Bituminous Street RecertificationBituminous Street Recertification

InitiativesInitiatives

Initiative ItemsInitiative Items

Stone Matrix Asphalt (SMA)Stone Matrix Asphalt (SMA) Longitudinal Joint Spec and other methods Longitudinal Joint Spec and other methods

for longitudinal joint improvement.for longitudinal joint improvement. Asphalt Film Thickness SpecificationAsphalt Film Thickness Specification

Stone Matrix Asphalt (SMA)Stone Matrix Asphalt (SMA)or or

Stone Mastic AsphaltStone Mastic Asphalt

SMASMA

““Premium” mix based on European Premium” mix based on European TechnologyTechnology

Designed for high trafficDesigned for high traffic Gap graded skeleton of high quality Gap graded skeleton of high quality

aggregate carries the load (55-80% +No.4)aggregate carries the load (55-80% +No.4) Mastic consisting of asphalt (+6%), fines Mastic consisting of asphalt (+6%), fines

(8-12%), and fibers fill the voids.(8-12%), and fibers fill the voids.

Why SMA?Why SMA?

High stability with rutting and deformation High stability with rutting and deformation resistance.resistance.

Increased durability (high binder content)Increased durability (high binder content) Good frictional propertiesGood frictional properties Reduced water sprayReduced water spray Lower traffic noiseLower traffic noise

BackgroundBackground

SMA was designed in Germany in the 1960’s as SMA was designed in Germany in the 1960’s as an overlay that would be resistant to studded tire an overlay that would be resistant to studded tire damage.damage.

SMA is widely used in Germany, the Netherlands, SMA is widely used in Germany, the Netherlands, and Scandinavia as an overly or surface course to and Scandinavia as an overly or surface course to resist load-induced rutting and studded tire resist load-induced rutting and studded tire damage.damage.

SMA introduced in the US in 1990.SMA introduced in the US in 1990.– 2 Projects in Minnesota in early 90’s; Lake City and 2 Projects in Minnesota in early 90’s; Lake City and

TH 169.TH 169.

How is SMA Different?How is SMA Different?

GradationGradation Asphalt ContentAsphalt Content Dust ContentDust Content Stabilizing AdditivesStabilizing Additives

Filler SiloFiller Silo

Filler SiloFiller Silo

FiberFiber

FiberFiber

Applications for SMAApplications for SMA

High Traffic Volume Premium Surface MixtureHigh Traffic Volume Premium Surface Mixture– Ensure stone-on-stone contactEnsure stone-on-stone contact

– Increase film thickness masticIncrease film thickness mastic» Working together to provide long term pavement durabilityWorking together to provide long term pavement durability

IntersectionsIntersections Round-aboutsRound-abouts Container facilitiesContainer facilities

SMA Overlays of PCCSMA Overlays of PCC

High film thickness and gap graded High film thickness and gap graded structure helps to retard reflective cracking.structure helps to retard reflective cracking.

Polymer-modified binders add additional Polymer-modified binders add additional elasticityelasticity

High film thickness reduces raveling when High film thickness reduces raveling when reflective cracks occur.reflective cracks occur.

Pilot SMA SpecificationPilot SMA Specification Use of a mineral filler.Use of a mineral filler. Require Require use of asphalt stabilizer (fibers). use of asphalt stabilizer (fibers). 100 design gyrations, 16% VMA, 4% voids.100 design gyrations, 16% VMA, 4% voids. Minimum asphalt set by combined aggregate Minimum asphalt set by combined aggregate

specific gravity.specific gravity. Minimum asphalt grade, PG 70-28Minimum asphalt grade, PG 70-28 Require bulking of cores by Corelok method. Require bulking of cores by Corelok method. Test strip required.Test strip required. Minimum mat density, 94.0% of Gmm.Minimum mat density, 94.0% of Gmm.

TH 23 SMATH 23 SMA

I – 35 SMAI – 35 SMA

I – 35 SMAI – 35 SMA

I – 35 SMAI – 35 SMA

Mixing TempsMixing Temps

Supplier should provide Contractor with Supplier should provide Contractor with optimal mixing temperatures.optimal mixing temperatures.– Supplier had provided SMA producer on I-35 Supplier had provided SMA producer on I-35

with the mixing temperatures, but, ….with the mixing temperatures, but, …. Generally speaking, mixing temperatures Generally speaking, mixing temperatures

above 325F are rare.above 325F are rare.– But, this is determined between Supplier and But, this is determined between Supplier and

Contractor. Contractor. – However, if you are aware of Contractor However, if you are aware of Contractor

mixing above 325F, contact Bituminous Office mixing above 325F, contact Bituminous Office or Chem Lab immediately. or Chem Lab immediately.

Typical HMA Plant Mixing Typical HMA Plant Mixing TemperaturesTemperatures

PG 58-28PG 58-28– 260 to 310 F260 to 310 F

PG 58-34PG 58-34– 260 to 310 F260 to 310 F

PG 64-28PG 64-28– 265 to 320 F265 to 320 F

PG 64-34PG 64-34– 265 to 320 F265 to 320 F

PG 70-28PG 70-28– 275 to 325 F275 to 325 F

Methods to Improve Methods to Improve Longitudinal Joint PerformanceLongitudinal Joint Performance

In Minnesota:In Minnesota:– Joint AdhesiveJoint Adhesive– Echelon Paving Echelon Paving – Longitudinal Joint Density RequirementLongitudinal Joint Density Requirement

LJ Deterioration LJ Deterioration (High Severity)(High Severity)

What are some causes of poor LJ What are some causes of poor LJ performance?performance?

LACK OF DENSITY AT (or near) THE COLD JOINTLACK OF DENSITY AT (or near) THE COLD JOINT» Less dense at longitudinal joints due to unconfined compaction at edge Less dense at longitudinal joints due to unconfined compaction at edge

of the first paver pass.of the first paver pass.

» Typically, 2-3% lower than mat densityTypically, 2-3% lower than mat density Cracking and RavelingCracking and Raveling

Improper Construction PracticesImproper Construction Practices» Raking of the jointRaking of the joint

» Overlapping of new mat with previously placed matOverlapping of new mat with previously placed mat

Longitudinal Joint DistressLongitudinal Joint Distress

Typically observed as cracking and raveling Typically observed as cracking and raveling along the centerline of the roadway.along the centerline of the roadway.– Cracks allow water to penetrate into the Cracks allow water to penetrate into the

underlying layers.underlying layers.– Raveling widens the crack and accelerates Raveling widens the crack and accelerates

overall damage to roadway.overall damage to roadway.

Joint AdhesiveJoint Adhesive

Tacking material for longitudinal cold Tacking material for longitudinal cold joints.joints.

Provides waterproofing and binding Provides waterproofing and binding membrane between adjacent mats.membrane between adjacent mats.

Typically, applied 1/8” thick over the face Typically, applied 1/8” thick over the face of the first pass.of the first pass.

TH 10 -- Joint Adhesive TH 10 -- Joint Adhesive (2001)(2001)

TH 10 -- Joint AdhesiveTH 10 -- Joint Adhesive

TH 10 -- Joint AdhesiveTH 10 -- Joint Adhesive

TH 10 -- Joint AdhesiveTH 10 -- Joint Adhesive

Joint Adhesive PerformanceJoint Adhesive Performance

Used on 4 mile test section on TH 10 near Used on 4 mile test section on TH 10 near Perham.Perham.

To date, both sections performing well.To date, both sections performing well.

Echelon PavingEchelon Paving

Side by side paving that allows construction Side by side paving that allows construction of a “hot” joint.of a “hot” joint.

Theoretically, will result in density of the Theoretically, will result in density of the longitudinal joint being equal to the density longitudinal joint being equal to the density of the adjacent mat.of the adjacent mat.

MnDOT Provision for Echelon MnDOT Provision for Echelon PavingPaving

……“……“The hot joint must be constructed by The hot joint must be constructed by having the second pass of bituminous having the second pass of bituminous placed within 10 minutes from the time the placed within 10 minutes from the time the first pass is placed.”first pass is placed.”

Echelon Paving -- TH 494Echelon Paving -- TH 494

Echelon PavingEchelon Paving

Echelon PavingEchelon Paving

Longitudinal Joint Density Longitudinal Joint Density SpecificationSpecification

Pilot specificationPilot specification– Improve performance of longitudinal joints.Improve performance of longitudinal joints.

» Improve long term performance of the roadway.Improve long term performance of the roadway.

– Require cores to be taken adjacent to joint.Require cores to be taken adjacent to joint.– Includes Incentive/disincentiveIncludes Incentive/disincentive

Joint Density LotsJoint Density Lots

Joint density will be evaluated on 20% of Joint density will be evaluated on 20% of the lots established for mat density.the lots established for mat density.– So, for 1-5 (mat) density lots there would be 1 So, for 1-5 (mat) density lots there would be 1

lot/day where joint density would be evaluated.lot/day where joint density would be evaluated.– If 6 (mat) density lots (>5,000 tons/day), 2 If 6 (mat) density lots (>5,000 tons/day), 2

lots/day for joint density evaluation.lots/day for joint density evaluation. The Engineer will randomly determine, at The Engineer will randomly determine, at

the end of the day, which lot(s) will be the end of the day, which lot(s) will be evaluated for LJ density.evaluated for LJ density.

Longitudinal Jt. Coring Longitudinal Jt. Coring LocationsLocations

In addition to the 3 cores/lot for mat density In addition to the 3 cores/lot for mat density determination, an additional 3 cores/lot will be determination, an additional 3 cores/lot will be taken for evaluation of longitudinal joint density.taken for evaluation of longitudinal joint density.– 1 core on right side of the mat1 core on right side of the mat

– 1 core on left side of the mat1 core on left side of the mat

– 1 companion core for the dot1 companion core for the dot

Cores are cut within 6 inches from the edge of the Cores are cut within 6 inches from the edge of the top of the mat for both confined and unsupported top of the mat for both confined and unsupported edges.edges.

LJ Density RequirementsLJ Density Requirements

Percent Density for:Percent Density for:– Confined Edge -- (2.5% lower than mat density)Confined Edge -- (2.5% lower than mat density)– Unsupported Edge -- (5.5% lower than mat Unsupported Edge -- (5.5% lower than mat density)density)

Incentives included in specificationIncentives included in specification

District 7 --TH 19 District 7 --TH 19

TH 19 – Core LocationTH 19 – Core Location

TH 19 -- 4 RollersTH 19 -- 4 Rollers

District 4 --TH 32District 4 --TH 32

District 4 --TH 32District 4 --TH 32

District 7 --TH 22District 7 --TH 22

Asphalt Film ThicknessAsphalt Film Thickness

Why AFT?Why AFT?– VMA does not ensure adequate film thickness. VMA does not ensure adequate film thickness.

» VMA is based on maximum aggregate size, not the overall VMA is based on maximum aggregate size, not the overall gradation. gradation.

VMA = VVMA = Vbebe + V + Vaa

AFT = VAFT = Vbebe/SA; where SA represents gradation/SA; where SA represents gradation

– As SA increases, the VAs SA increases, the Vbe be must also increase in order to must also increase in order to

maintain AFT.maintain AFT.

– F/A is a design consideration only and there is not F/A is a design consideration only and there is not necessarily a correlation between F/A and AFT.necessarily a correlation between F/A and AFT.

Why AFT ?Why AFT ?

Minimum AC ContentMinimum AC Content– Doesn’t account for changes in AC absorption.Doesn’t account for changes in AC absorption.– Doesn’t account for changes in gradation or Doesn’t account for changes in gradation or

surface area.surface area.– Doesn’t account for changes in aggregate SpG.Doesn’t account for changes in aggregate SpG.

» Lighter aggregate has more surface area per pound.Lighter aggregate has more surface area per pound.

Why AFT ?Why AFT ?

Minimum VMAMinimum VMA– Accounts for AC absorption, butAccounts for AC absorption, but– Doesn’t have a good correlation with changes Doesn’t have a good correlation with changes

in aggregate surface area.in aggregate surface area.– Often encourages addition of sand to increase Often encourages addition of sand to increase

VMA.VMA.» Addition of sand usually reduces AFT.Addition of sand usually reduces AFT.

Why AFT ?Why AFT ?

Minimum AFTMinimum AFT– Accounts for AC absorptionAccounts for AC absorption– Has a direct correlation with calculated surface Has a direct correlation with calculated surface

area.area.

Asphalt Film ThicknessAsphalt Film Thickness

2005 Projects2005 Projects– District 3:District 3: TH 94TH 94– District 6:District 6: TH 218TH 218– District 8:District 8: TH 9TH 9– Metro:Metro: TH 25TH 25

» 2004 Project2004 Project District 2:District 2: TH 11TH 11

AFT for 2006AFT for 2006

Continue AFT Pilots in each of the Districts.Continue AFT Pilots in each of the Districts. Development of the “next phase” AFT.Development of the “next phase” AFT.

– No tie to VMA.No tie to VMA.– Pay tied to individual and moving average AFT.Pay tied to individual and moving average AFT.– Broadband gradation requirements.Broadband gradation requirements.

Questions ?Questions ?