NACE Conference APRIL 9-13, 2017 CINCINNATI, OH

Transcription

1 NACE Conference APRIL 9-13, 2017 CINCINNATI, OH

2 EVALUATION AND PRESERVATION OF BRIDGE DECKS UTILIZING GPR AND HYDRODEMOLITION AND INTRODUCING LATEX MODIFIED CONCRETE

3 OUTLINE Case Study of Missouri Bridge Deck Evaluation Utilizing GPR with Hydrodemolition Rehabilitation Process of Preserving Bridge Decks with Fast Track Hydrodemolition and Latex Modified Concrete

4 Evaluation with GPR of 12 Bridge Decks in Missouri GOALS: Demonstrate use of GPR as non-invasive Method to investigate bridge deck condtions Show that GPR can be used as a reliable and faster means to assess the deck condition Implement GPR as a long-term process to assist with scoping and forecasting Use GPR data to help with cost estimating on rehab jobs

5 Testing Included Visual investigation of top surface GPR scans using GSSI SIR-3000 and GSSI 1.5 GHz antenna (push cart) Extraction and visual review of cores Sampling for chloride concentrations All testing done by Missouri University of Science and Technology Initial testing done in 2012

6 Testing Included Closer look at 3 bridges to compare GPR results with actual deterioration Total Surface Hydrodemolition used to remove deteriorated / weakened concrete Surveyed material depths of concrete removed by using LIDAR

7 For 3 Bridges (A1193, A1297, A1479) APAC served as prime contractor for the project Removed deteriorated concrete by hydrodemolition (Hydro-Technologies, Inc) Installed Latex Modified Concrete Overlay Deck work performed in 2013 Bridge decks did not have overlays

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9 Bridge A1297, US 50, Morgan County, Missouri

10 Ground Penetrating Radar (GPR) Non-destructive geophysical tool that uses pulsed electromagnetic radiation to image the top, base, and interior of a bridge deck Pulses of electromagnetic radiation emitted are partially reflected by top of bridge deck, the base of the deck, and from features such as embedded reinforcing steel bar (rebar) and delaminations Hand Cart used to collect the data

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12 Example of GPR Data Showing Reflections from Top and Bottom Transverse Rebar. Lower Reflection Amplitudes (Top Layer of Rebar) are Normally Indicative of Deterioration.

13 Ground Pentrating Radar (GPR) Analysis of reflected signal (magnitude and arrival time) enables operator to estimate depth to each reflector and to assess overall condition of bridge deck. Results based on reflection amplitude from the top transverse layer of reinforcement and do not represent the condition of the concrete below the top transverse reinforcement.

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15 Ground Pentrating Radar (GPR) Most significant output of GPR investigation was a map depicting variations in the amplitude of the reflection from the top of the transverse layer of rebar. Based on the interpretation of the amplitude map, the interpreter is able to identify areas of the bridge deck where there is: 1) no evidence of deterioration, 2) evidence of moderate deterioration, or 3) evidence of extensive deterioration.

16 Interpretation of Deterioration No evidence of deterioration = Depth < 0.75 inches Moderate deterioration = 0.75 < Depth < top mat of rebar Extensive deterioration = Depth > top mat of rebar

17 GPR Amplitude Map Based on Top Bar Reflection

18 Chloride Testing GPR responds to the presence of saline moisture Chloride ion concentration levels expected to correlate with GPR results Regions with higher chloride ion concentration lower reflection amplitudes (higher likelihood of deterioration) Threshold value for water-soluble chloride for corrosion to initiate is 0.15% by weight of cement Results indicated that chloride ion concentration levels were less than the threshold limit for areas tested.

19 Milling (after GPR) prior to hydrodemolition

20 Bar exposure after hydrodemolition in more deteriorated areas of deck

21 LIDAR used to map depth measurements of concrete removal

22 GPR Bridge A1193 LIDAR

23 Bridge A1193

24 GPR Bridge A1297 LIDAR

25 Bridge A1297

26 Bridge A1479

27 Bridge A1479

28 GPR Scan vs. Actual Removals

29 Bridge A1193

30 Bridge A1297

31 Partial Conclusion (for bridges that underwent hydro) Areas of deck where GPR interpretations indicated extensive deterioration generally corresponded to areas with greater concrete material removal depths after hydrodemolition. Areas where GPR interpretations indicated moderate or no evidence of deterioration generally corresponded to areas with lesser material removal depths. Apparent discrepancies between the GPR interpretations and the concrete removal depths can be attributed to the fact that GPR responds to the presence of saline moisture in the deck, whereas hydrodemolition removes weaker concrete.

32 Partial Conclusion (for bridges that underwent hydro) GPR and rehabilitation results are expected to correlate best in those areas where the pore space within physically degraded concrete is infilled with slightly saline moisture. Further analysis of GPR-Hydro results could improve the interpretation of GPR results for future bridge scans as well as better calibrate results. Acquisition of ground-coupled GPR data is relatively slow and normally requires lane closures. Air-launched GPR may be a more appropriate tool for rapidly assessing the relative condition of multiple bridges.

33 Continuation of Study Additional bridges to be hydro d in 2017 to validate test results Use previous GPR and comparison results to help better calibrate equipment Goal is for better interpretation of GPR results for future bridge scans to better prepare for repair estimates Looking for better efficiency with air-launched equipment

34 Process of Preserving Bridge Decks with Fast Track Hydrodemolition and Latex Modified Concrete

35 What is Hydrodemolition? A concrete removal technique that utilizes high pressure water to: * Remove weakened (or sound) concrete through thrust of water jet, * Pressurize and break apart cracks and microcracks within concrete, and * Cause rapid erosion of the cement matrix and fine aggregates from the surrounding coarse aggregates.

36 Hydrodemolition Robot

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39 .And turn it into this.

40 Fast Track Hydrodemolition Selective Concrete Removal Technique Only Removes Deteriorated or Weakened Concrete Provides Highly Roughened and Bondable Surface High Production Rates Cost Effective Alternative for Deck Restoration and Preservation Commonly Used in Conjunction with Latex Modified Concrete

41 Depth of Delamination will Vary

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43 Jackhammering - Archaic Method of Concrete Removal Damage to Rebars Vibrations in Rebars cause Damage to Embedded Steel Causes new Micro Cracks No Selective Removal Labor Intensive Hard on Labor Force Slow and dusty

44 Removal of sound concrete - unnecessary

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46 Effects of Jackhammering

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48 Fast Track Hydrodemolition Mechanically Mill deck surface Set up water control plan Calibrate robot and perform total surface treatment of deck Clean up and pour dense concrete overlay

49 Mechanical Milling Any overlay must be removed down to original deck Mill into original deck surface to specified depth (minimum of ½ ) Mill for depth most cost effective

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51 Water Control Water Control Plan Adhere to Federal Clean Water Act Adhere to all state and local requirements May need discharge permits For larger jobs recycling of water

52 Calibrate robot and perform total surface treatment

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54 Cleaning Clean up closely behind robot with vacuum equipment Do not leave loose debris or let slurry dry on the deck Sound deck Perform minor hand-chipping where required (inaccessible areas, debonded patches) Final Cleaning - Powerwash (7500 PSI minimum recommended) Thoroughly wet and cover deck

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64 KEYS TO GOOD BOND HIGHLY ROUGH AND BONDABLE (mechanical bond) CLEAN SURFACE FREE OF EXCESS WATER NO MICRO-FRACTURES LMC (added chemical bond)

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67 Latex Modified Concrete Characteristics Developed as Deck Overlay Material in late 1960 s Thin Bonded Overlay Material Very Adhesive Great Bonding Strength Shields Existing Deck from Chlorides Adds 25 + Years of Service Life to Bridge Deck

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73 Controlled Cost with Hydro/LMC All Total Surface Hydro paid per PQ of deck area meaning no costly overruns Excess concrete paid per actual volume of material placed cost of material only GPR tool to estimate amount of deterioration (for excess concrete)

74 SUMMARY GPR is a technology that can be used to help with deck evaluations and repair estimates. Fast Track Hydrodemolition is the preferred method of concrete removal and surface preparation for bridge deck restoration. When combined with Hydrodemolition, Latex Modified Concrete provides in excess of 25 years service life for bridge decks.

75 Questions? Patrick Martens, PE Bridge Preservation Engineer Bridge Preservation and Inspection Services