Thursday, December 16, 2010

PERFORMANCE AND ECONOMIC EVALUATION OF CEMENT CONCRETE ROADS-WITH CASE STUDIES

Based on the structural behaviour, highway or airport pavements can generally be classified in to two-flexible pavement and rigid pavements.in India we mainly use flexible pavement for road construction, because of the high initial cost for rigid pavements. Main advantage of the rigid pavement is that maintenance needed is very less. When we compare the life cycle cost of both bituminous and concrete roads, bituminous roads has got more life cycle cost than the concrete roads. But noise pollution is a problem connected with cement roads. For reducing noise pollution, noise barriers and a special type of concrete called whisper concrete can be used.

Key words: pavements, bituminous, cement concrete, vehicle operating cost, fuel consumption, life cycle cost, noise barrier, whisper concrete.

1.0 INTRODUCTION

Road transport in India has been developing at a very fast rate in view of various advantages it enjoys. Motor vehicle population is currently witnessing a sharp rise, accompanied by technology upgradation. The present condition of road so appalling that serious economic losses like fuel wastages, delays, congestion, accidents and pollution hazards are posing daunting challenges. The new roads should be capable of handling the increase in the number of motor vehicles with comfort, speed and safety.

The most important and expensive component of a highway or runway is the pavement structure. The pavement should be stable and non-yielding, to allow the heavy wheel loads of road traffic to move with least possible rolling resistance. The road surface should be even along the longitudinal profile to enable fast moving vehicles to travel safely and comfortably at the design speed. Based on the structural behaviour pavement are generally classified into two categories. They are

i. Rigid pavements

ii. Flexible pavements


Undergraduate Student, Department Of Civil Engineering, N.S.S College Of Engineering, Palakkad -08, Kerala

1.1 Rigid Pavements

Rigid pavements are those which possess noteworthy flexural strength or flexural rigidity. The stresses are not transferred from grain to grain to the lower layers. The rigid pavements are made up of Portland cement concrete either plain, prestressed or reinforced concrete. The pavement has the slab action and is capable of transmitting the wheel load stresses through wider area below.Cross section of rigid pavement is shown in fig1.


Fig 1 rigid pavement

1.2 Flexible Pavement

Flexible pavements are those, which on the whole have low or negligible flexural strength and are flexible in their action. Thus if lower layer of the pavement or soil subgrade is undulated the flexible pavement surface also get undulated. A typical flexible pavement consists of;

i. Soil Subgrade

ii. Sub-Soil Course

iii. Base Course

iv. Surface Course

Cross section of a flexible pavement is given in fig 2.


Sub-base course


Fig 2 flexible pavement

The load transfer is by grain to grain transfer through the points of contact in the granular structure. The load spreading ability of layers depends upon the type of material and the mix design factors. Bituminous concrete is one of the best flexible pavement layer materials.

2.0 ECONOMICS OF CEMENT CONCRETE PAVEMENTS IN COMPARISON WITH BITUMINOUS PAVEMENTS

The initial cost of a pavement is governed by many considerations, the most important of which are

i. Soil support strength

ii. Traffic likely to use the facility

iii. Design life

iv. Pavement specification adopted

v. Cost of stone aggregate

vi. Cost of binder

A comparison of the cost of a cement concrete and bituminous pavement can be meaningful only if the two pavements are designed for similar conditions. For a bituminous pavement, this implies that suitable strengthening layers are added to keep the pavement in a traffic-worthy condition. A sensitivity analysis study has been carried out by Cement Manufacturer’s Association of India, 1989, to cover the common range of values. The analysis was based on

i. Cost of aggregate

ii. Cost of cement

iii. Cost of bitumen

This study was conducted for a new two-lane road having a traffic intensity of atleast 1000 commercial vehicles per day.

Table 1 Cost of materials considered (Rs /cum as per 1989)

Case 1

Case 2

Case 3

Case 4

Stone agg 20-40mm

100

125

15

175

Stone agg 10-20mm

145

145

170

195

Fine agg sand

55

65

75

85

Gravel

65

75

85

95

Table 2 Bitumen cost considered (Rs/ tonnes)

Case 1

Case 2

Case3

Case 4

3250

3500

3750

4000

Table 3 cost of cement considered (Rs/ bag)

Case 1

Case 2

Case 3

Case 4

50

55

60

65

Table 4 Initial cost of flexible pavement

(Rs.Lakhs/ Km of two-lane road)

Soil CBR Value: 5%

Cost of bitumen

(Rs/tonne)

Cost of stone aggregates

Case 1

Case 2

Case 3

Case 4

3250

17.96

19.22

20.38

21.62

3500

18.60

19.86

21.02

22.26

3750

19.24

20.50

21.66

22.90

4000

19.88

21.14

22.30

23.54

Table 5 Initial cost of cement concrete pavement

(Rs.Lakhs/Km of two-lane road)

CBR value 5%

Cost of cement

(Rs/Bag)

Cost of stone aggregates

Case 1

Case 2

Case 3

Case 4

50

18.02

18.34

18.64

18.97

55

18.80

19.12

19.42

19.75

60

19.56

19.88

20.18

20.51

65

20.32

20.64

20.84

21.27

The above results shows that, for medium (CBR 5%) and good soil, cement concrete pavement is cheaper when the cost of stone aggregates is high. This is irrespective of the price of cement and bitumen.


While considering the total life cycle cost, the rigid pavements are found to be more economical than flexible pavements. This is illustrated through another study carried out by G.S TAUNK in a 4-lane road of Rajasthan state namely Udaypur-Dabok road. He calculated the economics of pavements in view of the following aspects.

i. Initial cost of pavement

ii. Annual maintenance cost

iii. Fuel saving

iv. Vehicle operating cost (v o c)

v. Interest rate on the initial extra investment

vi. Renewal coat

Table 6 design parameters

Intensity of traffic

2350 C V in year 1990

Traffic growth rate

7%

Design life in years

20 years after opening to traffic

Vehicle damage factor

2.5

Completion period of project

3.5 years

28 days compressive strength of concrete

40Mpa

Poisson’s ratio

.15

Modulus of elasticity of concrete

3´105kg/cm2

CBR of subgrade soil

5%

2.1 Flexible Pavement

2.1.1 Structural Section

i. Semi dense bituminous carpet -40mm

ii. Dense bituminous carpet -75mm

iii. Water bound macadam base course -225mm

iv. Granular sub base -375mm

2.2 Rigid Pavement

Since the CBR value is less than 10% as per IRC recommendation of IRC 15-2002 a sub base of 10cm lean concrete should be provided. Thickness of slab shall be 25cm of concrete 1:1:2

2.3 Maintenance Cost

From the cost evaluation Mr. G.S Taunk found that the maintenance cost for 1 km bituminous surface is roughly of Rs 0.30 lakhs. But in the case of cement concrete pavement maintenance cost is of Rs. 0.05 lakhs.

2.4 Fuel Saving

The fuel saving can be achieved by

i. Maintaining good riding quality over its life time

ii. By the rigidity of concrete slab

The fuel consumption is dependent on the speed and roughness of the surface. The roughness is practically same in the case of cement concrete roads. But in the flexible pavements the roughness is changing in every year.

Table 7 variation of roughness in BT and CC

Year

Roughness CC mm/km

Fuel consumption in CC

Roughness in BT mm/km

Fuel consumption in BT

Remarks

0

2000

186.077

2000

186.077

1

2000

186.077

2500

186.677

2

2000

186.077

3000

187.277

3

2000

186.077

3500

187.877

Renewal

4

2000

186.077

4000

188.477

5

2000

186.077

2000

186.077

The fuel consumption is calculated using an equation

FC = 44.008+(3904.64/v)+0.0207v2+0.0012 RG

V = 60 km per hour

FC = fuel consumption of vehicle (truck) in cement concrete per km

V = speed in km/hr

RG = roughness in mm/km

2.5 Vehicle Operating Cost

Vehicle operating cost increases due to surface roughness. The concrete pavements maintain its roughness value over its design life; the flexible pavement deteriorates in its riding quality over the years, causing extra voc.

2.6 Renewal Coat

There is no need of renewal coat on cement road but after every fourth year renewal coat has to be laid over flexible pavements. The cost of renewal will be Rs.3.50 lakhs/ km for 2- lane road.

After the study Mr. G S Taunk found that after 9 years the cement concrete road is beneficial. This can be illustrated with the help of a graph


Mumbai - Pune Expressway is another classic example for cement concrete pavement. The government of Maharashtra decided to use cement concrete pavement for the construction of new expressway from the following analysis

i. The whole life cycle cost for 30 years for flexible and rigid pavement was worked out

ii. While working out this cost, capital cost as well as recurring maintenance cost was considered

iii. The benefit accruing to user on account of lesser fuel consumption for the concrete was not considered

iv. The analysis of whole life cycle showed that rigid pavement is economical

v. The total cost of the project was also worked out with flexible pavement and rigid pavement

vi. If revealed that the incremental cost on account of rigid pavement is only 6%

Pavement Specification

Number of lane -6

Thickness of pavement -350mm in embankment section

-270mm in rocky cutting

Grade of cement -M40

Dry lean concrete -M10

Dry lean concrete thickness -150mm in embankment section

-100mm in rocky cutting portion

W.M.M -75mm

Drainage layer -150mm

3.0 PERFORMANCE EVALUATION OF CONCRETE ROADS

3.1 Raw Materials

Cement is a major new material used in cement concrete roads. This ensures easy availability as well as lower cost and saving of foreign exchange. Bitumen is the major component of flexible pavement. This is a byproduct of imported crude.

3.2 Repairing Works

Most of the roads are crowded with traffic in every time. The nominal traffic remains suspended only for a brief period of 3-4 hours in the late night. This makes repairing work very difficult. After most of the repairs the vehicle traffic starts before the repaired surface is hardened enough and the repaired bitumen going away with the vehicles. In concrete pavement since the maintenance needed is very less such problems are not present.

3.3 Pot Holes And Undulations

Heavy rainfall with inadequate camber and drainage is one of the major causes of failure in the bituminous road. Due to this, potholes and undulations are formed which results in the reduction of speed of traffic. Breakdown due to pot holes aggravate traffic jams. Since the rigid pavements are made up of concrete slabs pot holes and undulations are not present.

3.4 Cost Of Transport

The lower speed of vehicle due to bad condition of road reduces drastically the availability of vehicles and there by increasing per ton cost of transport. The vehicles turn round time going one to another location and back plays large role in reducing the utility of the vehicle and there by per ton or per person cost of transport. The cement concrete road shall ensure higher speeds, lesser and lesser brake down of vehicles and there by short turn around time which can definitely reflect into the economy of transport of goods and people.

3.5 Fuel Consumption Of Vehicles

The fuel consumption of bituminous roads is found to be higher than for the vehicles on cement concrete roads. This is due to the flexibility of bituminous roads which needs large fuel to drive vehicles on it. The impact of fuel saving based on current vehicular traffic in India is estimated to be Rs.5600 crore per year. The fuel saving on concrete road is given below.

Table 8 fuel savings cement concrete roads

Pay load (T)

Gross vehicle weight (T)

Fuel consumption of optimum speed of 33km/hr in cement concrete/km

Percent saving

Bituminous surface

Concrete surface

0(empty)

7.1

120.46

109.85

8.8

5

12.1

148.91

138.30

7.1

10

17.1

177.36

166.75

6.0

15

22.1

205.81

195.20

5.2

3.6 Weather Conditions

In India because of high temperature in summer of the states it is commonly noticed that bitumen gets melted during the peak summer months. The heavy traffic picks up most of the melted bitumen and exposes the aggregate. Then the rain comes and the results are obvious. Weather has no effect on cement concrete roads.

3.7 Skin Resistance

Cement roads have high skid resistance and therefore higher speed of vehicles can be tolerated without accidents. Many accidents on bituminous roads are simply caused by skidding of the loaded vehicles at higher speed.

3.8 Pollution

Due to bad road conditions the vehicles need frequent changes of gears and braking and speeding which in itself is a large contributing factor for additional fuel consumption. The vehicles which are speed up and then, road condition will also have tendency to develop higher levels of pollution.

3.9 Soil Conditions

In many areas the surface on which the road is laid has weak soil. Bituminous roads are laid on such soils relying on the principle of UDL breakdown very soon due to settlement. In the case of concrete roads because of slab design principle, it stands undisturbed even when there is no full support below the surface. This makes it the best choice for poor soil condition.

3.10 Light Reflection

Cement concrete road surface is lighter in colour than bituminous road. The reflection of lights from the street light or from the vehicle lights is far better on cement concrete roads than on bitumen road which absorbs the light. This is very helpful in safe driving in night as well as reducing the level of illumination in the towns to obtain the same.

3.11 Thickness

Concrete road requires less thickness than bituminous road for the same loading and for the same soil conditions. Therefore, there is a conservation of the material itself by resorting to cement concrete roads. The benefit becomes larger and larger as the soil condition becomes poorer and poorer.

3.12 Total Cost

The budgetary cost of cement concrete road of 7m width (2lines) and 1km long is approximately Rs.45 lakhs. The cost of bituminous road will be nearly the same or marginally lower. However, when coming to life cycle cost, concrete road will always be cheaper by 5% to 40 %.

4.0 ADVANTAGESS AND DISADVANTAGES OF CONCRETE ROADS

4.1 Advantages

i. Life and salvage value are more of cement concrete road.

ii. Concrete pavement gives hard resistant surface. So it is better choice for higher volume.

iii. It gives good riding quality.

iv. It helps in fuel saving.

v. It can withstand high intensity of traffic with practically maintenance free performance.

vi. Concrete is not affected by oil/acid spilling from vehicles. Thus concrete surfaces are suitable in car parking, bus depots, airports and truck parking.

vii. Penetration of water is less into sub grade.

viii. Concrete surface being light coloured are good for night driving.

ix. Good skid resistance over a very long period.

x. Where zero maintenance is imperative (eg. Tunnels) cement concrete road is the best choice.

xi. Concrete roads are not affected by extremes of weather.

xii. Environmental pollution will be reduced in case of rigid pavement.

xiii. Saving in foreign exchange in cement concrete roads s almost all materials are indigenous.

xiv. Material consumption is about 50% of flexible material.

4.2 Disadvantages

i. High initial cost.

ii. It is not possible to dig trenches across the pavement for laying of utilities.

iii. In day, it reflects more light which is not desirable.

iv. They are noisy.

v. Time taken for construction is too long.

5.0 REMEDIAL MEASURES

Roads are extremely valuable assets for any nation and therefore they shall be more looked upon with permanency in view. The initial cost comparison between cement concrete roads and bitumen road is inappropriate method of making judgment and the only comparison which is truthful is comparing the life cycle cost.

It has been approved by studies that for any given cost for store aggregates the life cycle cost of cement concrete road is lower than the bitumen road irrespective of the price of cement life cycle cost is the criteria. The difference in life cycle cost between these two kinds of roads varies from 5% to 40% i.e. bituminous road is costlier by 5 to 40%than cement concrete road.

Another major problem with cement concrete pavement is the noise pollution. The noise barrier is usually constructed in the form of a vertical wall of appropriate height and thickness and it can be in timber, brick, steel, concrete or even earth. The noise barriers have the capacity to reduce the noise levels by 10-15 dB (A). The construction of noise barriers involves expenditure.

Besides the construction of barrier, a certain degree of noise migration is also possible by the adoption of an appropriate pavement surface. Considerable effects have already been made in advanced countries- mainly in Europe and Japan. To find alternatives to mitigate the problem and it was observed that noise abatement in both the concrete as well as asphalt surfaces is possible when their surface are made ‘porous’. The porous concrete is termed as whisper concrete r exposed aggregate concrete.

5.1 Advantages Of Whisper Concrete

i. Safe and skid resistant surface.

ii. Improved riding quality.

iii. Longer life.

iv. Rut free surface.

v. No special maintenance needed.

vi. Suitable for all road conditions.

vii. Environmental friendly.

viii. Durable.

6.0 CONCLUSION

From the studies it is proved that the cement concrete roads have more life than flexible pavements. The maintenance required is also negligible in the case of concrete roads. But developing countries cannot afford heavy investment at the initial stages; though after some time the concrete pavement is prove to be economical.

ACKNOWLEDGEMENT

I express my sincere gratitude to my seminar guide Dr A K Raji, Senior lecturer, Department of Civil Engineering, without whose valuable guidance and support the seminar would not have been a success.

REFERENCES
  1. “Background paper for presentation on cement concrete roads”; Cement Manufacturer’s Association, Volume II
  2. “India’s First access controlled Expressway Mumbai-Pune”; Cement Manufacturer’s Association, 2001.
  3. IRC 37-2001; Guidelines for the design of flexible pavements, The Indian Road Congress 2001.
  4. IRC 58-2002; Guidelines for the design of plain jointed rigid pavements for highways, The Indian Road Congress- 2002.
  5. “Pavement quality concrete for Section B: An overview Mumbai-Pune Expressway”;
  6. Jalota A V and Tikoo P N, The Indian Concrete journal, June 2000.
  7. “Whisper concrete for pavements”; Mohan S, Dutta N and Sharin S M, The Indian Concrete journal, July 2004.
  8. “Why cement concrete roads”; Rawal M P, NBM & CW, October 2000.
  9. “Rigid pavement Vs Flexible pavement”; Indian highways, February 1998.
  10. “Sensitivity analysis of cost of flexible and concrete pavements”; Cement Manufacturer’s Association, Volume I

3 comments:

  1. i want this seminar soft copy.......plz send me fast in my id - prags7cool@gmail.com

    ReplyDelete
  2. sorry pragya.. cant send t.. its all this wat i have..

    ReplyDelete
  3. Interesting blog ....good information very helpful to readers ...thanks for sharing keep posting..!
    For More Information CC Road Construction Companies

    ReplyDelete