 Advances in Technology Innovation, vol. 2, no. 1, 2017, pp. 22 - 24 22 Experimental Study of Leaching and Penetration of Nitrite ions in Nitrite-type Repair Materials on the Surface of Concrete Masumi Inoue 1,* , Heesup Choi 1 , Yuhji Sudoh 2 , and Koichi Ayuta 1 1 Department of Civil and Environmental Engineering, Kitami Institute of Technology, Hokkaido, Japan. 2 Chemicals Division. Basic Chemicals Department, Nissan Chemical Industries, Ltd., Tokyo, Japan. Received 29 January 2016; received in revised form 25 March 2016; accepted 28 March 2016 Abstract This study aimed to clarify the leaching properties of nitrite ions in nitrite-type repair materials exposed to rainfall. Repaired concrete specimens were prepared for leaching tests using a lithium nitrite solution, and the amounts of leaching and penetration of nitrite ions were measured under simulated rainfall. The results demonstrated that the amount of leaching could be controlled by using polymer cement paste and mortar surface coatings containing lithium ni- trite solution, and by using polymer cement mortar surface coatings following direct lithium nitrite solution coatings. Furthermore, the amount of nitrite ion leaching in all cases was lower than the discharge standard value estab- lished by the water pollution control law. Keywords: Nitrite-type repair material, nitrite ion, leaching, penetration, polymer cement mortar, polymer cement paste 1. Introduction In general, nitrite-type repair materials are commonly used for the purpose of minimizing of corrosion of reinforcements in concrete structures. It is widely known that nitrite ions effectively regenerate passive films on rein- forcement surfaces of concrete as they penetrate the surrounding areas [1-3]. However, since nitrite ions easily dissolve in water, there is concern that they can be leached from the sur- faces of repair materials upon exposure to rain- fall. The aim of this study was to elucidate the leaching properties of nitrite ions in nitrite-type repair materials exposed to rainfall. Repaired concrete specimens were prepared for leaching tests using a lithium nitrite solution, and the amounts of leaching and penetration of nitrite ions were measured under simulated rainfall conditions. 2. Method The repair methods, which used a 40% water solution composed of lithium nitrite (LN40), are shown in Table 1. These methods are widely used in repair work sites. The repaired concrete specimen is shown in Fig. 1. The water-cement ratio was 60%. The specimen was demolded one day after casting, cured in water (20±1 °C) until the age of seven days, and then stored in room-temperature con- ditions (20±1 °C and 50±5% relative humidity). After curing, the test surface was polished with a sand paper, and cleaned via air-cleaning, and the specimens were repaired using LN40. After repairing, the repaired specimens were cured in room-temperature conditions (20±1 °C and 50±5% relative humidity) for seven additional days. The specimen surfaces excluding test surfaces were coated with an epoxy resin in order to prevent nitrite ion penetration. The installation conditions of the specimens are shown in Fig. 2. Specimens were installed at a 35° angle and attached to an acrylic plate on the side. In the leaching test, distilled water simulating rainfall was sprayed to the specimen test surfaces. The amount of water sprayed each day was 1.86 g/mm 2 , a value reflecting the av- * Corresponding author, Email: m-inoue@mail.kitami-it.ac.jp Advances in Technology Innovation, vol. 2, no. 1, 2017, pp. 22 - 24 23 Copyright © TAETI erage annual rainfall in Japan (about 1,700 mm). A wet-dry cycle consisted of one day of spraying and three days of drying, a pattern reflecting the average annual rainfall in Japan (about 128 days). The wet-dry cycle was repeated for one year (91 cycles). Distilled water was sprayed every two hours from 10:00 AM to 4:00 PM on a spraying day. The amount of water sprayed each time was 0.465 g/mm 2 (a quarter of 1.860 g/mm 2 ). Distilled water flowing down the test surface was collected after every spraying, and the leached nitrite ion (NO2 - ) concentration was measured using ion chromatography. In the penetration test, distilled water simulating rain- fall was sprayed using the same method as the leaching test. However, the NO2 - concentration in the repair material and repaired concrete was measured at 6 months (45 cycles) and 1 year (91 cycles). Table 1 Repaired concrete specimens Name of specimen Repair method NO2 - solid amount (g) Leaching Penetration N Non repair 0 - LN Coating of LN40 6.26 0.70 LNPCP Surface coating by PCP*1 using LN40 (Thick- ness:2mm) 12.4 1.34 LNPCM Surface coating by PCM*2 using LN40 (Thick- ness:5mm) 22.9 2.54 LN+PCM Surface coating by PCM*2 after coating of LN40 (Thickness:5mm) 6.26 - *1: Polymer cement paste, *2: Polymer cement mortar Table 2 Leaching ratio of NO2 - amount of leaching to NO2 - solid amount after 91cycles Repair method LN LN PCP LN PCM LN +PCM NO2 - solid amount in repair material (g) 6.3 12.4 22.9 6.3 After 91 cycles NO2 - leaching (g) 1.39 0.52 0.93 0.49 NO2 - leaching ratio (%) 22.2 4.2 4.1 7.8 (a) Leaching test (b) Penetration test Fig. 1 Specimen overview Fig. 2 Installation conditions of specimens 3. Results and Discussion The NO2 - concentration changes found in the leaching test are shown in Fig. 3, and the ratio of NO2 - amount of leaching to NO2 - solid amount after 91cycles is shown in Table 2. The NO2 - leaching amount of LN was largest after every cycle, and the leaching ratio of NO2 - solid amount after 91 cycles was about 22%. The NO2 - leaching amount of LN+PCM after one cycle decreased by about 70% compared with that of LN. This is because the NO2 - leaching was controlled by the PCM coating. On the other hand, the NO2 - leaching amount of LNPCM was larger than that of LNPCP. However, the leaching ratio of NO2 - solid amount of LNPCM was almost same as that of LNPCP, as shown in Table 2. This implies that there is no actual difference between the leaching properties of LNPCP and LNPCM. It was confirmed that the NO2 - concentration in all the repair methods changed at roughly 10 cycles. Afterwards, the change in NO2 - concentration was small. Although small amounts of NO2 - were de- tected, the concentrations of all repair methods after 10 cycles were almost same as that of N (non-repair). Therefore, it is thought that NO2 - hardly leached after 10 cycles for this experi- mental range of conditions. Considering the discharge standard of the water pollution control law, the NO2 - leaching amount of all cases in Advances in Technology Innovation, vol. 2, no. 1, 2017, pp. 22 - 24 24 Copyright © TAETI every cycle was smaller than that of the dis- charge standard value (329 ppm). The ratio of NO2 - amount of leaching and penetration to NO2 - solid amount in repair ma- terials after 91 cycles is shown in Fig. 4. The NO2 - penetration and leaching ratio of LN were about 74% and 22%, respectively. On the other hand, in the case of LNPCP and LNPCM, both addition ratios of the amount of ion penetration in concrete and residual ions in the repair mate- rials were about 90%. Furthermore, both leach- ing ratios were equal to about 4%. Therefore, it is thought that NO2 - leaching can be controlled using PCP or PCM containing LN40. The total ratios of NO2 - amounts of leaching and penetra- tion including residual ions in repair materials were about 93-96%, and there was little differ- ence between NO2 - solid amount of repair ma- terial and total NO2 - solid amount after 91 cycles. However, the difference was within the range of measurement error of ion chromatography. Therefore, it is thought that the behavior internal and external of NO2 - in nitrite-type repair materi- als was mostly evaluated. Fig. 3 Change of NO2 - concentration in leaching test 4. Conclusions The aim of this study was to clarify the leaching properties of nitrite ions in nitrite-type repair materials upon exposure to rainfall. Re- paired concrete specimens were prepared using lithium nitrite solution for leaching tests, and the amounts of leaching and penetration of nitrite ions were measured under simulated rainfall. The following conclusions were drawn from the investigation. 1) It was confirmed that the NO2 - concentration in all repair methods changed at approximately cycle 10. Subsequent changes in NO2 - con- centration were small. 2) The NO2 - leaching amounts of all repair methods in all cycles were smaller than that of the discharge standard value. 3) The NO2 - leaching can be controlled using PCP and PCM surface coatings with the ad- dition of LN40 and surface coating by PCM after direct coating with LN40. Fig. 4 Ratio of NO2 - amount of leaching and penetration to NO2 - solid amount in repair materials after 91 cycles References [1] A. M. Rosenberg, et al., “A corrosion in- hibitor formulated with calcium nitrite for use in reinforced concrete,” ASTM, STP 629, pp. 89-99, 1977. [2] A. Kobayashi, S. Ushijima, I. Kamuro, and M. Koshikawa, “A study on the protection of steel in concrete by penetrative corrosion inhibitor,” Journal of Japan Society of Civil Engineers, vol. 1990, no. 420, pp. 51-60, 1990. [3] T. Hori, S. Yamasaki, and Y. Masuda, “A study on the corrosion inhibiting effect of mortar with high nitrite content,” Concrete Research and Technology, vol. 5, no. 1, pp. 89-98, 1994.