Module 2-5 Field Sampling and Testing

 Identify reasons for conducting field sampling and lab testing  Describe typical field sampling and testing procedures  Describe laboratory test methods and their applications  Describe the use of field and laboratory test results in rehabilitation design Learning Objectives

Reasons for Conducting Field Sampling and Lab Testing  Complement and verify NDT  Absence of NDT  Diagnose causes (mechanisms) of distress  Identify structural characteristics and layer material properties in existing pavement  Economics  Recycling  Emphasis on rehabilitation

Typical Field Sampling and Testing Procedures  Material specimen sampling  Coring  Auger  Split-spoon  Shelby (push) tube  Test pit  Field testing  Dynamic cone penetrometer (DCP)  Ground penetrating radar (GPR)?

Coring  Widely used method for:  Laboratory test samples  Layer thickness determination (or verification)  Visually characterizing layer material types and conditions  Relatively inexpensive  Coring plans used to assess variability along a project

Coring Removing a Core

Coring Layer Thickness Verification

Coring Distress Cause Identification

Coring Sampling Approaches  Uniform spacing, e.g., every 500 m   Based on review of “strip” charts  Distance Along Roadway

Coring Sampling Locations and Frequency  Standard location  Outside lane  Outer wheel path  Frequency (no. of samples) depends on:  Variability (uncertainty)  Project size (anticipated rehab cost)  Traffic and safety issues  Typical spacing: 100 to 800 m

Dynamic Cone Penetrometer (DCP)  Device for measuring in-situ strength of paving materials and subgrade soils  Correlated to California Bearing Ratio (CBR)

Cone angle 60 o Handle Hammer (17.6 lb) Cone Steel rod (0.64 in) 22.6 in 39.4 in (variable) 1 in = 25.4 mm 1 lb = kg 0.79 in DCP Device

DCP Testing Process

Example DCP Results No. of Blows Depth Base HMA Subbase Subgrade Soil

Ground Penetrating Radar (GPR) HMA Base Subbase Subgrade Soil GPR Transmitter/Receiver Conceptual Output

Laboratory Test Methods and Their Applications  Type of material  Basic property being measured  Material’s state of stress Test methods (and their applications) are dependent upon:

Typical Properties Measured in Lab GeneralProperty Various Test Measures Stiffness M R, E*, R-value Strength CBR, indirect tension, unconfined compression Compaction , AVC Constituents , AC, gradation, contaminants Permeabilityk Volume Stability PI, 

Resilient Modulus  Surrogate for Young’s (elastic) modulus  Fundamental engineering property  Loading conditions:   E MRMRMRMR  Triaxial compression  Axial compression  Indirect tension

Resilient Modulus Test Triaxial Compression Used primarily for testing of unbound materials (re-compacted specimens or push tube samples)

Resilient Modulus Method of Determination Strain,  Deviator Stress,  D Plastic Strain Resilient Strain Total Strain PP RR M R = DD RR

Resilient Modulus Test Axial Compression  Used primarily for testing of bound materials (prepared specimens or core samples) OEM, Inc. © 2000 LoadRam LoadCell LVDT Gage Length  Heavier duty test equipment is used to measure compressive strength to measure compressive strength

Complex Modulus (E*)  a.k.a.: dynamic modulus  Applicable to bituminous materials  Equipment and test procedure almost identical to resilient modulus under axial compression  Primary difference is in load pulse (haversine vs. sinusoidal)  AASHTO 2002 Guide for Design of New and Rehabilitated Pavement Structures

Hveem Resistance Test (R-value)  Stiffness measure for unbound materials  Standard axial stress (  v ) is applied  R-value is basically the ratio of the applied vertical pressure (  v ) to the developed lateral pressure (  h ) vvvv hhhh 150mm 100 mm

California Bearing Ratio (CBR) Test  Strength measure for unbound materials  Piston advanced at 1.3 mm / min. rate  Measure load at 2.5 mm penetration (P 2.5 )  CBR = 100  (P 2.5 /P std ) SaturatedSpecimen 50 mm diameter piston 150 mm 180 mm

Indirect Tension Test  a.k.a.: Splitting tension or split tensile test  Used to determine the tensile strength and/or Mr of any bound material  100 or 150 mm diameter (D) specimens  Sample length should be at least half the diameter  Prepared samples or cores

Evaluating Pavement Layers Subgrade Soils  Soil classification (Unified or AASHTO)  Moisture content and density  DCP  Resilient modulus:  Measure in the lab  Backcalculate from NDT data  Estimated from correlation with R- value, CBR, or other soil properties

Evaluating Pavement Layers Unbound Base & Subbase Layers  Visual inspection  Layer thickness  Degradation or contamination by fines  DCP  Density and moisture content  Resilient modulus

Evaluating Pavement Layers HMA Surface and Stabilized Base Layers  Visual inspection of cores  Layer thickness  Stripping, segregation, erosion  Asphalt content and gradation  Resilient modulus  Lab measured (indirect tension)  Backcalculated

Other Considerations  Volume stability  Stripping  Seasonal variations in moisture  Permeability

Use of Field and Lab Tests in Rehabilitation Design  Help characterize existing support and quantify effect of deterioration  Field and lab testing vary depending on:  Material type (i.e., subgrade soil, unbound base or subbase, and HMA surface or stabilized base)  Candidate types of rehabilitation treatments (for example, recycling justifies a higher level of lab testing)

 What are two situations where field sampling and lab testing may be required?  What kind of sampling and testing would you now consider?  What is the motivation for resilient modulus testing?  Name two ways in which field/lab test results can be used in rehab design? Review

Key References  Washington State Department of Transportation (WSDOT) WSDOT Pavement Design Guide. Washington State Department of Transportation, Olympia, WA.  Livneh, M “The Use of Dynamic Cone Penetrometer in Determining the Strength of Existing Pavements and Subgrades.” Proceedings, 9 th Southeast Asian Geotechnical Conference. Bangkok, Thailand.