Dublin Airport Runway 10/28 Evaluation

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Dublin AirportRunway 10/28

Evaluation

Pavement Evaluation

November 2014

47071009

Prepared for:Dublin Airport Authority plc

UNITEDKINGDOM &IRELAND


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DAA Dublin Airport Runway 10/28 Evaluation

PAVEMENT EVALUATIONNovember 2014

i

REVISION SCHEDULE

Rev Date Details Prepared by Reviewed by Approved by

0 Sept 2014 Draft Jonathan EastwoodSenior Engineer

Martyn JonesAssociate

Bachar HakimTechnical Director

1 Nov 2014 Final - IncorporatedDAA comments

Jonathan Eastwood

Senior Engineer

Martyn Jones

Associate

Bachar Hakim

Technical Director

URS12 Regan Way

Chetwynd Business ParkChilwellNottinghamNG9 6RZUnited Kingdom

Telephone: +44(0)115 907 7000Fax: +44(0)115 907 7001

Cover aerial photograph - Contains Ordnance Survey Data Crown Copyright and database right 2014. Reproduced from OrdnanceSurvey digital mapdata. Crown copyright 2014. All rights reserved. Licence number 0100031673. Copyright Natural England 2014.Material is reproduced with the permission of Natural England 2014. Copyright English Heritage 2014. Reproduced under the terms ofthe Click-Use Licence. (C) URS 2014.


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Executive SummaryA Pavement Evaluation was undertaken by URS on Runway 10/28, the 34 Threshold, Taxiways B7, E1, E2,E3, E4, E5, E6 and E7 at Dublin Airport, Eire. The evaluation comprised a Heavy Weight Deflectometer

(HWD) Survey, Diamond Rotary Coring, Dynamic Cone Penetrometer (DCP), Ground Penetrating Radar(GPR), a coarse visual survey and laboratory testing of recovered materials.

The main purpose of the investigation was to assess the current condition of the existing pavements,determine the Pavement Classification Number (PCN) and provide treatment options to ensure a minimum20-year pavement life. The findings of the evaluation are as follows:

The majority of the pavements are jointed concrete pavements with dowelled transverse joints.Runway 10/28 has had a Thin Porous Friction Course surface. Taxiways E3 and E4 have hadprevious asphalt overlays. Part of Taxiway E1 is fully flexible.

A coarse visual inspection, performed at night, indicates that Runway 10/28 has reflective cracksfrom the underlying concrete joints, a number of which been repaired. Runway 34 Threshold

appears to be in good visual condition, benefitting from a recent overlay. Areas of B7 displayextensive map cracking on the surface indicative of Alkali Silica Reaction (ASR), to a lesser extentmap cracking is also present on E7. Fine longitudinal cracking is also present on B7, E2 and E6.

The concrete surface cracking depth varies from 30mm to 150mm. Of the PQC cracks cored, nonewere full depth.

The petrographic analysis indicates that ASR and Secondary Ettringite is present in Taxiways B7, E2and E7. The occurrence of ASR is reported as rareto commonwhile the Secondary Ettringite iscommon. It is not known if the ASR and Secondary Ettringite is still expansive/reacting. Nopetrographic analysis was undertaken on samples for E5 and E6.

The compressive strengths of the Pavement Quality Concrete (PQC) are variable with valuesranging from 30N/mm2to over 60N/mm2.

The laboratory testing of the asphalt materials show relatively low Indirect Tensile Stiffness Modulus(ITSM), indicating some deterioration and micro-cracking of the asphalt matrix.

The pavements have been divided into a number of characteristic sections based on theconstruction type, average construction thickness, location and relative performance under loadingby the HWD.

The Boeing B777-300ER has been taken as the design aircraft for all pavements. This is based onthe significant loading effect and frequency of the aircraft. The B777-300ER has a Maximum Take-Off Weight (MTOW) of 352,000kg and a Tridem gear configuration.

A mixed traffic analysis has been performed to determine the equivalent number of coverages of thedesign aircraft over a 20-year design life. The coverages indicate Low (10,000) to Medium (100,000)traffic dependant on the pavement usage.

An analysis of the past traffic would indicate that the structural life of Runway 10/28 has alreadybeen exhausted, or is approaching exhaustion.

The design aircraft is considered to be at 100% MTOW for departing aircraft to Runway 10/28, the34 Threshold, B7 and E1. For the runway exits E2, E3, E4, E5, E6, and E7 this has been reduced to80% MTOW to account for arriving aircraft.

It is estimated that the design aircraft represents an overload operation of approximately 15% overthe calculated PCN, with a frequency greater than 5% when considering aircraft with an ACN within10% of the PCN.


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The calculated PCN values for Runway 10/28, B7, E1, E3 and part of E4 are insufficient for thedesign aircraft over the 20 year design life and will require structural strengthening.

Taxiways E2, E5, E6 and E7 are also recommended for structural treatment to address the observed

cracking and preserve the integrity of the pavement.

The overlay material should comprise Marshall Asphalt with a Porous Friction Course Surfacingmaterial, adhering to DMG27 Appendix C Defence Estates, Specification 13: Marshall Asphalt forAirfield Pavement Works and Specification 40: Porous Friction Course for Airfields.

An alternative overlay design, enabling a reduction in overlay thickness, comprises French asphaltmaterials EME2 and BBA surfacing (un-grooved).

In order to ensure the continued structural integrity and serviceability of the pavement, a routinemaintenance programme should be in place to repair any surface defects that may develop duringthe design period.


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7

TREATMENT RECOMMENDATIONS ............................ 38

7.1

General ............................................................................ 38

7.2

Material Options ............................................................. 38

7.3 Structural Treatments.................................................... 39

7.4 Non Structural Treatments ........................................... 41

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CONCLUSIONS .............................................................. 42

FIGURE 1 LOCATION PLAN

FIGURE 2 CORE LOCATIONS AND CHARACTERISTIC SECTIONS

APPENDIX A STRUCTURAL EVALUATION WITH THE HEAVYWEIGHT DEFLECTOMETER (HWD)

APPENDIX B CORE LOGS

APPENDIX C DYNAMIC CONE PENETRATION RESULTS (DCP)

APPENDIX D LABORATORY TEST RESULTS

APPENDIX E TABLES OF HWD DEFLECTIONS

APPENDIX F PROFILES OF HWD DEFLECTIONS

APPENDIX G CORRELATIONS BETWEEN DEFLECTIONPARAMETERS AND BACK-ANALAYSED STIFFNESSES

APPENDIX H GROUND PENETRATING RADAR

APPENDIX I TABLES OF JOINT PERFORMANCE


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GLOSSARY

AC Asphaltic Concrete

ACN Aircraft Classification Number

ASR Alkali Silica Reaction

ATC Air Traffic Control

BBA Beton Bitumeux Aeronautique

CBR California Bearing Ratio

CST Compressive Strength Test

DCP Dynamic Cone Penetrometer

DLC Dry Lean ConcreteDMG Design & Maintenance Guide

EME2 Enrob Module lev

FAA Federal Aviation Administration

Fdn. Foundation

FOD Foreign Object Damage (or Foreign Object Debris)

HBM Hydraulically Bound Material

HRA Hot Rolled Asphalt

HWD Heavy Weight Deflectometer

ITSM Indirect Tensile Stiffness Modulus

LC Lean Concrete

MA Marshall Asphalt

MTOW Maximum Take Off Weight

OEW Operating Empty Weight

PAH Poly-Aromatic Hydrocarbon

PCN Pavement Classification Number

PFC Porous Friction Course

PQC Pavement Quality Concrete

RWY Runway

SAMI Stress Absorbing Membrane Interface

TWY Taxiway


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1 INTRODUCTION

This report describes a pavement evaluation of Runway 10/28 and associated Taxiways at

Dublin Airport, Eire, undertaken by URS on behalf of Dublin Airport Authority as part ofContract Ref:DA13-1117 Runway 10/28 Structural Overlay.

The evaluation included the following areas:

Runway 10/28

Threshold of Runway 34

Taxiway Bravo 7 (B7)

Taxiways Echo 1 to Echo 7 (E1 to E7)

A section of Taxiway Bravo 4 (B4) - additional request

The survey extents are shown in Figure 1.

1.1 Purpose of the Evaluation

The purpose of this evaluation was to:

Assess the overall condition of the existing pavement layers and foundation

Determine the current Pavement Classification Number (PCN) for the existingpavements in accordance with DMG27, and also using COMFAA as a means ofproviding an independent (alternative methodology) assessment for comparison

Calculation of residual life

Provide treatment recommendations to ensure a minimum 20-year design future life

1.2 Elements of the Evaluation

The evaluation comprised the following elements:

A structural evaluation using a URS Heavy Weight Deflectometer (HWD), as detailedin Appendix A

A Rotary Coring survey

A Dynamic Cone Penetration (DCP) survey

A Ground Penetrating Radar (GPR) survey

A laboratory based materials test programme on the extracted samples

Analysis of all survey data obtained from the evaluation (in conjunction with trafficinformation) in order to achieve the objectives listed in Section 1.1


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1.3 Historical Records

The historical information has been compiled from a number of previous evaluation reportsand a powerpoint slide showing approximate ages of the airfield pavements, provided by DAA.

This information is summarised below.

Runway 10/28 was constructed in 1989 and comprised a rigid construction of 370mmPavement Quality Concrete (PQC) on 150mm Lean Concrete (LC) on 200mm Granularcapping material on the existing subgrade.

In 2011 Runway 10/28 received a Porous Friction Course (PFC) overlay of approximately 25-35mm. It is also understood that in 2011, prior to the overlay, a number of partial depth or fulldepth repairs were undertaken to localised areas, as indicated on drawing DA13-1117-C002provided by DAA. No other details of the repairs, other than the location were available. Since2011, localised repairs have been undertaken at the joint locations to maintain reflectivecracks occurring in the PFC.

The parallel Taxiway B7 and runway exits E2, E5 and E7 were also constructed in 1989, alongwith and of a similar rigid construction to Runway 10/28.

Runway exit E6 is understood to be constructed in 1996 and is thought to be a similarconstruction to the adjacent pavements (Runway 10/28, B7, E7 and E5).

The Threshold 34 area was an extension to Runway 16/34 constructed in 1964/65, comprisinga rigid construction of 300mm PQC over 150mm LC. This was subsequently overlaid withMarshall Asphalt in 1989/90 as part of the Runway 10/28 works.

The main width of Taxiway E4 was originally the 05 Threshold of the now defunct Runway05/23. It was an extension to Runway 05/23 constructed in 1960/61, comprising 325mm PQCand laid directly on the subgrade. This was overlaid with approximately 130mm asphalt in1966.

Taxiway E4 also comprises a narrow section, adjacent to Runway 10/28, which was the end ofthe parallel taxiway to the 05 Threshold. Taxiway E3 was also part of the parallel taxiway tothe 05 Threshold. No construction details were available for this taxiway, however it isassumed the original concrete construction is similar to E4 with an asphalt overlay of unknownthickness.

No specific construction details were available for Taxiway E1. It is assumed it wasconstructed in in 1964/65 along with the 34 threshold extension. The north-east part ofTaxiway E1 was possibly re-constructed in rigid pavement in 1996, although this has not beenconfirmed in the available historical records.

No detailed construction history was available for the section of Taxiway B4. However, it is

understood that the pavement construction comprises approximately 520mm Asphalt over500mm to 600mm LC.


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centre of a slab line to enable the slab centre to be tested, with the test spacing staggeredbetween offsets where possible. The test spacing for the taxiways varied, with the spacingreduced for short taxiway lengths to enable a minimum number of tests per offset.

On Runway 10/28 the offsets and test spacing coincided with a previous HWD surveyperformed by PMS Ireland, with the inclusion of two additional outer offsets.

All runway and taxiway offsets were referenced to the left and right of the centreline relative tothe direction of increasing survey chainage. On the curved taxiways all chainages are basedon the existing centreline with the chainage adjusted to match on the outer and inner offsets.

Table 2 details the nominal HWD test spacing adopted for each pavement and survey line.

TABLE 2: HWD OFFSETS AND NOMINAL TEST SPACING

Location Offset from the Centreline[1]

Nominal Test Spacing[2]

(m)

Runway 10/28 3m Left & Right

9m Left & Right

15m Left & Right

30

30

100

34 Runway 4m Left & Right

10m Left & Right

25

B7 3m Left & Right

9m Left & Right

30

E1 3m Left & Right

10m Left & Right

25

E2 3m Left & Right

9m Left & Right

25

E3 3m Left & Right

9m Left & Right

30

E4 3m Left & Right

6m Left & Right

30

E5 3m Left & Right

9m Left & Right

30

E6 0m Centreline

6m Left & Right

12m Left & Right

30

E7 3m Left & Right

9m Left & Right

30

B4 3m Left & Right

9m Left & Right

20

Notes:[1] Runway and Taxiway offsets referenced to Left and Right of centreline corresponding to the direction of

increasing survey chainage.[2] Test spacing dependant on slab positioning and pavement length, excluding 10/28 where specific

spacing was used.


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Three loading drops were performed at each test location. A nominal test pressure of 1.5MPawith a 450mm diameter loading plate was applied during the HWD testing for all locations.This corresponds to a (simulated moving aircraft) wheel load of 24.5 tonnes

The average internal asphalt temperature is of particular importance due to the temperaturesusceptibility of asphalt material. Wherever HWD testing was performed on asphaltpavements the air and pavement temperatures (at the surface and approximately mid-depth ofasphalt) were recorded. The measured temperatures are shown in Table 3 for each shift.

2.3 Visual Survey

A course visual survey was performed during the HWD survey to assist in the assessment ofthe pavements. It should be noted that these observations were made during the hours ofdarkness under limited vehicle/mobile lighting and are not definitive. The following paragraphssummarise the findings.

2.3.1 Runway 10/28

Runway 10/28 has a thin porous friction course surface (PFC) which generally extends toapproximately 1m from the outer edge of the concrete slabs. The PFC generally appears to bein reasonable condition. There are areas of repairs above transverse and longitudinal jointlocations. There are also signs of further reflective cracks, partly masked by the PFCproperties. Outside the PFC surfacing, at the runway edge, map cracking was observed on theoccasional slab, although a rare occurrence. This map cracking was characterised bywhite/brown deposits filling the cracks, similar to that produced by Alkali Silica Reaction(ASR).

2.3.2 34 Threshold

Runway 16/34 appears to have a porous asphalt surface course, which is not noted within thehistorical records. The surface appears to be in a reasonable condition for the main part.However, towards the north of the area, just before the CAT II Hold Bar, there is a surfacechange to an apparently much older asphalt surface. This asphalt shows signs of distress withweathering and cracking present.

TABLE 3: SITE TEMPERATURES

Shift Date Location Temperature (oC)

Mid-Depth Surface Air

1 30/06/2014 10/28 - 14.6 11.6

2 01/07/2014 19.4 15.3 12.7

3 02/07/2014 10/28, E1, & B7 19.4 16.0 15.9

4 03/07/2014 B7 - 15.7 16.0

5 04/07/2014 E6, E5, E4, E3 16.9 17.1 11.8

6 07/07/2014 B4, 10/28 Joints 17.9 12.9 12.5

7 08/07/2014 B4, E2 16.3 13.3 12.0


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2.3.3 Taxiway B7

Taxiway B7 is a concrete pavement which is affected by cracking. There appears to be twodistinct areas based on the observed cracking. The first area, from the edge of Runway 10/28

to the corner where Taxiway B7 becomes a parallel taxiway, is characterised by a number ofslabs showing map cracking, similar to ASR cracking, of varying degrees. Photograph 1(included in Section 3.4 of this report) shows a slab in this area with pronounced mapcracking. The second area is the parallel section of Taxiway B7 running from the corner toTaxiway B6. In this section the map cracking reduces and a number of slabs display one ormore fine longitudinal cracks of varying length, some nearly full length of the slab. Thesecracks are predominately in the direction of traffic. Some of these cracks are possiblyshrinkage cracks as against ASR related cracking, although some do exhibit white/browndeposits indicating that ASR may still be present, although not as significant as the first area.

2.3.4 Taxiway E1

Taxiway E1 comprises two distinct sections; an asphalt surface from the 34 Threshold Edge to

the Hold Bar and a concrete surface from the Hold Bar to Link 1. The asphalt section appearsto be in a relatively good condition with no defects observed. The concrete section alsoappears to be in relatively good condition south of the CAT x Hold Bar. Beyond the CAT xHold Bar, at top of E1 (actually in Link 1) there is significant distress with cracked slabs andvariable asphalt slab replacements.

2.3.5 Taxiway E2

Taxiway E2 is a concrete pavement which generally appears to be in reasonable condition.However, close inspection does show a number of slabs with fine longitudinal cracking similarto the parallel section of B7.

2.3.6 Taxiway E3

Taxiway E3 has an asphalt surface with some longitudinal and transverse cracking. Thecracking appears to have reflected from the underlying concrete joints.

2.3.7 Taxiway E4

Taxiway E4 has an asphalt surface with two distinct sections. The first section, comprising theold parallel taxiway section and the south end of the defunct Runway 05/23 section is an oldasphalt surface. This is weathered with occasional open lane joints and longitudinal andtransverse cracks. The remaining part of Taxiway E4, the north section adjacent to BravoTaxiway, has had a relatively recent Porous Friction Course overlay and has no apparentdefects.

2.3.8 Taxiway E5

Taxiway E5 is a concrete pavement which generally appears to be in a reasonable condition.However, the occasional slab does exhibit a fine width (possibly shrinkage) longitudinal crack.

2.3.9 Taxiway E6

Taxiway E6 is a concrete pavement which generally appears to be in reasonable condition.

2.3.10 Taxiway E7

Taxiway E7 is a concrete pavement. A number of slabs exhibit fine longitudinal cracking,possibly shrinkage cracks, along with some map cracking typical of ASR.


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2.3.11 Taxiway B4

Taxiway B4 has an asphalt surface with occasional small patches.

2.4 Coring Survey

A Rotary Coring survey was performed to extract samples of the bound layers in order todetermine the construction depths and confirm material types, at discrete locations, andprovide samples for laboratory testing. A hydraulically operated coring trailer was employed,using water cooled diamond tipped core barrels of nominal diameter 162mm to provide a coresample of nominal diameter 150mm.

A total of 34 cores were taken across all the pavements included in the evaluation. The coreswere spaced regularly throughout each pavement area along a particular HWD offset. Thecore locations were logged using a GPS unit and are shown in Figure 2.

A site core log including locations details, approximate measurements, condition and site

photograph, was completed for each core upon extraction. The cores where placed inindividually labelled bags and then returned to URS laboratory in Nottingham, UK for formallogging and laboratory testing.

As part of the logging process a PAK Marker spray test is used to initially identify the presenceof poly-aromatic compounds typically found in tar. The spray test is not a definitive indicator ofthe presence of poly-aromatic compounds, which can be found in other pavement constructionmaterials at lower concentrations, but it is a strong indicator of tar materials. The PAK Markerspray test proved negative for all asphalt layers extracted.

The cores are in good agreement with the historical construction records, allowing for normalconstruction thickness tolerances.

Of note are Cores 28 and 29 taken from Taxiway B7, where the Lean Concrete (LC) appearsto have completely disintegrated during the coring process, resulting in only fragments of theLC being extracted. This might indicate that the LC is extremely weak and/damaged throughthis area.

Ten of the cores, predominately along Taxiway B7 but also Taxiways E2, E6 and E7, weretaken on visible surface cracks in the concrete pavement. None of the cracks proved to be fulldepth, with the crack depth ranging from 30mm to 146mm.

No cores were taken from Taxiway B4, with only HWD testing requested by DAA oncemobilised to the site.

The core details are summarized in Table 4. The core logs are presented in Appendix B,where the individual layer thicknesses of each discrete identified layer are shown.


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TABLE 4: SUMMARY OF CORE DATA

Location Chainage(m)

OffsetfromCentreline

CoreNumber

Thickness (mm)[1]

Asphalt PQC LC

Runway10/28

15 3m Right 1 35 385 DL-229mm 160

303 3m Left 2 35 370 180

603 9m Right 3 30 380 160

903 15m Left 4 30 390 150

1215 3m Right 5 30 370 190

1503 3m Left 6 30 395 175

1749 15m Right 7 30 355 V 165

2085 9m Left 8 30 380 V 170

2385 3m Right 9 30 380 175

2553 3m Left 10 25 385 150

E1 62 3m Left 11 520 - -

86 3m Right 12 - 340 140 V

E2 52 3m Left 13 - 380 165 V

161 3m Left 14 - 385 V, CTD-46mm 165

E3 80 5m Right 15 95 330 125175 4m Left 16 80 310 90

E4 30 3m Right 17 285 365 V -

100 4m Left 18 80 275 V -

150 4m Right 33 90 320 -

E5 50 3m Right 19 - 380 140

125 3m Left 20 - 380 190

E6 50 5m Right 21 - 340 180

150 6m Left 22 - 370 140

267 6m Right 23 - 395 V, CTD-65mm 205

E7 100 3m Left 24 - 380 160

167 2.5m Right 25 - 385 CTD-126mm 135 V


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TABLE 4: SUMMARY OF CORE DATA



CoreNumber

Thickness (mm)[1]

Asphalt PQC LC

B7 25 4m Right 26 - 350CTD-41mm 190

96 2.5m Left 27 - 370 CTD-116mm 140 BU

149 7m Right 28 - 385 CTD-149mm - HBU

270 3m Left 29 - 380 V, CTD-30mm - HBU

347 4m Right 30 - 380 CTD-30mm 260

446 2m Left 31 - 375 V, CTD-65mm 145 V

517 3m Right 32 - 375CTD-30mm 125

34 Threshold 60 4m Right 34 185 315 NR

Notes:[1] All thicknesses rounded to the nearest 5mm.HBM Denotes Hydraulic Bound MaterialCTD, Denotes Crack Top Downand depthBU, HBU Denotes Broken Upand Highly Broken UprespectivelyDL-20mm Denotes Delaminated and depthV Denotes VoidingNR Denotes Not Recovered

2.5 Dynamic Cone Penetrometer Testing

A Dynamic Cone Penetration (DCP) survey was performed at each core location, after

extraction of the bound layers, to enable assessment of the underlying foundation and todetermine (where possible) the granular layer thickness. The exception to this was Core 34 onthe 34 threshold, which was omitted due to time restrictions between aircraft movements.

The penetration depth was targeted to achieve approximately 1m below the base of the boundlayer. Full penetration (considered as penetration deeper than 800mm below the base of thebound layer) was achieved at 11 of the 33 locations. Partial penetrations can be due to thepresence of large sized aggregate and/or a particularly strong granular material and/or upperfoundation, it does not definitively indicate a high CBR value for the subgrade.

The DCP penetration rate was correlated with the California Bearing Ratio (CBR) using therelationship detailed in IAN 73/06 (2009)1to provide a CBR profile with depth.

The DCP results generally show a reasonable subgrade CBR with values ranging from 7% togreater than 20%. Where the penetration depth was sufficient, a relatively stiff upper layer ofbetween 200mm and 400mm thick can be identified. However, at three locations (Core 15, 18and 33) the upper layer is weaker than the underlying foundation layers.

The DCP median CBR results for the upper and lower foundation layers are summarized inTable 5. The DCP profiles of interpreted CBR with depth through the unbound foundationlayers presented in Appendix C.

As no cores were taken from Taxiway B4, no DCP tests were possible.

1IAN 73/06 Interim Advice Note,Design Guidance for Road Pavement Foundations (Draft HD25), Highways Agency, February 2009.


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TABLE 5: SUMMARY OF DCP DATA



CoreNumber

Depth ofPenetrationBelow BoundBase (mm)[1]

InterpretedUpperFoundationThickness(mm)[1]

Median CBR (%)

Upper Fdn. Lower Fdn.

Runway10/28

15 3m Right 1 495 50 47 100

303 3m Left 2 1045 75 90 41->100

603 9m Right 3 380 275 55 >100

903 15m Left 4 250 145 13 >100

1215 3m Right 5 1070 195 88 24-85

1503 3m Left 6 330 335 100 -

1749 15m Right 7 250 50 70 >100

2085 9m Left 8 920 105 36 14-83

2385 3m Right 9 265 165 8 100

2553 3m Left 10 910 70 42 20->100

E1 62 3m Left 11 190 90 62 100

86.5 3m Right 12 165 165 100 -

E2 52 3m Left 13 945 270 95 7-30

161 3m Left 14 960 220 65 16-31

E3 80 5m Right 15 940 455 11 36

175 4m Left 16 130 130 100 -

E4 30 3m Right 17 175 175 100 -

100 4m Left 18 1030 315 19 14-39

150 4m Right 33 1035 185 13 20-75

E5 50 3m Right 19 210 70 40 >100

125 3m Left 20 625 170 39 70->100

E6 50 5m Right 21 640 365 100 >100

150 6m Left 22 225 95 26 >100

267 6m Right 23 860 55 95 70

E7 100 3m Left 24 405 405 100 -

167 2.5m Right 25 360 165 19 >100


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TABLE 5: SUMMARY OF DCP DATA



CoreNumber

Depth ofPenetrationBelow BoundBase (mm)[1]

InterpretedUpperFoundationThickness(mm)[1]

Median CBR (%)

Upper Fdn. Lower Fdn.

B7 25 4m Right 26 360 95 52 >100

96 2.5m Left 27 210 105 56 >100

149 7m Right 28 395 90 70 >100

270 3m Left 29 225 110 51 >100

347 4m Right 30 915 120 22 28->100

446 2m Left 31 230 85 95 >100

517 3m Right 32 220 45 45 >100

Notes:Fdn. Denotes Foundation[1] Thicknesses rounded to the nearest 5mm.

2.6 Ground Penetrating Radar

A Ground Penetrating Radar (GPR) survey was undertaken by URS on the 34 Threshold andE1 areas within the 16/34 runway strip. This was due to the operational need to keep Runway16/34 active during the surveys, resulting in a severely limited access window between aircraftmovements in which to extract cores. The GPR survey provided continuous profiles across thepavement which enabled the layer thickness variation and possible construction changes to be

mapped.A 900MHz ground coupled GPR antenna, mounted to a hand cart was utilised to collect thedata. The GPR survey was performed on the HWD test offsets with additional transverseprofiles taken across the area.

The GPR survey of the 34 Threshold extended from the south edge of Runway 16/34, past theCAT II Hold Bar (the limit of the current evaluation) to the CAT III Hold Bar. This was to enablecalibration of the GPR data by tying into core locations from a previous survey undertaken onRunway 16/34 in 2013. Core 34 from the current survey was also used for the GPR datacalibration.

The GPR profiles of the 34 Threshold indicate a relatively consistent pavement, generallywithin normal construction tolerances, with no major construction changes within the asphaltand PQC layers. A slight reduction in asphalt thickness is noted from approximately 150m,which corresponds to the end of the Porous Asphalt overlay. A greater variation exists in thethickness of the underlying LC layer, possibly indicating some deterioration at the base.

The GPR survey of Taxiway E1 extended from the edge of the 34 Threshold to the beginningof the concrete surface at the CAT II Hold Bar. The GPR profiles of Taxiway E1 indicate areasonably consistent fully flexible pavement from Chainage 0m to approximately Chainage72m. There is then a transition zone, of approximately 25m, where the pavement is flexiblecomposite with 200mm Asphalt over 300mm PQC over 200mm LC. Beyond this the pavementbecomes rigid and the GPR survey was ended.

The GPR construction profiles are presented in Appendix D.


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3 LABORATORY TESTING

3.1 General

A programme of laboratory testing was undertaken by URS on selected specimens of therecovered core samples to determine the material characteristics.

The laboratory test results are presented in Appendix E and summarised below.

3.2 Indirect Tensile Stiffness Modulus

Indirect Tensile Stiffness Modulus (ITSM) testing was undertaken by URS on the asphaltmaterial, in accordance with BS EN 12697-26:20042, at three temperatures (10oC, 20oC &30oC) using the Nottingham Asphalt Tester (NAT). The results of which were used to supportthe HWD back-analysed stiffness moduli and provide information on the temperaturesusceptibility of the materials.

A total of 10 intact samples from seven cores taken from Taxiways E1, E3, E4 and the 34Threshold were selected based on providing an overview of the asphalt materials present inthe pavements. No samples were selected from the PFC surfacing of Runway 10/28 becausehis layer is not deemed to be structural and also the sample is likely to have been too thin totest after preparation.

It should be noted that aged material may yield higher ITSM values due to binder hardeningand be more susceptible to fatigue cracking. Typical asphalt stiffness values for Hot RolledAsphalt (HRA) are 1750-4500MPa (for 100-50 pen, aged material), with a larger range forAsphalt Concrete (AC) of 1750-10000MPa at the UK design temperature of 20oC.

All samples are deemed to be AC as against HRA, determined by visual identification andhistorical information. AC includes Marshall Asphalt (MA).

Of the 10 samples tested 7 samples were found to have an ITSM stiffness at 20oC lower thanexpected for typical aged asphalt material. One of these samples, Core 33 Layer 2 fromTaxiway E4, had a significantly weaker 20oC ITSM stiffness of less than 1000MPa.

Stiffness values far in excess of the upper limit of the typical range suggests a material that issubject to significant binder hardening and consequently susceptible to fatigue cracking. Noneof the samples had an ITSM stiffness at 20oC higher than expected.

The ITSM stiffness values presented at a temperature of 20oC may be factored up by x1.0 tox1.5 for comparison with the back-analysed stiffness moduli to account for the differentconfinement and loading rates employed by the two methods, i.e. NAT and HWD.

In addition, 3 samples were indicated as having a degree of increased susceptibility to changein temperature, indicated by a large range in stiffness between the different temperatures.

The ITSM laboratory test results are summarised in Table 6.

2BS EN 12697-26:2012 Bituminous mixtures, Test methods for hot mix asphalt, Stiffness, BSI, August 2004.


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TABLE 6: INDIRECT TENSILE STIFFNESS MODULUS


Offsetfrom

Centreline(m)

CoreNumber

Layer Material[1]

BulkDensity

(kg/m3)

ITSM (MPa)

10oC 20oC 30oC

E1 62 3m Left 11 2[2} [3] AC 2390 3160 1010 410

3[3] AC 2413 3510 1480 600

E3 80 5m Right 15 2 AC 2356 2770 1850 650

175 4m Left 16 1[2] AC 2164 9120 2760 2660

E4 30 3m Right 17 1 AC 2296 3530 2650 2460

2[3] AC 2373 3720 1410 520

100 4m Left 18 1[2]

[3]

AC 2313 4910 1460 700

150 4m Right 33 2[3] AC 2307 770 510 360

34 Threshold 60 4m Right 34 2[3] AC 2210 2020 1270 880

3[3] AC 2310 2490 1370 870

Notes:ITSM Denotes Indirect Tensile Stiffness Modulus.AC Denotes Asphalt Concrete and includes Marshall Asphalt[1] Material type determined by visual identification and historical information[2] Denotes asphalt material which may be unduly susceptible to changes in temperature.[3] Denotes a stiffness value (at 20oC) outside the typical range expected for aged asphalt material.

3.3 Compressive StrengthThe compressive strength testing of the PQC materials was determined by URS inaccordance with BS EN 12504-13and BS EN 12390-14, 35and 76. A total of 25 intact samples(from 25 cores) were tested to provide a good overview of all the PQC strengths.

The aggregate type for all PQC materials has been identified as crushed rock. A number oflow compressive strength results (less than 35N/mm2) were obtained. The estimated in-situcube strengths of the PQC materials is:

1960 concrete material (E3 & E4) ranges from 21.5N/mm2to 57.0N/mm2with anaverage of 39.9/mm2

1964 concrete material (34 Threshold) is 26.0N/mm

2

1989 concrete material (Runway 10/28, B7, E2, E5, E7) ranges from 24.0N/mm2to

69.0N/mm2with an average of 43.2N/mm2

1996 concrete material (E6) ranges from 36.0N/mm2to 63.05N/mm2with an averageof 46.2N/mm2.

3BS EN 12504-1:2009 Testing concrete in structures, Cored specimens, Taking, examining and testing in compression, BSI,September 2009.4BS EN 12390-1:2000 Testing hardened concrete, Shape, dimensions and other requirements for specimens and moulds, BSI, March2000.5BS EN 12390-3:2009 Testing hardened concrete, Compressive strength of test specimens, BSI, May 2009.6BS EN 12390-7:2009 Testing hardened concrete, Density of hardened concrete, BSI, May 2009.


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The compressive strength results are summarised inTable 7.

TABLE 7: COMPRESSIVE STRENGTH TESTING


OffsetfromCentreline(m)

CoreNumber

Layer BulkDensity(kg/m

3)

Comp.Strength(N/mm

2)

Est. in-situ CubeStrength(N/mm

2)[1]

Age

Runway10/28

15 3m Right 1 2 2360 25.7 25.5 1989

303 3m Left 2 2 2400 42.5 42.0 1989

603 9m Right 3 2 2370 32.4 32.0 1989

903 15m Left 4 2 2400 64.6 64.5 1989

1215 3m Right 5 2 2370 39.5 39.0 1989

1749 15m Right 7 2 2410 35.9 35.5 1989

2085 9m Left 8 2 2390 49.8 49.0 1989

2385 3m Right 9 2 2410 39.8 39.5 1989

2553 3m Left 10 2 2410 40.3 40.5 1989

Echo 1 105.5 3m Right 12 1 2410 46.3 46.0 -

Echo 2 52 3m Left 13 1 2430 51.3 51.5 1989

161 3m Left 14 1 2400 42.8 43.5 1989

Echo 3 80 5m Right 15 3 2450 42.7 42.5 1960

175 4m Left 16 3 2480 21.6 21.5 1960

Echo 4 30 3m Right 17 4 2550 47.6 49.0 1960

100 4m Left 18 2 2450 26.6 26.5 1960

150 4m Right 33 2430 56.4 57.0 1960

Echo 5 50 3m Right 19 1 2380 30.8 31.0 1989

125 3m Left 20 1 2340 35.1 35.0 1989

Echo 6 50 5m Right 21 1 2380 36.1 36.0 1996

150 6m Left 22 1 2400 62.3 63.0 1996

267 6m Right 23 1 2390 39.9 39.5 1996

Echo 7 100 3m Left 24 1 2340 35.2 35.0 1989

167 2.5m Right 25 1 2380 35.5 36.0 1989


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TABLE 7: COMPRESSIVE STRENGTH TESTING


Offsetfrom

Centreline(m)

CoreNumber

Layer BulkDensity

(kg/m3)

Comp.Strength

(N/mm2)

Est. in-situ Cube

Strength(N/mm

2)[1]

Age

Bravo 7 25 4m Right 26 1 2430 68.7 69.0 1989

96 2.5m Left 27 1 2410 37.0 37.5 1989

149 7m Right 28 1 2360 34.1 33.5 1989

270 3m Left 29 1 2440 67.9 68.0 1989

347 4m Right 30 1 2420 24.1 24.0 1989

446 2m Left 31 1 2430 50.2 49.5 1989

517 3m Right 32 1 2420 65.3 65.5 1989

34 Threshold 60 4m Right 34 4 2430 26.1 26.0 1964

Notes:Comp. Denotes CompressiveUn. Denotes unknown age[1] Based on an additional calculation in BS 1881-120 (superseded)

3.4 Petrographic Analysis

Petrographic analysis was undertaken, by RSK Environment Ltd on behalf of URS, todetermine the presence of Alkali-Silica Reaction (ASR). Alkalisilica reaction (ASR) is themost common form of alkaliaggregate reaction. It occurs when the alkaline pore fluid andsiliceous minerals in some aggregates react to form a calcium alkali-silicate gel. This gelabsorbs water, producing a volume expansion which can disrupt the concrete. For damage tooccur, all three components (alkali, silica and water) must be present.

The main external evidence for damage to concrete due to alkalisilica reaction is cracking.Another indicator of ASR is that the cracks are filled with a white/brown/grey deposit which isthe alkali-silicate gel. In unrestrained concrete the cracks have a characteristic randomdistribution often referred to as map cracking where there is a network of fine cracks boundedby a few larger cracks. This form of cracking can result in a loss of strength and make thepavement more susceptible to frost attack, which increases the risk of Foreign Object Debris(FOD).

The pattern of map cracking evident on Taxiway B7, shown in Photograph 1 taken near core27, is an indication of the presence of ASR. White/brown deposits were also noted

occasionally at the longitudinal cracks.


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Photograph 1 Suspected ASR Cracking

Five concrete samples were selected for petrographic analysis. This included one sample fromeach of Runway 10/28, Taxiway E2 and E7, and two samples from Taxiway B7.

The analysis indicates that all samples appeared to be well mixed and exhibited goodcompaction. The voiding was generally estimated to range from 0.5% to 1.5%, with theexception of Core 6 where it was estimated to be 3%. Common rounded air voids (


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TABLE 8: PETROGRAPHIC SUMMARY


CoreNumber

Defect ASR SecondaryEttringite

Runway 10/28 1503 6 None None None

E2 161 14 Longitudinal crack Rare Common

E7 167 25 Longitudinal crack Common Common

B7 96 27 Map cracking Common Common

B7 446 31 Longitudinal crack Sporadic Sporadic

Notes:ASR Denotes Alkali-silica reaction

Rare Defined as only found by thorough searchingSporadic Defined as only occasionally observed during normal examinationCommon Defined as easily observed during normal examination


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4 HWD DATA ANALYSIS

4.1 Interpretation of HWD Data

The HWD testing was performed using a 450mm diameter loading plate and geophoneslocated at standardised pre-determined radial distances of 0.0m, 0.3m, 0.6m, 0.9m, 1.35m,1.8m and 2.25m, respectively, from the centre of the applied load.

Due to variations in the pavement response, the contact pressure applied by the HWD variesslightly from test to test. In order to compare test points for this survey, the data wasnormalised to the target contact pressure of 1.5MPa. The seven normalised deflectionreadings are tabulated in Appendix F. The key deflection parameters, which are used in theback-analysis in order to calculate the pavement layer stiffness performance are described inTable 9.

TABLE 9: SUMMARY OF KEY DEFLECTION PARAMETERS FOR BACK-ANALYSIS

HWD Deflection Parameter Performance Indicator

Central Deflection (d1) Overall pavement response (All pavements)

Deflection Difference (d1-d2) Response of PQC layer in rigid pavements (Runway 10/28, B7, E1Rigid, E2,E5, E6, E7)

Response of asphalt layer in flexible composite pavements (E3, E4)

Deflection Difference (d2-d4) Response of LC layer of rigid pavements (Runway 10/28, B7, E1Rigid, E2,E5, E6, E7)

Response of PQC layer of flexible composite pavements (E3, E4)

Deflection Difference (d3-d4) Response of the LC layer in flexible composite pavements (E3)Deflection Difference (d1-d4) Response of the asphalt in fully flexible pavements (E1Flex)

Response of all bound layers in the flexible composite and rigid pavements

Outer Deflection (d6) Foundation response

Profiles of the key deflection parameters have been plotted against chainage and are shown inAppendix G. In general, higher deflections indicate poorer performance and/or thinnerpavement layers, with peaks indicating distressed areas or cracks. A study of the deflectionprofiles enables the relative condition of the foundation and pavement layers to be assessedqualitatively.

The deflection profiles appear to indicate that the bound layers in particular (indicated by d1-d2,d2-d4,d1-d4,and d3-d4) have the greatest influence on the overall pavement performance for allpavements. This is shown by the bound layer deflection parameters mirroring the overallpavement response parameter (d1) more closely than the foundation response (d6). However,there are isolated areas and peaks were the foundation does have a greater influence.

On Runway 10/28 high deflection peaks are noted in the 10 Threshold area across all of thesurvey offsets. The foundation appears to be more variable in this area. Occasional highpeaks are also noted on the 9m and 3m offsets between chainage 800m to 2000m. Thesepeaks appear to coincide with areas of weaker foundation and also with asphalt repairs asshown in DAAs drawing DA13-1117-C002, provided with the tender brief.


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The rigid taxiways appear to be reasonably consistent and exhibit fairly low deflections. Theflexible composite taxiways exhibit higher, and a slightly more variable level of deflection.There is a particularly high isolated peak on Taxiway E3 at chainage 120m on the 3m Rightoffset.

4.2 Characteristic Sections

The pavements were divided alphabetically into Characteristic Sections A to I based on:

Structure type, e.g. flexible, rigid or composite;

Average material layer thicknesses; and

Pavement response to HWD loading based on the deflection profiles; typically theoverall pavement deflection response indicated by d1(where HWD testing wasperformed).

The Characteristic Sections identified are detailed in Table 10, together with their extents, andthe average interpreted layer thickness used for the back-analysis procedure. They are alsopresented on a plan of the airside pavements in Figure 2.

TABLE 10: CHARACTERISTIC SECTIONS

CharacteristicSection

Location Chainage

(m)


(m)

Average Interpreted LayerThickness

[1]& Type

From To AS PQC LC

A Runway 10/28 0 2600 All 30 [2] 380 170

B 34 Threshold 0 140 All 185 315 170

C B7 0 585 All - 375 135

D E1 0 95 All 520

E E1 95 190 All - 340 140

F1 E2 0 175 All - 380 170

F2 E5 0 150 All - 380 170

F3 E6 0 290 All - 380 170

F4 E7 0 225 All - 380 170

G E3 0 220 All 85 320 100

H E4 0 50 All 285 365 -

I E4 50 190 All 85 300 -

J B4 0 119 All 520 - 550

Notes:AS Denotes AsphaltPQC Denotes Pavement Quality ConcreteLC Denotes Lean Concrete[1] All thickness rounded to the nearest 5mm[2] PFC considered a non-structural layer and has been ignored in the back-analysis process


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The construction of Taxiway B4 is understood to be 500mm Asphalt over 500mm to 600mmLC. For the back-analysis, the thickness of LC has been taken as 550mm.

A summary of the 50th(median level) and 85th(i.e. only 15% of the deflections were found to

be higher) percentile deflection parameters for each section are shown in Table 11.

TABLE 11: NORMALISED DEFLECTION PARAMETERS


Location DeflectionPercentile

Normalised Deflection Parameters (mmx10-3)[1]

Overall Asphalt PQC LC Fdn.

A Runway 10/28 85th 228 - 28 45 93

50th 177 - 21 35 69

B 34 Threshold 85th 361 217 22 23 87

50th 304 139 14 18 65

C B7 85th 247 - 30 51 106

50th 198 - 21 40 82

D E1

(ch:0-95m)

85th 475 292 - - 76

50th 413 254 - - 62

E E1

(ch:95-160m)

85th 248 - 24 48 116

50th 232 - 21 45 109

F1 E2 85th 240 - 25 47 116

50th 216 - 20 37 93

F2 E5 85th 200 - 35 41 70

50th 167 - 22 37 59

F3 E6 85th 240 - 32 48 103

50th 189 - 21 36 73

F4 E7 85th 246 - 33 48 95

50th 191 - 21 40 74

G E3 85th 346 86 49 46 105

50th 252 50 20 24 85

H E4

(ch:0-50m)

85th 264 131 65 - 55

50th 179 88 24 - 44

I E4

(ch:50-190m)

85th 302 87 73 - 92

50th 253 47 53 - 73

J B4 85th 272 175 - 38 67

50th 204 113 - 25 35

Note:[1] HWD deflections have been normalised to a contact stress of 1.5MPa


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4.3 Back-Analysis of HWD Data

4.3.1 General

All the points obtained from HWD testing, except those tests at joint or crack locations(summarized in Section 4.4), were included in a detailed back-analysis procedure to determinethe effective stiffness of the pavement layers. The analytical method used is outlined inAppendix A.

DMG27 gives guidance and limitations on the complexity of the pavement structure foranalysis. This includes modelling all asphalt layers as one combined layer, having a maximumof four layers including the foundation layer and a minimum layer thickness of 75mm.

As such the PFC overlay on Runway 10/28 does not meet the minimum thickness for analysis.In addition, PFC surfacing is not considered to provide a significant structural contribution.Therefore the PFC overlay has been ignored in the analysis and calculations.

A two layer pavement structure was used to analyse the fully flexible section of E1; comprisingthe asphalt as layer 1 and foundation as layer 2.

A three layer pavement structure was used to analyse Runway 10/28, the rigid section ofTaxiway E1, E2, E5, E6, and E7; comprising the PQC as layer 1, the LC as layer 2 and thefoundation as layer 3. A three layer pavement structure was also used to analyse Taxiway E4;comprising asphalt as layer 1, PQC as layer 2 and the foundation as layer 3.

A four layer pavement structure was used to analyse the 34 Threshold and Taxiway E3;comprising the asphalt as layer 1, the PQC layer 2, the LC as layer 3 and the foundation aslayer 4.

The HWD data back-analysis software Elmod 68was used to derive the pavement layerstiffnesses for each test location based on the pavement layer thicknesses detailed in Table10. The method of back-analysis was Linear Elastic Theory which treats the foundation as alinear material, as required by DMG27.

4.3.2 Back-analysed Material Stiffness

The back-analysed stiffness results are presented in Appendix H in the form of correlationsbetween the effective layer stiffnesses obtained from the back-analysis and the appropriatedeflection parameter for each Characteristic Section. A summary of the 50thand 15thpercentile stiffnesses, corresponding to the 50thand 85thpercentile deflection levels of theappropriate deflection indicator respectively, is presented in Table 12 for each CharacteristicSection. Taxiways E2, E5, E6 and E7 have a single correlation as they have the sameconstruction thickness.

The stiffness of asphalt material is highly sensitive to temperature with the stiffness reducingas the asphalt warms up and increasing when the asphalt cools down. As such it is commonpractice to adjust the back-analysed asphalt stiffnesses to a reference or design temperatureto allow comparison. In the UK the reference temperature is normally taken as 20oC and it isconsidered that this reference temperature is also appropriate for Ireland. The stiffnesses forthe asphalt material corrected to the reference temperature are show in parenthesis in Table12.

8Elmod 6, Evaluation of Layer Moduli and Overlay Design, Dynatest


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TABLE 12: BACK-ANALYSED STIFFNESSES: 50TH

AND 15TH

PERCENTILE


Location DeflectionPercentile

Correlated Back-Analysed Layer Stiffnesses (MPa)[2]

Asphalt PQC LC Fdn.

A Runway 10/28 15th - 18700 3200 400

50th - 25600 5900 >500

B 34 Threshold 15th 1000 (1000) 19400 8200 280

50th 1600 (1600) 32200 11500 420

C B7 15th - 18700 6900 190

50th - 27000 10700 260

D E1

(ch:0-95m)

15th 3100 (2800) - - 250

50th 3600 (3200) - - 310

E E1

(ch:95-190m)

15th - 28700 9500 180

50th - 33200 10800 190

F1 E2 15th - 21300 6300 160

50th - 27300 11500 210

F2 E5 15th - 14800 8700 310

50th - 24600 11400 390

F3 E6 15th

- 16300 5700 180

50th - 26000 12300 290

F4 E7 15th - 15900 5900 210

50th - 25200 9200 290

G E3 15th 1800 (1500) 10700 5200 210

50th 3600 (2900) 28900 13300 300

H E4

(ch:0-50m)

15th 2200 (1800) >40000 - 120

50th 3400 (2900) >40000 - 170

I E4

(ch:50-190m)

15th 1600 (1300) 24800 - 230

50th 3400 (2900) 38900 - 330

J B4 15th 2000 (1800) 7000 350

50th 3300 (3000) 37000 >500

Notes:Fdn. Foundation[1] All thickness rounded to the nearest 5mm[2] HBM and asphalt stiffness values rounded to 100MPa or 10MPa if under 1000MPa; foundation stiffness

values rounded to10MPa.[3] Asphalt material stiffness is shown at site temperature along with the stiffness adjusted to the reference

temperature of 20oC in parentheses.


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In most cases good correlations were obtained for all layers, albeit with some degree ofvariation in the LC layer of all pavements.

On Characteristic Section D (comprising the fully flexible section of Taxiway E1) there are a

few points in the foundation layer which exhibit a higher than average stiffness and are setapart from the remaining points. These points are all located adjacent to the white line edge ofthe 34 Threshold and it is therefore likely that the actual structure at this location is that of the34 Threshold, i.e. asphalt over PQC. The correlation removes the effects of these points fromthe overall stiffness result for Characteristic Section E.

No correlation was possible for the PQC (layer 2) of Characteristic Section H (Taxiway E4chainage 0m to 50m). Only four test points were undertaken in this small area and the PQCstiffness were all greater than 40,000MPa.

4.4 Transverse Joint/Crack Testing

In order to assess the condition of the concrete joints, HWD testing was also carried out

across selected transverse joint locations.In the case of Runway 10/28 the joint locations were selected to coincide, where possible, withthe previous survey. These joint locations are now reflective joints in the PFC overlay, laidafter the previous survey. The PFC conceals a number of joint locations; particularly on the 9moffset which is not generally loaded by aircraft. A likely joint location that could not be locatedwith certainty was not tested. It should also be noted that the reflective crack may not alwaysbe directly above the concrete joint, but can be slightly offset and this would affect the result.

Regular random joint locations were chosen for the rigid taxiways. In addition, on the asphaltoverlaid taxiways a number of suspected reflective cracks were also chosen.

The Load Transfer Efficiency (LTE) and Slab Rotation were calculated to provide anassessment of the joints and cracks. This testing is performed using two additional geophones(d8and d9) located at radial distances -0.3m and -0.4m, respectively, behind the centre of theloading plate.

The LTE assesses the ability of the concrete slab to transfer the load between adjacent slabs.The ability of a concrete pavement to transfer the load depends on a number of factors,whether dowel bars are present, if an alternative interlocking method such as an Omegajointhas been used and the thickness of the slab. The ambient temperature also affects the LTE asthe concrete slab expands in warm temperatures, closing the joint and giving a greateraggregate and/or frictional interlock. Generally this type of testing should be performed when itis cold to give the worst case scenario, an upper limit of 15oC is suggested by DMRBHD29/079. Due to the relatively good weather at the time, testing below 15oC was not alwayspossible. However, the temperatures were not significantly above this suggested limit.

DMG 27 Table 27 gives guidance on acceptable LTE for undowelled PQC joints. An LTE thatis 250mm with poor loadtransfer on a strong base. However, the construction history indicates the transverse joints aredowelled and this is supported by relatively high LTE results. As such alternative guidance istaken from DRMB HD30/9910, which suggests that a LTE


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The Slab Rotation gives an indication of the support at the slab edge. A negative value of SlabRotation is indicative of poor slab support. Both LTE and Slab Rotation are explained ingreater detail in Appendix A.

The key deflection performance indicators used to calculate LTE and Slab Rotation aresummarised in Table 13.

TABLE 13: SUMMARY OF PERFORMANCE INDICATORS FOR JOINTS / CRACKS

HWD Deflection Parameter Joint Performance Indicator

Deflection difference (d8-d9) Indicators of Joint/Crack Load Transfer

Deflection ratio (d9/d8)

Slab Rotation Indicator of Slab Edge Support

The results of the transverse joint/crack tests analysis are tabulated in Appendix I, showingeach of the performance indicators against chainage. Test locations where the LTE is


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The results for Runway 10/28 have been split into symmetrical offsets. It can clearly be seenthat the joints along the 15m offsets, which are generally unloaded, are performing better thanthe 9m and 3m offsets. The 3m offsets, which generally take the most loading, are performingthe poorest.

The joint tests for the taxiways have not been separated into offsets due to the limited amountof tests. However, they also generally follow the trend where the performance of the innerloaded offsets is worse than the outer non-loaded offsets.

The LTE results are generally good with the average for all pavements greater than 75%, witha small number of isolated locations exhibiting poor LTE. The Slab Rotation is more variablewith the averages of Taxiways E1, E2, E5, E6 and E7 being negative indicating there hasbeen a loss of slab support at the edges.

4.5 Discussion of Results

Reference is made to DMG27 Ed. 3 published by Defence Estates, which relates back-

analysed material stiffness to material condition, as summarised in Table 15. The percentilevalues that are commonly compared for design purposes are the 15 thpercentile of asphaltmaterial corrected to the reference temperature of 20oC; the 50thpercentile of LC materials;and the 15thpercentile of the foundation.

TABLE 15: TYPICAL BACK-ANALYSED STIFFNESS VALUES (DMG27)

Condition Stiffness (MPa) at 20oC

Pavement QualityConcrete (PQC)

Dry LeanConcrete (DLC)

Asphalt Foundation

Excellent >30000 >15000 >7000 >200

Good 20000 to 30000 8000 to 15000 4000 to 7000 100 to 200

Average 10000 to 20000 3000 to 8000 1000 to 4000 -

Poor


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The majority of the ITSM stiffnesses at 20oC are low suggesting the possibility of microcracking within the asphalt matrix. This is not particularly surprising considering some of theasphalt materials are understood to have been laid 25 years ago, with some lower layersnearly 50 years old. Of particular note is the second asphalt layer of Core 33, from Taxiway

E4, which has an extremely low ITSM value of 510MPa at 20oC.

4.5.2 Pavement Quality Concrete

The 50thpercentile back-analysed stiffness of all the PQC materials can be considered asGood, with some Characteristic Sections even considered as Excellent. However, a low 15thpercentile value is noted for the PQC of Characteristic Section G (Taxiway E3) indicating thatthis older pavement (originally a parallel taxiway to the disused runway) is more variable.

A degree of variation is noted between the 50thand 15thpercentile back-analysed stiffness,indicating deterioration. This is likely to be due to trafficking. In the pavements constructed in1989, as part of the Runway 10/28 development; this deterioration may also be due to theonset of ASR and the formation of Secondary Ettringite.

The compressive strength results are considerably more variable with some very low valuesobtained. Four out of 25 samples tested had a compressive strength less than 30N/mm2. Thenet effect will be to bring the average compressive strength down and result in a relatively lowflexural strength, which is an important characteristic when determining the ability of a rigidpavement to withstand future trafficking.

The map cracking evident on Taxiway B7 has been identified as ASR related. ASR is alsoidentified at some longitudinal crack locations which also exhibit white/brown deposits fillingthe cracks. Some of the longitudinal cracks on Taxiway E2 and the eastern end of Taxiway B7do not exhibit white/brown deposits in-filling the cracks. The petrographic analysis indicatesthat the ASR is less apparent and less advanced in these slabs.

The formation of Secondary Ettringite has been identified in the majority of cores wherepetrographic analysis was undertaken. It is unclear, and there is some debate in the industry,as to whether the Secondary Ettringite is the cause of the cracking, or rather it has been ableto develop due to the cracking and ingress of water enabling leeching.

No information is available as to when the longitudinal cracking started to appear. It is possiblethat it may have started as early life shrinkage cracks. These have then developed through theonset of Secondary Ettringite and sometimes ASR. However, if they have developed morerecently they may be the initial onset of structural cracking. Being top down cracks and oflimited depth, as recorded in Table 4, the former explanation is more likely.

4.5.3 Lean Concrete

The 50thpercentile back-analysed stiffness of the LC material for all but one Characteristic

Section can be considered as Good. Characteristic Section A, comprising Runway 10/28, hasa lower 50thpercentile back-analysed stiffness and is considered to be of Averagecondition.

The disintegrated LC layer observed in Cores 28 and 29 of Taxiway B7 is not apparent in theback-analysed stiffness results. A detailed review of the analysis indicates that there are fourHWD test locations in the vicinity of Cores 28 and 29 where the LC back-analysed stiffness isbelow 5000MPa and low compared to other locations. However, the LC layer stiffness at thesefour locations is still greater than 3000MPa and therefore is still considered to be of Averagecondition and would not justify downgrading to granular material in accordance with DMG27.

The variation between the 50thand 15thpercentile back-analysed stiffness, indicating somedeterioration, can be expected due to the initial dry shrinkage and the thermal shrinkageduring its in-service life.


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With the absence of cores, there is a degree of uncertainty as to the actual pavement structureof B4. The 50th percentile back-analysed stiffness of the second layer, presumed LC, is highwhich may indicate a PQC material. However, the 15th percentile back-analysed stiffness ofthis layer is very low for a PQC layer with any integrity. It would therefore be prudent to

assume that the future performance will be more akin to a LC layer.

4.5.4 Foundation

The 15thpercentile back-analysed stiffness of the foundation material is considered to beGoodoverall, with a number of Characteristic Sections considered Excellent. NoCharacteristic Sections are considered to have a Poorfoundation.

The back-analysed stiffness is a measure of the overall foundation performance,encompassing weak/strong sub-layers. This includes any granular fill or subbase type materialthat may be present. The DCP, where penetration is possible, provides CBR profiles withdepth and can highlight weaker layers within the pavement structure.

A number of locations failed to penetrate to a depth which would enable reasonableassessment of the foundation, possibly due to large aggregate or a stiff foundation. Wheresignificant penetration was achieved, the foundation generally has a minimum CBR of 7% to15%. The back-analysed stiffnesses support the overall CBR and are in general a reasonablematch.


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5 TRAFFIC DATA

5.1 General

In order to determine if the existing pavements are suitable for the anticipated future life, it isnecessary to estimate the volume of traffic they will be required to take over the future designlife.

DAA supplied the historical aircraft data from 2000 to 2014. The data was interrogated by URSto determine the historical percentages of traffic departing from each runway end; and thepercentage of arriving traffic using the runway exits E2 to E7.

DAA also supplied the traffic forecasts for 2015 to 2019 inclusive and for 2024, based on atypical busy dayfor each year. The traffic for the busy dayfor years 2020 to 2023 were basedon interpolation between 2019 and 2024. A 2% increase, advised by DAA, was applied to allaircraft from 2024 onwards to provide a suitable 20 year design period.

It is normal practice to consider the number of departing aircraft only in the calculation, with allaircraft assumed to be at Maximum Take-Off Weight (MTOW). Arriving aircraft are consideredto be taken into account by the fact that not all departing aircraft will be at MTOW, and theyare therefore generally discounted from the calculation. This is appropriate for Runway 10/28,B7, E1 and the 34 Threshold; however it may not be appropriate for the runway exits (E2, E3,E4, E5, E6 and E7) which are unlikely to take departing aircraft of any significant weight.

As such, for the runway exits only the arriving aircraft have been considered at 80% of theMTOW. The value of 80% is based on previous advice from BAA (British Airport Authority)Pavement and Infrastructure Team. The Aircraft Classification Number (ACN) for each aircrafthas been calculated using linear interpolation between the MTOW and Operating EmptyWeight (OEW).

The aircraft mix was condensed by removing the smaller aircraft which would have little or noimpact on pavement performance and life. The aircraft data is taken from various sourcesincluding DMG27 and Transport Canadas Aircraft Loading Tables12.

The design aircraft has been taken as the Boeing B777-300ER. This is due it having both asignificant number of movements and a high Aircraft Classification Number (ACN), andtherefore a high damaging effect compared to the other aircraft using Dublin Airport. TheB777-300ER has a MTOW of 348,000kg and a Tridem gear layout. The design life has beentaken as 20 years, which is typical for asphalt pavements.

Table 16 details the aircraft mix along with the details of each aircraft.

12Aircraft Loading Tables, Aircraft Classification Numbers, Technical Program, Transport Canada, 2004


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TABLE 16: AIRCRAFT MIX

Aircraft MTOW(kg)

Load onMain

Gears(%)

MainGear

Type

ACN Details

Rigid Pavement k MN/m3

Flexible Pavement CBR%

High150

Med80

Low40

UltraLow20

High15

Med10

Low6

UltraLow3

A300 F4-600 172000 47.3 DT 49.2 58.9 69.2 78.3 48.1 54.3 66.3 83.7

A310-300 157000 47.3 DT 45.9 55.1 65 73.9 45.5 51.2 62.6 79.7

A319 76000 45.8 Dual 44.3 46.8 49.1 51.0 38.8 40.6 44.6 50.5

A320 77000 46.6 Dual 46.2 48.8 51.2 53.2 40.5 42.4 46.8 52.6

A321 94000 47.5 Dual 56.5 59.4 62.1 64.3 49.4 52 57.6 63.2

A330-200 233000 47.8 DT 53.7 62.4 74.3 86.9 58.5 63.5 73.8 99.8

A330-300 213000 47.6 DT 54 62.6 74.3 86.7 58.2 63.3 73.4 99.3

A350-900 268000 46.8 DT 64 71 83 96 66 70 80 110

A380-800 560000 19 DT 56.3 65.9 78.2 94.6 58.4 63.7 75.3 105.5

B737-300 64000 45.8 Dual 38.5 40.4 42.3 43.8 33.2 35 39 43.1

B737-400 69000 46.9 Dual 42.1 44.4 46.5 48.2 37 39.1 43.9 47.8

B737-700 78000 45.8 Dual 41.6 43.9 46 47.7 36.2 38 42.2 47.2

B737-800 80000 46.8 Dual 49.3 51.8 54.2 56.1 42.9 45.4 50.4 55.3

B757-200 109000 45.6 DT 30.7 36.8 43.4 49.3 29.7 33 40.5 53.0

B767-200 176000 45.5 DT 43.6 52.2 62.3 71.7 45 49.8 60.1 80.5

B767-300ER 186000 46.1 DT 48.2 57.5 68.3 78.2 48.8 54 65.9 86.8

B777-300ER 348000 46.2 Tridem 65.8 85.3 109.3 131.5 63.6 71.1 89.1 120.1

B787-800 228000 45.64 DT 61 71 84 96 60 66 81 106

Notes:ACN Denotes Aircraft Classification NumberMed. Denotes MediumDT Denotes Dual Tandem gear layoutBold The design aircraft is shown in bold


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5.2 Mixed Traffic Analysis

A mixed traffic analysis was undertaken in accordance with DMG27 to determine the numberof coveragesof the design aircraft. DMG27 definescoverages as the number of times a

particular point on the pavement is expected to receive a maximum stress as a result of agiven number of aircraft passes. The number of anticipated movements of each aircraft typeover the design life is calculated, based on forecast data. Then each aircraft is converted to anequivalent number of coveragesof the specific design aircraft to give the total number ofcoveragesof the design aircraft over the design life. This is done by considering variousfactors including the weight, gear layout, damaging effect of each aircraft, pavement type andsubgrade condition.

Table 17 details the equivalent number of coveragesof the design aircraft for each pavement.

TABLE 17: NUMBER OF COVERAGES OF THE DESIGN AIRCRAFT

Location Percentage of TotalNumber of Movements

Comment EquivalentCoverages

Runway 10/28 93% All departures on Runway 10/28 29211

34 Threshold(ch:0m to 60m)

69% All departures on Runway 28 andRunway 34

21673

34 Threshold

(ch:60m to 140m)2% All departures on Runway 34


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5.3 Past Traffic Analysis

DAA provided the historical data of all traffic arriving and departing on all runways for theperiod from 2000 to the present day. This data was analysed, using the mixed traffic analysis

procedure, to identify the volume of departing traffic the runway pavements have carried since2000.

The original design aircraft and frequency (i.e. coverages) that Runway 10/28 was designed toaccommodate were unavailable. However, three aircraft scenarios have been considered as acomparison. The A330-200/300 which came into service with Aer Lingus in 1994; the B737-800 which came into service in 1998 and currently accounts for the vast majority of aircraftmovements at Dublin; and the B777-300ER which is considered, due to its weight and relativedamaging effect, as the design aircraft going forward in this report.

Table 18 presents the amount of historical coverages departing from each runway end.

TABLE 18: PAST TRAFFIC (2000 TO 2014)

Design Aircraft Equivalent Coverages

Runway 10 Runway 28 Runway 34

B737-800 177,711 408,127 4,421

A330-200/300 32,897 79,934 1,032

B777-300ER 1,250 2,930 34

Noting that Runway 10/28 was constructed in 1989, and the PFC is not considered a structurallayer, the period 2000 to 2014 represents 60% of the time that Runway 10/28 has beenoperational. It would be incorrect to assume the actual number of equivalent coverages is 40%higher than indicated in Table 18, due to introduction of heavier aircraft and their increasedfrequency during its lifetime. However, it would be reasonable to assume the actual equivalentcoverages is certainly in the region of 25% higher over the total life of Runway 10/28

Although the number of coverages that Runway 10/28 was designed to take is unavailable, itis reasonable to deduce from the above table that the structural design capacity has beenexhausted or is approaching exhaustion.


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6 PCN CALCULATION AND PAVEMENT LIFE

6.1 General

The ACN/PCN method of designating airfield pavements was originally developed in 1981 byICAO13. The name "ACN/PCN" is derived from the classification of aircraft according to theirAircraft Classification Number (ACN), and pavements according to their PavementClassification Number (PCN).

It should be noted that the ACN/PCN system is a method of reporting the relative strength of apavement in order to evaluate airfield operations. It is not intended to be used for pavementdesign.

6.2 ACN/PCN Method

The ACN is a function that expresses the relative severity of loading on a pavement whensupported by a subgrade of particular strength. The ACNs are reported separately for: rigid

and flexible pavements, for four standard categories of subgrade (representing ranges ofsubgrade strength and characterised by a standard value at the middle of the range),Maximum Take Off Weight (MTOW) and representative Operating Empty Weight (OEW).

The corresponding PCN is the value of ACN which applies an unrestricted loading to thepavement of equal severity to the maximum allowed for a pavement to survive a design life.Generally, to allow for unrestricted movements (or load applications of aircraft) a pavementshould have a greater or equal PCN to the corresponding ACN of the aircraft.

The PCN number is reported as a five-part code as follows:

PCN/a/b/c/d where:

PCN = the highest permitted ACN for unrestricted usea = the type of pavement: R=rigid, F=flexibleb = the subgrade categoryc = the maximum tyre pressure allowed:

W = high, no limitX = medium, limited to 1.5 MPaY = low, limited to 1.0 MPaZ = very low, limited to 0.5 MPa

d = pavement design or evaluation methodT = technicalU = by experience of in-service aircraft.

The pavement subgrade categories are:

A = HighB = MediumC = LowD = Ultra Low.

The ranges of subgrade strength covered by these categories are shown in Table 19.

13International Civil Aviation Organisation (ICAO), Aerodrome Design Manual, 1981.


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TABLE 19: ACN/PCN SUBGRADE CATEGORIES

Subgrade

Category

Pavement

Type

Characteristic

Subgrade Strength

Range of

Subgrade Strengths

A

High

Rigid k=150 MN/m3 All k values above 120 MN/m3

Flexible CBR 15% All CBR values above 13%

B

Medium

Rigid k=80 MN/m3 k=60-120 MN/m3

Flexible CBR 10% CBR 8-13%

C

Low

Rigid k=40 MN/m3 k=25-60 MN/m3

Flexible CBR 6% CBR 4-8%

D

Ultra Low

Rigid k=20 MN/m3 All k values below 25 MN/m3

Flexible CBR 3% All CBR values below 4%

Note:k Modulus of Subgrade Reaction

6.3 Characteristic Subgrade

The CBR values have been converted into an appropriate Modulus of Subgrade Reaction (k-value) in accordance with DMG27, which provides an empircal relationship between CBR andthe k-value. It should be noted that a CBR of 10% does not convert directly to a k-value of80MN/m3. A characteristic subgrade strength for each pavement was selected based on theinterpreted DCP test data supported with the back-analysed foundation stiffnesses. These areshown in Table 20.

TABLE 20: SUBGRADE CATEGORY


Location PavementType

k-value(MN/m

3)

CBR (%) SubgradeCategory

A Runway 10/28 Rigid 80 - B

B1 34 Threshold

(ch:0m to 60m)

Rigid 80 - B

B2 34 Threshold

(ch:60m to 140m)

Rigid 80 - B

C B7 Rigid 60 - B

D E1 (ch:0-95m) Flexible - 10 B

E E1 (ch:96-190m) Rigid 60 - B

F1 E2 Rigid 60 - B

F2 E5 Rigid 60 B

F3 E6 Rigid 60 - B

F4 E7 Rigid 60 - B

G E3 Rigid 50 - C

H E4 (ch:0-50m) Rigid 60 - B

I E4 (ch:50-365m) Rigid 80 - B

J B4 Flexible - 10 B


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TABLE 21: PCN OF CHARACTERISTIC SECTIONS


Location ACN of DesignAircraft at

Subgradecategory

B777-300ER

PCN

DMG27 COMFAA Code

A Runway 10/28 85.3 72.6 71.2 /R/B/W/T

B1 34 Threshold 85.3 98.6 79.1 /R/B/W/T

B2 34 Threshold 85.3 105.0 >120 /R/B/W/T

C B7 97.3 79.0 80.5 /R/B/W/T

D E1 (ch:0-95m) 71.1 51.8 78.3 /F/B/X/T

E E1 (ch:96-190m) 97.3 81.4 81.2 /R/B/W/T

F1 E2 72.1 82.0 81.7 /R/B/W/TF2 E5 72.1 81.6 61.4 /R/B/W/T

F3 E6 72.1 75.9 68.4 /R/B/W/T

F4 E7 72.1 82.0 114.1 /R/B/W/T

G E3 72.1 63.0 36.8 /R/C/X/T

H E4 (ch:0-50m) 50.5 118.0 >120 /F/B/X/T

I E4 (ch:50-365m) 72.1 51.0 72.2 /R/B/X/T

J B4 [1] 71.1 >120 >120 /F/B/X/TNote:Bold Indicates an insufficient PCN

[1] Pavement construction details provided by DAA

6.5 Pavement Life and Overlay Requirements

The theoretical pavement lives and overlay requirements have been calculated in accordancewith DMG27 and the FAA software FAARFIELD16.

As discussed, DMG27 utilises the mixed traffic analysis and the equivalent coveragesof thedesign aircraft. The theoretical overlay is calculated by assessing the pavement structuredeficiency using the design charts within DMG27 for the specific ACN.

The FAAs FAARFIELD software, which accompanies AC150/5320-6E17, utilises multi-layeredelastic theory to analytically calculate the remaining life and overlay requirement for the total

traffic mix. It should be noted that COMFAA, used for the calculation of the PCN, andFAARFIELD, used for the calculation of theoretical life and overlay, are different methods andcan produce different results. It is possible that a pavement which is determined to havesufficient PCN by COMFAA may require an overlay in FAARFIELD. When results are different,the FAARFIELD results should be taken as the over-riding condition.

FAARFIELD appears unable to analyse a pavement structure which comprises PQC layerresting directly on the foundation, i.e. with an absence of a LC layer, with a number of error

16FAARFIELD, FAA Rigid Flexible Iterative Elastic Layered Design, v1.302, Airport Technology R&D Team, Federal AviationAdministration, 201017Advisory Circular 150/5320-6E, Airport Pavement Design and Evaluation, Federal Aviation Administration, 2009


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messages encountered during the analysis and unrealistic results obtained. In order tocircumvent this part of the PQC layer was converted to a LC layer.

The theoretical overlays are presented in Table 22. It should be noted that they are the

minimum thickness of asphalt overlay required in order to achieve the required PCN. They donot take into account any additional factors such as a minimum thickness requirement in orderdelay reflective cracking or a minimum constructible layer thickness.

TABLE 22: THEORETICAL OVERLAY AND REMAINING LIFE


Location RequiredPCN

DMG27 FAARFIELD

Theoretical Overlay

Marshall Asphalt

(mm)

TheoreticalOverlay

P-401 / P-403 HMA

(mm)

ResidualLifewithoutOverlay

(years)

A Runway 10/28 85.3 95 100 5.5

B1 34 threshold 85.3 - 40 6.0

B2 34 threshold 85.3 - - >20

C B7 97.3 120 155 10

D E1 (ch:0-95m) 71.1 105 - >20

E E1 (ch:96-190m) 97.3 80 160 20

F2 E5 72.1 - -[1] >20

F3 E6 72.1 - -[1] >20

F4 E7 72.1 - - >20

G E3 72.1 75 110 20

I E4 (ch:50-365m) 72.1 80 100 [1] 20Note:[1] COMFAA and FAARFIELD results mismatch

Estimate of Residual Life is based on the structural condition only. It does take into accountthe functional condition of the PFC.

6.6 Pavement Overloading

The current PCN for Runway 10/28, as published by the Irish Aviation Authority18, is70/R/B/W/T. The ACN of the design aircraft (B777-300ER) is 85.3 for a Category B subgrade(k-value of 80MN/m3) for unrestricted use.

The term unrestricted useis not specifically defined and is a design parameter which is left toairport operators to decide what is acceptable. Airfield pavements are unlikely to fail suddenly,unless they are subject to extreme overloading. Regular aircraft movements by aircraft with an

18Aeronautical Information Publication, Dublin International Airport, Irish Aviation Authority, 2014


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ACN greater than the actual PCN will have an adverse effect on the pavement by reducing thepavement life, result in earlier maintenance costs and increased whole life costs.

DMG27 guidance indicates that a 10% difference in ACN over PCN is generally considered

acceptable; providing the pavement is not showing signs of structural distress and theoverload operations do not exceed 5% of the annual departures of aircraft with an ACN closeto the PCN.

A 10% to 25% overload operation would justify regular inspections of a competent engineer,and should stop as soon as distress is apparent. DMG27 design models have indicated that a5% frequency of overload operations of between 10% to 25% (ACN over PCN) can reduce thepavement life by 25% to 75%.

A fully laden B777-300ER represents an overload operation of approximately 15%, based onthe ACN of 85.3 for a Subgrade Category B. If you consider only the aircraft within the trafficmix that have and ACN that is within 10% of the calculated PCN, which excludes the highfrequency B737/A321 type aircraft, the number of historical B777-300ER departures is over

5% frequency.This would indicate that the Runway 10/28 is currently being overloaded by a significantamount.


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7 TREATMENT RECOMMENDATIONS

7.1 General

Characteristic Sections A, C, D, E, G and I (comprising Runway 10/28 and Taxiways B7, E1,E3, part of E4 respectively), do not have sufficient PCN for the anticipated traffic over thedesign life and will require structural strengthening in accordance with DMG27.

Additionally, while not specifically identified as having a deficient PCN, structural treatment isalso recommended for Characteristic Sections F1, F3 and F4 (comprising Taxiways E2, E6and E7, respectively). This is due to the presence ASR and Secondary Ettringite as indicatedby the petrographic results; the presence of longitudinal cracking; and the need to delayfurther deterioration in the existing pavement structure.

The presence of ASR and Secondary Ettringite is likely to be an issue if it continues toprogress. The current PQC top-down crack depths are identified in Table 4. It is likely to

result in expansion of the slabs which will disrupt the asphalt overlay and shorten life of theoverlay. The only risk-free way to avoid this is to replace the slabs affected by ASR andSecondary Ettringite. However, this may problematic and have significant cost implications ifRunway 10/28 needs to be active during the day and rehabilitation works are to be undertakenduring night closures only.

Both ASR and Secondary Ettringite require the presence of silica, alkali and water to react andprogress. The silica and alkali are present in the matrix of the PQC and cannot be removed orreduced, without the aforementioned slab replacement. We therefore need to prevent theingress of water, and this should stop or at least slow any further progression of the ASR andSecondary Ettringite.

The treatment options have been considered in accordance with DMG27 and DMG3319. Whena jointed concrete pavement has been overlaid with asphalt material, reflective cracks willpropagate through the asphalt from the underlying joints. The rate of crack initiation andtherefore crack propagation through asphalt depends on vertical and horizontal movements atthe slab edges due to traffic loading and thermal expansion, respectively. To delay theappearance of reflective cracking DMG33 recommends a minimum thickness of MarshallAsphalt overlay.

In addition to the minimum overlay recommendations, DMG33 details other ways to addressreflective cracking including prior Crack and Seat treatment of the PQC. Crack and Seatinginvolves breaking the slab into smaller sections, effectively downgrading the PQC to LC,creating more joint locations which results in a smaller overall strain in the asphalt at each jointlocation. Crack and Seat treatment is beneficial if excessive vertical or horizontal movementsare expected. The transverse PQC joints are dowelled, with very good load transfer indicatedat the vast majority of locations. Therefore Crack and Seat treatment is not recommended inthis instance.

7.2 Material Options

The structural strengthening should be with asphalt material. Asphalt material has theadvantages of being quicker to construct and open to traffic, and is easier to repair and re-profile.

19Design & Maintenance Guide 33, Reflection Cracking on Airfield Pavements A Design Guide for Assessment, Treatment Selectionand Future Minimisation, Defence Estates, July 2005


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7.2.1 Marshall Asphalt

In order to delay the propagation of reflective cracks over a medium term (8 to 11 years), bywhich time up to 15% reflective cracking is to be expected, DMG33 recommends a minimum

of 150mm Marshall Asphalt (MA) overlay. In order to delay reflective

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Dublin Airport Runway 10/28 Evaluation

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