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0IJTST 16 ARTICLE IN PRESS No. of Pages 10, Model 3G
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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
Evaluating the performance of sustainable perpetual pavements using recycled asphalt pavement in China
Saud A. Sultan a* Zhongyin Guob
a Department of Transportation Engineering, Faculty of Engineering, Al-Mustansiriyah University, Baghdad, Iraq b School of Transportation Engineering, Tongji University, 4800 CaoAn Gonglu, Shanghai, China
ARTICLE INFO ABSTRACT
The vast highways network in China is moving from the phase of construction to the phase of maintenance, and with introduction of new technique of perpetual pavement in the last decade, it is necessary to consider recycling as one of the promising solutions for rehabilitation of old asphalt concrete pavement and ultimately to convert them into perpetual pavements. The aim is to reuse the existing pavement materials for several reasons, mainly to preserve natural resources such as aggregates, and to satisfy economic requirements by reducing the cost of highway construction and rehabilitation. A detailed testing program has been carried out on recycled asphalt pavements materials (RAP) to evaluate their mechanical and structural characteristics to be used for the construction and rehabilitation of road pavements. Different types of RAP mixes have been stabilized by Portland cement to find the most suitable one from the point of view of design, construction, economy and environment. The analysis of life cycle costs has been carried out using system analysis and management of pavement program (SAMP5). The analysis of life cycle costs showed that the use of Portland cements with small percentages improves the structural characteristics of recycled asphalt materials to be used as stabilized base pavement layers for new or rehabilitated old road pavements and also for the construction and rehabilitation of perpetual pavements. A large amount of savings in construction and rehabilitation cost has been achieved by the use of stabilized RAP materials in addition to important contributions to the environment and preserving of natural resources.
© 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/).
Introduction
General
Asphalt pavements are exposed to growing excessive traffic load repetitions and heavy axle loads, severe environmental conditions, and poor maintenance activities which have lead to structural and functional failure. The maintenance and reconstruction costs are increasing rapidly due to the extensive volume of the deteriorated road pavements worldwide,
Peer review under responsibility of Tongji University and Tongji University Press. * Corresponding author. E-mail addresses: sasultan2003@yahoo.com (S.A. Sultan), zhongyin@tongji.edu.cn (Z. Guo).
http://dx.doi.org/10.1016/j.ijtst.2017.01.001
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/).
Article history:
Received 26 September 2016
Received in revised form 10 November 2016
Accepted 3 January 2017
Available online xxxx
Keywords: Perpetual Pavement Recycled asphalt Life cycle
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on the other hand the reconstruction of distressed pavement using recycling technique is evolving as best practice to reconstruct (or improve) pavement serviceability level and structural capacity at low cost.
Semi rigid pavements in China
In China, the semi-rigid base asphalt pavement has been normally appointed as typical structure for high class highway design and construction. 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 constructed mainly from asphalt concrete layer (friction layer) and semi rigid base layer (load bearing layer) as shown in Fig. 1. The cement is used to stabilize base and sub-base granular materials as shown in Table 1. The advantages of semi-rigid base asphalt pavement according to Chinese experience are as follows, (Wang, 2013):
(1) Good foundation with suitable capacity.
(2) Enhancing the bearing capacity of road structure and suitable for heavy traffic loads plus large traffic volumes.
(3) Decreasing rutting depth of full pavement structure under thin asphalt layer.
(4) Lower material cost, the cost of 1 cm thickness of asphalt concrete layer is equal to 4-5 cm of semi-rigid material.
While, the disadvantages of semi-rigid base asphalt pavement according to Chinese experience are as follows:
(1) Bonding is insufficient between semi-rigid base and asphalt surface. This weak bonding is the cause for water ingress distresses, rutting and even cracking.
(2) Reflecting cracking, especially in cold area, is a certain proportion of cracking.
(3) The semi-rigid base is not strong enough; the structural bearing capacity is not more than 50 million standard axle loads.
Chinese current asphalt pavement design method is based on ''Asphalt pavement design specifications" (JTJ D50, 2006), using multi-layered elastic continuous system theory. The design is established on the principle of limiting stresses to minimize fatigue damages. According to these specifications, the traffic characteristics are determined in terms of the number of repetitions of a single-axle load applied to the pavement on two sets of dual tires. The standard axle load is taken as 100 kN known as BZZ-100 axle. Fatigue, rutting and cracking represent the usual pavement damages and are taken into consideration during pavement design. Those parameters are equally more important than the design indexes. In asphalt pavement design methodology, which is used in China for many years, the surface deflection has been used as design index and the flexural stress at the bottom of the base layers as principal parameter (Njock and Yueguang, 2015; Zhang, 2009).
Perpetual pavements (PP) in China
China started to design, construct, and test PP expressway sections such as Yan Jiang expressway in Jiangsu province in 2004, Xu Wei expressway in Henan province in 2005, and Binzhou test road in Shandong province in 2005, (Wang, 2013). Chinese pavement designers try to build their own PP experience by employing their long time experience with long life semi rigid pavement structures. Fig. 2. shows two types of typical pavements with semi rigid base in China, the first is semirigid perpetual pavement of Qing Huangdao freeway, and the second is conventional semi rigid pavement, (Wang, 2013). Fig. 3. shows new perpetual pavement control experiment sections on Shanghai to Tianjin motorway near Binzhou,
Fig. 1. Conventional asphalt pavement with semi rigid base layer in China.
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Table 1
Properties of conventional asphalt pavement materials with stabilized and unstabilized base/subbase layers in China, (Njock and Yueguang, 2015). Modulus at 15 °C, 10 Hz
Resilient modulus (MPa)
Poisson's ratio
Thickness (cm)
Stabilized
Asphalt concrete surface Asphalt concrete base Cement stabilized base Cement stabilized sub base Subgrade
Unstabilized
Asphalt concrete surface Asphalt concrete base Unstabilized base Unstabilized sub base Subgrade
1400 1200 600 280 50
0.25 0.25 0.20 0.25 0.40
0.25 0.25 0.30 0.35 0.40
4.0 6.0 20.0 30.0
4.0 6.0 20.0 30.0
Fig. 2. Perpetual and conventional asphalt pavement with semi rigid base layer in China, (Wang, 2013).
90 Shandong Province (Yang et al., 2006; Wang, 2013). A perpetual pavement structure should have unique mechanical and
91 physical characteristics that lead to long-term performance. The Washington State Department of Transportation (WSDOT)
92 defined several conditions to qualify a pavement to be considered as perpetual. It should be designed for a 50-year structural
93 design life; its wearing course should be designed for 20 years design life; its layers should be specifically designed so that all
94 distresses occur in the top surface course layer, with the result that the primary maintenance activity expected throughout
95 the design life would be mill and overlay rehabilitation (Mahoney, 2001). The design theory behind perpetual pavement is
96 that distresses are limited to top-down cracking in the top asphalt lift, which is designed as a high-quality Hot Mix Asphalt
97 (HMA) layer (Newcomb and Hansen, 2006; Thompson and Carpenter, 2006). The pavement structural integrity is maintained
98 throughout the service life by milling and overlaying, plus patching when surface cracks are observed. Cracks must be
99 repaired in order to limit the roughness of the pavement, to increase skid resistance, to enhance tire-pavement interaction,
100 and to reduce noise, (Newcomb et al., 2001; Battaglia et al., 2010). The lower HMA layers are designed to resist fatigue crack-
101 ing and permanent deformation.
102 The use of RAP in road pavement
103 Reuse of old asphalt paving materials has been started in the mid of 1970s. More than 40 states in the USA placed
104 reclaimed asphalt pavement (RAP) projects by 1982 (FHWA, 2011). RAP, is now routinely used in nearly all 50 states. Federal
105 Highway Administration estimates that nearly 30 million tons are recycled each year, saving taxpayers more than $300 mil-
106 lions annually by reducing material and disposal costs (CEE, 2011). In the early 1990s, FHWA and the U.S. Environmental
107 Protection Agency (EPA) estimated that more than 90 million tons of asphalt pavement were reclaimed (i.e., converted into
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90 80 70 60 50 40 30 20
SMA, PG 76-22
SP-19.PG 76-22
SP-25. PG 64-22
Liine-Kilii Dust-Fly Asli Granular (CSGL)
Lime-Kilii Dust-Fly Asli Stabilized Soil
Lüne Treated Soil
Shanghai to Tianjin motorway near Binzhou
Fig. 3. New perpetual asphalt pavement with semi rigid base layer in China, (Yang et al., 2006).
material suited for use) every year, and over 80 percent of RAP was recycled, making asphalt the most frequently recycled material in the world. RAP is most commonly used as an aggregate and virgin asphalt binder substitute in recycled asphalt paving, but it is also used as a granular base or sub base, stabilized base aggregate, and embankment or fills material. In USA, 33 million tons of RAP is used per year for recycling purpose which is around 80% of the total amount of RAP collected from old bituminous pavements (Holtz and Eighmy, 2000). The amount of RAP used for recycling per year is about 0.84 million tons in Sweden, 7.3 million tons in Germany, 0.53 million tons in Denmark and around 0.12 million tons in Netherlands (Holtz and Eighmy, 2000). In the year 1995, 20 million tons of recycled hot mixes were produced inJapan, which constituted 30% of the total hot mix production (Ikeda and Kimura, 1997). RAP produced from surface courses (compared to binder courses) is usually of a higher quality because of higher quality aggregates used in the original construction (Saeed, 2008).
Stabilization of RAP material with Portland cement
The reclaimed asphalt pavement has been used as a coarse aggregate substitute in two different normal concrete mixes having 28 days cube compressive strengths of 33 and 50 MPa. RAP has been used with 25, 50, 75,100% replacement of coarse aggregate (Al-Oraimi et al., 2007). The results have showed that the slump has been decreased with the increase in RAP content, the compressive and flexural strength have been decreased as well with the increase in RAP content. The general trend of strength development, as well as the relations between flexural strength, elastic modulus, and compressive strength for the RAP mixes agreed well with that for normal concrete. The percentage of RAP should be limited according to the application. Low slump should also be considered when utilizing RAP in the mixes. RAP-base blend treated with 2.0, 4.0, and 6.0 percent cement has average 7-day compressive strength values of 233,417, and 624 psi, respectively (Newcomb et al., 2001). The base and sub base have average final dielectric values of 18.1 and 27.4, respectively, indicating that both materials are moisture-susceptible. On the other hand, after the 10-day soak, the RAP-base blend treated with 2.0, 4.0, and 6.0 percent cement has average final dielectric values of 5.3, 5.2, and 5.4, respectively, indicating that cement treatment helps the materials improve to a non-moisture-susceptible condition. It is recommended in a study, that to achieve a 300-psi unconfined compressive strength as required by TX DOT, the optimum cement contents are statistically about 4%, 3% and 2% percents for mixes of 100%, 75% and 50% RAP, respectively (Deren et al., 2011). Percentage of particles passing No. 40 sieve in general, and passing No. 200 sieve in particular, in a RAP mix significantly impact its strength and modulus. Since the lack of these particles in RAP is common, RAP mixed with granular base (including recycled base) materials with higher fines content can improve the quality of the mixes, Asphalt content in RAP does not seem to have a considerable impact on strength and modulus of cement-treated RAP mixes. Particle size distribution of coarse aggregate only has a minor impact on strength and modulus of cement-treated RAP mixes.
Objectives of this study
Highway transportation is considered as vital factor in China's economic growth; more than 90% of the high grade highways have been constructed in China during the last decades. Most of these highways have been constructed as asphalt con-
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140 crete pavement with semi rigid base and with low capacity in comparison with perpetual pavements. Most of these high-
141 ways have reached their service life capacity. The rehabilitation and reconstruction of asphalt layers will create huge quan-
142 tities of non environment friendly deteriorated asphalt. The question is whether these highways will be rebuilt with similar
143 pavement layers as they were before, or increasing their capacity to meet the huge increase in number and weight of truck
144 traffic volumes, or ultimately to renovate these pavements to be perpetual pavements using the reclaimed asphalt pavement
145 materials. The objective of this study is to investigate the possibility of using cement stabilized recycled old asphalt pave-
146 ment materials as semi rigid base layer for renovating old conventional asphalt pavement to new perpetual pavements. This
147 alternative pavement material will be evaluated from the point of view of; life cycle costs, structural capacity, and environ-
148 ment aspects. As compared with conventional layers, stabilized RAP materials must be cost effective and establish acceptable
149 performance in terms of strength and durability.
150 Testing of recycled asphalt materials
151 A detailed field and testing program has been carried out on recycled asphalt pavement (RAP) materials. Mixes with dif-
152 ferent percentages of RAP materials, crushed natural aggregate, and Portland cement have been prepared and tested to find
153 the most suitable one from the point of view of economy and environment. The laboratory testing program has been carried
154 out to design stabilized mixes using different proportions of milled asphalt, crushed stone, and cement. These laboratory
155 tests have been used to determine mechanical properties of the cement stabilized RAP materials with crushed natural stone.
156 The unconfined compression strength (UCS) and modulus of rupture (Fr) of these stabilized mixes have been determined by
157 testing cubes and beams as shown in Figs. 4 and 5 with different cement contents respectively. More details about this field
158 and laboratory testing program which have been carried on 26 km recycled highway project can be found in Sultan and Tong
159 (2000). The resilient modulus has been calculated using the recommended Eq. (1) by AASHTO (2008) for cement stabilized
160 soil materials as shown in Fig. 6.
163 E = 1200(UCS) (1)
164 where E is the resilient modulus, psi and, UCS is the unconfined compressive strength, psi.
165 Fig. 4. shows the relationship between the unconfined compression strength (UCS) and the cement content (Cc) for dif-
166 ferent mixes of cement stabilized materials. These mixes have been prepared by mixing different percentages of milled
167 asphalt, crushed stone, and Portland cement. Increasing the percentage of cement content and the crushed stone has a sub-
168 stantial effect on the unconfined compression strength (UCS) value. The optimum percentage of crushed stone and cement
169 will be determined depending on the design value of the resilient modulus required for economical and durable pavement.
170 The relationship between the modulus of rupture (Fr) and the cement content (Cc) for the stabilized mixes is shown in Fig. 5.
171 Increasing the cement content and the percentage of crushed stone, increases the modulus of rupture (flexural strength) of
172 the stabilized mixes. The only mix, which had a different behavior, is the mix that contains 50% of crushed stone and 50% of
173 milled asphalt. The modulus of rupture of this mix is the lowest in comparison with other mixes. The relationship obtained
174 between the resilient modulus (Mr) and the unconfined compression strength (UCS) for the stabilized mixes is shown in
a- 12 Ph
S 11 ft, 10
■9 6
X 100% crushed stone + 0% RAP aggregate 67% crushed stone + 33% RAP aggregate N--. 50% crushed stone + 50% RAP aggregate 33% crushed stone + 67% RAP aggregate
. __ —
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Percentage of Portland cement (%)
Fig. 4. The relationship between the unconfined compression strength (UCS) and the cement content (Cc) for different mixes of Portland cement stabilized RAP and crushed natural aggregates.
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' ».. 100% crushed stone + 0% RAP aggregate +, 67% crushed stone + 33% RAP aggregate 50% crushed stone + 50% RAP aggregate "'A-. 33% crushed stone + 67% RAP aggregate
^^^^ i
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Percentage of Portland cement (%)
Fig. 5. The relationship between the modulus of rupture (Fr) and the cement content (Cc) for different mixes of Portland cement stabilized RAP and crushed natural aggregates.
175 Fig. 6. It is important to notice that the flexural strength of the cement stabilized RAP materials which is represented by the
176 modulus of rupture (Fr) is important to control the cracking of the designed mix. Selecting higher modulus of rupture (Fr)
177 reduces the possible bottom up cracking. For cement content from 3 to 5% the modulus of rupture is from 0.30 to 0.6 which is
178 considered as safe value against this type of cracks (Yoder and Witczak, 1975).
179 Pavement design and management
180 The pavement design process has as its objective the design and management of the pavement through its lifetime in
181 order to minimize the total cost to the general public. The operation or performance of pavement systems involves the inter-
182 active of numerous variables such as material properties, environment, traffic loading, construction practices, maintenance
183 activities and management constraints. In order to select an optimum pavement strategy, methods are needed that consider
184 the interaction of these variables and constraints. The development of an operational pavement systems model, called
185 SAMP5, a computer program developed by NCHRP project 1-10 (Hudson and McCullough, 1973; Nair and Chang, 1973;
186 Lytton et al., 1975). System analysis model for pavement (SAMP) is an extension of the algorithms in the particular version
& 12000
■5 10000
£ 8000
"».. 100% crushed stone + 0% RAP aggregate 67% crushed stone + 33% RAP aggregate +-.. 50% crushed stone + 50% RAP aggregate 33% crushed stone + 67% RAP aggregate
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Percentage of Portland cement (%)
Fig. 6. The relationship between the resilient modulus (Mr) and the cement content (Cc) for different mixes of Portland cement stabilized RAP and crushed natural aggregates.
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187 (SAMP5). There are seven classes of input variables as follows: (1) material properties, (2) environment and serviceability, (3)
188 load and traffic, (4) constraints, (5) traffic delay, (6) maintenance and (7) program control and miscellaneous. The approach
189 to meet this need was the development of the operational pavement system model (SAMP5), a computer program produced
190 during the work on NCHRP project 1-10 (Hudson and McCullough, 1973; Nair and Chang, 1973; Lytton et al., 1975). The
191 SAMP5 computer program adopts the view that routine maintenance and future rehabilitation (overlay) are part of the total
192 pavement management process. Future costs are discounted to the present and the total cost is used as the criterion for
193 determining which pavement structure is the optimum one. The total cost includes the users cost (this cost is due to the
194 delay associated with bypassing an overlay activity). These costs are weighted equally with actual construction cost. It is also
195 generally agreed that pavement material would have a salvage value which depends mainly upon their expected future use.
196 Pavement design is normally a repeated process, in which the designer assumes a certain combination of thickness of layered
197 materials and subsequently checks the layered systems for adequacy form the point of view of traffic and environmental
198 deterioration, construction, and rehabilitation costs, as well as cost of future seal coats, overlays and routine maintenance.
199 The program analyses the input and gives the output that the designer of the pavement can connect between the cost and
200 maintenance after service life by choosing the best design for the pavement needed. Therefore, the need for pavement with
201 long life with minimum maintenance cost seems to be a valuable objective.
202 SAMP5 variables
203 A sample of the definitions of SAMP5 input and output variables are available in the literature. More details about the
204 algorithm and the operation as well as modifications of the computer program SAMP5 are available in the literature
205 (Sultan and Tong, 2000; Hudson and McCullough, 1973; Nair and Chang, 1973; Lytton et al., 1975; Sultan, 1995; Sultan
206 and Guo, 2016).
207 Analysis of pavements with cement stabilized RAP materials in China
208 Three different pavement structures in China have been chosen for the life cycle cost analysis; two of them are perpetual
209 pavements in addition to one conventional semi rigid pavement as shown previously in Figs. 2 and 3. above using the mod-
210 ified SAMP5 program. The objective of this analysis is to carry out a comparison between these different pavement structures
211 in terms of present total cost (which includes construction cost, maintenance cost, and user cost), total service life in years,
212 maximum number of 18 kips (8.6 tons) equivalent single axle loads, time to overlays, and thickness of overlays. These pave-
213 ment structures will be evaluated to find their fatigue and rutting performance in terms of tensile strain at the bottom of
214 asphalt layer and compressive strain on the surface of subgrade using the computer program Kenpave (Huang, 2004) and
215 using fatigue and rutting models of Asphalt Institute (1986) as shown in Eqs. (2) and (3) respectively.
218 Nf = 0.0796(et)~3'291 (£1 )~0-854 (2)
219 where Nf = number of load repetition to fatigue failure (20% cracking), et = tensile strain at the bottom of asphalt layer, E1 -
220 = modulus of asphalt layer, psi.
223 Nd = 1.365 x 10~9(evr4477 (3)
224 where Nd = number of load repetition to rut failure (rut depth = 1.2 cm), ev = compressive strain on the subgrade surface.
225 SAMP5 input variables
226 In order to compare the performance of the selected pavement structures, the input variables of SAMP5 will be kept con-
227 stant for each of the studied pavement. The only variable is the materials type and thicknesses of each different design in
228 order to find life cycle costs by trial and error. We have pavement designs and we want to find the value of SAMP5 input
229 variables combination that gives similar designs to our selected PP designs (back calculation); therefore, trial and error tech-
230 nique has been carried out. SAMP5 allows ranges for pavement layers thickness and overlays in addition to many other vari-
231 ables that can be selected as mentioned in this paper previously. More details are mentioned in literature (Sultan and Tong,
232 2000; Hudson and McCullough, 1973; Nair and Chang, 1973; Lytton etal., 1975; Sultan, 1995; Sultan and Guo, 2016), which
233 are beyond the scope of our research paper. The input values of SAMP 5 variables which include the thickness of pavement
234 layers, cost and properties of pavement materials, program constraints, and others have been obtained from pavement test
235 sections as reported by the literature (Wang, 2013; Yang et al., 2006). The properties of materials used in this analysis are
236 shown in Table 2. The scenario which will be used in this analysis, that after 20 years first service life period of perpetual and
237 conventional semi rigid base pavements, a certain rehabilitation process is required. In the analysis, the first service life
238 should has no need for structural overlays, only routine maintenance is required to deal with asphalt surface functional dis-
239 tresses which can be solved by milling and replacing of the upper deteriorated asphalt layer in contact with traffic loads
240 without the need for structural rehabilitation (APA, 2002). After 20 years, recycling of the deteriorated surface asphalt pave-
241 ment is required and the resulting RAP materials will be mixed with crushed natural stone and stabilized with Portland
242 cement to form a new upper base layer. Later, new perpetual surface asphalt layers are placed on this new base to build
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Table 2
Pavement materials properties as input to SAMP5 analysis.
Mat. No. Material Type Cost US $/m3 Modulus MPa Salvage Value (%)
1 STONE-MATRIX ASPHALT SMA, PG 76-22 183.01 4480 30.00
2 PERFORMANCE MIX SP-19, PG 76-22 163.40 4480 90.00
3 PERFORMANCE MIX SP-25, PG 64-22 163.40 4480 90.00
4 RICH BOTTOM LAYER OPEN GRADED 25, PG 70-22 156.86 3450 90.00
5 PERFORMANCE MIX SP-12.5 WITH +0.6% BINDER, PG 76-22 163.40 4485 90.00
6 PERFORMANCE MIX SP-12.5 WITH +0.6% BINDER, PG 64-22 163.40 4485 90.00
7 CEMENT STABILIZED BASE 58.82 830 70.00
8 RAP STABILIZED BASE (33% RAP & 67% CRUSHED STONE) WITH 3% CEMENT 45.20 4000* 70
9 LIME-KILN DUST-FLY ASH GRANULAR BASE (CSGL) 54.90 485 70.00
10 LIME-KILN DUST-FLY ASH STABILIZED SOIL 19.61 240 70.00
11 LIME STABILIZED SOIL 19.61 110 70.00
* Determined from test results in Fig. 6.
243 new perpetual pavement in addition to convert conventional semi rigid pavement into new perpetual pavement for the sec-
244 ond twenty years service life period as shown in Figs. 7 and 8.
245 SAMP5 output results
246 SAMP5 gives the best feasible designs in an increasing order of total cost for the specified magnitudes of about 100 input
247 variables. In our study, it is important to evaluate different specified pavement structures from the economical and life cycle
248 costs point of view. Table 3. has been prepared to show the present total cost and the maximum number of 18 kips (8.6 tons)
249 equivalent single axle loads for the specified total service life for two service periods. The first period of 20 years has been
250 assumed to have no structural overlays. After 20 years (first service period), structural rehabilitation is required by milling
251 the old asphalt layers, mixing with crushed stone and 3% Portland cement to form new cement stabilized RAP layer as new
252 base layer. Later, new perpetual pavement asphalt layers are placed on the top of cement stabilized RAP base layer separated
253 by geotextile fabric layer as shown in Figs. 7 and 8 above. It should be noted that for PP-3, the milling of extra 15 cm of the
254 old lime stabilized base has been carried out to keep the thickness of the pavement structure constant, while the thickness of
255 P-2 and PP-3 has been increased considering the structural needs. The routine maintenance costs and the user costs have the
256 same values for all the analyzed pavement structures because in the analysis assumption, the first service life period should
257 has no structural overlay and only routine maintenance is required. In the second 20 years service period, the user costs have
258 higher values because of the delay associated with overlay construction but they have been discarded from the results due to
259 their equal values for the studied pavement structures. The service life has been obtained in away that the pavement struc-
260 ture satisfies the predefined failure criterion of 70 micro strains for the fatigue and 200 micro strains for rut. Table 4. has
261 been prepared to show the results of mechanistic analysis of the selected pavements for the two service periods.
Fig. 7. Perpetual and conventional asphalt pavement with semi rigid base layer after recycling surface asphalt layers and adding new cement stabilized RAP base layer and new asphalt surface layers.
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Table 3
SAMP5 output results for different analyzed pavement structures.
Pavement Max. service Life (no Max. number of Total Present Time to first structural Structural overlay
structure structural overlay) (years) ESAL (millions) Cost (US $/m2) overlay (years) thickness required (cm)
number
First service period 20years (Figs. 2 and 3)
PP-1 20 20 44.17 20 10
P-2 Conventional 20 20 39.42 20 10 semi rigid
PP-3 20 20 41.06 20 10
Second service period 20 years (Figs. 7 and 8) (After first service period, recycling old asphalt layers and adding cement stabilized RAP layer with new asphalt layers)
PP-1 20 40 54.77* 20 10
P-2 Conventional 20 45 47.62* 20 10 semi rigid
PP-3 20 20 49.26* 20 10 * Total present cost includes the two service periods cost.
Fig. 8. Perpetual pavement of Shanghai to Tianjin motorway near Binzhou after recycling surface asphalt layers and adding new cement stabilized RAP base layer and new asphalt surface layers.
Table 4
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) First service period 20years (Figs. 2 and 3)
PP-1 7.5 15.7 200 147.12
P-2 Conventional semi rigid 20.3 17.6 200 88.22
PP-3 19.8 186 200 68.88
Second service period years (Figs. 7 and 8) (After first service period, recycling old asphalt layers and adding cement stabilized RAP layer with new asphalt layers)
PP-1 23.3 146 200 200
P-2 Conventional semi rigid 24.1 154 200 160
PP-3 23.5 130 200 200
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262 Analysis of results and conclusions
263 The analysis of results can be summarized as follows:
264 (1) The use of cement stabilized RAP materials as base layer in new or rehabilitated perpetual pavements in China
265 increases the service life, and structural capacity while reduces the cost of rehabilitation.
266 (2) The use of cement stabilized RAP materials as base layer in upgrading semi rigid asphalt pavement to perpetual pave-
267 ment in China increases the service life, and structural capacity while reduces the cost of rehabilitation.
268 (3) The use of cement stabilized RAP materials as base layer reduces the need for thick asphalt and contributes to the
269 preservation of natural recourses and the environment.
271 References
272 American Association of State Highway and Transportation Officials, (AASHTO), 2008. Mechanistic-Empirical Pavement Design Guide - A Manual of
273 Practice, Washington, DC 20001, USA.
274 Al-Oraimi, S. et al, 2007. Recycling of Reclaimed Asphalt Pavement in Portland Cement Concrete. Department of Civil and Architectural Engineering, Sultan
275 Qaboos University, Muscat, Sultanate of Oman.
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