Micro-milling The Economics A Rehabilitative Strategy for Savings Presented By: Sheila Hines Georgia Department of Transportation

Talking Points GDOT rationale for micromilling Specification Development and Verification Projects and Economics Conclusions

GDOT Rationale for Micro-milling

Standard Pavement Structure for Interstates 12.5 mm SMA PFC

Micro-milling Specification Development and Verification The Key Points

Rough Milling VS Micro Milling Rough Milling Ridge-to-ridge pitch ~ 25 mm Ridge-to-valley Depth ~ 10 mm Micro Milling Ridge-to-ridge pitch ~ 9 mm Ridge-to-valley Depth ~ 3 mm

Section 432: Mill Asphaltic Concrete Pavement (Micromill) Specification The use of the micromilled pavement as a temporary riding surface shall be for a maximum of ___ days Difference between ridge and valley of the mat surface shall not exceed 1/16 in (1.6 mm) Target, 1/8 in (3.2 mm) Correction 1000 ft. test section Laser Road Profiler acceptance testing measured indices must meet 0f 825 mm/km Target, 900 mm/km Correction *Conventional milling must meet Laser Road Profiler acceptance testing me measured indices 0f 1025 mm/km Target and 1175 mm/km Correction on interstates

Verification Objectives Verify specification for micro-milled surface texture in order to meet short- and long-term performance requirements Confirm that requirements can be determined via routine quality acceptance procedures Confirm that requirements are achievable and that benefits of micro-milling are cost- effective using current technology

Verification Approach Select appropriate instruments for measuring ridge-to-valley (RVD) milled surface texture depths Measure milled surface texture depths in 8 test sections Analyze data to determine compliance with RVD specifications Evaluate performance of PEM overlay on micro- milled surface

First Project -Specification Verification I-75 Near Perry Georgia

I-75 Near Perry Georgia 12.5 mm OGFC Surface Mix 15 years +

Severe Testing Using APA Under 64º C Existing OGFC Removed and Testing Performed on Underlying Dense- Graded Surface Mix

Ultra Light Inertia Profiler (ULIP) and Circular Track Meter (CTM) 150 ft

RVD Data Provided by ULIP (I) ULIP measured surface texture depth at 0.5 mm intervals and with 0.01 mm accuracy Base length unit (100 mm) selected, and maximum RVD within base length unit captured by software 450 RVD values collected for each 150-ft. measurement run

Typical Micromilled Surface Profile (100 mm base length) 2.1 mm

RVD Results from ULIP Section ID Mean Profile Depth (mm) RVD Data, mm Meanp90p95 Conventional Milling S S S3* S4-1* S4-2* S S S S S

Estimation of Maximum RVD Values Section ID Maximum Direction Ratio From CTM Estimated Maximum RVD, mm Meanp90p95 C (1) S S S3 (2) S4-1 (2) S4-2 (2) S S S S S

Laser Road Profiler

I-75 The Economics Project Let April 2007 o Original Estimated Rehabilitation Cost $70 million Project Completed December 31, 2007 o Final Payment Statement $8.1 million GDOT projected savings $3.1million per year over 20 year design life  Currently $ 21.7 million savings

I-95 Near I-16

Micromilled Surfaces on I-95

Mean RVD & IRI for Each Lane: I-95 Project LaneNB1SB1NB2SB2NB3SB3 Mean RVD, mm Average High Low IRI, mm/km Average High Low

I-95 – The Economics Project Let February 2009 o Original Estimated Rehabilitation Cost $31.3 million Project Completed May 2011 o Final Payment Statement $ 11.8 million GDOT projected savings $975,000 per year over 20 year design life  Currently $ 3.4 million savings

I-285 Project

Run Type Final State Route Contract ID B Total Lane Miles 28.0 Project limits miles of milling, inlay and plant mix resurfacing on I-285/SR 407. Beginning at Ashford Dunwoody RD. Contractor E.R. Snell Contractor, Inc. PROJECT AVERAGES Mix OGFC Preconst.NewResurface Contractor Code: 2SN250 Spec. Target 750 Spec. Corrective 825 MTV % Change Test Limits Direct. M/F Direct. M/F Direct. M/F Direct. M/F East West FromToLane1Tar.Corr.DateLane2Tar.Corr.DateLane1Tar.Corr.DateLane2Tar.Corr.Date MM7/24/10496MM8/7/11434MM7/24/10418MM7/31/ MM7/24/10454MM8/7/11439MM7/24/10409MM7/31/ MM7/24/10482MM8/7/11547MM7/24/10450MM7/31/ MM7/24/10606MM8/7/11520MM7/24/10446MM7/31/ MM7/24/10638MM8/7/11478MM7/24/10448MM7/31/ MM7/24/10534MM8/7/11528MM7/24/10444MM7/31/ MM7/24/10616MM8/7/11478MM7/24/10456MM7/31/11 M = MEETS F = FAILS SI = SMOOTHNESS INDEX

64.3 Lane Miles 1 Mile Section Failed to Meet 3.2 mm Correction Tolerance Severe Cracking Observed in Milled Area

I-285 – The Economics Project Let April 2011 o Original Estimated Rehabilitation Cost $32 million Project Completed December 31, 2011 o Final Payment Statement $12.2 million GDOT projected savings $990,000 per year over 20 year design life  Currently $ 2.97 million savings

SR 400 Dawson County

SR 400 DAWSON/FORSYTH COUNTIES MICRO MILLING PROJECT Mile Post NB LN 1 OGFC IRI M MILL IRI M MiILL RVD NB LN 2 OGFC IRI M MILL IRI M MILL RVD Mile Post SB LN 1 OGFC IRI M MILL IRI M MILL RVD SB LN 2 OGFC IRI M MILL IRI M MILL RVD

SR 400 – The Economics Project Let June 2012 Project Completed November 2012 o Final Payment Statement $3.6 million

Conclusions Three projects have verified Specifications o One project (SR 400) has displayed early raveling Micro-milling provides a smooth textured platform for new drainage course Careful project selection is necessary to assure successful micro-milling outcomes Savings associated with micro-milling have resulted in a change of business practice for GDOT o Interstate projects now let with anticipated future micro-milling Mica schist—Materials defined in ASTM C 294 as phyllite or schist. Use GDT 104 to analyze these materials. (Use this requirement for Interstate Construction, SMA mixes, OGFC mixes and all surface mixes on roadways ≥ 25,000 ADT).

Questions Sheila Hines State Bituminous Construction Engineer Georgia Department of Transportation (404)