Balanced Mix Design: Cracking and Rutting. Rebecca McDaniel Missouri Asphalt Conference November 29, 2017

Transcription

1 Balanced Mix Design: Cracking and Rutting Rebecca McDaniel Missouri Asphalt Conference November 29, 2017

2 What is Balanced Mix Design? Asphalt mix design using performance tests on appropriately conditioned specimens that address multiple modes of distress taking into consideration mix aging, traffic, climate and location within the pavement structure. FHWA BMD Task Force

3 Rutting and Instability

4 Thermal Cracking

5 Reflective Cracking

6 Fatigue Cracking Top-down or bottom-up.

7 Longitudinal Cracking Construction or traffic related.

8 Moisture Damage

9 Rutting Pre-Superpave Cracking Post-Superpave Balanced Mix Design

10 Solutions for Rutting Stiffer binder (with or without modifiers) Lower binder contents Higher recycled contents

11 Solutions for Rutting Stiffer binder (with or without modifiers) Lower binder contents Higher recycled contents All may increase the chances of cracking.

12 Solutions for Rutting Stiffer binder (with or without modifiers) Lower binder contents Higher recycled contents All may increase the chances of cracking. Volumetrics alone cannot identify problems.

13 Performance Testing Tests that are related to the performance of the materials and the pavement structure in which they will be used. Specimens conditioned to reflect service conditions related to distress type. Mix design and/or QA

14 Rutting Resistance Tests Hamburg Wheel Tracking Device (T 324) Asphalt Pavement Analyzer (APA) (T 340) Asphalt Mix Performance Test (AMPT) (T 378) Superpave Shear Tester (SST) (T 320, D7312)

15 Dynamic Modulus and Flow Number Stiffness Pavement Design Stress Strain Rutting Time

16 Cracking Resistance Tests (SCB) Semi-Circular Intermediate 3 Bend (SCB) Test (ASTM D8044) - LTRC temperature (25 ) initiation and propagation notch depths, 4 specimens each, aged 5 days at 85 C Jc = critical strain energy release rate

17 Cracking Resistance Tests (SCB) Illinois Flexibility Index Test (I-FIT) (TP124) Intermediate 1 fracture resistance notch depth, 4 specimens, no aging Flexibility Index (FI) identifies brittle mixes Fracture Energy, Gf, area under curve/notch area FI = 0.01 Gf/ m

18 Cracking Resistance Tests (SCB) IDT Energy Ratio and Fracture Energy (TP 105) Low temperature fracture energy, fracture toughness and stiffness PG Low temp +10 C and PG Low temp - 2 C From Pooled Fund Study 776, Investigation of Low Temperature Cracking in Asphalt Pavements

19 Cracking Resistance Tests Disc-Shaped Compact Tension (ASTM D7313) Fracture resistance at 10 C (50 F) or lower (PG Low temp +10 C recommended) One notch, 8-16 hrs conditioning Good for ductile binders (i.e., polymer modified) MN, IA, WI

20 Cracking Resistance Tests Overlay Tester (ASTM work item, TX-248-F) Reflective cracking, correlation to thermal cracking Empirical Sensitive to binder content, RAP, RAS Best 3 of 5 replicates TX, NJ

21 Cracking Resistance Tests Bending Beam Fatigue Test (AASHTO T 321) Repeated bending at 20 C or other temp, 2 hr conditioning Cycles to failure (crack formation or 50% reduction of initial stiffness)

22 Other Cracking Tests Superpave IDT (T 322) Low temperature creep compliance, energy ratio Fundamental material properties Thermal Stress Restrained Specimen Test (TSRST) (TP 10) Low temperature fracture as temperature drops Simplified Viscoelastic Continuum Damage (S-VECD) (TP 107) Test at 1 temp in AMPT to predict fatigue at range of temps Fundamental material properties, mechanistic

23 Other Types of Tests Durability Cantabro LA Abrasion machine??? Moisture T Sensitivity 283 Hamburg???

24 How to Choose? Wet - Freeze Dry - Freeze Dry No Freeze Wet No Freeze

25 How to Choose? What are the critical distresses in your state/area? Choose a test appropriate for those distresses Fatigue: Bending beam, overlay test, LTRC SCB or I-FIT, S-VECD Thermal Cracking: Low Temperature SCB, DCT, IDT Creep, TSRST Reflective Cracking: DCT, I-FIT, Overlay Tester

26 Keep in Mind Relationship to performance/distress of interest Testing time, cost and complexity Variability

27 Optimized Mix Design Mix Design Goals Durability Stability Constructability Production Goals Required Quality Lowest Cost for Required Quality Manageable Risk Level Shane Buchanan, Mix ETG, April 2015

28 Different Levels of Implementation Volumetric mix design then check performance test results Use volumetrics plus performance test results to design mix Performance test results to design mix, measure volumetrics

29 Example Proposed Interaction Plot Al-Qadi et al., FHWA-ICT , 2015

30 Field Acceptance Field acceptance may rely on: Volumetrics only Some performance tests for information only Volumetrics and performance test as initial verification Volumetrics and performance test as ongoing quality measure Plus field density, smoothness, etc.

31 Ultimate Goal Optimize performance Right mix in right place Account for effects of materials, production, maybe construction May eventually allow increased innovation

32 Rebecca S. McDaniel NCSC, Purdue University West Lafayette, IN 765/ ext Thanks to Isaac Howard, Shane Buchanan, FHWA, Mix ETG Task Force