Nondestructive Testing Nondestructive Testing and Data Analysisand Data Analysis

Module 2-3

Learning ObjectivesLearning 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

IntroductionIntroduction

Subgrade Soil

Base/Subbase

SurfaceSUR

SUB

SUR

AxleLoad

Pavement Responses Pavement Responses Under LoadUnder Load

NDT Load

“Strong”Pavement

“Weak”Pavement

Strong vs. Weak Strong vs. Weak PavementsPavements

NDT SensorsNDT Load

Measurement of Surface Measurement of Surface DeflectionDeflection

r

Types of NDT EquipmentTypes of NDT Equipment

Static Vibratory Impulse Surface wave propagation

““Static” Load DevicesStatic” Load Devices Benkelman

California Traveling Deflectometer La Croix Deflectograph

Beam

Vibratory Equipment Vibratory Equipment (steady state dynamic)(steady state dynamic)

Dynaflect Road Rater

m

h

k

Impulse Equipment: Impulse Equipment: Falling Weight Falling Weight DeflectometerDeflectometer

Typical FWD EquipmentTypical FWD EquipmentKUABDynatest

JILS Other: Phonix

Rolling Wheel Rolling Wheel DeflectometerDeflectometer

Measures speed, amplitude, and wavelength

Sensors

Amplitude

Spectral Analysis ofSpectral Analysis ofSurface Waves (SASW)Surface Waves (SASW)

Factors for Consideration Factors for Consideration in Selecting NDT in Selecting NDT

EquipmentEquipment Operational characteristics Data quality Versatility Cost

Factors That Influence Factors That Influence Pavement DeflectionsPavement Deflections

Load factors Pavement factors Climatic factors

Projected deflection:

40-kN = 0.25 mm

Measured deflection:

40-kN = 0.35 mm

0 10 20 30 40 50

0.028

0.10

0.20

Measured 40-kN deflection

Load (kN)

Def

lect

ion

(mm

)

0.40

0.30

0.35

Load FactorsLoad Factors(Stress Sensitivity)(Stress Sensitivity)

0.25

Pavement FactorsPavement Factors

Distress Subsurface variations Random variability

Climatic FactorsClimatic Factors

Temperature Moisture Frost penetration

TimeDec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov

Def

lect

ion

Period ofDeep Frost

Period of Slow Strength Recovery

Period of Rapid Strength Recovery

Period of Strength Loss

Seasonal Variation in Seasonal Variation in Pavement DeflectionPavement 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 SurveysConducting NDT Surveys

Testing Locations and Testing Locations and FrequencyFrequency

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 Temperature MeasurementMeasurement

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 Uses of Deflection Testing DataTesting Data

Uniformity of project

– Design sections for rehabilitation

– Locations for sampling / testing

Backcalculate layer moduli

– Pavement layers

– Subgrade soil resilient modulus

0 1000 2000 3000

0.75

0.50

0.25

0

Distance Along Roadway (m)

Max

imum

Def

lect

ion

(mm

)Project VariabilityProject Variability

Backcalculation…Backcalculation…

What is the origin?What is the origin?

OUTPUTINPUT MODEL

L

P

L / 2

b

h

PL3

48EIbh3

12I = δ

δ

Simple Backcalculation Simple Backcalculation CaseCase

LayerCharacteristics

Surface

NDT Loadr

BackcalculationBackcalculationTypical Pavement CaseTypical Pavement Case

E1 1 D1

E2 2 D2

E3 3

Base /Subbase

SubgradeSoil

Backcalculation Programs Backcalculation Programs for HMA Pavementsfor HMA Pavements

Most are based on multi-layer elastic theory

Approaches:

– Iterative solution

– Deflection basin matching

BackcalculationBackcalculation- Rules of Thumb -- Rules of Thumb -

Deflections away from the load – mostly a function of Esubgrade

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 ValuesTypical Modulus Values

MaterialGeneral Range

(MPa)Typical Value

(MPa)

HMA 1,500 - 3,500 3,000

PCC 20,000 - 55,000 30,000

ATB 700 - 6,000 1,500

CTB 3,500 - 7,000 5,000

LCB 7,000 - 20,000 10,000

Granular base 100 - 350 200

Granular soil 50 - 150 100

Fine-grained soil 20 - 50 30

ReviewReview

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 ReferencesKey References AASHTO. 1993. AASHTO Guide for Design of

Pavement Structures. AASHTO T256-77. “Standard Recommended

Practice for Pavement Deflection Measurements.” Standard Specifications for Transportation Materials and Methods of Sampling and Testing, Part II.

NHI. 1994. Pavement Deflection Analysis. NHI Course No. 13127. Report No. FHWA-HI-94-021. Federal Highway Administration, Washington, DC.

Key References (cont.)Key References (cont.) ASTM. 1999. “Nondestructive Testing of

Pavements and Backcalculation of Moduli,” STP 1375, American Society for Testing and Materials, West Conshohoken, PA