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IMPACT OF NEW ASPHALT TECHNOLOGIES

ON

PAVEMENT LIFE-CYCLE COSTING IN ONTARIO

John Emery and Ludomir Uzarowski John Emery Geotechnical Engineering Limited

Toronto, Ontario

Paper Prepared for Presentation at the Experience with the Characterization of Pavement Materials Session of the 2002 Annual Conference of the Transportation Association of Canada, September 15-18,

Winnipeg, Manitoba.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the assistance of Professor Susan Tighe from the University of Waterloo with the HDM-4 analysis and pavement performance predictions.

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ABSTRACT

Life-cycle cost analysis is an effective decision-making tool for pavement designers and highway agencies. Given adequate historical data on asphalt performance and the use of rational pavement design methods, the designer can readily determine which pavement design alternative is the most cost-effective for the particular location. The use of high-performance, premium materials and new, enhanced technologies in asphalt pavement construction provide benefits to the roadway owner and user when their costs are considered over the increased service life of the pavement. The implementation of timely, systematic asphalt pavement maintenance and rehabilitation enhances the use of these materials and methods and improves their overall cost-effectiveness. Life-cycle cost analyses indicate that improvements in pavement smoothness, quality control through end-result specifications and use of high quality materials such as performance graded asphalt cement, heavy duty binder course and stone mastic asphalt mixes substantially reduce the overall life-cycle costs of the asphalt pavement. This is particularly evident for higher volume roads and when user costs such as delay are considered. The elements of pavement life-cycle cost analysis, design considerations and the impact of hot-mix asphalt materials and technology advancements made in Ontario over the last 10 to 15 years are presented.

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1. INTRODUCTION In recent years, highway agencies have adopted life-cycle costing analysis (LCCA) to assist in the selection of the most appropriate pavement type for highway projects. LCCA is considered to be an important decision-support tool, and its effectiveness is highly dependent on the application of good practice. This has lead to close scrutiny of the process by the road building industry and as a result, some changes have been made to properly characterize the cost effectiveness of alternative pavement types. In 1996, the Ontario Ministry of Transportation (MTO) jointly with the Ontario Hot Mix Producers Association and the Ready Mix Concrete Association commissioned a study to review the life-cycle costing methodology being used by the MTO. The initial MTO LCCA Study was completed in 1998 and a supplementary study that included six new (current) asphalt technologies in Ontario was completed in 2000. The MTO LCCA Study was completed for typical 400 Series highways (major routes) carrying an annual traffic of 2 million flexible (asphalt pavement) Equivalent Single Axle Loads (ESALs) or 3 million rigid (concrete and composite pavements) ESALs. The initial study resulted in a report [1] that, in the view of the hot-mix industry, had some shortcomings. The biggest concern was the lack of consideration given to the technical advances in hot-mix materials and construction methods over the last decade. There were also some technical concerns with the modeling used to predict the pavement performance and the pavement sections used to compare the life-cycle costs of hot-mix asphalt (HMA) and portland cement concrete. At the request of the hot-mix industry, the MTO completed a supplementary study [2] to further assess the impacts on life-cycle costing of recent HMA technical advances implemented in Ontario. The hot-mix industry formed a Study Team to provide HMA technology input to the MTO for the supplementary study. The use of a well-recognized asphalt pavement design method such as the American Association of State Highway and Transportation Officials AASHTO 93, combined with high quality asphalt paving materials and construction, in conjunction with timely maintenance and rehabilitation procedures, will result in more cost-effective asphalt pavements. Although the initial cost of some alternatives can be somewhat higher (10 to 30 percent for stone mastic asphalt (SMA) for example), the increased durability and rut resistance provided pays off in reduced maintenance and lower user delay costs. The very positive life-cycle performance and cost impacts of the HMA technology advances made in Ontario over the last 10 to 15 years can be demonstrated through pavement performance monitoring and service life cost analyses. 2. BACKGROUND The pavement engineer is required to select, from the wide variety of pavement structure types, the most appropriate, practical and cost-effective alternative that meets the functional requirements of the particular project. Gillespie said in “Principles and Practice of Road Making” in 1847: “A minimum of expense is, of course, highly desirable; but the road which is truly the cheapest is not the one which has cost the least money, but the one which makes the most profitable returns in proportion to the amount expended on it.” After more than 150 years, this statement still holds true. The process of determining the best pavement alternative should therefore be based on an economic analysis of the construction, maintenance and rehabilitation requirements for each alternative, and relative impacts on the user. The choice of pavement type for a project should consider a number of key factors: traffic (number of heavy vehicles and axle loading); soil characteristics (subgrade strength); weather; drainage; constructability; cost; recycling; and performance. Each of these factors should be addressed specifically on a project by project basis. Other factors such as availability and quality of local materials, availability of contractors, impact on traffic (user delays) and

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safety, and the surface(s) of the existing adjacent pavements, all play a role in the decision making process. To stimulate competition, highway agencies may consider alternative structurally equivalent sections. If this is the case, an economic analysis, and value engineering for major projects, should be completed to select the most cost-effective option among the various alternatives [3 and 4].

3. LIFE-CYCLE COST ANALYSIS (LCCA) Life-cycle costing is the economic assessment of competing, technically suitable systems over their design life. There are a number of methods of economic analysis that can be used in the evaluation of alternative design strategies [3], but the net present worth method is most commonly used for pavements. This method considers future streams of costs and/or benefits to compare alternative investments. The cost or value of money is an integral part of LCCA and it is important that the sensitivity of factors such as interest rates and inflation be evaluated. The present worth method allows for comparison of initial capital costs to the future expenditures in constant dollars and is generally well understood by decision-makers and suits the requirements of most agencies. The discount rate (the nominal increase in the value of money over time) used in the present worth method is derived basically as the difference between the interest rate and inflation rate over the analysis period. The selection of the most appropriate discount rate is an important component in the life-cycle cost analysis procedure. Although there have been periods when the difference between the inflation and the interest rate has been relatively high, these periods have tended to be relatively short. Typically the historical discount rate over a 20 year period has been be tween 3 and 5 percent. The analysis period (Figure 1) represents the time or accumulated traffic (ESALs) during which the construction, maintenance and rehabilitation activities for each pavement are evaluated, and typically ranges from 30 to 50 years; at least one major rehabilitation activity should be included in the analysis period. The major initial and future costs that should be considered during a pavement LCCA are: agency costs such as initial construction costs (capital cost); maintenance costs; rehabilitation costs and salvage and residual costs (‘negative’ costs); and user costs such as delay time costs, vehicle operating costs and accident costs (typically differential user delay costs only are considered).

Pavement Life

Pav

emen

t C

ondi

tion

Analysis Period

Major Rehabilitation Activity

Figure 1 The analysis period should include at least one major rehabilitation.

Time

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Initial Construction Costs (Capital Costs) The initial construction cost simply involves the tender items cost (quantities and unit costs) and associated agency engineering cost for each alternative pavement structure. This should be the easiest information to obtain, as material quantities can be directly estimated based on their thickness in the structure and the widths of the pavement and shoulders. Unit prices can often be obtained from the agency database, which may include average prices over a period of time based on contract bids. Some agencies go as far as publishing their typical costs on an annual basis. Maintenance Costs Systematic routine and major maintenance activities should be scheduled over the service life of an asphalt pavement; for example a systematic program for routing and sealing can be implemented where all asphalt pavement cracks are routed and sealed shortly after initial construction or placement of an overlay, and at timely intervals thereafter. Rehabilitation Costs Some form of asphalt pavement rehabilitation will generally be required to maintain the pavement condition at, or above, a minimum acceptable serviceability level and extend the service life of the asphalt pavement alternatives for the life-cycle analysis period being considered. The scheduling for such activities is highly dependent upon the asphalt pavement materials employed and the systematic maintenance program adopted. Realistic estimation of the service life of new pavements, and pavement maintenance and rehabilitation activities required during the service life, are considered to be essential components in LCCA. Salvage and Residual Values The salvage and residual values simply represents the salvage potential (recycling value for instance) and remaining functional serviceability of the investment at the end of the analysis period. The remaining life of the pavement at the end of the analysis period can be substantial and must be considered in comparing pavement alternatives. User Delay Costs User delay costs are incorporated in the life-cycle cost analysis and represent the impact of scheduled maintenance and/or rehabilitation activities on the roadway users. The user delay cost is estimated by assigning a financial penalty for the time that the pavement is not available for use by the public. The incorporation of user delay costs in life-cycle cost analysis tends to discourage frequent or lengthy maintenance activities. Most major maintenance and rehabilitation activities are scheduled for off-peak hours, and generally do not require around the clock occupation of the lane. Pavement Type Selection Life-cycle costing can be a powerful tool in selecting the ‘best’ pavement type. All engineering factors must be properly and carefully considered in the analysis [3]. It is critical that pavement alternatives evaluated using LCCA procedure are structurally and functionally equivalent. The pavement design procedure described in the American Association of State Highway and Transportation Officials (AASHTO) 1993 Guide for the Design of Pavement Structures (or its computerized version DARWin) is widely used

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(Figure 2). Structurally comparable pavement designs can be developed for flexible (conventional and deep-strength asphalt) and rigid (concrete and composite) pavements. Innovations and improvements in asphalt technology have resulted in asphalt pavements being selected for highway, airport and heavy duty industrial pavements where previously rigid pavements had been preferred. Figure 2 AASHTO procedure for determining thickness of layers using a layered analysis approach. The design of composite pavements (asphalt concrete over portland cement concrete base) is empirical, with the asphalt concrete surface credited as having little or no contribution to structural capacity, and considered to only provide a riding/wearing surface. However, even when consideration is given to increased structural capacity as a result of the asphalt concrete layer(s), composite pavements are not generally competitive on a LCC basis. Unfortunately, the alternative pavement structure design thicknesses analysed in the MTO LCCA Study [1 and 2] are not considered equivalent by the separate hot-mix industry Study Team for the traffic levels specified. According to the ASHTO 93 Guide and the New York pavement design method based on AASHTO 93 [5], the asphalt pavement was significantly over designed. The design traffic loading specified by the MTO for the study was very broad, ranging between 1.0 and 2.0 million annual ESALs. According to AASHTO 93, as shown in Table 1, 240 mm of asphalt concrete should be sufficient to withstand the design traffic of 45 million ESALs over a period of 17 years as compared to the 320 mm adopted in the MTO LCCA Study. The thickness of the asphalt concrete can be reduced to 230 mm for 1.5 million annual flexible ESALs and 20 year service life, and can be even further reduced to 210 mm for 1.0 million annual flexible ESALs and 20 year service life.

Table 1 Asphalt Pavement Designs Using AASHTO 93 Guide

ANNUAL TRAFFIC

(million ESALs)

SERVICE LIFE

(years)

DESIGN TRAFFIC

(million ESALs)

ASSUMED SUBGRADE

CBR

SUBBASE (mm)

GRANULAR BASE (mm)

OGDL (mm)

THICKNESS OF

ASPHALT LAYERS

(mm) 17 45 35 450 100 100 240 20 56 35 450 100 100 260

2.0

50 254 35 450 100 100 320 17 34 35 450 100 100 220 1.5 20 42 35 450 100 100 230 17 22.5 35 450 100 100 205 1.0 20 28 35 450 100 100 210

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It is also important to recognize that the pavement structure must provide sufficient frost action mitigation. The ‘rule of thumb’ for pavement design in Ontario is that the thickness of pavement structure should be not less than about 65 to 70 percent of the frost penetration (about one metre in the Toronto area), which is 650 to 700 mm, which the deep strength asphalt concrete pavement readily provides. Pavement Serviceability and Performance Pavement serviceability is function of factors such as roughness and distresses. In the AASHTO 93 Guide, the serviceability is expressed as the Present Serviceability Index (PSI). Similar indices are used by other highway agencies. For example, the MTO uses Pavement Condition Index (PCI), which is determined on the basis of pavement roughness (or ride comfort) and observable pavement distresses [6]. In the performance evaluation, pavement roughness is the main factor used to measure the pavement condition [7] and to define the life-cycle of pavements [8].

It is imperative for the LCCA to be meaningful that the pavement performance evaluation of all pavement structure alternatives be equivalent. The Pavement Condition Index methodology and pavement survival method (time to overlay) can result in significantly different service lives. This difference is a reflection of the method of pavement performance evaluation, not the actual pavement performance. 5. IMPACT OF NEW TECHNOLOGIES ON PAVEMENT LIFE-CYCLE Historical performance data is used to develop the pavement performance analyses, which often do not properly reflect the recent advances in asphalt technology where complete historical performance is not documented. The initial MTO LCCA Study was based on asphalt technology which was well over a decade old. Therefore, the hot-mix industry considered it necessary that the initial MTO LCCA Study be updated to include these advancements and formed a separate Study Team to provide HMA input to the MTO. The advancements in established procedures and asphalt technology in Ontario implemented over the last 10 to 15 years include construction materials, mixing, production and placement procedures and specifications for hot-mix asphalt, that are considered to significantly extend the life of asphalt pavements. The following asphalt technology advancements were recommended by the hot-mix industry Study Team to be included in the life-cycle costing analysis: 1. pavement smoothness specification for HMA; 2. end-result specifications for HMA; 3. heavy duty binder course (HDBC); 4. performance graded asphalt cement (PGAC); 5. open-graded drainage layers (OGDL); 6. stone mastic asphalt (SMA); 7. Superpave mix design methodology; 8. aggregate quality characteristics changes for HMA; 9. new production and placement technologies for HMA; 10. quality control (QC) plans for HMA; and 11. large stone binder course (LSBC). Due to budget and time constraints, only the first six items involving hot-mix asphalt were considered in the MTO supplemental LCCA study, and their impact on LCCA as summarized in the following sections. In addition, the impact of the other items is also briefly described. The impact of the new technologies is based on detailed review of large number of texts, articles, technical papers and reports, and included the

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analysis of the Long Term Pavement Performance (LTPP) data [9 to 12]; only some of the key references are listed in the References section. The World Bank HDM-4 Highway Development and Management program (Photograph 1) was used to analyze and quantify the impact of the new technologies on pavement life cycles. Previous versions of HDM have been used for over two decades to combine technical and economic appraisals of road projects, to prepare road investments and to analyze road network strategies.

PHOTOGRAPH 1 The HDM-4 Highway Development and Management program developed by

the World Bank is a powerful tool that can be used in life -cycle cost analysis. HDM-4 Pavement Performance Analysis HDM-4 was used by the hot-mix industry Study Team to determine how changes in materia ls quality, ride quality and surface condition influence pavement performance. HDM-4 provides a roughness value and a summary of distresses that would be expected for the in-service pavement conditions. A matrix shown in Table 2 was developed to examine how the materials, ride quality and surface quality influence the pavement performance. In this study, conditions for a typical southern/central Ontario 400 Series freeway pavement were used as input values. Table 3 summarizes how the analyses were used to compare the performance predictions provided by HDM-4.

Table 2 Matrix for HDM-4 Analysis

ANALYSIS NUMBER

MATERIAL QUALITY

RIDE QUALITY

SURFACE CONDITION

1 Good Good New 2 Fair - hard Good New 3 Fair - soft Good New 4 Good Fair New 5 Fair – hard Fair New 6 Fair – soft Fair New 7 Good Good Good 8 Fair - hard Good Good 9 Fair - soft Good Good

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Table 3 Comparison Methodology

PURPOSE OF COMPARISON

DESCRIPTION RELEVANCE OF COMPARISON TO ONTARIO

Material Quality Compare analyses: 1, 2 and 3 4, 5 and 6 7, 8 and 9

Use of high quality materials, improved material testing, introduction of end result specifications (ERS).

Ride Quality Compare analyses: 1 and 4 2 and 5 3 and 6

Introduction of smoothness specification.

Surface Condition Compare analyses: 1 and 7 2 and 8 3 and 9

Introduction of ERS, advanced production and paving technologies such as material transfer vehicles (MTVs), and quality of materials.

As HDM-4 provides a summary of roughness in terms of International Roughness Index (IRI) and a summary of distresses, the IRI value had to be converted to a Riding Comfort Rating (RCR) value [8]. The Pavement Condition Index (PCI) was then calculated by using the RCR values and the Distress Manifestation Index (DMI) based on the predicted pavement distresses [6]. The PCI values for the respective analyses were then calculated. A summary of typical results for the HDM-4 analyses and calculated PCI values at the end of the pavement design period are shown in Table 4.

Table 4 HDM-4 Roughness and Surface Distress Values, and Calculated PCI at the End of Pavement Design Period

ANALYSIS

NO. IRI

International Roughness

Index (mm/km)

CRACKS (%)

RUT DEPTH (mm)

POTHOLES (number)

PCI Pavement Condition

Index

1 1.94 21 12 0 79 2 2.25 100 7 9 68 3 2.25 14 21 0 74 4 3.32 21 12 0 70 5 3.62 100 7 9 61 6 3.65 14 22 0 67 7 2.10 74 14 3 64 8 2.08 99 9 8 57 9 2.26 13 23 2 63

In the first three analyses, the difference between good and fair-hard materials results in a decrease in the PCI value from 79 to 68 (14 percent decrease). Analyses 4, 5 and 6 demonstrate the difference due to materials quality in combination with a fair ride quality when compared with the analyses 1, 2 and 3 results for good ride quality. The resulting differences in PCI due to the ride compared with the quality are shown to be similar to those determined for materials quality (reduction in PCI value from 70 to 61, i.e. a 13 percent reduction). This analysis emphasizes the influence that materials quality has on PCI.

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Comparisons between a good ride quality and fair ride quality were also completed. The average difference in PCI between pavements, which had a good ride quality versus a fair ride quality, ranged between 9 and 11 percent. The improvements were very consistent across the range of materials qualities. Such improvements would be anticipated if a smoothness specification was introduced. A third analysis examined the influence of surface condition on PCI. The difference in PCI for a new surface condition compared with a good surface condition varies between 15 and 19 percent depending on the quality of materials, and assuming that the ride quality is good. The surface condition would be mainly affected by the use of new placement technologies (material transfer vehic le (MTV) for instance), ERS and the quality of materials. As the quality of the materials decrease, the difference or improvement in PCI is smaller. Based on these analyses, it is evident that materials, ride and surface condition quality have a very significant impact on PCI. It is possible to quantify this using HDM-4. The total change in the PCI ranged from 2 to 28 percent (Table 5) depending on the quality of materials, ride and surface conditions. Clearly, the introduction of ERS and the smoothness specifications greatly influence performance and thus the overall life of the pavement. The increase in the pavement service life due to the above pavement condition improvements can be estimated using the pavement performance curve (PCI versus age of pavement relationship).

Table 5 Summary of HDM-4 Asphalt Pavement Performance Analysis

INFLUENCE OF QUALITY

COMPARISON PERCENT DIFFERENCE IN PCI

Material Good, Fair-hard, Fair-Soft 2 - 14 Ride Good, Fair 9 - 11

Surface Condition New, Good 15 - 28 Total 2 - 28

Smoothness The MTO’s smoothness specification was designed to produce more durable and safer roads and improve driver comfort. Better smoothness will improve the pavement performance [13] and reduce the number of times a road must be rehabilitated, minimizing driver inconvenience and maximizing benefits from construction dollars . Detailed information on the MTO’s smoothness specification is given by Kai Tam in a CTAA 1999 technical paper [14]. The smoothness specification for flexible pavements has been implemented gradually over the past 5 years and the hot-mix paving industry has responded with better construction techniques (the use of MTVs for instance). MTO Special Provision SP103F31 “Asphaltic Concrete Surface Tolerance and Payment Adjustment for Surface Smoothness” is currently being used on all MTO contracts having at least 5000 tonnes of surface course hot-mix asphalt and where the posted speed is greater than 60 km/h. In Ontario, current data indicates that the use of stringent smoothness specifications has resulted in a 50 percent reduction in the Profile Index (PI) from 400 mm/km in 1995 to 200 mm/km in 1999 (Photograph 2). While it is generally considered to be difficult to isolate and quantify the cost benefits resulting from smoother pavements, MTO did acknowledge that smoother pavements increase durability and reduce

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maintenance costs; this improvement should allow the time for the first major pavement rehabilitation (overlay) to be postponed by two years. The hot-mix industry Study Team used the HDM-4 program to quantify the impact of the improvement in smoothness on asphalt pavement performance. The asphalt pavement condition improvement in terms of PCI in Year 20 due to improved initial smoothness varied from 9 to 11 percent, which results in about a 4 year extension to the life of the pavement. PHOTOGRAPH 2 The California Profilograph is used by MTO to check the smoothness of

asphalt and concrete pavements. End-Result Specifications for HMA End result specifications represent a profound change in how roads are designed and constructed. Traditionally, method specifications outline in minute detail what needs to be done. The end result specification (ERS) uses a different approach. Rather than telling the contractor what to do, it establishes what needs to be achieved. By giving the contractor responsibility for the quality of the product, ERS also gives the contractor considerable latitude in selecting innovative materials and construction techniques. Detailed information on the MTO’s ERS is given by Tam in a CTAA 1999 technical paper [14]. MTO introduced the ERS in 1991 with full-scale implementation in 1995. The ERS includes the mix attributes (optimum asphalt cement content, appropriate aggregate gradation and proper air voids) and pavement attributes (compaction, smoothness, segregation and thickness). The ERS also implements a bonus and penalty system for the contractor, and requires that testing laboratories and technicians to be certified. MTO paid some $ 5,000,000 in bonuses to asphalt paving contractors during the 1998 construction season, and this obviously reflects the positive effect of construction quality on the performance of asphalt pavements and the resulting agency savings. It is considered that Ontario now has one of the most comprehensive ERS in North America. The quality of the construction process is one of the most significant factors affecting how well a pavement will perform under traffic loading. ERS has had an impact not only on improved material quality but also on construction technology, including construction equipment improvements (use of MTV for instance). Other positive impacts of ERS include linking the work quality and pavement performance, measurement of

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quality on continuous scale, quantitative acceptance (not subjective), incentives for contractor to provide consistent quality, and identifiable and correction (replacement) of rejectable workmanship and materials. As with smoothness specifications, it is somewhat difficult to isolate and quantify the benefits of ERS. With the somewhat limited performance data to date, it is difficult to assess the impact of ERS on the life-cycle costs of asphalt pavements. Monismith et al, [15] clearly indicates that reduced standard deviations for asphalt cement content, compaction, air voids, and aggregate gradation have direct impacts on the occurrence of cracking (fatigue) and rutting response of asphalt pavements, and these impacts (reductions) are possible to quantify. MTO acknowledged that the primary LCC benefits of ERS implementation are reduction in pavement performance variability and a reduction in future maintenance costs due to reduced localized distress areas along a project, but did not give any credit for in terms of asphalt pavement life extension. Unfortunately, no MTO pavement performance data prior to, and after, ERS implementation was available. Therefore, the hot-mix industry Study Team used the HDM-4 program to quantify the impact of quality improvement due to ERS implementation on the performance of asphalt pavements. This analysis shows that the PCI of asphalt pavement at Year 20 can be 6 to 11 percent higher due to good construction quality (this does not include the improvement in asphalt pavement smoothness), and corresponds to an increased service life of 2 to 4 years. Heavy Duty Binder Course (HDBC) Over the past ten years, MTO has modified its quality requirements for aggregates used in hot-mix asphalt. While these modifications have improved performance for all types of HMA mixes, the most significant improvement has probably been in Heavy Duty Binder Course (HDBC) mixes. HDBC mixes in Ontario incorporate 100 percent crushed aggregates from quarry sources (Photograph 3) with a minimum 40 percent retained on the 4.75 mm sieve. HDBC mixes offer excellent resistance to permanent deformation (rutting); optimized HDBC (in terms of stone content) provides good stability and constructibility (compactibility and limited segregation susceptibility) [16]. Those benefits were acknowledged in the MTO LCCA Study [2] which recommended the continued use of HDBC to avoid excessive rutting before rehabilitation is required, but did not indicate any life-cycle cost benefit for the pavements incorporating HDBC mixes. This does not suggest that HDBC is not cost-effective, but rather, that it may be difficult to quantify the obvious benefit. A comparison between the asphalt pavement performance on the Queen Elizabeth Way (a major 400 Series highway) (QEW), where mixes similar to HDBC (using essentially 100 percent crushed aggregates) have been used and on other sections analyzed in the MTO LCCA Study indicated that the service life of such pavements was about 2.5 years longer. The Ontario hot-mix technology with respect to rut resistance can be considered the leading edge technology and will only increase with the use of Superpave. HDM-4 was used by the hot-mix industry Study Team to quantify the impact of using HDBC or HL 8 (HS) High Stability binder course mixes in Ontario, and indicated that the PCI would be 4 to 6 percent higher after 20 years of service, resulting in about 3 years additional service life.

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PHOTOGRAPH 3 The excellent resistance to rutting of the Heavy Duty Binder Course (HDBC)

asphalt mix is mainly provided by good quality, 100 percent crushed aggregates.

Performance Graded Asphalt Cement (PGAC) Developed under the Strategic Highway Research Program, performance graded asphalt cement binders (PGACs) represent a new way to characterize asphalt cement binders and are specified primarily based on climatic conditions and traffic loading. These are performance-based criteria designed to improve durability, rutting and fatigue resistance, and in particular, to reduce thermal cracking. The Superpave PGAC tests (Photograph 4) measure physical properties that can be related directly to field performance by engineering principles [17]. MTO introduced the use of PGACs in Ontario in 1996. In 1998, PGACs became mandatory in all MTO contracts. For pavements carrying heavy traffic travelling at slower speeds, the PGAC grade can be increased by one or even two grades to enhance the rutting resistance of the asphalt mix. The asphalt cement binder contributes up to one-third of a pavement’s rutting resistance, over half of the fatigue cracking resistance and almost 90 percent of low temperature cracking performance. By using the most suitable cement for the climate and traffic conditions, the pavement performance can be dramatically improved. It has been documented that the amount and timing of rout and seal in the maintenance and rehabilitation schedule is significantly reduced if PGAC asphalts are used. According to the MTO LCCA Study, the use of premium PGACs (PG64-28) extends the asphalt pavement service life by at least two years. Polymer Modified Asphalt (PMA) Cements The use of modified asphalt cements offers a means to reduce the frequency of maintenance required at sites carrying heavy traffic and provide longer service life for constructed pavements and maintenance treatments. Modifiers include styrene butadiene block copolymers, ethylene vinyl acetate copolymers, ethylene methacrylate copolymers, low density polyethylene and crumb rubber. Ontario has been using PMAs since the late ‘80s. There has also been significant experience with PMAs in the US, Europe and Australia. Thermoplastic polymers are characterized by softening on heating and hardening on cooling. Polymers, when mixed with asphalt cement, increase the stiffness of the binder at high temperatures and reduce the stiffness at low temperature. Increasing the asphalt cement stiffness at high temperatures automatically increases the stiffness of asphalt mix, thus improving the load spreading ability and increasing the structural

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strength and expected design life of the pavement, particularly its resistance to rutting. Increasing the elastic component of the asphalt cement improves the flexibility of asphalt mix and its resistance to fatigue and thermal cracking. Typically, adding polymers to asphalt cement increases binder costs between 10 and 30 percent. LCC analyses on numerous projects in Ontario have indicated that the savings resulted from the use of polymer-modified asphalts (e.g. elastomers) can range from $ 3k per lane/km to $ 11k per lane/km, and the initial life can be extended from about 4 to 6 years [18 and 19].

PHOTOGRAPH 4 Laboratory testing of PGAC. The testing is based on asphalt cement

performance-based characteristics. Open Graded Drainage Layer Proper drainage is considered one of the main factors influencing the pavement performance. Nine out of ten roads are considered to have drainage problems, and water often causes more pavement failures than traffic. Using an open grading drainage layer (OGDL) was believed to provide a solution to road drainage problems. Whether the OGDL provides a significant improvement to the performance of flexible pavements is not yet clear. To date, just two asphalt pavement projects in Ontario have used this system and while there has been more experience with OGDL in the US, it is difficult to assess the benefits of OGDL. An asphalt-treated open graded drainage layer (typically 100 millimetres thick) is placed between the hot-mix asphalt binder course and the granular base, with subdrain system connected to ditches or storm drains installed to provide continuous drainage. MTO currently specifies asphalt-treated OGDL for high volume 400 Series highway pavements (asphalt and concrete). National Asphalt Pavement Association (NAPA) indicates that properly constructed and maintained OGDL should add at least 1 to 2 years to pavement service life. Monismith on the other hand indicates that there is no direct benefit of using OGDL in asphalt pavements [20]. The supplementary MTO LCCA Study indicates that while the OGDL drainage characteristics do not necessarily improve the performance of asphalt pavements, the added depth included in the design provides additional structural integrity. It is, however, the hot-mix industry Study Team’s technical opinion that if

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OGDL is considered to be ineffective as an improved drainage system for asphalt pavements, it should be replaced with 100 mm of high quality granular base material. This will not affect the thermal regime for asphalt pavements and the savings can be very significant. Stone Mastic Asphalt Stone Mastic Asphalt (SMA) is a high quality hot-mix asphalt used for surface courses. SMA is a gap-graded mix with a high percentage of coarse aggregate that forms a stone ‘skeleton’ within a rich modified asphalt cement matrix plus fibres. As well as improved frictional properties, SMA provides better resistance to permanent deformation (rutting) and fatigue, mitigates reflective cracking and offers better skid resistance. SMA has been used extensively in Europe for over twenty years and is becoming more common in North America. SMA mixes have been used in Ontario for high volume municipal roads (Photograph 5) and highways and for special applications such as the Toronto Molson Indy racetrack [21. SMA is now considered a standard, high quality, improved performance surface course mix in Ontario. After a visit to Ontario in 2000, Carlos Rosenberger, a District Engineer with the Asphalt Institute wrote: “I was most impressed with all five of the stone matrix asphalt (SMA) projects I inspected; from Don Mills Road (placed in 1992) to Route 2A (placed in 1997) each looked very uniform and of high quality.” SMA increases pavement life and reduces maintenance costs. It is, however, more expensive and can cost between 10 and 30 percent more than conventional mixes. According to the MTO LCCA Study, SMA extends the asphalt pavement service life by at least 5 years and should be considered for high volume highways. PHOTOGRAPH 5 Stone Mastic Asphalt (SMA) pavement on Highway 2A in Toronto. The SMA

surface course placed in 1997 is in excellent condition with no cracks or rutting distresses.

Superpave Mix Design Methodology The Strategic Highway Research Program in the US developed Superpave as a complete system for designing superior performing pavements. Superpave has three interrelated components:

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1. PGAC selection and specification; 2. volumetric mix design system; and 3. mix performance prediction system. While Ontario has widely adopted the use of PGACs, experience with the Superpave design system has been somewhat limited. Photograph 6 shows a Superpave pavement on County Road 2 in the County of Frontenac, Ontario constructed in 1996. Superpave has been widely accepted in the US. In 1999, almost half the US state Departments of Transportation paving projects used Superpave. By the end of 2001, that figure is expected to be almost 85 percent. MTO is currently using Superpave on selected contracts until full implementation by the 2003 and 2004 paving seasons. US experience indicates that Superpave mix designs can extend the life of pavements approximately 5 years compared to pavements designed using the conventional Marshall design method. Contractors have reported that using Superpave increases costs initially but that costs stabilize with experience. The use of Superpave was not included in the MTO LCC analysis. PHOTOGRAPH 6 Superpave surface course on County Road 2 in the County of Frontenac,

Ontario. After 5 years of service the pavement is in very good condition. Other Materials and Technology Advancements Large Stone Binder Course (LSBC) has been successfully used by Toronto Transportation since 1994, and is a standard binder course mix in Toronto. Major LSBC projects were constructed on Markham Road (1994) and Finch Avenue in Toronto. Both sections have performed very well to date. Major benefits of using LSBC include increased amount of stone in the mix (almost stone to stone contact as shown in Photograph 7), reduced amount of asphalt cement required (3.5 percent), and good resistance to rutting [23]. Improvements in aggregate quality characteristics in premium asphalt mixes included: 1. Changes to aggregate quality control in a big way in 1996. Before 1996, common aggregate related

problems included aggregate bulking (due to excessive amount of flat or elongated particles) and

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mix rutting. After 1996, quality control was built into aggregate specifications. Limiting the amount of flat or elongated particles for coarse aggregates from 20 percent and then to 15 percent improved the resistance to rutting and reduced the potential for aggregate bulking in the mix. Currently a limit on flat or elongated particles for fine aggregates is considered with testing/research underway.

2. Placing limits on natural sand (excessive amount of natural sand reduces the resistance to rutting) in HL 1 and Dense Friction Course (DFC) mixes.

3. Introducing the Micro-Deval aggregate degradation test first to fine and then coarse aggregates. This test has helped to eliminate poorer quality aggregates (elimination of soft aggregates that result in premature deterioration for instance) and contributed to more consistent aggregate quality.

4. Evolution of the DFC surface course mixes. Changing gradation requirements (opening the mix) allowed more asphalt cement to be added which improved coating and mix workability and durability.

The Ontario hot-mix industry has also invested heavily in new technology and in its asphalt plants and construction equipment. The use of new asphalt production and placement technology has improved quality and, in some cases, reduced costs in virtually every aspect of pavement design and construction. The use of MTVs (Photograph 8), being one of the best examples, is now common place in Ontario and has improved the smoothness of the asphalt pavements and helped to reduce the incidents of segregation. PHOTOGRAPH 7 Comparison of Heavy Duty Binder Course (top lift) and Large Stone Binder

Course (bottom lift).

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PHOTOGRAPH 8 Material transfer vehicles (MTVs) used on major paving contracts in Ontario

significantly improved the quality of asphalt pavements in terms of smoothness and mix uniformity (no gradation or thermal segregation).

5. SUMMARY The predictive performance modelling for this study was done mainly by using the World Bank’s Highway Development and Management Program (HDM-4). The hot-mix industry Study Team’s analyses show that when the performance improvements due to new asphalt technologies are fully realized, the service life of asphalt pavements will be significantly extended. It should be noted however that these technologies are interrelated and therefore the extension in the life of the pavement is not necessarily cumulative. A conservative estimate in the MTO LCCA Study indicated that the service life of deep strength asphalt pavements increased from 17 years for traditional asphalt technology to 19 or even 21 years (with SMA) if the asphalt technology advancements are considered. If the HDM-4 performance modeling is utilized, there would be an estimated further two years extension in the service life of these asphalt pavements to 21 to 23 years depending on the specific surface course HMA adopted. 7. REFERENCES 1. Smith KL, Gharaibeh NG, Darter MI, Von Quintus H, Killingsworth B, Barton R, Kobia K.

“Review of Life-Cycle Costing Analysis Procedures” Report for Ministry of Transportation of Ontario (1998).

2. Hein DK, Hajek JJ, Smith KL, Darter MI, Rao S, Killingsworth B, Von Quintus H. “The Benefits of

New Technologies and Their Impact on Life-Cycle Models”, Report for Ministry of Transportation of Ontario (2000).

3. AASHTO. Guide for Design of Pavement Structures American Association of State Highways and

Transportation Officials (1993).

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4. OHMPA. “Life-Cycle Cost-Effectiveness, Hot Mix Asphalt Pavements in Ontario” Ontario Hot Mix Producers Association (1997).

5. New York State Department of Transportation. “The New York State Thickness Design Manual for

New and Reconstructed Pavements” Technical Services Division, New York State Department of Transportation (1993).

6. MTO. Pavement Design and Rehabilitation Manual SDO-09-01, Ministry of Transportation of

Ontario (1990). 7. Kazmierowski T, Ningyuan L, Sharma B. “Measuring Performance of Asphalt Pavements Using the

International Roughness Index” Proceedings Canadian Asphalt Association 45 299-317 (2000). 8. TAC. Pavement Design and Management Guide National Project Team, Transportation Association

of Canada (1997). 9. FHWA. “Key Findings from LTPP Analysis 1990-1999” FHWA-RD-00-085, US Department of

Transportation, Federal Highway Administration (2000). 10. Turner-Fairbank Highway Research Centre. “Long-Term Pavement Performance Information

Management System Data Users Reference Manual” Publication No. FHWA-RD-97-001, Research and Development, Turner-Fairbank Highway Research Center, US Department of Transportation, Federal Highway Administration (1997).

11. FHWA. “LTPP, Data Pave 2.0” CD ROM, US Department of Transportation, Federal Highway

Administration (1999). 12. FHWA. “Maintaining Flexible Pavements The Long Term Pavement Performance Experiment

SPS-3 5 Year Data Analysis” Publication No. FHWA-RD-97-102, US Department of Transportation, Federal Highway Administration (1998).

13. Brook JD. “Pavement Smoothness” Technical Paper T-123, Pavement Technology Inc. 14. MacLean RD, Virani A, Tam KK. “End Result Specifications for Hot Mix

Canadian Asphalt Association 44 1-26 (1999). 15. Deacon JA, Monismith CL, Harvey JT. “Pay Factors for Asphalt-Concrete Construction: Effect of

Construction Quality on Agency Costs” Technical Memorandum TM-UCB-CAL/APT-97-1, California Department of Transportation (1997).

16. Tam KK, Virani A, Blair J. “Ontario Experience with Heavy Binder Mixes” Proceedings Canadian

Asphalt Association 40 305-321 (1995). 17. AI. Superpave Performance Graded Asphalt Binder Specification and Testing SP-1, Asphalt

Institute, Lexington, Kentucky (1995). 18. Carrick JA, Fraser B, Hein D, Emery J. “Pavement Performance and Life-Cycle Cost Evaluation of

a Polymer-Modified Asphalt Cement” Proceedings Canadian Asphalt Association 41 445-463 (1996).

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19. Tighe SL, Haas R. “Performance Modeling and Economic Analysis of Polymer-Modified Asphalt

Pavements” Proceedings Canadian Asphalt Association 42 1-31 (1997). 20. Harvey JT, Roesler J, Coetzee NF, Monismith CL. “Caltrans Accelerated Pavement Test

(CAL/APT) Program - Summary Report Six Year Period: 1994-2000” Report for California Department of Transportation (2000).

21. Kennepohl G, Aurilio V, Uzarowski L, Emery J, Lum P. “Ontario’s Experience with SMA and

Performance to Date” Proceedings Canadian Asphalt Association 44 495-516 (1999). 22. Brooks D, Hein D, Uzarowski L, Emery J. “Municipal Implementation of Superpave Technology”

Proceedings Canadian Technical Asphalt Association 43 425-442 (1998). 23. Burlie R, Emery J. “Evaluation of Urban Asphalt Concrete Rutting” Proceedings Canadian Asphalt

Association 42 256-283 (1997).