CALCIUM NITRATE MIXED CEMENT MORTAR FOR REPAIRING CORRODED RC STRUCTURES. University of Ruhuna, Sri Lanka

Transcription

1 Special Session on Construction Materials & Systems, 4 th International Conference on Structural Engineering and Construction Management 2013, Kandy, Sri Lanka, 13 th, 14 th & 15 th December 2013 SECM/13/100 CALCIUM NITRATE MIXED CEMENT MORTAR FOR REPAIRING CORRODED RC STRUCTURES B.H.J. Pushpakumara 1, G. Sudhira De Silva 2 and G.H.M.J. Subashi De Silva 3 1 Department of Civil and Environmental Engineering, Faculty of Engineering, University of Ruhuna, Sri Lanka janaka201@gmail.com 2,3 Department of Civil and Environmental Engineering, Faculty of Engineering, University of Ruhuna, Sri Lanka 2 sudhira@cee.ruh.ac.lk ; 3 subashi@cee.ruh.ac.lk Abstract Chloride induced corrosion of embedded steel reinforcement is one of the major deterioration modes of Reinforced Concrete (RC) structures. Concrete and mortar are commonly used to repair the damaged area due to corrosion. Use of corrosion inhibiting materials with repair compounds would minimize further corrosion. Calcium nitrate is commonly used with concrete as a corrosion inhibitor. The objectives of this study are to evaluate the efficiency of calcium nitrate mixed cement mortar for corroded RC structures and to determine the optimum dosage of calcium nitrate. Calcium nitrate dosages mixed with cement mortar were varied from 0% to 25% by the mass of cement in steps of 5% was used in the investigation. Eight numbers of RC beams were cast and subjected to Accelerated Corrosion Test Method (ACTM) until initiation of corrosion crack was detected. Possibility of corrosion was evaluated by measuring resistivity using resistivity meter. Corroded RC beams were covered by using 10 mm thick calcium nitrate mixed mortar. The beams were again subjected to ACTM for accelerating corrosion until the onset of 0.2 mm wide corrosion crack. The efficiency of repair mortars was evaluated by measuring free and total chloride ions, rust formation (i.e., mass of rust and reduction in bar diameter) and possibility of corrosion was evaluated by measuring resistivity. Rapid Chloride Permeability Test (RCPT) was conducted to evaluate the chloride permeability of calcium nitrate mixed cement mortars. Test results showed that 5% of calcium nitrate mixed cement mortar effectively minimizes further corrosion of reinforcements in concrete beams. Keywords: Corrosion, Repairing mortar, Calcium nitrate, Chloride concentration, Resistivity 1.0 Introduction In Sri Lanka, many Reinforced Concrete (RC) structures are located along the coastal belt. One of the serious problems affecting the service life of RC structures situated in coastal area is the formation of cracks and delaminating due to the disruptive stresses arising from chloride induced corrosion of steel reinforcements (Figure 1). When structures are in critical in corrosion, they need massive renovation or re-construction that will consume considerable portion of country s budget. The use of effective repairing and retrofitting methods at right time helps to increase the service life of RC structures; as a result there will be an enormous saving of country s budget. 22

2 Mortars are commonly used to repair delaminated areas. Also, further corrosion of embedded steel reinforcements can effectively be prevented by mixing corrosion prevention materials with mortars. Jennifer et al. (2000) have stated that, diffusion of chloride ions into the region of steel reinforcements can be minimized by increasing the density of repairing mortars, fixing free chloride ions by chemical reactions and applying water proofing materials. These repair mortars could normally consist of more than one type of cement (special cement, like ultra-fine alumina cement), additions (silica fume, slag or fly ash), aggregates (normal, light weight and special type fillers), admixtures (such as plasticizers), polymer additives, fine polymer fibres and air-entrainers and accelerators (Saraswathy & Song, 2008). (a) (b) Figure 4: Existing corroded RC bridge girders (a) Bridge at Hikkaduwa and (b) Bridge at Koggala Corrosion inhibitors are commonly used with concrete to minimize corrosion of embedded steel reinforcements. Most of the corrosion inhibitors act by chemically stabilizing the steel surface, and some of them also act to reduce the permeability of concrete (Jennifer et al., 2000). Researchers have concentrated on the use of sodium nitrate, potassium chromate, sodium benzoate, stannous chloride, calcium nitrite and calcium nitrate as corrosion inhibitors (Prabakar et al., 2009). However, Jennifer et al. (2000) found that the use of sodium and potassium salts reduced the strength of concrete and gave mixed results on corrosion inhibition. Therefore, calcium nitrite and calcium nitrate are currently used with concrete to minimize corrosion. Both nitrite and nitrate form a passive layer of Fe 2 O 3 around steel reinforcement which causes the reduction of corrosion. When considering nitrite reaction, nitrite converts into nitrate during the formation of the passive layer (Justnes, 2004). Accordingly, calcium nitrate would be an effective inhibitor that can be used with mortar to form the passive layer around the surface of steel reinforcement. Repairing of corroded RC structures is highly needed in order to increase the service life of these structures. Investigation of new repairing mortars, that will prevent or minimize the corrosion, is an urgent need for increasing the service life of RC structures in Sri Lanka. Use of corrosion inhibiting materials with mortar will delay the corrosion, eventually helping to increase the service life of RC structures. The main objective of this study is to investigate the effectiveness of a new mortar which is prepared by mixing calcium nitrate with cement mortar for repairing existing corrosion damaged RC structures. In addition, the optimum percentage of calcium nitrate in the mix is also evaluated in this study. 2.0 Methodology Performances of mortar were assessed by measuring free and total chloride ion concentrations, rust formation and resistivity for possible corrosion rates. In addition, Rapid Chloride Permeability Test (RCPT) was conducted to evaluate the chloride ion permeability through types of mortar included in the investigation. Eight RC beams were cast with Grade 20 concrete and steel reinforcements having 16 mm diameter. Three steel stirrups of 6 mm bar diameter, at middle and 100 mm away from the middle were used in each steel reinforcement cage. Two conducting wires were also set in each reinforcement cage for the purpose of connecting electricity to the reinforcement during experiments. The cross section of the RC beams is 80 mm x 130 mm, and their length is 380 mm. The clear cover to reinforcement is 10 23

3 mm. Arrangement of reinforcements in RC beams is shown in Figure 2. All RC beams were cured in water for 28 days. After curing and before performing ACTM (Stage 1), one beam was tested for free and total chloride ion concentration, rust formation and resistivity. Corrosion of remaining seven RC beams was accelerated by using Accelerated Corrosion Test Method (ACTM) until the initiation of corrosion included cracks. Resistivity of RC beams was measured by using resistivity meter and possible corrosion rate category of RC beams was identified by referring the instruction manual of the resistivity meter. After performing ACTM until initiation of corrosion, one RC beam was again tested (Stage 2) for free and total chloride ion concentrations and rust formation. Remaining six RC beams were covered with a layer of cement mortar: five beams with calcium nitrate mixed cement mortar and the remaining beam with OPC mortar without calcium nitrate (i.e., control beam). The mortar was prepared with the cement sand ratio of 1:6 for control beam. Cement in the mortar was partially replaced by adding calcium nitrate dosages varying from 5% to 25% by the mass of cement in steps of 5%. Surfaces of the RC beams were chipped, and 10 mm thick repairing mortar layer was applied on chipped surfaces, making the final clear cover to reinforcement as 20 mm (Figure 2). Repairing mortar layer Figure 5: Schematic diagram of cross section of RC test beam (Dimensions are in mm) After applying mortars, these six RC beams were again kept immersed in water for 28 days of curing. Followed by curing, RC beams were again subjected to ACTM until forming 0.2 mm wide corrosion crack. Then, free and total chloride ion concentrations, rust formation and resistivity of the six RC beams were measured (Stage 3). Eighteen mortar cylinders; comprising three cylinders having each percentage of calcium nitrate (i.e., 0%, 5%, 10%, 15%, 20% and 25%) were cast to evaluate the chloride ion permeability of mortar by using RCPT. 2.1 Laboratory experiments Accelerated corrosion test method (ACTM) Initial clear cover 5% of Cl - solution 5 V DC supply unit Copper bars (a) RC specimens (b) (c) Figure 6: Acceleration corrosion test method: (a) Schematic diagram of experimental set-up for ACTM (b) Supplying the DC and (c) Measuring the crack width 24

4 ACTM was based on the electrochemical polarization principle. The corrosion of embedded steel reinforcements was accelerated as specified in FDOT (2000) and Sahmaran et al. (2008). The beams were immersed in a sea water container where the Cl - concentration of sea water was improved up to 5% by adding NaCl. The NaCl concentration of sea water sample was measured by using titration against AgNO 3 of concentration of M (mol/l) and was found as g/l. The current for the system was supplied by using a DC power supply unit (Figure 3 (a)). The positive terminal of the unit was connected to the embedded steel reinforcements and the negative terminal was connected to the copper bars which were placed under the RC beams. Then, a small current was supplied to the system with the constant voltage of 5 V. Finally, the corrosion crack width was monitored with time as shown in Figure 3(c), until 0.2 mm width was attained Free and total chloride ion concentrations Test samples were prepared by collecting the concrete powder from several locations of each RC beam; three points at 400 mm x 150 mm surface: centre point and two points 100 mm away from the centre, at both sides. At each point, samples were collected at the depth of 10 mm and 20 mm for beams at Stage 1 and Stage 2. In addition, concrete powder samples were collected at 10 mm, 20 mm and 30 mm depth for beams at Stage 3. The power sample collected at10 mm depth of Stages 1 and 2 beams, and 20 mm depth of Stage 3 beams were similar (i.e., they were near the level of steel reinforcement). Furthermore, the samples collected at 20 mm depth of Stages 1 and 2 beams, and 30 mm depth of Stage 3 beams are similar. For each beam, the concrete powder samples, which were collected at the same depth, were mixed and separately sieved through 75 µm sieve. For each depth, two samples of 5 g were prepared to measure total and free chloride ion concentrations. One 5 g sample was mixed with 50 ml of 0.05 mol/l nitric acid (HNO 3 ) and stirred for 10 minutes using a magnetic stirrer to extract acid-soluble chlorides which were mostly equivalent to total chloride ions. Free chloride ion concentration was measured using the remaining 5 g sample. The sample was mixed with 50 ml distilled water and stirred for 10 minutes using a magnetic stirrer to extract water-soluble chloride ions which were mostly equivalent to free chloride ions. Each solvent sample was filtered through a filter paper and 20 ml samples were prepared. Finally, all filtered samples were titrated against M silver nitrate (AgNO 3 ) and the free and total chloride ion concentrations were measured Rust formation Rust formation of embedded steel reinforcement was measured by using two methods: mass of rust (W) and reduction in bar diameter (Φ r ). The steel reinforcements were carefully removed from the beams and the bar surface was scrapped in order to collect rust. The mass of the collected rust was measured. The bar diameter (Φ) was measured by using a vernier calliper and the reduction in bar diameter (Φ r ) was determined. The average values of mass of rust (W) and reduction in bar diameter (Φ r ) were calculated to represent the rust formation on steel reinforcements Resistivity Resistivity meter (James RM-8000) was used in assessing the possible rate of corrosion in steel reinforcements with the electrical resistivity measurement method. Two holes with the diameter of 6 mm, which are at 50 mm apart (along the steel reinforcement) and 8 mm deep, were drilled on the surface of beam (Figure 4 (a)). The stainless steel template, which was provided with the resistivity meter, was used to identify the location of the additional holes (Figure 4 (b)). The two holes were filled with conductive gel (Figure 4 (c)). This was necessary to create good contact between concrete and the resistivity meter probes which were immersed into the holes as shown in Figure 4(d). Resistivity (in kω cm) was measured and the possible corrosion rate of steel reinforcements was categorized by referencing the resistivity levels provided with the Resistivity meter; possible corrosion rate for resistivity: <5 = Very high, 5-10 = High, = Moderate to low and >20 = Insufficient (Instruction manual). 25

5 (a) (b) (c) (d) (e) Figure 7: Procedure of measuring resistivity (a) Preparation of 8 mm depth hole (b) Preparation of additional hole at 50 mm apart (c) Use of conductive gel (d) Placing resistivity meter and (e) Measuring resistivity Rapid chloride permeability test Figure 8: RCPT experimental setup Rapid Chloride Permeability Test (RCPT) was performed on every type of cement mortar to evaluate chloride ion permeability following the ASTM C1202 procedure as described by Ganesan et al. (2007). Eighteen mortar cylinders, comprising three cylinders for each calcium nitrate percentage, and having diameter of 100 mm and height of 50 mm were cast by using 1:6 cement sand mortar. Cement in the mortar was partially replaced by calcium nitrate dosages varying from 0% to 25% by the mass of cement in steps of 5%. After 90 days of curing, all the cylinders were placed in RCPT experimental setup (Figure 5). Two copper electrodes were connected to terminals and the positive terminal was immersed in 0.3 N NaOH solution reservoir while the negative terminal was immersed in 3% NaCl solution reservoir. The cylinders were connected between two reservoirs as shown in Figure 5(b). With constant voltage of 60 V, DC was supplied to the system; the current through the cylinder was recorded at 30 minute intervals over a period of 6 hours. The total Charge Passed (CP) through the specimen was computed by Simpson s rule (Equation 1) following ASTM C1202 procedure as described by Ganesan et al. (2007). where CP is total charge passed in coulombs, I 0 is the initial current in Ampere (A) and I t is current in Ampere (A) at time t, measured in minutes. (1) 3.0 Results Performances of the calcium nitrate mixed mortars were investigated by measuring free and total chloride ion concentrations, rust production, resistivity and permeability and are presented in this section. 26

6 Cl - concentration (kg/m 3 ) Cl - concentration (kg/m 3 ) 3.1 Free and total chloride ion concentration The Cl - concentration was determined at three different stages: before performing ACTM (Stage 1), after performing ACTM until initiation of corrosion (Stage 2) and after performing ACTM on mortar laid RC beams until 0.2 mm wide corrosion crack was formed (Stage 3). Table 1 shows free and total chloride ion concentrations of RC beams at Stages 1 and 2. Table 1: Free and total chloride ion concentrations at Stages 1 and 2 Depth level Stage 1 Stage 2 Free (kg/m 3 ) Total (kg/m 3 ) Free (kg/m 3 ) Total (kg/m 3 ) 10 mm mm Figure 6 (a) and (b) respectively show free and total Cl - concentrations of RC beams at Stage 3. At Stage 3, depths of 10 mm, 20 mm and 30 mm respectively represent the end of almost internal layer of mortar, embedded steel reinforcement level and 10 mm away from reinforcement level into RC beam area OPC 5% 10% 15% 20% 25% 0 OPC 5% 10% 15% 20% 25% (a) CaNO 3 mixed percentage (%) 10 mm 20 mm 30 mm (b) CaNO 3 mixed percentage (%) 10 mm 20 mm 30 mm Figure 9: Chloride ion concentrations (a) Free Cl - concentration (b) Total Cl - concentration It can be seen from Figures 6(a) and 6(b) that, both free and total chloride ion concentrations of 5% and 10% calcium nitrate mixed cement mortar are lesser value compared to OPC (0%) mortar. This trend was common for all depth levels (i.e., 10 mm, 20 mm and 30 mm). After 10% calcium nitrate level, free and total Cl - concentrations are increasing with increasing the calcium nitrate percentages (i.e., 15%, 20% and 25%). At 20 mm depth level, total Cl - concentrations of OPC, 5% and 10% calcium nitrate mixed cement mortar are kg/m 3, kg/m 3 and kg/m 3, respectively. 3.2 Rust formation The rust formation was measured at three different stages: before performing ACTM (Stage 1), after performing ACTM until initiation of corrosion (Stage 2) and after performing ACTM for mortar laid RC beams until 0.2 mm wide corrosion crack was formed (Stage 3). Table 2 shows the rust formation results for calcium nitrate mixed cement mortar laid RC beams. 27

7 It can be seen from Table 2 that, the rust production (Stage 3) of 5% (W = g and Φ r = 0.52 mm) and 10% (W = 1.49 g and Φ r = 1.65 mm) of calcium nitrate mixed cement mortar applied beams are less than that of OPC mortar (W = 2.04 g and Φ r = 2.30 mm) applied beams. For calcium nitrate dosages greater than 5%, the rust formation was observed to be increasing with increasing calcium nitrate percentage (i.e., 10%, 15%, 20% and 25%). Table 2: Rust production Inspection Stage Average weight of rust (W) (g) Average bar diameter (Φ) (mm) Average reduction in bar diameter (Φ r ) (mm) Stage Stage (0%) OPC % Stage 3 10% % % % Resistivity Table 3 shows the resistivity of RC beams measured at three Stages: before performing ACTM (Stage 1), after performing ACTM until initiation of corrosion (Stage 2) and after performing ACTM for mortar laid RC beams until 0.2 mm corrosion crack was attained (Stage 3). In Table 3, it can be clearly seen that resistivity of 5% (13.5 kω.cm) and 10% (9.6 kω.cm) calcium nitrate mixed cement mortar laid RC beam is a higher than that of OPC mortar (4.7 kω.cm) laid RC beam. In addition, resistivity of RC beams at Stage 1 (33.1 kω.cm) and Stage 2 (17.8 kω.cm) are higher than that at Stage Rapid chloride permeability test (RCPT) Figure 7 (a) and (b) show, respectively, the variation of current with time and the corresponding charge passed (CP) values (calculated by using Eq.(1)) for calcium nitrate mixed cement mortar cylinders. It can be seen from Figure 7 (b) that, the charge passed (CP) through 5% (5238 C) and 10% (6990 C) calcium nitrate mixed cement mortar are lower than that through control (OPC) mortar (7086 C). Furthermore, with calcium nitrate level increasing beyond 5%, the amount of charge passed is increasing with increasing calcium nitrate percentage (i.e., 10%, 15%, 20% and 25%). 28

8 Current (A) Charge passed (Coulumbs) Table 3: Resistivity of RC beams Inspection Stage Average resistivity (kω.cm) Stage Stage % (OPC) 4.7 5% 13.5 Stage 3 10% % % % Time (min) OPC 5% 10% 15% 20% 25% (a) Figure 10: RCPT results (a) Variation of current with time (b) Charge passed values 0 (b) 4.0 Discussion According to the JSCE (2001), the critical Cl - concentration is 0.3 ~ 0.6 kg/m 3, and when the Cl - concentration exceeds 1.2 ~ 2.4 kg/m 3, the corrosion incorporating micro-cracks might be initiated (Veerachai et al., 2005). Simply, when the Cl - concentration of RC beams is higher than 0.6 kg/m 3, the critical Cl - level, was achieved (i.e., corrosion risk initiate) and when it increases to 1.2 kg/m 3, the corrosion is initiated on embedded steel reinforcement. The threshold of Cl - concentration for onset corrosion is considered as 1.2 kg/m 3 ( Gunesekara et al., 2011). 29

9 Since the steel reinforcements were embedded at depth of 20 mm in beams at Stage 3, most critical depth region related to corrosion was considered as less than 20 mm depth. The total Cl - concentration, at 20 mm depth of OPC mortar applied beam (1.261 kg/m 3 ) (Figure 6 (b)) is higher than the threshold value of 1.2 kg/m 3, hence the beam was corroded. The total Cl - concentrations at the same depth, 5% and 10% of calcium nitrate mixed cement mortar applied RC beams (0.735 kg/m 3 for 5% and kg/m 3 for 10%) were less than the threshold value of 1.2 kg/m 3 ; hence the corrosion risk is minimized. The total Cl - reduction, at 20 mm depth level, in the beam repaired with 5% and 10% of calcium nitrate mixed cement mortar was kg/m 3 and kg/m 3, respectively. Therefore, compared to OPC mortar, 5% and 10% of calcium nitrate mixed cement mortar reduces Cl - concentration near embedded steel reinforcements by 41.7% and 35.5%, respectively. In addition, 5% of calcium nitrate mixed cement mortar shows higher Cl - reduction compared to 10% of calcium nitrate mixed cement mortar. The rust formation (both mass of rust and reduction in bar diameter) of OPC mortar applied beam is higher compared to that of 5% and 10% of calcium nitrate mixed cement mortar applied beams (Table 2). Further, rust formation of 5% of calcium nitrate mixed cement mortar applied beam is less than (i.e., W = g, Φ r = 0.52 mm) the corresponding amount in OPC mortar applied beam (control beam) (i.e., W = 2.04 g, Φ r = 2.30 mm) and 10% of calcium nitrate mixed cement mortar applied beam (W = 1.49 g and Φ r = 1.65 mm). This implies that the calcium nitrate dosage up to 5% of OPC reduces the corrosion of embedded steel reinforcements with respect to only OPC mortar. According to Table 3, possible corrosion rates of RC beams which were at Stage 1(33.1 kω.cm) and Stage 2 (17.8 kω.cm), are Insufficient and Moderate to low, respectively. Therefore, RC beams at Stage 1 were not corroded while corrosion in RC beams at Stage 2 was initiated. In addition, possible corrosion rate with OPC mortar (i.e., 4.7 kω.cm) applied beam is Very high (resistivity < 5 kω.cm) while that is High (resistivity between 5 to 10 kω.cm) in the RC beams repaired by using 10% calcium nitrate mixed cement mortar (i.e., 9.6 kω.cm) and Moderate to lower (resistivity between 10 to 20 kω.cm) in the RC beams repaired with 5% calcium nitrate mixed cement mortar (i.e., 13.5 kω. cm). These results imply that the internal corrosion level of the beam repaired with 5% of calcium nitrate mixed cement mortar has significantly reduced. According to Figure 7 (b), charge passed values through 5% (5238 C) and 10% (6990 C) calcium nitrate mixed mortar are lower than the corresponding value for the OPC mortar (7086 C). Further, 5% calcium nitrate mixed mortar shows the lowest charge passed which reflects reduction in chloride ion diffusion through repair cement mortar compared to that through OPC mortar. Reducing chloride ion diffusivity helps to reduce the Cl - concentration near embedded steel reinforcements, helping to delay the on set of corrosion, and to reduce its rate. Justnes (2004) shows that the 4% of calcium nitrate as an inhibitor for concrete is sufficient to minimize the corrosion risk of RC structures. Further, Prabakar et al. (2009) have used 1%, 2%, 3% and 4% of sodium nitrate (NaNO 3 ) with concrete and predicted that the 4% of sodium nitrate is sufficient to prevent corrosion risk. The use of large amount of NO 3 - causes the increasing of ion diffusion through concrete (Justnes, 2004). Nitrate ions create alkaline condition in concrete which helps to form iron oxide (Fe 2 O 3 ) film around the embedded steel reinforcement (Justnes, 2004). The formation of this iron oxide film prevents the diffusion of Cl - to steel reinforcement. Therefore, the steel reinforcements have passivated and prevent the corrosion. Further, calcium ions (Ca 2+ ) may react with chloride ions and produce calcium chloride, which helps to minimize the amount of free chloride ions. The free chloride ions are directly involved with the corrosion. Use of 5% of calcium nitrate with cement mortar helps to reduce the diffusion of chloride ions, form iron oxide film, which helps to repassivate steel reinforcements and minimize the amount of free chloride ions. 30

10 5.0 Conclusion Corrosion of steel reinforcements in concrete causes the deterioration of Reinforced Concrete (RC) structures. The service life of RC structures can be increased by repairing the deteriorated locations. Use of corrosion inhibiting materials with an effective repairing mortar can minimize the propagation or continuation of corrosion in existing corroded RC structures. The efficiency of calcium nitrate mixed cement mortar for containing further corrosion of corroded RC structures was experimentally evaluated based on the measurements of free and total chloride ion concentrations, rust formation, resistivity and chloride ion permeability, and the findings are presented in the paper. It was found that the 5% and 10% of calcium nitrate mixed cement mortar shows better performances compared to OPC (control specimen) mortar. Compared to OPC mortar, 5% and 10% of calcium nitrate mixed cement mortar reduces Cl - concentration near the embedded steel reinforcements by around 42% and 35%, respectively. Considering all the experimental results, mortar with 5% calcium nitrate performs better than those having 10% or more calcium nitrate. Therefore, the use of partial replacement of cement with 5% of calcium nitrate by mass can be considered as the dosage for preparing cement mortar with optimum performance to minimize the continuation of corrosion and hence to enhance the service life RC beams. Acknowledgement The authors wish to express their special thanks to Research Grant of Transforming University of Ruhuna to International Status (TURIS-2011) for providing necessary funds and Faculty of Engineering, University of Ruhuna for providing technical assistance for carrying out the research work presented in this paper. Authors sincere thanks to Prof. Hiroshi Mutsuyoshi, Department of Civil and Environmental Engineering, Saitama University, Japan for providing necessary experimental materials and technical guidance. References Florida Department of Transportation (FDOT) (2000): An Accelerated Laboratory Method for Corrosion of Reinforced Concrete Using Impressed Current, Manual of Florida Sampling and Testing Methods, Tallahassee, FL, pp. 6 Ganesan, K., Rajagopal, K. and Thangavel, K. (2007): Chloride resisting concrete containing rice husk ash and bagasse ash, Indian Journal of Engineering & Materials Sciences, Vol.14, pp Gunasekara, M.P.C.M., Mutsuyoshi, H. and Sumita, A. (2011): Renovate RC structures with newly developed mortar considering chloride binding and inverse diffusion phenomenon, International Conference on Structural Engineering, Construction and Management (ICSECM), Kandy, Sri Lanka Jennifer, L.K., David, D. and Carl, E.L. (2000): Evaluation of corrosion protection methods for reinforced concrete highway structures, Structural Engineering and Engineering Materials, SM Report No.58, University of Kansas Center for Research, Inc., Lawrence, Kansas Justnes, H. (2004): Preventing chloride induced rebar corrosion by anodic inhibitors Comparing calcium nitrate with calcium nitrite, Proceeding of 29 th Conference on Our World in Concrete and Structures, Singapore, pp NDT James Instruments Inc.: Instruction Manual - RM-8000 Resistivity Meter, James Instruments Inc., Chicago, U.S.A. 31

11 Prabakar, J., Manoharan, P.D. and Neelamegam, M. (2009): Performance evaluation of concrete containing sodium nitrate inhibitor, Proceedings of the 11 th International Conference on Nonconventional Materials and Technologies (NOCMAT), Bath, United Kingdom Saraswathy, V. and Song, H. (2008): Evaluation of cementitious repair mortars for corrosion resistance, PortugaliaeElectrochimicaActa, 26/5, pp Sahmaran, M., Li, V.C. and Andrade, C. (2008): Corrosion Resistance Performance of Steel- Reinforced Engineered Cementitious Composite Beams, ACI Materials Journal, V. 105, No. 3, pp Veerachai, L., Toshimitsu, S., Yuichi, T. and Masayasu, O. (2005): Estimation of corrosion in reinforced concrete by electrochemical techniques and acoustic emission, Journal of Advanced Concrete Technology, Vol. 3, No.1, pp