WisDOT Base Aggregate Density Program

Midwest Geotechnical ConferenceIndianapolis, IndianaSeptember 22, 2015

Bob Arndorfer

Historical Practice Research Study/Findings Goals/Benefits Development and Highlights of New

Specification Pilot Projects Issues/Modifications Necessary Moving Forward

WisDOT Base Density Outline

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Where we were 3 years ago Observational Method

Compact “until there is no appreciable displacement either laterally or longitudinally, under the compaction equipment.”

Somewhat Vague Have Been Attempts to Reduce Subjectivity – Limited Success

History of WisDOT Base Density

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Subjective – No Consistent Method of Acceptance

No Documentation During Construction Non-uniform Compaction Results Issues Raised by Paving Contractors Other States Using More Advanced Means

Issues With Old Method

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Department Goal - Move to Performance Specs For Material Acceptance Qual Mgmt Program (QMP) - Contractor tests/monitorReduces Departmental oversight and staff timeGive contractor more control of their operations

Ultimate Goal: Increase Pvmt. Performance

Based on all this – Department Decided toHave Some Research Done on This Topic

Issues Cont’d.

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Many National Studies Using Different DevicesDynamic Cone Penetrometer (DCP)Lightweight Deflectometer (LWD) Intelligent CompactionGeogaugeNuclear GaugeSand ConeOther

Other Base Density Methods

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Investigate the Effectiveness of Our Current Methods, Survey Other States, Layout Future

Titled: ‘Feasibility Analysis of Base Compaction Specification’

Completed in 2012 by University of Wisconsin- Milwaukee (PI was Professor Hani Titi)

Investigated 11 Existing, and 10 New, HMA Pavement Projects

Look at Current, and Long-term, Base Performance

WisDOT Research Study

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Projects Located in Various Geographic and Geologic Regions of the State

ME Sensitivity Analysis Using DARWin-ME Investigate Density-based and Modulus-based

Methods Look at Cost Implications of Differing

Compaction Methods

Research Study – Cont’d.

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Investigate Project Material Records Investigative Methods on Existing Projects

FWDVisual Pavement Distress Surveys

Investigative Methods on Current ProjectsLightweight DeflectometerDynamic Cone PenetrometerSand ConeGeogaugeLab Tests including Resilient Modulus

Research Study – Methods

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Out of 49 States and 13 Canadian Ministries, Only 4 Use Subjective Observation Methods for Acceptance – WI Was One of Four

Over 90% of the 63 Contacted Highway Agencies Used Density-Based Methods for Quality Control of Aggregate Bases

Major Findings of Research

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71% of Highway Agencies Follow ASTM or AASHTO Test Methods

63% Use Nuclear Density Test Measurements 44% Use Standard Proctor for Max Density -

Target Density: 95-100% 27% Use Modified Proctor for Max Density -

Target Density: 90-100%

Major Findings – Cont’d.

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High Variability of WI Bases Being PlacedField DensityMoisture

HMA Pavement Performance Was Related to Spatial Variability and Non-uniform Density of Base Course

Well Performing HMA Pavements Exhibited Low Levels of Spatial Variability and Good Uniformity in Aggregate Base Courses

Major Findings – Cont’d.

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The Uniformity of Base Density Appears to be More Critical Than Level of Compaction

Mechanistic-Empirical (ME) Sensitivity Analysis Showed Reduced Life (Increased distress levels) in Pavements With Lower Base Modulii

Base Density Work on 63% of Projects Had No Significant Impact on Project Schedules

53% of Responding Agencies Reported Density Implementation Has No Cost Impacts on Projects

.

Major Findings – Cont’d.

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42% of Highway Agencies are Looking for New Methodologies to Replace/Complement Their Current Density-Based Specifications

Recommend Quantitative Method of Acceptance Based on Testing

Suggest Investigating Continuous Compaction Control Techniques

Recommend Transitioning to Modulus-based Testing (More research needed to fully implement this.)

Major Findings – Cont’d.

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Better Bases Facilitate Better HMA Compaction, Resulting in Longer Pavement Life

Measurements Will Increase Consistency of Base Placement Operations and Results

Measurement Will Provide Consistent/Defined Method of Base Acceptance – Not Subjective

Reduce Long-term HMA Pavement Maintenance Costs

Benefits of Base Course Density

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Reduce Contractor Risk at Time of Bidding and Provide More Equity

Provide Project Documentation of Compactive Levels Achieved

Any Construction Cost Increases Will Still Result in Reduced LCCA Costs

Move WisDOT/Contractor to QMP – Allow Contractor More Control of Their Operations

Transition From Method Spec. to Performance Specification

Benefits Cont’d.

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Based on Study Results – Need New Spec Aggregate Responsibility at WisDOT - ?? WisDOT and Industry Meetings Application Issues to Address

What Types of ProjectsDefine Size of ProjectsWhere Used on Projects

Base Compaction Methods Already Being Used for WisDOT Airport Construction

WisDOT Moves to Develop Spec.

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Developed Two Specifications/Test MethodsMilled/Pulverized and OverlayBase Aggregate – Different testing based on

percentage of RAP/RCA (Cut-off at 20% RAP/RCA) Contractor to Provide QMP Plan Required Certified Testers QC and QV Requirements Set Dispute Resolution – Third-party Lab (Vague) How to Address Failures – Contractor to Take

Corrective Actions Until Spec is Met

Highlights of Specification

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Target Density Limit: 95% T-180 Modified Proctor

Additional Proctor if Gradation Varies ≥ 10% on Any One Sieve

Departmental QV Testing at Frequency of 30% of Contractor QC Testing

Payment Based on Ton or SY Basis

Highlights of Specification – Cont’d.

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Base Aggregate Density Testing Frequency – Every 1000 tonsGradation and Proctor – Every 3000 tonsPayment based on Tons

Mill/Pulverize and OverlayDensity Testing Frequency – Every 3000 SYGradation – Every 9000 SYAdditional Proctor if AC content changes by ≥ 1.5%

by visual observationPayment based on SY

Highlights of Specification – Cont’d.

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WisDOT Generally Works Closely With Industry When Developing Specifications

Different PerceptionsPaving industries in favor of itGrading industry less enthusedAggregate producers opposedWI Transportation Builders Association has concerns

FHWA – Supports Movement to Density Department – Favors Measurement

Industry Reactions

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Difficult to Bid - Unknowns Increased Contractor Workload Perceived Increased Contractor Risk Potential For Project Delays if Issues May Require More Compactive Effort by

Contractor Subgrade (Lower Layers) May Not Have

Required Density

Industry Concerns

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Multiple Sources May be Used - Complications Frequency of Testing – How Much? Consider a Density Incentive? Concerns Over Failed Tests and Remediation Potential Project Delays Due to Required

Testing Concern Over Timing of Base Acceptance –

(Delays in acceptance or Changes due to environmental conditions.)

Industry Concerns – Cont’d.

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HMA Projects Only – Pvmt. Design Process Travel Lanes and Shoulders Only Pay Quantity Based on Total Material (Ton/SY) Include Payment for Compaction Water Base Aggregate 1¼”

Quantity ≥ 30,000 tonsSubgrade Improvement or QMP Subgrade, or Both

Mill/Pulverize and RelayQuantity ≥ 40,000 SY

Project Application Guidelines

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Final Specification Language Developed Various Geographic and Geologic Areas Different Contractors Density Results Used In One of Two Ways

Project ControlFor Information Only

Incorporate Into Pilot Projects - 2013

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Pilot Specification Used on 11 Projects8 Base Aggregate3 Mill/Pulverize and Relay

Generally Went Well, Some Issues Meeting Density Requirements

At End of Construction Season - Department Met With Industry to Discuss Improvements and Implement Revisions

2013 Pilot Projects

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2013 Project Results

2013 Pilot Project Results

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0 2 4 6 8 10 12 14 16 18 2080

85

90

95

100

105

110

Percent Moisture

Perc

ent M

axim

um D

ensi

ty

95% Target

95% of T180 Difficult to Consistently Achieve Issues With Density Measurements When

RAP/RCA >20% More Definition Needed on Corrective Actions

and Acceptance Methods for Material Not Meeting Density

Findings of 2013 Projects Used to Modify Spec for 2014 Pilot Projects

Findings From 2013 Pilots

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Pilot Specification Used on 9 Projects 8 Projects Base Aggregate, 1 Project Mill 576k tons Base Agg, 41k SY Mill/Relayed HMA Revised Specifications

Base - Require 93% T180Base - Testing frequency increased to 1500 tonsBase - In addition to dry density, can determine target

density by wet density or control strip method (>20%)Mill/Overlay – Only use control strip for target densityCorrective Actions Clarified

2014 Pilot Projects

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2014 Pilot Project Results

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0 2 4 6 8 10 12 1489

91

93

95

97

99

101

103

105Density Results

Target Percent Max. Density (93%)

Linear (Target Percent Max. Density (93%) )

Percent Moisture

Perc

ent M

axim

um D

ensi

ty Pass Percentages

95% Max Density: 50%94% Max Density: 72%93% Max Density: 97%

Variation of QC and QV Proctor Values Issues With Proctor Test Requirement When

Gradation Changes by ≥ 10% on Any Sieve Desire to Use Family of Curves Timing of Density Testing and Acceptance Need For Pre-placement Meeting Need to Establish Dry-back Moisture Test

Frequency

Concerns From 2014 Pilots

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Use QC Proctor Value for All Testing Once Verified by QV Tests (Require ≤3 pcf difference)

New Proctor Necessary When Moving Average of Four Gradation Tests Differs by ≥10% on Any Sieve

QC Can Use Family of Proctor Curves Dry-back Moisture Content Required Every

9000 tons Base

Revisions Based on 2014 Results

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Contractor to Provide Description of Placement Methods, Staging, Equipment, Etc. in QMP

Require Pre-placement Meeting Clarification on Retesting and Documentation

of Corrected Lots

2014 Revisions – Cont’d.

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Will be Standard Special Provision for 2016 Construction Season

Apply to all HMA Projects That Meet Criteria Monitor to See if Additional Updates Necessary Incorporate Into PCC Pavement ? Lead to Water Bid Item on All Base Projects ? Contractors Not Complaining Much - Improving Contractors Realizing Importance of

Water for Compaction

Future Directions

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Base Agg. Research Report Can Be Found At: http://wisdotresearch.wi.gov/whrp/flexible-pavements

Questions?

Questions

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