l Wd Implementation Wa Ash to 2014
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Transcript of l Wd Implementation Wa Ash to 2014
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?