Volume 23 Preprint 20


Corrosion protection of reinforced steel embedded with Portland cement doped Mangrove ( Rhizophora apiculata ) bark tannin inhibitor in 3.5 % NaCl solution

Izariff Zulham, Farah Athena Zakaria, Nur Amirah Ishak, Tuan Sherwyn Hamidon, M. Hazwan Hussin*

Keywords: Mangrove Bark, tannins, reinforced steel, corrosion inhibitors, surface coating

Abstract:
The concrete that coated the reinforced steel could not protect the steel from long exposure to oxygen in the air and presence of chloride in the sea water that will corrode the reinforced steel. Thus, corrosion protection need to be applied. Corrosion inhibitor is applied by layering the reinforced steel or the concrete with chemicals that could prevent Hydroxide ions and Chloride ions from reacting with the reinforced steel. Most inhibitors that are used in the building industry are harmful to the environment as they contain high concentration of heavy metals. Green corrosion inhibitors containing tannin which is obtained from plants has been proven to provide protection against the corrosion of the reinforced steel. Mangrove bark tannin is a potential green corrosion inhibitor as it is biodegradable, inexpensive, do not contain toxic compounds and utilises mangrove barks from the mangrove trees that have been cut down by the coal industries in Malaysia.

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ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 Corrosion protection of reinforced steel embedded with Portland cement doped Mangrove (Rhizophora apiculata) bark tannin inhibitor in 3.5 % NaCl solution Izariff Zulham1, 2, Farah Athena Zakaria2, Nur Amirah Ishak2, Tuan Sherwyn Hamidon2, M. Hazwan Hussin2* 1Department of Petroleum Engineering, Faculty of Engineering, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak Darul Ridzuan, Malaysia 2Materials Technology Research Group (MaTReC), School of Chemical Sciences Universiti Sains Malaysia, 11800 Penang, Malaysia *Corresponding author: mhh@usm.my; mhh.usm@gmail.com Abstract The concrete that coated the reinforced steel could not protect the steel from long exposure to oxygen in the air and presence of chloride in the sea water that will corrode the reinforced steel. Thus, corrosion protection need to be applied. Corrosion inhibitor is applied by layering the reinforced steel or the concrete with chemicals that could prevent Hydroxide ions and Chloride ions from reacting with the reinforced steel. Most inhibitors that are used in the building industry are harmful to the environment as they contain high concentration of heavy metals. Green corrosion inhibitors containing tannin which is obtained from plants has been proven to provide protection against the corrosion of the reinforced steel. Mangrove bark tannin is a potential green corrosion inhibitor as it is biodegradable, inexpensive, do not contain toxic compounds and utilises mangrove barks from the mangrove trees that have been cut down by the coal industries in Malaysia. Keywords: Mangrove Bark, tannins, reinforced steel, corrosion inhibitors, surface coating. 1. Introduction Reinforced steel is commonly used in construction of buildings, bridges and even offshore oil platforms such as CG Doris platform, named as Ekofisk 1 that is the first concrete based platform located in the North Sea in Norwegian Water in 1973 .1 According to Naterer2, one of the newest offshore structure is Hebron Platform which is located in Newfoundland, 1 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 Canada and was built in 2017. Reinforced steel has many useful properties such as high strength to withstand high impact load, resistant to rough conditions and high modulus elasticity which helps the steel to regain its shape after it is stretched in tension without breaking. Unfortunately, the reinforced steels have a few disadvantages. The common occurrence in reinforced steel is that they are going to corrode or rust overtime especially in sea water where there are presence of chloride ions and the conductivity of water is high which will increase the rate of corrosion.3,4 When corrosion occurred, the reinforced steel will be slowly eaten away and become thinner each day making it looks orange and rough. Overtime, the reinforced steel will become weak and could not support the tensile stress of the building that may causes the building to crack and possibly collapse from weather, powerful impact or even gravity itself. 5 In a construction, concrete is used together with reinforced steel as it can resists weathering, high strength and could act as corrosion protection. Rivetti et al.6 reported that the concrete is a physical barrier that protects steel from corrosion, and the alkalinity of concrete leads to the formation of a passive layer around the reinforcement, which increases protection against corrosive processes. However, concrete is a porous material and has cracks that allow the entrance of aggressive agents, destabilizing the passive layer and corroding steel.6,7 The corrosion is the major cause of deterioration of concrete structures and several methods of protection and repair have been developed such as corrosion inhibitors. Corrosion inhibitors are chemicals which are used to reduce the corrosion rate of a steel by forming a layer on the steel and protect them from corrosion.8 They are commonly used due to the lower cost and ease of application. Corrosion inhibitors can be divided into two groups which are organic and inorganic. Inorganic inhibitors are very excellent in protecting the metal from corroding but the health and environmental risks are too high. In other case, organic inhibitors do not pose any threat to the human health and the environmental and less expensive when compared to inorganic inhibitors. Organic inhibitors or green inhibitors are obtained from parts of the plants which do not causes any harm to the environment. Reinforced steel is commonly used in constructions because of its versatility and structural strength but it is not a perfect material as it could corrode overtime. The corrosion of structural steel is an electrochemical process that requires the simultaneous presence of moisture and oxygen. According to Page9, the iron in the steel is oxidised to produce rust, which occupies approximately six times the volume of the original material. The rate at 2 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 which the corrosion process progresses depends on a number of factors, but principally the 'micro-climate' immediately surrounding the structure. The objective of this research is to introduce green corrosion inhibitor in order to replace the inorganic inhibitors that can cause environmental damages. The effect of tannin on the structural steel is observed and the corrosion rates is calculated. 2. Materials and methods 2.1 Preparation of extracts About 30 g of mangrove bark powder was measured on mass balance. Next, 300 mL of 70% acetone was prepared by mixing 210 mL of acetone and 90 mL distilled water in a 500 mL conical flask. The weighed mangrove bark powder was then mixed with the 70 % acetone solution. The solution then left on the digital orbital shakers, WiseShake Sho2D for 24 h with 145 rpm rotation. The solution was then filtered with a vacuum filter to get rid of the undissolved solid residue. The filtered solution were then evaporate by using the Rotary Evaporator (RotaVap) at 55 °C with 70 rpm. Once all the acetone has been removed, the solution then freeze dried in the Labconco Freeze Dry System to remove all the water in the solution to obtain the tannin. The tannin extracted was measured and the percentage yield tannin per extraction was calculated. 2.2 Characterization of mangrove bark tannins extracts 2.2.1 Fourier transform infrared spectroscopy (FTIR) analysis The FTIR spectra of tannin sample was analyzed in a direct transmittance mode to record the IR spectra using Perkin Elmer model system 2000 instrument. The spectra was collected at the region between 4000-400 cm-1 with a resolution of 4 cm-1 and 20 scans per sample. The samples were prepared using potassium bromide (KBr) technique, in a proportion of 1:10 (w/w). 2.2.2 Ferric reducing power antioxidant test Four solutions which are phosphate buffer at pH 6.6, potassium ferricyanide, trichloroacetic acid and iron(III) chloride hexahydrate of 250 mL each were prepared. Next, 100 ppm of stock solution of standard ascobic acid was prepared by diluting 10 mg of ascobic acid in 500 mL of distilled water. From the stock, 80 ppm, 60 ppm, 40 ppm and 20 ppm of ascobic acid were prepared by diluting 8 mL, 6 mL, 4 mL and 2 mL of the 100 ppm solution to get different concentration of ascobic acid. Next, 2.5 mL of tricholoracetic acid was added into 3 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 each tubes. 5 plastic tubes were used and each tube was inserted with 2.5 mL of different concentration of ascobic acid. 2.5 mL of phosphate buffer and 2.5 mL of potassium ferricyanide were then added into each tubes. The tubes were shaken and incubated in WiseBath for 20 min at 50 °C. Another plastic tube was prepared and filled with 10 mL of distilled water. All of the six tubes were placed in the centrifugation machine at 4000 rpm for 20 min to separate the fluids based on density. After the fluids have been separated according to their densities, 2.5 mL liquid at the upper layer of each tubes were removed. Similar procedure was repeated in replacement of 2.5 mL of 50 ppm tannin solution. The mixture absorbance was measured at 700 nm. 2.3 Corrosion inhibition tests 2.3.1 Preparation of metal specimen The rust from 4 reinforced steel were thoroughly removed by using 400, 600 and 800 grade of sandpaper. PVC pipe of 2 cm diameter were cut into 4 smaller pipe with 5 cm of height. Next, the cement was prepared by 8:10 water to cement ratio, 16 g water and 20 g of Portland cement for each pipe. The first pipe would be only water and cement. The second, third and fourth pipe were added with 1%, 3% and 5% wt of tannin respectively. A reinforced steel then inserted in each pipes and the cement was poured gently. The reinforced steel was clipped to a retort stand in order to make it stand straight and the bottom of the pipes are sealed with aluminium foil to prevent the cement from overflowing. The cement was left to dry for 3 days. 2.3.2 Electrochemical measurements 3.5% of NaCl was prepared by diluting 35 g of NaCl in 1000 mL of distilled water. Next, the cement from the pipe was removed by cutting off each sides of the pipes carefully. All the cement were marked at 2.5 cm of height and soaked in the NaCl up to the mark. The reinforced steel then connected with the crocodile clips (as working electrode) and the Pt (counter) and SCE electrodes were placed into the NaCl solution. A total time of 30 min open circuit potential was done and a potential range of ± 250 mV from Eocp were selected for the potentiodynamic polarization test (with scanning rate of 0.5 mV s-1). From the Tafel plot, icorr and Ecorr were obtained and the corrosion rate was calculated. 3. Results and discussion 3.1 Fourier transform infrared spectroscopy (FTIR) 4 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 Fourier Transform Infrared Spectroscopy (FTIR) is used to identify organic and inorganic materials by measuring the absorption of infrared radiation by the material versus the wavelength. When a material is hit by the infrared radiation, it will absorb the radiation and causes the molecules to vibrate faster. The bands from the infrared absorption will identify the molecular components and structures. The FTIR Spectrometer is used to modulate the wavelength that is absorbed by the material. Figure 1 shows the FTIR spectra for the mangrove bark tannin. All the spectra display numerous of absorption peaks, which indicates the complex nature of the absorbent. The broad and strong band ranging from 3,000 cm-1 to 3,600 cm-1 indicates the presence of hydroxyl groups coming from lignin, cellulose, and hemicellulose which are necessary for the ability to prevent corrosion. Figure 1: FTIR spectrum of Mangrove bark tannin 3.2 Ferric reducing power antioxidant test Ferric reducing antioxidant power (FRAP) test is broadly utilized technique that uses antioxidants as reductants in a redox linked colorimetric reaction, wherein Fe3+ is reduced 5 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 to Fe2+. Ferric (Fe3+) to ferrous (Fe2+) ion reduction. Antioxidants are molecules which act as reducing agents by donating electrons to oxidants or also called as free radicals to stabilize them and minimize the damage caused by free radicals to DNA, cells and organ systems. Antioxidants include substances such as polyphenols; flavonoids; vitamins and enzymes like glutathione peroxidase and superoxide dismutase. Fe3+ - Probe + Reducing Antioxidant  Fe3+ - Probe (A=594nm) According to the antioxidant profiles of both extracts (Figure 2), it can be seen that the tannin extract undergoes reduction. When the solution undergoes reduction, the yellow colour of the solution changes to various degree of green and blue depending on the reducing power of each extract. Obtaining higher absorbance readings corresponds to the higher reducing ability of the test solution. The tannin extract has a high content of reductants to reduce Fe3+ ions to form Fe2+ ions. Thus, ferric reducing power assay further justifies that the tannin extract provides high percentage inhibition efficiency. Figure 2: Antioxidant of mangrove bark tannin extract compared to ascorbic acid standard 6 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 3.3 Corrosion inhibition test Since the corrosion reaction is mostly electrochemical, corrosion behavior of metals can be evaluated with electrochemical techniques Polarization methods such as potentiodynamic polarization, potentiostaircase, and cyclic voltammetry are often used for laboratory corrosion testing. These techniques can provide significant useful information regarding the corrosion mechanisms, corrosion rate and susceptibility of specific materials to corrosion in designated environments. Polarization methods involve changing the potential of the working electrode and monitoring the current which is produced as a function of time or potential. In this work, potentiodynamic polarization test has been done for each cement sample for four weeks. Each of the sample gives different results based on the percentage amount of tannin presence in the cements as recorded in Table 1. The results obtained has been plotted with Log i vs E. The potentiodynamic anodic and cathodic polarization plots for mild steel specimens in 3.5% NaCl solution with and without the mangrove bark tannin at three different concentrations are given in Figure 3(A) to Figure 3(E), which are called Tafel plot and they shows the relationship between the current generated in an electrochemical cell and the electrode potential of a specific metal. As the inhibitor concentration increased, the corrosion current densities of mild steel decreased. This behavior happened because of the adsorption of the chloride ion present in the mangrove bark tannin which prevent the chloride ion to pass through the cement. The corrosion rate can be clearly seen after calculating the corrosion rate from the Tafel plots in each concentration of mangrove bark tannin. By finding the corrosion potential (Ecorr) polarization resistance (Rp) and corrosion current density (icorr), we can determine the corrosion rate for each sample. The formula used to find the corrosion rate is: 𝐶𝑜𝑟𝑟𝑜𝑠𝑖𝑜𝑛 𝑅𝑎𝑡𝑒 = (0.13 𝑥 𝐼 𝐶𝑜𝑟𝑟 𝑥 𝑆𝑡𝑒𝑒𝑙 𝐸𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 𝑊𝑒𝑖𝑔ℎ𝑡) / 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑠𝑡𝑒𝑒𝑙 (Eq. 1) 7 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. Table 1: Potentiodynamic Volume polarization analysis 1% and 3% tannin ISSN 1466-8858 23, Preprint 20 of blank first(0%), submitted 27 March 2020 in 3.5% N immersion. Week 0 Tannin Week 1 Week2 Wee 0 1 3 0 1 3 0 1 3 0 iCorr (µA) 30.16 21.69 19.42 127 72.22 5.451 166.6 82.07 12.9 136 ECorr (mV) -567.7 -582.5 -673.4 -579.3 -564.8 -504.1 -634.6 -557.2 -542.7 -58 Rp (ohms.cm2) 863.9 1201 1342 205.1 360.8 4780 156.4 317.4 2020 191 Corrosion Rate 1.463 1.052 941.9e-3 6.161 3.503 264.4e-3 8.081 3.981 625.7e-3 6.59 Concentration (%) (mpy) 8 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 Figure 3: Tafel plot after; (A) 0 week, (B) 1 week, (C) 2 weeks, (D) 3 weeks and (E) four weeks of immersion in 3.5% NaCl solution. Based on Figure 4, the cement with 0% tannin have a higher rate of corrosion compared to the cements with 1% tannin and 3% tannin. This is because the chloride from the NaCl solution could penetrate through the cement and corrode the reinforced steel. With the presence of tannin, the rate of corrosion is significantly lower because the tannin could prevent the chloride from passing through the cement. A few experiments have been done to study the ability of mangrove bark tannin as a corrosion inhibitor. 9 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 There are few methods to decrease the rate of corrosion by using green corrosion inhibitor that will not affect the environment when using it which is tannin. One of the way is to increase the pH value of the tannin to decrease the corrosion rate as to neutralize the acidity found in the mangrove bark. There are also a few other type of tannins can be used other than mangrove bark tannin. One of the tannin is mimosa tannin which can be obtained from the bark of the Black Wattle Tree (Acacia mearnsii) that can be found in Australia. It has the anticorrosive properties in the tannin to prevent corrosion of metal. A pH level of 2.5 has been tested the best for this type of tannin. Lastly, decrease the water to cement ratio in order to create a watertight concrete and proper cover for the reinforced steel. By lowering the water to cement ratio, the cement will be highly impermeable. Thus, harder for the oxidation process to occur and from chloride ions to enter through the cement. Figure 4: Corrosion rate versus time plot. 4. Conclusion In conclusion, mangrove bark tannin FTIR indicates the presence of hydroxyl groups coming from lignin, cellulose, and hemicellulose which are necessary for the ability to prevent corrosion. Ferric reducing power assay suggested that the tannin extract provides further 10 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 higher percentage inhibition efficiency as the concentration increases. From the potentiodynamic polarization shows the presence of tannin results in the rate of corrosion that is significantly lower as the tannin could prevent the chloride from passing through the cement. Acknowledgement The authors would like to thank Universiti Sains Malaysia for Short-term grant (304/PKIMIA/6315100) financial supports. Mr. Tuan Sherwyn Hamidon would like to acknowledge USM Institute of Postgraduate Studies for providing the USM Graduate Assistance Scheme. References 1. Zaleski-Zamenhof, L. C., Gerwick, B. C., Hellesland, J., Matsuishi, M., & Zhang, X. (1990). Concrete marine structures: A state-of-the-art review. Marine Structures, 3(3), 199–235. doi:10.1016/0951-8339(90)90026-n 2. Naterer, G. (2018, March). New Hebron offshore oil platform a Canadian engineering marvel. Retrieved December 5, 2019, from http://theconversation.com/new-hebronoffshore-oil-platform-a-canadian-engineering-marvel-90626 3. Jianxia, S. (2012). Durability Design of Concrete Hydropower Structures. Comprehensive Renewable Energy, 377–403. doi:10.1016/b978-0-08-087872-0.00619-3 4. Hansson, C. M. (2016). An introduction to corrosion of engineering materials. Corrosion of Steel in Concrete Structures, 3–18. doi:10.1016/b978-1-78242-381-2.00001-8 5. Woodford, Chris. (2007/2018) How buildings work. Retrieved December 30, 2019, from https://www.explainthatstuff.com/howbuildingswork.html. 11 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 6. Rivetti, M. L. S., Neto, J. da S. A., Júnior, N. S. de A., & Ribeiro, D. V. (2018). Corrosion Inhibitors for Reinforced Concrete. Corrosion Inhibitors, Principles and Recent Applications. doi:10.5772/intechopen.72772 7. Montemor, M. ., Simões, A. M. ., & Ferreira, M. G. . (2003). Chloride-induced corrosion on reinforcing steel: from the fundamentals to the monitoring techniques. Cement and Concrete Composites, 25(4-5), 491–502. doi:10.1016/s0958-9465(02)00089-6 8. Popov, B. N. (2015). Corrosion Inhibitors. Corrosion Engineering, 581–597. doi:10.1016/b978-0-444-62722-3.00014-8 9. Page, C. L. (2007). Corrosion and protection of reinforcing steel in concrete. Durability of Concrete and Cement Composites, 136–186. doi:10.1533/9781845693398.136 12 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 23, Preprint 20 first submitted 27 March 2020 13 © 2020 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers' comments, be published online at http://www.jcse.org in due course. Until it has been fully published it should not normally be referenced in published work.