INITIAL COST COMPARISON OF RIGID AND FLEXIBLE PAVEMENTS: UNDER DIFFERENT
TRAFIC AND SOIL CONDITIONS
T. Akakin
Turkish Ready Mixed Concrete Association, Turkey
tumer.akakin@thbb.org
Y. Engin
Turkish Ready Mixed Concrete Association, Turkey
yasin.engin@thbb.org
S. Ucar
Turkish Ready Mixed Concrete Association, Turkey
selcuk.ucar@kgsii.com.tr
ABSTRACT
In this paper, the economic analysis has been done on both flexible and rigid pavements. These
cost analyses play a great role on the decision-making stages in selection of pavement types. In
this analysis initial cost of rigid and flexible pavements have been determined for both flexible
pavements and rigid pavements according to AASHTO 93 (American Association of State Highway
and 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. The
planners often think that the flexible pavement is cheaper than the rigid pavements. In fact this is
not always the case. In the last decade the price of bitumen which is the main ingredient of flexible
pavement has increased because of the increase in crude oil prices. However the rigid pavement’s
main ingredient cement price is declining especially in Turkey.
Government executives frequently have to choose between concrete and asphalt paving materials
for roads and highways. In the last few years in asphalt which caused a dramatic escalation in
asphalt prices – reflected in a 250% increase during 2005-2008. It is likely that once the economic
recovery gains traction, large shortages may reappear, oil prices will rise and asphalt prices will
resume their upward climb. From 2003 to 2008 oil prices increased nearly 300%. During the same
period, liquid asphalt increased 250%. The increases in asphalt prices during this period were not
only a result of rising oil prices, but also by changes in oil refining practices which has led to a
reduction 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% from
record 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 growth
is expected to be characterized by developing and transitional economies – adding new demand
pressures on oil prices. By 2015 oil prices are conservatively expected to exceed $133 per barrel –
reestablishing past peaks. Longer term projections made by the United States government suggest
that 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 concrete
between 2003-2010 is given in Figure 2 in USD. The concrete price in Turkey ,with concrete pump
price included, is about 40USD/m3. Taking these changes in the market into account in this
analysis 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.
2.1. DESIGN METHODS
In this research the design of rigid pavements and flexible pavements is done according to
AASHTO 1993. The pavement layers are given in Figure 3 and Figure 4. Rigid pavement is
designed according to AASHTO93 with layers ; concrete pavement and sub base course of
crushed stone.
The principal criterions in the design of pavements are traffic and subgrade. The number of
recurrences of an equivalent standard single axle load of 8.2 tonnes on the road within a selected
period was derived from Annual Average Daily Traffic (AADT) values and taken as the traffic load
in this study.
This study examines 11 different categories of traffic. These categories were determined on the
basis of the conditions on Turkish Highways and the number of recurrences of an equivalent
standard single axle load of 8.2 tonnes within the selected period of analysis, that is T8,2 varies
between 20 millions to 250 millions.
Another important criterion in pavement design is the load bearing capacity of subgrade soil. In this
study, the load-bearing capacity of four different soil types were used in analysis. Modulus of
resilience values is ranged from 5000 to 20.000psi. 5.000-10.000-15.000-20.000psi.
4
2
1
5
2
6
12
13
7
8
9
11
15
14
10
16
Figure 3. Flexible Pavement Cross-section
1. Width of driving lanes
9. Crushed stone sub base layer
2. Shoulder width
10. Road Base (Subgrade soil)
4. Platform width
11. Backfill slope
5. Wearing course surfacing
12. Horizontal slope of road
6. Binder course surfacing
13. Shoulder slope
7. Bituminous base course
14. Ditch slope
8. Plant mix base and shoulder backfill course 15. Cut off slope
4
2
1
2
5
12
11
13
14
6
16
10
Figure 4. Rigid Pavement Cross-section
1. Width of driving lanes
2. Shoulder width
4. Platform width
5. Concrete pavement
6. Crushed stone sub base layer
10. Road Base (Subgrade soil)
11. Backfill slope
12. Horizontal slope of road
13. Shoulder slope
14. Ditch slope
15. Cut off slope
15
2.2. PAVEMENT PROPERTIES
2.2.1. Geometrical Properties
Cost analyses for one type of flexible pavement and two types of rigid pavement were made for 11
different traffic categories. The geometrical properties of the road for which cost analysis was
made are as follows:
Length of road: 1000 m
Platform width: 12 m
Total shoulder width: 5 m
Width of driving lanes: 7 m (2 lanes)
In the rigid pavement, both the course of concrete pavement and the base course continue without
any change into the shoulders. In the flexible pavement a plant mix backfill layer takes the place of
the hot bituminous base course in the shoulders while wear and binder courses continue into the
shoulder.
Dowels and tie-rods are used in the joints of jointed unreinforced concrete pavements. Three
longitudinal joints are placed over the total road width, with one between the two lanes and two
where driving lanes meet the shoulders. Transverse joints shall be cut at an average of every 5 m
as contraction joints. Joints are sawed down 1/3 joint thickness and a fiber is placed, coated up to
15 mm and sealed with cold joint sealer. Dowels are placed at an average of every 30 cm in
transverse joints. Dowels are flat, S220a class, 25mm diameter and 60 cm long. While tie-rods are
ribbed, S420a class, 12mm diameter and 80 cm long and are placed every 80 cm in longitudinal
joints. Dowels are coated with bitumen to prevent both adhesion with concrete and corrosion.
The following parameters are chosen for flexible and rigid pavement
1.
Reliability
a.
Reliability level in percent (R)
%50
b.
Combined standard error (So)
0.5
2.
Serviceability
a.
Initial serviceability index (pi)
4.5
b.
Terminal serviceability index (pf)
3
The 1993 AASHTO Guide offers the following relationship between k-values from a plate bearing
test and resilient modulus (MR):
The results according top AASHTO 1993 can be found in Tables 1-8 and the cost analysis can be
found in Figures 3-6.
2.2.2. Material Properties
Following 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 at
http://training.ce.washington.edu/WSDOT/ below Figure 5 and Figure 6 we solved the layer
thicknesses for variable sub base and traffic loads.
Figure 5. Washinton University computer program for Rigid Pavement Design
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 for
Rigid, asphalt pavements for different subsoil conditions and different traffic load is given in below
Table 1-8 the thickness layers and the cost of the 1 km road are given in Figures 7-10. The costs
are calculated with 2009 prices for the works done for each pavement type for each work. As given
in short form in Table 9.
Table 1. Layer thicknesses for Flexible Pavement for 5.000psi subgrade
Traffic Category
Pavement
(cm)
20
Surface
5
Bituminous
12.5
Base
Graded
crushed
24
stone
Crushed
Stone Sub 20
base
40
60
80
100
120
140
160
180
200
250
5
5
5
5
5
5
5
5
5
5
15
16.5
17.5
19
19
19
20
20
20
21
25
27.5
29
29
31.5
32.5
31.5
33.5
35
33.5
20
20
20
20
20
20
20
20
20
20
Table 2. Layer thicknesses for Flexible Pavement for 10.000psi subgrade
Traffic Category
Pavement
(cm)
20
Surface
5
Bituminous
12.5
Base
Crushed
Stone Sub 25
base
40
60
80
100
120
140
160
180
200
250
5
5
5
5
5
5
5
5
5
5
15
16.5
17.5
19
19
19
20
20
20
21
25
25
25
25
25
28
28
28
30
30
Table 3. Layer thicknesses for Flexible Pavement for 15.000psi subgrade
Traffic Category)
Pavement
(cm)
20
Surface
5
Bituminous
12.5
Base
Crushed
Stone Sub 15
base
40
60
80
100
120
140
160
180
200
250
5
5
5
5
5
5
5
5
5
5
15
16.5
17.5
19
19
19
20
20
20
21
15
15
15
15
15
15
15
15
15
15
Table 4. Layer thicknesses for Flexible Pavement for 20.000psi subgrade
Traffic Category
Pavement
20
(cm)
Surface
5
Bituminous
12.5
Base
Crushed
Stone Sub
5
base
40
60
80
100
120
140
160
180
200
250
5
5
5
5
5
5
5
5
5
5
15
16.5
17.5
19
19
19
20
20
20
21
5
5
5
5
5
5
5
5
5
5
Table 5. Layer thicknesses for Rigid Pavement for k=250pci with dowel bar
Pavement
20
(cm)
Concrete
25
Pavement
Crushed
Stone Sub 15
base
Traffic Category
40
60
80
100
120
140
160
180
200
250
26.5
29
30
30
31.5
32.5
32.5
34
34
35
15
15
15
15
15
15
15
15
15
15
Table 6. Layer thicknesses for Rigid Pavement for k=500pci with dowel bar
Pavement
(cm)
20
Concrete
Pavement
Crushed
Stone Sub
base
Traffic Category
40
60
80
100
120
140
160
180
200
250
24
25
27.5
29
30
30
31.5
31.5
32.5
32.5
34
15
15
15
15
15
15
15
15
15
15
15
Table 7. Layer thicknesses for Rigid Pavement for k=750pci with dowel bar
Pavement
(cm)
20
Concrete
22.5
Pavement
Crushed
Stone Sub 15
base
Traffic Category
40
60
80
100
120
140
160
180
200
250
25
26.5
27.5
29
30
30
31.5
31.5
32.5
34
15
15
15
15
15
15
15
15
15
15
Table 8. Layer thicknesses for Rigid Pavement for k=1000pci with dowel bar
Pavement
20
(cm)
Concrete
Pavement
Crushed
Stone Sub
base
Traffic Category
40
60
80
100
120
140
160
180
200
250
21
25
26.5
27.5
29
29
30
30
31.5
31.5
34
15
15
15
15
15
15
15
15
15
15
15
Table 9. Cost of works
Analysis:
Code
Pose No
Concrete Pavement
Definition
Unit
CONCRETE MIX COMPONENTS
SUB-TOTAL
Preparation of Concrete Mix (400 M3 /day capacity)
SUB-TOTAL
PAVING AND LEVELLING CONCRETE (400 M3 /Day)
Quantity
Unit Cost
M3
67,71
M3
35,5
7
110,2
1 m3 Total =
OTHER
WORKS
OF
CONCRETE
PAVEMENT
(JPCP)
CURING CONCRETE
SUB-TOTAL
OPENING JOINTS
SUB-TOTAL
PLACEMENT OF JOINT FILLER
SUB-TOTAL
JOINT REINFORCEMENTS
SUB-TOTAL
Analysis::
Meas. Unit: M2
M2
0,86
M2
2,19
M2
4,06
M2
1 m2 Total =
Analysis::
Wear Course Construction
Binder Course Construction
Bituminous Base
Construction
Course
Plantmix
Base
Construction
Course
Construction of Subbase
36,12
Meas. Unit: TON
1 Ton Total =
Analysis::
81,33
Meas. Unit: TON
1 Ton Total =
Analysis::
88,2
Meas. Unit: TON
1 Ton Total =
Analysis::
96,5
Meas. Unit: TON
1 Ton Total =
Analysis::
5
12,12
Meas. Unit: TON
1 Ton Total =
Analysis::
Meas. Unit: M3
Cost (TL)
Turkish Lira
Construction of Sand-Gravel
Subbase
31,25
Meas. Unit: TON
1 m3 Total =
14,74
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
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 road
increases gradually in all cases. For 5.000psi, 10.000psi and 15.000psi sub base asphalt
pavement is expensive for all traffic loads. As the traffic load increases the asphalt pavement cost
increases even more. Also, with the decrease in the sub base strength the asphalt pavement cost
increases more. The cost of asphalt pavement for 5.000psi sub base soil cost is 60% more then
the cost of the road for 20.000psi sub base for 250 millions cycle of traffic load. However the
concrete pavement cost for 5.000psi sub base and 20.000psi sub base remains the same.
So we can conclude that concrete pavement is less effected by the sub base conditions and
asphalt pavement is effected more and layer thicknesses increase with the decrease in sub base
conditions and traffic loads. And concrete pavements should be chosen with high traffic loads or
even low traffic loads with low sub base strength.
Figure 11. Initial cost of asphalt and concrete pavements (PCA)
Asphalt pavement price increases not in only in Turkey but globally. The initial bid paving cost of a
new road for asphalt pavement is also increasing around the world with increasing asphalt prices.
The price change of asphalt and concrete pavement is given in Figure 11. PCA calculated for a
one mile “standard” two lane roadway, asphalt had a $120,000 cost advantage over a concrete
paved road in 2003 – roughly a 30% advantage. With 2009 prices concrete paved roads, has an
$82,000 cost advantage over asphalt paved roads. And with 2010 prices concrete roads are
$58,500 cheaper per one mile “standard” two lane roadway. In the longer term oil prices are
expected to reach more than $180 per barrel by 2030 according to the Energy Information Agency
(EIA). So comparative initial bid costs will increasingly favour concrete paved roads. PCA
estimates by 2015 concrete paved roads will enjoy a $500,000 initial bid cost advantage over
asphalt for a one mile “standard” two lane roadway – roughly a 41% savings.
Figure 12. Life cycle cost comparison of asphalt and concrete pavement (PCA)
Even with concrete’s sustainability advantages, some estimates of life-cycle costs favours asphalt
over concrete. PCA calculates concrete paved roads enjoyed more than an $185,000 advantage
over an asphalt paved road during fiscal 2009 – roughly a 25% savings. PCA estimates concrete’s
life cycle cost advantage per one mile “standard” two lane roadway will increase to more than
$730,000 – roughly 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 then
flexible pavements, in contrast to what is generally thought. However with the strength increase in
subgrade the asphalt pavement costs and rigid pavement costs get closer.
With increasing petrol prices the cost of asphalt pavements will be even higher. So concrete
pavement should be highly considered in choosing the pavement types.
REFERENCES
UCAR Selcuk; AKAKIN Tümer, ENGIN Yasin, (2007) “Cost Comparison of Rigid and Flexible
Pavements : Applications in Turkey” ERMCO Seville Congress June 2007
American Association of State Highway and Transportation (1993) “Guide for Design of Pavement
Structures”
Update: Paving, The New Realities, Portland
http://www.cement.org/asphaltreport-July%202009.pdf
http://training.ce.washington.edu/WSDOT/
Cement
Association,
16
July
2009,