Cracking Propensity of Recycled Superpave Mixtures with Highly Absorptive Aggregates and RAP and RAS

Transcription

1 Cracking Propensity of Recycled Superpave Mixtures with Highly Absorptive Aggregates and RAP and RAS Presented By Masoumeh Tavakol Master s Student Department of Civil Engineering Kansas State University By Masoumeh Tavakol, Mustaque Hossain, Blair Heptig 2015 Mid-Continent Transportation Research Symposium, August 19 20

2 Outline Introduction Laboratory Testing Data Analysis Summary

3 Introduction Background Problem Statement Research Objective Terminology (RAP, RAS) Methodology

4 Background According to Federal Highway Administration, recycled materials in pavements are used for: Cost savings potential Engineering performance Reduction in landfilling Sustainability But, based on the literature, fatigue cracking potential may increase in recycled mixtures.

5 Problem Statement What is the effect of using recycled materials on cracking performance of the HMA recycled mixtures? Objective Evaluation of the cracking propensity of the recycled mixtures by conducting Dynamic Modulus tests

6 Reclaimed Asphalt Pavement (RAP) Product of hot-mix asphalt pavement recycling: Contains around 5-6% asphalt binder Milled RAP* Recently use of RAP has been increasing because of : higher cost of virgin asphalt binder scarcity of quality aggregates sustainability awareness *National Center for Asphalt Technology, NCAT

7 Recycled Asphalt Shingles (RAS) Obtained from 2 different sources: 1-Roofing application (Tear-off asphalt shingles) 2-Factory scrap (Manufacturer waste asphalt shingles) * RAS Prior to Grinding** Ground RAS Contains 20-35% asphalt binder Use is limited to 5% in recycled mixtures * **National Center for Asphalt Technology, NCAT

8 Methodology Three different mix designs of the Kansas Department of Transportation (KDOT) hot-mix asphalt (HMA) were selected as control mixtures. Percent of recycled materials was increased in 3 steps for each mixture. Dynamic Modulus test was performed on all mixtures. Data was analyzed using: AASHTOWare Pavement ME Design software and cracking propensity of the mixtures was evaluated. Mix No.1 Step No. Total (RAP+RAS) 1 (KDOT) 15% 2 20% 3 35% Mix No.2 Step No. Total (RAP+RAS) 1 (KDOT) 15% 2 20% 3 30% Mix No.3 Step No. Total (RAP+RAS) 1 (KDOT) 15% 2 20% 3 30%

9 Laboratory Testing Materials and Mix Design Moisture Susceptibility Test Dynamic Modulus Test

10 Materials 10 different virgin aggregates 2 different sources of RAP / 2 different sources of RAS (US59)CS-1 (US59)RAP Percent Passing (US59)CS-1A (US59)CS-2 (US59)CH (US59)SSG (US59)RAS mm 1.18mm 2.36mm 4.75mm 9.5mm 12.5mm 19mm 25.4mm 37.5mm Sieve Size to the 0.45 power Aggregate gradation for the first source of materials

11 Mix Design Mix Design Procedure 1. Aggregate Structure Design (KDOT Requirements) 2. Binder Grade Selection 3. Finding optimum % binder to fulfill KDOT requirements 4. Check for Moisture Susceptibility

12 Mixture Aggregate Gradation KDOT Requirement Mix No.1 KDOT Mix Second Mix 70 Final Mix Virgin aggregates (Course and fine) * Percent Passing Maximum Density KDOT-Requirement KDOT-Requirement mm 1.18mm 2.36mm 4.75mm 9.5mm 12.5mm Sieve Size to the mm 25.4mm 37.5mm Mixture gradation for the Mix No.1 RAP RAS Mixture structure components *National Center for Asphalt Technology, NCAT

13 PG Binder Grade Selection Virgin binder grade is selected based on the project site temperature: No RAP/RAS binder grade for all the mixtures: PG70-28 When recycled materials are used, virgin binder grade should be adjusted: Binder Selection Guidelines for RAP Mixtures (McDaniel and Anderson, 2001) Recommended Virgin Asphalt Binder Grade %RAP No change in binder selection <15 Select virgin binder one grade softer than normal Follow recommendations from blending charts >25

14 (1) Aggregates are blended and heated (2) Binder and aggregates are mixed (3) HMA Mixture

15 Typical sample (4) Mixture heated for 2 hours (5) Mixture is compacted

16 Finding % Airvoid of Samples Theoretical maximum specific gravity (Gmm) %aaaaaaaaaaaaaa = GGGGGG GGGGGG GGGGGG Bulk specific gravity(gmb)

17 Compute Other Properties KDOT Requirements for mixture volumetric properties Mixtures Surface Course (SR-9.5A) Intermediate Course (SR-19A) Total Asphalt Content (%) N des (%) Voids in Mineral Aggregates (%) Voids Filled with Asphalt (%) Dust to Binder Ratio Min Min * *

18 Moisture Susceptibility Test Predicts the ability of an asphalt mix to withstand stripping Stripping: uncoated aggregates * Stripping: Moisture damage can cause a reduction of adhesion between the asphalt binder and aggregate called stripping. No moisture damage Moisture damage *

19 KT-56 Test Procedure 6 samples 3 Wet Samples 3 Dry Samples 3 conditioned samples with freeze-thaw cycles 3 unconditioned samples tested dry 3.75 Target air void of 7%

20 3 wet samples conditioning procedure: (1) Vacuum saturated up to 70-80% of air void (2) Freezing cycle for at least 16 hours (3) Kept in 60 o C water bath for 24 hour and at 25 o C water bath for 2 hours

21 Testing: Samples are broken to measure peak load and calculate Indirect Tensile Strength (ITS) : IIIIII = PPPPPPPP LLLLLLLL ππππππ (4) Samples are tested to measure peak load

22 Tensile Strength Ratio TTTTTT = AAAAAAAAAAAAAA tttttttttttttt ssssssssssssssss oooo cccccccccccccccccccccc ssssssssssss AAAAAAAAAAAAAA tttttttttttttt ssssssssssssssss oooo ddddddssssssssssss KDOT requirement: TSR > 80% %TSR 15% recycled 20% recycled Mix #1 Mix #2 Mix #3

23 Dynamic Modulus Test It represents asphalt s viscoelastic nature: How stiffness changes from winter to summer and how it changes for fast or slow moving traffic. Determined by applying sinusoidal loads at different frequencies and temperatures. E* = σ ε 0 0 * Asphalt Mixture Performance Tester (AMPT) *

24 Test Procedure Test Temperature 4C 21C 37C Load Frequencies (Hz) samples are prepared! Samples are tested at different temperatures with different load frequencies

25 Test Results Mix No.1-15% recycled C 21C 37C Dynamic Modulus (MPa) Load Frequencies (Hz) Dynamic modulus test results for Mix No.1 (15% recycled)

26 Dynamic Modulus Master Curve E* master-curves were generated by shifting data according to the time temperature superposition principle as described in AASHTO PP61 to predict dynamic modulus values at any given load frequency and temperature. A single smooth master curve is obtained by shifting the data collected for different temperatures and frequencies.

27 10000 Master Curve for Mix C Dynamic Modulus(Mpa) % recycled 20% recycled 35% recycled Load frequency(hz)

28 10000 Master Curve for Mix C 1000 Dynamic Modulus(Mpa) % recycled 20% recycled 30% recycled Load frequency(hz)

29 10000 Master Curve for Mix C Dynamic Modulus(Mpa) % recycled 25% recycled 15% recycles Load frequency(hz)

30 Data Analysis Using AASHTOWare Pavement ME Design software

31 Design Strategy Layer Type Binder Grade % RAP % RAS A (15%recycled-Mix No.1 & No.2) B (20%recycled-Mix No.1 & No.2) C (up to 30%recycled-Mix No.1 & No.2) D (15%recycled-Mix No.3) E (20%recycled-Mix No.3) Surface PG Intermediate PG Surface PG Intermediate PG Surface PG Intermediate PG Surface PG Intermediate PG Surface PG Intermediate PG F (25%recycled-Mix No.3) Surface PG Intermediate PG Control (No recycled material) Surface PG Intermediate PG

32 Traffic Initial two-way AADT Percent Trucks Directional Distribution Operational Speed (mph) Traffic Growth Rate 10,400 7% 60% 60 3% % Truck Axle Load (kip) Adjustment Factor Month % Truck Truck Class Kansas AASHTO Me Kansas AASHTO ME Kansas AASHTO Me Single axle-load spectra for class 9 trucks Monthly adjustment factors vehicle class distribution

33 Fatigue Cracking Prediction AC Top-Down Fatigue Cracking (ft/mile) AC Top-Down Fatigue Cracking (ft/mile) Control Mixture A B C D E F Design Strategy 0 Control Mixture A B C D E F Design Strategy Default Traffic Kansas Traffic Default Traffic Kansas Traffic Top-down fatigue cracking for A-4 (on left) and A-7-6 (on right) soil structure

34 Summary

35 Summary and Conclusions: Pavement ME Design software predicted significant top-down fatigue cracking in pavements with mixtures containing RAP and RAS compared to the conventional mixture. Mixtures with lower RAP and RAS content showed better cracking resistance.

36 Acknowledgments Kansas Department of Transportation, Dr. Mustaque Hossain, Major professor, Shuvo Islam, Abu Sufian, All graduate and undergraduate students contributing to this research study.

37 Questions?