Designing and Producing High Reclaimed Asphalt Pavement and Recycled Asphalt Shingles Mixtures

Transcription

1 TRANSPORTATION RESEARCH BOARD Designing and Producing High Reclaimed Asphalt Pavement and Recycled Asphalt Shingles Mixtures Monday, September 25, :00-3:30PM ET

2 The Transportation Research Board has met the standards and requirements of the Registered Continuing Education Providers Program. Credit earned on completion of this program will be reported to RCEP. A certificate of completion will be issued to participants that have registered and attended the entire session. As such, it does not include content that may be deemed or construed to be an approval or endorsement by RCEP.

3 Purpose Discuss NCHRP Synthesis 495. Learning Objectives At the end of this webinar, you will be able to: Understand key recycled materials that need to be determined for mix designs and quality control Describe how recycled material properties can influence mix design volumetric calculations Discuss options for determining the total useful asphalt content in a recycled material mixture Describe stockpiling and asphalt plant factors which can limit the maximum amount of recycled materials added during production

4 Designing and Producing High Reclaimed Asphalt Pavement (RAP) and Reclaimed Asphalt Shingles (RAS) Presenters: Mary Stroup-Gardiner, Gardiner Technical Services Tony Felix, Reeves Construction Group Tim Aschenbrener, Federal Highway Administration (FHWA) Moderator: Ben Bowers, Virginia Department Of Transportation (VDOT)

5 Overview Literature review: Focus: Actual use rather than just allowed Defined high RAP as asphalt mixtures containing more than 25% RAP RAS: 5% RAS maximum and most used percent Two AASHTO agency surveys: State Materials Engineers Material properties, mix designs, performance testing State Construction Engineers Production and placement

6 Main Points Key Virgin and Recycled Material Properties Optimum Asphalt Cement Content Mix Design Testing Production and Placement

7 Understand Key Recycled Material Properties Asphalt Cement Properties Selecting Virgin AC Grade Asphalt Cement (AC) Content Aggregate Properties

8 Asphalt content determined for each recycled material with: 30 Ignition Furnace Solvent Extraction No. of Agencies RAP (not fractionated) RAP, Coarse RAP, Fines RAS RAP + RAS (combined) Majority of solvent extraction is with centrifuge

9 Asphalt Cement Properties Recovery Abson recovery (8 agencies) Rotavapor (8 agencies) Other (6 agencies) 20% no longer use solvent extraction so no option for recovery Testing As-recovered dynamic shear rheometery (DSR) high temp. most common (8 agencies) DSR after rolling thin film oven testing (RTFOT) (6 agencies) Infrequent low temp testing

10 How is Virgin AC grade determined? No. of Agencies Upper PG Grade Decreased by 1 Lower PG Grade Decreased by 1 Lower PG Grade Decreased by 2 True PG <= RAP > 25% RAP >5% RAS RAP + RAS

11 Recycled Material Aggregate Properties Aggregates After ignition furnace (15 agencies) After solvent extraction (9 agencies) Gradation, mm most common Several agencies will evaluate key properties after blending with aggregate Assume acceptable when RAP from state projects (18 agencies)

12 No. of Respondents Specific Gravities After Ignition After Solvent Theoretical Max. RAP Coarse RAP Fine RAP RAS RAP + RAS Recycled material aggregate effective specific gravities (G se ) frequently calculated from theoretical maximum specific gravity. Simpler from testing point of view can be problematic due to assumptions that need to be made to complete calcs.

13 Equations for Calculating Asphalt Content (AC) Asphalt Binder Ratio (ABR) Reclaimed Binder Ratio (RBR) Total Asphalt Content (TAC)

14 Research suggests that % virgin AC is more important to performance than PG grade Minimum Asphalt Binder Ratio (ABR) = Virgin Asphalt, % Total Asphalt Content, % MnDOT uses ABR based on specified virgin PG grade, type of recycled material, lift (65% to 80%) Maximum Reclaimed Binder Ratio (RBR) = [ (RAP AC) (RAP%) + (RAS AC) (RAS%) ] 100 Total Asphalt Content TxDOT uses RBR based on allowable substitute virgin PG grade, (20% to 40%)

15 Options for TAC Philosophies All of it is useful None of it is useful ( black rock ) Reality is somewhere in between..and differs by type of recycled material No. of Agencies % Available Predetermined by Agency Black Rock < 25% RAP or Less > 25% RAP RAS RAP + RAP

16 Total Asphalt Content (TAC) = [ F RAP (RAP AC) (RAP%) + F RAS ( RAS AC) (RAS%) + Virgin AC% ] Where: F RAP, F RAS = Asphalt availability factors RAP AC = Asphalt content of RAP, decimal form RAP% = Percent of RAP in mixture, % RAS AC = RAS Asphalt content, decimal form RAS% = Percent of RAS in mixture, % No. of Agencies TAC ABR RBR

17 MnDOT Study Batch Plant, 30 seconds, Only RAP and Aggregate (Source: Johnson, et al, 2013) 420F 490F 400F 10% RAP 24% RAP 24% RAP Run 1 Run 2 Run 3

18 290 F (143 C) Laboratory RAS Study Typical Texas Mixing Temperatures (Source: Zhou et al, 2013) 300 F 325 F (149 C) (163 C) 20% Tear Offs + Limestone 392 F (200 C) 20% Manufacturing RAS + Limestone

19 Impact of Recycled Materials on Mixture Volumetric Properties and Performance Testing

20 Mixture Volumetric Properties It is more difficult to obtain acceptable properties when compared to similar mixtures without any recycled material content for: 15 <= 25% RAP > 25% RAP 5% RAS RAP + RAS No. of Agencies Air Voids VMA VFA Dust to Asphalt

21 Performance Properties It is more difficult to obtain acceptable properties when compared to similar mixtures without any recycled material content for: No. of Agencies Rutting Mix Strength Thermal Cracking Increases with increasing RAP Increases with increasing RAS Moisture Sensivity Non-Thermal Cracking Increases with increasing RAP + RAS

22 Production and Placement Stockpiling Materials Quality Control (QC) Testing Plant Considerations Placement Inspection

23 AASHTO Construction Engineers Stockpiles Constructing stockpiles QC testing Plant Characteristics Batch plants Drum mix plants Case Study: Southeastern contractors

24 Large quantities are collected, then processed Consistency maintained by controlling milling & stockpiling procedures Stockpile different RAP sources separately RAP Stockpiles (Source: West, 2010) Moisture and speed of processing affect crushing and sizing Some processing is done with in-line crushers at plant Milling generates fines; can be major problem depending on agg type and miller type

25 RAS Stockpiles Separate tear offs (postconsumer) and manufacture waste Grind to max. size of 9.5-mm or smaller (6.35-mm, 4.75-mm, 2.36-mm) Source: Jackson, 2012 Cover to keep, dry and out of sun Water may be used during grinding and needs to drain Can mix with sand to minimize clumping May need to break up lumps prior to feeding into plant

26 QC Stockpile Sampling Loader bucket enters stockpile above ground level, backs up, and drops sample onto ground. Courtesy of Sam Johnson, Vulcan Materials Loader bucket is used to level top of sampling pile. (Note moisture even in agg stockpile) Quartering method is used to obtain aggregate sample for testing.

27 QC Testing (Both RAP and RAS) Measure AC content and gradations of both RAP and mix Ignition furnace most common Aggregate specific gravity Theoretical maximum specific gravity Moisture content RAS QC Testing Also evaluate for metal contaminates (Source: TxDOT test procedure designation Tex-217-F)

28 Example of QC Plan from Literature Review (West and Willis, 2013) RAP Material Property Test Methods Frequency Min. No. Tests per Stockpile AC% AASHTO T164 or AASHTO T308 1 per 1,000 tons 10 Recovered agg gradation AASHTO T30 1 per 1,000 tons 10 Recovered agg bulk specific gravity AASHTO T84 and AASHTO T85 1 per 3,000 tons 3

29 Suggested Changes to Current RAP and RAS Processing Requirements > 25% RAP Fractionate to meet mix design volumetrics (6 agencies) Cover stockpiles (3 agencies) Increase QC testing (2 agencies) RAS Need better determination of RAS AC contribution (2 agencies) Blend with sand Cover stockpiles

30 Production More difficult to uniformly feed into plant Add more cold feed bins Use in-line crushing or screening and sizing Need separate weigh bridges for RAP and RAS Gravimetric weigh belt From literature: Increase slope by 70%, clean out nightly to avoid clumping, opt. belt tension/slope and non-stick materials

31 Production Age of plant and drum 750 flighting important to 700 ability to produce high RAP mixes 550 Need to increase plant 500 temperature to remove 450 moisture Need to slow production 300 speed to remove moisture 250 Superheated Temp. for Agg, F RAP Moisture Content, % (Source: Brock and Richmond, 2007) 50% 40% 30% 20% 10%

32 Production (Southeastern Contractors) Batch Plants Screw conveyor or belt scale to move material into pugmill Additional venting capability on weigh box is needed to handle steam Add recycling material which bypasses main vibrating screen Drops directly into the No. 1 bin Alternatively, use separate drying unit and feed directly into pugmill

33 Production (Southeastern Contractors) Drum Mix Plants >25% RAP, RAS, and RAP + RAS mixes tend to generate higher drum exhaust entering baghouse Move RAP collar closer to discharge point Need to change flighting to help with heat transfer, mixing, and retention time in drum Limit silo storage time

34 Placement Agencies: More likely to form crust on mix in paver wings Temperature segregation More difficult to obtain joint density Tends to flow out of truck in portions rather than flow continuously Handwork may be more difficult *>225.0 C *<125.0 C Southeastern contractors More temperature-sensitive (compaction issue) RAP asphalt doesn t seem to transfer well or blend Mixes tend to have less film thickness (dry)

35 Key Points for Field Inspectors Agencies: Quality, uniform stockpiles essential Check temperatures Stay on top of segregation and joint density Look for dry, bony mix, clumps of materials Southeastern contractors All of the above plus: Check: Thermal segregation Coating of material Visible contaminates and over-sized chunks of RAP

36 Case Study: Routine Use of High RAP Mr. Tony Felix, Reeves Construction Group Summary and Key Points Mr. Tim Aschenbrener, FHWA

37 The Georgia Asphalt Industry s Approach to Improving Performance & Durability of High RAP Pavements

38 The Issues Poor In-Place Mix Performance, 2012 All Dense Graded Mixes: Dry with an aged appearance. Segregation, texture, temperature sensitive. Rapidly fatigue, resulting with top down cracking within the first few years of service. Stiff & harsh with a small window of workability. Difficult to achieve acceptance density requirements. Smoothness/ride quality requirements are often difficult to achieve.

39 New Construction Project in 2012 In-Place Mix only 3 Months Old Accelerated Wear Under Typical Construction/Traffic Staging

40 New Construction Roadway Less Than 3 Years Old with Top Down Cracking Throughout The Project Limits

41 The Solution Began with Industry PARTNERING Prevention GDOT & Georgia Asphalt Pavement Association How to Improve In-Place Pavement Durability & Performance Through Mix Design Procedures? Goals: Identify the root causes. What has changed? Modify design process to represent WHAT IS ACTUALLY WORKING ON THE ROAD. Need to acknowledge that what's on the road is what matters and the design process is only a start. Designs may need tweaking to be representative of the road. How to implement needed changes

42 The Root Causes Roadway Issues were similar to those experienced in the late 1990 s when Georgia began using Superpave Mix Design Procedures Four Gyration Levels Traffic Count Dependent Very High Gyration Level For Higher Traffic Roadways Different Orientation of Materials through Gyration Process Really Doesn't Simulate Compaction on the Roadway Coarser Aggregate Gradation for Most Mix Types Produced Rut Resistant Mixes With Lower AC contents In-Place Permeability and Durability Became an Issue How Were The In-place Mix Performance Issues Resolved Back Then? Sheila Hines, GDOT State Bituminous Construction Engineer: Modified the Mix Design Procedure (2005) to one Gyration Level (65) Fined Up Gradation Limits of Most Dense Graded Mix Types Specified Additional Performance Testing for Approval - Permeability - Hamburg Wheel Tracking (Special Mixes) All of these changes resulted in mixes with increased AC contents and improved performance

43 The Root Causes So, what Else Has Changed Since 2005? From 2005 Present, the RAP usage increased from 10%-15% up to 30% RAP with Binder 100%. Most RAP Stockpile Processed to -9/16 have an Average AC of 5%. AC Contribution to total mix AC went from approx..5% to 1.5% Higher Percentage of RAP Resulting in Higher Binder Replacement in New Mix

44 The Action RAP Study January 2012 By Sheila Hines, GDOT State Bituminous Construction Engineer GDOT s Research Concept Determine the amount of actual transfer of AC from RAP to the virgin aggregate during production. It was assumed that there would be sufficient transfer to actually calculate an approximate amount of recycled AC available to blend with the virgin material.

45 Pre-weighed Virgin Aggregate is Pre-heated 400 F

46 RAP is Weighed Out Equivalent to 25 % of Virgin Rock

47 Pre-heated Virgin Rock & Room Temperature RAP are Introduced to a 300 F Pugmill Mixer and Blended for 1 Minute

48 Combined Material is Removed From Pugmill and Separated

49 Separated Virgin Aggregate is Weighed No Measurable Difference is Detected

50 RAP Study January 2012 It was agreed that the PRE-COATING OF THE RAP AGGREGATE WAS A BENEFIT. GDOT decided to determine what AC content was required to achieve the primed coating on the RAP aggregate. 1. RAP samples from a majority of RAP stockpiles approved by GDOT were sampled and tested using the ignition oven to determine the AC content. 2. Additional RAP samples that the AC was not removed from were photographed and then placed in the oven for heating for 1 hour and photographed again. These samples were used for visual comparison in the next step. 3. AC was mixed with the extracted RAP aggregate samples in % increments. 4. The RAP samples with the newly added AC were then visually compared with the RAP samples from step The percent of new AC required to provide similar coating of the RAP aggregate as that of the original RAP sample was determined and used to calculate the percent of effective AC in the RAP

51 2.75 % AC Added to RAP Aggregate

52 RAP AC Contribution AC Content For RAP = 4.46 % AC Content Selected As % Required to Coat Aggregate = 2.75 GDOT Considered Effective AC Contribution : (2.75/4.46)*100 = 61.7% Statewide Average was ~ 60% 75% - Negotiated With Industry As Starting RAP AC Contribution To Total AC

53 The Argument. This Was Lab Work What about the Real World?

54 A Georgia Contractor Agreed to Assist with This Study Two approved mix design, virgin aggregate & RAP only, were mixed through an actual Drum Plant

55 19mm SP with 30% RAP Ran out of Reject Chute -9/16 RAP, Approx. 5% AC

56 19mm SP with 30% RAP Ran out of Reject Chute Back Dragged with Loader

57 19mm SP with 30% RAP Held in Silo for 20 minutes

58 9.5mm Type II w/30% RAP Held in Silo for 15 minutes

59 9.5mm SP with 30% RAP Ran into silo and held for 15 minutes Placed in a bag while 300 F. When cooled there was no consolidation or stiffening. Material was in loose state as if virgin aggregate from a stockpile.

60 Rap fine fractions from cooled bag.

61 The Conclusion RAP is mainly a primed aggregate that offers little to no transfer to the virgin stone. RAP Aggregate AC Absorption is already addressed Less neat AC is needed to reach same effective AC content as Non-RAP mixes.

62 The Solution Corrected Optimum AC (COAC) Calculation Reclaimed Asphalt Pavement (RAP) in Mix Design = 28 % AC in RAP = 4.16% Total Optimum AC in Mix Design = 5.45% RAP AC Contribution to the Total= 1.16% Using GDOT s 0.75 AC Contribution 1.16% x 0.75 = 0.87% 1.16% % = 0.29 % JMF COAC = 5.45% % = 5.74% All Mix Design Performance Testing is conducted at 5.74% COAC All Mix Design Volumetrics is conducted at 5.45% OAC

63 The Question How Does the Additional Neat AC Affect the Mix? 1. Actual field placement 2. Laboratory testing

64 More than 200 field verifications of Plant Produced Mix have been completed no issues Verification Tests Results: Original Mix Design Tests Results Gmm by T-209 Gmm by T Gmb by GDT-166 Gmb by GDT Air Voids: 1.2 Air Voids: 2.9 GSE: GSE: VMA 13.2 VMA 14.1 Vbe 12.0 Vbe (from mix design) 11.2 TSR by GDT-66: TSR by GDT-66: Conditioned (PSI) (kpa) Conditioned (PSI) (kpa) Control (PSI) (kpa) Control (PSI) (kpa) 98.6 Retained Strength, % 93.0 Retained Strength, % APA by GDT-115 mm 1.88 APA by GDT-115 mm 1.55 Field Verification Results Job Mix Formula Deviation AC by GDT-83 or 125 % 4.86 AC by GDT-83 or 125 % Sieves 37.5 mm (1-1/2") mm (1-1/2") mm (1") mm (1") mm (3/4") mm (3/4") mm (1/2") mm (1/2") mm (3/8") mm (3/8") mm (No. 4) mm (No. 4) mm (No. 8) mm (No. 8) μm (No. 50) μm (No. 50) μm (No. 200) μm (No. 200) Lot Average Air Voids 5.9 Sieves

65 Design Procedure Modifications Implemented COAC For All Mixes Established Minimum AC Contents Design Volumetrics are Calculated at Opt. AC Design Performance Testing Specimens made at COAC Established Minimum Film Thickness Requirements

66 Revised Existing GDOT RAP Mix Designs with COAC Corrected Optimum AC Content (COAC) Mix Type Mix ID Number Design Original Optimum AC Mix Design % RAP AC % in RAP Credited AC Non Creditied AC Corrected Optimum AC OOAC CAC NCAC COAC 12.5 mm SP 555R12.5SP mm SP 555R

67 Improvements & Benefits Significant reduction in number of density related pay reductions 40 percent reduction over 4 year period Improved and more uniform surface texture Expected better durability

68 One of First COAC Projects at 2+ years

69 1. Mixes are richer 2. Easier to meet density requirements 3. Statewide Smoothness improved 4. More forgiving and placement friendly.

70 Best Practices are Still Needed Handling and Material Properties Evaluation GDOT uses Standard Operating Procedure 41 for RAP stockpile approval Provides guidelines for RAP stockpile approval process Establishes RAP limitations based on variation of AC contents and gradations Details requirements for replenishing RAP stockpiles Establishes testing frequencies for sampling and testing of approved stockpiles

71 Best Practices Limit And Reduced Variability For Better Control 1. Processing and Fractionating 2. Stockpile Management 3. Handling Millings and Demolition Materials

72 Don t Fear Communication Fear of communicating issues and addressing challenges observed on the project is a time bomb waiting to explode! QUALITY Delivery BUDGET The Importance of DOT and Contractor s Partnership in Achieving Quality Construction

73 Questions Remember, Once the Contractor-DOT relations deteriorate, the work suffers.

74 Summary and Key Points Designing and Producing High Reclaimed Asphalt Pavement (RAP) and Reclaimed Asphalt Shingles (RAS) Mixtures Mr. Tim Aschenbrener, FHWA

75 Key Recycled Material Properties Asphalt content Ignition furnace Solvent extraction Asphalt binder properties Increases both high and low PG temperature Note: 20% of agencies no longer do solvent extractions so they can t test recovered asphalt Impact on mixture is dependent on RAP and RAS Quantity Sources

76 Key Recycled Material Properties Aggregate properties Gradation and minus mm (P200) Less than 20% evaluate other properties Bulk specific gravity of the aggregate (G sb ) Aggregates from ignition furnace or solvent extraction Recommended for RAP Effective specific gravity of the aggregate (G se ) From the maximum theoretical specific gravity (G mm ) and asphalt content Most commonly used method Not recommended for RAP Acceptable for RAS

77 Mix Design and Volumetric Properties Selecting virgin asphalt binder grade Less than ~ 15-20% RAP - typically no change Grade bumping (bump down high and/or low temperature) Blending charts by extracting, recovering and testing Mixture design by mixture design Using statewide typical values is very practical

78 Mix Design and Volumetric Properties Reclaimed asphalt binder contribution Three philosophies: 1. Black Rock (0% contributing) Only used by a couple of agencies for RAP May contribute to respondents comments like mix looks dry 2. Fully contributing (100%) 3. Partially contributing (some (??) percentage) Reality is somewhere in between all and none Availability factors

79 Mix Design and Volumetric Properties Requirements are moving towards: Reclaimed binder ratio (RBR) Ratio of reclaimed binder to total binder content Maximum (e.g. 0.25) Asphalt binder ratio (ABR) Ratio of virgin binder to total binder content Minimum (e.g. 0.75) Binder ratio requirements often vary based on: Surface vs. lower lifts Higher vs. lower traffic Quantity of RAS

80 Mix Design and Volumetric Properties Survey results for using higher recycled materials Generally, more difficult to meet mixture volumetric properties Rutting can decrease Both non-thermal and thermal cracking can increase Moisture sensitivity may increase Many thought no influence Some concerns related to fines Performance testing

81 Stockpiling and Asphalt Plant Factors RAP Stockpiling Process RAP as needed Consistency Increase QC testing Possibly fractionate to control Moisture content Cover if possible Note: The necessity of using these techniques to produce consistent, quality asphalt mixtures will vary based on RAP sources, amount of RAP used in the mix design, etc.

82 Stockpiling and Asphalt Plant Factors RAS Stockpiling Process to 9.5-mm or finer Stockpile tear-off (postconsumer) and manufactured waste shingles separately Increase QC testing Check for contaminates, including metals Moisture - keep covered Clumping - add sand to minimize

83 Stockpiling and Asphalt Plant Factors Feeding recycled materials Increase number of cold feed bins Feed systems Volumetric cold feed bin (steep sides to prevent bridging) Gravimetric weigh belt (make sure recycled material is not sticking) Cold feed bin on load cells (reverse weigh) very promising but more expensive

84 Stockpiling and Asphalt Plant Factors Production Moisture content directly influences ability to dry and heat RAP Having separate units for drying and mixing helps keep temperature down Adjust drum flights and production rates for better heat transfer Plant needs to be capable of managing: Higher temperature exhaust Increased volume of exhaust into baghouse

85 Tips for Inspectors Stockpiles Clumping Moisture Visible contaminates Placement Mix temperatures and thermal segregation Clumping Mat density Dry mix look Sampling

86 Today s Participants Ben Bowers, VTRC, Virginia DOT, Ben.Bowers@vdot.virginia.gov Mary Stroup-Gardiner, Gardiner Technical Services, marystroupgardiner@outlook.com Tony Felix, Reeves Construction, TFelix@reevescc.com Tim Aschenbrener, FHWA, timothy.aschenbrener@dot.gov

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