initial cost comparison of rigid

8/11/2019 Initial Cost Comparison of Rigid

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INITIAL COST COMPARISON OF RIGID AND FLEXIBLE PAVEMENTS: UNDER DIFFERENTTRAFIC AND SOIL CONDITIONS

T. AkakinTurkish Ready Mixed Concrete Association, Turkey

[email protected]

Y. EnginTurkish Ready Mixed Concrete Association, Turkey

[email protected]

S. UcarTurkish Ready Mixed Concrete Association, Turkey

[email protected]

ABSTRACT

In this paper, the economic analysis has been done on both flexible and rigid pavements. Thesecost analyses play a great role on the decision-making stages in selection of pavement types. Inthis analysis initial cost of rigid and flexible pavements have been determined for both flexiblepavements and rigid pavements according to AASHTO 93 (American Association of State Highwayand Transportation (1993) Guide for Design of Pavement Structures) design guideline.

The pavements were designed under different traffic conditions and different soil conditions.According to the output of design parameters the layer thicknesses and costs are calculated.

KEY WORDS

PAVEMENT / CONCRETE ROAD / COST COMPARISON / INITIAL COST

1. INTRODUCTION

Initial cost is generally the major factor in deciding the type of the pavement in design. Theplanners often think that the flexible pavement is cheaper than the rigid pavements. In fact this isnot always the case. In the last decade the price of bitumen which is the main ingredient of flexiblepavement has increased because of the increase in crude oil prices. However the rigid pavementsmain ingredient cement price is declining especially in Turkey.

Government executives frequently have to choose between concrete and asphalt paving materialsfor roads and highways. In the last few years in asphalt which caused a dramatic escalation in

asphalt pricesreflected in a 250% increase during 2005-2008. It is likely that once the economicrecovery gains traction, large shortages may reappear, oil prices will rise and asphalt prices willresume their upward climb. From 2003 to 2008 oil prices increased nearly 300%. During the sameperiod, liquid asphalt increased 250%. The increases in asphalt prices during this period were notonly a result of rising oil prices, but also by changes in oil refining practices which has led to areduction in heavy crude production and reduced supply.

Global economic weakness has resulted in a 50% decline in oil prices during the past year.Despite reduced paving demand and lower oil prices, asphalt prices have declined only 12% fromrecord high levels during the same period.

Oil price scenario given in Figure 1. reflects significant changes in global energy demand.

Emerging markets are increasingly becoming a major driver. Longer term world economic growthis expected to be characterized by developing and transitional economies adding new demandpressures on oil prices. By 2015 oil prices are conservatively expected to exceed $133 per barrel


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reestablishing past peaks. Longer term projections made by the United States government suggestthat oil prices may exceed $180 per barrel by 2030.

Figure 1. Oil price scenario - Oil prices between 1990-2010 and 2015 estimates (PCA)

Figure 2. Change in ready Mixed Concrete Prices between 2003-2010 in Turkey (USD/m3)

However in this period the prices of concrete prices are nearly dormant. The price of concretebetween 2003-2010 is given in Figure 2 in USD. The concrete price in Turkey ,with concrete pumpprice included, is about 40USD/m3. Taking these changes in the market into account in thisanalysis we compared the initial costs of asphalt and concrete pavements.

2. CALCULATIONS

The pavement analysis is done according to AASHTO 1993 with the following conditions.


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2.1. DESIGN METHODS

In this research the design of rigid pavements and flexible pavements is done according toAASHTO 1993. The pavement layers are given in Figure 3 and Figure 4. Rigid pavement isdesigned according to AASHTO93 with layers ; concrete pavement and sub base course ofcrushed stone.

The principal criterions in the design of pavements are traffic and subgrade. The number ofrecurrences of an equivalent standard single axle load of 8.2 tonnes on the road within a selectedperiod was derived from Annual Average Daily Traffic (AADT) values and taken as the traffic loadin this study.

This study examines 11 different categories of traffic. These categories were determined on thebasis of the conditions on Turkish Highways and the number of recurrences of an equivalentstandard single axle load of 8.2 tonnes within the selected period of analysis, that is T8,2 variesbetween 20 millions to 250 millions.

Another important criterion in pavement design is the load bearing capacity of subgrade soil. In thisstudy, the load-bearing capacity of four different soil types were used in analysis. Modulus ofresilience values is ranged from 5000 to 20.000psi. 5.000-10.000-15.000-20.000psi.

12 2

4

5 6

8

9

7

10

11

1213

14 15

16

12 2

4

5

6

10

11

1213

14 15

16

Figure 3. Flexible Pavement Cross-section

1. Width of driving lanes 9. Crushed stone sub base layer2. Shoulder width 10. Road Base (Subgrade soil)4. Platform width 11. Backfill slope5. Wearing course surfacing 12. Horizontal slope of road6. Binder course surfacing 13. Shoulder slope7. Bituminous base course 14. Ditch slope8. Plant mix base and shoulder backfill course 15. Cut off slo e

Figure 4. Rigid Pavement Cross-section

1. Width of driving lanes 11. Backfill slope

2. Shoulder width 12. Horizontal slope of road4. Platform width 13. Shoulder slope5. Concrete pavement 14. Ditch slope6. Crushed stone sub base layer 15. Cut off slope10. Road Base (Subgrade soil)


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2.2. PAVEMENT PROPERTIES

2.2.1. Geometrical PropertiesCost analyses for one type of flexible pavement and two types of rigid pavement were made for 11different traffic categories. The geometrical properties of the road for which cost analysis wasmade are as follows:

Length of road: 1000 mPlatform width: 12 mTotal shoulder width: 5 mWidth of driving lanes: 7 m (2 lanes)

In the rigid pavement, both the course of concrete pavement and the base course continue withoutany change into the shoulders. In the flexible pavement a plant mix backfill layer takes the place ofthe hot bituminous base course in the shoulders while wear and binder courses continue into theshoulder.

Dowels and tie-rods are used in the joints of jointed unreinforced concrete pavements. Threelongitudinal joints are placed over the total road width, with one between the two lanes and twowhere driving lanes meet the shoulders. Transverse joints shall be cut at an average of every 5 mas contraction joints. Joints are sawed down 1/3 joint thickness and a fiber is placed, coated up to15 mm and sealed with cold joint sealer. Dowels are placed at an average of every 30 cm intransverse joints. Dowels are flat, S220a class, 25mm diameter and 60 cm long. While tie-rods areribbed, S420a class, 12mm diameter and 80 cm long and are placed every 80 cm in longitudinaljoints. Dowels are coated with bitumen to prevent both adhesion with concrete and corrosion.The following parameters are chosen for flexible and rigid pavement1. Reliabilitya. Reliability level in percent (R) %50b. Combined standard error (So) 0.52. Serviceability

a. Initial serviceability index (pi) 4.5b. Terminal serviceability index (pf) 3The 1993 AASHTO Guide offers the following relationship between k-values from a plate bearingtest and resilient modulus (MR):

The results according top AASHTO 1993 can be found in Tables 1-8 and the cost analysis can befound in Figures 3-6.

2.2.2. Material PropertiesFollowing are the specifications of the concrete we decided to use in road pavement:Strength: C40 (fck=40 MPa),Cement dosage: 375 kg/m3,

Water/cement ratio: 0.41,Maximum aggregate size: 30 mm,Consistency: S1 (between 0-5 cm).

As for the flexible pavement, the specifications of the material chosen are as follows:Bitumen type: AC 60/70,Bitumen weight ratio for wear coarse: 5.35%,Bitumen weight ratio for hot bituminous base: 4%.

Using the variables above with the equation solver provided by Washington University athttp://training.ce.washington.edu/WSDOT/ below Figure 5 and Figure 6 we solved the layerthicknesses for variable sub base and traffic loads.
http://training.ce.washington.edu/WSDOT/http://training.ce.washington.edu/WSDOT/http://training.ce.washington.edu/WSDOT/


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Figure 5. Washinton University computer program for Rigid Pavement Design


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Figure 6. Washinton University computer program for Rigid Pavement Design

3. RESULTS

The pavement thicknesses are calculated with the parameters above and the results are given forRigid, asphalt pavements for different subsoil conditions and different traffic load is given in belowTable 1-8 the thickness layers and the cost of the 1 km road are given in Figures 7-10. The costsare calculated with 2009 prices for the works done for each pavement type for each work. As givenin short form in Table 9.


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Table 1. Layer thicknesses for Flexible Pavement for 5.000psi subgrade

Pavement

(cm)

Traffic Category

20 40 60 80 100 120 140 160 180 200 250

Surface 5 5 5 5 5 5 5 5 5 5 5Bituminous

Base12.5 15 16.5 17.5 19 19 19 20 20 20 21

Gradedcrushed

stone24 25 27.5 29 29 31.5 32.5 31.5 33.5 35 33.5

CrushedStone Sub

base20 20 20 20 20 20 20 20 20 20 20


Pavement

(cm)

Traffic Category

20 40 60 80 100 120 140 160 180 200 250

Surface 5 5 5 5 5 5 5 5 5 5 5

BituminousBase

12.5 15 16.5 17.5 19 19 19 20 20 20 21

CrushedStone Sub

base25 25 25 25 25 25 28 28 28 30 30


Pavement

(cm)

Traffic Category)

20 40 60 80 100 120 140 160 180 200 250

Surface 5 5 5 5 5 5 5 5 5 5 5

BituminousBase

12.5 15 16.5 17.5 19 19 19 20 20 20 21

Crushed

Stone Subbase 15 15 15 15 15 15 15 15 15 15 15


Pavement

(cm)

Traffic Category

20 40 60 80 100 120 140 160 180 200 250

Surface 5 5 5 5 5 5 5 5 5 5 5

BituminousBase

12.5 15 16.5 17.5 19 19 19 20 20 20 21

CrushedStone Sub

base5 5 5 5 5 5 5 5 5 5 5


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Table 5. Layer thicknesses for Rigid Pavement for k=250pci with dowel bar

Pavement

(cm)

Traffic Category

20 40 60 80 100 120 140 160 180 200 250

ConcretePavement

25 26.5 29 30 30 31.5 32.5 32.5 34 34 35

CrushedStone Sub

base15 15 15 15 15 15 15 15 15 15 15


Pavement(cm)

Traffic Category

20 40 60 80 100 120 140 160 180 200 250

ConcretePavement

24 25 27.5 29 30 30 31.5 31.5 32.5 32.5 34

CrushedStone Sub

base15 15 15 15 15 15 15 15 15 15 15


Pavement

(cm)

Traffic Category

20 40 60 80 100 120 140 160 180 200 250

ConcretePavement

22.5 25 26.5 27.5 29 30 30 31.5 31.5 32.5 34

CrushedStone Sub

base15 15 15 15 15 15 15 15 15 15 15


Pavement

(cm)

Traffic Category

20 40 60 80 100 120 140 160 180 200 250ConcretePavement

21 25 26.5 27.5 29 29 30 30 31.5 31.5 34

CrushedStone Sub

base15 15 15 15 15 15 15 15 15 15 15


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Table 9. Cost of works

Analysis: Concrete Pavement Meas. Unit: M3

Code Pose No Definition Unit Quantity Unit CostCost (TL)

Turkish Lira

CONCRETE MIX COMPONENTS

SUB-TOTAL M3 67,71Preparation of Concrete Mix (400 M3 /day capacity)

SUB-TOTAL M3 35,5

PAVING AND LEVELLING CONCRETE (400 M3 /Day) 7

1 m3 Total = 110,2

Analysis::OTHER WORKS OFCONCRETE PAVEMENT(JPCP)

Meas. Unit: M2

CURING CONCRETE

SUB-TOTAL M2 0,86

OPENING JOINTS

SUB-TOTAL M2 2,19

PLACEMENT OF JOINT FILLER

SUB-TOTAL M2 4,06

JOINT REINFORCEMENTS

SUB-TOTAL M2 51 m2 Total = 12,12

Analysis:: Wear Course Construction Meas. Unit: TON

1 Ton Total = 96,5

Analysis:: Binder Course Construction Meas. Unit: TON

1 Ton Total = 88,2

Analysis::Bituminous Base CourseConstruction

Meas. Unit: TON

1 Ton Total = 81,33

Analysis::

Plantmix Base Course

Construction Meas. Unit: TON

1 Ton Total = 36,12

Analysis:: Construction of Subbase Meas. Unit: TON

1 Ton Total = 31,25

Analysis::Construction of Sand-GravelSubbase

Meas. Unit: TON

1 m3 Total = 14,74


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Figure 7. Concrete and Asphalt pavement cost analysis for 5000psi subgrade soil

Figure 8. Concrete and Asphalt pavement cost analysis for 10.000psi subgrade soil


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Figure9. Concrete and Asphalt pavement cost analysis for 15.000psi subgrade soil

Figure 10. Concrete and Asphalt pavement cost analysis for 20.000psi subgrade soil

With the increase of traffic load the pavement thicknesses increase and the cost of the roadincreases gradually in all cases. For 5.000psi, 10.000psi and 15.000psi sub base asphaltpavement is expensive for all traffic loads. As the traffic load increases the asphalt pavement costincreases even more. Also, with the decrease in the sub base strength the asphalt pavement costincreases more. The cost of asphalt pavement for 5.000psi sub base soil cost is 60% more thenthe cost of the road for 20.000psi sub base for 250 millions cycle of traffic load. However theconcrete pavement cost for 5.000psi sub base and 20.000psi sub base remains the same.


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Figure 12. Life cycle cost comparison of asphalt and concrete pavement (PCA)

Even with concretes sustainability advantages, some estimates of life-cycle costs favours asphaltover concrete. PCA calculates concrete paved roads enjoyed more than an $185,000 advantageover an asphalt paved road during fiscal 2009 roughly a 25% savings. PCA estimates concreteslife cycle cost advantage per one mile standard two lane roadway will increase to more than$730,000roughly a 45% savings by fiscal 2015.

3. CONCLUSIONS

As seen in Table 1-8 and Figure 7-10 , construction cost for rigid pavements are cheaper thenflexible pavements, in contrast to what is generally thought. However with the strength increase insubgrade the asphalt pavement costs and rigid pavement costs get closer.

With increasing petrol prices the cost of asphalt pavements will be even higher. So concretepavement should be highly considered in choosing the pavement types.

REFERENCES

UCAR Selcuk; AKAKIN Tmer, ENGIN Yasin, (2007) Cost Comparison of Rigid and FlexiblePavements : Applications in Turkey ERMCO Seville Congress June 2007

American Association of State Highway and Transportation (1993) Guide for Design of PavementStructures

Update: Paving, The New Realities, Portland Cement Association, 16 July 2009,http://www.cement.org/asphaltreport-July%202009.pdf

http://training.ce.washington.edu/WSDOT/
http://www.cement.org/asphaltreport-July%202009.pdfhttp://www.cement.org/asphaltreport-July%202009.pdfhttp://training.ce.washington.edu/WSDOT/http://training.ce.washington.edu/WSDOT/http://training.ce.washington.edu/WSDOT/http://www.cement.org/asphaltreport-July%202009.pdf

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