Li Hongmei Ni Fujian

(School of Transportation, Southeast University, Nanjing 210096, China)

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Investigation of cost-effectiveness of highway asphalt pavement maintenance treatments based on rutting development analysis

Li Hongmei Ni Fujian

(School of Transportation, Southeast University, Nanjing 210096, China)

To investigate the cost-effectiveness of different maintenance treatments of highways in Jiangsu Province, the historical pavement maintenance records, traffic load information and pavement performance data in the pavement management system (PMS) are recorded and analyzed. Compared with the growth model, the linear model, the logarithm model and the exponential model, the cubic model has higher regression accuracyR2and it can capture the sigmoid shape of the deterioration curve. So it is selected to simulate the pavement rutting development. The benefit over cost ratio is calculated to quantify the treatment cost-effectiveness. The analysis results show that thin hot mix asphalt (HMA) overlays and micro surfacing are more cost-effective than the other two treatments on light and moderate traffic roads. Hot in-place recycling and thick HMA overlays have much longer service lives and greater cost-effectiveness under heavy or extra heavy traffic.

asphalt pavement; maintenance treatment; cumulative equivalent single axle loads; cubic model; cost-effectiveness

Asphalt pavements cover more than 85% of the highways built in China. Most of the highways in Jiangsu Province are semi-rigid base asphalt pavements and the pavement surface thickness varies from 16 to 20 cm. The pavement performance of highways deteriorates year by year under traffic loads[1]. Most of the highways in Jiangsu Province were built more than 10 years ago and stresses of various types and severity levels have affected the pavements.

The fundamental purpose of maintenance is to delay deterioration and major repairs. The cost-effectiveness of a pavement treatment can be defined as the relationship between the long-term cost of a pavement maintenance treatment over a given evaluation period and improvement in the serviceability of the pavement[2]. Several studies have been done to evaluate and define various methods for determining the cost-effectiveness of maintenance treatments[3-4].

Due to the lack of pavement conditions and traffic related data and analysis methods, limited findings of the pavement performance in China were attained in previous studies. Now detailed information of pavement structure, weather, environment, traffic, axle loads, performance detection and historical maintenance activities are recorded in the developed pavement management system (PMS) of Jiangsu Province. Moreover, various pavement maintenance treatments have been employed for a sufficient number of years. The actual performance and effects of those treatments can be observed. Therefore, it is urgent and of great importance that a thorough investigation is taken into the effectiveness of those maintenance treatments to provide effective and economic maintenance strategies.

1 Pavement Maintenance Information

1.1 Pavement maintenance treatments

Three widely used asphalt pavement treatments in Jiangsu Province are micro surfacing, hot mix asphalt (HMA) overlay, and hot in-place recycling (HIPR). Micro surfacing is a mixture of polymer-modified asphalt emulsion, fine aggregate, mineral filler, and water, uniformly spread over the pavement surface in one or two thin layers. The HMA overlay consists of 2 to 6 cm thick heated and mixed asphalt placed over the existing pavement surface. In this study, two typical thicknesses, 2.5 and 4 cm, are evaluated. Hot in-place recycling consists of heating, scarifying, mixing, placing, and compacting the upper layer of an existing asphalt pavement. Normally, 70% to 100% of the material in a mix is recycled in-place. Virgin aggregate, new asphalt binders, recycling agents, and/or new hot mix asphalt may be added as needed.

1.2 Traffic and loads

Due to the large variance of traffic and axle loads, the cumulative equivalent single axle loads (ESALs) is usually calculated to characterize traffic level based on measured traffic flow[5]. According to the Chinese specifications for design of highway asphalt pavement[6], asphalt pavements with different traffic levels can be classified based on cumulative ESAL repetitions of one lane in the design service life. Although the design life of highways in China is between 15 and 20 years, all the highways in Jiangsu Province have not reached their design lives yet. Using axle load data from weigh-in-motion (WIM) stations since the opening of different highways till 2012, cumulative ESALs were calculated. Tab.1 summarizes calculated cumulative ESALs until 2012 on highways included in the study, based on which the traffic levels of each highway can be identified.

Tab．1 Cumulative ESALs till 2012 and traffic levels of investigated highways

RoadnameRoadcodeDirectionPavementage/aLanenumberCumulativeESALs/(106times·lane-1)TrafficlevelYanJingS29NorthBound1022.66LightSouthBound1022.82LightNingXuS49NorthBound1124.72LightSouthBound11211.88ModerateLianXuG3WestBound11223.04HeavyEastBound11217.07HeavyXiGuangG2NorthBound13328.63HeavySouthBound13333.31ExtraheavyJingHuG2NorthBound12237.07ExtraheavySouthBound12276.47Extraheavy

1.3 Selection of performance indicators and thresholds

To evaluate treatment effectiveness, two pavement performance indicators including the international roughness index (IRI) and the rutting depth were selected[7]. Both IRI and rutting depth increase with time and usually upper performance thresholds are required to trigger pavement maintenance treatment. In this study, 15 mm rutting depth and 3 m/km IRI value were selected as the upper benefit cutoff values[8].

Accumulative ESALs is an important factor influencing pavement performance. Fig.1 shows relationships between pavement performance and accumulative ESALs in the initial six years for new constructed or rehabilitated highways with different traffic levels. It is noted that when rutting reaches the threshold value (15 mm) for heavy and extra heavy highway sections as shown in Figs.1(c) and (d), the IRI values generally remain much lower than the treatment triggering threshold (3 m/km). Thus, the rutting depth is a more critical performance indicator and will be adopted as a performance indicator in the following study.

(a)

(b)

(c)

(d)

2 Rutting Performance Models

Regression analysis can be used to predict future pavement deterioration based on abundant condition measurements data from the past. This method is simple and efficient when a large volume of data is available, and, thus, has been widely used in PMS. The traffic index of cumulative ESALs and pavement service time can both be used as influence factors for the regression model of the rutting depth. From the perspective of cost-effectiveness analysis of maintenance treatments, time has been selected as the independent variable to set the regression model of the rutting depth. By referring to previous research results[9], the linear model, the logarithm model, the cubic model, the exponential model and the growth model have been adopted for the regression analysis.

The do-nothing relationship defines the pavement performance over time that will be expected if no or only minor routine maintenance is conducted. The post-treatment relationship defines the pavement performance over time that will be expected if a treatment is applied. Fig.2 shows different regression model curves of the rutting depth of thick HMA overlays (4 cm) at the heavy traffic level. From the statistical analysis of abundant maintenance projects, for the model accuracy, the cubic model has the highest regression accuracyR2, followed by the growth model, the linear model, the logarithm model and the exponential model. In terms of regression accuracy and significance levels, the linear model, the growth model and the cubic model are all suitable for different pavement sections. Since the cubic model has the highestR2and is capable of capturing the sigmoid shape of the deterioration curve, it is selected to simulate the rutting development.

Fig.2 Pavement rutting depths under heavy traffic after the thick HMA overlays

3 Cost-Effectiveness Analysis

Typically, cost-effectiveness is expressed as a ratio of costs and benefits[2,10]. The costs are in terms of unit costs. Maintenance projects at different pavement sections are usually carried out in different years. In order to compare their costs, the present value is calculated to account for the effects of inflation.

(1)

whereCis the present value;Fis the future cost or current cost;iis the discount rate and the value can be adopted as 6% in China;nis the age of the maintenance project.

The benefits associated with the application of a maintenance treatment is based on the improvement in performance compared with that for the “do-nothing” alternative[2].

As shown in Fig.3, for a specific condition indicator, the benefits are determined by the difference in computed areas associated with the post-treatment performance indicator curve and the do-nothing curve.

Fig.3 Calculation of benefit area associated with increasing condition indicator

(2)

APT=∫x3-x10(U-EPT)dx-∫x2x1(U-EDN)dx

(3)

(4)

whereADNis the computed do-nothing area;APTis the computed post-treatment area;Uis the upper benefit cutoff value;EDNis the equation defining the do-nothing condition indicator relationship;EPTis equation defining the post-treatment condition indicator relationship;x1is the pavement age at treatment application;x2is the pavement age at which the do-nothing curve intersects the upper benefit cutoff value;x3is the overall post-treatment analysis period (in terms of pavement age);Bis the benefit.

4 Project Case Study

The historical maintenance projects conducted by the maintenance department of Jiangsu Province have been investigated. The do-nothing performance curve can be established by using the pavement condition data of the section adjacent to the maintenance section when the surface ages are available. Those adjacent pavement sections have the same base and subgrade, traffic and environmental conditions. By setting a threshold value of 15 mm, the service life of treatment can be determined based on the rutting performance models. All the maintenance costs were converted to the present worth in 2004 in this study.

Tab.2 and Fig.4 show that the characteristics of the benefit over cost ratio are quite different under different traffic levels. Due to the low cost, the benefit over cost ratios of thin HMA overlays and micro surfacing are higher than those by the other two treatments at light traffic level and moderate traffic level. Hot in-place recycling and thick HMA overlays have much longer service lives and greater cost-effectiveness under heavy or extra heavy traffic.

Tab．2 Results of cost-effectiveness analysis of different maintenance treatments

TreatmentmethodTrafficlevelApplytimeCost/(yuan·m-2)SamplesnumberServicelife/aBenefitBenefitovercostratioMicrosurfacingLight200431.5845.50.690.0219Moderate200530.2264.20.660.0218Heavy200431.8323.30.560.0176Extraheavy200432.0482.80.570.0178ThinHMAoverlay(2.5cm)Light200731.7166.00.740.0233Moderate200732.0205.50.810.0253Heavy200535.6203.60.600.0169Extraheavy200536.0503.10.610.0169ThickHMAoverlay(4cm)Light200743.2167.00.870.0201Moderate200743.5306.20.910.0209Heavy200547.5305.50.910.0192Extraheavy200548.01204.50.890.0185Hotin-placerecyclingLight200738.9286.50.810.0208Moderate200543.2305.60.820.0190Heavy200543.6305.00.830.0191Extraheavy200641.5304.20.840.0202

Fig.4 Benefit over cost ratios of maintenance treatment at different traffic levels

5 Conclusion

Three widely used asphalt pavement treatments in Jiangsu Province are micro surfacing, hot mix asphalt overlay, and hot in-place recycling. The rutting depth is a more critical pavement performance indicator and is used to determine the effectiveness of treatment. The cubic rutting model not only has higherR2, but can also capture the sigmoid shape of the deterioration curve. The cubic model has been selected to simulate the pavement rutting development.

In the cost-effectiveness analysis, the benefit over cost ratio is used as an index to quantify treatment cost-effectiveness. Thin HMA overlays and micro surfacing are more cost-effective than the other two treatments on light and moderate traffic roads. Hot in-place recycling and thick HMA overlays with much longer service lives have greater cost-effectiveness under heavy traffic or extra heavy traffic.

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基于車轍發(fā)展分析的高速公路瀝青路面養(yǎng)護(hù)措施的費(fèi)用-效益研究

李紅梅 倪富健

(東南大學(xué)交通學(xué)院, 南京 210096)

為了調(diào)查江蘇省各種路面養(yǎng)護(hù)措施的費(fèi)用-效益,對(duì)路面管理系統(tǒng)的養(yǎng)護(hù)歷史資料、交通軸載信息、路面性能的數(shù)據(jù)進(jìn)行觀察和分析. 與增長(zhǎng)模型、線性模型、對(duì)數(shù)模型和指數(shù)模型相比,立方模型具有更高的回歸精度,能夠捕捉路面性能衰退曲線,因此采用立方模型來模擬路面車轍的發(fā)展. 計(jì)算效益費(fèi)用比來定量評(píng)價(jià)路面養(yǎng)護(hù)措施的費(fèi)用-效益. 研究結(jié)果表明,在中、低交通條件下,熱拌瀝青薄層罩面和微表處比其他養(yǎng)護(hù)措施的費(fèi)用-效益更大； 在重、特重交通高速公路上,熱再生和厚熱瀝青罩面具有更長(zhǎng)的使用壽命和更大的費(fèi)用-效益.

瀝青路面;養(yǎng)護(hù)措施;累計(jì)當(dāng)量單軸荷載;立方模型;費(fèi)用-效益

U416.217

The Science and Technology Project of Jiangsu Provincial Communications Department (No.7621000078)．

：Li Hongmei, Ni Fujian．Investigation of cost-effectiveness of highway asphalt pavement maintenance treatments based on rutting development analysis[J]．Journal of Southeast University (English Edition),2014,30(3):343-347．

10.3969/j.issn.1003-7985.2014.03.016

10.3969/j.issn.1003-7985.2014.03.016

Received 2013-11-29．

Biographies：Li Hongmei (1983—), female, graduate; Ni Fujian (corresponding author), male, doctor, professor, nifujian@gmail.com．