Scholarly article on topic 'Feasibility of perpetual pavement stage construction in China: A life cycle cost analysis'

Feasibility of perpetual pavement stage construction in China: A life cycle cost analysis Academic research paper on "Civil engineering"

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Abstract of research paper on Civil engineering, author of scientific article — Zhongyin Guo, Saud A. Sultan

Abstract The main objective of pavement design and management is to build sustainable pavement structure with minimum costs during its whole life. There are many uncertainties in the process of pavement design pertaining many of its variables, such as future traffic estimation, long time behavior of materials, future weights and types of traveling vehicles, availability of funds etc. Therefore, it is important to apply pavement stage construction technique during the process of pavement design and management to minimize the risk associated with these uncertainties. From the beginning of 2000, the research and application of perpetual asphalt pavement (PP) technology has been deployed in China. The semi rigid base for asphalt pavement has been normally considered as typical component of high class highways in the design according to the Chinese experience since 1997. The research objective is to apply pavement stage construction for the evaluation of life cycle costs of Chinese perpetual and traditional semi rigid pavements using operational pavement management system in addition to examine its suitability for design and construction of more economical and durable flexible pavements. It has been found that the stage construction of asphalt layers in PP over semi rigid pavement foundation will create more sustainable and trusted pavement structures in spite of 2–5% increase in present total cost.

Academic research paper on topic "Feasibility of perpetual pavement stage construction in China: A life cycle cost analysis"

 International Journal of Transportation Science and Technology xxx (2017) xxx-xxx

© Contents lists available at ScienceDirect International Journal of Transportation Science and Technology journal homepage: www.elsevier.com/locate/ijtst Transportation Science &. Technology

Feasibility of perpetual pavement stage construction in China: A life cycle cost analysis

Zhongyin Guoa, Saud A. Sultan b,*

a School of Transportation Engineering, Tongji University, 4800 CaoAn Gonglu, Shanghai, China

b Department of Highways and Transportation Engineering, Faculty of Engineering, Al-Mustansiriyah University, Baghdad, Iraq

ARTICLE INFO ABSTRACT

The main objective of pavement design and management is to build sustainable pavement structure with minimum costs during its whole life. There are many uncertainties in the process of pavement design pertaining many of its variables, such as future traffic estimation, long time behavior of materials, future weights and types of traveling vehicles, availability of funds etc. Therefore, it is important to apply pavement stage construction technique during the process of pavement design and management to minimize the risk associated with these uncertainties. From the beginning of 2000, the research and application of perpetual asphalt pavement (PP) technology has been deployed in China. The semi rigid base for asphalt pavement has been normally considered as typical component of high class highways in the design according to the Chinese experience since 1997. The research objective is to apply pavement stage construction for the evaluation of life cycle costs of Chinese perpetual and traditional semi rigid pavements using operational pavement management system in addition to examine its suitability for design and construction of more economical and durable flexible pavements. It has been found that the stage construction of asphalt layers in PP over semi rigid pavement foundation will create more sustainable and trusted pavement structures in spite of 2-5% increase in present total cost.

© 2017 Tongji University and Tongji University Press. Publishing Services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

Article history:

Received 29 November 2016 Received in revised form 21 January 2017 Accepted 22 January 2017 Available online xxxx

Keywords: Stage

Construction Perpetual Pavement Lifecycle

Introduction

Stage construction of pavement

Planned stage construction is a process of providing fully adequate pavements with the most effective use of materials, energy, and funds as reported by Asphalt Institute (1991). Stage construction is the construction of roads pavement by applying successive layers of asphalt concrete according to design and to a predetermined time schedule. The design of planned stage construction should not be confused with the design of major maintenance or the rehabilitation of existing pavements. The procedure is based on the assumption that the second stage will be constructed before the first stage shows serious signs of distress.

Peer review under responsibility of Tongji University and Tongji University Press. * Corresponding author. E-mail address: sasultan2003@yahoo.com (S.A. Sultan).

http://dx.doi.org/10.1016/j-ijtst.2017.01.005

2046-0430/® 2017 Tongji University and Tongji University Press. Publishing Services by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

There are several circumstances in which stage construction is advantageous:

1- When funds are inadequate to construct the full design thickness, the pavement may be designed for construction in two stages.

2- Accuracy problems in estimating traffic for a period of 20-25 years make planned stage construction attractive.

3- Experience indicated that pavements overlaid after they had been subjected to traffic performed somewhat better than new pavements of equal design.

4- Pavement distresses that develop during the first stage can be restored.

5- Savings may be realized from reduced final thickness or from extended life of the original pavement.

Recent studies by Abaza and Ashur (2011) and Vavrik et al. (2009) recommended the use of stage construction to achieve perpetual pavements to benefit from its advantages. The only concern is whether the costs associated with stage construction may have an impact on the present total cost in spite of stage construction benefits. According to AASHTO (1993), if the analysis period is 20 years (or more) and the practical maximum performance period is less than 20 years, there may be a need to consider stage construction in the design analysis.

When considering in stage construction design alternatives, it is important to consider the impact of compound reliability. The overall reliability for example of two stage strategy (each stage is designed for 90% reliability) would be 0.90 x 0.90 or 81%. Therefore, the following equation should be considered to check the overall and individual reliability of stage construction:

R(stage) = (Roverall)1/n (1)

where n is equal to the number of stages included in the initial pavement design.

In the stage construction, the traffic growth should be estimated for each stage. The future number of 18 kips equivalent standard axle load repetitions is estimated by multiplying the first year 18 kips equivalent standard axle load repetitions (ESAL) by the growth factor (G). Growth factor (G) can be obtained from the following equation, (AASHTO, 1993):

G =[(1 + g)n - 1]/g (2)

where G is the growth factor, g is the traffic growth rate divided by 100, and n is the number of years. For example, if the traffic growth rate is 5% (g = 0.05) and n = 20 years, then the growth factor G equals to 33.066. Table 1 shows the AASHTO traffic growth factors as a solution of Eq. (2) above (AASHTO, 1993). Increasing the annual growth rate and/or the analysis period (as the case in perpetual pavement) may increase the AASHTO growth factor to up to unreasonable value of hundred times to be multiplied by first year traffic. For this reason, the consideration of stage construction becomes more necessary especially if we recall that perpetual pavements should serve for long period up to 50 years and growth rate more than 7%.

Perpetual pavements

The fast increase in traffic volumes and the loadings on road pavements has focused the light on the need for durable pavements that will last for long time with minimum costs. The perpetual pavement (PP) is defined by Asphalt Pavement Alliance (APA) (2002) as ''An asphalt pavement designed and built to last longer than 50 years without requiring major structural rehabilitation or reconstruction and needing only periodic surface renewal in response to distresses confined to the top of the pavement". The perpetual pavement technology has an important role in prolonging the service life of pavement with minimizing maintenance and user costs over that life. The initial thick structure of perpetual pavement has the ability to reduce stresses within pavement layers under increasing traffic loads meanwhile, its higher initial construction cost and asphalt materials behavior on very long service life should be examined thoroughly. The perpetual pavement may not need to be reconstructed and the only need is to replace the deteriorated surface periodically. The long life of PP is attributed to the use of special formulated asphalt concrete mixes for the construction of asphalt concrete layers. The thickness of asphalt layers in PP is usually thick (from 20 to 50 cm). The thickness of PP is determined by limiting the tensile strain at the bottom of asphalt layer (fatigue criterion), while the total thickness of PP structure is determined by limiting the compressive strain on the surface of sub grade (rutting criterion). The upper surface layer is designed to resist wear and top-down cracking, the intermediate asphalt binder layer is designed to resist the rutting and fatigue, and the lower asphalt base layer is designed to resist bottom-up cracking. In PP, the possibility of traditional fatigue cracking is reduced, and pavement distress is limited to the upper layer of the structure. From the beginning of 2000, the research and application of perpetual asphalt pavement (PP) technology has been deployed in China. The semi-rigid base asphalt pavement has been normally appointed as typical structure for high class highway design and construction in China. Semi-rigid base asphalt pavement is the main pavement structure in China since 1997; it comprises about 90% of total pavement structures. The semi rigid is comprised mainly from asphalt concrete layer (friction layer) and semi rigid base layer (load bearing layer) (Wang, 2013).

Table 1

AASHTO traffic growth factor, (AASHTO, 1993).

Analysis Period Years (n) Annual growth rate percent (g)

No Growth 2 4 5 6 7 8 10

1 1.0 1.00 1.00 1.00 1.00 1.00 1.00 1.00

2 2.0 2.02 2.04 2.05 2.06 2.07 2.08 2.10

3 3.0 3.06 3.12 3.15 3.18 3.21 3.25 3.31

4 4.0 4.12 4.25 4.31 4.37 4.44 4.51 4.64

5 5.0 5.20 5.42 5.53 5.64 5.75 5.87 6.11

6 6.0 6.31 6.63 6.80 6.98 7.15 7.34 7.72

7 7.0 7.43 7.90 8.14 8.39 8.65 8.92 9.49

8 8.0 8.58 9.21 9.55 9.90 10.26 10.64 11.44

9 9.0 9.75 10.58 11.03 11.49 11.98 12.49 13.58

10 10.0 10.95 12.01 12.58 13.18 13.82 14.49 15.94

11 11.0 12.17 13.49 14.21 14.97 15.78 16.65 18.53

12 12.0 13.41 15.03 15.92 16.87 17.89 18.98 21.38

13 13.0 14.68 16.63 17.71 18.88 20.14 21.50 24.52

14 14.0 15.97 18.29 19.60 21.02 22.55 24.21 27.97

15 15.0 17.29 20.02 21.58 23.28 25.13 27.15 31.77

16 16.0 18.64 21.82 23.66 25.67 27.89 30.32 35.95

17 17.0 20.01 23.70 25.84 28.21 30.84 33.75 40.54

18 18.0 21.41 25.65 28.13 30.91 34.00 37.45 45.60

19 19.0 22.84 27.67 30.54 33.76 37.38 41.45 51.16

20 20.0 24.30 29.78 33.07 36.79 41.00 45.76 57.27

21 21.0 25.78 31.97 35.72 39.99 44.87 50.42 64.00

22 22.0 27.30 34.25 38.51 43.39 49.01 55.46 71.40

23 23.0 28.84 36.62 41.43 47.00 53.44 60.89 79.54

24 24.0 30.42 39.08 44.50 50.82 58.18 66.76 88.50

25 25.0 32.03 41.65 47.73 54.86 63.25 73.11 98.35

26 26.0 33.67 44.31 51.11 59.16 68.68 79.95 109.18

27 27.0 35.34 47.08 54.67 63.71 74.48 87.35 121.10

28 28.0 37.05 49.97 58.40 68.53 80.70 95.34 134.21

29 29.0 38.79 52.97 62.32 73.64 87.35 103.97 148.63

30 30.0 40.57 56.08 66.44 79.06 94.46 113.28 164.49

31 31.0 42.38 59.33 70.76 84.80 102.07 123.35 181.94

32 32.0 44.23 62.70 75.30 90.89 110.22 134.21 201.14

33 33.0 46.11 66.21 80.06 97.34 118.93 145.95 222.25

34 34.0 48.03 69.86 85.07 104.18 128.26 158.63 245.48

35 35.0 49.99 73.65 90.32 111.43 138.24 172.32 271.02

Perpetual pavements in China

China started to design, construct, and test PP expressway sections such as Yan Jiang expressway inJiangsu province in 2004, Xu Wei expressway in Henan province in 2005, and Binzhou test road in Shandong province in 2005 as reported by Wang (2013). Two PP are selected from pavement test sections on Shanghai to Tianjin motorway near Binzhou, Shandong Province for the purpose of analysis in this paper as reported by Yang et al. (2006) and are shown in Fig. 1. Semi-rigid base asphalt pavement is the main pavement structure in China since 1997. Two semi rigid pavement structures are selected for the purpose of analysis in this paper, one represents PP of Qing Huangdao freeway and the other is a conventional semi rigid pavement as reported by Wang (2013) and are shown in Fig. 2. These four pavement sections have been chosen because of their better performance in comparison of all reported cross sections as reported by Sultan and Guo (2016). The increasing of the asphalt layers thickness would increase the total stiffness of the pavement structure and decrease the stresses transmitted to the sub grade layer. Due to the large thickness of asphalt layers in PP, higher resistance to bottom-up fatigue cracking, structural rutting, and thinner granular base/sub base layers are expected in comparison with the conventional pavement designs. Since the evolving of AASHO pavement design method in the late 1950's, many examples of conventional road pavements which last for more than its design period are reported around the world with only suitable maintenance and rehabilitation of surface layers (Tarefder and Bateman, 2009). The full depth asphalt pavements are well known everywhere since early 1970's (Yoder and Witczak, 1975). The only difference which characterized PP is its design for long time period more than 50 years and for high number of equivalent single axle loads up to 100 millions, which requires thorough analysis of its life cycle performance.

Chinese pavement designers try to build their own PP experience by employing their long time experience with long life semi rigid pavement structures. Different PP designs have been implemented in the construction of new expressways, but the long time performance of these pavements and the comparison with long life semi rigid pavements need further studies as highlighted by Guy et al. (2015) and Tran et al. (2015).

PP-1 PP-2

Fig. 1. Two perpetual pavement test sections on Shanghai to Tianjin motorway near Binzhou, Shandong Province, Yang et al. (2006).

Fig. 2. Semi rigid perpetual of Qing Huangdao freeway and conventional semi rigid pavements, Wang (2013).

Pavement management system

The pavement design process has as its objective the design and management of the pavement throughout its lifetime in order to minimize the total cost. The performance of pavement systems involves the interaction of numerous variables such as material properties, environment, traffic loading, construction practices, maintenance activities and management constraints. In order to select an optimum pavement strategy, methods are needed that consider the interaction of these variables and constraints. The development of an operational pavement systems model, called SAMP5, a computer program developed by NCHRP project (Hudson and McCullough, 1973). Systems analysis model for pavement (SAMP) is an extension of the algorithms in the particular version (SAMP5). There are seven classes of input variables as follows: (1) material

properties, (2) environment and serviceability, (3) load and traffic, (4) constraints, (5) traffic delay, (6) maintenance and (7) program control and miscellaneous. An operational flexible pavement systems model (SAMP5) has been developed. The approach to meet this need was the development of the operational pavement system model (SAMP5), a computer program produced during the work on NCHRP project (1-10), (NCHRP reports 139 (Hudson and McCullough, 1973), 140 (Nair and Chang, 1973), and 160 (Lytton et al., 1975)). The SAMP5 computer program adopts the view that routine maintenance and future rehabilitation (overlay) are part of the total pavement management process. Future costs are discounted to the present and the total cost per square yard is used as the criterion for determining which pavement is the optimum. Including in the total cost is the users cost a term for the expense to the traveling public of being delayed while detouring on overlay activity. These costs are weighted equally with actual construction cost. It is also generally agreed that pavement material would have a salvage value which depends mainly upon their expected future use. Pavement design is normally a repeated process, in which the designer assumes a certain combination of thickness of layered materials and subsequently checks the layered systems for adequacy form the point of view of traffic and environmental deterioration, construction, and rehabilitation costs, as well as cost of future seal coats, overlays and routine maintenance. The program analyses the input and gives the output that the designer of the pavement can connect between the cost and maintenance after pavement life in years by choosing the best design for the pavement needed. Therefore, the need for pavement with long life with minimum maintenance cost seems to be a valuable objective. SAMP5 computer program has been modified to take into consideration AASHTO, 1993 pavement design. More details about the algorithm and the operation as well as modifications of the computer program SAMP5 are available in the literature (Hudson and McCullough, 1973; Nair and Chang, 1973; Lytton et al., 1975; Sultan, 1995; Sultan and Tong, 2000). This program will be used in this research to evaluate the performance and life cycle costs of different PP in China.

Research objectives

Recent studies by Abaza and Ashur (2011) and Vavrik et al. (2009) have recommended the use of stage construction technique to build more economical perpetual pavement structures for different reasons as highlighted previously. Therefore, the main objective of this research is to study the feasibility of using stage construction technique in the design and construction of perpetual pavement in China because of its unique properties as compared with other international PP structures to find more economical plus reliable PP structures. The converting of the traditional semi rigid pavement in China to high class modern perpetual pavement by stage construction will be studied too, through the following steps:

1- Comparing life cycle costs of modern perpetual pavements with traditional semi rigid pavements using SAMP5.

2- Applying stage construction technique on modern perpetual pavements and traditional semi rigid pavements using SAMP5 to find the life cycle costs.

3- Comparing the controlling fatigue cracking and rutting criteria of each studied pavement structure.

Methodology

In order to achieve the objectives of this research the following steps have been carried out:

1. Properties of perpetual pavement in China

A comprehensive data survey procedure has been carried out on constructed PP in China to find the required values of the input variables for this research analysis purposes. The results of field tests on existing PP projects have been considered, calibrated and compared with design values in order to determine the most reasonable ones as reported by different researchers.

2. Pavement management system

In order to carry out the life cycle costs analysis using SAMP5, computer program (which has been modified to use AASHTO, 1993 design method), it is necessary to determine the magnitude of its input variables. The magnitude of SAMP5 input variables has been kept constant for each of the studied pavement for comparison purposes except the thickness of pavement layers, properties of materials, design life, and number of equivalent axle loads in order to find life cycle costs. The magnitude of some SAMP5 input variables has been obtained from PP test sections as reported by different researchers (Yang et al., 2006; Wang, 2013). The magnitude of the rest of SAMP5 which are related to program constraints, operation, movement of vehicles through the overlay construction zone, etc. are as reported by Sultan (1995), Sultan and Tong (2000), and Sultan and Guo (2016) respectively.

3. Mechanical empirical analysis

The selected PP structures will be subjected to mechanical empirical analysis to find their fatigue and rutting stresses and strains in terms of tensile strain at the bottom of asphalt layer and compressive strain on the surface of sub grade using the computer program Kenpave (Huang, 2004) and using fatigue and rutting models of Asphalt Institute (Asphalt Institute, 1986) as shown in Eqs. (3) and (4) respectively.

Nf = 0.0796(et )~3'291(Ei)~0'854 (3)

where; Nf = number of load repetition to fatigue failure (20% cracking), et = tensile strain at the bottom of asphalt layer, E1 -= modulus of asphalt layer.

Nd = 1.365 x 10~9(£v)~4477 (4)

where; Nd = number of load repetition to rut failure (rut depth = 1.2 cm), ev = compressive strain on the sub grade surface.

Analysis of PP in China

Three different PP structures in China are chosen for the life cycle cost analysis in addition to one conventional semi rigid pavement as shown in Figs. 1 and 2 above using the modified SAMP5 program. The objective of this analysis is to carry out a comparison between these different pavement structures in terms of present total cost (which includes construction cost, maintenance cost, and user cost), total service life in years, maximum number of equivalent 18 kips (8.6 tons) equivalent standard axle loads, time to structural overlays, and thickness of structural overlays.

SAMP5 input variables

In order to compare the performance of the selected pavement structures, the input variables of SAMP5 will be kept constant for each of the studied pavement. The only variable is the materials type and thicknesses of each different design in order to find life cycle costs by trial and error. The input values of SAMP5 variables which include the thickness of pavement layers, cost and properties of pavement materials, program constraints, and others have been obtained from PP test sections. More details about the input variables are as reported recently by Sultan and Guo (2016).

SAMP5 output results

SAMP5 can evaluate the interaction of about 100 input variables which cover a wide range of design, construction, maintenance, performance, economy and management variables. SAMP5 gives the best feasible designs in an increasing order of total cost for the specified magnitudes of the 100 input variables. Each run of the program for different combination of

130 120 110 100 90 80 70 60 50 40 30 20 10 0

1 SMA, PG 76-22 SP-19. PG 76-22 SP-25. PG 64-22 Liirie-Kilii Dust-Fly Asli Granular Liine-Kiln Drat-Fly Ash Stabilized Soil

Asphalt

r Asphalt

Semirigid

PP-1 PP-2

Fig. 3. Stage one of perpetual pavement test sections shown in Fig. 1.

pavement layers with different materials gives 30 optimum possible designs in increasing cost order. In our study, it is important to evaluate different specified pavement structures by trial and error from the economical and life cycle costs. In order to apply stage construction technique on the selected perpetual pavements in Fig. 1 above, a first stage of 20 years has been suggested for the construction of these two pavements as shown in Fig. 3. While for stage two, it has been suggested to be similar to the pavements in Fig. 1. For two semi rigid pavements in Fig. 2 above a first stage has been suggested for the construction of these two pavements as shown in Fig. 2.

While for stage two, it has been suggested to be similar to the pavements in Fig. 4. SAMP5 presented three models to handle traffic delay associated with overlay construction. A comparison between these three models showed small difference in the values and small values in general. The low magnitude of user costs is the main advantage of perpetual pavements in comparison with conventional pavements as mentioned above. SAMP5 results showed small difference between the analyzed pavement structures according to its traffic handling models that ease the traffic movements around overlay site. The periodic maintenance costs and the user costs results are almost the same for all the analyzed pavement structures because in our analysis scenario, all the studied pavements will be overlaid after 20 years and they will have the same user and maintenance costs. Therefore; these costs will be deleted from the comparison of results.

The scenario for the analysis is to implement two-stage construction technique on the selected pavement structures for comparison purposes depending on present total cost which includes initial construction cost and overlay construction cost minus the salvage values. This scenario suggests that the asphalt layers of the analyzed pavement structures will be laid into two stages. In the first stage of 20 years, only 17.5 cm of 32.5 cm asphalt will be laid for PP-1. While, in the second stage (after 20 years) the remaining thickness of asphalt (15 cm) will be laid after milling the deteriorated asphalt surface layers. The laying of asphalt layers should be according to the original sequence of layers as shown in Fig. 1. For the rest of the analyzed pavement structures (PP-2, PP-3, and P-4) the laying of asphalt layers into two-stages is shown in Figs. 2 and 3 after milling the deteriorated asphalt surface layers at the end of 20 years (first stage). Table 2 and Table 3 have been prepared to show the results of life cycle costs and mechanistic analysis of the selected pavement structures in Figs. 1 and 2 using full construction technique as reported by Sultan and Guo (2016). Table 4 and Table 5 have been prepared to show the results of life cycle costs and mechanistic analysis on the selected pavement structures in Figs. 3 and 4 using two-stage construction technique. It should be noted that the cost of asphalt overlay in the second stage has been discounted to the present time.

Analysis of results and conclusions

Table 6 has been prepared to summarize the results of analysis that has been carried out on selected pavement structures in China using two-stage construction technique. The comparison between these results shows that the present total cost of two-stage construction technique in constructing perpetual pavements in China is 2-5% higher than the full construction. In spite of the slight increase in the total construction costs, the stage construction can be the right answer for the uncertainties

70 § 60

X. 50 •5 40 30

PP-3 Semirigid P-4 Conventional Semirigid

Qiiig Hilling(l;io freeway

Fig. 4. Stage two of semi rigid perpetual pavement test sections shown in Fig. 2.

F&g SMA. PG 76-22

SP-19, PG 76-22 SP-25. PG 64-22

Table 2

SAMP5 results for perpetual pavement using full construction (with no stage construction) as mentioned by Sultan and Guo (2016).

Pavement structure number Total service life (years) Max. number of ESAL (millions) Present total cost (US $/m2)

PP-1 40 80 44.66

PP-2 20 20 41.06

PP-3 20 20 44.17

P-4 20 20 39.42

Table 3

Mechanistic analysis of perpetual pavement using full construction with no stage construction as mentioned by Sultan and Guo (2016).

Pavement structure number HMA tensile micro strain Sub grade compressive micro strain Cracking life (millions) Rut life (millions)

PP-1 15.5 184 200 72.30

PP-2 19.8 186 200 68.88

PP-3 7.5 15.7 200 147.12

P-4 20.3 17.6 200 88.22

Table 4

SAMP5 results for perpetual pavement in Figs. 3 and 4 using two-stage construction technique.

Pavement structure number

Service life (years)

Max. number of ESAL (millions)

Present total cost (US $/m2)

Stage construction (stage one)

Stage construction (stage two)

20 20 20 20

40 20 20 20

20 20 20 20

80 20 20 20

37.36 41.06 44.17 39.42

10.08 2.88 4.32 4.15

Table 5

Mechanistic analysis results for the pavement structures.

Pavement structure number HMA tensile micro strain Sub grade compressive micro strain Cracking life (millions) Rut life (millions)

Stage construction (stage one)

PP-1 17.3

PP-2 19.8

PP-3 7.5

P-4 20.3

Stage construction (stage two)

PP-1 15.5

PP-2 16.7

PP-3 6.6

P-4 18.4

197 186 157 176

184 179 144 133

200 200 200 200

200 200 200 200

53.06 68.88 147.12 88.22

68.30 81.49 215.50 308.07

Table 6

Comparison between full and staged construction of analyzed pavements in China.

Pavement structure Total service life (years) Max. number of ESAL (millions) Present total cost (US $/m2)

Full const. Two-stage const. Full const. Two-stage const. Full const. Two-stage const.

PP-1 40 60 80 100 44.66 47.44

PP-2 20 40 20 40 41.06 43.94

PP-3 20 40 20 40 44.17 48.49

P-4 20 40 20 40 39.42 43.57

associated with future traffic estimation, long time behavior of materials, future weights and types of traveling vehicles, availability of funds etc.

Therefore, stage construction of PP asphalt layers over semi rigid pavement foundation will create more sustainable and trusted pavement structures. These results are in good agreement with recommendations of many researchers around the world as mentioned in the literature above.

Recommendations for future research

1- It is recommended to carry out further research on the possibility of using recycled asphalt pavement materials in the stage construction of new PP or to convert old and deteriorated conventional asphalt pavements to PP.

2- It is recommended to carry out further research on the possibility of using recycled semi rigid pavement materials in the stage construction of new PP or to convert old and deteriorated conventional semi rigid pavements to PP.

References

American Association of State Highway and Transportation Officials, 1993. AASHTO Guide for Design of Pavement Structures. Washington, D.C., USA. Abaza, K.A., Ashur, S.A., 2011. Investigating the accelerated deterioration of flexible pavement using two-stage design analysis approach. Eur. Transport Res. Rev. 3 (1), 23-34.

Asphalt Institute. 1986. Asphalt hot mix recycling, Manual Series No. 20 (MS-20), United States.

Asphalt Institute, 1991. Thickness Design of Asphalt Pavements for Highways & Streets Manual Series No. 21 (MS-21), United States. Guy, P. et al, 2015. Comparative study of French and Chinese asphalt pavement design methods. J. Appl. Sci. 15 (6), 923-928. Huang, Y.H., 2004. Pavement Analysis and Design. Pearson Education Inc., New Jersey.

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