nondestructive testing and data analysis module 2-3
TRANSCRIPT
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