Corrosion on Highway Structures Case Studies

The purpose of this section is to provide a review of case histories of corrosion effects on structures. Corrosion of steel and concrete on both substructures and superstructures may result in the reduction of the strength and capacity to withstand the design load of those structures. According to the National Bridge Inventory Database, the total number of bridges in the United States is approximately 600,000, of which half were built between 1950 and 1994. The materials of construction for these bridges are concrete, steel, timber, masonry, timber/steel/concrete combinations, and aluminum.

Andersen (1956) indicates that corrosion was not a serious problem when the piles were completely below ground-water level, but it must be guarded against where sea water is present, where ground water has high salinity content, or where the piles are

subject to alternate wetting or drying. Hool and Kinne (1943) stated that the amount of corrosion on steel pipe piles in the ground was negligible.

Mason and Ogle (1932, as referenced in Andersen, 1956) inspected a large number of steel pile foundations in bridge structures in Nebraska. They found little, if any corrosion at depths greater than 18 in. below the stream bed or ground water level. The report estimated that the decrease in section due to corrosion had not been more than one percent in twenty years, except in an area where the soils are saline. The loss of section within the saline area was about 2 to 2.5 percent.

A 12 x 65 H-Pile driven to a depth of about 122 ft. in a swamp near the river side toe of the west approach ramp to the Airline Highway Bridge across Bonnet Carre Spillway in New Orleans was pulled out for corrosion assessment after 17 years. Examination after cleaning showed no measurable corrosion. Mill scale was intact over almost the entire surface except for the 3 ft. section in the zone of typical water table fluctuation.

Decker et al. (2008) carried out a study to evaluate the corrosion rate for an abandoned pile foundation on I-15 through the Salt Lake Valley in Utah. A total of 20 piles were extracted after service lives of 34 to 38 years. From each of the five sites, measurement of the soil index properties, pH, resistivity, cation/anion concentrations and water table were recorded. Corrosion behavior at individual sites was reported.

At the 2100 South site, three steel pipe piles were of diameter 12 in. and wall thickness of 0.19 in. filled with concrete and reinforcement limited to the top. The soil consisted of both silt and clay with occasional sand. The water table was above the pile cap. The chloride and sulfate in the soil were all above the FHWA corrosive limit as

reported by Elias and Christopher (1997) and the resistivity was below 394 ohm-in. The results of the analysis show an average loss of 2% and a maximum section loss of 4 % over 36 years of pile embedment in the soil at this location.

At the South Temple site, four spiral-welded steel pipe piles of diameter 12 in. and wall thickness of 0.19 in. filled with concrete and reinforcement limited to the top. The soil consisted of both silt and clay with one sand layer. The water table was about 3 ft. below the pile cap. The four piles were exposed to the soil-water environment for about 38 years. The results of the analysis showed an average loss of 5% and a maximum section loss of 12 % after 38 years of pile embedment in the soil-water environment.

At the 2nd South site, three corrugated steel pipe piles of diameter 12 in. and wall thickness of 0.065 in were filled with reinforced concrete. The soil consisted entirely of sand with a high water table. Because of the soil and the water table, only 6 ft. of the steel pipe pile was cut out before the saturated sand collapsed into the excavation. The corrosion rates for these corrugated steel pipe piles were severe to moderate with respect to the percent of section loss, with a maximum section loss of 29 % and an average of 13 %.

At the 6th South site, four corrugated steel pipe piles were removed from the site. The pipe piles were filled with reinforced concrete and step-tapered with depth. The first segment was 18 in. in diameter; the second segment was 16 in. in diameter and the last segment was 14 in. in diameter. The segment wall thickness ranged between 0.045 to 0.055 in. The corrugated pipe piles were removed after about 34 years of soil-water environment exposure. The corrosion rates for these steel pipe piles were severe to

moderate with respect to the percent of section loss, with a maximum of 51 % and average of 14 %.

At the 118th South site, two steel pipe piles were removed from the site. The steel pipe piles were 12.5 in. diameter, wall thickness of 0.25 in. and filled with concrete with reinforcement limited to the top. The piles were driven at a 1:4 batter. The piles were removed for corrosion analysis after 37 years of soil-water environment exposure. The corrosion rates for these steel pipe piles were moderate to severe with an average section loss of about 8% in fill material, 13 % in the native soil and a maximum section loss of 28 % near the water table fluctuation zone.

The thickness loss versus tensile capacity loss analysis was carried out on 12 specimens from the steel pile in all the sites. Axial tension tests were conducted on these specimens. The thickness losses on these specimens are within the range of 5 and 29%.From the results of the test, the average thickness loss was about 13.3% whereas the average loss in tensile load capacity was 10.7%. The tension tests indicate that the loss often sile capacity was directly related to the loss of thickness.