CC8 Nondestructive Testing

Introduction to Nondestructive Testing (NDT)

Nondestructive testing (NDT) is the examination of a material to determine its properties, serviceability, and condition without removing or damaging the material. This saves time and money compared to traditional destructive methods such as coring and excavation. In addition, NDT does not require any installation to be done during construction, which allows testing to be performed at any surface location. For NAPTF Construction Cycles (CCs), NDT is used to evaluate and monitor structural and functional changes in the pavement due to traffic loads. NDT data is a valuable resource for the research team at the NAPTF, playing an important role in defining the pavement’s response to loading and performance, and providing insight into parts of the pavement that cannot be seen.

 

CC8 NDT Summary

For CC8, sixteen NDT devices and methods were used throughout the four test phases to study the effects of traffic loads on the pavement structures. For each phase, tests were performed prior to trafficking to establish baseline data, during trafficking to monitor the changes in the pavement condition, and following trafficking to evaluate the effects of traffic loads. The test phases each required a unique selection of NDT methods to accomplish their individual research objectives and are detailed in the Comprehensive NDT Test Plans linked below.

 

CC8 Phase 1 Overload NDT Test Plan

CC8 Phase 2 Overlay NDT Test Plan

CC8 Phase 3 Joint Comparison NDT Test Plan

CC8 Phase 4 Strength & Fatigue NDT Test Plan

 

NDT Devices and Methods

Different NDT devices and methods evaluate different structural and functional characteristics of the test pavement. While some methods are used individually to provide unique information, some are used in conjunction with other methods for complementary and comparative studies. The devices and methods used for CC8 include: Heavy Weight Deflectometer, Light Weight Deflectometer, Portable Seismic Property Analyzer, Inertial Profiler, SurPro 2000 Profiler, Dipstick Profiler, Straightedge, Rail-to-Rail Profiler, Truss Profiler, Joint Groove Profiler, 2D and 3D imaging, Leica 3D Scanner, Ground Penetrating Radar, ELATextur, MIT Scan, and Visual Pavement Surveys. While each method is briefly detailed below, more detailed information is available at the FAA Nondestructive Testing webpage.

 

NDT Devices

HWD (click to Zoom)

The Heavy Weight Deflectometer (HWD) is operated by dropping a known weight onto pavement and measuring its deflection response. Through analysis, the strength of each pavement layer is estimated. More information can be found on the HWD page. HWD testing was performed weekly on select phases of CC8.

 

LWD (click to Zoom)

The Light Weight Deflectometer (LWD) is a lighter, more compact version of the HWD. Its principles and operation are similar, and it is also be used to estimate strength. More information can be found on the LWD page.

 

PSPA (Click to Zoom)

The Portable Seismic Property Analyzer (PSPA) is a device that generates and monitors seismic waves in the pavement to determine layer strength and thickness. Analysis can determine layer strength and thickness. More information can be found on the PSPA page.

 

Inertial Profiler (click to Zoom)

The Inertial Profiler is a vehicle-mounted system that uses multiple instruments to record surface profiles at high speeds. A profile can be used to quantify surface roughness and smoothness through software simulation. More information can be found on the inertial profiler page and ProFAA page.

 

SurPro 2000 (click to Zoom)

The SurPro 2000 is a walk-behind surface profiler owned by the FAA. As its name suggests, the profiler is pushed by an operator as it records a surface profile, which is comparable to those from other profilers. On CC8, it was used to determine roughness/ smoothness as well as to detect slab curling. More information can be found on the walk-behind surface profiler page.


Dipstick (click to Zoom)

The Dipstick is a walking road profiler that uses an inclinometer to record surface elevation as an operator “walks” the device down the path. Like the SurPro, it was also used to determine roughness/ smoothness and slab curling. More information can be found on the walking road profiler page.

 

Straightedge (click to Zoom)

The 12-foot Straightedge is used as a reference line for measuring deviation of the pavement surface from grade. Typically used for smoothness acceptance, it was used on CC8 to determine slab movement. More information can be found on the straightedge page.

 

Rail-to-Rail Profiler (click to Zoom)

The Rail-to-Rail Profiler (RTRP) is a large rail-mounted truss that spans the NAPTF with attached distance measuring laser equipment. The laser is able to record a transverse surface profile across the entire pavement section. It was used for roughness/ smoothness testing, slab curling, and distress monitoring on CC8. Testing was performed weekly on select sections.

 

Truss Profiler (click to Zoom)

The Truss Profiler is similar to the Rail-to-Rail Profiler, with the exceptions of it being smaller, covering only part of the section, and is supported on casters instead of rails. The smaller size made it optimal for monitoring joint curling and joint performance on CC8.

 

Joint Groove Profiler (click to Zoom)

The Joint Groove Profiler is a beam-type transportable profiler that measures the geometry of grooves in the pavement under it across a small section. This was done to measure joint deterioration over time at select locations.

 

Waylink 2D and 3D Imaging (click to Zoom)

The Waylink 2D and 3D Imaging system makes use of vehicle-mounted lasers that scan the pavement’s surface in wide strips. Through data merging and analysis, pavement distresses can be detected and viewed in software. More information can be found on the 2D/3D imaging page. Scans of select sections on CC8 were taken weekly.

 

Leica Scanstation P20 (click to Zoom)

The Leica Scanstation P20 is a 3D scanner that, when placed on the pavement, generates a precise 3D model of the surface. The model is made up of thousands of individually scanned data points, each with coordinates, intensity, and color data. On CC8, the Leica scanner was used to measure slab movement and distress formation over time.

 

Walk Behind GPR Cart (Click to Zoom)

Ground Penetrating Radar (GPR) uses antennas that direct electromagnetic waves into the structure and receivers that record the reflected signals. Various antennas can be mounted on a vehicle or on a push cart, as shown. On CC8, a cart-type GPR device was used to investigate layer thickness, thickness change, and the pavement support structure. More information can be found on the GPR page.

 

ELATextur (Click to Zoom)

The ELATextur, otherwise known as a macro texture laser scanner, is a compact, hand-transportable device that scans the pavement surface underneath it. This scan enables measurement of pavement texture, and was used on CC8 to monitor abrasion. More information can be found on the macrotexture laser scanner page.

 

MIT Scan (Click to Zoom)

The MIT Scan is a transportable rail-based device that uses the eddy current magnetic principle to detect conductive materials. On CC8, these would be the dowel bars present at some slab joints. The MIT Scan was used to verify the dowel bar placement after construction and after trafficking.

 

Pavement Visual Survey

A pavement visual survey is a meticulous examination of the entire pavement surface to identify distresses caused by traffic loading. It requires no equipment other than flashlights, chalk, and other basic hand tools to aid in locating and measuring very fine cracks. For CC8, a survey was performed each day after trafficking to document longitudinal cracking, transverse cracking, diagonal cracking, corner breaks, intersecting cracking, shattered slabs, and shrinkage cracking. Following the survey, the Structural Condition Index (SCI) was calculated to quantify the level of damage to the pavement

 

NDT Plan During Each Phase

Not all equipment was used on each phase of CC8, with time being spent to collect only data that would fulfill each Phase’s objectives. The following chart indicates the devices and methods used during each phase of CC8 trafficking.

Equipment

Phase 1

Overload

Phase 2

Overlay

Phase 3

Joint Comparison

Phase 4

Strength & Fatigue

HWD

X

X

X

X

LWD

 X*

PSPA

X

X

X

X

Inertial Profiler

X

SurPro Profiler

X

X

X

 X*

Dipstick Profiler

X

X

Truss Profiler

X

Rail-to-Rail Profiler

X

X

Joint Groove Profiler

X

X

Straightedge

X

2D/3D Imaging

 X*

 X*

Leica 3D Scan

 X*

GPR Push Cart

X

X

 X*

ELATextur

X

X

X

MIT Scan

 X*

X

X

Visual Survey

X

X

X

X

 

* NDT method was included in the test plan, but no records of data acquisition were discovered.

 

Testing Schedule

For each phase of CC8, tests were performed prior to, during, and following trafficking. The pre-traffic testing established the baseline data while post-traffic testing evaluated the effects of the traffic loads. Tests conducted during trafficking were used to monitor the development of damage and were performed daily and weekly, depending on the method employed. Additionally, Phases 2 and 3 paused trafficking midway through the experiment to perform the entire suite of NDT surveys. The CC8 testing schedule can be summarized as follows:

  • Phase 1: pre-trafficking- February 2016; post-trafficking- March 2016, September 2016 
  • Phase 2: pre-trafficking- September 2017; post ramp-up- October 2017; midway- November 2017; post-trafficking- February 2018
  • Phase 3: pre-trafficking- February 2018; midway- March 2018, April 2018; post-trafficking- November 2018
  • Phase 4: pre-trafficking- August 2018; post-trafficking- coming soon, testing is ongoing

 

NDT Results

NDT test data for CC8 is available for download by following the links below.

 

Phase 1 Overload Data

Phase 2 Overlay Data

Phase 3 Joint Comparison Data

Phase 4 Strength & Fatigue Data

 

From the daily pavement surveys, cumulative plots of crack mapping were prepared. On these plots, the distresses were color-coded to separate dates/passes on which the new distresses were observed. The observed cracks were then processed and analyzed as follows: linear cracks for each test item were measured and cumulatively added; and fatigue areas for each test item were measured and cumulatively added. SCI calculations for each Phase of CC8 were generated for each distress survey and can be found below.

 

CC8 Phase 1 Overload Pavement Distress Map and Log

CC8 Phase 2 Overlay Pavement Distress Map and Log

CC8 Phase 3 Joint Comparison Pavement Distress Map and Log

CC8 Phase 4 Strength & Fatigue Pavement Distress Map and Log (Coming Soon)

 

 

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