airpave software

AIRPAVE MANAGEMENT – AN INNOVATIVE INTEGRATED PAVEMENTMANAGEMENT SYSTEM FOR AIRPORT PAVEMENTS

byJens C. H. Hede, Pavement Engineer, Department of Roads and Airports, RAMBOLL,

Bredevej 2, DK-2830 Virum, DenmarkTel: +45 4598 6000, Fax: +45 4598 6700, [email protected], www.ramboll.com

andJorgen Andersen, Head of Department, Department of Construction, Copenhagen Airports

Lufthavnsboulevarden 6, DK-2770 Kastrup, DenmarkTel: +45 3231 2750, Fax: +45 3231 3172, [email protected], www.cph.dk

This paper presents the windows based Pavement Management System for airport pavements,AIRPAVE MANAGEMENT, developed in close cooperation between Copenhagen Airport andRAMBOLL. The overall objective of AIRPAVE MANAGEMENT is twofold; to provide an archivesystem, enabling the airport authority to handle and keep an easy track of all activity concerned withthe maintenance of the pavements and to use all information on hand in the prediction of the timingand type of any future maintenance needs. The archive system ensures that all relevant informationregarding the pavements is stored in the same database. In this way the user has an easy access to thehistorical development/information of the pavements. The most important feature of the system is themore complex approach of describing the condition, which is separated into three condition indices; astructural index, a functional index and an index describing the condition of the wearing course. Thisapproach is deemed necessary for the achievement of a more precise prediction of the type of futureinterventions. The type of maintenance applied by the system will depend on which of the threecondition indices reaches the user defined minimum service level of each particular homogenouspavement section. To get an even better estimate of the actual condition and future development of thepavements the system makes use not only of visual inspections but also of results from a range ofobjective measurements. The innovative approach of this pavement management system ensures abetter estimate of future maintenance and rehabilitation needs on a project level, which is of majorimportance to any airport authority, enabling them to optimise budget allocations and avoid wastefulplanning. Integrated into the PMS program is a Geographical Information System (GIS) whichenables a powerful presentation of the many and complex results of the system. Further the GIS is thetool where the archive part of the PMS program (the Management Information System, MIS) is bestviewed, as it shows the position and result of any of the information collected. The paper will inclosing as a case story present the successful implementation of AIRPAVE MANAGEMENT inCopenhagen Airport, one of the major airports in Europe.

BACKGROUND & OBJECTIVES

Copenhagen Airport is among the 10 biggest in Europe with some 18.5 million passengers and about420,000 metric tonnes of freight in 2000 generating about 300,000 aircraft movements. The airporthas three runways (in total 9,7 km), 24 major or minor taxiways (in total 28 km) and 106 stands, i.e. intotal some 3.0 million m2 of flexible, rigid, composite and semi-flexible pavements. These numbersare increasing yearly as the airport presently is carrying out an impressive expansion programme. Thefigure below gives an overview of Copenhagen Airport.

5th International Conference on Managing Pavements (2001)

TRB Committee AFD10 on Pavement Management Systems is providing the information contained herein for use by individual practitioners in state and local transportation agencies, researchers in academic institutions, and other members of the transportation research community. The information in this paper was taken directly from the submission of the author(s).

FIGURE 1 Overview of Copenhagen Airport

The maintenance and rehabilitation of the pavements in Copenhagen Airport is managed by a smallunit in the airport organisation, which for assistance hire in experts from RAMBOLL and otherconsultancy firms. This constellation has proven highly efficient.

Copenhagen Airport has from 1992 systematically conducted detailed surveys of the moreimportant pavements in the airport (runways and major taxiways) by means of visual inspections,measurements with falling weight deflectometer (E-moduli), ground penetration radar (thickness,voids/disintegration), surface profiler (rutting, roughness) and material analysis on drilled cores(material properties). The condition and the trends in the deterioration have been evaluated byobserving the changes in the results obtained of these measurements carried out on regular basis,rather than rely on the calculated values. For instance for airfield pavements where the loadingcharacteristics are significantly different from those known for roads, one has to use quite complexdesign tools in forecasting the service life. These complex models are not yet suitable for pavementmanagement purposes.

Relying on the development in the results rather than on the results themselves lead in 1992 to anre-evaluation of the service life of the most trafficked runway in Copenhagen Airport (RWY 04L-22R) until major periodic maintenance or rehabilitation is needed. Based on FWD/HWDmeasurements it was predicted in 1990 that the runway should be rehabilitated in 1992. Based on thedevelopment in the results of the measurements we now predict the need of periodic maintenance inthe year 2005-2007, even though we still, as the case has been for several years, compute very lowresidual service lives (even less then one year) when using state-of-the-art backcalculation systems.



As the method, developed and managed by RAMBOLL (1), proved successful it was decided to usethis as a basis for a pavement management system to assist in the planning of the future maintenancerequirements for the whole airport as such. Further it was of major importance to the airport authoritythat the system would be able to:

• Make use of the comprehensive data collected for each pavement in the assessment of itscondition;

• Predict in detail the necessary interventions in the future on a project level; and• Constitute an archive system assisting the airport authority in their daily work.

RAMBOLL was in 1997 commissioned to implement a pavement management system meeting theabove mentioned demands. The first step in this implementation was an investigation of the existingcommercial PMS programs. This investigation quickly revealed that the requirements of the airportauthority could not be met by purchasing an existing system. The main reason for this was thatexisting systems mostly only include visual inspections in the determination of the condition and thatthe condition was described by one index only, often the popular Pavement Condition Index (PCI).PCI is a very useful tool in the overall planning process of maintenance needs of a pavement system(network level) – however it does not provide enough information to determine which form ofintervention is most suitable in each specific situation (project level).

As it was concluded that no existing commercial pavement management system met the client'srequirements, it was decided to develop a new system, in close co-operation between CopenhagenAirports and RAMBOLL, specially designed to meet the demands for airfield pavements in general.The system named AIRPAVE MANAGEMENT integrate three systems:

• Management Information System (MIS);• Pavement Management System (PMS); and• Geographical Information System (GIS).

The MIS part stores all relevant information in respects of pavement evaluation and conditionrating, including pavement structures, results of survey or measurement carried out, and trafficloadings. The PMS part computes the present condition of each homogeneous pavement section andthe future performance under alternative maintenance and rehabilitation regimes. The PMS includesM&R catalogue, condition rating and technical and economic performance indicators. The conditionand performance of each pavement section is based on the results of the surveys and measurementsstored in the MIS. The GIS is the main portal to view the many and complex results of the system andthe information stored in the MIS. Additional to providing overview giving maps showing forinstance conditions, residual service life, works, pavement structures etc. the GIS shows the positionand type of each particular survey or measurement. Due to the direct links between the GIS and theMIS and PMS the user can view the results tables with computed values by choosing the visualelements (for instance a drilled core) on the GIS map. This makes it easy to access any pavementinformation.

A major part of this new system is the assessment of the condition and the description of theperformance of the pavements. This will be the scope for this paper. Other features will be reported inlater papers.

INNOVATIVE FEATURES

As mentioned above the development of AIRPAVE MANAGEMENT lead to several new innovativefeatures to meet the demands in managing airfield pavements. Among the more important we wouldlike to mention:



• A three rating system in describing the condition of the pavements;• The condition based on the a range of objective measurements;• The performance is forecasted based on the development in the measured results; and• The optimal maintenance strategy evaluated on several performance indicators.

In addition to these features AIRPAVE MANAGEMENT also allows storage of digital pictures ofsurface distresses and core samples. Further the system subdivide the pavements into homogeneoussections based to the variations in the results of the measurements.

Description of Condition

When designing or evaluating a pavement one must investigate both the functional and the structuralproperties. These two properties cannot in a meaningful way be incorporated into the same index. Forinstance a pavement which has reached the end of its structural life (i.e. the pavement cannot carryany more aircrafts) might very well still have a good functional condition (i.e. the surface is stilleven). See also argumentation of Ullidtz, (2).

Further experience has shown that interventions have been triggered by damage, which cannot bedescribed as structural damage or functional damage, but simply because the wearing course is “tooold”. This might result in fatigue temperature cracking or ravelling. If not dealt with both might resultin an accelerated deterioration in the structural and/or the functional condition.

Finally when a pavement has reached a state of deterioration where maintenance is needed, thedecision on the most suitable type of maintenance work has to be based on determining whichpavement property has reached its critical level (structural, functional). For instance if a pavementshows the need for strengthening (i.e. low structural condition) a thin surfacing is not a suitablesolution. The reason is that a thin surfacing only improves the functional property of the pavement,while the structural property would be virtually unaffected (due to the small thickness applied). Tomake the right decision one thus needs to know both the structural and the functional condition toavoid wasteful planning and unrealistic budget estimates.

Based on the above it was decided to operate with three indices in the pavement management systemto ensure a sufficient detailed description of the actual condition, which again will ensure a betterestimate of the requirements of future maintenance and thus the funding requirements. Besidesseparating the structural and the functional conditions into two different indices an additional indexdescribing the condition of the wearing course was adopted. The three indices introduced are:

• Structural Condition Index (bearing capacity);• Functional Condition Index (riding quality); and• Index for Wearing Course Condition (quality of wearing course).

The structural condition, often referred to as the bearing capacity, indicates how many loads still canbe applied to the pavement structure until the terminal condition is reached. The bearing capacity isoften calculated using analytical-empirical relationships (mechanistic approach).

The functional condition expresses the riding quality for the user. The roughness is of majorimportance for the user (in this case the airline companies) as the maintenance costs of aircrafts risesas the roughness increases. But also the rutting and the friction have major importance, as deep ruttingand low friction will increase the frequency/risk of accidents.

A long service life of the pavement is conditional upon the surface continuously preventing waterfrom penetrating into the pavement structure. This requires that the wearing course keeps a minimumflexibility.



If each of the above mentioned indices are kept above a given critical level the pavement isexpected to possess the properties needed. Whenever one of the condition indices reaches the criticallevel a suitable maintenance work needs to be carried out. In the table below examples are given foreach index of some typical surface distresses at the critical level and some suitable maintenanceworks.

TABLE 1 Typical surface distresses/characteristics and maintenance works to improve eachcondition index (flexible pavements)

Index Example of typical surfacedamage/characteristic

Example of typicalmaintenance works

Structural Condition Alligator crackingLongitudinal cracking

OverlayStrengtheningRehabilitation

Functional Condition RuttingLack of frictionHigh roughness

OverlaySlurry surfacing

Wearing Course Condition Temperature crackingRavelling

Surface sealingSlurry surfacingOverlay

Calculation of Condition

The method of evaluating pavement conditions described above does not presuppose a specificformula for the calculation of each index. Local experience should be used, thus ensuring adoption ofany specific local conditions. However it must be stressed that the calculation of the indices shouldnot only be based on visual surveys as is common in many existing systems. The distresses visible onthe surface of a pavement give an inadequate basis for the evaluation of the structural condition.Experiments have shown, (3), that the first visual cracks in the pavement surface of an asphaltpavement might not occur until the asphalt modulus has decreased by 70-80 per cent of the originalmodulus, i.e. at a very low structural level. In this case it is obvious that a condition index solelybased on visual inspections only gives a misleading description of the actual level of the structuralcondition, and the required strengthening works might not be planned in time. As regards thefunctional condition, the roughness has a major influence on the condition. However the roughness isvirtually impossible to assess during a visual inspection unless it is quite severe. The same is the casefor friction, which is another important functional property. In the same way as for the calculation ofthe structural condition index, the functional condition index should be based on results from morethan just a visual inspection. For the condition of the wearing course the flexibility of the bitumen isof major importance. Many temperature fatigue cracks and loss of aggregates and bitumen in thesurface can only indicate the stage of deterioration in the wearing course. A much better description isobtained by conducting material analysis in the laboratory on drilled cores. Here material propertiessuch as penetration and softening point can be determined directly. Such results should be used in thecalculation of the condition as well.

Thus for the reasons given above any condition rating should be based not only on visualpavement surface inspections but on a range of more objective measurements. However it should bestressed that the visual inspection is an important activity, as the results shall be taken into accountwhen evaluating results of objective measurements to understand deviations in the calculated results;for Falling Weight Deflectometer the presence of cracks are important, many patches can explain highvalues of the roughness measurement etc. Objective measurements could include the followingmeasurements as these are often carried out in connection with pavement condition surveys:



• Falling Weight Deflectometer (FWD/HWD);• Measure of roughness;• Measure of rutting;• Measure of friction; and• Material analysis on drilled cores.

But the measurements might include any other parameter, provided a deterioration curve or a residualservice life can be established. In the table below it is indicated which measurements could beincluded in the calculation of each condition index.

TABLE 2 Calculation of condition indices

Condition Index Primary Measurements Secondary MeasurementsStructural condition Visual inspection

Falling Weight DeflectometerRoughnessRutting

Functional condition Visual inspectionRoughness and Rutting

Falling Weight Deflectometer

Wearing coursecondition

Visual inspectionLaboratory testing

RoughnessRutting

A measurement is considered to be “primary” when the result can influence the final calculated indexsignificantly. Results from secondary measurements only count for small adjustments in the finalindex.

As stated the condition of each of the indices should be based in investigating the development inthe results from the surveys and measurements. Trendlines for the development in each measurementshould thus be established. As these trendlines will be adjusted each time a new measurement iscarried out the present condition and the future deterioration will continuously be recalculated,ensuring a better and better estimate of the condition.

The three condition indices should be calculated for each homogeneous pavement section in termsof pavement structure and condition. Homogeneous sections in terms of the condition is defined as thesmallest interval over which the results do not vary significantly, and can thus reasonably bedescribed by an average or percentile etc. This could be done automatically by using mathematicaltools such as delineation by the AASHTO cumulative difference approach, (4).

Evaluation of Performance

The evaluation of the performance should be based on condition indices from several years. SomePMS programs only make use of one year measurements and then project the condition to the criticallevel. This method is subject to significant uncertainties. Normally the deterioration of a pavementwill follow a continuous and smooth curve. The curve can however obtain an accelerateddevelopment when approaching its critical level. When several condition indices have been calculatedthe timing of the future intervention (the residual service life) could be found by projecting the curveas indicated in the figure below.



OO

OO

O

Critical level

O

Actual

development

Projected

development

Calculated condition indices

Condition

Time

FIGURE 2 Timing of future intervention (only one condition is shown)

The projection of the condition (the deterioration curve), where several theoretically possible curvesneeds to be investigated, will be done for each of the three condition indices (structural, functionaland wearing course), in the figure only one index is shown. The first of the three deterioration curvesreaching its particular critical level determines the timing (and type) of the first coming intervention.Carrying out an intervention will lift up the condition index of that particular condition, but might alsohave an effect on the other condition curves.

In table 1 some works were suggested depending on which of the three indices had reached itscritical level. In the table below is indicated the effect on each condition by applying each particularwork.

TABLE 3 Effect of maintenance work on conditions

Structural Functional Wearing courseSurface sealing - ÷ +Slurry surfacing - + + +Ultra thin overlay - + + + + +Overlay + + + + + + +Rehabilitation + + + + + + + + +Note: ÷ Negative effect, - No effect, + Minor effect; + + Some effect and + + + As new

From the table it is clear that defining a maintenance strategy is a complex task to carry out, as onewishes to take full advantage of the present or applied work. The optimum strategy ensures that whenmajor works have to be carried out, all conditions are at or close to the critical levels. If the conditionof the wearing course for instance reaches its critical level in a situation where the residual structuralservice life is only 3-4 years an ultra thin overlay will not be an optimum maintenance work to apply,as this will have a functional service life of 7-10 years. After 3-4 years the pavement needsstrengthening, which will imply adding further layers on top of the existing pavement, thus notmaking use of the rest of the 4-6 years of the expected functional service life of the previously appliedultra thin overlay.

It should be stressed that the condition indices and subsequently the performance curve is nonstatic. Whenever any new survey has been carried out, whether it be visual surveys, measurements

Regression line (deterioration curve)

Timing of intervention



with Falling Weight Deflectometer or surface profiler etc., all previous as well as the present indiceswould be recalculated and thus give an improved estimate of the condition and performance.

Evaluation of Optimal Maintenance Strategy

For each homogeneous section the optimal maintenance strategy has to be chosen. Any number ofalternative strategies can be investigated simultaneously. The most optimal strategy is then assessedbased mainly on the following economical and non-economical indicators:

• Net Present Value (NPV);• Capital Factor (CF); and• Relative User Cost (RUC).

The net present value is the discounted costs of any future maintenance and rehabilitation operationswithin the user specified analysis period. This is a very common evaluation tool in comparingalternative intervention strategies.

The capital factor is included to take into account the performance of the invested capital. Thefactor is based on the structural residual life at the beginning and at the end of the analysis periodrespectively, as it is deemed that the structural index is the best indicator of the performance ofinvested capital. The factor is included to take into account that one might have a significantlydeteriorated pavement at the end of the analysis period (although the condition indicators are all abovethe specified minimum service level) compared to the condition at the beginning of the analysisperiod. In this case one has eaten of the invested capital through the analysis period. Some times theeffect is taken into account by assessing the salvage value of the pavement at the end of the analysisperiod. This is a valued tool when comparing alternative new pavement structures. For pavements inservice however, the present residual service life (i.e. at the start of the analysis period) should also beconsidered. If the capital factor is less than one, this means that the invested capital has been eatenduring the analysis period, i.e. the structural residual life of the pavement is shorter at the end of theperiod than it was at the beginning.

For roads many relationships between pavement characteristics such as roughness, rutting etc. andthe cost of the users (vehicle operating costs, VOC) have been established. Of the more importantstudies one could mention the relationships used in the HDM-4 software (Highway Development andMaintenance), (5). For aircrafts the same imperial studies have not yet been undertaken, thus norelationships have been established. One of the first steps in this could be calculation of the G-force inthe aircraft, for which software now has been developed, (6). But this method does not include amodel for forecasting the G-force. We have chosen to include a relative measure of the user costs. Thearea between the actual deterioration curve of the functional condition (where characteristics such asroughness and friction are predominant) and the theoretical maximum condition could meaningfullybe considered as a measure of the user costs of the airline company. In this way a relative term of theextra user costs is calculated (compared to a perfect even surface).

The authors assess that in the future terms like user cost could be a competitive factor betweenairports, as the airline companies have an interest in minimising the operation costs by maximising thenumber of operations with each aircraft until maintenance is needed.

The figure below illustrates the decision making between two alternative strategies taking intoaccount the three major performance indicators.



0

20

40

60

80

100

1 3 5 7 9 11 13 15 17 19

Year

Func

tiona

l Con

ditio

n

ALT 1ALT 2

FIGURE 3 Decision making between alternative strategies

In the figure it is assumed that non of the other indices not shown in the figure (structural and wearingcourse) reaches their critical values during the analysis period. In the example shown in the figureabove the following performance indicators could be calculated.

TABLE 4 Performance indicators (related to figure 3)

Net Present Value[currency]

Capital Factor[ratio]

Relative User costs[ratio]

ALT 1 63.0 0.67 0.45ALT 2 52.4 1.00 0.52

The example shows that “ALT 2” is the most optimal for the airport authority as this strategy resultsin the lowest discounted maintenance and rehabilitation costs and the capital invested is kept equal.However for political reasons the authority might choose “ALT 1” as this results in less user costs forthe airline companies.The example illustrates that selecting the optimal maintenance and rehabilitation strategy is not asimple task as the performance indicators (NPV, CF and RUC) often do not give a clear picture ofwhich of the alternative strategies are the most optimal in the given situation.

IMPLEMENTATION OF AIRPAVE MANAGEMET IN COPENHAGEN AIRPORT

AIRPAVE MANAGEMENT has been implemented in Copenhagen Airport. The implementationbegan in 1999, where the first test runs was conducted. Based on the results from these initial runs theprogram was further developed through 1999 and 2000 to its present level, and final implementationhas been finalised.

The airport has been geometrically divided into areas and parcels. An area is defined as a separateairport element, for instance RWY 04L-22R. A parcel is a part of an area, for instance the leftshoulder of RWY 04L-22R. Copenhagen Airport has been divide into about 60 areas (excludingaprons) and about 280 parcels.

As AIRPAVE MANAGEMENT is windows based all entries and results are done or viewed inwindows as shown below.



FIGURE 4 Examples of windows in AIRPAVE MANAGEMENT

During the implementation phase the following tasks needed to be concluded:

• Geometrical description of the airport elements (areas, parcels, pavement types etc.);• Establishment of a maintenance and rehabilitation catalogue (types, costs, effects etc.);• Entries of survey results in the databases (visual inspection, E-moduli, roughness etc.);• Calculation of homogeneous sections;• Investigation of the performance of alternative maintenance and rehabilitation strategies; and• Viewing/evaluating the results (budget plans, work plans etc.).

Based on the results of the surveys conducted (visual inspections, Falling Weight Deflectometermeasurement, roughness measurements, rutting measurements, friction measurements and materialanalysis) homogeneous sections have been determined by the system. A Homogeneous section can bea whole parcel or a part of this (typically given by a chainage). To each homogeneous sectionalternative maintenance and rehabilitation strategies are described and the consequences in termseconomy and performance throughout the user chosen analysis period (in this case 20 years) has beencomputed. Based on this the optimum strategy has been chosen. In the figure below is given anexample of the performance (i.e. the development/deterioration in structural and functional indicesand in the index of the wearing course) of a homogeneous section of RWY 04L-22R.



Service Level

Stre

ngth

enin

g

Ove

rlay

Reh

abili

tatio

n

0

20

40

60

80

100

07-1993 07-1998 07-2003 07-2008 07-2013 07-2018 07-2023 07-2028 07-2033 07-2038

Wearing Couse Functional Structural Rating_WC Rating_F Rating_S

Area

Station fromStation to

Parcel:

04L-22R

-0.0060.954

BaneStrategyResidual lifeCapital factorNet Present Value

A-43.250.006,123,000

FIGURE 5 Example of performance curve

The results from the system (maintenance works, cost streams, conditions, results frommeasurements, surface types and budget simulations etc.) can be viewed in user defined tables andfigures in different degrees of detail, depending on the needs of the user. Typically all the results canbe viewed on the following levels; the whole airport (board presentation), areas and homogeneoussections.

FIGURE 6 Example of standard reports (maintenance costs on airport and area levels andbudget simulation)

To enable an overall view of the main results a GIS program has been fully integrated with the PMSprogram. The user can add and remove layers of results to make the user environment he or shewishes. As an example of the GIS presentation the figure below has been included.

Analysis period

Trendline for condition of wearing course

Trendline for functional condition

Trendline for structural condition



FIGURE 7 Example of GIS reports (pavement surfaces)

Based upon the implementation of AIRPAVE MANAGEMENT in Copenhagen Airport the followingresults are achieved:

• Easy access to important historic information of the pavements (pavement structures, surveysconducted and results, maintenance applied);

• More complex and precise description of the condition of the pavements;• Improved estimate of the actual condition of the pavements by the use of a range of objective

measurements;• Improved estimate of timing and types of future maintenance and rehabilitation needs;• Optimum choice of strategy for each homogenous section based on economic as well as non-

economic performance indicators; and• Results presented in user defined standard reports or in the fully integrated GIS program.

Results from the use of the system in Copenhagen Airport shows that the condition of the wearingcourse often is the trigger of interventions. Thus this condition index is, as expected, important whenplanning maintenance works of airfield pavements. If no problems with friction are experienced theresults shows that the functional condition index would only have minor effect on the decisions onmaintenance works. For this condition index high ratings would generally be computed.

The methodology used in AIRPAVE MANAGEMENT (the three-rating system) has been applied inCopenhagen Airport since the beginning of the nineties. Using this method has resulted in postponingmajor runway rehabilitation works, thus leading to significant M&R cost reductions. It was based onthis successful use that it was decided to implement the methodology into a pavement managementsystem, thus ensuring that the methodology would be systematically applied to the whole airport.

It is expected that AIRPAVE MANAGEMENT continuously will be improved to meet the growingdemands of airport pavement maintenance and rehabilitation.



REFERENCES

(1) Korsgaard, Hede, Andersen and Andersen, “Evaluation of the Condition of an Airfield PavementBased on Changes in Yearly Measurements”, 5th International Conference on the BearingCapacity of Roads and Airfields, Norway, 1998

(2) Ullidtz, ”Pavement Analysis”, Elsevier Science Publishers B.V., 1987(3) Ullidtz, ”Modelling Flexible Pavement Response and Performance”, Polyteknisk Forlag, 1998(4) AASTHO Guide for Design of Pavement Structures, AASHTO, 1986(5) Highway Development & Management Manual, HDM-4, version 1.0, PIARC 1999(6) Gerardi, “Runway unevenness best detected by periodic assessment that can unveil hidden

bumps”, ICAO Journal, October 1999



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