Connecting South Dakota and the Nation SDDOT Pavement Research Update

Transcription

1 Connecting South Dakota and the Nation SDDOT Pavement Research Update David Huft SDDOT Research Program Manager & Intelligent Transportation Systems Coordinator

2 Projects in this Presentation Extent, Severity, and Location of Chip Seal Loss on the South Dakota State Road Network Improved Performance of Recycled Asphalt Mixes Improved Prediction of Performance of Asphalt Mixes Using a Creep Constitutive Model Gravel Surfacing Guidelines for South Dakota Update of Local Road Surfacing Criteria Effect of Wide Base Super Single Tires on Pavements Specification and Validation of Roadway Evaluation Equipment NOT Evaluation of Warm Mix Asphalt Concrete Pavement

3 SD Extent, Severity, and Location of Chip Seal Loss Objectives Determine extent, severity, and location of chip seal loss Determine to what extent SD recommendations have been implemented Identify relationships of chip seal loss to design specifications, construction, SD recommendations, and winter maintenance practices Identify potential relationships for chip seal success Other Useful Outcomes Protocol for evaluating chip seal distress Concise data collection field survey for chip seal performance Work by Allen Jones, SDSU

4 Poor chip seal performance SD38, equivalent winter maintenance cycles SD37, equivalent winter maintenance cycles

5 Good chip seal performance SD 47, equivalent winter maintenance cycles US 14, equivalent winter maintenance cycles

6 What s the Difference? Construction data from 357 projects from 2007 to 2011 ~4,000 miles of asphalt surface treatment (chip seal and sand seal) SDDOT personnel field surveyed 205 chip seals Emulsions 187 sites AE150S 161 sites CRS 2P Specified Application Rate Minimum 0.21 gal/y 2 Average 0.30 gal/y 2 Maximum 0.42 gal/y 2 Measured Application Rate Minimum 0.26 gal/y 2 Average 0.31 gal/y 2 Maximum 0.76 gal/y 2

7 What s the Difference? Specified cover aggregates 1A, 1B, 2A, type 3 variations of modified and unmodified Actual used aggregates Same as specified Specified aggregate application rate Minimum 14 lbs/y 2 Average 21.7 lbs/y 2 Maximum 28 lbs/y 2 Measured aggregate rate Unknown Plan Maximum Flakiness Index, FI (%) Lowest 25 Average 30.8 Highest 33 Tested FI (%) Lowest 5 Average 21.7 Highest 35 Tested Fines (%) Minimum 0.1 Average 0.8 Maximum 3.0

8 SD Recommendations Use uniformly graded aggregates Limit fines to 1% Limit Flakiness Index to 30% overall Limit Flakiness Index to 20 to 25% for high volume roads Use polymer modified emulsion

9 SD Improved Performance of Reclaimed Asphalt Pavement Mixes Potential Barriers to Use Availability Imposed limits on RAP percentage Determining the right amount and grade of virgin asphalt binder in blend Achieving uniform aggregate coating Mix quality and consistency, especially with high RAP content and polymer modified binders; Excessive fines and moisture from RAP Stiffening, diminished resistance to fatigue cracking Uncertainties with other recycled materials, such as asphalt shingles Inferior, inconsistent performance of recycled mixes Randy C. West

10 Objectives Describe current practices for specification, design, production, testing, and placement of RAP in hot and warm mix paving operations in SD & US. Identify best practices for Suggest revisions to SDDOT specifications, practices, and pavement preservation practices Develop guidance for using RAP

11 SDDOT RAP Use and Savings Year Mix Using RAP (tons) RAP Use (tons) Virgin Binder Replaced (tons) Aggregate Replaced (tons) ,165 45,758 3,645 42,113 Cost Savings ,840 57,126 3,874 53, , ,802 10, ,488 $6,124, , ,096 10, ,173 $6,262, ,346 93,735 6,232 87,503 $3,625, , ,506 9, ,993 $6,648,095 Total 3,279, ,023 44, ,523 $22,661,085

12 Observations So Far SDDOT practices are somewhat unique: SDDOT takes ownership of RAP generated from milling projects then essentially gives the RAP to the contractor on specific jobs by plan notes, SDDOT specifies quantity of RAP to be used in mixes Most mixes produced with portable plants for one project. Cost of hauling materials motivates contractors to use entire quantity of RAP Asphalt binder paid as a separate bid item from mixes to discourage minimizing asphalt content to be more competitive Contractors perceive mixes with 20% RAP to be dry ; may need early crack seal and chip seal Multiple chip seals and 1 milling depths of 1 may hurt RAP binder content and aggregate gradation Millings typically only tested as part of mix design. Most contractors take only three samples of millings to determine asphalt content, gradation, aggregate specific gravity. RAP generally not tested during HMA production. Contractors assume that SDDOT central lab checks asphalt contents of the RAP samples

13 Observations So Far For mainline paving, target RAP content usually 20% First mix adjustment to control air voids usually to reduce asphalt content (up to 0.3%), then gradation adjustments On some projects (particularly western SD) VMA criterion reduced by 0.5% to maintain RAP content Contractors indicate good practices for RAP stockpile management, except material uniformity not checked Contractors willing to use in line RAP crushers to ensure millings pass a 1.5 screen Not clear to the researchers how the quantity of RAP generated balances with the amount used back in mixes if 1 is milled and overlays are 1.5 thick (typical)

14 Preliminary Thoughts, Possible Recommendations Retain RAP ownership as a last resort Set max allowable RAP on project, give contractor ownership of RAP and responsibility to meet design and QC requirements Establish process by which contractors can use RAP they own on projects and negotiate splits so all parties benefit Use skid steer milling to sample RAP for project design Lower target air void content 0.1% for every 5% RAP; maintain VMA by adding a little more asphalt binder Eliminate exceptions made on air voids, density, etc. Identify best methods to determine RAP properties (binder content, aggregate specific gravity) Verify RAP processing (mixing, crushing, screening) does not hurt gradation Use baghouse fines in mix designs so production drop in VMA can be reduced Consider lower RAP content (~15%) in western SD where limestone is predominant aggregate to maintain VMA Revisit hydrated lime requirement, especially in limestone region; adjust binder content as necessary Gather more information from projects with performance problems attributed to RAP

15 SD Improved Prediction of Performance of Asphalt Mixes Using a Creep Constitutive Model Constitutive Model Relationship between two physical quantities specific to a material or substance approximating the material s response to external fields or forces Dr. Lance Roberts Objectives Assess feasibility of developing a creep compliance test to predict pavement performance Develop a mechanistic constitutive model to predict rutting, fatigue cracking, thermal cracking, and topdown cracking for use in the DARWin ME Pavement Design Guide protocol Assess the effectiveness of the test method and model in predicting asphalt pavement performance Exploratory Project

16 Sample Preparation SDDOT Q2 and Q4 Mixes

17 Creep Testing psi temp 72 F x x 104 F x 140 F X x Slow loading rates (10 days)

18 Creep Testing Total Strain F, 100 psi 77 F, 150 psi 77 F, 200 psi 104 F, 150 psi 140 F, 100 psi 77 F, 100 psi 77 F, 150 psi 77 F, 200 psi 104 F, 150 psi 140 F, 100 psi 104 F, 100 psi Time, days

19 Constant Mean Stress (CMS) a - Increasing c - Decreasing STRESS DIFFERENCE ( a - c) VOLUMETRIC STRAIN

20 Brazilian Test or Indirect Tension Test

21 Results So Far Creep and CMS testing indicate the Q2 mix will begin to microcrack at a slightly higher stress difference (higher load) Once microcracking has begun, the Q2 mix will continue to crack and deform substantially (damage), whereas the Q4 mix may not fail The research team is developing a method to use the test results with DARWin software to predict performance of various mixes The ultimate goal is a testing program that can assess mix performance and compare mixes to find the most costeffective pavement design

22 SD Effect of Wide-Base Super-Single Tires on Pavements Suggested by SD Trucking Association Hoped to lift 500 lb/in restriction on 445/455 mm tires Dual/ 275 Work by Hao Wang /

23 Objectives Based on others research, assess effects of allowing 20,000 pound loads on single axles equipped with 445mm and 455mm wide base tires on state and local roads in South Dakota Assess need for additional research involving physical testing or modeling

24 Tire-Pavement Contact Area and Stress (Wang and Al Qadi 2009; 2011) Vertical Contact Stress (kpa) Dual-tire Assembly Wide-base Tire ribs Transverse Contact Stress (kpa) Dual-tire Assembly Wide-base Tire ribs

25 Damage Ratios on Thin & Thick Asphalt Pavement Distress Thin Asphalt Thick Asphalt Fatigue Cracking Top Down Cracking N/A Primary Rutting * Subgrade Rutting N/A References Wang and Al Qadi, 2011 Pascale et al Greene et al Ponniah et al. 2006

26 Damage Ratios on State Highway Network Code Type AC Base % of Total System Miles Damage Ratio Weighted Damage Ratio FD Full Depth >10 no 2.3% THK Thick 5 10 yes 33.5% TonS Thin on Strong 2 5 > % TonW Thin on Weak 2 5 < 8 7.1% 1.88* AonC AC on PCCP yes PCC 8.1% 1.0** BLOT Bituminous surface treatment 0.7% 1.88* PCC PCC Pavements 21.6% 1.0** Total 100% 1.228

27 SB154: Allows 445/455 mm Tires on Major SD Highways 85!( 20!( 79!( 75!( 73 12!( 65!( 10!( 20!( 63!( 47!( 45!( 10!( !( 37!( !( !( 34!( 44!( 73!( 73!( 63!( 63!( 44!( 44!( 73!( 53 and any locally designated highway within the corporate limits of any municipality adjacent to the Interstate highway system !( 47!( 20!( 20!( 26!( 45!( !( 34!( 34!( !( !(!( 90 50!( 47 45!( 37!( 18 25!( !( 50!( 28!( 25!( 25!( 44!( 42 81!( 19 14!( 15 29!( 11

28 Future Work Analyze impact of new wide base tires on the full range of road surfaces (including unpaved) in SD Quantify possible increase of life cycle agency cost if allowing the same load limit on wide base single tires and dual tires on other state and local roads Consider three important contributing factors to pavement damage ignored in previous studies: unbalanced loads between dual tires, wheelpath wandering, and dynamic loading

29 SD Gravel Surfacing Guidelines for South Dakota >75% of local SD roads unpaved managing them is a challenge! Biggest complaints are: rough condition, corrugation or washboard too much loose aggregate on the surface How critical is gravel quality to this and how does it affect total cost? Objectives Identify and describe current and best practices for design and maintenance Assess the performance of test sections built with materials at, above, and below state specs Develop gravel roads guidelines

30 Findings from County Highway Superintendent Surveys Majority use DOT spec gravel and confirm with tests (gradation, PI, fractured faces) About 30% use unprocessed or screened bank run materials A few use RAP millings or concrete rubble Some amend PI content above 5%, many do not Maintenance mostly performed according to scheduled cycles, while some agencies use distress to trigger About half report grading frequencies >11 times/year, generally once/month Most believe high quality materials are cost effective

31 SDDOT Gravel Road Test Project Three types of gravel Substandard but commonly used: no spec except top size <1 Just meets SDDOT Gravel Surfacing Spec: % passing #200 sieve is low or plasticity index (PI) at bottom of range at 4 Modified SDDOT Spec: >10% passing #200 sieve and PI > 7 Hand County NE of Miller Custer County NW of Custer Brookings County S of Volga

32 Sections built with 3-4 of new gravel after surfacing prep and shaping, compacted and not

33 Road mixing to get high quality surface gravel

34 Custer County Test Sections Differences apparent soon after construction

35 Brookings County Test Sections Only one month after construction Modified Section Substandard Section

36 Corrugation, Road Width Change

37 Observations Meeting basic SDDOT spec cuts loose aggregate by ⅓ to ½ Project to complete later this year Biggest difference in Brookings County, near end of corn harvest with: 405 tons/mile of loose aggregate on substandard section 71 tons/mile on modified section Blading up to four times on substandard section to once on modified

38 SD Update of Local Road Surfacing Criteria Prior research project SD (2004) provided local road managers manual and spreadsheet methods for Life Cycle Cost Analysis Current work by SDDOT Research Dustin Artz & Megan Steever Objectives Address surface changes Update default cost values and treatment definitions Represent SD local road traffic Include subgrade and material quality Update software tool

39 How to choose between surfacing types? Life Cycle Cost Analysis (LCCA) Compares all costs involved through the entire life of the road: Initial construction Routine maintenance Significant rehabilitation treatments May include user costs Used by SDDOT, cities, and counties 39

40 Life Cycle Cost Surface Comparison (10-Year Illustration, 250 ADT) $9,000 $8,000 $7,000 Gravel Total Cost: $29,900/mile Blotter Total Cost: $22,100/mile $6,000 $5,000 $4,000 $3,000 $2,000 $1,000 $0 Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Gravel Blotter

41 LCCA Tool $200,000 Cumulative Costs for Different Surface Types Cumulative costs, dollars $160,000 $120,000 $80,000 $40, $ HMA Years since initial Blotter construction Gravel or last major Stabilized rehabilitation Gravel

42 Specification and Validation of Roadway Evaluation Equipment 1) Identify SDDOT s needs for roadway evaluation equipment through: assessments within SDDOT reviews of other equipment presently in use appraisals of emerging technology 2) Develop equipment specification and acceptance criteria 3) Validate the roadway evaluation equipment Work by SDDOT Office of Research

43 Roadway Video Images Very High Resolution Asset Inventory Type Location Dimensions Map Interface Forward Camera Side Viewing Camera

44 Longitudinal Profile Features Inertial Profiler Shorter data interval Enables faulting measurement Roline Sensor Removes effect of PCC tining and grooving SDDOT Applicability Same operation as SDDOT s current equipment Improved IRI quality Plus faulting from LMI Technologies

45 Transverse Profile Data Elements Transverse Profile Possible but unused with current equipment Rut Depth 3 point estimate with current equipment Prone to wheel path wander (variability, under estimation) Vedula, et. al The three sensor rut bar does not provide repeatable and accurate rut depth measurements and would not provide adequate network level rut depths for pavement management systems. Inconsistent rut depth measurements obtained over time would be problematic for determining rehabilitation needs. Adequacy of Rut Bar Data Collection FHWA RD January 2001

46 Grayscale & Elevation Images Elevation Grayscale Combined

47 Crack Presence, Width & Classification

48 LIDAR Survey (Future?) Data Elements LIDAR Point Cloud Not possible with current equipment Collection Needs Asset Inventory Preliminary Survey Structure Clearances Mandli Communications, 2012

49 Other Systems Considered Ground Penetrating Radar Pavement Texture Pavement Noise On Board Sound Intensity 360 video Sign Retroreflectivity Pavement Marking Retroreflectivity

50 New SDDOT Vehicle Concept

51 Questions? Please contact David Huft SDDOT Research Program Manager