Office of Materials and Road Research Asphalt Compaction Evaluation using Rolling Density Meter (TH 52 and TH14 Field Trials) Dr. Shongtao Dai, MnDOT Dr. Kyle Hoegh, MnDOT Dr. Lev Khazanovich, U. of Pittsburgh NRRA Pavement Conference (May 24, 2017) Mn/DOT Office of Materials and Road Research

Rolling Density Meter (RDM) RDM: A GPR device. One channel or multi-channels Specific designed to measure HMA compaction density SHRP2 R06C Research Product (2013) Dielectric values related to air voids. Rolling Density Meter (RDM)

SHRP2 R06C Implementation (2015) Objective: Evaluate RDM equipment. Provide support to states to assist to implement RDM. Partnership FHWA, AASHTO, CH2M Hill University of Minnesota MnDOT Maine DOT Nebraska DOT Field Trails Maine: HWY 9 near Clifton Nebraska: HWY2, Lincoln Minnesota: TH.14 and TH.52

Benefits Pavement density has great effects on performance. Lack of density --- localized failure 1989 – “Effect of Compaction on Asphalt Concrete Performance” (Wash.DOT) Each 1% increase in air voids (over 7 percent) tends to produce ~10 percent loss in pavement life. Core used to determine density At a particular location, does not represent the entire pavement density Need a way to obtain full coverage of the surface GPR is a good tool: Continuous profile

Principal Wave propagation in solids Provides full coverage

Questions Measurement difference among the antenna pairs?

Underlying layer effect on surface measurement? How thick does the HMA layer need to be so that the underlying layer (agg. base) has no effects? Surface layer dT Underlying layer h1 =v* t1 /2 v= c/1 dT ~ 0.439us

Fr ~ 0.5 v (tr/fc)1/2 Footprint area of an antenna (Fresnel Zone)? at D=18”, Fr (Radius) ~ 6” (for 1.5Ghz) D=12”, Fr (Radius) ~ 3.8” (for 2.5Ghz-RDM)

Field Testing and Assessment Method Selected MN TH52 (D6) and TH14 (D6) 7 miles on TH52 and 11 miles on TH14 Objectives: Develop methods to assess compaction uniformity and quality Make recommendation for feasibility of implementation. i.e. when it can and can’t be used Gathering data necessary for specification development.

MN Project #1 (Summer 2016) TH52 (D6): ~7 miles M&O: Mill 1.5” and overlay 2x1.5” 4 Test Sections (FHWA/AASHTO funding) No added binder + 4 rollers (control) Added binder (+0.5%) + 4 rollers No added binder + 5 rollers Added binder (+0.5%) + 5 roller The entire 7 mile project was scanned 30 scans per foot 3 antenna measurements per pass Core calibrations along the entire project were used to develop a model relating RDM measurements to air void measurements 1.5” 1.5” 3” Exist

MN Project #2 (Summer 2016) TH14 (D6): 14 miles M&O: Mill 2” and overlay 2” and1.5” 6 Test Sections: ¾” mix + 3 rollers (control) ¾” mix + 4 rollers ½” mix + 3 & 4 rollers ½” mix (Evotherm) + 3 rollers ¾” mix (Evotherm) + 3 rollers Scanned 11 Miles on Top lift 30 scans per foot 3 antenna measurements per pass Core calibrations along the entire project were used to develop a model relating RDM measurements to air void measurements 1.5” 2” 4-5” Exist

Results On-Site Identification of high and low levels of compaction Mainline Survey: multiple passes On-Site Identification of high and low levels of compaction Joint Survey: one antenna close to joint

TH14 TH52 Relating Dielectric Measurements to Air Void Content 32 cores from TH52 31 cores from TH14 TH14 TH52

Similar relationships on Nebraska and Maine projects Nebraska HWY 2 July 19, 2016 1.25 in” overlay 1000 ft surveyed Collected eight cores Maine HWY 9 July 13, 2016 1500 ft surveyed Collected five cores

Histogram Use histogram to assess uniformity and quality. All Data Collected Sampling Rate = 0.4 in/scan. > 26 million measurements Analysis based on 4 in. moving average Equivalent to >1 million cores Summary Stats 93.2% median density STD: 1.18 97.5% locations density> 90.8%

TH 52 – Mainline Number of Roller Effects Section with added binder+5 rollers has highest density Median Density: Blue: 93.4% Yellow: 93.1% Green: 93% Red: 94%

TH 52 – Longitudinal Joint Top lift Mainline vs Confined and Unconfined Joints Summary: 93.5% (ML), 92.6%(CJ) and 91.4%(UCJ) SD: 0.94(ML); 1.22(CJ); 1.8(UCJ) Density: UCJ/ML=97.7%; CJ/ML=99% Core data: UCJ/ML=95.1% CJ/ML = 99.1% 97.5% locations: > 91.6%(ML), > 90.2% (CJ) > 87.8% (UCJ)

TH 52:Comparison with other Factors Import RDM data into Veta for comparison with IR and other data

TH 14 – Mainline Comparison of Test Sections Mix B (3/4-) to A(1/2-): not much difference on compaction. Adding a roller: density slightly increased on this project. . Median Density: Blue: 94.1% Red: 94.2% Yellow: 93.5% Green: 93.3%

TH 14 – Longitudinal Joint Evotherm helped on the joint compaction density Median Density: Red: 93.1% (ML) Blue: 93.1% (ML) Yellow: 92.9%(CJ+Ev) Green: 91.5% (CJ) (CJ+Ev)/ML=99.7% Core: 93.8%(ML) 93.5%(CJ+Ev)- only 2 cores CJ/ML= 99.6%

Implementation Recommendations for Acceptance Recommendation #1 - Mainline: Require dielectric distribution readings from RDM per 500ft. Ex: Require E of 5.31 >= 92% density? E of 5.31 includes > 95% data Take cores at E=5.31, Then measure density

Recommendation #2 – Longitudinal Joint: Require RDM readings at the longitudinal Joint and X distance away from the Joint, use ratio of dielectrics between LJ and ML. (No cores required) Ex: Ratio of E >= 95%

MnDOT’s Plan 2017 Field Testing Objective: 2 to 3 construction projects in 2017 will be selected for more data collection. A consultant will be hired for part of the data collection. The focus will be placed on: 1) Educating consultant and contractors on this new technology 2) Further verifying the developed statistical method. 3) Testing application feasibility of vehicle mounted RDM system on construction projects; If all things go well, a few projects will require the device in 2018

Summary RDM is a good tool for mapping a continuous coverage of the relative compaction levels (higher dielectric = higher compaction) Histograms and general statistics can be used to give a complete assessments of the in-place compaction Potential Uses: Assess compaction density and uniformity for QC/QA. Provide on-site feedback to contractor of high and low compaction locations that they can cross-check with differences in mix or paving strategies in those locations to determine optimal construction procedures Identification of trends in the air void content maps that can be cross-checked with IC and other data to determine the most critical factors in achieving higher density

Acknowledgements FHWA/AASHTO for providing RDM MnDOT district materials and constructions UMN students Nebraska and Maine DOTs

Thank you!