Repair Vulnerability of Corrosion Patch Repairs at the Steel

Article pubs.acs.org/IECR

Repair Vulnerability of Corrosion Patch Repairs at the Steel Intersection Areas of Reinforced Concrete Slabs Influenced by Harsh Weather Muhammad Wasim,† Raja Rizwan Hussain,*,† and Muhammad Ali Baloch‡ †

CoE-CRT, Civil Engineering Department, and ‡CEREM, Mechanical Engineering Department, College of Engineering, King Saud University, Riyadh, 11421, Saudi Arabia ABSTRACT: This paper aims at finding the effect of harsh weather on corrosion repair of reinforced concrete slabs at the rebar intersections. Concrete slabs were tested to get an insight into the existence of macro-cell phenomenon in the rehabilitated patches of the corroded reinforced concrete members and the durability of repairs under the coupled effect of high constant humidity and high temperature. The specimens were prepared having a total chloride concentration in mixing water as 3% and 5% by mass of binder and the intersection steel areas simulating the patch repairs that were kept uncontaminated. After two years of corrosion potential observations, the specimens were broken to find the gravimetric mass loss and to get the true picture of the corrosion of steel at the intersection of the repaired patches of reinforced concrete.

1. INTRODUCTION Repair of corroded reinforced concrete (RC) structures is a matter of significance for researchers working in modern construction repair industry. In common construction practice, patch repair is considered to be the most applicable and adept technique for the repair of corroded concrete areas of existing structures. This patch repair of a structural member involves the extraction of loose concrete that has cracked and delaminated, surface treatment of the affected corroded steel of the patch area, and application of the fresh patching materials, which normally regains the original profile of the member. The cost incurred for the repair of corroded reinforced structures is very significant; therefore, a complete understanding of the cause of deterioration and application of adequate rehabilitation techniques is needed to facilitate durable repair. Several researchers have investigated and reported the deterioration of reinforced concrete (RC) structures due to the corrosion of steel in the past.1−6 The corrosion of RC members is reported to be the most due to chloride ingression into concrete from the external environment.6−10 Moreover, the chloride induced corrosion is investigated to be contingent on temperature.11 The authors of this research paper previously investigated and established the phenomenon of macro-cell formation in the simulated repaired reinforced concrete patches of the specimens having steel in the longitudinal direction in prismatic specimens only. They also corroborated that the presence of high chloride content aided by severe environmental conditions, i.e., varying temperature and high constant humidity, not only break the passive film which protects steel from further corrosion but also accelerate the corrosion of reinforcement steel bars even in repaired reinforced concrete patches.12 However in the previous research, the element that remained unexplored in the investigated repaired patches was the existence of steel in the perpendicular direction forming an intersection which is more vulnerable to corrosion after repair. Therefore to investigate the durability or the vulnerability of the © 2014 American Chemical Society

repairs of the concrete slabs at the intersection areas under the harsh weather conditions leads to the objectives of this research.

2. EXPERIMENTATION Deformed round carbon steel bars 13 mm in diameter were used as reinforcing material in the experimental specimens. Type I cement in compliance with the requirements of ASTM C150 has been used. Coarse aggregates were a blend of 20 mm and 10 mm crushed limestone, and the fine aggregates were a blend of natural red sand and manufactured sand obtained from the crushed limestone satisfying the ASTM limits and criteria. The water to cement ratio was kept at 0.45 for all the mixes. Table 1 will illustrate the mix proportion of the specimens. 2.1. Specimen Preparation and Experiment Scheme. This experimental investigation is an improved extension of the Table 1. Mix Proportions total chloride (% mass of binder)

nos. 1, 2 at 50 °C nos. 3, 4 at 40 °C nos. 5, 6 at 30 °C nos. 7, 8 at 50 °C nos. 9, 10 at 40 °C nos. 11, 12 at 30 °C

5% at the ends

3% at the ends

Received: Revised: Accepted: Published:

August 26, 2013 January 18, 2014 January 24, 2014 January 24, 2014

specimens

2656

W/C

OPC kg/m3

fine aggregate kg/m3

coarse aggregate kg/m3

0.45

371

756

1031

0.45

371

756

1031

dx.doi.org/10.1021/ie402901y | Ind. Eng. Chem. Res. 2014, 53, 2656−2660

Industrial & Engineering Chemistry Research

Article

previous research finding in which specimens were prepared for finding the effect of varying temperature and constant high humidity on the repaired corroded patches of reinforced concrete structures.12 Here, in this research 1 m × 1 m × 0.5 m slabs were prepared having steel in both direction of the cross section; the schematic diagram of these specimens is shown in Figure 1.

electrical signal through a connection to the steel bar. In GECOR, this signal is confined to the steel rebar in a circle with a diameter of 110 mm. For further illustration of corrosion measurement setup, consider Figure 2. Special care was given in wetting the

Figure 2. Corrosion measurement device.

concrete surface of the specimens before taking half-cell potential measurements because it is one of the most important points in the measurement of half-cell potential so that the resistivity of the concrete is reduced to such an extent which does not affect experiment measurement results. If the measured value of half-cell potential does not stop fluctuating during the measurement, it means that the surface of the concrete is not wet enough and the resistivity of the concrete is hindering the formation of proper contact between the electrode and the concrete electrolyte.

Figure 1. Schematic representation of the identical test specimen. (a) Plan view of the test specimen. (b) Three-dimensional view of the test specimen.

3. EXPERIMENT RESULTS 3.1. Corrosion Potential Measurements. Corrosion potentials were measured for 2 years of all the specimens kept at varying temperature under constant humidity in the environmental chambers. Figure 3 shows the schematic diagram

For the preparation of a typical slab for this research, the ends were cast first with the chloride contaminated concrete, and the next day the middle portion having steel at the intersection was cast with the uncontaminated concrete simulating the actual patch repair in the field. After demolding, the prepared test specimens were kept at 50, 40, and 30 °C temperature conditions and 85% relative humidity in environmental control chambers. The steel rebar corrosion potential was measured for all specimens using a GECOR device13 and ASTM C-876.14 The GECOR device is quite valuable and versatile for the corrosion measurement of steel in concrete. The GECOR measures the corrosion rate as reflected by the corrosion current density and the half-cell corrosion potential. A true measure of the corrosion rate is possible by the polarization resistance technique. It has been well-established by Stern and Geary that the corrosion current is linearly related to the polarization resistance, which gives a direct quantitative measurement of the amount of steel turning into oxide at the time of measurement. By Faraday’s equation, this can be extrapolated to direct metal sectional loss. The corrosion current values in GECOR (GECOR-8, 2012) are calculated from the polarization resistance Rp using the relation Icorr = B/Rp, where Icorr is given in microamps per squared centimeters when Rp is given in kiloohms per squared centimeters and B = 26 mV. Icorr is directly proportional to corrosion rate through the relation, corrosion rate (μm/year) = 11.6Icorr. This gives a tool for quantifying the average reduction of rebar diameter over time. The measurement of corrosion rate usually involves applying

Figure 3. Representation of the corrosion potential measurements at different points.

of test specimen having green circles at different locations from where the corrosion potential readings were taken in order to get a clear understanding of the corrosion phenomenon taking place in the simulated repaired patches. For exact and accurate interpretation of the obtained results, an average of the corrosion potentials in contaminated and uncontaminated areas at different points was recorded. The following results were obtained: (1) At the middle noncontaminated portion of the specimen having 5% chloride at the other end portions and kept at 2657



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50 °C (nos. 1 and 2), the maximum corrosion of −0.229 V was found after 2 years as compared to −0.269 V at 30 °C in the middle zero chloride portion of the same specimens (nos. 5 and 6). The results are shown in Figures 4 and 5. (2) The maximum corrosion potential reading of the specimens nos. 1 and 2 was found −0.351 V as

Figure 5. Corrosion potential measurement for 3% chloride contaminated specimen at the end kept at (a) 50, (b) 40, and (c) 30 °C.

compared to high chloride induced potentials of −0.417 V (Figure 4) of the same specimen nos. 5 and 6 at 30 °C (Figure 5) after completion of 2 years. These results were in compliance with the above result at the middle portion that showed the decline in corrosion potentials at elevated temperature. (3) At the middle noncontaminated portion of the specimen nos. 3 and 4 which were put at 40 °C, a maximum

Figure 4. Corrosion potential measurement for 5% contaminated chloride specimen at the end kept at (a) 50, (b) 40, and (c) 30 °C. 2658



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corrosion potential of −0.381 V was found, being higher than the other specimens at 30 and 50 °C. (4) The highest corrosion potential of −0.497 V was found in specimen nos. 3 and 4 as compared to −0.351 V at the contaminated ends of the specimen nos. 1 and 2. After 365 days of observation, significant decline was observed that potential dropped from −0.699 to −0.489 after one more year of observations. (5) In the 3% chloride contaminated specimens (nos. 7 and 8) at the end, the corrosion potential of −0.255 V was obtained as compared to high −0.311 V of the same specimens (nos. 11 and 12) which were kept at 30 °C. (6) In specimen nos. 7 and 8, the corrosion potential of −0.195 V at the middle noncontaminated portion was obtained as compared to −0.201 V at 30 °C. 3.2. Gravimetric Mass Loss. Finally after two years of observations, the specimens were broken for gravimetric mass loss to calculate the % mass loss of steel in these specimens. The obtained steel from the specimen was then split into three pieces. The following results were obtained: 1. The steel bar from the end portion of 5% chloride contaminated concrete gave the highest percent mass loss of 3.7 at 40 °C while the steel bar at the intersection gave 2.79% mass loss. When the steel taken for mass loss was from the end portion of the same specimen kept at 30 °C, the highest percent mass loss of 3.11% and 2.09% was obtained from its intersection steel. However interestingly even after exposure of 2 years, the steel of the end portion of the same specimen kept at 50 °C gave the highest percent mass loss of 3.31 and the steel at the middle gave 2.27% mass loss which was lower than the mass loss at 40 °C. The results are shown in Figure 6. 2. The steel from the end portions of 3% chloride contaminated concrete specimens kept at 30, 40, and 50 °C gave 2.65, 3.11, and 2.75% mass loss respectively. While from the middle uncontaminated portion of these specimens 1.75, 2.19, and 1.88% mass losses were obtained, respectively, as shown in Figure 6. Similarly from the 3% chloride contaminated specimens, percent mass losses at 50 °C were as compared to the mass loss at 40 °C, verifying the obtained results of corrosion potentials and authenticating the originality of this research.

Figure 6. Corrosion potential measurement for 3% and 5% chloride contaminated specimen at the end kept at (a) 30, (b) 40, and (c) 50 °C.

in this paper, point toward the alarming situation that could exit in the repaired portion of the chloride contaminated concrete due to macro-cell formation and could cause further destruction due to formation of an anodic ring around the repaired patches. Moreover, the long-term serviceability and durability of the whole structure becomes a question mark even though its corroded patches are repaired with the common repair techniques assuming the structure to be safe. Therefore by considering the obtained results, it is expected that this data would be used as a benchmark for patch repairs of the reinforced concrete structures and necessary mitigation techniques should be applied in accordance to this research data for successful repairs. Also, the experimental evaluation of the durability or the vulnerability of the reinforced concrete foundations will emerge as the consequence of this research for the scope of future research.

4. DISCUSSION It can be seen from the obtained results of all the specimens at varying temperature that corrosion potential is decreasing with the passage of time. The obtained results authenticate the previous research findings.12 From the previous research, it was inferred that in the case of the specimens having the highest concentration of Cl and highest temperature showed an interesting falling trend and reduction in the corrosion potential values with the increase in temperature. The reason for this phenomenon explained in that research was the reduction of oxygen solubility in the pore solution at high temperature and the blockage of concrete pores at high relative humidity and high temperature which resulted in discontinuity of interconnected concrete pores. In this long-term research, the same trend as obtained from previous 1 year observations was observed. But, interestingly the corrosion potential was further decreased owning to the same reason as explained above. The obtained results presented

5. CONCLUSIONS It is corroborated from the experimental findings of this research that corrosion develops in repaired patches of RC structures in a form of macro-cell corrosion and its severity varies with temperature in a nonuniform way. The severity of recorrosion in repaired patches at the rebar intersection points is found to be even more than that of the longitudinal rebar. It is observed that temperature escalated the corrosion process in 2659



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repaired intersection patches from 30 to 40 °C. However, it was interesting to observe the decrease in corrosion potential and corrosion mass loss at 50 °C in comparison to those at 40 °C at the contaminated and noncontaminated portions simulating the actual patch repair portions of the experimental specimens even at the cross rebar intersection areas. One reason for this decline in corrosion at 50 °C could be the reduction of oxygen solubility in the pore solution at high temperature resulting in an oxygen controlled corrosion reaction at high chloride concentration. Another reason could be the blockage of concrete pores at high relative humidity and high temperature resulting in discontinuity of interconnected concrete pores and finally resulting in the shortage of oxygen at such a high relative humidity (RH) and high temperature condition, especially at the more congested rebar intersection areas. Furthermore, the results presented in this paper point toward the alarming situation that could exist in the repaired portion of the chloride contaminated concrete due to macro-cell formation and cause further destruction due to formation of an anodic ring around the repaired patches at the later stages. Therefore, it is expected that this data would be used as a benchmark for patch repairs of the reinforced concrete structures and that necessary mitigation techniques will be applied in accordance with this research data for successful repairs. Also, experimental evaluation of the durability or the vulnerability of the reinforced concrete foundations should emerge as the logical next step of this research and the scope of future research.

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Steel/Concrete Interface by Combination Sensors. Anal. Chem. 2006, 78, 3179−3185. (9) Hussain, R. R.; Tetsuya, I. Enhanced electro-chemical corrosion model for reinforced concrete under severe coupled environmental action of chloride and temperature. Constr. Build. Mater. 2010, 25, 1305−1315. (10) Schiessl, P.; Raupach, M. Influence of Temperature on the Corrosion Rate of Steel in Concrete Containing Chlorides. First International Conference of Reinforced Concrete Material in Hot Climates, Alain, UAE, Apr 24−27, 1994. (11) Hussain, R. R.; Tetsuya, I. Novel Approach Towards Calculation of Averaged Activation Energy Based on Arrhenius Plot for Modeling of the Effect of Temperature on Chloride Induced Corrosion of Steel in Concrete. J. ASTM Int. 2010, 7, 1−8. (12) Wasim, M.; Hussain, R. R. Unique Declining Electrochemical Trend of Macro-Cell Half-Cell Potential with Increase in Temperature at Constant High Humidity for Corroding Steel Bars in Repaired Concrete Patches. Int. J. Electrochem. Sci. 2012, 7, 1412−1423. (13) GECOR-8. http://www.ndtjames.com/Gecor-8-p/c-cs-8.htm (accessed June 11, 2013). (14) ASTM C 876-09. Standard test method for corrosion potentials of uncoated reinforcing steel in concrete; American Society for Testing and Materials: Warrendale, PA, 2009.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +966590011078. Postal Address: PO Box: 800, CoE-CRT, Civil Engineering Department, College of Engineering, King Saud University, Riyadh, 11421, Saudi Arabia. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

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REFERENCES

This project was supported by King Saud University, Deanship of Scientific Research, College of Engineering Research Center.

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Repair Vulnerability of Corrosion Patch Repairs at the Steel

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