Sustainable Materials and Design for Alaskan Pavements

Transcription

1 Sustainable Materials and Design for Alaskan Pavements Jenny Liu, Ph.D., P.E. University of Alaska Fairbanks November 18, 2016 UAA Professional Development Seminar Outline Background Sustainable materials Warm mix asphalt (WMA) Recycled asphalt pavement (RAP) Paving interlayers Materials characterization for pavement design Asphalt concrete (AC) Asphalt treated base (ATB) Granular base Conclusions 2 1

2 Background Paving industry are constantly seeking sustainability: Improve pavement performance, increase construction efficiency, conserve resources and advance environmental stewardship Innovations are continuously being developed Unique engineering challenges in Alaska - extreme climatic conditions and unavailability of quality materials locally in some rural areas Material properties are limited for mechanisticempirical pavement design 3 Warm Mix Asphalt (WMA) WMA demonstration in Petersburg, Alaska Sasobit was added to reduce the mixing and paving temperatures Paved ~ 8 miles of road and a new ferry terminal parking lot Placed in a single 3 lift 311 F 230 F Sasobit WMA additive 4 2

3 One year later 3

4 Characterization of WMA Binders and Mixtures 3 different Sasobit contents (0.8%, 1.5%, and 3% by weight of binder PG 58-28) Binder characterization Viscosity (RV), binder performance grade (DSR, BBR, DTT), low temperature performance (BBR, DTT, ABCD) Mixture characterization Dynamic modulus, rutting performance (flow number and APA), low temperature performance (IDT creep stiffness and tensile strength), moisture susceptibility (TSR ratio) 7 Binder Testing Results 8 4

5 AMPT and Rutting Flow number and microstrain 9 Asphalt Pavement Analyzer and Rutting 10 5

6 Moisture Sensitivity 11 Low Temperature Performance Stress and Strength (MPa) 10 9 Control_Stress Control_Strength 0.8S_Stress 0.8S_Strength 8 1.5S_Stress 1.5S_Strength 7 3.0S_Stress 3.0S_Strength Temperature ( o C) 12 6

7 WMA - Summary Engineering benefits over conventional HMA Reduced mixing and compaction temperatures Improved workability and rutting resistance Insignificant effect on moisture susceptibility Insignificant effect on resistance to low temperature cracking A decrease of tensile strength for WMA mixtures at low temperatures Cracking temperatures of WMA mixtures increased with the increase of Sasobit content. However, the increase was very slight 13 Recycled Asphalt Pavement (RAP) Economic and environmental benefits of using RAP have been acknowledged and high RAP content is promoted In Alaska, 15% RAP is allowed in the wearing course, up to 25% RAP in the binder or base course. Engineering properties of RAP mixtures are lacking. 14 7

8 Materials and Performance Tests Materials Materials collected in two ADOT regions (Central and Northern), up to 35% RAP by weight, two mix types (Type II-A and Type II-B), three asphalt binders (PG 52-28, PG and PG 52-40) Performance tests Mix dynamic modulus values at different temperatures, used in pavement design/analysis procedures ( E* ) Rutting performance at intermediate and high temperatures (flow number) Low-temperature thermal cracking performance (IDT creep stiffness and strength) 15 Dynamic Modulus (le*l) Master Curves Central Region Northern Region 16 8

9 Flow Number Central Region Northern Region 17 IDT Strength Results Northern Region Central Region 18 9

10 Low Temperature Performance 0 0 Cracking Temperature ( C) Central Region Cracking Temperature ( C) Northern Region Preliminary Cost Analysis 20 10

11 RAP - Summary Incorporation of RAP increased dynamic modulus and flow number of HMA, indicating the addition of RAP may improve the rut-resistance of HMA in Alaska IDT strength results did not follow a general trend when temperature varied Adding certain amounts of RAP may not affect the low temperature performance of some mixes A rough estimate of $13.3/ton savings can be reached if a 25% RAP is used 21 Paving Interlayers Multiple benefits of using paving interlayers in AC overlays have been recognized: waterproofing control against infiltration of free surface water into base and subgrade retarding of reflection of existing cracks and distresses How it functions in Alaska and which interlayer type works best are unknown PGM-G50/50 Bi-axial, two-yarn PGM-G100/100 Bi-axial, three-yarn PGM-G 4 Multi-axial 22 11

12 Shear Test 23 Permeability Test Maximum acceptable permeability, cm/s ASTM PS

13 Pavement Structural Analysis AKFPD - Alaska Flexible Pavement Design 25 FEM Simulation G50/50 (bi-axial) Model configuration G 4 (multi-axial) Meshed model 26 13

14 FEM Simulation Results G50/50 (bi-axial) G 4 (multi-axial) Distribution of tensile stress 27 FEM Simulation Results 28 14

15 Field Evaluation 29 Field Evaluation Results Section Control (area 4) G 4 (areas 2 & 3) Transverse crack (#) Longitudinal crack, NB (ft) Longitudinal crack, SB (ft) Previous medium-major 7 minor 0 13 minor New 2 4 minor 4 medium-major 0 Total 11 minor 304 medium-major 13 minor Previous 8 minor 63 minor 14 minor New 2 minor 14 minor 0 Total 10 minor 77 minor 14 minor 0 Previous 1 major 78 minor 60 minor G50/50 (area 9) G100/100 (area 10) New minor Total 1 major 78 minor 80 minor Previous 1 major 0 0 New Total 1 major Previous Data collected in May 2015; 2 New Data collected in June

16 Paving Interlayer - Summary Laboratory investigation confirmed the benefits of adding a paving interlayer Pavement structural analysis showed fatigue resistance of reinforced was higher than control G100/100 reinforced showed the highest fatigue resistance, G 4 ranked 2 nd FEM analysis revealed G 4 reinforced had more effective stress distribution and less maximum tensile strain than G50/50 reinforced All interlayer-reinforced test sections showed better pavement performance than the control 31 Alaskan Materials for Pavement Design Asphalt concrete (AC) Granular base Asphalt treated base (ATB) Hot asphalt treated Emulsion treated Foamed asphalt treated RAP treated base (50%:50% blend) Current AKFPD Default values available only to three seasons Only one binder content is considered for ATB Data required for emerging materials and technologies 32 16

17 Limitations of AKFPD Design Guide Table 5.1: Pavement Layer Moduli (ksi) Summer Material Type P 200 Spring & Fall Winter Asphalt Concrete Aggregate Base < 6% Select A < 6% Select B < 10% Select C & Subgrade < 30% Stabilized Base Course Moduli (ksi) Summer Material Spring & Fall Winter RAP (50:50) (1) CAB, 3% Emulsion (1) CAB, 4% Asphalt (2) (1): lightly-bound: use Ullidtz (2): heavily-bound: use TAI 33 Characterization of Alaska Materials AC dynamic modulus ( E* ) Materials collected from 21 projects across Alaska All three ADOT regions covered Granular base resilient modulus (M R ) Fines content ( 3.15% - 12%) Temperature (-10ºC 20ºC) Moisture content (OMC±2%) Freezing temperature gradient (low high) ATB M R Three binder contents for each ATB M R test conducted at three temperatures 34 17

18 Characterizing E* Using AMPT 35 Characterizing M R Using Triaxial Test Setup 36 18

19 Direct Measurement of AC E* 37 AC E* Prediction - Original Witczak Model 38 19

20 AC E* Prediction - Modified Witczak Model 39 Predicted vs. measured E* for all mixes (original Witczak model, Level 3) Predicted vs. measured E* (modified Witczak model, Level 3) 40 20

21 M R Modeling for Granular Base M R k2 k3 oct 1 a 1 pa pa kp Free water uptake was allowed during freezing k * f * W * W * f c s s c k * f * W * W * f c s s c k * f * W * W * f c s s c No water intake occurs during freezing k * f 1.111* W 0.197* W * f c s s c k * f 0.966* W 0.118* W * f c s s c k * f 1.551* W 0.233* W * f c s s c f c = fines content (%), W s = moisture content (%) 41 Predicted vs. Measured M R Open system Close system 42 21

22 M R of ATBs HATB, R 2 = EATB, R 2 = Measured at 20 o C, representing summer. 43 M R of ATBs FATB, R 2 = RAP, R 2 =

23 Conclusions A number of sustainable materials (WMA, RAP, paving interlayers) have been used in Alaskan pavements A number of engineering benefits of Sasobit-modified WMAs were identified over conventional HMA RAP mix improved rutting resistance, and adding certain amounts of RAP may not affect the low temperature performance of some Alaskan mixes Improved performance were confirmed by adding paving interlayers, and the multi-axial paving interlayer had more effective stress distribution than traditional bi-axial interlayer 45 Conclusions Typical Alaska paving materials have been characterized to provide inputs for mechanistic-empirical pavement design Explore more emerging materials and technologies (different WMA techniques, higher RAP contents, and more paving interlayer types, etc.) Build up long-term performance data and evaluate potential environmental impacts Life cycle cost assessment 46 23