement.

1 Introduction

Bituminous pavements in built up areas are usually subjected to adverse

moisture conditions due to inadequate and clogged drainage resulting in heavy

damage during every monsoon though the proportion of traffic carrying heavy

loads is not high. Concrete pavement appears to be the obvious solution for

such locations but the initial cost of the conventional concrete pavement is

quite high because of higher thickness. A new type of thinner concrete

pavement with shorter panel size similar to the white topping over bituminous

pavements as per IRC:SP:76-2008(1) can be used in the construction of

concrete pavements for village roads and city streets because of low flexural

stresses caused by shorter panel sizes. Such pavements may be termed as

Panelled concrete pavement. Thinner concrete pavements in the form of short

slabs of dimensions 0.5m x 0.5 to 2.0mx2.0m formed by creating weakness by

saw cutting to one third depth can be a low cost option for a durable

pavement. White topping with short panels has been used as overlay over

damaged bituminous pavements with success at many locations in Delhi,

Mumbai,Pune, Bangalore etc. Indian Roads Congress has brought about a

guidelines IRC:SP:76-2008(1) for thickness design.

1. Executive Engineer,PWD,West Bengal, chattarajrajib@gmail.com

2. Former Professor and Head,,Civil Engg. Dept.IIT Kharagpur, bbpandey40@gmail.com

Using similar concept, concrete slab with short panels formed by saw

cutting to one third the depth of slab thickness can be laid over the granular or

cement treated sub base or any other non-conventional type like stone brick

pavement for the construction of road pavements at a lower cost than a

conventional concrete pavement. The present paper describes the design

aspect and construction of a short panelled concrete pavement over stone

brick pavement with very poor drainage for a street in a small town in

Burdwan district of West Bengal. Though heavy traffic is not much, the

drainage condition is poor and bituminous pavements were getting damaged

frequently. It is expected that such a pavement, constructed as short panelled

concrete pavement would last much longer in spite of poor drainage condition

due to low proportion of heavy vehicles. A new type of concrete pavement

termed as Panelled Concrete Pavement is of size 1.0mx1.0m using the concept

of white topping (1) was used in the construction in the project. Construction

details and checks for the safety of pavements against cracking due to wheel

load have been examined. The constructed pavement completed in March

2012 has been performing well during the last ten months including a rainy

season in between.

2 Review of literature

Examples of panelled pavements over granular or cementitious bases are not

very common. Most concrete pavements with short slabs are laid as overlays

over milled bituminous pavements and the overlay is generally assumed (1) to

be bonded to the milled bituminous base. A number of concrete pavements (

2-9) with panels of size 0.5mx0.5m to 1.5mx1.5m with thickness from 50mm

to 150mm have been constructed in USA including India. Such pavements

were laid as overlays over damaged bituminous pavements and known as

white topping. Bonding of Concrete slab with the milled bituminous surface

was considered in the analysis. No analytical design method is available

currently. An approximate design method is suggested in IRC: SP: 76-2008(1).

There is plenty of gap in the knowledge about the values of flexural stresses

caused by wheel loads that may develop in the slab due to wheel load.

3 Analysis

3.1 If a pavement is made of small concrete blocks as shown in Figure 1, there

is only compressive stress at the bottom.

If the size of the slab is increased, tensile stresses are caused in the slab due to

the bending moment from the overhanging part of the slab and the reaction

from the soil/foundation. For wall or column, the foundation slab is thick and

the deflection caused by loads is nearly constant implying uniform reaction

from the foundation soil. Since the deflection along the thin slab of a

pavement is larger near the points of load application and decreases with

distance from the loaded area, the reactive pressure that is proportional to the

deflection is not constant. Three dimensional Finite element method is the

only method of stress analysis in such slabs of finite dimension. The foundation

is considered as a Winkler foundation, also known as Dense Liquid foundation,

and the pressure at a point is proportional to the deflection caused by the slab

and is given as

p= k δ ….1

Where p= pressure on the slab from the soil, MPa

K= modulus of subgrade reaction , MPa/m

δ = deflection of the slab,m

3.2 Figure 3.3 shows a 4.0 m x 4.0 m pavement consisting of sixteen panels

each a metre in length and width with one third depth from the surface saw

Figure 3.1 Compressive pressure at the bottom

Figure 3.2 Tensile stresses in slab due to bending moment in a large slab

M M

cut to create a plane of weakness to induce full depth cracks to form

interlocking panels due to zigzag cracks.

Stress is analysed by placing a dual wheel carrying a load of 50 kN at a tyre

pressure of 0.8 MPa tangential to an edge as shown in Figure 3.3. The other

dual wheel assembly of the concerned axle would be about 2.00m away from

the centre of the dual wheel causing little interference in stresses caused by

the loaded panel shown in Figure 3.3.The slabs may have load transfer at the

weakened saw cut joints because of lower panel size. If there are plenty of

overloaded vehicles, the interlocking behaviour of joints may become

negligible resulting in very low load transfer across a joint. It is, therefore, safer

to compute stresses considering that there is no load transfer through the

joints. Stress computation is done considering that other slabs do not share

any load. ANSY’s Finite Element Software has been used for stress analysis

4 Site details

4.1 The site is located in Mankar town, Burdwan district of West Bengal, 140

km westwards from Kolkata. The work of short panelled concrete pavement

was done on a 600 meter long stretch of very bad conditioned road with

150mm thick granular subbase and 150mm thick jhama brick consolidation and

75mm thick stone brick on top for a length of 400 meter and the rest 200

meter length of road was topped with thin premix carpet and seal coat. It is

located in a built up area which is subjected to water logging during the

monsoon bringing about damage and depression on the stone brick surface

and large ditches to the premix carpeted surface(Photo-1,2 &3). The road

Figure 3.3 4.0mx 4.0 m pavement with 1.0 mx1.0 m panels formed by

saw cutting to one third depth of the slab saw cut

Dual wheel

carries a traffic of about 428 Commercial Vehicles Per Day and some heavily

loaded vehicles are also expected. Axle load data is not available.

Photo-1—Dillapited condition of the road during rainy season.

Photo-2—Pre work condition of the pavement with poor drainage.

Photo-3—Stone brick set pavement with damaged spots.

4.1 It was decided to construct a concrete pavement of 4.50m wide with

150mm depth PQC of M-40 grade with panel size of 1m x 1m formed by sawing

to a depth of about 50mm. There was no scope of greater width because of

built up area on either side of the road. A lean concrete base of an average

thickness of 100mm with M-10 grade was done to provide a uniform support

as a levelling course below the panelled concrete pavement.

5 Construction of concrete pavement

5.1 Both M-10 and M-40 grade concrete was done as Ready mix

Concrete.(Photo-4 & 5).

Photo-4—RMC plant site.

Photo-5 – RMC plant and transit mixer.

The source of coarse aggregate was Panchami variety, Dist: Birbhum(W.B).

50% of 20mm down and 50% of 10mm down stone aggregates were mixed to

achieve 20 mm graded aggregate of nominal size as per Table-1 of IRC-44 and

Table-2 of IS-383. The fine aggregate was Damodar river sand of Zone-III as per

Table-2 of IRC-44 and Table-4 of IS-383. The cement used was OPC-43 grade.

Super plasticizer was used as chemical admixture. The design mix of M-40

grade concrete was done as per IRC-44(2008) read along with IS-

10262(2009).The mix proportion of M-40 concrete stood per m3 of concrete as

450kg cement, 644kg sand, 649kg 20mm down stone chips, 649kg 10mm down

stone chips,162 kg free water and 5.4 kg of superplasticizer.

5.2 Quality control measures for concreting work was taken both at RMC plant

site (Photo-6 &7) and the construction site(Photo-8 & 9). Concrete cubes from

every batch were taken both for M-10 and M-40 concrete. Concrete cubes

were taken at construction site also. Slump was set at plant site as 100-

125mm. The slump obtained at the construction site was in the range of 70-80

mm. Work was done during the month of March when the ambient

temperature was around 380C. Thus, the drop in slump value was quite

expected, in fact, due to this reason the initial slump at plant site was kept at a

bit higher side. The characteristic compressive strength of concrete cubes were

tested at 28 days, some were tested on 7 days. On an average, the

characteristic compressive strength for lean concrete was obtained as 23 MPa

and for PQC it was 48MPa.

Photo-6—Taking of concrete cubes and slump at plant site.

Photo-7-- Testing of characteristic compressive strength of concrete cubes.

Photo-8—Slump testing at site.

Photo-9—Taking concrete cubes at site.

5.3. The laying of concrete was done manually. The undulation of the stone

brick pavement was levelled with 100mm average thick of lean concrete (M-

10). Also the correction of camber had been made in this layer. Over the

stretch on which M-10 lean concrete was laid in a day’s work, say 100 to 120

meter, on the very next day the PQC of 150mm M-40 grade concrete was laid

on the same stretch. Camber was kept as 2%.(Photo-10 & 11).

5.4. Creating a discontinuity on the top one third depth of the concrete

pavement became a challenging problem. Alternative to saw cutting was

examined. Measures like putting metal and plastic strips and coated plywood

(Photo-12) were also explored. After the initial hardening of the concrete, even

the coated plywood was difficult to be detached to get a distinct groove of

3mm. Since there was little time for experimentation with different

alternatives, the conventional method of construction of joint cutting with a

diamond saw to one third the depth of the slab was adopted. (Photo-13).

Grooving with diamond cutter up one third depth was done immediately on

the next day morning of the previous day’s execution of M-40 grade concrete.

The appropriate time for cutting the groove is very important in the sense of

making a distinct as well as easily cut able groove with diamond cutter.

Photo-10–Laying of concrete from transit mixer.

Photo-11—Laying of lean concrete as levelling course.

Photo-12 – making discontinuity with coated plywood strip.

Photo-13 – Making 3mm groove by diamond cutter.

5.5 Immediately after making groove with saw cutting, curing was started.

Curing was done with total inundation under water for at least 28 days (Photo-

14 & 15). For the long period of curing as well as the concreting work, the road

was blocked for 50 days. Local block administration and district administration

extended their co-operation to arrange for a diverted route.

Phot-14—Curing of concrete by total inundation under water.

Photo-15—Curing started just after making groove by saw cutting.

6 Modulus of subgrade reaction and stress computation

6.1 The subgrade has a CBR of 5 and the corresponding k value is 42MPa/m as

per Table 2 of IRC: 58:2011. Considering Tables 3 and 4 of IRC: 58:2011, the

effective k value over 100mm lean concrete base is about 230MPa/m. It may

be mentioned that only fourth root of k value matters in flexural stress

computation and a little variation in its value has negligible effect on flexural

stresses. A value of 200 MPa/m is used in the analysis of stresses.

6.2 For the loading condition shown in Figure 3.3 assuming no load transfer

across the joints, the computed stress for the dual wheel load of 50 kN

corresponding to the legal axle load limit of 100kN (10.2 Tons) having a tyre

pressure of 0.8 MPa is found as 1.70 MPa which is well below the 28 day

modulus of rupture of 4.4 MPa for M40 concrete pavement. Curling stress due

to temperature gradient is very low (10) and may be neglected all together.

Since occasional overloading due to construction traffic is very common for

most roads, the pavement will be safe even if the axle load is 200 kN since the

computed stress value for this load is 3.40 MPa. Repeated action of traffic also

will not be able to cause early damage due to low stresses. Load transfer at the

joints and slight bonding with the lean concrete will impart additional strength.

It may be noted that for the same dual wheel load of 50 kN, pavement width -

3.75m, transverse joint spacing - 4.0m, the flexural stress due to load and

temperature differential as per IRC:SP:62:2004(11) is found as 4.66 MPa for

West Bengal. A much higher thickness is needed if fatigue is also considered.

7 Cost comparison

7.1 Cost of this short panelled concrete pavement of 150 mm M-40 grade PQC

along with 100 mm lean concrete with allied items had come Rs. 1500/- per sq.

meter. Cost would have come even lower, had there been no lean concrete as

levelling course. In comparison to this type of pavement, the other alternatives

which are generally adopted on roads with poor and clogged drainage such as

short lived 50mm thick Bituminous Macadam and 25mm Mastic Asphalt had

been estimated as Rs. 1000/- per sq. meter and conventional rigid pavement of

250 mm PQC and allied items were estimated as Rs. 3300/- per sq. meter.

8.0 Conclusions

1. Panelled concrete pavements can be a good alternative for reducing the cost

of concrete pavements for built up areas, rural roads, bus bays etc.

2. Stresses are reduced drastically in concrete pavements with panels of size

1.0 m x 1.0 m.

3. If alternative route can be arranged, this type of pavement is very easy to

construct with much higher durability than Mastic Asphalt surfaced bituminous

pavement and serviceability expected to be same as conventional rigid

pavement at much lower cost.

4. This technology can be emerged to be a good and long-term solution to the

perpetual maintenance problem of the roads with poor drainage.

Gratitude: The authors gratefully acknowledge the permission granted by

Sri Bibek Raha, the then Chief Engineer, PWD, Govt.of West Bengal, to execute

this new technology for the first time in a problematic road of West Bengal.

References

1. IRC:SP:76-2008 (2008).“Tentative Guidelines for Conventional, Thin and Ultra- Thin

Whitetopping”, Indian Roads Congress, New Delhi.

2. Jundhare, D.R. et al. (March 2011). “Edge stresses and deflections of unbonded conventional

whitetopping overlay”, The Indian Concrete Journal, pp. 35-44.

3. Rasmussen, R.O. and Rozycki, D.K.. (2004). “Thin and ultra-thin Whitetopping-A Synthesis of

Highway Practice.” NCHRP Synthesis 338, Transportation research Board, Washington, D.C.

4. Speakman, J. and Scott III, H.N.(1996) “Ultra-Thin, Fiber- Reinforced Concrete Overlays for Urban

Intersections,” Transportation Research Record 1532, Transportation Research Board, National

Research Council, Washington, D.C., pp. 15–20.

5. Armaghani, J. and Tu, D.(1999) “Rehabilitation of Ellaville Weigh Station with Ultra-Thin

Whitetopping,” Transportation Research Record 1654, Transportation Research Board, National

Research Council, Washington, D.C., pp. 3–11.

6. Cole, L.W. and Mohsen, J.P.(1993) “Ultrathin Concrete Overlays on Asphalt,” Presented at the TAC

Annual Conference, Ottawa, ON, Canada.

7. Lahue, S.P. and Risser, R.J.(Sep. 1992) Jr., “Ultra-Thin Concrete Overlay Supports Truck Loads,”

Concrete Construction, Sep. 1992, pp. 664–667.

8. Cole, L.W.(1997), “Pavement Condition Surveys of Ultra-Thin Whitetopping Projects,” Proceedings

of the 6th International Purdue Conference on Concrete Pavement Design and Materials for High

Performance, Vol. 2, Indianapolis, Ind., pp. 175–187.

9. Wen, Haifang., Li, Xiaojun. and Martono, Wilfung. (2010) “Performance Assessment of Wisconsin’s

Whitetopping and Ultra-thin Whitetopping Projects.” WHRP, Transportation Research Board.

10. .IRC:SP:62-2012( Revised Draft),’ Guidelines for design and Construction of Cement concrete

pavement for rural Roads’, Indian roads Congress, New Delhi

11.IRC:SP:62-2002,’ Guidelines for design and Construction of Cement concrete pavement for rural

Roads’, Indian roads Congress, New Delhi.