LIME IN HOT MIX ASPHALT THE TEXAS EXPERIENCE. Darren Hazlett P.E. Retired Director Texas Department of Transportation Construction Division

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1 LIME IN HOT MIX ASPHALT THE TEXAS EXPERIENCE Darren Hazlett P.E. Retired Director Texas Department of Transportation Construction Division

2 Population 28 million

3 Texas Department of Transportation is responsible for 190,000 lane miles of roadway

4 856 miles/1377 km

5 896 miles/1442 km

6 Austin

7 University of Texas State Capitol

8 Population: 1 Million

9 Use of Hydrated Lime in Hot Mix Asphalt - USA - Hydrated Lime in Hot Mix Asphalt Use lime all mixes Use lime some mixes No lime or unknown 17

10 What is the Magnitude? Texas Department of Transportation Use of Lime in HMA Approximately 25% of HMA contains Lime In the last 12 months TxDOT contracted for 8.5M tons (7.7Mt) of HMA This translates to 80,000 tons (72Kt) of lime for HMA Estimated that private/other-entity work doubles these numbers US HMA production is 370M tons with average 10% lime using lime

11 Texas DOT Specs for Antistrip Agent Determine the dosage needed to achieve the moisture resistance requirements during design if an antistripping agent is required. Use this addition rate in the production mixture. Add between 0.5% and 2.0% of hydrated lime or commercial lime slurry solids by weight of the individual aggregate treated when using lime. Add liquid antistripping agent, when used, to the binder, in accordance with the manufacturer s instructions. Do not exceed the manufacturer s maximum recommended dosage rate.

12 Texas DOT Specs for Antistrip Agent Lime. Incorporate lime in a manner that thoroughly and uniformly distributes lime onto the aggregate surface or into the mixture. Use metering equipment, as approved, to ensure the required quantity of lime is used. Hydrated Lime. Add hydrated lime to the aggregate by one of the following methods, unless otherwise shown on the plans: Mix in an approved pug mill mixer with damp aggregate containing water at least 2% above saturated surface dry conditions. Add into the drum-mix plant immediately before asphalt binder addition or in the pug mill of the weigh-batch plant before asphalt binder addition. Dry mix aggregates and lime before adding asphalt binder when a weigh batch plant is used. Commercial Lime Slurry. Add commercial lime slurry to the aggregate by one of the following methods unless otherwise shown on the plans: Mix in a suitable pug mill mixer with the aggregate. Mix with aggregate between the plant cold feeds and the dryer or mixing drum during mixture production.

13 Hydrated Lime can Address (I will Talk About These) Moisture Sensitivity (Stripping) Moisture Sensitivity and Rutting Binder Hardening (Oxidation) Where are we now in Texas

14 Moisture Sensitivity (Stripping) Boil Test AASHTO T-283 History

15 Moisture Sensitivity AASHTO T-283 Empirical test used to characterize aggregates Passing threshold 80% TSR TSR (%) Alabama California Illinois South Carolina Texas Un-treated Liquid Lime Ref: Sebaaly, et al 147

16 In the Past Up until the late 1990 s TxDOT was experiencing approximately 3 premature failures per year related to stripping and/or rutting Conventional tests such as T-283, Hveem Stability, Boil Test, Static Creep etc. did not show a very good correlation with performance. Mixes would pass all of these tests yet fail on the roadway Two extensive field studies showed that AASHTO T-283 (Tex-531-C) did a poor job identifying mixtures susceptible to moisture damage CTR Study: 8 TxDOT Districts, 92 test sections TTI Study: 3 Districts, over 35 pavements

17 Moisture Sensitivity & Rutting Hamburg Wheel Tracking Device

18 Typical Test Results Rut Depth Creep Slope Stripping Inflection Point (SIP) Stripping Slope Number of Failure Number of Passes

19 Moisture Sensitivity/ Rutting (1) Hamburg Wheel - Corpus Christi Gravel Rut Depth, mm Number Passes (X1000) Ref: Texas Department of Transportation No Additive Liquid Hydrated Lime

20 Moisture Sensitivity/Rutting (2) Hamburg Wheel - Basalt Mixtures Rut Depth, mm Number Passes (X1000) Ref: Texas Department of Transportation No Additive Liquid Hydrated Lime

21 Stripping Susceptible Mix

22 Investigations Different Aggregate, Same Binder

23 Rutting: mm # of Passes: 18,900* Temp: 50C District: W.Falls Mix Type: Stone Filled(0.5) Binder: Aggr.: Limestone Additive: Lime (2%) ID:

24 Rutting: 2.9 mm # of Passes: 20,000 Temp: 50C District: W.Falls Mix Type: Stone Filled(0.5) Binder: Aggr.: Granite+ Additive: Lime(1%) ID:

25 Investigations Same Aggregate, Different Binder Source

26 Rutting: 12.5 mm # of Passes: 10,200 Temp: 50C District: Abilene Mix Type: Superpave Binder: (Source 1) CSJ: Aggr.: Limestone Additive: None ID: Lab Mix Notes:

27 Rutting: 2.8 mm # of Passes: 20,000 Temp: 50C District: Abilene Mix Type: Superpave Binder: (Source 2) CSJ: Aggr.: Limestone Additive: None ID: Lab Mix Notes:

28 What Does the Hamburg Test Tell Us? Hamburg is a torture test that is an indicator of a hot mix paving mixture s susceptibility to premature failure that may be attributed to factors including: A weak aggregate structure Inadequate binder stiffness Moisture Damage (Lime still proves an almost universal antistrip agent.) Inadequate binder to aggregate adhesion Murphy s Law, etc, etc, etc.

29 BINDER HARDENING (OXIDATION)

30 Effect of HL on Asphalt Binder Hardening Utah DOT Field Study 6000 Viscosity (60C), Stokes Time in Years No Additive Hydrated Lime Ref. Jones, 1997

31 How do you Specify Lime for Oxidation Resistance? Each combination of lime and asphalt react differently Can t quantify the effect and put it in a binder specification Could we just say to use lime because we know it is beneficial? (Some TxDOT engineers specify lime as a mineral filler because they know they get higher performing mixtures.)

32 Where Are We Now in Texas? (Unintended Consequences) We have solved some problems. We have created other problems It is COMPLICATED

33 What have we learned about Hamburg testing Hamburg does a better job of identifying mixtures that are susceptible to premature failure (T-283, Hveem, Creep, etc.) Higher (stiffer) PG grade binders do better Adding liquid antistrips or lime usually improves the Hamburg results Harder aggregates do better (Igneous -Vs- limestone) Stone on stone mixes do better than dense mixes There are no absolutes... Do not assume... Measure!

34 The Present We have Solved Some Problems Stripping and rutting problems have decreased dramatically (To practically ZERO) The Hamburg Wheel has proven to be the best identifier of mixtures susceptible to premature failure

35 TxDOT HMA Specifications Superpave and TxDOT Traditional Dense Graded Mixtures Hamburg in Design Hamburg in Production Treatment, if needed, is contractor s choice (lime or liquid) Lime may be specified as a mineral filler Permeable Friction Course and Stone Matrix Asphalt Mixtures Hamburg in Design Hamburg in Production Lime is required (may use liquid also) Use either o o PG 76, fibers, and lime, or Asphalt Rubber Binder and lime.

36 TxDOT Specifications Grade 12.5 mm rut PG 64 10,000 PG 70 15,000 PG ,000

37 We have Created Other Problems Hamburg only tells one side of the story Rutting resistance - versus- Fatigue cracking Fatigue cracking is increasingly becoming our biggest problem! Relatively thin (and overly stiff) layers of hot mix placed on flexible base can be a recipe for disaster Thick and stiff (OK) Thin and flexible (OK) Thin and stiff (no good)

38 TxDOT Funding Problems Pennies to the Pavement ( ) Reduce Cost of HMA. Discourage requiring lime as a mineral filler Binder substitution More RAP Use RAS Thin up overlays

39 The Complicated Part (How to Increase Hamburg Passes) Change Aggregate (Use Harder Aggregates) Change Mix Type or Gradation (More Stone on Stone Contact) Use Antistrip Agents (Lime/Liquid Agents) Lime Works Almost Universally. Some Liquid agents soften the binder Change Asphalt (Some Asphalts are Better) Reduce Asphalt Content

40 Fixing The Problem In addition to Volumetrics In addition to Hamburg Need another test to guard against mixtures being brittle and prone to cracking

41 Balanced Mix Design Semi-Circular Bend Test (SCB) Beam Fatigue Test Others Texas Overlay Test

42 Overlay Test Troxler Instrotek AMPT 174

43 Balanced Mix Design Approach HWT OT Number of Passes (12.5 mm Rut Depth) y = x R 2 = y = 2E-07x R 2 = OT Number of Cycles Asphalt Content (%)

44 Conclusions & The Future Lime has beneficial effects when added to HMA TxDOT has found lime to be almost universal in its ability to prevent stripping in HMA Use of the Hamburg Wheel Test by DOTs is growing Many DOTs are investigating balance mix design to protect against rutting and cracking

45 Who says Concrete does not Rut?

46 Thank You