NUCLEAR VS. NON-NUCLEAR TESTING AND TRANSITION – DEVELOPMENT OF CURVES

Mark LindemannNDOR Geotechnical Engineer

Outline

Background on previous field testing

Research – Non-nuclear field testing

Cost Savings of Going Non-Nuclear

Fundamentals of LWD

LWD Correlation

Field Implementation

Density and Moisture Testing

Volumemeasure Test Method

Density and Moisture Testing

Nuclear Density & Moisture Gauge (NDG)

NON-NUCLEAR DENSITY TESTING

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

Non-Nuclear Research

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)

Asphalt Non-Nuclear

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.

Asphalt Non-Nuclear

Asphalt Non-Nuclear

Asphalt Non-Nuclear

Non-Nuclear Research

Non-Nuclear Research - Soils

Field Research: EDG, M+DI, LWD

Compared to Nuclear Moisture Density Gauge

Density of Soil from Shelby Tubes (ASTM D2937)

Water Content via Oven Dry Method

Soils Non-Nuclear

Electrical Density Gauge (EDG) Uses high radio frequency waves to electrical

dielectric properties of soil. Requires complex correlation of expected

field density & moisture values ahead of time. Need to perform some other test method for

density and moisture in the field first.

Results: Density, % Moisture, % Compaction

For each soil type – Need a Soil Model

Soils Non-Nuclear

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.

Soils Non-Nuclear

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

Soils Non-Nuclear

Light-Weight Deflectometer (LWD)

Measures soil surface deflection

Provides Modulus, Deflection, Velocity

No moisture content results

Soils Non-Nuclear

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)

Benefits/Limits of Density Testing

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.

Benefits/Limits of Stiffness Testing Non-Nuclear

Good Correlation to FWD Technology Poor Correlation to Lab Modulus Results Variations between LWD Models Not Really “Lightweight” Results are Material and Device dependent

Need to use the same device for all testing Greater Precision Promotes Uniformity

Goal is uniform moisture and stiffness Agreement between construction QA and pavement

design. Soil Stiffness – direct measurement that can be used to

determine structural capacity of a soil (rutting). Longer pavement life.

No moisture testing capability.

Cost / Savings

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

Cost / Savings

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

LWD Technology

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-u2) x so x a / do

Eo = Modulus

f = Plate Rigidity factor (2) = u Poisson’s Ratio (0.35)

so= Maximum contact stress

a = Plate Radiusdo= Maximum deflection

LWD Models

Zorn Keros Dynatest Prima Loadman ELE

LWD Test Method

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)

Other LWD Research

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

Zorn LWD

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

Typical Deflection Plot

Deflection Results

Normal ResultFor unbound materials

Deflection Results

ReboundCommon for Bound materials

If rebound is >20%Of Peak

Re-seat and retest

Deflection Results

Variable

May be poorCompaction

Deflection Results

Testing

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

Field Testing

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

Ave. Velocity vs % Compaction

Dynamic Modulus vs % Compaction

Ave. Deflection vs % Compaction

Modulus Requirement

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 ModulusCorrelation to NGI

Deflection Requirement

Deflection is easy to understand

Two Specifications

1. Provide Target Value for each NGI

2. Perform Test Strip / Calibration Area

Field Specification 1

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

First – Make sure moisture is within Spec.

Refer to Chart for Deflection Requirements

Goal: Maximum Deflection for Each NGI Soil Type

1.2

Target Value = Max Deflection 1.2 mmFor 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 = 7Under ConcreteTop 3’

NGI = 7Under AsphaltBelow 3’

Field Specification 2

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

Field Specification 2

Field Specification 2

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

Moving Forward

Finalize and Implement Specifications

Eliminate all Nuclear Gauges

Build NGI Chart

Find a reliable field moisture testing device

QUESTIONS?