PPTG PPTG Thin Overlays Task GroupThin Overlays Task Group

(TOADS)(TOADS)Team Overlay Asphalt DebatersTeam Overlay Asphalt Debaters

Presented byPresented by

Basem Muallem (CT) - Tony Limas (Industry)Basem Muallem (CT) - Tony Limas (Industry)April 19, 2005April 19, 2005

Toads Initial MeetingsToads Initial Meetings

Caltrans co chairCaltrans co chair– Bill MosesBill Moses

Elected industry co chairs Elected industry co chairs – Skip Brown (no relation to Lance)Skip Brown (no relation to Lance)– Tony Limas (Back Up)Tony Limas (Back Up)

Toads Initial MeetingsToads Initial Meetings

Requested input from TG membersRequested input from TG members– Outlined issues and priorities Outlined issues and priorities – Proposed changes to specificationsProposed changes to specifications– Discuss current state of pavements in CADiscuss current state of pavements in CA

TOADS TOADS Initial Work PlanInitial Work Plan

Prioritize the IssuesPrioritize the IssuesSet time tables to address issuesSet time tables to address issuesTG to provide recommendations to TG to provide recommendations to CaltransCaltransCaltrans shall consider and approve Caltrans shall consider and approve several recommendations to be successful several recommendations to be successful with thin lift pavementswith thin lift pavementsSafety for the public and employees will be Safety for the public and employees will be enhancedenhanced

Issues Received from Task GroupIssues Received from Task GroupIssue:Issue:

Specifications require maximum aggregate size Specifications require maximum aggregate size in HMA mixture too large for specified lift in HMA mixture too large for specified lift thickness resulting in mat segregation and thickness resulting in mat segregation and excessive in-place air voidsexcessive in-place air voids

Recommendation:Recommendation: Select maximum aggregate size in accordance Select maximum aggregate size in accordance

with industry standards to:with industry standards to:

– Attain target air voids to slow oxidation and reduce stripping Attain target air voids to slow oxidation and reduce stripping potentialpotential

– Reduce permeability in mat and at jointsReduce permeability in mat and at joints– Minimize segregationMinimize segregation– Provide longer life pavements Provide longer life pavements

Industry StandardIndustry Standard

“ “if the nominal maximum if the nominal maximum aggregate size exceeds aggregate size exceeds one third of the one third of the compacted lift thickness compacted lift thickness of the pavement layer, of the pavement layer, the surface texture of thethe surface texture of the

mix can be affected, and the degree of density mix can be affected, and the degree of density of the mix obtained by compaction may be of the mix obtained by compaction may be reduced.” reduced.”

Industry StandardIndustry Standard

“ “the layer thickness the layer thickness should be should be should be should be equal to or greater equal to or greater than three times the than three times the nominal maximum nominal maximum aggregate size.”aggregate size.”

Recommended Lift Thickness for Recommended Lift Thickness for Quality Pavements Quality Pavements

19-mm Maximum Medium requires a 57-mm to 76-mm lift 19-mm Maximum Medium requires a 57-mm to 76-mm lift thickness thickness

12.5-mm Maximum Medium requires a 38-mm to 50-mm 12.5-mm Maximum Medium requires a 38-mm to 50-mm lift thicknesslift thickness

9.5-mm Maximum requires a 29-mm to 38-mm lift 9.5-mm Maximum requires a 29-mm to 38-mm lift thicknessthickness

Issues ContinuedIssues Continued

Issue:Issue: Newer non-nuclear (electrical impedance) Newer non-nuclear (electrical impedance)

density gauges are replacing nuclear density density gauges are replacing nuclear density gauges in the industry. Caltrans does not allow gauges in the industry. Caltrans does not allow the use of the newer non-nuclear gauges. the use of the newer non-nuclear gauges.

RecommendationRecommendation Caltrans should seriously consider adopting Caltrans should seriously consider adopting

existing test procedures and modify existing test procedures and modify specifications to accept the use of non-nuclear specifications to accept the use of non-nuclear density gauges. density gauges.

Issues ContinuedIssues Continued

Issue: Issue:

Contractors are not using pneumatic tire rollers Contractors are not using pneumatic tire rollers on thin lift overlays when paving over rutted on thin lift overlays when paving over rutted and/or uneven substrates.and/or uneven substrates.

Recommendation: Recommendation:

Encourage the utilization of pneumatic tire rollers Encourage the utilization of pneumatic tire rollers on thin lift overlays (Except for ARHM) when on thin lift overlays (Except for ARHM) when paving over a rutted and/or uneven substrates.paving over a rutted and/or uneven substrates.

Issues ContinuedIssues Continued

Issue:Issue: HMA bid quantities are based on the specified HMA bid quantities are based on the specified

lift thickest resulting in significant underuns and lift thickest resulting in significant underuns and insufficient layer thickness when the pavement insufficient layer thickness when the pavement substrate is rutted or uneven. substrate is rutted or uneven.

Recommendation: Recommendation: Base bid quantities on the thinnest or median lift Base bid quantities on the thinnest or median lift

thickness anticipated to eliminate significant thickness anticipated to eliminate significant underuns.underuns.

Issues ContinuedIssues Continued

Issue:Issue:

The single ambient temperature spec (50The single ambient temperature spec (50°F °F min.min.) is not (by itself) adequate to determine if ) is not (by itself) adequate to determine if there will be adequate time to compact the there will be adequate time to compact the pavement to the desired density (in-place air pavement to the desired density (in-place air voids). voids).

Recommendation:Recommendation:

Include other factors to determine if the Include other factors to determine if the compaction window is reasonable.compaction window is reasonable.

Other factors should include: Other factors should include: mix temperaturemix temperature

substrate temperaturesubstrate temperature

ambient temperatureambient temperature

wind velocitywind velocity

lift thickness lift thickness

MultiCool Software Program MultiCool Software Program computes the time available computes the time available for compaction.for compaction.

Example:Example: 300 300 °° F. mix temperature F. mix temperature

5050°F substrate temperature°F substrate temperature

5050°F ambient temperature°F ambient temperature

5 MPH wind5 MPH wind

2-inch Lift (Time VS. Temp)2-inch Lift (Time VS. Temp)03001281.42269.853260.974253.435246.746240.667235.078229.9

9225.0910220.5811216.3612212.3913208.6414205.115201.7616198.5817195.56

18192.6919189.9620187.3521184.8622182.4823180.2124178.0225175.93

1-inch Lift (Time VS. Temp)1-inch Lift (Time VS. Temp)0

3001

265.482

244.423

228.774

216.285

205.966

197.237

189.728

183.179

177.39

A 2-inch lift takes approximately 25 minute to reach cessation temperature

A 1-inch lift takes approximately 10 minutes to reach cessation temperature

Under Similar Conditions:

Other Considerations for Thin Lift AC Other Considerations for Thin Lift AC Paving:Paving:

– Coordinate truckingCoordinate trucking– Consider changing initial compaction Consider changing initial compaction

temperatures temperatures – Include CQS1H in specs for a tack coatInclude CQS1H in specs for a tack coat– Review all thin lift specs for needed Review all thin lift specs for needed

improvementsimprovements– Remove automatic screed control Remove automatic screed control

requirements for thin lift overlays with the requirements for thin lift overlays with the exception of the joint matcherexception of the joint matcher

Gather Existing Best Practices Gather Existing Best Practices for Thin Lift Pavingfor Thin Lift Paving

Utilize Existing Experiences from:Utilize Existing Experiences from:– FHWAFHWA– Other DOTOther DOT– Super PaveSuper Pave– PG BindersPG Binders– NCPPNCPP– NCATNCAT– TRBTRB

TOADS MISSIONTOADS MISSION

Bring Added Value to our State by:Bring Added Value to our State by:

– Constructing longer lasting Pavements Constructing longer lasting Pavements

– Reducing cone zone daysReducing cone zone days

– Making California pavements saferMaking California pavements safer

– Makes the movement of goods and services more Makes the movement of goods and services more efficient. (Vital to California's Economy)efficient. (Vital to California's Economy)

Thank you, and be safe!Thank you, and be safe!

Questions?