sustainability of perpetual pavement designs: a …docs.trb.org/prp/12-0736.pdf1 2 sustainability of...

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Sustainability of Perpetual Pavement Designs: A Canadian Prospective 2

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Mohab Y. El-Hakim, MASc, EIT 6 PhD Candidate 7

Department of Civil and Environmental Engineering 8 University of Waterloo 9

200 University Avenue West 10 Waterloo, ON, Canada N2L 3G1 11

Telephone: (519) 888-4567 ext. 33872 12 [email protected] 13

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Susan L. Tighe, PhD, PEng 17 Professor and Canada Research Chair in Pavement and Infrastructure Management 18

Department of Civil and Environmental Engineering 19 University of Waterloo 20

200 University Avenue West 21 Waterloo, ON, Canada N2L 3G1 22

Telephone: (519) 888-4567 ext. 33152 23 Fax: (519) 888-4300 24

[email protected] 25

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Corresponding Author: Mohab Y. El-Hakim 30

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Word Count: 5386 words + 3 x 250 (tables) + 2 x 250 (figures) = 6636 32

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TRB 2012 Annual Meeting Paper revised from original submittal.

El-Hakim, Tighe 2

Abstract 1

Sustainability of road construction is one of the key factors affecting the global environment, 2 economy and social development in future. Several research projects are currently underway to 3

study different construction approaches, materials, designs that can improve the sustainability of 4 roads. The Ministry of Transportation of Ontario (MTO) constructed a test section in partnership 5

with University of Waterloo, TransCanada Highway in Southern Ontario, the Ontario Hot Mix 6 Producers Association (OHMPA) and various other partners to evaluate the use of perpetual 7

flexible pavement design on Highway 401. Although perpetual pavement is characterized by 8 higher construction costs compared to conventional flexible pavement designs, they require less 9

maintenance and less frequent rehabilitation over the 50 year lifecycle if designed and 10 constructed properly. Pavement design can save on materials and energy used in maintenance 11

over the pavement lifecycle and reduces the noise and emissions accompanied by maintenance 12 activities. All these benefits lead to decrease in maintenance cost through the pavement lifetime 13

and improve sustainability. 14

The use of perpetual pavement designs on heavy traffic volume roads and on interstate highways 15

will improve the sustainability of the road network through long life performance. These 16 highways are typically subjected to heavier truck loading compared to local roads and thus 17

usually exhibit rapid deterioration and require more frequent maintenance. Due to the importance 18 of highway conditions and their significant effect on freight and persona transportation, 19

structural capacity and performance of highway pavements should be maintained to the highest 20 standards to ensure the safety and high level of service. Perpetual pavement designs are capable 21

of achieving high structural capacity and can resist deterioration by minimum surface treatment. 22

The case study presented in this paper examines how perpetual pavement designs can be a 23

feasible solution for constructing sustainable roads. The test section constructed on Highway 401 24 in Woodstock, Ontario will be explained and analyzed. This case study was chosen as three 25

different mix designs were installed in this project. A conventional pavement design mix, 26 perpetual design without Rich Bottom Mix (RBM) and a perpetual design with RBM were 27

constructed next to each other to compare their performance using different sensors. Recycled 28 Asphalt Pavement (RAP) was also used in all pavement layers in this project. Using recycled 29

materials proved to enhance the pavement mechanical characteristics and maximized the 30 efficient use of resources. 31

INTRODUCTION 32

In the last few centuries, the construction of reliable well functioning road network 33

became an essential issue to maintain an acceptable level of living standard and facilitate both 34 economic and social development of the nations. Personnel and freight transportation has major 35

impact on the economic growth of the nations. According to Transport Canada, seventy three 36 percent of the Canadians drive their vehicles to commute to work. In addition to this, another 37

seven percent of the employees use buses as the main public mode of transportation. 38 Furthermore, forty one percent of the Canadian freight is transported by trucks using the 39

Canadian highway and road network. The Highway and road network pavement condition plays 40 a vital role in the social and economic development of Canada. According to the 2008 survey by 41

Statistics Canada, Ontario has the highest population density with a share of 38.8% of the total 42 Canadian population (1). Due to the high population density in Ontario, the Highways and road 43


El-Hakim, Tighe 3

networks in Ontario are serving more vehicles than any other province. This high traffic is 1 applying extremely heavy loads over the Ontario highway network which causes tremendous 2

deterioration of the pavement condition in the major highways. 3

The Ontario Ministry of Transportation (MTO) is experimenting with thick perpetual 4

asphalt pavement as a long life pavement tool. The reason for using perpetual pavements is to 5 improve the highway’s structural capacity to withstand the freeze-thaw cycles. Perpetual 6

pavement test sections were installed in Red Hill Valley parkway in Great Toronto Area (GTA) 7 region and connecting Highway 403 and Queen Elizabeth Way (QEW). This highway serves 8

100,000 vehicles per day and is projected to sustain 30 million Equivalent Single Axle Loads 9 (ESAL) over 20 year period and about 90 million ESAL over 50 years (2). 10

The second perpetual pavement test section constructed in Ontario was located on the 11 eastbound lanes of Highway 401 between exits 238 and 250 in southwestern Ontario. Highway 12

401 is one of the most vital highways in Ontario as it connects to Quebec from the east to 13 Windsor and then to America at the west end of the highway. The 800 km long highway is 14

considered one of the world's busiest highways, with an estimated Annual Average Daily Traffic 15 (AADT) of over 420,000 in 2005 (3). This 15.3 km long section of the highway is located 16

between Waterloo and Woodstock Ontario. The construction of this test section included three 17 different pavement designs and instrumentation of various types of sensors that are the state-of-18

the-art technology used in pavement performance monitoring and evaluation of pavement 19 deterioration. 20

The case study presented in detail throughout this paper is the perpetual pavement test 21 section constructed on Highway 401. The structural and economic analysis of perpetual 22

pavement design in comparison to the conventional designs will illustrate the benefits of using 23 perpetual pavements which leads to constructing more sustainable roads. 24

SUSTAINABILITY OF ROADS 25

During last few decades, the concept of sustainability has gained momentum. 26 Sustainability is defined by the United Nations as “The development that meets the needs of the 27

present without compromising the ability of future generations to meet their own needs” (4). 28 Applying the sustainability definition on construction field would result in a set of processes by 29

which a profitable and competitive industry delivers buildings, structures and roads which 30 enhances life quality while maximizing the efficient use of natural resources and energy. 31

One of the key factors enhancing sustainability of roadway construction is increasing 32 pavement durability and lifetime. This philosophy of pavement design is the same as the 33

perpetual pavement design concept which enhances pavement structural capacity and extends its 34 lifetime to 50 years using reduced maintenance and rehabilitation activities and surface 35

treatments compared to the conventional pavement designs. 36

Recycling of pavement materials is a major contributing factor in the construction of 37

sustainable roads. The sustainability concept is advanced when natural recourses are managed to 38 fulfill the current needs while ensuring the following generations have sufficient resources to 39

meet their needs too. The recycling of pavement materials contributes to natural material saving. 40 The asphalt mixes used in constructing the test section, contained high quality Reclaimed 41

Asphalt Pavement (RAP). The pavement patched during rehabilitation activities are structurally 42 evaluated and assessed. This aging asphalt material is then crushed, sieved and used as aggregate 43


El-Hakim, Tighe 4

material for producing new asphalt mixes. In addition, the RAP is currently used in granular 1 layers such as the base and subbase. The benefit of using RAP material in asphalt mixes is not 2

only economic but there are also environmental gains, and structural improvements. The RAP 3 material has been in-service as part of pavement mix for years and thus was subjected to traffic 4

and environmental impacts. The addition of RAP increases stiffness to the asphalt mix and 5 reduces the permanent deformation as rutting. 6

The quantification of pavement sustainability could be implemented using several rating 7 systems. Various green initiatives introduced recently as LEED, Greenroads 1.0, GreenLITES 8

and GreenPave are offering credits to using recycles materials, reducing pollution due to 9 construction activities and introducing innovative designs (5). The MTO is exclusively using 10

GreenPave rating system to quantify the sustainability of roads and Highway projects. The 11 GreenPave ranking system offers up to three credit point for long-life pavement designs and up 12

to six points for using recycled material. Considering only those two aspects would result in 13 achieving up to nine points on the GreenPave ranking system (5). This would be enough to 14

award a certain project the bronze certification level. Considering the use of local materials, the 15 reuse of asphalt and improving construction quality can easily lead to upgrade the project’s 16

certification level to gold certification. GreenPave ranking system illustrates clearly the current 17 incentive adopted by the MTO towards improving pavement quality to become long-life 18

pavements. 19

PERPETUAL PAVEMENT DESIGN 20

A perpetual pavement structure should have unique mechanical and physical 21

characteristics to accomplish long term performance. Washington State Department of 22 Transportation defined several conditions that result in a pavement being considered a perpetual 23

pavement design (6, 7). The perpetual pavement sections should have a 40 to 50 year structural 24 design life. The wearing course of a perpetual section should have a design to sustain a 20 year 25

design life. The perpetual pavements layers are specifically designed so that all their distresses 26 occur in the top surface course layer. Thus, a mill and patch rehabilitation is expected to be the 27

primary maintenance activity throughout the pavement design life (6, 7). 28

The perpetual pavement design theory limits the distresses to top-down cracking in the 29

top asphalt lift which is designed as a high-quality, thin HMA layer. The pavement is maintained 30 by milling and patching maintenance activity once pavement surface cracks are noticed on the 31

road surface. These must be repaired to limit the pavement roughness, to increase skid resistance, 32 to increase tire-pavement interaction and to reduce noise (7, 8). The lower HMA layers are 33

designed to resist fatigue cracking, rutting, and permanent deformation. The perpetual pavement 34 design structural performance is a function of the traffic loads, speed, climate, subgrade and 35

pavement parameters, materials, construction, pavement compaction and maintenance quality (9, 36 10). The perpetual pavement is expected to sustain a long-life pavement performance by limiting 37

the maximum tensile strain at the bottom of HMA (11, 12, 13). 38

The common theme for designing a perpetual pavement HMA section should consider 39

designing every layer of the pavement cross section to fulfill the following conditions (7, 14, 15): 40

1. Construct the pavement section over a sound subgrade. Soil stabilization and treatment 41

can be used to enhance the subgrade structural capacity. 42


El-Hakim, Tighe 5

2. Assemble a fatigue resistant HMA base layer to resist bottom-up fatigue cracking. This 1 layer needs to be flexible to withstand freeze-thaw cycles without crack initiation taking 2

place through it. 3

3. Install a rut resistant intermediate HMA layer. This layer is responsible for maintaining 4

the rutting deterioration values within the accepted limits throughout the pavement 5 lifetime. 6

4. A renewable surface course. This layer is designed to maintain skid resistance, reduce 7 tire-pavement interaction noise and provide surface drainage through the road slopes. 8

The design of the fatigue resistant base layer can be implemented by using a softer binder 9 and higher binder content. This increases the asphalt flexibility and eliminates crack 10

development when subjected to traffic loading and freeze-thaw cycles. Rich Bottom Mix (RBM) 11 layer incorporates an above optimum binder content. These layers showed superior performance 12

and resistance to fatigue cracking (11, 14, 16, 17). In addition, RBM layers reduce moisture 13 susceptibility and enhance field compaction as it reduces in-place air voids in the field from 14

7.0% to less than 6% (14). 15

The intermediate layer is designed as a rut resistant layer. This can be achieved through 16

designing a stable and durable layer with the new Superpave design methodology. The stability 17 of asphalt mix is a result of stone-on-stone contact in the course aggregates. Thus, this layer is 18

characterized by large nominal maximum size adding internal friction to the mix (12, 16). An 19 appropriate high temperature grade of asphalt binder is the factor which enhances the durability 20

of the asphalt mix. The high temperature grade should be that of a surface grade to alleviate 21 structural rutting. 22

The wearing surface layer is designed to withstand traffic and environmental conditions. 23 It should be rut-resistant layer and eliminate surface cracking while providing a reliable surface 24

drainage to prevent splash and spray. The surface course is usually designed as a dense-graded 25 superpave mix, Stone Matrix Asphalt (SMA) or Open Graded Friction Course (OGFC).While 26

SMA and OGFC are expecting to result in better long-term performance results, the dense-27 graded superpave mix is an acceptable option (14). 28

CANADIAN EXPERIENCE 29

Several test roads have been constructed in Canada since 1970’s (18). Brampton Road Test was 30 one of the landmark test sections that enabled researchers to develop a pavement deterioration 31

model. The deterioration model considered six different categories of subgrades in Ontario and 32 correlated the results of elastic layer analysis with the AASHTO Road Test section to evaluate 33

the deterioration due to traffic loading. Moreover, the deterioration due to environmental impact 34 was encountered in the model by considering the deterioration data from Brampton Road Test 35

(18). Canadian experience with constructing test roads to monitor pavement performance since 36 the 1990’s has been continuous. Laval University Road Experiment Site and subsequently the 37

University of Waterloo constructed the CPATT Test Track in 2002 to monitor the performance 38 of various flexible and rigid pavement designs. Several extensions were made by constructing 39

new sections to test state-of-the-art pavement materials. In 2005, University of Calgary 40 constructed the UC Test Road to evaluate the pavement performance of flexible pavement 41

designs (19). These newer constructed test sections did not include any perpetual pavement 42 sections. Nevertheless, the Canadian experience of constructing perpetual pavements started as 43


El-Hakim, Tighe 6

early as 1957. The Don Valley Parkway was awarded by Asphalt Pavement Alliance (APA) as 1 the first perpetual pavement in Canada (20). This highway was originally constructed in 1957 2

and was maintained by only two thin surface replacements within 47 service years. 3 Subsequently, the first project designed as perpetual pavement was constructed on Highway 406 4

in 2004. Hot mix asphalt installed was 250 mm thick including 80 mm of RBM layer of 5 Superpave 25.0 (21). More recently, Red Hill Valley Parkway was reconstructed using perpetual 6

pavement in 2007. The perpetual pavement total thickness was 760 mm including 240 mm of 7 Asphalt layers of Superpave design method. This project was designed as deep strength 8

conventional pavement and as a perpetual pavement. The total thickness of both designs was 9 identical but 80 mm of granular material in subbase layer was transferred to intermediate 10

Superpave 19 HMA with Rich Bottom Mix. This layer enhanced the pavement structural 11 performance (22). Several laboratory tests were performed to determine the mechanistic 12

properties of different pavement layers. This test section is instrumented with both pavement and 13 traffic monitoring systems. The pavement monitoring system included the installation of pressure 14

and moisture gauges in the subgrade, asphalt strain gauges in the RBM, Superpave 25 and SMA 15 layers. In addition, temperature sensors are installed in the subgrade, granular and HMA layers to 16

monitor the temperature of different pavement layers. The traffic monitoring system included 17 traffic loops and Weigh In Motion (WIM) sensors that collects and stores traffic data (vehicle 18

speed, loading and spacing) (22). 19

The latest Canadian perpetual pavement test section is the case study presented in this 20

paper. It was constructed on Highway 401 in southwestern Ontario. The construction phase of 21 the project was implemented in 2010. Further details about this test section will be presented in 22

the following sections. In addition, structural and economic analysis comparing the perpetual 23 designs to the conventional designs will be presented. 24

HIGHWAY 401 TEST SECTION 25

The Ministry of Transportation in Ontario (MTO), Ontario Hot Mix Producers 26 Association (OHMPA), the Centre for Pavement and Transportation Technology (CPATT), 27

Natural Science Engineering Research Council (NSERC), Stantec Consultants and McAsphalt 28 Industries Ltd. are partnering to evaluate the pavement performance of three flexible pavement 29

designs. The three pavement designs include two perpetual pavement designs and one 30 conventional flexible pavement design. The three flexible pavement designs are monitored by 31

sensors in the different pavement layers including asphalt, Granular and subbase layers. Sensors 32 are capturing tensile strain at the bottom of asphalt layers, vertical pressure on top of subgrade, 33

moisture in the subgrade and temperature of different layers. 34

The two perpetual pavement sections have 420 mm thickness of asphalt layers, while the 35

conventional design includes 300 mm thickness of asphalt layers. The two perpetual pavement 36 sections were constructed using the same asphalt mixes and having the same thickness with 37

exception of the bituminous (binder) content in the bottom asphalt layer. One of the two 38 perpetual designs is having additional 0.8% of binder content above the optimum value. The 39

additional binder content increases the flexibility of the layer and enhances the structural 40 capacity to resist fatigue bottom-up cracking at low temperatures. The perpetual section with 41

RBM, perpetual without RBM and the conventional pavement cross sections are presented in 42 Figures 1, 2 and 3 respectively. 43


1

FIGURE 1-a Perpetual Pavement with RBM 2 3

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FIGURE 1-b Perpetual Pavement without RBM5

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FIGURE 1-c Conventional Pavement 8

STRUCTURAL EVALUATION 9

The structural and performance evaluation of various pavement designs can be 10 demonstrated through the value of tensile strain measured by sensors at the bottom of asphalt 11

layers. The value of tensile strain reflects the ability of bottom-up crack propagation. This 12 distress type is the dominant factor leading to rapid deterioration rate of pavements. Since strain 13

data is collected on continuous basis all-year-round, the amount of the available strain data 14 shows strong evidence that it is following normal distribution. Thus, comparison between the 15

mean tensile strain at the bottom of asphalt layers in the three pavement designs was executed 16 using statistical t-test. Table 1 presents the t-test results comparing the mean strains in the three 17

pavement designs. 18

The statistical t-test proved with strong evidence that the perpetual pavement with RBM 19

is characterized by small tensile strain compared to the perpetual design without RBM and the 20 conventional design. However, the perpetual design without RBM is subjected to less tensile 21

strain compared to the conventional pavement design. 22


El-Hakim, Tighe 8

TABLE 1 Statistical t-test comparing Tensile Strain in different Pavement Sections 1

Perpetual With RBM Vs.

Perpetual Without RBM

Perpetual With RBM

Vs. Conventional

Perpetual Without RBM

Vs. Conventional

Null Hypothesis μ1 - μ2 = 0 μ1 - μ3 = 0 μ2 - μ3 = 0

Alternate

Hypothesis μ1 - μ2 < 0 μ1 - μ3 < 0 μ2 - μ3 < 0

Confidence Level 95% 95% 95%

P-Value 3.08E-171 7.8349E-257 2.1034E-134

μ1 3.80 3.80 8.90

μ2 8.90 22.86 22.86

Variance 1 85.08 85.08 269.99

Variance 2 269.99 3970.20 3970.20

Result Reject Null Hypothesis Reject Null

Hypothesis Reject Null Hypothesis

The bottom-up crack propagation arises when the 90th percentile of tensile strain at the 2 bottom of asphalt mix exceeds the fatigue endurance limit. The fatigue endurance limit was 3

estimated through various research projects and it depends on the physical and mechanical 4 properties of the aggregates and the binder. The value of fatigue endurance limit was estimated 5

to be approximately 70 microstrains (8, 23). Figure 4 presents the cumulative tensile strain in the 6 different pavement sections. The analysis of the strain data shows that the 90th percentile of the 7

perpetual pavement with RBM section is the lowest compared to other sections. The tensile 8 strain at that section was 13 microstrains. The perpetual section without RBM section 9

encountered higher strain values during all seasons and the 90th percentile of that section is 17 10 microstrains. The conventional section is noticed to have relatively good performance compared 11

to the other sections and the 90th percentile of that section was 20 microstrains. Yet, the 12 maximum tensile strain at the conventional section reached 500 microstrains. While the 13

perpetual section with RBM was noticed to have less variability in strain spectrum. 14

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FIGURE 2 Strain Data for Different Sections 16

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140

Cu

mm

ula

tive

Per

cen

tile

Tensile Strain (μS)

Perpetual Pavement with RBM

Perpetual Pavement Without RBM


El-Hakim, Tighe 9

Further structural analysis investigation was implemented using Mechanistic-Empirical 1 Pavement Design Guide (MEPDG). The structural analysis was created using the physical and 2

mechanical properties of the pavement mixes. The model inputs were obtained through 3 laboratory testing executed in the Centre for Pavement and Transportation Technology (CPATT) 4

in University of Waterloo. The results of the numerical model matched with the field tensile 5 strain collected to-date. The MEPDG results were analyzed to design a maintenance and 6

rehabilitation program for the different pavement designs. 7

LIFE CYCLE COST ANALYSIS 8

Life Cycle Cost Analysis (LCCA) was also performed to evaluate the perpetual design 9

with RBM and the conventional design method. The LCCA was implemented based on a 10 predicted structural analysis performed by Mechanistic-Empirical Pavement Design Guide 11

(MEPDG). The structural analysis was integrated with recommended maintenance and 12 rehabilitation programs designed for similar projects in Ontario and recommended by the MTO. 13

The maintenance and rehabilitation schedule for 70 year analysis period was designed based on 14 the MEPDG results and the best practice recommended by the MTO. 15

It is important to note that the LCCA was performed under the following assumptions: 16

The best possible unit cost estimates for pavement material, maintenance and 17 rehabilitation, and labor in Ontario were obtained through the MTO. The final LCCA 18

reports submitted to MTO in 1998 and 2006 were used for estimating the material, 19 maintenance and rehabilitation costs (24, 25). However, some unit costs were assumed 20

based on national averages. 21

The LCCA evaluation period was 70 years for the two pavement design alternatives. 22

Preventative maintenance, scheduled maintenance, and/or rehabilitation treatments were 23 assumed based on the recommendations of MTO reports. 24

Inflation costs per treatment and/or maintenance activities were not used and were assumed 25

constant between different rehabilitation options. This is a common practice used in 26 LCCA. 27

LCCA was conducted at three and four percent discount rates. 28

Initial construction costs will include labor and materials costs associated with the 29 construction of the pavement structure. 30

User delay costs during maintenance and rehabilitation activities were not considered in 31 LCCA due to the lack of sufficient data and to simplify the LCCA calculation. 32

The construction cost of 1 km of the conventional and perpetual pavement designs is 33

presented in table 2 and 3 respectively. 34


El-Hakim, Tighe 10

TABLE 2-a Construction Cost of Conventional Pavement Design 1

Length

(m)

(40 mm) SP

12.5 FC2

Density = 2.56

t/m3

(170mm) SP

19

Density = 2.41

t/m3

(90 mm) SP

25

Density =

2.34 t/m3

(200 mm)

Granular A

Density = 3.12

t/m3

(200 mm)

Granular B

Density =

2.05 t/m3

SUM

1,000 $244,224 $719,024 $279,572 $238,680 $92,250 $1,573,749

1,000 $244,224 $719,024 $279,572 $238,680 $92,250 $1,573,749

SUM $3,147,498

TABLE 2-b Construction Cost of Perpetual Pavement Design 2

Length

(m)

(40 mm)

SP 12.5

FC2

Density =

2.56 t/m3

(180mm) SP

19

Density =

2.41 t/m3

(100 mm)

SP 25

Density =

2.34 t/m3

(100 mm)

SP 25

RBM

Density =

2.44 t/m3

(200 mm)

Granular

A

Density =

3.12 t/m3

(550 mm)

Granular

B

Density =

2.05 t/m3

SUM

1,000 $244,224 $761,319 $310,635 356,850 $238,680 $253,688 $2,165,395

1,000 $244,224 $761,319 $310,635 356,850 $238,680 $253,688 $2,165,395

SUM $4,330,791

The LCCA model was performed using the Stantec LCCA program. Tables 4 and 5 3

present the maintenance and rehabilitation schedule for both conventional asphalt and perpetual 4 pavements, respectively. 5

The LCCA total Net Present Value (NPV) of the perpetual pavement was calculated using 3 and 6 4 percent discount rates, for an analysis period of 70 years. The deterministic NPV results were 7

$5,716,951 and $5,285,569 for 3 and 4 percent respectively. The LCCA total NPV costs of the 8 conventional pavement were $6,058,267 and $5,223,858, respectively for the same discount 9

rates. The LCCA results show the perpetual asphalt pavement is more cost effective over the life 10 cycle. Although the construction costs of the perpetual pavement design is expected to be 30 11

percent more expensive as compared to the conventional design, the overall NPV of the 12 perpetual pavement is lower than that of the conventional design by 5.6 percent. 13

Moreover, if user delay costs and environmental impacts are evaluated and included in 14 the economic analysis, the difference between perpetual and conventional pavement designs will 15

amplify giving more advantage to perpetual design. In addition to the more intensive 16 maintenance treatments, the conventional pavement design is scheduled to be partially 17

reconstructed after 30 and 60 years from construction. This partial reconstruction activity 18 projects rehabilitation to the asphalt layers (surface HMA, intermediate HMA and HMA base 19

layers). The alternative to this partial reconstruction activity is usually a thick asphalt overlay to 20 increase the pavement thickness. Based on the structural and economic evaluation of both 21

alternatives, the overlay solution will overcome some structural deformations but it will not be 22 able to address the more serious bottom up cracks. These cracks will continue to propagate due 23

to load repetitions and freeze thaw cycles and the pavement deterioration after the overlay is 24 expected to be faster than the partial reconstruction alternative. Thus the partial reconstruction 25

rehabilitation treatment alternative is expected to be more cost effectively in the long term. 26

27


El-Hakim, Tighe 11

1 TABLE 3-a Maintenance Schedule of 2 Conventional Design 3

TABLE 3-b Maintenance Schedule of 4 Perpetual Design 5

6

7

8

9

10

11

12

13

Maintenance Activity Year

Rout and Crack Sealing (352 m/km) 3



5% Mill and patch 50 mm 9




Tack Coat 19

Mill 50 mm Asphalt Pavement 20

Superpave 12.5 FC2 - 50 mm 20





Partial Reconstruction of Pavement 30








Tack Coat 49

Mill 50 mm Asphalt Pavement 50

Superpave 12.5 FC2 - 50 mm 50





Partial Reconstruction of Pavement 60





Maintenance Activity Year

Rout and Crack Sealing (280m/km) 4


3% Mill and Patch 40 mm 10



Mill 50mm Asphalt pavement 21

SMA- 50 mm 21

Tack coat 21






SMA- 50 mm 38

Tack coat 38





SMA- 50 mm 58

Tack coat 58

3% Mill and Patch 40 mm 60

Reconstruction of Pavement 62




El-Hakim, Tighe 12

Although the construction costs of the perpetual pavement design is expected to be 30 1 percent more expensive compared to the conventional design, the overall LCCA NPV costs of 2

the perpetual pavement is higher than that of the conventional design by four percent. The 3 LCCA analysis shows the perpetual pavement design can provide several advantages over the 4

entire life cycle of the asset. Furthermore, if user delay costs are incorporated, the LCCA will 5 further result in long life pavement design such as perpetual pavements so that future 6

maintenance and rehabilitation and the associated user delays are limited. Extension of analysis 7 period to exceed the 70 year limit requires detailed maintenance and rehabilitation records. 8

Unfortunately the current documented maintenance and rehabilitation data is insufficient to 9 create a longer analysis period. 10

CONCLUSION 11

Perpetual pavement designs are long life pavements with at least 50 year design life. 12 Although the initial construction cost of perpetual pavements is higher than that of conventional 13

pavement designs, the benefit of constructing the perpetual designs would be noticeable on the 14 long term. Perpetual pavements are considered the most sustainable pavement designs for heavy 15

traffic roads due to their superior structural performance. Thus, limiting the maintenance and 16 rehabilitation activities. The reduction of maintenance schedule would result in decrease in 17

natural recourses consumption, energy saving and pollution reduction. The benefits resulting 18 from perpetual design emphasizes that sustainable roads and perpetual designs are counterparts. 19

Currently, the constructed test section is being monitored and structurally evaluated 20 through various data collected from embedded sensors and laboratory testing. The ongoing 21

investigation will enable researchers to evaluate the benefits of constructing perpetual designs on 22 heavy traffic roads. 23

ACKNOWLEDGEMENT 24

The authors gratefully acknowledge the support of the Ministry of Transportation of Ontario 25 (MTO), Ontario Hot Mix Producers Association (OHMPA), the Natural Science and 26 Engineering Research Council of Canada (NSERC), Stantec Consulting, Capital Paving, and 27

Aecon. Special appreciation is also extended to Becca Lane, Joseph Ponniah, Keny Nadalin, 28 Chris Raymond and Tom Kazmerouski from the MTO. We also appreciate the efforts of CPATT 29

colleagues Carl Haas, Ralph Haas and Gerhard Kennepohl. 30

References 31

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