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37 NACE INTERNATIONAL: VOL. 55, NO. 10 MATERIALS PERFORMANCE OCTOBER 2016 entraining agent (to avoid freezing damage). The cement type used was ordinary Port- land cement (325 kg/m 3 ) and the water/ cement ratio was 0.45 to 0.46. The only dif- ference between the two reported concrete types is that one of them contains 12 kg/m 3 of the organic corrosion-inhibiting admix- ture, which is based on amino alcohols, and marketed by Sika as FerroGard 901 † . Measurements During the past 18 years of concrete specimen exposure, a number of periodic measurements were performed to docu- ment the field performance of the different concretes. 10 These include: • The galvanic current flowing between the front and back layers of the rein- forcing steel. The interval for current measurement is three years. • The potentials on the concrete sur- face facing the road. 11 The potentials were measured with a saturated cop- per/copper sulfate (Cu/CuSO 4 ) refer- ence electrode (CSE) positioned at different spots on the concrete sur- face, and mapped . The measuring grid was equally spaced in both hori- zontal and vertical directions (100 to 150 mm). The interval for potential mapping is three years. • The chloride content in the exposed faces of the concretes. To determine chloride profiles, concrete powder was collected by drilling at intervals † Trade name. FIGURE 1 Photograph of L-shaped concrete specimens exposed to chloride-containing splash water on a highway in the Swiss Alps. FIGURE 2 Time evolution of the galvanic current between the front and back layers of the reinforcing steel mats in the reference concrete and the concrete containing the corrosion- inhibiting admixture. to a depth of 50 mm. The chloride content in the powder sample was analyzed by acid digestion and titra- tion. The first chloride profile was taken after nine years of exposure, with one profile taken per wall ele- ment. At exposure times of 13, 16, and 18 years, two chloride profiles were taken per concrete wall element. After 18 years of exposure, the concrete cover was removed from selected areas of the specimens with an electrically powered jackhammer to permit visual inspection of the corrosion state of the reinforcing steel. Results and Discussion Electrochemical Monitoring Figure 2 shows the galvanic current measured between the front and back rein- forcing steel mats in the wall elements over time. During the first seven years, these currents were below the measureable accu- racy, thus negligibly low. In the reference concrete, the galvanic current started in- creasing at approximately eight to nine years of exposure, with a significant in- crease after ~16 years. On the other hand, no marked increase of the galvanic current was observed in the concrete with inhibitor during the entire 18-year duration of the field test. The increase in galvanic current measured in the reference concrete indi- cates the onset of corrosion on the front side of the wall element after approxi- mately eight to nine years, while the negli- gibly low level of galvanic currents ob- ser ved in th e concret e containing th e corrosion inhibitor suggests the absence of relevant macrocell corrosion. These results were supported by the potential maps of the wall elements. 10 Visual Inspections Over time, more cracks and rust stains appeared on the front surface of the refer- ence concrete element than on the element made from the inhibitor-containing con- crete. After 18 years of exposure, selected small areas of reinforcing steel of the front mats were visually inspected in both ele- ments after locally removing the concrete cover. These inspected areas were selected based on the potential maps. In the refer- ence concrete, parts of the reinforcing steel mats exhibiting relatively negative steel potentials (–350 mV vs. CSE) were found to have localized corrosion attack, with up to 1.5-mm deep corrosion pits. In contrast, the reinforcing steel in the concrete con- taining the admixed corrosion inhibitor was found to b e essenti al ly free from