Minnesota s DCT Implementation Update

Transcription

1 Minnesota s DCT Implementation Update John Garrity MAAPT 12/06/2017 1

2 Development and Implementation of DCT Specification Pilot Implementation Implementation of Performancebased Specification (MnDOT) Refinement Efforts (Spec. finalization, conditioning process, training etc.) Final Specification

3 What is the DCT? Disk-Shaped Compact Tension Test Low-temperature performance test for asphalt mixtures Thermal cracking is major distress in MN Low-temperature cracking PFS recommended DCT to measure thermal fracture resistance of asphalt-aggregate mixtures

4 2013 DCT Experimental Projects Contractor provide samples at mix design TSR pucks, 7% AV, +/- 0.5% UMD perform DCT tests Passing value of G f > 400 J/m 2 Testing conducted on design and production mixes If production mix fails, adjust mix & try again 4

5 2013 Project Data Fracture Energy (J/m 2 )

6 Round Robin Study Inter-laboratory reproducibility study Samples collected during Summer/Fall 2014, with testing completed in Spring of projects selected from around the state Participating labs included AET, Braun, and MnDOT 6

7 Average Fracture Energies: All Labs

8 Allowable Differences between Contractor and Department Test Results

9 Pilot DCT Provision Highlights Project Selection Design Production Sampling

10 Pilot Project Selection Include on New Construction or Reconstruction only. DCT requirement on Wear Mix only (top 4 ) Minimum Wear mixture approx. 20,000 tons.

11 Design Contractor Mix Design must meet minimum fracture energy. Test temp: use LTPPBind 3.1 (98% reliability) at location +10C. Modified Ratio of Added Asphalt/Total Asphalt from 80% to 75%. Full-scale production of the wearing mixture can t begin until fracture energy of plant produced mix has been verified. Wear mixture production limited to 200 tons. Contractor can substitute wear mixture for non-wear to verify fracture energy. Minimum Average Fracture Energy Design & Production Requirements for Wearing Course Traffic Level/PG Grade Design Fracture Energy (J/m 2 ) Production Fracture Energy (J/m 2 ) Traffic Level 2-3/PG XX Traffic Level 4-5/PGXX

12 Production DCT Testing Required when: An aggregate proportion change for a single stockpile aggregate greater than 10% from the currently produced mixture. A cumulative change on any one aggregate product exceeds 10% from the original MDR. A change in added asphalt that decreases by more than 0.3% below that shown on the MDR. An aggregate or RAP source is changed. An increase of 5% in RAP content or 1% in RAS content. A change in binder suppliers or sources.

13 Production Sampling & Testing For each day of wear course production obtain at least three (3) full 3.5 gallon pails or 10 x 10 x 8 corrugated boxes for the Department. Department testing showed little change in fracture energy on successive paving days.

14 2017 Pilot Project Mix Design Fracture Energy Project TH Mix Design G f Design Req. G f SP I35 A 440: 662 J/m2 B 330: 557 J/m2 500 J/m2 450 J/m2 SP TH J/m2 500 J/m2 SP TH J/m2 500 J/m2 SP TH J/m2 450 J/m2

15 2017 Pilot Project Fracture Energy Summary Project TH Design G f MnDOT G f Production SP I35 A 440: 662 J/m2 B 330: 557 J/m2 A 440: 584 J/m2 B 330: 596 J/m2 Contractor G f Production A 440: 582 J/m2 B 330: 603 J/m2 SP TH J/m2 664 J/m2 599 J/m2 SP TH J/m2 607 J/m2 518 J/m2 SP TH J/m2 474 J/m2 611 J/m2

16 2017 DCT Concerns Time to perform DCT testing (3 days). Having DCT requirement when only wearing course mix on the Project. Number of test specimens (12 pucks). Need for samples to be re-heated and then compacted DCT Observation As Granite washed sand was replaced with Limestone washed sand fracture energy went down. Addition of 8% limestone sand resulted in a loss of 150 J/m2.

17 Next Steps Continue DCT Pilot projects in 2018 Construction season. Move towards Balanced Mix Design Combine DCT and Hamburg Wheel Track testing to evaluate permanent deformation and cracking. Balanced Mix Design Goal is to achieve the combination and proportions of binder, aggregate, and other ingredients to pass the criteria of performance tests for permanent deformation and cracking types for a given level of traffic, climate, and pavement structure.

18 Thank you