Corrosion Prevention for Extending the Service Life of Steel Bridges (2018)

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65 Steel bridges contain horizontal surfaces and other geometries that tend to collect water and debris. Collected debris has a variety of negative impacts including increasing steel corrosion. Bridge cleaning is becoming more common as highway agencies focus on asset management and preservation practices. Sixteen of the states responding to the survey indicated that they performed some type of bridge washing as a corrosion-prevention measure. In addition to removing soluble salts, bridge cleaning helps keep drainage paths clear and removes poultice. Both uncoated and coated steels last longer if they are not subject to the immersion condition that exists under ponding water. Bridge cleaning activities may include flooding drainage paths, pressure washing, and/or removing debris by sweeping/shoveling (“dry cleaning”). Northern states often perform bridge cleaning in the spring after the end of the road- salting season. Runoff from bridge cleaning is a potential environmental concern. Organic material can affect the dissolved oxygen content of water bodies beneath the bridge. The cleaning operation may dislodge paint or other debris that contains heavy metals such as lead, zinc, or copper. States need to perform washing activities in accordance with the rules established by the local envi- ronmental agencies. These rules may limit when certain bridges may be washed, the pressure and/or volume of wash water, the use of chemical additives, and the frequency of washing. Benefits of Bridge Cleaning In 2010, the Midwest Bridge Working Group performed a survey on bridge washing. Six states indicated that they wash the best they can every 1 to 2 years with emphasis on certain structures/ structure areas. The general sense was that there is a benefit, but some dissent existed and there was no quantifiable analysis. The University of Washington performed a study to identify the key variables for and ben- efits of a bridge-washing program (Berman et al. 2013). The report provided a brief literature review and results of a survey on bridge-washing practices. At least 11 states reported washing their bridges once every 1 to 5 years (Figure 39). Based on a literature review and nationwide survey, it was concluded that bridge washing is beneficial, but “little information on the effects of bridge washing exist and it is only deemed beneficial based on anecdotal assumptions” (Berman et al. 2013). Rhode Island DOT (RIDOT) has reported that the agency’s bridge-washing and drainage- maintenance program improves bridge inspection quality and bridge inspector safety and pro- vides service life benefits. An evaluation of Pontis data suggests an average savings of $20,000 per bridge every 8 years if the bridges were washed and cleaned on a regular basis. C H A P T E R 5 Bridge Cleaning

66 Corrosion Prevention for Extending the Service Life of Steel Bridges The University of Pittsburgh investigated the effectiveness of cleaning practices on three Pennsylvania bridges that experience anti-icing and deicing practices typical for the Northeast (Alland et al. 2013). After the winter salting season, the structures were washed using pressure washers and potable water. The study included the testing of the surface before and after washing using the ARP Instruments soluble salt meter (SSM) owing to its ease of use on easily accessible, flat steel surfaces. Figure 40 shows a typical set of measurements using the SSM. Figure 41 shows a summary of the data collected at 15 locations. The data show a salt reduction of between 20% and 95%, depending on the location. Palle et al. (2003) of the Kentucky Transportation Center (KTC) evaluated bridge cleaning, bridge cleaning with additives, and surface preparation. In their study, the sleeve style test was used for all salt measurements. The KTC study showed three examples of washing a structure with water at a pressure of 3,500 psi. Table 16 shows the results of their study before and after washing. Most test areas show nearly a complete remediation of chloride, even in low quantities. Figure 39. Frequency of bridge washing in various states (re-created from Berman et al. 2013). Figure 40. Typical data set for salt concentration before and after washing.

Bridge Cleaning 67 Bridge Cleaning with Additives Independent testing showed that the use of a soluble salt remover can cause a 50% reduction in surface chlorides versus water washing after abrasive blasting steel panels in a lab scenario (KTA-Tator 1995). Another study (written by the manufacturer) documented the value of washing with an additive during cleaning of bridges in Illinois (Johnson 2003). The reported data suggest that the additive can reduce the total salts by up to 83%, whereas water alone reduced the total salt levels by 56% or less. No matter the initial chloride concen- tration, the final chloride concentration was between 8.3 and 9.4 µg/cm2. In the report, the data for the salt remover wash is identical for the urban and suburban structures, a possible reporting error. The KTC study included the use of the same additive while pressure washing. Unfortunately, the test area in which it was used did not have salts before cleaning, making the postwash mea- surement of 0 µg/mL of little value. Figure 41. Summary of data on washing effectiveness for salt removal. Test Area A: I-71 Crossing Over I-75 (µg Cl–/mL) Location 1A 2A 3A 4A Prewash 23 7 7 25 Postwash 1 7 0 0 Test Area C: I-71 Crossing Over I-75 (µg Cl–/mL) Location 1C 2C 3C 4C Prewash 7 5 11 15 Postwash 0 0 0 3 Test Area A: KY-355 (µg Cl–/mL) Location 4A Prewash 8 Postwash 0 Table 16. Prewash and postwash chloride measurements by KTC.