Incorporating Recycling into Pavement Design Where does it Fit?

Transcription

1 Incorporating Recycling into Pavement Design Where does it Fit? AEMA-ARRA-ISSA-PPRA Fall Meeting Niagara Falls, Ontario October 13-15, 2015 David Hein, P. Eng., Principal Engineer Vice-President, Transportation

2 Recycling History New Construction 50s/60s/70s Very little recycling done Aging infrastructure, desire to reduce cost and development of new equipment and oil crisis of the 70s led to focus on recycling methods Initial focus on recycling of asphalt and concrete Desire to reuse for the same products 2

3 Hot Recycling Methods In Plant Cold Gran In Place Cold in place Full depth reclamation 3

4 Basic Types of Recycling Use of wastes and by-products Polymers, ground rubber, baghouse fines, slags, bottom/boiler ash, fly ash, foundry sand, cement and lime kiln dust, mineral processing waste, RAP, RAS, glass, etc. Plant based recycling (milled or crushed RAP) Hot in-place recycling Cold in-place recycling (emulsions and RAP) Full depth reclamation (may be stabilized as well, chemicals, cement, emulsion, foamed asphalt) 4

5 Recycling Goals for Pavement Design Select the most appropriate treatment for the roadway Provide maximum value/benefit from the recycled product Minimize impact to construction operations and traffic Achieve similar or better performance than virgin materials Reduce energy footprint and GHG emissions Conserve conventional materials Reduce life-cycle costs 5

6 Key Considerations Condition of the existing pavement Service life expectations Need for strengthening Thickness and variability of the existing asphalt Width of the roadway and widening expectations Grade restrictions Traffic both during construction and future Time of year Urban/rural Utilities 6

7 Many Pavement Design Methods 7

8 Early Pavement Design Experience based designs Macadam and Telfford from the U.K. Angular aggregate over a well compacted subgrade 75 mm (6 in) subbase generally 200/300 mm (8-12 in) 25 mm (1 in) surface to provide a smooth ride Move to sheet asphalt and bitulithic pavements in early

9 Early Pavement Design Macadam Telford 9

10 Early Pavement Design Asphalt Institute California procedure based on CBR U.S Corps of Engineers for Airports Significant advancements in 1940s 10

11 Early Pioneers Westergaard (stresses due to rolling loads) Terzaghi ( father of soil mechanics) Casagrande (soil mechanics and foundations) O. James Porter (CBR test procedure) Frederick Field (asphalt mix design) Ralph Proctor (moisture/density) James Land (Alabama Hwys) Thomas Middlebrooks (Corps) 11

12 Early Pioneers Josepth Boussinesq (mathematician) Ludwig Bermester (geometric formulation) John Redus (foundations) Per Ullidtz (layered elastic theory) 12

13 Traffic Subgrade support Layer support Surface support Definition of failure Rutting Cracking Smoothness Design Parameters 13

14 Pavement Design Simple based on Catalog or Experience Protect the subgrade from excessive deformation (rutting) Protect the surface from cracking (asphalt or concrete) Average Annual Daily Truck Traffic (AADTT) - 25 Year Pavement Design Collector Minor Arterial ,000 1,500 Subgrade Strength 30 MPa (CBR=3) 40 MPa (CBR=4) PCC HMA PCC HMA 180 mm PCC 200 mm Granular A 40 mm SP mm SP mm Granular A 350 mm Granular B 180 mm PCC 200 mm Granular A 40 mm SP mm SP mm Granular A 300 mm Granular B 190 mm PCC 200 mm Granular A 40 mm SP mm SP mm Granular A 400 mm Granular B 190 mm PCC 200 mm Granular A 40 mm SP mm SP mm Granular A 350 mm Granular B 200 mm PCC 200 mm Granular A 40 mm SP 12.5 FC1 90 mm SP mm Granular A 450 mm Granular B 200 mm PCC 200 mm Granular A 40 mm SP 12.5 FC1 80 mm SP mm Granular A 350 mm Granular B 200 mm PCC 200 mm Granular A 40 mm SP 12.5 FC1 100 mm SP mm Granular A 450 mm Granular B 200 mm PCC 200 mm Granular A 40 mm SP 12.5 FC1 100 mm SP mm Granular A 350 mm Granular B 14

15 Advantages/Limitations Based on experience Generally limited to new materials (controlled properties) Difficult to assess the potential for new processes and materials Need for performance data generally long-term Reconstruction & Rehabilitation Sequencing 15

16 AASHO Road Test (late 1950 s) (AASHO, 1961) 16

17 Methodology Uses Structural Number (SN) approach Required SN determined based on heavy traffic, safety factors and subgrade support capability Pavement design uses thickness and structural layer coefficient (surrogate for resilient modulus) The higher the SN, the higher the structural capacity SN = a D + a D m + a D m Surface Base Subbase 17

18 Structural Layer Coefficients (SLC) Material SLC New and Recycled Hot Mix 0.42 Existing Hot Mix 0.14 to 0.28 Cold In-Place Recycled Mix 0.28 to 0.38 RAP/Granular Blend Expanded Asphalt Stabilized 0.20 to 0.25 Cold Mix Asphalt 0.11 to 0.24 Granular Base 0.14 Pulverized Asphalt and Granular Base 0.10 to 0.14 Granular Subbase 0.06 to 0.09 Open Graded Base 0.06 to 0.14 Rubblized Concrete 0.14 to

19 Advantages/Limitations Relatively simple Contribution value of each layer recognized Easily understood for design Entire layer classified based on structural capacity Premise is that thicker is better Does not accurately account for the influence of environment (moisture/temperature) etc. on pavement design Material properties can vary significantly Typically over designs the pavement structure 19

20 Move to more Mechanistic Design Axle Load Surface ε Base/Subbase SUR ε SUB δ SUR Subgrade Soil 20

21 Mechanistic-Empirical Design Uses advanced inputs to predict the mechanisms of failure (structural and functional) Correlated with field results to ensure the models are accurate Fatigue Cracking IRI Thermal Cracking Longitudinal Cracking Rutting 21

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23 And now the short Answer Incorporating recycling into pavement design where does it fit? 23

24 Pretty Much Everywhere Recycling is an integral part of modern pavement design Use of recycling is a learning process RAP Early angst, reduced quality compared to virgin, variability of RAP CIP Concerns limited to low traffic levels, compaction, curing CIREAM Impact of water on recycled product FDR Uniformity of mixing, mix design, existing pavement variability Development of performance models for recycled materials 24

25 Example Project 25

26 Alternatives Considered Rehabilitation Designs Alternatives Reasons for no further review i) Mill/Pave Considered ii) Mill/Crack Repairs/Pave Considered iii) Ac Stabilization/Pave Considered iv) Remove AC/Pave Considered v) Hot-In-Place Recycling Not Considered Structural Deficiencies vi) Cold-In-Place Recycling Partially Considered Pavement too thin in Areas vii) Micro Surfacing Not Considered Existing Pavement Distressed viii) Surface Treatment Not Considered High Traffic Volumes 26

27 Key Considerations Condition of the existing pavement (surface, rutting, crossfall, structural capacity, etc.) Service life expectations Maintenance of traffic Constructability Life-cycle cost 27

28 Rut Depth & Cross Fall Township Rut Depth (mm) Left Wheel Path Right Wheel Path Mean Cross Fall (%)

29 Existing Pavement Structure Township Existing Pavement Structure Range Thickness (mm) Average HMA Granular HMA Granular HMA Granular

30 Maximum Asphalt Thickness 10.0 Asphalt Concrete Core Thicknesses 9.0 Maximum Asphalt Thickness (inches) Station 30

31 Establish Performance Models Full Depth Reclamation with Expanded Asphalt Stabilization HMA Resurfacing Mill HMA Overlay Re-stripe Surface HMA Resurfacing Mill HMA Overlay Re-stripe Surface Pulverize, Granular Base Addition and Placement of new Asphalt Concrete Maint Crk Seal Maint Surf Treat Maint Surf Patch Crk Seal Maint Crk Seal Maint Surf Treat 0 t 1 t 2 t 3 t 4 Time, years 31

32 Life Cycle Cost Analysis Analysis Period Expenditure Initial Construction Cost Rehabilitation Costs Routine Maintenance Costs Year Salvage Value 32

33 Option #1 #2 #3 #4 Life-Cycle Cost Summary LIFE CYCLE COST ANALYSIS Initial Description Construction Cost M&R Cost ** Total Cost ** Reconstruct as New Flexible Pavement $399,738 $157,689 $557,427 Full Depth HMA Removal and New $299,397 $157,689 $457,086 HMA Pulverize with New HMA $277,461 $157,689 $435,151 Pulverize, Expanded AC and HMA Overlay $239,334 $184,435 $423,769 * Figures exclude identical items such as subdrains, pavement markings, guide rails, etc. ** Costs are Net Present Values based on a 5% discount rate. 33

34 Recommended Alternative Pulverize, with AC Stabilization and new HMA surface course (lowest LCCA) Cross-Section 50 mm SP Surface Course 150 mm Stabilization with Foamed Asphalt Pulverized Existing Pavement 34

35 What is the End Result? Cost-effectively extend service life Improved ride Reduced GHG emissions Sustainable and responsible solution 35