John Bergman, P.E. Project Manager HDR ICA 62 Brigade St., Suite A3 Charleston, SC 29403

Transcription

1 January 15, 2018 John Bergman, P.E. Project Manager HDR ICA 62 Brigade St., Suite A3 Charleston, SC Sub: Re: Field Memo Water Intrusion into Tendon Ducts I-526 James B. Edwards Bridge over the Wando River in Charleston, SC Dear Mr. Bergman: In preparing a tendon for scanning, Sixense/Freyssinet cleaned off the top of a tendon highpoint adjacent to the diaphragm of Eastbound Pier 24 (Tendon EB S, i.e. Eastbound Bridge Span 24 Segment 1 Tendon 2401 South Side). A section of epoxy popped off and water poured out of the tendon for a full 2 minutes. The presence of water in the tendon duct may be a sign of severe corrosion activity. At the direction of HDR ICA, Freyssinet opened a section of tendon duct for most of the external tendons adjacent to Pier 24 and Pier 29 diaphragms in both the Eastbound and Westbound bridges. Table 1 summarizes the inspected tendon locations. A total of 45 locations were opened as part of this inspection. Siva Corrosion Services, Inc (SCS) was present for these additional tendon openings to document the visual condition of the grout and strands. SCS performed a full tendon evaluation of two locations in the Eastbound where water was identified in the tendon duct, as well as one location in the Westbound where strand corrosion (but not water) was observed. This field memo discusses field observations of the tendons opened adjacent to Piers 24 and 29. HDR ICA Page 1 of 9

2 Eastbound Bridge Tendons Table 1. Summary of tendons opened as part of this inspection. No. Location No. Location No. Location 1 EB N 16 EB M2N 31 WB S 2 EB N 17 EB M3N 32 WB-24-1-M1N 3 EB N 18 EB N 33 WB-24-1-M2N 4 EB S 19 EB M1S 34 WB-24-1-M3N 5 EB S 20 EB M2S 35 WB N 6 EB S 21 EB M3S 36 WB M1N 7 EB-24-1-M1N 22 EB S 37 WB M2N 8 EB-24-1-M2N 23 EB N 38 WB N 9 EB-24-1-M3N 24 EB N 39 WB S 10 EB N 25 EB N 40 WB N 11 EB-24-1-M1S 26 EB S 41 WB N 12 EB-24-1-M2S 27 EB S 42 WB N 13 EB-24-1-M3S 28 WB N 43 WB S 14 EB S 29 WB N 44 WB S 15 EB M1N 30 WB N 45 WB S Total number of locations opened per Pier: EB-Pier 24 = 14, EB- Pier 29 = 13, WB-Pier 24 = 8, WB Pier 29 = 10. The inspected tendons were typically in acceptable condition. Voids and white grout were common, but exposed strands typically exhibited minimal corrosion (see Figure 1). However, water and corrosion were observed in two main span tendons: EB S and EB N (i.e. Eastbound Bridge Span 28 Segment 11 Tendon 2801 North Side). SCS performed full tendon evaluations of both locations. A void with severe corrosion staining was observed at both locations. SCS removed grout from these locations to allow for visual inspection of the strands. Significant section losses were observed on strands exposed in the voids (up to approximately 30% section loss/0.06 depth pits). Strands encased in grout exhibited little to no corrosion. Figures 2 through 7 show the condition of the tendons before and after examination. Corrosion potentials in 2401S ranged from -167 mv to -198 mv (indicating low probability of active corrosion). Corrosion potentials in 2801N ranged from -199 mv to -235 mv (which are in the uncertain corrosion range). The measured in-situ corrosion rates were low (< 0.3 mpy). The ph of the grout was high (ph=13) at both locations, indicating good quality grout. Moisture content was high (25% to 35% by weight grout); this is expected for locations exposed to rainwater. Chloride contents ranged from 0.017% to 0.059% by weight cement (below the 0.08% limit for new structures). The sulfate contents ranged from 2.7% to 3.2% by weight grout (close to the 3% maximum typically seen for tendon grout). Overall, corrosion data indicates that grout at these locations will protect strands from corrosion, except where strands are not completely encased in grout. HDR ICA Page 2 of 9

3 Figure 1: Eastbound-Pier 24-Downstation-Tendon 3S Strand is exposed in void; no significant corrosion was observed on the strand. Figure 2: Eastbound-Pier 24-Upstation-Tendon 2401S Severe corrosion staining in void. HDR ICA Page 3 of 9

4 Figure 3: Eastbound-Pier 24-Upstation-Tendon 2401S Condition of strands opposite of void. Figure 4: Eastbound-Pier 24-Upstation-Tendon 2401S Heavy pitting of wires of the top strand in the voided region of the tendon (1 to 3 inches from the top of the opening). HDR ICA Page 4 of 9

5 Figure 5: Eastbound-Pier 29-Downstation-Tendon 2801N Severe corrosion staining in void. Figure 6: Eastbound-Pier 29-Downstation-Tendon 2801N Condition of strands opposite of void. HDR ICA Page 5 of 9

6 Figure 7: Eastbound-Pier 29-Downstation-Tendon 2801N Heavy pitting of wires of the top strand in the voided region of the tendon (1 to 3 inches from the top of the opening). It rained the day after the tendons were opened for inspection. During the rain storm, water was observed leaking through the downstation construction joint at Pier 24. Additionally, water was collecting in the voids of both tendons with corrosion. This confirms that water is leaking through deck and into the voided tendon ducts at these locations. (No water was observed in any other opened tendon ducts in the Eastbound bridge.) Tendons 2401S and 2801N are anchored in the top slab near the construction joint West of Pier 24 and East of Pier 29. It is possible that water is leaking through the joint in the deck and entering the duct through the nearby anchorage. Westbound Bridge Tendons The inspected tendons were typically in acceptable condition. Voids and white grout were common, but exposed strands typically exhibited minimal corrosion (see Figure 8). In the Westbound bridge, water was observed leaking through the construction joint West of Pier 24. However, no water was observed in any of the tendons anchored at Pier 24 or 29. Strand corrosion was observed at one location at Pier 29 (WB N); see Figure 9. This corrosion appears to be unrelated to water leakage into the bridge. HDR ICA Page 6 of 9

7 Figure 8: Westbound-Pier 24-Downstation-Tendon 3N Strand is exposed in void; no significant corrosion was observed on the strand. Figure 9: Westbound-Pier 29-Upstation-Tendon 3N Strand is exposed in void; corrosion observed on the top strand where exposed. HDR ICA Page 7 of 9

8 SCS performed a tendon evaluation of WB N. Evaluation included removing and collecting grout for laboratory testing and to allow for visual inspection of the strands. After removing grout, moderate pitting corrosion was observed on the exposed wires (see Figure 10). Strands covered in grout were in good condition. Corrosion potentials were more positive than -200 mv (indicating low probability of active corrosion). The measured in-situ corrosion rate was low (0.5 mpy). The ph of the grout was high (ph=12), indicating good quality grout. Moisture content was 22.6% by weight grout (below the 25% maximum typically seen for tendon grout). The chloride content was 0.018% by weight cement (well below the 0.08% limit for new structures). The sulfate content was 2.1% by weight grout (below the 3% maximum typically seen for tendon grout). Corrosion data indicates the grout will protect strands from corrosion, except where strands are not completely encased in grout. Figure 10: Westbound-Pier 29-Upstation-Tendon 3N Condition of the strands after examination. The exposed wires (yellow arrow) showed surface pitting. Strands covered in grout were in good condition. During the rain storm on 11/9/17, moisture was observed inside the plastic wrap of four previously inspected locations (see Figure 11): S-WB S, S-WB S, S-WB N, and S-WB S. Except for S-WB N which exhibited heavy efflorescence, these locations were dry during initial inspection. Only after rainfall did they exhibit moisture. This suggests that water from the deck is getting into the tendon anchorages and traveling down the tendon duct. HDR ICA Page 8 of 9

9 Figure 11: S-WB S Moisture was observed inside a previously tested and sealed location. Please do not hesitate to call if you have questions or need additional information. Thank you for the opportunity to be of service. Very Truly Yours, Stuart Mundth Project Manager SCS, Inc. HDR ICA Page 9 of 9