Hema sumanth. B and Vasugi. k
Keywords: Corrosion, w/c ratio, High strength concrete, Impedance
Abstract:
Corrosion is one of the main factors which effect the life of reinforced concrete structures. The cross-sectional area of the rebar embedded in the concrete will be reduced during the process of corrosion which result in the degradation of structure. Reducing the w/c ratio, adding different pozzolanic materials and coating of rebars are the effective methods to prevent the corrosion of steel and also to improve the mechanical characteristics of the materials. In the present study, high strength concrete is developed for the w/c ratio’s 0.25,0.3 and 0.35. It is aimed to detect the corrosion potential, corrosion rate and electrical resistance of steel rebar embedded in the high strength concrete for different water-cement ratio cylinder samples by using half-cell potential and electrochemical impedance spectroscopy(EIS). The obtained results reveal the vital role of w/c ratio. With increase in w/c from 0.25 to 0.35 the corrosion rate, corrosion potential increased and electrical resistance decreased.
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ISSN 1466-8858 Volume 23, Preprint 12 first submitted 11 February 2020 Effect of w/c ratio on the corrosion of rebar embedded in high strength concrete Hema Sumanth. B1 and Vasugi. K* 1post graduate student, School of Civil Engineering, VIT university, Chennai, India *Corresponding author, School of Civil Engineering, VIT university, Chennai, India E-mail: vasugi.k@vit.ac.in Abstract Corrosion is one of the main factors which effect the life of reinforced concrete structures. The crosssectional area of the rebar embedded in the concrete will be reduced during the process of corrosion which result in the degradation of structure. Reducing the w/c ratio, adding different pozzolanic materials and coating of rebars are the effective methods to prevent the corrosion of steel and also to improve the mechanical characteristics of the materials. In the present study, high strength concrete is developed for the w/c ratio’s 0.25,0.3 and 0.35. It is aimed to detect the corrosion potential, corrosion rate and electrical resistance of steel rebar embedded in the high strength concrete for different water-cement ratio cylinder samples by using half-cell potential and electrochemical impedance spectroscopy(EIS). The obtained results reveal the vital role of w/c ratio. With increase in w/c from 0.25 to 0.35 the corrosion rate, corrosion potential increased and electrical resistance decreased. Keywords: Corrosion, w/c ratio, High strength concrete, Impedance 1. Introduction The durability of concrete structures is one of the key issues facing around the world. Among those corrosion of steel in concrete is the main factor for deterioration because it is directly effects the structural and mechanical properties of components [1]. The passivation of top layer of steel due to alkaline environment is called corrosion of steel which will effects the structure by a gradual processes called as initiation, propagation, cracking, deflection and collapse [2]. Aggressive types like chloride ions (Cl-), carbon dioxide (CO2), sulfur dioxide(SO2), moisture content which are present in the environment can pass through the concrete pores which affects the rebar and concrete cover. Distance between two reinforcing bars may also leads to defects [3]. Usage of high quality and grade dense concrete in construction can minimize the possibility of corrosion of reinforcement [4]. Structural elements made of high-strength concrete are generally densely reinforced. Even though corrosion is slow process there are few techniques like impressed current method or galvanostatic method, Alternative sea water spray test, Alternative drying and wetting cycles method which are accelerates the corrosion process for research works [5]. During any corrosion cycle, the corrosion current must flow through the electrolyte from the site of the anode to the cathode, and the resistance of the concrete affects the flow of the anode. Higher electrical resistance can impede the flow of these currents and therefore, depending on the resistance of the concrete, the corrosion cycle can be stifled © 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 12 first submitted 11 February 2020 or accelerated [5]. But in case of high strength concrete it will be different because of less porosity. The concrete itself will act as electrolyte which allows the current to flow through it which affects the entire microstructure and probability of concrete. Aghajani et al.,[6] had studied the effect of DC current on permeability of concrete and this acceleration technique has been developed to study the cracking of concrete cover, load bearing capacity, behaviour of bond due to corrosion of reinforcement. Bhalgamiya et al., [7] also studied the concept of acceleration technique to introduce corrosion in the concrete. In spite of this there are no studies in the literature specifically investigated on high strength concrete. The present study aims to investigate the effect of w/c ratio on the corrosion of embedded steel rebar in the high strength concrete. The corrosion rate and corrosion potential has been recorded and studied with various methods. 1.1. Background Chloride induced corrosion is an electrochemical process which occurs due to penetration of chloride ions into the concrete to react with passive layer of reinforcing steel which results in the depassivation[8]. There is often talk about a critical or threshold concentration of chloride-ion in an attempt to determine the degree to which the passive substrate breaks down. 0.6% by mass of cement, with 0.4% being stated as the minimum value released for free chloride material [9]. Once steel is exposed to chloride ions, corrosion can spread aggressively by pitting, which can generate further acidity from products of corrosion. The reinforcement becomes cathodic when the location of pits exists at the localized anodic areas and as chloride ions move towards the positive anodic region, this process is further accelerated[6]. The established procedures for the corrosion risk assessment of structural concrete are nondestructive tests, such as half-celled potential surveys and surface resistivity tests[10] . Both approaches can be used together for an aggressive corrosion risk assessment [11]. A key factor in the working life of structural concrete is the ability of chloride ions to penetrate into the concrete cover. In addition, chloride ions can pass into concrete through the combination of transport systems, including capillary suction, diffusion and permeation absorption[12]. The most dominant mechanisms in chloride environment are absorption and diffusion which occurs simultaneously in the process of alternative wetting and drying which is considered the most accurate method. The concrete structure can affect its ability to withstand ingress of chloride ion. The transfer of liquids takes place mainly via the cement matrix and depends on the continuity, tortuosity and radius of the pores[13]. Cement content also has a chloride-binding ability that decreases the free chloride ions in the pore solution of concrete and increases the degree of concentration guiding diffusion [14]. This binding occurs because of adsorption and chemical reactions to cement matrix components which lead mainly to formation of calcium chloroaluminate hydrate. The capacity of binders can be improved by using different materials like flyash, GGBS because due to the secondary hydration which produces C-S-H gel[15]. With the presence of 0.4 and 0.6 range, the important role of the w/c ratio in the permeability capacity of the concrete is well known. The permeability of the w/c ratio of 0.45 is significantly reduced, ideally © 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 12 first submitted 11 February 2020 0.4. concrete with a lower w/c ratio have been shown to be less sensitive to carbonation and external chemical attacks. The interpretation of the w / c ratio for the results of transport is that an improvement in the w/c ratio leads to an increase in pores size and porosity. The lower ratio of w/c produces less pore and smaller pores in the same degree of hydration, while a high ratio of w / c results in greater pores, e.g. a reduction in the w / c ratio, from 0.75 to 0.57, leads to a reduction of penetration depth to about one-third of the total [16]. 2. Methodology 2.1. Materials and Mix design A 53 Grade ordinary portland cement is used as a binding material. The chemical composition of cement used in this study given in Table 1. Fine sand and coarse gravel with the size of 4.75 mm (fineness modulus of 3.1) and 10 mm respectively. Generally for high strength concrete w/c ratio ranges from 0.23 to 0.35[17]. The w/c ratio used in the present study for preparing samples are 0.25,0.3 and 0.35. HYSD rebars of grade Fe 500 with 10 mm diameter of length 300 mm is used as reinforcement in concrete samples and the properties of rebar is given in Table 2. Conplast SP-430 which confirms the standards of BS 5075, BS: EN 934-2 and ASTM C494 is used as a water reducing agent. Firstly, Cement and aggregate were dry mixed in the drum mixer for 2 minutes or until the mass is uniform and then water is added and mixed for another 5 minutes. The fresh concrete is then placed in the 100×150 mm steel moulds with rebar kept at center. The mix design used in the study is given in the Table 3. Table. 1 Chemical composition of ordinary portland cement Constituent % Compound % SiO2 19.8 C3 S 62.7 Al2O3 4.3 C2 S 10.2 Fe2O3 2.0 C3 A 8.2 CaO 63.9 C4AF 6.2 MgO 2.4 SO3 3.0 Na2O 0.1 K2 O 0.7 Others 0.6 Free Lime 1.0 LOI 2.2 Table. 2 Chemical compositions of Fe500 rebar Constituents % Carbon 0.25 Phosphorus & Sulphur 0.40 Phosphorus + Sulphur 0.075 CE 0.42 Nitrogen 120 © 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 12 first submitted 11 February 2020 Table. 3. Mix design of high strength concrete samples for M60 grade Materials 0.25 w/c 0.3 w/c 0.35 w/c Cement (53 Grade) 520 kg/m3 520 kg/m3 520 kg/m3 Fine Aggregate 972.6 kg/m3 954.62 kg/m3 935 kg/m3 Coarse Aggregate 934.45 Water Super plasticizer kg/m3 881.2 kg/m3 830 kg/m3 130 kg/m3 156 kg/m3 182 kg/m3 kg/m3 kg/m3 10.4 kg/m3 10.4 10.4 2.2. Preparation of Concrete Samples The fresh concrete samples are casted in 150×150×150 mm cube moulds for compressive strength test and 100×150 mm cylinder molds for corrosion investigation. A total of 9 cylinder specimens with rebar casted for corrosion study and 9 cube samples for compressive strength test. The schematic representation of cylinder sample is given in Figure 1. After casting the cube samples are then cured in normal water and cylinder samples with embedded rebar is cured in 0.5 M NaCl solution for 28 days. Fig. 1. Schematic representation of concrete cylinder specimen corrosion is a slow process even in the aggressive environment. So for the study of short duration it is difficult to achieve the exact degree of corrosion. For the research studies the process of corrosion should be accelerated with available techniques. Both chloride induced and carbon induced corrosion mechanisms will affect the structure to a great extent. In the present study chloride induced corrosion was chosen because chloride induced corrosion is generally more pernicious and expensive to repair as well. 2.3. Process of Accelerating corrosion There are few techniques to accelerate the corrosion process like impressed current method, salt spray test (SST), cyclic corrosion test (CCT). Salt spray method is not accurate because the corrosion in the environment compared with the outdoor is different and Cyclic corrosion test can give the good results but it requires long test time[18]. So in this impressed current method is used to accelerate the corrosion of rebars embedded in the concrete. © 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 12 first submitted 11 February 2020 2.3.1. Impressed current technique The setup used for the impressed current method for a single specimen is given Figure 2 and the setup for the number of samples which are connected in series is given in Figure 3. The setup consists of DC power supply, counter electrode and electrolyte, in this study stainless steel plates are used as counter electrodes. The positive terminal (anode) of DC power supply is connected to the rebar and negative terminal (cathode) is connected to stainless steel plate. The current will be impressed from stainless steel plate (cathode) to rebar through the medium of sodium chloride which is used as electrolyte in the present investigation. Fig. 2. Simplified Test set-up for accelerated corrosion test Fig. 3. Test set-up for accelerated corrosion test A constant current will be applied to initiate the corrosion process and the response is monitored with data logger continuously. The applied current for introducing corrosion is not efficient fully in causing loss of mass to that theoretically predicted by Faraday’s law[19]. That means Iapp is not exactly equals to Icorr. Austin et al. [20] have suggested a modified version of Faraday’s law, The below equation 1. relates the theoretical and actual mass loss due to corrosion. 𝐼𝑐𝑜𝑟𝑟 = ( 𝑡𝑎 𝑎𝑐 𝑡𝐴𝑐 ) 𝐼𝑎𝑝𝑝 (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 12 first submitted 11 February 2020 Where Icorr = corrosion current density; t = Total time of current applied; ta = Duration of application for corrosion; Ac = Area of rebar in which current is applied; ac = area of the depassived part of the rebar. 2.4. Test Methods Compressive strength test was performed according to the standards of ASTM C39/C39 M on three specimens of each w/c ratio using Compressive Testing Machine (CTM) which is given in Figure 4. The load applied gradually at the rate of 140 kg/cm2 per minute on the surface of the cube till the specimen fails. load at failure of specimen to the total area of cube gives the compressive strength. Fig. 4. Compressive strength test for cube concrete specimens To determine the corrosion potential, half-cell potential test has been carried out by taking the close intervals on the surface of the concrete. In the present investigation as per the standards of ASTM C876, all the cylinder samples are tested after the 28 days of acceleration i.e before the accelerating the corrosion process. The experimental set up followed in this study is given in Figure 5. The setup consists of working electrode, reference electrode and voltmeter. The positive terminal of voltmeter is connected to the rebar and negative terminal is connected to the half-cell. The recorded potential values show the probability of corrosion of rebar. Fig. 5. Set-up for Half-cell potential test © 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 12 first submitted 11 February 2020 Electrochemical Impedance Spectroscopy (EIS) test has been carried out on the all the specimens before and after the application of DC stray current. It is common technique in electrolysis, mainly used to study the harmonic response of the system. A small, sinusoidal variation is applied to the working electrode potential and resulting current is analyzed in the frequency domain. In this study All the samples are monitored monthly and also the electrochemical measurements (EIS) also performed on all the samples. EIS measurements were performed using Gamry 600 potentiostat. The schematic diagram of EIS setup is given in Figure 7. By applying 10 mV in a range of 100 kHz down 3.7 mHz all the samples are tested for EIS. The measurements are taken by using counter electrode and reference electrode. Both are short-circuited and connected to the reference electrode. In this study graphite bar is used and working electrode is connected to the rebar and results plotted in Zview software. And an equivalent circuit diagram is given Figure 6 to fit the EIS data. Fig.6. Equivalent circuit diagrams to fit EIS data Fig. 7. Schematic set-up for electrochemical measurements 3. Analysis of Results 3.1. Compressive Strength Test: The compressive strength of high strength concrete with different water cement ratios are given in Table 4. The compressive strength of concrete for 0.25 w/c is more i.e., 49.12 MPa and for 0.3 and 0.35 w/c are 46.71 MPa, 45.31 MPa respectively. There is an increase of 3.08% from water-cement ratio 0.35 to 0.3 and 5.12% from 0.3 to 0.25 and 8.4% from 0.35 to 0.25. It is also observed that there © 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 12 first submitted 11 February 2020 is an increment in the compressive strength with decrease in the water-cement ratio because the porosity of concrete will get reduced. Which means less water filled pores will develop between the grains. Table. 4. Compressive strength of High strength concrete w/c ratio Specimen-1 Specimen-2 Specimen-3 Average(MPa) 0.25 0.3 44.22 50 53.166 49.12 48.44 44.356 47.33 0.35 46.71 48 44.17 43.778 45.31 3.2. Close Interval of Half-Cell Potentials The half-cell potentials of rebar embedded in concrete was recorded weekly by following 2d of ponding which are referred as dry and wet readings. Surface-saturated concrete is recommended as it increases electric contact between the reference electrode and steel to take half-cell potential [11]. So in this study only wet half-cell readings are presented and discussed. Figure 8 shows the development of half-cell potentials of rebar with different water-cement ratios. Initially before initiation of acceleration the potentials are measured which shows negligible or probability of corrosion is low as per the standards ASTM C 876. After the application of current supply, the potentials are changed with increase in the time for all the three water-cement ratios which shows the probability of corrosion is high to severe. And also observed that as the water-cement ratio increase the porosity of concrete increases which causes more probability of corrosion. 0.3 w/c 0.35 w/c 0.25 w/c -800 Half-cell Potentials (mv) -700 -600 -500 -400 -300 -200 -100 0 0 10 20 30 40 50 Time:Days Fig. 8. Development of half-cell potential over time for different water-cement ratios © 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 12 first submitted 11 February 2020 3.3. Electrochemical Impedance Spectroscopy(EIS) After the curing the samples in NaCl solution for 28 days, before and after the initiation of acceleration, all the samples are tested for EIS and Nyquist spectrum plots has been drawn for the all samples which are given Figures 9-12. 0.35 w/c 0.3 w/c 0.25 w/c 30000 25000 Z im (Ω.cm2) 20000 15000 10000 5000 0 0 5,000 10,000 15,000 20,000 Z re (Ω.cm ) 2 Fig. 9. Nyquist plot of concrete samples before applying DC current 50 Days 36 Days 14 Days 7 Days 30000 Z im (Ω.cm2) 25000 20000 15000 10000 5000 0 0 10000 20000 30000 40000 50000 60000 Z re (Ω.cm ) 2 Fig. 10. Nyquist plot of concrete samples prepared with 0.25 w/c © 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 12 first submitted 11 February 2020 50 Days 36 Days 14 Days 7 Days 20000 Z im (Ω.cm2) 15000 10000 5000 0 0 2000 4000 6000 8000 100001200014000160001800020000 Z re (Ω.cm2) Fig. 11. Nyquist plot of concrete samples prepared with 0.3 w/c 50 Days 36 Days 14 Days 7 Days 16000 14000 Z im (Ω.cm2) 12000 10000 8000 6000 4000 2000 0 0 10000 20000 30000 40000 50000 60000 70000 Z re (Ω.cm2) Fig. 12. Nyquist plot of concrete samples prepared with 0.35 w/c Figure 9 shows the Nyquist plot of all the concrete samples prepared with 0.25,0.3and 0.35 w/c before the application stray current. From the graph high frequency curves has been observed. In this spectra the denser samples i.e samples prepared with low w/c ratio the diameter and height of the curve is higher which indicates the high resistivity and low permeability of concrete samples. Figures 10-12 shows the Nyquist plots of concrete samples prepared with 0.25,0.3 and 0.35 w/c after the application of stray current for a period of 50 days. EIS test has been carried out for an interval of 7,14,36 and 50 days respectively. It is well known that as the time chloride time extends the radius of half-circle of Nyquist plots curve increases[6]. The plots present the non-conventional nature of diffusion tail at the frequencies and the slop between imaginary and real impedance will be greater than 45 degrees which represents the fast transition from passive / film interface solution capacitive to rebar-interface © 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 12 first submitted 11 February 2020 passive film diffusional behaviour, and could be due to the mass transfer resistance of the passive film and the consequently high diffusivity of ions via the passive film. Exposure conditions and DC supply over a long period of time through concrete in a chloride-flow atmosphere have a quick liquidation impact on the portlandite, increasing the size of pores and creating a new concrete pore network. 3.4. Corrosion rate of concrete samples 0.35 w/c 0.3w/c 0.25 w/c 0.016 Corrosion Rate (mmpy) 0.014 0.012 0.010 0.008 0.006 0.004 0.002 0.000 0 10 20 30 40 50 Time:Days Fig. 13. Corrosion rate of concrete samples for different water-cement ratios Figure 13 shows the corrosion rate of concrete samples prepared with different water-cement ratios. As shown, the concrete samples prepared with 0.25 water-cement ratio has lowest corrosion rate. After the exposure of 30 days it again increased but it is quite less than concrete samples prepared with 0.3 and 0.35 water-cement ratios. compare with all the specimens, concrete samples with 0.35 w/c showed the highest corrosion rate. Which shows that as water-cement ratio increases the corrosion rate also increases because of porosity, so that chloride ion can pass through pores of concrete and reaches steel. 3.5. Electrical Resistance of Concrete Samples Figure 14 represents the electrical resistance of concrete samples prepared with different water cement ratios. The change in the w/c ratio of 0.25 to 0.35 caused an increase, which indicates a less permeable concrete, in electric resistivity levels. Initially at the age of 5 to 20 days the electrical resistance of all the samples are almost same i.e nearly 50 micro ohms. Thereafter the electrical resistance of samples prepared with 0.35 w/c got reduced compared with 0.3 and 0.25 w/c. At the age of 30 days there is a deviation observed in the electrical resistance between samples prepared with 0.3 and 0.25 w/c. To order reducing the concrete porosity and how these pores become interconnected, the electric resistivity measurements are also influenced by the hydration intensity. The electrical conduction © 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 12 first submitted 11 February 2020 moves into the fluid of pores in the hardened concrete matrix, to regulate the electrical resistivity of the concrete by proportional volume of the interconnected pores. Change of the w/c ratio (at set cement level) results in a greater fraction of the hydrated cement paste in the cement mix and an improved conductivity of the concrete. From the obtained results it is concluded that as increase in the w/c ratio there is a reduction in the electrical resistivity. Electrical Resistance (Micro Ohms) 0.25 w/c 0.3 w/c 0.35 w/c 250 200 150 100 50 0 0 10 20 30 40 50 Time:Days Fig. 14. Electrical Resistance of concrete samples with different w/c ratios 3.6. Corrosion Current density(icorr) versus Time Corrosion current density of high strength concrete samples is studied for the period of 50 days and the results plotted is shown in Figure 15. The concrete samples prepared with 0.35 w/c has shown to have more corrosion current density followed by 0.3 w/c and 0.25 w/c. The peak current density for 0.35 w/c has obtained at the 25th day and started reducing and the peak current density for 0.3 w/c, 0.25 w/c are obtained on 7th and 36th day. 0.35 w/c 0.3 w/c 0.25 w/c 30 icorr (mA/cm2) 25 20 15 10 5 0 0 10 20 30 40 50 Time:Days Fig. 15. Corrosion Current Density (icorr) verses Time(days) © 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 12 first submitted 11 February 2020 4. Conclusion In reinforced concrete structure the corrosion process regularly leads to serious damage that reduces structural life. In this present investigation, the effect of water-cement ratio on the corrosion behaviour and performance of HYSD rebar of grade Fe500 embedded in high strength concrete is evaluated with half-cell potential method and electrochemical impedance spectroscopy technique and following conclusions are drawn. i. From the compressive strength test there is an increase of 3.8% from 0.35 to 0.3 w/c ,5.12% from 0.3 to 0.25 w/c and 8.4% from 0.35 to 0.25 w/c. The compressive strength of concrete samples prepared with 0.25 w/c has high strength compare with 0.3 and 0.35 w/c. It is concluded that compressive strength increases with decrease in the water-cement ratio. ii. Before the application of stray current, the probability of corrosion is low according to ASTM standards but after the application the probability increases with increasing time intervals. So it is concluded that half-cell potential method is useful to detect the corrosion probability and corroded area iii. Initially concrete samples prepared with 0.35 w/c has more probability of corrosion followed by 0.3 and 0.25 w/c. So from the obtained results it is concluded as the water-cement ratio decreases the probability of corrosion also decreases. iv. Nyquist plots from electrochemical impedance spectroscopy shows the capacitive curve with low frequency. With increase in the time the circle of Nyquist plot curve increases. From the results the impedance of samples prepared with 0.25,0.3 and 0.35 w/c were outlined. v. The impedance of all samples at the interval of 50 days increased. It means still the top layer of passive layer doesn’t exhaust completely. The rebars are still in the passive state vi. The corrosion rate of concrete samples prepared with 0.35 w/c are more followed by 0.3 and 0.25 w/c. from the results it is concluded that the corrosion rate increases with increase in water-cement ratio. vii. The change in the w / c ratio of 0.25 to 0.35 caused an increase, which indicates a less permeable concrete, in electric resistivity levels. With increase in the w/c there is decrease in electrical resistivity. References [1] 'Concrete deterioration detection using distributed sensors', R. Regier and N. A. Hoult, Proc. Inst. Civ. Eng. Struct. Build, 168, 2, pp118–126, 2015. [2] 'A galvanic sensor for monitoring the corrosion condition of the concrete reinforcing steel: Relationship between the galvanic and the corrosion currents', E. V. Pereira, R. B. Figueira, M. M. L. Salta, and I. T. E. da Fonseca, Sensors,9,11, pp8391–8398, 2009. © 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 [3] Volume 23, Preprint 12 first submitted 11 February 2020 'Electrochemical sensors for monitoring the corrosion conditions of reinforced concrete structures: A review', R. B. Figueira, Appl. Sci.,7,11, 2017. [4] 'Corrosion of steel in high-strength self-compacting concrete exposed to saline environment', H. A. Yousif, F. F. Al-Hadeethi, B. Al-Nabilsy, and A. N. Abdelhadi, Int. J. Corros.,20, 2014. [5] 'Smart sensing technologies for structural health monitoring of civil engineering structures', M. Sun, W. J. Staszewski, and R. N. Swamy, Adv. Civ. Eng.,20, 2010. [6] 'Effects of DC stray current on concrete permeability' A. Aghajani, M. 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