Nondestructive Testing and Data Analysis Module 2-3

Learning Objectives  Describe pavement responses to load  List non-destructive testing (NDT) devices and characteristics  List factors that influence pavement deflection  Describe procedures for conducting NDT  Describe the uses of NDT data

 NDT - Valuable engineering tool for assessing: –Variability –Structural adequacy (in situ material properties)  Fast and produces repeatable results  Used by most states for project and some network level evaluation Introduction

Subgrade Soil Base/Subbase Surface SUR  SUB  SUR Axle Load  Pavement Responses Under Load

NDT Load “Strong” Pavement “Weak” Pavement  Strong vs. Weak Pavements

NDT Sensors NDT Load  Measurement of Surface Deflection r

Types of NDT Equipment  Static  Vibratory  Impulse  Surface wave propagation

“Static” Load Devices  Benkelman  California Traveling Deflectometer  La Croix Deflectograph Beam

Vibratory Equipment (steady state dynamic) Dynaflect Road Rater

m h k Impulse Equipment: Falling Weight Deflectometer

Typical FWD Equipment KUABDynatest JILSOther: Phonix

Rolling Wheel Deflectometer

Measures speed, amplitude, and wavelength Sensors Amplitude Spectral Analysis of Surface Waves (SASW)

Factors for Consideration in Selecting NDT Equipment  Operational characteristics  Data quality  Versatility  Cost

Factors That Influence Pavement Deflections  Load factors  Pavement factors  Climatic factors

Projected deflection:  40-kN = 0.25 mm Measured deflection:  40-kN = 0.35 mm Measured 40-kN deflection Load (kN) Deflection (mm) Load Factors (Stress Sensitivity) 0.25

Pavement Factors  Distress  Subsurface variations  Random variability

Climatic Factors  Temperature  Moisture  Frost penetration

Time DecJanFebMarAprMayJunJulAugSepOctNov Deflection Period of Deep Frost Period of Slow Strength Recovery Period of Rapid Strength Recovery Period of Strength Loss Seasonal Variation in Pavement Deflection

 NDT must be used in conjunction with information from distress survey  Accurate layer thickness information is essential  Time of testing –Time that best represents effective year-round condition is also good –Seasonal (year-round) testing is desirable Conducting NDT Surveys

Testing Locations and Frequency  Typically outer lane only – in the outer wheel path  Both directions - staggered  30 to 150 m (100 to 500 ft) intervals –More intensive testing may be used to investigate cause of distress –Excessive deflection in one area may indicate the need for intensive testing

Temperature Measurement  Needed for correction of deflections and backcalculated HMA modulus values  Develop deflection vs. temperature relationships using data from select sites –Drill hole to mid-depth and add oil –Measure deflection and air, surface and mid- depth temperature (hourly, if possible)  For every deflection point, measure air and pavement surface temperature

Uses of Deflection Testing Data  Uniformity of project –Design sections for rehabilitation –Locations for sampling / testing  Backcalculate layer moduli –Pavement layers –Subgrade soil resilient modulus

Distance Along Roadway (m) Maximum Deflection  (mm) Project Variability

Backcalculation… What is the origin? OUTPUT INPUT MODEL

L P L / 2 b h PL 3 48EI bh 3 12 I = δ  δ Simple Backcalculation Case

Layer Characteristics Surface NDT Load r Backcalculation Typical Pavement Case E11D1E11D1 E22D2E22D2 E33E33  Base / Subbase Subgrade Soil

Backcalculation Programs for HMA Pavements  Most are based on multi-layer elastic theory  Approaches: –Iterative solution –Deflection basin matching

Backcalculation - Rules of Thumb -  Deflections away from the load – mostly a function of E subgrade  Underlying “rigid” layers – do affect deflections and analysis results  Multiple bound layers – may not be a unique solution  Modulus of “thin” layers - may be difficult to determine

Typical Modulus Values Material General Range (MPa) Typical Value (MPa) HMA1, ,5003,000 PCC20, ,00030,000 ATB ,0001,500 CTB3, ,0005,000 LCB7, ,00010,000 Granular base Granular soil Fine-grained soil

Review  Why are we concerned about a pavement’s response to load?  What is the primary NDT device?  What are three factors that influence pavement deflection?  What is the typical NDT test spacing?  What are two primary uses for NDT data?

Key References  AASHTO AASHTO Guide for Design of Pavement Structures.  AASHTO T “Standard Recommended Practice for Pavement Deflection Measurements.” Standard Specifications for Transportation Materials and Methods of Sampling and Testing, Part II.  NHI Pavement Deflection Analysis. NHI Course No Report No. FHWA-HI Federal Highway Administration, Washington, DC.

Key References (cont.)  ASTM “Nondestructive Testing of Pavements and Backcalculation of Moduli,” STP 1375, American Society for Testing and Materials, West Conshohoken, PA