NDT in Grouted PT Inspection for · PDF filehong-gang cao ctlgroup 2007 pti technical...

NDT in Grouted PT Inspection NDT in Grouted PT Inspection for Bridges for Bridges

PTI Technical Conference & ExhibitionPTI Technical Conference & Exhibition

Miami, FLMiami, FL

May 8, 2007May 8, 2007

HongHong--gang Cao gang Cao

CTLGroupCTLGroup

2007 PTI TECHNICAL CONFERENCE SESSION 5- NDT IN GROUTED PT INSPECTION FOR BRIDGES HONG-GANG CAO

(C) COPYRIGHT POST-TENSIONING INSTITUTE, ALL RIGHTS RESERVED of 37

The NDT Applications in PT The NDT Applications in PT inspection:inspection:-- Locating embedded tendonsLocating embedded tendons

-- Evaluation of void in grouted tendonsEvaluation of void in grouted tendons

-- Locating break and crack along tendon Locating break and crack along tendon strand / wire near anchoragestrand / wire near anchorage

-- Inspection of cable condition through Inspection of cable condition through videoscopevideoscope

-- Corrosion inspectionCorrosion inspection



Currently available techniques:Currently available techniques:

Impact Echo methodImpact Echo method

Impulse Radar or Ground Penetrating Radar Impulse Radar or Ground Penetrating Radar (GPR)(GPR)

Ultrasonic Pulse Echo Ultrasonic Pulse Echo

VideoscopeVideoscope examinationexamination

Others, e.g. XOthers, e.g. X--Ray, magnetic flux leakage, Ray, magnetic flux leakage, etc. etc.



Void Detection Using Impact Void Detection Using Impact Echo MethodEcho Method



Project 1 Project 1 –– Bridge GirderBridge Girder

•• A 11A 11--span bridge supported by 9 parallel span bridge supported by 9 parallel precastprecast postpost--tensioned girders in each spantensioned girders in each span

•• 20 years old20 years old

•• 99 nos. of beams in total99 nos. of beams in total

•• Single postSingle post--tensioning tendon in each beamtensioning tendon in each beam



Web Web -- Plate structurePlate structure

Single TendonSingle Tendon



PP--Wave Speed:Wave Speed:

T = 0.19 mT = 0.19 m

ffT T = 8.8 kHz (Test on = 8.8 kHz (Test on solid concrete portion)solid concrete portion)

VpVp =2 * T * f=2 * T * fTT / 0.96 / 0.96 ≈≈3400 m/s 3400 m/s 0

50

100

150

200

250

0 5000 10000 15000 20000 25000 30000 35000

Frequency (Hz)



If fully grouted:If fully grouted: ffT T = 8.8 kHz (8.3 kHz used) = 8.8 kHz (8.3 kHz used) ffsteelsteel = 13.9 kHz= 13.9 kHz



If empty:If empty: ffT T < 8.8 kHz (or 8.3 kHz)< 8.8 kHz (or 8.3 kHz)ffvoidvoid = 26.7 kHz= 26.7 kHz



Results:Results:

•• 2200 points were tested in 99 beams 2200 points were tested in 99 beams

•• Two completely ungrouted tendon as Two completely ungrouted tendon as well as more than 20% partially well as more than 20% partially grouted ducts were notedgrouted ducts were noted

•• Boroscope examination was performed Boroscope examination was performed to verify the findingsto verify the findings

•• Overall success rate 80%Overall success rate 80%



IE Experience:IE Experience:

•• Good for plate type structure: slab, wall Good for plate type structure: slab, wall ……..

• Single tendon



Void Detection Using GPRVoid Detection Using GPR



Project 2Project 2–– External TendonExternal Tendon

•• Two similar mileTwo similar mile--long long bridgesbridges

•• 237 external cables or 237 external cables or 5,180 m (17,000 ft)5,180 m (17,000 ft) in in lengthlength

•• PE pipe diameter 4.5 in.PE pipe diameter 4.5 in.



Traditional way:Traditional way:

Visual inspection + mechanical Visual inspection + mechanical soundingsounding

CTL approach:CTL approach:

Impulse Radar + visual inspection + Impulse Radar + visual inspection + mechanical soundingmechanical sounding



TTmm = C / (4f = C / (4f √ε√ε))

εε = 5 to 12= 5 to 12

f = 1.5 x 10f = 1.5 x 1099 HzHz

TTmm = 22 mm = 22 mm Or Or

13% section area 13% section area

POLYETHYLENE PIPE

POST-TENSIONED STRANDS

22mm MIN.

GROUT



Radar Testing Along External Ducts



Empty duct Grouted



Partially grouted



Results:Results:

•• Approximately 2% of total cable length Approximately 2% of total cable length was empty or partially groutedwas empty or partially grouted

•• Majority of the voids found by sounding Majority of the voids found by sounding method was not seen by Radar. method was not seen by Radar. Boroscope examination proved only Boroscope examination proved only thin void or delamination between PE thin void or delamination between PE duct and grout.duct and grout.



Experience:Experience:Pros Pros ––

•• Radar finding important or significant voidRadar finding important or significant void

•• Save by using a costSave by using a cost--effective repair effective repair approachapproach

Cons Cons ––

•• Relatively expensive (time consuming) in Relatively expensive (time consuming) in inspectioninspection

•• WonWon’’t work on galvanized steel sheathing or t work on galvanized steel sheathing or other metallic base materialother metallic base material



Strand / Wire Break Inspection Strand / Wire Break Inspection --Ultrasonic PulseUltrasonic Pulse--EchoEcho

MethodMethod



Typical ResultsTypical Results



Ultrasonic PulseUltrasonic Pulse--EchoEcho

High frequency transducer capable of High frequency transducer capable of locating fine cracklocating fine crack

Typically effective over 4 to 5 ft at end Typically effective over 4 to 5 ft at end of Strandof Strand



Intrusive InspectionIntrusive Inspection

Seeing is Believing !



•• 500 ft long ramp500 ft long ramp

•• More than 100 tendonsMore than 100 tendons

•• BoroscopeBoroscope inspection through each inspection through each jointjoint

Project 3 Project 3 –– Video Scope InspectionVideo Scope Inspection



Tendon Layout plan – Half of the Bridge deck

1000 drill holes along segmental joints, 7/8 in. in 1000 drill holes along segmental joints, 7/8 in. in diameterdiameter



Drilling process:Drilling process:

•• Drilling holes using a template based Drilling holes using a template based on construction drawingon construction drawing

•• Unsuccessful near anchor zone Unsuccessful near anchor zone

•• GPR does the workGPR does the work



Tendon Ducts

GPR Survey



Use of Videoscope:Use of Videoscope:

•• 6mm diameter flexible tube, 10 ft long6mm diameter flexible tube, 10 ft long

•• TwoTwo--men crew completed survey in men crew completed survey in two weekstwo weeks

•• Video recording functionVideo recording function



Summary:Summary:

•• NDT techniques available in PT NDT techniques available in PT InspectionInspection

•• They do the job if used properlyThey do the job if used properly

•• Experience mattersExperience matters

•• Realistic expectationRealistic expectation



Thank YouThank You



NDT in Grouted PT Inspection for · PDF filehong-gang cao ctlgroup 2007 pti technical...

Documents

Transcript of NDT in Grouted PT Inspection for · PDF filehong-gang cao ctlgroup 2007 pti technical...