LIME IN HOT MIX ASPHALTTHE TEXAS EXPERIENCE

Darren Hazlett P.E.Retired Director

Texas Department of TransportationConstruction Division

Population 28 million

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

of roadway

856 miles/1377 km

896 miles/1442 km

Austin

University of Texas

State Capitol

Population: 1 Million

17

Use lime all mixesUse lime some mixesNo lime or unknown

Use of Hydrated Lime in Hot Mix Asphalt - USA -

Hydrated Lime in Hot Mix Asphalt

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

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.

Texas DOT Specs for Antistrip AgentLime. 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.

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

Moisture Sensitivity (Stripping)

•Boil Test•AASHTO T-283•History

147

Moisture SensitivityAASHTO T-283

Empirical test used to characterize aggregates

Passing threshold – 80% TSR

TSR (%) Alabama California Illinois South Carolina Texas

Un-treated 81 72 82 61 61

Liquid 83 91 85 81 100

Lime 90 95 87 87 98

Ref: Sebaaly, et al

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, HveemStability, 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 AASHTOT-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

Moisture Sensitivity & RuttingHamburg Wheel Tracking Device

Typical Test Results

Number of Passes

Rut

Dep

th

Creep Slope

Stripping Inflection Point

(SIP)

Stripping Slope

Number of Passes @ Failure

02468

1012141618

0 2 4 6 8 10 12 14 16 18 20

Number Passes (X1000)

Rut

Dep

th, m

m

No AdditiveLiquidHydrated Lime

Moisture Sensitivity/ Rutting (1) Hamburg Wheel - Corpus Christi Gravel

Ref: Texas Department of Transportation

Moisture Sensitivity/Rutting (2) Hamburg Wheel - Basalt Mixtures

02468

1012141618

0 2 4 6 8 10 12 14 16 18 20

Number Passes (X1000)

Rut Dep

th, mm

No AdditiveLiquidHydrated Lime

Ref: Texas Department of Transportation

Stripping Susceptible Mix

Investigations

Different Aggregate, Same Binder

District: W.Falls Mix Type: Stone Filled(0.5) Binder: 76-22

Aggr.: Limestone Additive: Lime (2%) ID: 540010

Rutting: 12.5+ mm # of Passes: 18,900* Temp: 50C

District: W.Falls Mix Type: Stone Filled(0.5) Binder: 76-22

Aggr.: Granite+ Additive: Lime(1%) ID: 540027

Rutting: 2.9 mm # of Passes: 20,000 Temp: 50C

Investigations

Same Aggregate, Different Binder Source

Rutting: 12.5 mm # of Passes: 10,200 Temp: 50C

District: Abilene Mix Type: Superpave Binder: 76-22 (Source 1)

CSJ: 0068-07-046 Aggr.: Limestone Additive: None

ID: 01500318 Lab Mix Notes:

Rutting: 2.8 mm # of Passes: 20,000 Temp: 50C

District: Abilene Mix Type: Superpave Binder: 76-22 (Source 2)

CSJ: 0068-07-046 Aggr.: Limestone Additive: None

ID: 01500380 Lab Mix Notes:

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.

BINDER HARDENING(OXIDATION)

Effect of HL on Asphalt Binder HardeningUtah DOT Field Study

0

1000

2000

3000

4000

5000

6000

0 1 2 3 4 5 6 7 8

Time in Years

Visc

osity

(60C

), St

okes

No Additive Hydrated Lime

Ref. Jones, 1997

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.)

Where Are We Now in Texas?(Unintended Consequences)

• We have solved some problems.• We have created other problems• It is COMPLICATED

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!

The PresentWe have Solved Some Problems

• Stripping and rutting problems have decreaseddramatically (To practically ZERO)

• The Hamburg Wheel has proven to be the best identifier of mixtures susceptible to premature failure

TxDOT HMA Specifications

Superpave and TxDOT Traditional Dense Graded Mixtures

Permeable Friction Course and Stone‐Matrix Asphalt 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

• Hamburg in Design• Hamburg in Production• Lime is required (may 

use liquid also)• Use either

o PG 76, fibers, and lime, oro Asphalt‐Rubber Binder and lime.

TxDOTSpecifications

Grade Passes @ 12.5 mm rut

PG 64 10,000

PG 70 15,000

PG 76 + 20,000

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)

TxDOT Funding ProblemsPennies to the Pavement

(2010-2014)• Reduce Cost of HMA.

– Discourage requiring lime as a mineral filler– Binder substitution– More RAP– Use RAS– Thin up overlays

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

Fixing The Problem

• In addition to Volumetrics• In addition to Hamburg• Need another test to guard against mixtures

being brittle and prone to cracking

Balanced Mix Design

• Semi-Circular Bend Test (SCB)• Beam Fatigue Test• Others• Texas Overlay Test

Overlay Test

174

Instrotek AMPT

Troxler

Balanced Mix Design Approach

y = 2E-07x12.635

R2 = 0.9829

y = 698467x-2.4408

R2 = 0.9505

0

5000

10000

15000

20000

25000

4.0 4.5 5.0 5.5 6.0 6.5 7.0Asphalt Content (%)

Num

ber o

f Pas

ses

(12.

5 m

m R

ut D

epth

)

0

500

1000

1500

2000

2500

3000

3500

4000

4500O

T Num

ber of Cycles

HWTOT

5.3

300

5.7

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

Who says Concrete does not Rut?

Thank You