Investigation of Hematite (α-fe2o3) Nanoparticle Treatment in Mitigating Corrosion in Reinforced Concrete

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1 Investigation of Hematite (α-fe2o3) Nanoparticle Treatment in Mitigating Corrosion in Reinforced Concrete F. F. Parreño 1, O. V. M. Antonio and M. D. L. Balela 2 Institute of Civil ngineering, University of the Philippines Diliman, Quezon City, Philippines. omantonio@up.edu.ph 1 Institute of Civil ngineering, University of the Philippines Diliman. 2 Department of Mining, Metallurgical and Materials Engineering, University of the Philippines Diliman. Abstract Corrosion of steel causes degradation of the strength and quality of reinforced concrete. This study investigated the use of hematite (α-fe2o3) nanoparticles for protecting steel from corrosion. Nanoparticle treatment was divided into two methods of application: α-fe2o3 nanoparticles were incorporated into the concrete through mixing and application from the concrete surface through an electrical connection. The evaluation of the effectiveness of the α-fe2o3 nanoparticles in hindering corrosion was done through half cell potential measurements, corrosion current monitoring, steel loss, surface crack mapping and rust stain rating. Results of evaluation among the five evaluation procedures suggested that the nano-mixed samples exhibited best condition and control samples have the worst conditions of corrosion. Surface-applied samples also have less corrosion compared to the control samples. Physical examination and surface rust stain ratings also conformed to this observation. Keywords: corrosion, nanoparticle, nondestructive test, half-cell potential, steel loss 1. Introduction The deterioration of steel reinforcements has become a national and international economic problem due to its associated repair and maintenance cost. Corrosion costs money and even lives, resulting in dangerous failures. It covers around 3% of the worlds GDP that is worth 2.2 trillion USD [1]. Although structural codes provide guidelines for concrete cover and water-to-cement ratio for concrete members exposed to corrosive environment, an emerging technology can be explored to address corosion problems. The performance of nanoparticle treatment in mitigating corrosion can be assessed to determine probable use of nanotechnology in reinforced concrete structures. With further study, nanotechnology can provide developed methods that will give less harm to the environment. This study aims to evaluate the metal oxide α-fe 2O 3 nanoparticles in protecting the steel against corrosion. Half Cell Potential Techniques will be performed to generate the potential distribution versus time plot which will be used to determine the probable occurrence of corrosion. Corrosion current will be monitored during the accelerated corrosion method. The corrosion current will be plotted with respect to time and from this curve, it is expected to obtain the theoretical value of the steel loss through Faraday's Second Law. The computed steel loss will be verified by washing the steel with acid solution. Also, physical examination will be performed. Surface cracks formed in the concrete will be traced and [ID291] 1

2 measured. In order to quantify the visual condition of the specimen, evaluation will be rated numerically by setting values for best and worst conditions. The metal oxide nanoparticles that will be used in the study are laboratory prepared hematite nanoparticles. This specific nanoparticle is chosen due to its compatibility to cement composition (Fe 2O 3). Two types of nanoparticle applications will be used. The first is the treatment mechanism using electrochemical circuit set-up while the second is directly adding the nanoparticles into the concrete mix. The corrosion mechanism that will be implemented in the laboratory is NaCl induced corrosion which is evident in marine environments even at vicinities of no direct contact with sea water. The concrete specimens that will be subjected to accelerated corrosion method do not simulates the actual chloride content but only aims to accelerate the rate of corrosion through laboratory methods. 2. Methodology 2.1. Preparation of Hematite Nanoparticles The first step was to mix 2 mmol iron chloride (FeCl 3) and 2 mmol of sodium sulphate (NaSO 4) into 80 ml deionized water (DI). The solution was heated in the oven for 1 hour for 120 C. After the heating process, the solution was left in the oven for several hours to cool down to room temperature. The particles were collected using a centrifuge. The collected particles were washed with DI three times and the final wash was done with ethanol. The retained particles in the centrifuge tubes were collected for oven drying at 80 C for 2 hours. The dried powder (FeOOH) was annealed in the furnace at 400 C for 2 hours with ramping rate of 2 C per minute. The powder was transformed from FeOOH to Fe 2O 3 nanoparticles Concrete Proportioning and Mixing Concrete strength of 5,000 psi with water-to-cement ratio of 0.4 was used as specified by the American Concrete Institute standards, ACI 318 for concrete exposed to corrosive environment. The maximum aggregate size used for all specimens was 19 mm and Ordinary Portland Cement was used as a binding medium. The concrete mix proportions were computed based on ACI which uses slump of 1 to 4 inches. Table 1 shows the proportions of the concrete components. All the concrete specimens have dimensions 150 mm by 150 mm by 200 mm with embedded 25 mm diameter steel bar. The dimensions were based on the concrete cover specified by ACI 318. The steel bars were cleaned to ensure no initial rust were present particularly at the surface area that was embedded in concrete. [ID291] 2

3 Slump mm Coarse Aggregates kg/m 3 Fine Aggregates kg/m 3 Cement kg/m 3 Water 200 kg/m Nanoparticle Mixed to the concrete Table 1: Concrete Proportioning based on ACI Maximum replacement level for the cement is up to 2% that gives noticeable increase in compressive strength [2]. 0.2% addition of the nanopowder to the cement was chosen for the treatment which yields 0.6 g per specimen. The addition of the nano-powder was made only at the inner 50 mm radius inside the rectangular specimen. This was to concentrate the Fe2O3 nanoparticles at the vicinity near the reinforcing steel. The inner concrete was mixed separately by hand and was poured into the mold using 75-mm diameter tube (Figure 1). Figure 1: Nanoparticles mixed in concrete 2.4 Nanoparticle Surface Application The nanoparticles were dispersed into deionized water (DI). The concrete was covered with sponged for the particles to retain during the electrical driving. Aluminum wire mesh was used for the conductor along the surface area of the specimen. The set-up was a parallel circuit applying minimal current ranging from 0.03 A to 0.15 A to avoid severe initiation of corrosion (Figure 2). Figure 2. Surface Treatment Set-up. [ID291] 3

4 2.5. Accelerated Corrosion Method Each batch of the samples was subjected to accelerated corrosion separately. The Florida Method was adapted for accelerated corrosion set-up except that the concentration of the Sodium Chloride (NaCl) was increased to 10%. The samples in the corrosion tank were set parallel in a direct current (DC) circuit, each sample in series with an ammeter. Throughout the corrosion period, the voltage was varied from 15 to 25 volts and the current was set to the maximum turn of knob. The maximum voltage of the equipment was 60 volts but using the maximum voltage will not be ideal for the set-up for it might melt the wires for overloading voltages. The accelerated corrosion was done for 12 days for each sample Corrosion Current Corrosion current was monitored while the specimen was subjected to accelerated corrosion. Integration of the corrosion current can approximate the loss of steel using Faradays Law [3], m = Atm C Fz where C= I(t)dt, m is the loss of mass, A tm is atomic mass of reaction ion, F is the Faraday s constant (96,485C/mol), and z is the valence of reaction. The current was monitored using multi meters (set to ammeters) measuring the corrosion currents for each specimen. (1) 2.7. Half Cell Potential Technique Half cell potential monitoring was performed in accordance to the specifications of ASTM C786 Standards for Half Cell Potential of uncoated reinforcing steel in concrete. The choice of reference electrode for the equipment was copper/copper sulphate (CSE). The half cell potential corrosion monitoring was set-up as shown in Figure 3. Figure 3: Half Cell Potential measurements on RC specimen 2.8. Steel Loss, Surface Crack Mapping, and Physical Examination The initial mass of steel was recorded for each specimen before they were embedded in concrete. After the corrosion process was finished, the concrete specimens were crushed using the Universal Testing Machine (UTM) in order to remove the steel bars. The steel bars were cleaned thoroughly and then weighed. The difference in the initial and post-corrosion mass was recorded as the actual steel loss. [ID291] 4

5 Cracks observed after corrosion were examined and the widths were measured. These cracks were plotted with their corresponding widths. The cracks were traced with respect to the grids lines for the Half-Cell Potential measurements. The grid were used as coordinates where the cracks traversed. The rust stains and steel loss data were quantified and analyzed. Moreover, a rating index was developed aside from the steel loss data. Four sides of each specimen were evaluated using the rating of 1 to 10 with 10 being highly stained. 3. Results and Discussions Scanning electron microscope (SEM) analysis was done to observe the morphology of the as-prepared α-fe 2O 3 nanoparticles formed by hydrothermal process. As shown in Figures 4a and 4b, the α-fe 2O 3 nanoparticles were clustered to form larger hierarchical structures with particle sizes of about 1 m. Also, high magnification images in Figures 4c and 4d show that these hierarchical structures were composed of smaller particles with diameters ranging from 50 to 150 nm. It can also be seen from the SEM images that the α-fe 2O 3 nanoparticles have anistropic shape, possibly short nanorods. Figure 4: SEM image of as-prepared α-fe 2O 3 nanoparticles (a) and (b) at 20,000 times magnification (c) and (d) at 35,000 times magnification. Half Cell potential measurements were obtained after 6 and 12 days of accelerated corrosion test. Table 3 shows the summary of the half cell potential values, their corresponding mean of potentials per sample and the standard deviation.considering the corrosion condition indicated by the mean of half-cell potentials, the control samples have mean potential less than -500 mv. Based on Table 2, the corrosion condition of the control samples (C1, C2, and C3) was identified to have severe corrosion. Nano-mixed [ID291] 5

6 (NM) samples were considered to have low (10%) risk of corrosion. This concrete condition can be classified as either moist carbonated concrete or moist chloride-free concrete. Surface- applied samples, (a) (b) Table 2: Average half-cell potential measurements of specimens after (a) 6 days (b) 12 days. SA1 and SA3 have potential mean which falls into the range of -350 mv to -200 mv. For these two samples, the corrosion behaviour is relatively lower than the control samples. These samples were classified to have intermediate corrosion risk. SA2 had exhibited larger potential values which were identified to be in the severe condition of corrosion. Referring to the resulting mean, surface-applied specimens were identified to have high (greater than 90%) risk of corrosion and further described to have moist chloride contaminated concrete. Among the three batches, the control samples had exhibited the severe corrosion condition, comparing the mean of potential values. The nano-mixed samples presented potential values that have least corrosion indication. The surface-applied samples exhibited occurrences of corrosion but observed to be less severe than the control samples. On the 12 th day of accelerated corrosion, the control samples exhibited majority of its potentials values less than -500 mv suggesting severe corrosion condition. On the other hand, the potential values given by nano-mixed specimen were suggesting low risk of corrosion occurrence. For surface-applied samples, the values can still be seen to be scattered based on the values of the standard deviation of SA2. Comparing the distribution of the potential values for the control, nano-mixed and surface-applied samples, it was found that control batch has the most severe corrosion, followed by the surface-applied which has intermediate severity and lastly, the nano-mixed sample which has the least severity among the three. The potential values were further investigated on the 12 th day of accelerated corrosion. [ID291] 6

7 The second measurement of the half cell potential values and corrosion condition differ from the first set of measurements. However, the ranking for the severity of corrosion remained the same. From being distributed at potential lower than -500 mv, control samples have varied its distribution from -670 to mv. Majority of the half cell potential values remained distributed at a range less than -500 mv. Compared to the first half cell potential measurements, the number of potential measurements reduced by 33.13%. 100% of potential values of nano-mixed samples were all found to occur at potential greater than -200 mv from the first measurement but in the second measurement, it was found that only % only remained to be greater than -200 mv. The control samples have the largest average theoretical steel loss followed by the surface-applied specimen. On the other hand, the nano-mixed samples have the least theoretical mass loss. The surfaceapplied samples have less steel mass loss by 45.14% than the control samples while the nano-mixed samples have less steel mass loss by % than the control samples. The nano-mixed sample performed better in reducing corrosion rate than the surface-applied samples by 17.41%. Based from the average of the mass loss, control samples have the highest magnitude of steel loss followed by the surface-applied specimen. Nano-mixed samples have the least theoretical mass loss. Surface-applied samples have less loss of steel mass by % than the control samples. Nano-mixed samples have less mass loss by % compared to control samples. The nano-mixed sample demonstrated significant difference in mass loss compared to the control samples. Surface-applied samples also were found effective in reducing the mass loss of reinforcement. There were cracks observed in one sample for each batch. C2 showed cracks that were traversing near the center at its face 3. The width of the vertical cracks varies from 0.10 to 0.30 mm. Nano-mixed sample NM3 at face 4 have traverse cracks with widths ranging from 0.05 mm to 0.30 mm. Nano-mixed samples were observed to have hairline cracks in the mid-part of the specimen after the 12 days corrosion. The larger cracks of width of 0.30 mm formed at the lower part of the nano-mixed specimen. The SA3 at face 1 has relatively larger crack widths compared to control and nano-mixed specimens. These widths of cracks vary from 0.50 to 0.75 mm. High surface stain rating was observed to occur to the specimens that cracked. Cracks became the passage of the rusts from the reinforcement to stain the concrete surface. Among the three batches of samples, the control batch acquired the highest surface stain ratings. Combining the steel loss rating, specimen C2 remained to have the highest rating in the physical examination. Averaging the ratings, the control batch got the highest rating average of 4.68 followed by surface-applied batch with 2.20 average rating and nano-mixed batch with an average rating of Based on the physical examination, the corrosion rate conformed to previous ranking where control samples have higher corrosion stain ratings than the surface-mixed and nano-mixed samples by 53% and 60.59%, respectively. [ID291] 7

8 4. Conclusion Based on the results gathered from each part of the corrosion monitoring methods, higher corrosion rate was observed in the control samples compared to the nano-treated specimens. The two methods that incorporated the nanoparticles in the concrete exhibited different behaviours in reducing the corrosion condition observed in each part of the monitoring. The nano-mixed sample performed best, considering the evaluating parameters used in this study. Surface application of the nanoparticles in concrete have also exhibited lower corrosion rate when compared to control samples. However, from the surface crack mapping, it was found that cracks formed in the surface-applied specimens were more severe than the control samples. It was suspected that steel reinforcement of the surface-applied samples expanded due to its longer exposure to electric current. Occurrence of corrosion aggravates the steel section expansion. Nano-mixed sample were found to have better results than the surface-applied sample throughout the non-destructive evaluation. This is due to the concentration of the nanoparticles in the inner core of specimens in the nano-mixed samples. Surface application of the nanoparticles to the samples was suspected to hinder the corrosion by blocking the pores at the surface of the concrete surrounding the steel reinforcing bar. References [1] G. Hays, Now is the Time, World Corrosion Organization, (2013), Retrieved Last April 26, 2016 from [2] A. Nazari, S. Riahi, S. Riahi, S.F. Shamekhi, and A. Khademno, Benefits of Fe2O3 Nanoparticles in concrete Mixing Matrix, Journal of American Science, 6(4), pp , [3] M. Pritzl, H. Tabatabai, and A. Ghorbanpoor, Laboratory Evaluation of Select Methods of Corrosion Prevention in Reinforced Concrete Bridges, International Journal of Concrete Structures and Materials, 8, No.3, pp , [4] ASTM C876 Standards for Half Cell Potential of Uncoated Reinforcing Steel in Concrete. [5] S. Agarwala, Z.H. Lim, E. Nicholson, and G.W. Ho, Probing the morphology-device relations of Fe2O3 nanostructures towards photovoltaic and sensing applications, The Royal Society of Chemistry, 4, pp , [6] FDOT, Florida Method of Test for an Accelerated Laboratory Method for Corrosion Testing of Reinforced Concrete Using Impressed Current (FM 5-522), Florida Department of Transportation, [7] J. Madrid, M. Balancan-Zapata, A. Torres- Acosta, and P. Castro-Borges, Effect of tropical marine microclimates on depassivation and corrosion induced cracking of reinforced concrete, Int. J. Electrochem. Sci., 9, pp , [8] K. Patil, H. Cardenas, K. Gordon, and L. Lee, Corrosion Mitigation in Reinforced Concrete Beams via Nanoparticle Treatment, ACI Materials Journal, Nov. - Dec. 2012, pp , [ID291] 8