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12 OCTOBER 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 10 An assessment and prioritization plan helped slow corrosion at a water treatment plant. Photo courtesy of Stephen Foster. P roper assessment and inspec- tion of infrastructure can be a critical step in establishing a successful maintenance and corrosion risk management program for reinforced concrete structures, including major marine and civil infrastructure. At the NACE International Corrosion Risk Management Conference held in May, NACE member Stephen Foster, senior associate at Wiss, Janney, Elstner Associ- ates, Inc. (W JE) (Austin, Texas), explained how the key to managing risk and miti- gating reinforced concrete corrosion starts with performing inspections and developing a routine assessment pro- gram. 1 These programs can identif y and prioritize the deterioration of concrete assets, he says, as well as the associated impact and suitable repair of any corro- sion-based distress. "Numerous inspection and assess- ment techniques are available on the market to perform detailed corrosion assessments, which can be useful in determining the extent and severity of corrosion, as well as the estimated remaining service life of the structure," Foster says. In his presentation, Foster cited a case study from a project undertaken by W JE at a wastewater treatment facility. The inf luent water contained moderate amounts of chlorides prior to treatment, ranging from 150 to 250 mg/L, and had a pH of 7.2 to 7.8. The facility was under - going a capital program to extend the operating life of its structures, which included trick ling f ilters, f irst and second stage clarif iers, gravity f ilters, and waste and eff luent thickeners. "The structures exhibited various forms of ongoing concrete material and steel corrosion distress," Foster says. "This included corrosion of embedded reinforcing steel, cracking, delamina- tions, the surface erosion or scaling of concrete, and corrosion of structural steel members." The facility had been in service since about 1986 with deterioration noted and ongoing for at least the past 15 years. The owner wanted to determine the most cost-effective approach for repair, with a desired life extension of 30 years. While localized repairs had been performed selectively on areas with corrosion- related distress, an overall condition assessment had not been implemented. As a result, Foster's team performed that assessment on each of the structures showing levels of observed deterioration. The f irst step was a f ield investigation, which included visual inspections and mechanical sounding to identif y concrete cracks, delaminations, spalls, and other distress. Concrete cover was measured with an electromagnetic cover meter and verif ied at core sampling locations and half-cell survey sites at ground locations. The cor- rosion activity was assessed with half-cell potential (HCP) surveys over selected areas of the structure with copper/copper sulfate (Cu/CuSO 4 ) reference electrodes and high-impedance voltmeters. Mean- while, corrosion rate measurements were performed using linear polarization tech- niques with a portable gauge equipped with an integrated guard ring and coun- ter electrode. The second step was laboratory test- ing analysis on the concrete cores, which included petrographic evaluation, chlo- ride content, carbonation of the near- surface region, and rapid chloride perme- ability. Several of the cores were taken at the reinforcing bars to expose the bar surface for visual examination to deter- mine the degree of corrosion and the depth of concrete cover. In each case, the level of corrosion was categorized as none, moderate, or heav y. "Performing these assessments pro- vides the foundation for developing a pri- oritization model for aging assets. This can help guide planning decisions to allo- cate resources for repair and corrosion mitigation measures to ensure the long- term viability and protection of the struc- ture," Foster says. "Based upon the assess- ment results, the appropriate corrosion mitigation strategies can be selected." After performing the assessments, Foster's team found that the sump was in the worst condition of the various struc- tures. The sump showed little to no dis- tress below the waterline—but above the Assessment, Prioritization Help Slow Corrosion at Water Treatment Plant MATERIAL MATTERS