SuperPave Considerations Roy D. McQueen, P.E. Roy D. McQueen & Associates, Ltd For presentation at 2010 FAA Hershey Conference

Overview Review EB 59A Background on Issues Research Results AAPTP ERDC FAA Requirements to Complete Specification

1 st Eastern Region Airports Conference

Engineering Brief 59A ITEM P ‑ 401 PLANT MIX BITUMINOUS PAVEMENTS (SUPERPAVE  )

References in EB 59A TAI Superpave Mix Design, Superpave Series No. 2 (SP ‑ 2) TAI Performance Graded Asphalt, Binder Specification and Testing, Superpave Series No. 1 (SP-1) Interim Item P ‑ 401 Plant Mix Bituminous Pavements (SUPERPAVE  )

Policy: Modification to Standards Gross aircraft weights <100,000 pounds: approval at Regional Office Gross aircraft weights > 100,000 pounds: approval by AAS-100

What’s the Big Differences Between FAA’s SuperPave & Marshall? The Compactor! Volumetrics measured the same Compaction (bulk sp.g.) measured the same Mix design & acceptance criteria are slightly different It’s still aggregate, sand, binder and air!

Binder Grade Selection and Grade Bumping Based on Gross Aircraft Weight* Determine binder requirements from the LTTP Bind software using 98 percent reliability with no traffic or speed adjustments. Increase the high temperature grade by the number of grade equivalents indicated (1 grade is equivalent to 6 degrees C) below. Use the low temperature grade as determined from LTTP Bind. (see NOTES) Aircraft Gross WeightHigh Temperature Adjustment to Binder Grade All Pavement Types weight < 12, < weight < 100,000 1 weight > 100,000 2 NOTE: PG grades above a –22 on the low end (e.g. 64–16) are not recommended. Limited experience has shown an increase in block cracking with -16 or -10 grade asphalts. *Same requirement for Marshall Mix Also AAPTP 04-02

AAPTP Study Binder Selection The base high-temperature PG grade should be determined using LTPPBind 3.1, for a surface layer (depth of layer surface = 0 mm), using a reliability of 98 %. The EHEs for both taxiways and runways are calculated using: EHEs = 10.4  (design tire pressure in lb/in 2 / 120) 2  annual departures. The high-temperature PG grade is then determined using LTPPBind 3.1, using the calculated value for EHEs as the design traffic level. For runways:LTPPBind 3.1 (“fast” traffic condition). For taxiways without stacking, speed adjustment for “slow” traffic For taxiways with some stacking, the high-temperature PG grade should be increased by 6  C; for taxiways with frequent stacking, the grade should be increased by 12  C. The high-temperature PG grade may be reduced one level (6  C) for lifts which are entirely 75 mm or more below the pavement surface. No additional grade reductions should be made.

PG+ Criteria for Polymer Modified Asphalts Rule of “90” “Gray” for sum ~90, e.g., PG Elastic Recovery (60% to 75%) typical for this region to ensure polymers at proper % Criteria varies by state

Primary SuperPave Mix Design Criteria > 60,000 lbs. 85 Gyrations 4% VTM VMA: 13% - 14% VFA: 65% to 78% Dust to asphalt ratio Coarse & Fine FAA > 45 < 60,000 lbs. 60 Gyrations 4% VTM VMA: 13% - 14% VFA: 65% to 78% Dust to asphalt ratio Coarse & Fine FAA > 42 A coarse gradation is defined as a gradation passing below the restricted zone. The restricted zone is defined in the Asphalt Insitute’s Manual Superpave, SP-2.

Gradation Requirements Runways – same as current P-401 Taxiways  Control Points  Restricted Zone ?

Off Maximum Density Line – Higher VMA

Primary SuperPave Acceptance Criteria > 60,000 lbs. 2.5% < VTM < 85 gyrations Compaction L = 92.5% G mm < 60,000 lbs. 2.5% < VTM < 60 gyrations Compaction L = 92.5% G mm

BACKGROUND ON ISSUES

FAA Standards for production and placement of hot mix asphalt (HMA) pavements have been in place for more than 50 years. So, why change?  Because we have to. No one supporting Marshall.  Modifications to both Federal and State Highway standard requirements have led to the SuperPave Design process and the use of the Gyratory Compactor

Major Issues Associated With Adopting SuperPave Required number of gyrations for mix design Volumetrics – appropriate level of VMA and VTM Gradation Requirements Field Compaction Standard

Establishing Design Gyrations Need to establish N design for the gyratory compactor Performance equivalent to well performing Marshall mixes Validation testing on a variety of mixes

Stated Differently: Make sure the new stuff works as good as the old!

Average PCI at Civil Airports Source: Report DOT/FAA/AR

Overview of FAA P blow Marshall for heavy duty Design VTM: 2.8% - 4.2%, 3.5% typical VMA typically 1% higher than EB 59A TSR for moisture susceptibility (75% - 80% min) Compaction function of lab Marshall density PWL acceptance:  Density: 90% above 96.3% 98% average  Air voids: 90% between 2% and 5%  Limits based on actual construction data

Density Limit Derivation 10 PD 90 PWL L 98% L = 98% (1.3%) = 96.3% Zs

Air Voids L=2%U=5% 3.5% D L = 2% + (1.28x0.65%) = 2.8%D U = 5% - (1.28x0.65%) = 4.2% Zs 2.8%4.2% 0.7%

Primary Differences Between P-401 Marshall and P-401 Superpave P-401 Marshall*  90% > 96.3% Marshall  Avg.~ 98% lab density  50 or 75 blows  2.8% - 4.2% design VTM  2% to 5% acceptance  1% higher VMA  Volumetric + Strength test P-401 Superpave**  90% > 92.5% MTD  Avg.~ 94.5% MTD  60 or 85 Ndes  4% design VTM  2.5% to 5.5% acceptance  1% lower VTM  Strictly volumetric * Limits are based on construction Data ** Limits not Based on construction Data

Major Issue: N design AAPTP Study ERDC Study FAA Study

SUMMARY of AAPTP STUDY

AAPTP Study Approach for Ndes: Compare In-place Density to Orig Ndes Compare with Marshall for Equivalent Performance Performance Tests Mixes: Included Southwest, West Coast Mixes Not all well-performing – some poor Several Military mixes Performance Test: Flow # Did not use P-401 volumetrics

Estimated Ndesign Values Based upon Performance Testing Airfield Gross Wt. Tire (lbs) p (psi) Ndesign Jacqueline Cochran Regional Airport 20,000 10, Mineral County Memorial Airport 12,500 6, Oxford-Henderson Airport 30,000 15, Little Rock Air Force Base 155,000 38, Naval Air Station Oceana* 66,000 33, Volk Field 42,500 21, Jackson International Airport 890,000 55, Newark Liberty International Airport 873,000 54, Palm Springs International Airport 800,000 52, N/A Spokane International Airport 400, , N/A N/A – Insufficient Data to Estimate Appropriate Ndesign Value * Evaluated mix rutted in the field. Performance tests inconclusive for civil airport mixes.

N equiv Results 75-blow Comparisons  Range: 32 to 59  Avg. = 49, STD = blow Comparisons  Range: 25 to 40  Avg. = 36, STD = 11 Volumetric criteria different from P-401: VMA 1% lower & VTM 1/2% higher

N design Values Based Upon Research Tire Pressure, psi Ndesign Less than to More than Recommended N design Values for Designing Airfield Mixes Tire Pressure, psi Ndesign Less than to More than No robust “Phase 2” type validation study EB 59A N-des may be problematic To what extent did volumetrics influence results No variability analysis

SUMMARY of ERDC STUDY

ERDC Study Approach Similar to FAA Study, i.e. Ndes from Comparative Marshalls Mixes Developed from P-401 Specification Requirements, i.e., Well Performing Mixes Not Considered 75-blow Marshall, only P-401 Volumetrics, i.e. VMA & 3.5% VTM

Variables Mineralogy: Limestone, Granite, Gravel Aggregate Size: ½, ¾, 1 inch Max Gradation: Coarse & Fine Sides of P-401 Band Sand: 10% Nat’l & 100% Crushed Binder: PG & PG Nequiv Range: 25 to 125

Analyses of Variability Sand:  N=75 (all crushed) vs. N=59 (10% natural)  p<0.001, significantly different Aggregate Type:  Gravel: N=50  Granite: N=84  Limestone: N=69  p<0.001, significantly different

ANOVA Type Analyses (2) Aggregate Size:  ½ inch: N=72  ¾ inch: N=66  1 inch: N=80  p=0.051, not significantly different Gradation:  Fine: N=80  Coarse: N=69  p=0.047, significantly (?) different Polymer vs. neat binders not significantly different

Conclusions Variability too cumbersome to warrant multiple compaction levels N design based on arithmetic average of 69 with a recommended value of gyrations % VTM EB 59A N equiv criterion may be problematic Validation study scheduled for

SUMMARY of FAA STUDY

Objectives Establish guidance for N-design Establish specifications for designing HMA using SGC that provides performance equivalent to Marshall mixes Verify on a range of mixes More comprehensive than other studies

Critical Issues Primary issue will be N-design levels consistent with 75 Marshall blows Effect on stability & flow SGC could also result in subtle changes in aggregate gradation to meet volumetrics Volumetric and compaction Issues for spec development

Research Program to Establish N-equiv Phase 1:  Determine N-equiv  Equivalent to 75-blow Marshall Phase 2:  Validate N-equiv  Performance Tests for N-equiv

Phase 1 Subtasks - completed Identify Mixtures and Binders Verify Mix Designs Perform 1 st and 2 nd Replicates of Gyratory Compaction & Volumetrics – 2 labs Perform Mixture Variation Experiment Compile, Analyze and Summarize Data

Mix Variables (1) All well-performing mixes Various mineralogy  Gneiss  Dolomite  Granite  Gravel  Basalt  Argillite  Diabase

Mix Variables (2) Nominal Maximum Aggregate Size  12.5 mm  19.0 mm  25.0 mm Varying natural sand content (0%, 7.5%, 15%) Binders  Neat asphalt  Polymers: Elastomeric (SBS) and Plastomeric (Novophalt)

Mix Designs Mix NameAirport Aggregate TypeNMAS Binder Grade* JFK/1993JKFGneiss12.5 mmAC 20 JFK/1997JFKDolomite19 mmPG JFK/1996JFKDolomite/granite25 mmPG Atlantic CityACYBasalt19 mmPG LexingtonLEXLimestone19 mmPG ElmiraELMCrushed gravel19 mmPG NAPTF---Argillite12.5 mmPG CharlottesvilleCHODiabase19 mmPG * Phase I limited to PG 76-22

Determining N-equivalent

Plot of Results with +/- 2s error bars

N-equivalent Results Average: 62 Minimum: 34 Maximum: 99 Standard deviation: 16 Like other studies – range is large

Phase 2: Performance Evaluation What is affect of asphalt content and/or gradation changes on rut resistance? What is affect on compactibility? What is affect on durability?

Experiment Design Test at N equiv and N des Rut resistance  AMPT / flow number  APA Compactibiltiy from compaction curve Durability from ASTM D 4867 (modified Lottman) Results due June 2010

FAA High Tire Pressure Study

Background Aircraft wheel loads and tire pressures are increasing:  L ~ 65,000 lbs.  P > 240 psi Reported pavement failures in hot climates overseas Have we reached “the end” with HMA?

Study Objectives Evaluate the rutting performance of asphalt mixes at the extreme boundary of operation with respect to tire pressure, wheel load, temperature and (low) speed.

Study Elements Full scale testing at NAPTF heated pavements Laboratory tests with different binders and different temperatures:  Binder: DSR, viscosity, other.  HMA: MSCR, Indirect Tensile (IDT), Dartmouth accelerated pavement tester, NCHRP protocols, other.  Under development Combine with SuperPave to improve HMA performance and N des = f (p)

Preliminary Conclusions

EB 59A N-equiv appears to be problematic EB 59A AAPTP ERDC FAA How to handle variations in N-equiv? % natural Sand Aggregate Type: Mineralogy or Angularity?  Other Considerations Volumetrics Compaction Standard

Other Considerations - Volumetrics Effect of 1% lower VMA and ½% higher air voids with Superpave:  1.5% lower % AC by volume (~ 0.7% by wt.)  Effect of potentially lower %AC on durability

Why is VMA Important? V a & VMA Related and V a is a pay item! Low VMA mixes are sensitive to minor variations in asphalt content Low VMA mixes can become tender Low VMA mixes may not allow for sufficient film thickness to ensure durability

Other Considerations - Compaction Effect of using %MTD in lieu of % lab for compaction control:  Example 1: 6% in-place air voids 4% laboratory air voids, V a 98% field compaction  Example 2: 6% in-place air voids 2% laboratory air voids, V a 96% field compaction

LESSONS Need to carefully establish N design to provide equivalent performance Be careful with changing volumetric criteria Dry mix – low durability Under-compacted – prone to rutting Combination = Disaster

Ultimate Objective of All Studies New P-401 specification (while Carl Steinhauer and I are still alive)

Questions?