Austin District s New PM Overlay Program

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1 Austin District s New PM Overlay Program

2 Problem: Unable to achieve the performance life from standard PM overlays Standard District Overlay Default: 2 D-GR TY C Can t afford premature failures with limited future funding Re-examined our standard non-structural overlay practices for pavement preservation purposes

3 Dense Graded Overlay Issues: Issues with raveling and failures due to segregation and low AC Fatigue & Top Down Cracking Due to premature aging and/or low AC Overly stiff mixtures due to recycled asphalt materials 2 years old overlay with RAP/RAS

4 Performed FWD testing on dense graded mixes in the surface with RAP/RAS HMA/Base Modulus Ratios > 10:1 Building in fatigue cracking to our pavement structures (16 to 20:1) Cracking during construction

5 Goal: Develop a new strategy for PM overlays in the Austin District Objective #1: Equal or better performance than current standard pavement preservation practices Resist to rutting and cracking Restore and improve ride Restore and improve skid resistance Objective #2: Less susceptible to premature distress Less susceptible to segregation & premature aging Objective #3: More costeffective Need to maximize every dollar

6 Identified inexpensive, high quality TY F aggregate source Modified CMHB-F mixture Modified design, gradation, & material requirements Final product: PG % SAC A TY F aggregate 30% Local, SAC B Screenings

7 First Mix Design Performance: Density = 97.5% AC = 6.7% Hamburg = 20, mm rut depth Indirect Tensile = 123 psi. Overlay Test = 453 cycles Rutting BALANCED DESIGN Cracking

8 Pavement Condition Severely fatigue and block cracked Multiple failures Crack widths 3/4 Construction: May 2009 No repair to failures or fatigue areas Heavy emulsion tack coat Overlay directly on existing pavement

9 Heavy Truck Traffic Turning Traffic Truck Loading (May 2009 to August 2011) Practically 100% Heavy Trucks (Haul trucks & Transports) >3.0 million total tonnage (material and trucks) shipped in and out since overlay

10 Performance as 9/16/11: No evidence of rutting or cracks reflecting No shoving or shear failure at turns No visible or physical segregation Ride is good. Skid Number Range = 51-64

11 Pavement Condition: Distress Score = 41 Fatigue & Longitudinal Cracking Traffic: ADT = 44,000 High Volume

12 No repair to distressed areas Heavy emulsion tack coat No evidence of rutting or cracking No raveling or shoving at numerous driveways Coring Information: Thickness = ¾ to 1 Well bonded

13 Skid Number = mid 40 s Improved Ride Ride Score FY 09 = 3.0 Ride Score FY 10 = 4.1 Ride Score FY 11 = 4.0 Added Bonus: Quiet Ride Properties Avg.= dba PFC ~ 98 dba

14 Did our overlay strategy meet our goals?: Objective #1: Equal or better performance than current standard pavement preservation practices Resist to rutting and cracking Yes; balanced mix design Yes; no distress detected, in spite of heavy traffic and poor pre-existing pavement conditions

15 Did our overlay strategy meet our goals?: Objective #1: Equal or better performance than current standard pavement preservation practices Restore and improve ride Yes; 1.1 point improvement in ride score Good Skid Resistance Yes; measured skid number in the mid 40 s Noise Reduction Yes; noise reduced to dba

16 Did our overlay strategy meet our goals?: Objective #2: Less susceptible to premature distress we think so Higher AC content Less susceptible to premature aging & long-term raveling and failures Promotes bonding of thin layer Fineness Easy to place Less susceptible to physically segregate No segregation detected at construction

17 Did our overlay strategy meet our goals?: Objective #3: More cost effective: YES!!!

18 First Full Project: July 2010 Letting 13.4 miles Budget~ $4 million Spot repair and Overlay South bound: 3 main lanes & Inside shoulder

19 Pavement Condition Severe raveling due to end load segregation and low asphalt contents Fatigue cracking and failures due to stripping and debonding at the last overlay interface Raveling at the construction joints

20 Given the financial constraint of ~$4 million, performed a cost analysis to determine What overlay option would allow us to overlay the whole project What overlay option was appropriate for interstate applications Assumptions All unit prices based on SAC A aggregate and PG76-22 Unit price based on avg. low bid price at the time Assumed all other costs (spot repair, traffic control, stripping etc) being the same

21 Total Area of Overlay = 389,271 SY Approx. Budget ~ $ 4 million AUSTIN DISTRICT - LOW BID AVERAGE UNIT PRICE THICKNESS TOTAL OVERLAY OV COST TOTAL SY FOR ($/TON) (IN.) TONAGE COST PER SY COST $4,000,000 TFCO $ $1,857,796 $4.8 $3,946, PFC $ $2,363,718 $6.1 $4,461, UTBHMWC $ $2,431,614 $6.2 $4,529, D-GR TY C $ $2,806,391 $7.2 $4,904, SMA-C $ $4,028,955 $10.4 $6,126, Yes, more economical!

22 Original Condition: Severe raveling Fatigue cracking and failures Stripping and debonded OBSI = 104 dba (noisy) IRI = After Thin Overlay Hamburg = 5.3 mm Overlay Test = 450 Cycles Skid = OBSI = 98.5 dba IRI = 35-39

23 BEFORE AFTER

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25 Full implementation in the Austin District with SS 3226 New material not a true CMHB-F Modified Design Modified Gradation Different Material Requirements

26 Original Condition ¼ to ½ Rutting IRI = +100 Hamburg = OVT = 1000 cycles After Thin Overlay Fill in ruts in one pass IRI = 64-72

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31 PG requirement PG with 2.5% latex at AC = 6.5% Hamburg = 8.3 OVT = 1200 cycles IRI (before) = 72 IRI (after) = 53 (26% improvement)

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33 First project performed with trackless tack Great bond strength With high softening point, less susceptible to bleeding in hot weather like underseals

34 SH 71 Milling off high fatigued cracked thin HMA surface Place thin overlay on top of base and milled surface Possible structurally superior alternative to 2 CRST SAC B FM 3406 First SAC B+ project Dolomite Limestone Soundness less than 7

35 Thin Overlay Cost Savings (Mix Only) HWY CSJ Traditional TOM Cost Savings IH-35 (NB/SB) ,2 $3,368,927 $2,428,209 $940,719 RM $527,723 $397,704 $130,019 RM $534,237 $347,254 $186,983 SH $857,518 $557,387 $300,131 FM $663,835 $431,492 $232,342 US $1,235,276 $802,929 $432,347 FM $439,619 $285,753 $153,867 Total Expense $7,627,135 $5,250,728 Total Cost Savings $2,376,407 Percent Savings 31%

36 Application Design Production Construction Economics

37 Application Only use on pavements requiring surface course restoration Do not use as a structural overlay Avoid pavement structures needing extensive rehabilitation Not recommended over areas with cracks wider than ¼ inch or a rut deeper than ½

38 Design Use high quality aggregate (soundness loss < 20) PG or asphalt SBS or latex modified asphalt only! No recycled asphalt! Will not supply crack resistance Min. AC = 6.0% Design with TGC Use a balance performance design approach

39 Balanced Performance Mix Design R u t D e p t h ( m m ) Design material based on required performance High ADT/Loading with significant structure (i.e.: IH-35) Low to Moderate ADT/Loading with thin structure (i.e.: RM 32) Rut Depth (mm) Overlay (PassesX100) O v e r l a y ( P a s s e s X ) AC Content (%)

40 Production Keep plant clean to prevent clumps = Pop outs Load Temperatures = ºF

41 Construction - Preparation Best Practice: Perform crack sealing and spot repair in highly distressed areas Milled-in shoulder texturing and raised profile markings will reflect through remove or fill Mill and fill spot repair areas with a fine dense graded mix Helps match the existing surface Promotes better ride with a thin overlay Surface must be VERY clean before placement Excessive dirt or dust may cause bonding issues with a thin overlay

42 Construction Seal & Bond Bond is critical for thin overlays Thin Overlay Mix (TOM) is fairly open graded, so a good seal is important to prevent moisture infiltration

43 Construction Seal & Bond Best Practices Light aggregate rates when using underseals Prefer heavy tacks - prevent bonding issues in areas with too much aggregate Windrow and transfer material with a shuttle buggy in the adjacent lane VERY clean surface to promote good bonding Take cores to verify bond and thickness

44 Thin Overlay did not bond to the traffic loops! Mill them out!!

45 Construction Placement Temperature 1 Thin overlay cools twice the rate of a 1.5 mat What are the challenges with placement temperature? What practices have you implemented to address these challenges?

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47 Best Practice: Place when ambient temp. 70º F or greater Use a shuttle buggy to maintain temperature Use insulated truck and trapped WMA additive helped as a compaction aid in cooler temperatures District may require WMA for hauls greater than 50 miles

48 Construction Placement & Compaction Best Practices Similar to PFC Limits hand work Irregularities shows up more dramatically in thin overlays No pneumatics Closes surface Macrotexture for skid resistance is diminished Cools too quick to take out impressions Rollers should be right behind the paver Harsh mix and cools quickly

49 Economics (Material Cost Only) Unit cost for TFCO increasing due to asphalt and aggregate increased costs ($100/ton) Still Cheaper than conventional mixes, especially given the longer design life: 2 TY C PG $7.15/SY (with recycled asphalt) 1.5 PFC PG $6.75/SY 1.5 TY D PG $5.60/SY (with recycled asphalt) TFCO PG $5.50/SY

50 Same as SS 3226, except: Allows blending of SAC A & B aggregates SAC B+: Soundness less than 20% loss Add Overlay Test requirement of min. 500 cycles Add tolerance limit of ¼ on the thickness Add requirement of a min. of 30 second permeability, especially when low density is suspected Pay for asphalt and aggregate separately

51 Met our goals and objectives of developing a new non-structural overlay option that is: More economical Big bang for the Buck Enables the District to cover more with less and for less Equal or better performance Less susceptible to premature distress Hopefully lower long-term maintenance costs

52 Touchdown!! Hook em Horns!!