USE OF GPR TO ESTIMATE DETERIORATION IN CONCRETE BRIDGE DECKS

Transcription

1 USE OF GPR TO ESTIMATE DETERIORATION IN CONCRETE BRIDGE DECKS Dr. Lesley Sneed, P.E. Assistant Professor of Civil Engineering Dr. Neil Anderson, Dr. Evgeniy Torgashov Department of Geological Engineering Aleksandra Varnavina, Aleksey Khamzin Department of Geological Engineering Brandon Goodwin Department of Civil Engineering March 13, 2014

2 Outline Project Objectives Methods of Investigation Results Conclusions and Ongoing Work 2

3 Problem Definition MoDOT has more than 10,000 bridges to monitor and maintain Average cost to rehabilitate a minor bridge in Missouri is $250,000 Planning ahead is important to allocate funds Material quantities must be estimated correctly to ensure project costs are within budget 3

4 Project Objectives 12 field investigations of 11 different bridge decks on MoDOT s road network Demonstrate proof of concept that advanced nondestructive testing/evaluation methods can be rapidly, effectively, and economically implemented to improve overall quality and cost of bridge deck evaluation 4

5 Bridge Locations 5

6 Methods of Investigation GPR Visual Deterioration Mapping Core Extraction Deck Rehabilitation 6

7 Ground Penetrating Radar (GPR) Electromagnetic (EM) pulses transmitted Changes in material cause the signal to be reflected Two-way travel time and amplitude of the signal is measured Source: johnpmorrissey.com 7

8 GPR Continued Real-time data can be viewed on the screen Very versatile tool can be used to locate buried objects, estimate concrete deterioration, determine layers in pavements and soils Can scan an entire bridge deck in a few hours using a ground coupled antenna as used in this project 8

9 GPR Data Acquisition GSSI 1.5 GHz ground coupled antenna Variable transverse spacing 9

10 Sample GPR Results Area without rebar Area with evidence of deterioration of concrete Area with no evidence of deterioration of concrete Depth estimate of reflectors Reflection from top layer of rebar Reflection from bottom layer of rebar 10

11 Visible Deterioration Mapping 11

12 Core Extraction Project Objectives Methods of Investigation Results Conclusions 12

13 Visual Core Rating Good: No delaminations or visible deterioration. Fair: Some visible deterioration including delaminations, however concrete is in large sections. Poor: Concrete shows a lot of deterioration and is in many pieces including several small pieces. 13

14 Deck Rehabilitation Top 0.25 in. scarified using mill Hydrodemolition machine to remove 0.5 in. minimum Deck was sounded, and any remaining deteriorated concrete removed using impact methods 14

15 Deck Rehabilitation Location and depth of material removal determined with Lidar (light detecting and ranging) Removal depths classified into 3 depth categories Reinforcing Bar 15

16 Bridge A1297 Year built: 1972 Length: 157 ft Width: 46 ft Direction of traffic: two-way Number of lanes: two 16

17 GPR and Visible Deterioration Mapping CP: Concrete Patch AFP: Asphalt Filled Pothole TC: Transverse Crack Numbers in parenthesis corresponds to item number No evidence of deterioration Evidence of moderate deterioration Evidence of extensive deterioration 17

18 GPR and Hydrodemolition Correlation 18

19 GPR vs. Hydrodemolition Video 19

20 Core A1 GPR No evidence of deterioration Evidence of moderate deterioration Core A1 Evidence of extensive deterioration Good Lidar Depth of material removal (inches) Core A1 20

21 Core A3 GPR No evidence of deterioration Evidence of moderate deterioration Core A3 Evidence of extensive deterioration Fair Lidar Depth of material removal (inches) Core A3 21

22 Bridge A1297 Condition Comparison Based on GPR Data Interpretation Percent of Deck GPR Hydro Demolition No evidence of deterioration Depth < 0.75 in Evidence of moderate deterioration 0.75 in.< Depth< Top of Rebar 9 24 Evidence of extensive deterioration Depth > Top of Rebar GPR Deterioration Estimate Hydro Demolition Material Removal Reinforcing Bar 22

23 Bridge A1297 Condition Comparison With Adjusted Threshhold Levels Percent of Deck GPR Hydro Demolition No evidence of deterioration Depth < 0.75 in Evidence of moderate deterioration 0.75 in.< Depth< Top of Rebar Evidence of extensive deterioration Depth > Top of Rebar GPR Deterioration Estimate Hydro Demolition Material Removal Reinforcing Bar Threshold values were artificially adjusted until the best correlation was achieved. 23

24 Bridge A1193 Condition Comparison With Adjusted Threshhold Levels 24

25 Bridge A1479 Condition Comparison With Adjusted Threshhold Levels 25

26 Discussion Results suggest that improved correlation is possible A statistical approach is being used to try to correlate the amplitude of the reflection with concrete removal depth for each data point for three bridges decks. The major challenge is to understand how to determine the GPR threshold values without the control data Therefore, currently the results are not predictive 26

27 Conclusions Deterioration was noted from GPR top reinforcement reflection amplitude in areas where visual deterioration was noticed Majority of cores with delaminations extracted from areas with lower GPR amplitudes Hydrodemolition showed that GPR could predict regions of deterioration with reasonable accuracy 27

28 Ongoing Studies Interpretation of GPR data to estimate through-thickness deterioration Calibration of GPR to hydrodemolition Determination of climate effects on GPR results Analysis of varying depths of reinforcement Air launched GPR studies 28

29 Acknowledgments Missouri Department of Transportation (MoDOT) Center for Transportation Infrastructure and Safety (CTIS) A National University Transportation Center (NUTC) at Missouri S&T Dr. Norbert Maerz & Ken Boyko, Missouri S&T 29

30 Thank You! Questions? 30