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REPORT
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number:  FHWA-HRT-16-007    Date:  January 2016
Publication Number: FHWA-HRT-16-007
Date: January 2016

 

Long-Term Bridge Performance (LTBP) Program Protocols, Version 1

Long-Term Bridge Performance Program Logo

Impact Echo Testing
LTBP Protocol #: FLD-DC-NDE-004


1.

Data Collected

 
1.1 Evidence of concrete delamination and other defects such as overlay debonding.  
1.2 Detection of anomalies such as material variation, flaws, and vertical cracks.  
1.3 Condition evaluation of grouted ducts.  
1.4 Actual deck slab thickness.  

2.

Onsite Equipment and Personnel Requirements

 
2.1 Equipment:  
2.1.1 PRE-PL-LO-004, Personal Health and Safety Plan.  
2.1.2 Impact echo (IE) equipment/device; either of the following are acceptable:  
2.1.2.1 Cart-mounted and semiautomated to control data collection line length and spatial location on deck, spacing between individual test measurements, triggering impact/source deployment, ease of use, etc.  
2.1.2.2 Hand deployed and triggered manually at each test point location.  
2.1.3 Data acquisition controller and software capable of sampling and recording at a minimum rate of 50 kHz.  
2.1.4 Data controller/storage device: laptop or data logger.  
2.1.5 Data conditioning and analysis software capable of filtering, clipping, segmenting, and discarding noise and waveforms unrelated to the IE data.  
2.1.6 Impact source capable of generating and a receiver capable of recording signals, with an acceptable signal to noise ratio that exists in a range of at least 2 to 25 kHz.  
2.1.7 Digital camera.  
2.2 Personnel: PRE-PL-LO-005, Personnel Qualifications.  

3.

Methodology

 
3.1 Use the local rectangular grid (FLD-OP-SC-001, Data Collection Grid and Coordinate System for Bridge Decks) to locate test points on the deck.  
3.2 Test Preparation: Clear any debris from the deck surface.  
3.3 Measurements:  
3.3.1 Collect data along any test line, as long as the location of every IE reading is properly recorded.  
3.3.2 Place the impact device and sensor in direct contact with the sampled concrete surface.  
3.3.3 Avoid hitting or resting on exposed aggregate, edges, or depressions within surface voids. Otherwise, erroneous signals may be generated, collected, and stored.  
3.3.4 Conduct IE testing on concrete decks with hot-mix asphalt or similar overlays with the overlay surface temperatures lower than 50 °F. Results depend on the temperature at the time of testing and should be corrected based on a reference temperature.  
3.3.5 During field operations, take care that the collected data in the time and frequency domains are consistent with expected signals from the structure being surveyed. For instance, it is expected that a frequency corresponding to the deck thickness dominates the frequency response of an intact portion of a deck. Other dominant frequency responses include very low resonant frequencies consistent with flexural oscillations, corresponding to shallow delaminations—those which should be audible during hammer sounding or the chain drag test. Also, there should be high-frequency resonant responses from deeper, less extensive delaminations or from incipient delaminations, either of which fully or partially blocks incident waveforms from reaching the bottom of the deck. Equipment must guarantee visualization of time histories for each collected signal, as well as frequency response and/or B-scan display obtained from a continuous set of measurements along a test line.

NOTE—There should be no chain drag, hammer sounding, coring, impact or hammer drilling, or similar operations producing high-frequency vibration (such as operation of an electric generator) in the proximity (within 100 ft) of the IE equipment. Operation of such equipment may produce frequency responses within the range of interest, which decrease the signal-to-noise ratio and makes it either difficult or impossible to collect and interpret data.
 
3.4 Traffic in the lanes outside of the work zone is permissible during the data collection.  
3.5 Final forms for collected data include time histories and frequency response of measured raw data at all x and y test locations from gridded deck. Processed data consists of condition grading based on resonant frequency response of IE data (grades 1 to 4), also on x-y coordinate system.  
3.6 Storing data, documents, and images:  
3.6.1 FLD-DS-LS-001, Data, Document, and Image Storage—Local, for local storage.  
3.6.2 FLD-DS-RS-001, Data, Document, and Image Storage—Remote, for remote storage.  
3.7 Reporting: Transfer all metadata, data, documents, and images to Federal Highway Administration (FHWA), and/or upload all metadata, data, documents, and images into the Long-Term Bridge Performance (LTBP) Bridge Portal.  

4.

Data Collection Table

 
4.1 Table:  
# Field Name Data Type Accuracy Unit Field Description Row Color
1 State
Text
 
 
State Code; e.g., Virginia = VA
Green
2 NBI structure number
Text
 
 
Item 8, structure number; from NBI Coding Guide
Green
3 Structure name
Text
 
 
Descriptive name for the bridge; e.g., Route 15 SB over I–66
Green
4 Protocol name
Text
 
 
Title of the protocol
Green
5 Protocol version
Text
Month and year
 
Month and year the protocol version was published; e.g., May 2015
Green
6 Personnel performing data collection activities
Text
 
 
First name(s) Last name(s)
Green
7 Date data were collected
Text
Exact date
 
mm/dd/yyyy
Green
8 Ambient air temperature
Number
1
°F
Range: -50 to 150
Green
9 Deck surface temperature
Number
1
°F
Range: -50 to 150
Green
10 Equipment name
Text
 
 
 
Green
11 Equipment manufacturer
Text
 
 
 
Green
12 Equipment model name and number
Text
 
 
If available
Green
13 Comments (equipment)
Text
 
 
 
Orange
14 Overlay material
Text
 
 
 
Green
15 Overlay thickness
Number
0.5
in.
 
Green
16 Bridge deck thickness
Number
0.5
in.
 
Green
17 Source type
Text
 
 
 
Green
18 Sensor type
Text
 
 
 
Green
19 Source sensor spacing
Number
0.1
in.
 
Green
20 Pulse period
Number
0.1
µs
 
Green
21 Pulse length
Number
1
µs
 
Green
22 Sampling rate
Number
1
 
 
Green
23 Samples per scan
Number
1
 
 
Green
24 Number of pretrigger samples
Number
1
 
 
Green
25 Span
Text
 
 
 
Blue
26 Test site
Text
 
 
Descriptive location of the test on the bridge (e.g., shoulder and lane1)
Blue
27 Location of test site (x-coordinate)
Number
1
ft
Longitudinal distance from the local grid origin
Blue
28 Location of test site (y-coordinate)
Number
1
ft
Transverse distance from the local grid origin
Blue
29 Voltage array
Array of numbers
0.000000001
V
Voltage array (time history) data for the point
The number of elements are the same as samples per scan (item23) and can be different numbers for each element
Range: -1 to +1
Yellow
30 Comments
Text
 
 
 
Orange
4.2 Table Key:  
Column Descriptions
#
Sequential number of data item
Field Name
Data field name
Data Type
Type of data, such as text, number, predefined list, binary large object (BLOB), or PDF file
Accuracy
Accuracy to which the data are recorded
Unit
Unit in which a measurement is taken and recorded
Field Description
Commentary on the data or list of items in a predefined list
Row Color Key
Green
Data items only entered once for each protocol for each day the protocol is applied
Pink
Logical breakdown of data by elements or defect types (not always used)
Blue
Data identifying the element being evaluated or the type of defect being identified
Yellow
LTBP data reported individually for each element or defect identified
Orange
Comments on the data collection or data entered

5.

Criteria for Data Validation

 
5.1 Verification and comparison should be made with results obtained from other NDE methods, including sounding methods, such as chain drag (FLD-DC-VIC-003, Chain Drag); acoustic methods; electromagnetic methods; as well as with ground truth data.  

6.

Commentary/Background

 
6.1 The purpose of this protocol is to provide a standard procedure for using IE testing to estimate deck thickness and detect and characterize the presence of delamination in bridge decks or other reinforced concrete elements. IE can serve additional purposes, such as for material evaluation, vertical crack characterization, detection of anomalies, concrete overlay debonding, etc.  
6.2 IE is based on the reflection of elastic (compressive) waves from interfaces of two materials that have significant contrast in acoustic impedances. Different reflectors, such as the surface of the deck bottom delaminations, deck bottom, cavities, ducts, etc., are delineated with different dominant frequency peaks in the recorded response spectrum. The frequency range of interest in the testing of bridge decks and concrete elements is between 2 and 25 kHz. The testing equipment consists of an impact source and a receiver (displacement or velocity transducer, or accelerometer).  
6.3 The test is also described in ASTM C1383-04 (2010), "Standard Test Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using the Impact-Echo Method."  

7.

References

 
7.1 LTBP Protocols:  
7.1.1 PRE-PL-LO-004, Personal Health and Safety Plan.  
7.1.2 PRE-PL-LO-005, Personnel Qualifications.  
7.1.3 FLD-OP-SC-001, Data Collection Grid and Coordinate System for Bridge Decks.  
7.1.4 FLD-DC-VIC-003, Chain Drag.  
7.1.5 FLD-DC-PH-002, Photographing for Documentation Purposes.  
7.1.6 FLD-DS-LS-001, Data, Document, and Image Storage—Local.  
7.1.7 FLD-DS-RS-001, Data, Document, and Image Storage—Remote.  
7.2 External:  
7.2.1 ASTMC1383-04(2010), Standard Test Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using the Impact-Echo Method, ASTM International, West Conshohocken, PA, 2010.  

 

 

 

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