INITIAL COST COMPARISON OF RIGID AND FLEXIBLE PAVEMENTS: UNDER DIFFERENT TRAFIC AND SOIL CONDITIONS ABSTRACT 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 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 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 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 2 11 7 8 9 5 6 12 13 14 15 16 10 Figure 3. Flexible Cross-section 1. Width of driving lanes 9. stone sub 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 course 14. Ditch slope 8. Plant mix and shoulder backfill course 15. Cut off slope 4 2 1 2 5 12 13 11 6 14 15 16 10 Figure 4. Rigid Cross-section 1. Width of driving lanes 11. Backfill slope 2. Shoulder width 12. Horizontal slope of road 4. Platform width 13. Shoulder slope 5. Concrete pavement 14. Ditch slope 6. stone sub layer 15. Cut off slope 10. Road Base (Subgrade soil)
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 course continue without any change into the shoulders. In the flexible pavement a plant mix backfill layer takes the place of the hot bituminous 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 : 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 and traffic loads.
Figure 5. Washinton University computer program for Rigid Design
Figure 6. Washinton University computer program for Rigid 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 for 5.000psi subgrade Surface 5 5 5 5 5 5 5 5 5 5 5 Bituminous Base Graded crushed stone 12.5 15 16.5 17.5 19 19 19 20 20 20 21 24 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 20 Table 2. Layer thicknesses for Flexible for 10.000psi subgrade Surface 5 5 5 5 5 5 5 5 5 5 5 Bituminous Base 12.5 15 16.5 17.5 19 19 19 20 20 20 21 25 25 25 25 25 25 28 28 28 30 30 Table 3. Layer thicknesses for Flexible for 15.000psi subgrade ) Surface 5 5 5 5 5 5 5 5 5 5 5 Bituminous Base 12.5 15 16.5 17.5 19 19 19 20 20 20 21 15 15 15 15 15 15 15 15 15 15 15 Table 4. Layer thicknesses for Flexible for 20.000psi subgrade Surface 5 5 5 5 5 5 5 5 5 5 5 Bituminous Base 12.5 15 16.5 17.5 19 19 19 20 20 20 21 5 5 5 5 5 5 5 5 5 5 5
Table 5. Layer thicknesses for Rigid for k=250pci with dowel bar Concrete 25 26.5 29 30 30 31.5 32.5 32.5 34 34 35 15 15 15 15 15 15 15 15 15 15 15 Table 6. Layer thicknesses for Rigid for k=500pci with dowel bar Concrete 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 for k=750pci with dowel bar Concrete 22.5 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 15 Table 8. Layer thicknesses for Rigid for k=1000pci with dowel bar Concrete 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: Concrete Meas. Unit: M3 Code Pose No Definition Unit Quantity Unit Cost Cost (TL) Turkish Lira CONCRETE MIX COMPONENTS SUB-TOTAL M3 67,71 Preparation 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 OTHER WORKS OF Analysis:: CONCRETE PAVEMENT Meas. Unit: M2 (JPCP) 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 5 1 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:: Analysis:: Bituminous Base Course Construction Plantmix Base Course Construction Meas. Unit: TON 1 Ton Total = 81,33 Meas. Unit: TON 1 Ton Total = 36,12 Analysis:: Construction of Sub Meas. Unit: TON 1 Ton Total = 31,25 Analysis:: Construction of Sand-Gravel Sub 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 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 strength the asphalt pavement cost increases more. The cost of asphalt pavement for 5.000psi sub soil cost is 60% more then the cost of the road for 20.000psi sub for 250 millions cycle of traffic load. However the concrete pavement cost for 5.000psi sub and 20.000psi sub remains the same.
So we can conclude that concrete pavement is less effected by the sub conditions and asphalt pavement is effected more and layer thicknesses increase with the decrease in sub conditions and traffic loads. And concrete pavements should be chosen with high traffic loads or even low traffic loads with low sub 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 s : Applications in Turkey ERMCO Seville Congress June 2007 American Association of State Highway and Transportation (1993) Guide for Design of Structures 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/