Mark Lindemann NDOR Geotechnical Engineer · Non-Nuclear Methods for HMA and Soil ... compaction of...

Mark Lindemann NDOR Geotechnical Engineer

Background on previous field testing

Research – Non-nuclear field testing

Cost Savings of Going Non-Nuclear

Fundamentals of LWD

LWD Correlation

Field Implementation

Volumemeasure Test Method

Nuclear Density & Moisture Gauge (NDG)

Why fix what isn’t broken? Nuclear Gauges –

Regulations Licensing Storage and transport Training Costs add up Have 84 gauges needing replacement Possible Fines

Approximately $250,000/ year

Falls in Line with Every Day Counts Initiative

Innovative Technologies

University of Nebraska – Dr. Yong K. Cho Non-Nuclear Methods for HMA and Soil

Density Historical research Field Research: PQI (HMA) Compare to Nuclear Density Gauge Bulk Specific Gravity of Asphalt Cores

(AASHTO T166)

PQI (Pavement Quality Indicator)

Measures the change in electromagnetic field as current is sent through the material.

Calibrated with average of 5 core densities and average of 5 PQI densities.

Results: Both Nuclear and PQI provided results very

close to asphalt core values Nuclear gauge closer to asphalt core values

(+1.07 lb/ft3) PQI gauge values -1.89 lb/ft3 to asphalt core

values.

Nuclear Results: Average difference of 1.71 pcf compared to

standard for density. Average difference of 0.22% for moisture.

EDG Results: Average difference of 9.86 pcf compared to

standard for density Average difference of 1.66% for moisture.

M+DI (Moisture Density Indicator) Uses Time Domain Reflectometry to send

electromagnetic pulse through soil Requires correlation of several points from

Proctor tests Takes 15 to 20 minutes per test. Had trouble with device at beginning Removed from testing

Light-Weight Deflectometer (LWD)

Measures soil surface deflection

Provides Modulus, Deflection, Velocity

No moisture content results

LWD Results: Compared Pass/Fail results based on 95%

compaction of devices to standard (lab) Nuclear Gauge: 72% correlation LWD: 54% correlation Overall – best correlation of new devices Suggest better way to determine target value

(not density)

Widely Accepted QA/QC Method Indirect Parameter of Strength Small Variations – Result Large Variation in

Stiffness Compaction Lab vs. Compaction Field Costs/Regulations of Nuclear Results are Material dependent based on a

small sample compared to that in the field.

LWD Initial Costs: $8,257 Thermal Paper: $20/ Year Maintenance/ Calibration: $300

Net Present Worth of Costs (NPW)= Initial Costs + Yearly Costs (P/A, 15 yrs, 10%)

NPW of Nuclear Gauge= $10,873 + $2,155(P/A, 15yrs, 10%) = $27,264

NPW of LWD = $8,257 + $320(P/A, 15yrs, 10%) = $10,690

Dynamic non-destructive testing tool Measure layer/surface modulus (stiffness)

How it works Transient Load on Loading Plate Accelerometer within the device measures the

deflection of the ground due to the load Soil Modulus back-calculated based on deflection

and assumed Poisson’s ratio. Results taken as an immediate indication of the

materials strength (ability to support roadway) http://www.youtube.com/watch?v=6WGgosXlHss

Modulus Calculation:

Eo = f x (1-υ2) x σo x a / do Eo = Modulus f = Plate Rigidity factor (2) υ = Poisson’s Ratio (0.35) σo= Maximum contact stress a = Plate Radius do= Maximum deflection

Zorn Keros Dynatest Prima Loadman ELE

ASTM E 2835-11 for LWD without Load Cell ASTM E2583-07 for LWD with Load Cell Plate Size Drop Height Falling Weight Type and location of Sensors Significant variability between manufacturers Seating Load (3 Drops) Testing Load (3 Additional Drops)

MnDot Research – Beginning 1997 NCHRP – 382 & 456 Colorado DOT Vermont DOT US Army Corps of Engineers UK – Fleming, Frost, and Lambert Virginia Transportation Research Council Kansas DOT Louisiana Transportation Research Center

Several LWD models with variety of differences

Steel spring buffer and accelerometer in plate Critical to use same device with same plate

diameter, drop height, and falling mass Hand-held recording instrument

SD card memory Graphical and numerical results Printout of results GPS capability

Normal Result For unbound materials

Rebound Common for Bound materials If rebound is >20% Of Peak Re-seat and retest

Variable May be poor Compaction

Recipe for Good Compaction Know Soil Type Moisture Control Limit Lift Thickness Compaction Testing Stiffness/ Strength of materials

Target = Minimum Modulus or Maximum Deflection Based on Material Type Moisture Content

May Require A Test Strip

Side by Side LWD Tests & Nuke Tests

Bag Samples for Lab

Determine NGI & Moisture

Compare Deflection vs % Compaction for each Soil Type (NGI)

PI= 20 LL = 45 % Ret.= 50

Chart 1 = 3.5

Chart 2 = 3.5

NGI = 7

Modulus in Laboratory is complicated, expensive, and time consuming. Test methods have continually changed over the

years NDOR – Resilient Modulus Research based on

Nebraska Soil Types (NGI) Correlate well with FWD Do not correlate with LWD

Resilient Modulus Correlation to NGI

Deflection is easy to understand

Two Specifications

1. Provide Target Value for each NGI

2. Perform Test Strip / Calibration Area

Maximum Deflection based on Nebraska Group Index (PI, LL, #200)

First – Make sure moisture is within Spec.

Refer to Chart for Deflection Requirements

1.2

Target Value = Max Deflection 1.2 mm For Equivalent to 95% Compaction

Nebraska Group Index

Concrete Upper 3' Concrete Below 3' Asphalt Upper 3' Asphalt Below 3'

Max Deflection (mm)

Max Deflection (mm)

Max Deflection (mm)

Max Deflection (mm)

-2 0.5 0.5 0.5 0.5

-1 0.5 0.5 0.5 0.5

0 0.5 0.5 0.5 0.5

1 1 1.5 0.5 1.5

2 1 1.5 0.5 1.5

3 2 3 1 3

4 2 3 1 3

5 2 3 1 3

6 2 3 1 3

7 1.5 3 0.75 3

8 1.5 3 0.75 3

9 1.5 3 0.75 3

10 2 4 1 4

11 2 4 1 4

12 2 4 1 4

13 2 4 1 4

14 3 5 2 5

15 3 5 2 5

16 3 5 2 5

17 4 6 3 6

18 4 6 3 6

19 5 8 4 8

20 5 8 4 8

21 5 8 4 8

22 6 9 5 9

23 6 9 5 9

24 6 9 5 9

NGI = 7 Under Concrete Top 3’

NGI = 7 Under Asphalt Below 3’

Deflection Data for Soil Type not available

Perform a Test Strip/ Calibration Area First Test Moisture Size of Test Strip – 200’ Length x Width of

Embankment, Two-8” Lifts 3 LWD Tests/ Roller Pass – Random Locations

Continue LWD/ Roller Pass Testing Target Deflection Value Obtained when: Moisture Content Acceptable Range (based on PL or

Standard Proctor) Average of Deflection Tests for three consecutive

passes does not change significantly with each additional pass (when change is < 10%)

Obtain Rep. Sample from test strip for further lab testing

Passing Test = < 1.1 x Target Value

Re-Evaluate when:

More than 20% of test measurements are less than 0.8 x TV

Failing results consistently occur even though adequate compaction observed.

Perform new Test Strip

Finalize and Implement Specifications

Eliminate all Nuclear Gauges

Build NGI Chart

Find a reliable field moisture testing device

QUESTIONS?