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Publication Number: FHWA-RD-02-086
Date: August 2006

Chapter 7. Project Summary

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Evaluation and comparison of SFC and LMC-III overlays were performed at a total of four locations. The test sites were in Ohio and Kentucky. Each location included SFC and LMC-III overlays on opposite directions of a bridge structure. All overlays were installed in 1992. This study evaluated the overlays each year between 1994 and 1998. Table 62 summarizes the test data and observations for all test sites. All overlays had high initial bond strengths, and the bond strengths remained high over the study period when tested away from delaminations. The overlays were generally rated as good condition in 1998, after 6 years of service. However, both overlays at the U.S. 41 Henderson, KY site were rated as fair due to extensive cracking. Cracking was found in portions of the overlays at each site. Most of the cracking increased with time. However, some spans of each type were crack-free in 1998.

The percent delamination varied with test site. The U.S. 52 test site in Ohio had the least amount of delamination (less than 1 percent). The LMC–III overlay at U.S. 41 KY had the highest amount of delamination in 1989 with 18.2 percent. At I–270 in Ohio, both overlays had moderately high levels of delamination, about 7 percent.

The bridge at I–270 OH had the highest chloride in the existing deck and corrosion of the steel was likely before the overlays were placed. A high probability of corrosion was measured over most of the two I–270 decks in 1994. The potentials had shifted more positive in 1997 indicating that corrosion may be slowing slightly, with an additional 10 percent of both decks becoming more positive than –250 mV CuCuSo4 half–cell potential. U.S. 41 KY, NB LMC–III may have had sufficient chloride in the original deck to initiate corrosion and had moderately high negative potentials in about one third of the deck (1994). The potentials of both overlays at this site have shifted more negative (corrosive) between 1994 and 1997. The remaining two sites, I–265 KY and U.S. 52 OH, had mostly positive potentials in 1994 and they did not shift significantly in 1997.

By 1998, the average (acid-soluble) chloride in the SFC overlays was 0.10 percent at 9.5 mm (0.375 inch) and 0.04 percent at 20.6 mm (0.8125 inch) depth. The LMC-III overlays were similar but slightly higher at 0.13 percent at 9.5 mm (0.375 inch) and 0.08 percent at 20.6 mm (0.8125 inch).

Good performance can be achieved from both SFC and LMC-III overlays. However, the service life of the overlays tends to vary based on the site location. While most of the overlays continue to provide good service after 6 years, the SFC and LMC-III overlays on U.S. 41 in Henderson, KY, show significant distress in the form of cracking and delamination. Significant repairs are needed for these two overlays. Generally, cracking and delamination of the overlays tend to increase with time. All overlays should be inspected bi-annually for cracking and delamination. Routine maintenance including crack and delamination repairs should be considered to extend the service life of the SFC and LMC-III overlays.

Table 62. Summary of all test sites.
Location Type General Condition (1998) Cracking Percent Delamination 1998 (m2) Potentials More Positive Than –250 mV Chlorides Exceed Threshold Prior to Overlay ? (water–soluble) Average Chloride in Overlay (1998) (acid-soluble) %
1994 1997 Difference 0.25 to 0.5 inch 0.625 to 1 inch
I–270 NB, OH SFC Good–Fair Yes 6.60 14.2 24.1 + 9.9 Yes 0.14 0.03
I–270 SB, OH LMC-III Good–Fair Yes 7.00 1.7 13.1 + 11.4 Yes 0.24 0.13
U.S. 52 WB-P, OH SFC Good Yes-Minor 0.87 - 96.8 - No 0.10 0.07
U.S. 52 EB, WB-T, OH LMC-III Good Yes 0.14 98.8 97.3 -1.5 No 0.13 0.09
I–265 SB, KY SFC Good–Fair Yes 4.50 85.6 86.5 + 0.9 Maybe 0.11 0.04
I–265 NB, KY LMC–III Good Yes–Minor 0.90 98.2 98.4 + 0.2 Maybe 0.08 0.05
U.S. 41 SB, KY SFC Fair Yes 3.70 91.4 78.8 -12.6 No 0.06* 0.01*
U.S. 41 NB, KY LMC-III Fair Yes 18.20 67.0 61.6 - 5.4 No-Maybe 0.09* 0.04*
Average SFC - - 3.90 63.7 71.5 + 7.8 - 0.10 0.04
Average LMC-III - - 6.50 66.4 67.6 + 1.2 - 0.13 0.08

* Average of acid- and water-soluble data.

 

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