2 Humboldt Mfg. Co. Norridge, Illinois U.S.A. Manufacturer & Distributor since 1909 Testing Equipment For Road Building Materials: Asphalt Concrete Soil Laboratory Apparatus Mr. Scott Fiedler Product Manager
3 In-place stiffness & modulus Young’s Modulus Elastic Modulus Resilient Modulus resistance to change in shape in direction of stress Layer Stiffness resistance to deflection
4 Why Stiffness Based Compaction? (Why Measure Stiffness?) Objective To Improve Load Bearing Capability Reduce Variability –Enable Effective Load Transfer & Distribution, Pavement To Subgrade Material Moduli New Benefits –Minimized Pavement (Surface) Damage –Double Surface Life Stiffness Makes Engineering Sense
5 Improvements With Stiffness Measurements Optimum Compaction Effort –Reduce Over-Compaction Reduce Variations –Reduce Maintenance & Repair Costs –Longer Lasting Smooth Surface Verify Supporting Base Properties –Increase Surface Performance and Life
6 Benefits Of Stiffness Based QC Compaction Minimized Pavement Surface Damage –> 50% Increase In Roadway Life –> 50% Decrease In Roadway Maintenance Cost Directly Links Construction With Design –Design & Construction Parameters Are The Same –Enables Performance Specifications And Contractor Warranties –Enables Use Of Reasonable Design Margins No Over Specification No Over Construction
7 Variability Control Of Compaction Process Enable Control Of Variability Increase Life & Load Capacity.
8 “ By reducing the variability of layer stiffness to +/- 25% of the mean, the life of the pavement surface will double over current practice.” (FHWA) Easily Achieved ! Stiffness Variability Is Important
9 What GeoGauge Measures In-Place (In-Situ), 230 to 310mm Layer From Surface –During The Compaction Process For Effective QC/QA Effective Young’s Modulus (elastic,resilient) –Influenced By Normal Construction Boundaries –Influenced By Construction/Contractor Operation –Modulus Of A Layered Composite Material –Modulus Of A Composite Material Lower Than The Sum Of The Moduli Of The Constituent Materials Effective Stiffness Of Composite Or Layered Structure –Influenced By Material Modulus, Layer Dimensions And Layer Boundaries –230 to 310 mm from surface
10 GeoGauge Vibrates Ground & Measures the Deflection Superior Steady-State Sinusoidal Loading Technology 7,400 cycles !
11 Basic GeoGauge Specifications 280 x 270 mm, 10 kg Effective Young’s Modulus: 610 MPa Effective Layer Stiffness: 70 MN/m Depth: 230 to 310 mm From Surface Battery Power Measurement Duration: 75 Seconds No License Required
12 GeoGauge Schematic
13 GeoGauge Features Does Not Interfere Or Delay Construction Detects Small Differences Self-Contained & Hand-Portable Quick Not Affected By Construction Vibration, Wind or Slope Robust, Reliable, Low Cost & Easy To Use Established Bias, < 1% COV Established Precision, Typically < 7% COV Meets ASTM D6758
14 GeoGauge Procedure Is Simple Inspect GeoGauge & Power On Select Mode & Poisson’s Ratio Prepare & Smooth Ground Seat Foot –Place & 1/2 turn on soft materials –Place & 1/4 turn with wet sand over hard materials or rough surfaces Take Measurement: 75 sec. Record Data
15 Remove Lose Material Smooth Surface Simple, Quick & Safe ! Moist Sand Fill Voids Pat Firmly Sand Pad Place GeoGauge Press Measure Button Result In 75 Seconds
16 Seating On Hard or Rough Surfaces Use Wet Sand To Ensure Maximum Contact
17 GeoGauge Applications Compaction QC/QA –Unbound & Bound Materials –Soil, Soil-Aggregates & Aggregates Cement Treated Materials –Minimize Asphalt Surface Reflective Cracks Subgrade & Base Stabilization –Ensure Required Strength & Minimize Construction Down Time Trench / Utility Cut Backfill –Ensure Duplication Of Original Properties Hot & Cold Mix Asphalt QC/QA –Compaction & Strength Evaluation Forensic Investigations
18 Stiffness-Based Specifications FHWA / 25 State DOTs Development Of AASHTO Standard Specifications Underway For 2006 Construction Season
19 Specified For QC/QA of Roadway Layers & Cement-Treated Bases
26 Correlation to Other Moduli PFWD (small plate) PFWD (large plate) DCP (6" avg.) DCP (3" avg.) GeoGauge sc compaction ng compaction Section 17, Mn/ROAD 13 Pavement Sections at 5 MnDOT Sites Modulus (MPa) Compaction (%) Subgrade & Base Materials In 6 TXDOT Districts GeoGauge, E G, (MPa) E F = 4.08E G Correlation Coefficient:.80 FWD vs. GeoGauge Modulus FWD, E F (MPa) GeoGauge, E G, (MPa) Seismic vs. GeoGauge Modulus E S = 6.27E G Correlation Coefficient:.79 Seismic, E S (MPa)
27 GeoGauge Operation Principle Cyclic Vertical Loading 7400 X –25 Discrete Frequencies 100 To 196 Hz, 4 Hz Increment, 2 Seconds Each Each Frequency = 1 Test, Result is Average of 25 –Self-Filtering –Ground Anomaly / Infinitely Variable 2 Geophone Sensors & 1 Driver –1 Force –1 Displacement
28 Operation Principles cont. Stiffness = Force over Displacement. At Low Frequencies, ground-input impedance is dominantly stiffness controlled.
30 Operation Principles cont. Relationship Of Stiffness To Young’s & Shear Modulus. (Poulos & Davis)
31 Operation Principles cont. Averaging Over Operating Frequencies & Substituting Velocity, V, for Displacement, X, Ground Stiffness Is As Follows. Avoids the need for non-moving reference for displacement & permits accurate measurement of small displacements
32 Calibration Principles
33 Review Stiffness Based Compaction QC/QA Makes Sense –Minimized Pavement Damage –Directly Links Construction With Design –Enables Use Of Reasonable Design Margins GeoGauge Measures Stiffness –In-Place Layer Stiffness & Modulus Of Composite Materials GeoGauge Is Practical For QC/QA –Small, Light, Quick, Simple & Non-Invasive Many Applications –Roadway & General Compaction –Subgrade, Base & Pavement –Soil, Aggregate & Asphalt
34 Verifier Mass Ensures Operation Measures ‘stiffness’ value of compliant-mounted mass. (10.0 kg) Average of 3 to 5 measurements, remove & rotate 45 to 90 degrees between measurements. Should be /- 5%. (Between -8.8 & -9.8) –Negative sign represents mass.
35 Verify Operation Daily To be made at the beginning of every test day. Ensures operation is correct. Deviations can be easily corrected by calibration on same Verifier Mass.
36 GeoGauge ™ Use & Seating Procedure Seating & Measurement Procedures For Proper GeoGauge Measurements
37 GeoGauge Seating Procedure Established Jointly with State DOTs, FHWA & Humboldt –Procedure Standardized –ASTM D6758 –Operator Bias Minimized or Eliminated
38 Firmly Hand-Pack Wet Sand One small handful –Fills cavities –Hand-packing does not change material properties Make Sand Pad approximately 150mm dia. x 3 to 6mm thick Placing and quarter-twist of GeoGauge further reduces amount of sand between ring foot and material surface
39 Practice, Practice, Practice A must for new technicians or users –Becomes proficient & confident –Ensures reliable measurements on projects –Practice on ‘real’ compacted surfaces Recommended for experienced users Profiles & Identifies Deviations Faster –Quickly addresses problems while equipment still on-site –Primary QC benefit
40 Confirm Measurement Precision Minimum of three (3) measurements on representative site and material. At the beginning of each test day and each site. Confirm precision. –About 8% COV or less is good. –Practice & experience improves COV.
41 Suggested Supplies Brush to remove loose materials Gloves & knee-pads –Helps to prepare surfaces more quickly All supplied by technician or user. Not shown: paper & pen to document measurement data, material type & water content, layer thickness and other conditions for database purposes.
42 Prepare Surface Use a solid scraper to remove any loose, dry, hard top materials and to make surface flat. Use brush to help remove readily loose materials. Surface must be moist and free of loose materials before wet sand is applied. –Any user supplied flat scraper or stiff brush can be used.
43 Brush Away Loose Material Can be used instead of scraper plate. Use brush to quickly remove loose material. Do not ‘pick’ or remove protruding attached stones or disturb material.
44 Container of Wet Sand Use fine, well- graded & clean manufactured sand that has good adhesion when wet. Often called masonry or mortar sand. 10 to 15% moisture is ideal.
45 Place Wet Sand A small handful is generally all that is required for freshly compacted material. Drop onto the surface. Sand may not be required if ring-foot pattern is clearly visible without sand, which indicates soil is soft enough to conform to ring-foot for complete contact.
46 Small Handful of Wet Sand
47 Firmly Hand-Pack Wet Sand Spread the sand to a pad shape about 150mm dia. & no more than 6mm thick. –Use more sand for a thicker pad when required where surface is rough. Pack firmly, equal & smooth.
48 Always Use Wet Sand Ensures Full & Equal Annular Contact –Repeatability –Thin layer of sand has no influence Well-Graded, Fine Mortar or Masonry Sand –Provides good adhesion –10 to 20% moisture Sand may not be required if, without sand, a complete 360 degree ring-foot pattern is clearly visible, which indicates soil is soft enough to conform to ring-foot for complete contact.
49 Place GeoGauge Rest GeoGauge ring-foot on center of sand pad. No addition downward force.
50 Twist One/Quarter Turn With both hands on side of GeoGauge, apply a one-quarter turn or twist only, to complete the seating. –Do not apply additional downward force. Most critical step in seating the GeoGauge.
51 Press ‘MEAS’ Button Gently Press the ‘MEAS’ button, without shaking the GeoGauge Take one-step back to avoid influence of body- weight Measures the surface noise before actual stiffness measurements.
52 Results in 75 Seconds Displays the lowest signal-to-noise ratio of the 25 discrete frequency. Displays the standard deviation of the 25 discrete frequency. Finally displays the stiffness or modulus values. Record data.
53 Acceptable ‘Foot-print’ Good, equal annular print is acceptable. Try to twist one-quarter turn on its axis as good as practical. Acceptable foot-print pattern can only be determine after measurement Practice will improve acceptance