Cathodic protection of concrete structures containing ...

Cathodic protection of concrete structures containing calcareous aggregates in tropical-humid marine environments M. Sosa, R. Camacho, T. Pe´rez and J. Gonza´lez-Sańchez Centro de Investigacioń en Corrosioń, Universidad Autońoma de Campeche, Campeche, Mexico Abstract Purpose – To evaluate the performance of two cathodic protection (CP) systems applied to steel reinforced concrete structures manufactured with calcareous aggregates and exposed to the tropical-humid marine environment at the Yucatań peninsula in Mexico. Design/methodology/approach – Rectangular concrete beams were manufactured using a water/cement ratio ¼ 0.65, with and without the addition of NaCl in the mixing water. Specimens subjected to CP, eight to impressed current cathodic protection (ICCP) and eight to sacrificial anode cathodic protection (SACP) were partially immersed in natural seawater during 360 days. The half cell potential (HCP) and the current consumption were recorded during the total exposure time. Findings – The measured HCP values of the steel rebar in the beams subjected to SACP did not attain protection potential levels. However, the galvanic couple Zn-steel provided enough current for the protection of the steel. Visual inspection of concrete cores extracted from the beams indicated that corrosion products were not present at the steel-concrete boundary. On the other hand, the ICCP applied to eight concrete beams provided excellent corrosion protection to the steel rebar. Originality/value – This work revealed that the SACP system (thermally sprayed zinc) works well in high relative humidity environments and can be successfully used to protect steel reinforced concrete structures manufactured with calcareous aggregates which are endemic of the region and commonly used for infrastructure construction in the Yucatań peninsula. Keywords Cathodic protection, Concretes, Structures, Corrosion environments Paper type Research paper

concrete and the water to cement ratio (Manual de Inspeccioń, 1998). High values of water to cement ratio induce the formation of cavities and air pores inside the concrete paste which facilitate the transport of contaminants through it, which eventually reach the steel rebar and promote the corrosion process. Most of the civil, industrial, communications and tourist infrastructure located in the Mexican coast at the Yucatań peninsula is built with reinforced concrete, for example, harbours, bridges, highways, hotels, hospitals and shopping centres. In 2000, the Mexican Transport Institute carried out an evaluation of the effect of corrosive environments on the degradation of the bridges of the national infrastructure network of roads and highways in Mexico (Torres et al., 2000). This author reported that one of the eight most important bridges in the region, the second largest bridge in Mexico (Puente de La Unidad with an extension of 2,300 m), had a high risk of suffering chloride induced corrosion. Four bridges presented intermediate risk, and three showed low risk of corrosion degradation. In Mexico, the most common remedy used in order to expand the lifetime of corrosion damaged concrete structures in marine environments consists of: cleaning the surface, painting or replacing segments of the rebar and the application of new concrete paste. However, this repair

Introduction Corrosion of the steel rebar is the principal precursor of the degradation processes on concrete structures, which involves a very high cost in terms of maintenance, reparation and substitution of components and structures (Holcomb and Cryer, 1998). For properly manufactured concrete structures the corrosion rate is low and minimal maintenance meet the safety requirements for decades. However, the corrosion rate increases to an unacceptable level if the concrete at the steel depth becomes either carbonated or chloride-contaminated (or both), which is typically found on concrete structures built in marine coastal zones. This induces the progressive corrosion of the steel rebar and the accumulation of voluminous solid corrosion products in the concrete pore space around the steel. The higher volume of the corrosion products formed at the rebar induces tensile stresses against the concrete body producing cracking of the concrete paste due to the low tension strength of concrete (Rincoń et al., 1991; Andrade et al., 2000). Even though there are several factors that promote the corrosion of steel rebar, the most important are the high concentration of chloride ions in the The current issue and full text archive of this journal is available at www.emeraldinsight.com/0003-5599.htm

The authors would like to acknowledge The Autonomous University of Campeche for the opportunity to conduct this work. Additionally, they would like to acknowledge the support of CONACYT (Mexican Government) for the financial support to the Research Project No. 2002C01-40484.

Anti-Corrosion Methods and Materials 54/2 (2007) 103– 110 q Emerald Group Publishing Limited [ISSN 0003-5599] [DOI 10.1108/00035590710733601]

103

Cathodic protection of concrete structures

Anti-Corrosion Methods and Materials

M. Sosa, R. Camacho, T. Pe´rez and J. Gonza´lez-Sańchez

Volume 54 · Number 2 · 2007 · 103 –110

procedure gives poor results in terms of durability and cost. For the past decade, impressed current and sacrificial anode cathodic protection (SACP) have been applied successfully to reinforced concrete structures in the USA (Brousseau et al., 1997; Funahashi et al., 1997). Cathodic protection (CP) is presently recognized as the only methodology for which extensive service experience exists to control effectively ongoing corrosion of reinforcing steel in chloridecontaminated concrete structures. The rebar embedded in concrete normally is passive due to the alkaline nature of the cement paste (pH , 12.5-13.9), which facilitates the formation and maintenance of a passive iron oxide film. The use of impressed current cathodic protection (ICCP) permits the application of the required current to protect a steel reinforcement, which assures the safe performance and durability of concrete structures. Nevertheless, this system requires continuous maintenance programs and is susceptible to interruptions due to energy supply disturbances on which the ICCP depends completely. The versatility and controllable nature of the current supplied to the structure to be protected using ICCP and the option of adapt the technique to special situations (in relation to different geometries and extensions) have been important essential considerations when considering practical remedial measures (Holcomb and Cryer, 1998; Brousseau et al., 1997; Bermu´dez et al., 1996). The SACP system forms a galvanic cell with the structure to be protected. Several researchers have studied the performance and reliability of SACP applied to the steel rebar in reinforced concrete structures and the results indicated that aluminium and zinc exhibit the best efficiency and that the conductivity of the concrete is a fundamental parameter for the satisfactory performance of this protection system (Funahashi et al., 1997; Whiting et al., 1996; Hartt, 1997). Most previous studies and experience related to the corrosion mitigation technique concern to ICCP as opposed to SACP because of the high resistivity of the electrolyte (concrete pore water) and the higher driving voltage that the former affords. However, instances of successful application of SACP to substructure components of coastal bridges in Florida have been reported (Kessler et al., 1990, 1997; Kessler, 1991, 1993; Powers et al., 1992) and interest exists in determining the utility of this CP approach for colder or drier (or both) exposure conditions. It has been reported that the humidity of the concrete is of paramount importance for the adequate performance of the thermal sprayed SACP. Recently, Covino utilised hygroscopic salts over the concrete surface in order to retain moisture in the concrete which helps to maintain the adequate performance of the galvanic cell, thereby ensuring that CP of the steel rebar is maintained (Covino et al., 1999). An interesting and useful method that permits the quantitative characterisation the SACP of embedded steel in concrete in terms of the electrochemical behaviour of the anode, which controls the CP effectiveness, has been proposed by Hartt (2002). The procedure is described according to the influence of various system and corrosion cell parameters. The method also can be used for the projection of the galvanic anode performance and of CP system life. The present paper reports the experimental results of ICCP and SACP (by thermally sprayed zinc) systems applied to reinforced concrete beams partially immersed in natural seawater exposed to a tropical-humid marine environment. Analyses of the data gave definite information about the

performance of both protection systems on reinforce concrete exposed to the tropical-humid marine environment of the Yucatań peninsula in Mexico.

Experimental procedure Specimen preparation Twenty concrete beams with square section area of 20 £ 20 cm and 100 cm long were manufactured using a water to cement ratio of 0.65, fine and coarse aggregates (calcareous aggregates commonly used at the Yucatań peninsula), and composed portland cement, Mexican Standard NMX-C-414-ONNCCE (2003). All beams had embedded an armor consisting on four steel bars of 0.95 cm of diameter and 110 cm length linked by seven steel square rings of 0.32 cm diameter and 60 cm length. The steel armor was embedded with a minimum 25 mm concrete cover as shown in Figure 1. In order to study the effect of sodium chloride contamination on the performance of the CP system, and to accelerate the corrosion process of the steel rebar, ten beams were manufactured with mixing water containing 35 g/l of NaCl. Table I presents the material proportions used to prepare the concrete specimens. The specimens were allowed to cure for 28 days in Ca(OH)2 saturated solution, during which the half cell potential (HCP) of the steel rebar was measured continuously. After curing, anodic polarization was applied to the steel rebar in order to induce corrosion damage with the specimens were immersed in seawater in a vertical orientation. The anodic polarization was conducted for a period of 28 days by the application of an anodic current density of 3.0 mA/cm2 to a total steel rebar area of 1,500 cm2 (considering the seawater level was always 5 cm below the upper end of the concrete specimen). According to reports of similar investigations an anodic current density higher than 1 mA/cm2 is required to corrode the steel rebar embedded in concrete (Chess et al., 1998). The response of the steel rebar to the anodic polarization was evaluated by measuring Figure 1 Concrete specimens configuration and dimensions

Table I Material proportions used to manufacture the concrete beams NaCl Coarse content in Cement Fine aggregate aggregates Water the mixing content content content content water Beams (kg/m3) (kg/m3) (kg/m3) (l/m3) (g/l) 10 10

104

312.5 312.5

750 750

687.5 687.5

206.25 206.25

35 0




Volume 54 · Number 2 · 2007 · 103 –110

Figure 2 Zinc coated beams partially immersed in natural seawater

continuously the HCP according to the standard ASTM C876 (1995). Exposure conditions Four concrete beams not subjected to CP were used as control samples, two of them were exposed to the atmosphere and the other two were immersed in natural seawater. The other 16 concrete specimens were partially immersed in natural seawater, eight under SACP and eight under ICCP. The evaluation of the electrochemical condition on the steel rebar was assessed by the measurement of the HCP, which was monitored continuously on the 20 specimens during 360 days. Table II summarises the exposure conditions for the 20 concrete specimens. Application of the cathodic protection Sacrificial anode cathodic protection (SACP) Thermal sprayed zinc was applied to eight concrete beams. A sandblast pre-treatment was applied on the four longitudinal faces of the beams in order to obtain a surface that was free from contaminants and with a roughness that ensure the proper adhesion of the thermal sprayed zinc (the anode). Immediately after the surface pre-treatment, the surfaces of the beams were coated with zinc. A surface area of 20 £ 60 cm was coated at each face of the beams. The zinc coated surface area of the specimens was not in contact to the seawater during the exposure period as shown in Figure 2. In order to determine the electric current consumed by the SACP of the steel, a voltmeter was connected to the ends of a 10 V precision resistor which was positioned between the zinc coating and the steel rebar. In order to increase the capability for water retention inside the concrete pores and consequently reducing the resistivity of the concrete, a saturated LiBr solution was applied on the upper end surface of the beams after 180 day of exposure. Impressed current cathodic protection (ICCP) A cathodic current was applied to the beams immersed in seawater in order to change the HCP of the steel to a value of 2 950 mV vs Ag/AgCl, which is considered to be the protection potential (Baeckmann et al., 1997; Berkeley and Pathmanaban, 1990). A metallic mesh surrounding the beams immersed in seawater was used as counter electrode to form the electrochemical cell along the steel rebar and a power supply, as shown schematically in Figure 3. The steel armor of the concrete specimens and the anodic mesh were connected in parallel to the power supply. In order to determine the

electric current consumed by the CP of the steel, a voltmeter was connected to the ends of a 10 V precision resistor which was positioned between the power supply and the steel rebar.

Table II Exposure conditions for the concrete beams

Exposure conditions and composition 2

Marine atmosphere, no Cl Marine atmosphere, with Cl2 Partially immersed in seawater, no Cl2 Partially immersed in seawater, with Cl2 Partially immersed in seawater, no Cl2 Partially immersed in seawater, with Cl2 Partially immersed in seawater, no Cl2 Partially immersed in seawater, with Cl2

Cathodic protection system ICCP SACP 2 2 2 2 2 2 þ þ

2 2 2 2 þ þ 2 2

105

Number of specimens

Specimen coding

1 1 1 1 4 4 4 4

AS AC IS IC ZS ZC CS CC




Volume 54 · Number 2 · 2007 · 103 –110

Figure 3 Schematic representation of the arrangement for ICCP

Figure 4 Steel rebar HCP for the control specimens as a function of exposure time

Measurement of the HCP of the steel rebar on control beams The evaluation of the electrochemical behaviour in terms of the HCP of the steel rebar in the control beams was used as a guide for the probability of corrosion damage on steel rebar. The measurement of the HCP was conducted following the standard ASTM C876 for 360 days. Table III presents this guide including some important observations.

Two specimens (IS and IC) utilising a similar concrete mixture were immersed in natural seawater. The HCP values shifted from 2400 to 2 500 mV during the first 180 days of the exposure period and from 2400 to 2 650 mV vs Ag/AgCl during the next 180 days. These values suggest that under that exposure conditions (i.e. no applied CP) steel rebars embedded in the concrete beams immersed in natural seawater exhibited a high probability of corrosion. However, it was observed that sodium chloride additions to the mixing water did not show a significant effect upon the HCP for the immersed HCP specimens.

Visual examination of the steel rebar After the exposure period of 360 days, concrete cores were extracted from one beam of each CP system in order to carry out visual evaluation of the condition of the steel rebar. A special water lubricated and cooled drill was used to core a 7.5 cm diameter sample from the test beams.

Beams subjected to cathodic protection Figure 5 shows the values of HCP of the steel rebar as a function of the exposure time for concrete beams subjected to CP. Specimens subjected to SACP presented variable potential values during the first 100 days of exposure reaching values up to 2 700 mV vs Ag/AgCl. From day 110 to day 200 of exposure the potential moved to more positive values around 2 500 mV and finally from day 210 to the end of the exposure period the potential of the steel rebar reached values of around 2 800 mV vs Ag/AgCl. These last potential values can be considered adequate protection values for the steel rebar under CP.

Results Specimens without cathodic protection Figure 4 shows the HCP for the control specimens; two exposed to the tropical-humid marine atmosphere one concrete specimen manufactured without NaCl and the other with NaCl. These specimens (AS and AC), showed a significant difference in the HCP induced by the presence of NaCl in the mixing water. The values of HCP of the beam AS were in a range from 2200 to 200 mV vs Ag/AgCl. Therefore, the probability of corrosion damage was slight or almost nil, which means that the steel was passive according to ASTM C876. In the case of the beam AC, the HCP was in range 2350 to 2 180 mV vs Ag/AgCl. It is well known that in concretes containing NaCl, steel rebar takes up more negative values, leaving it at intermediate- to high-risk of corrosion.

Determination of the electric current consumption Figure 6 shows the electric current consumption at the cathode (steel rebar) of the CP system for the case of ICCP and SACP. After 90 days of polarization at 2 950 mV vs Ag/AgCl the potential of the rebar shifted from 2 950 to 21,050 mV vs

Table III Evaluation criteria for corrosion damage on steel rebar in terms of Ecorr vs Cu/CuSO4 electrode ASTM-C-876 Potential (mV) vs Cu/CuSO4 > 2200 mV 2200 to 2 350 mV < 2350 mV < 2500 mV

ASTM Criteria for corrosion of steel in concrete for different standard half cells Potential (mV) vs Ag/AgCl Potential (mV) vs calomel Corrosion condition .2 106 mV 2106 to 2256 mV ,2 256 mV ,2 406 mV

.2 126 mV 2126 to 2276 mV ,2 276 mV ,2 426 mV

106

Low (10 per cent risk of corrosion) Intermediate corrosion risk High (,90 per cent risk of corrosion) Severe corrosion




Volume 54 · Number 2 · 2007 · 103 –110

Figure 5 HCP of the steel rebar as a function of the exposure time for concrete beams subjected to CP

Table IV Practical CP current density requirements for varying steel conditions Current density mA/cm2 Environment surrounding of reinforcement steel reinforcement 0.01 0.1 and 0.3 0.3 and 0.7 0.8 and 2.0

2.0 and 5.0

Alkaline, no corrosion occurring, low oxygen resupply Alkaline, no corrosion occurring, exposed structure Alkaline, chloride present, dry, good quality concrete, high cover, light corrosion observed on rebar Chloride present, wet, poor quality concrete mediumlow cover, widespread pitting and general corrosion on steel High chloride levels, wet fluctuating environment, high oxygen level, hot, severe corrosion on steel, low cover

Source: Chess et al. (1998)

Figure 7 Sample extracted from a concrete specimen in which the steel rebar was subjected to ICCP during 360 days Figure 6 Electric current consumption as a function of time during exposure of concrete specimens under CP conditions

the effectiveness of the ICCP system applied to the steel rebar. The pH estimated by using acid/base indicators timolphthaleine and phenolphthalein sprayed over the core surface in the past adjacent to the steel rebar showed no pH decrease below pH 10.5, which represents no risk of carbonation and corrosion of the steel. Figure 8 shows cylindrical cores extracted from concrete beam subjected to SACP. After 180 days of exposure the CP system was not established properly and the steel rebar presented incipient corrosion (Figure 8(a)). As exposure time increased the SACP system improved its performance protecting the rebar from corrosion as the quantity of corrosion products did not increase after 360 days of exposure as shown in Figure 8(b).

Ag/AgCl and remained at that level for the following 90 days. For this level of potential, a current density between 2 and 5 mA/cm2 was found in the CP system. During the last 90 days of the experiment the potential shifted to 2 950 mV vs Ag/AgCl. This resulted in a decrease of the current density consumption, which was then in the range from 1 to 3 mA/cm2. The criteria for current protection value are presented in Table IV. The concrete specimens subjected to SACP in general exhibited higher cathodic current flow compared with the current measured for beams subjected to ICCP. For the SACP protected beams the current density was from 3 to 6 mA/cm2. However, despite this cathodic current density, the steel rebar did not attain protection potential levels. Visual analysis Figure 7 shows a cylindrical core extracted from a beam that had been cathodically protected by impressed current in which the transverse section area of the steel rebar exhibited no apparent signs of corrosion. This observation corroborates

Discussion Beams without cathodic protection The HCP measured on control concrete beams exposed to the tropical-humid marine atmosphere resulted more activity 107




Volume 54 · Number 2 · 2007 · 103 –110

Figure 8 Cylindrical cores extracted from concrete beam subjected to SACP after: (a) 180 and (b) 360 days

than for beams manufactured with the addition of NaCl in the mixing water than was the case for specimens fabricated without sodium chloride. The samples with sodium chloride exhibited a high probability to suffer from corrosion degradation in terms of the HCP measured which ranged from 2 350 to 2 180 mV vs Ag/AgCl. In this case, the effect of chloride ions in the concrete was very evident. Beams manufactured without the addition of sodium chloride presented values of HCP in the range from 2 75 to 150 mV vs Ag/AgCl. At this HCP value the rebar was passive and the probability of corrosion activity was low. For the case of control concrete beams immersed in natural seawater we found that the HCP was more negative compared to specimens exposed to the atmosphere. Very similar HCP values were found for specimens manufactured with and without the addition of NaCl in the mixing water. Under conditions of partial immersion in natural seawater, the presence of NaCl in the concrete paste seemed to have no effect on the electrochemical behaviour of the steel rebar embedded in concrete. Beams with and without NaCl presented HCP fluctuations during the total exposure period following the same pattern. The condition of the steel rebar is critical for the case of concrete structures immersed in natural seawater as the HCP values indicate that there is high probability of corrosion.

conditions. These specimens showed current density values from 1 to 3 mA/cm2, which was an appropriate current to ensure protection to the steel rebar, as was proposed by Chess et al. (1998). Beams under SACP The steel reinforced concrete specimens subjected to SACP by zinc thermally sprayed presented variable HCP values around 2 700 mV Ag/AgCl during the first 90 days of exposure. The change of potentials from 2700 to 2 800 mV vs Ag/AgCl placed the steel rebar in a thermodynamic condition that can be considered to be protected against corrosion. The change of HCP to more negative values could be due to the increase in humidity in the atmosphere and in the concrete matrix with water saturated concrete pores, which induced a diminution of the concrete resistivity thereby improving the ionic current flow through the concrete. The characteristics of the aggregates used for the concrete specimen manufacture play a significant role in this respect as calcareous gross and fine aggregates have lower density than do siliceous materials. A decrease of the HCP of the steel rebar was observed few days after the application of a saturated LiBr solution to the upper end of the concrete beams. The potential values registered were more negative than 2 800 mV vs Ag/AgCl, which is considered to be the protection potential value. Regarding the current consumption associated with the two different CP systems applied, the SACP exhibited higher current density values than did the ICCP system. Current densities from 3 to 6 mA/cm2 were registered during the major percentage of the exposure period. In this case, the amount of zinc thermally sprayed, which formed a uniform and

Beams under ICCP As expected, the steel rebar embedded in concrete specimens subjected to ICCP reached the protection potential level, 2 950 mV vs Ag/AgCl. During the total exposure period these beams were maintained at this potential level which ensured the stability of the steel rebar under these exposure 108




Volume 54 · Number 2 · 2007 · 103 –110

References

continuous layer over the surface of the concrete beams, induced high galvanic current when connected to the steel rebar. The relative humidity, (RH . 70 per cent) prevalent during the year in the tropical-humid marine atmosphere of Campeche city, and the properties of the concrete manufactured with calcareous aggregates, resulted in the effective behaviour of the galvanic cell formed by the couple Zn-steel rebar. In the case of the concrete specimens subjected to ICCP, it was found that the steel rebar was easy to polarise to the protection potential level of 2950 mV vs Ag/AgCl with current density consumption from 2 to 5 mA/cm2. Under these conditions the steel rebar embedded in concrete beams exposed to partial immersion in natural seawater was protected against corrosion during the total exposure period. The performance of both of the CP systems used was not affected by the presence of NaCl in the concrete, as the values of HCP for the steel rebar and the current consumption are very similar for beams with and without NaCl. However, corrosion of the steel was assisted by the presence of the chloride ions in the concrete as the salt induces instability of the passive condition of the steel, as shown by the behaviour of the rebar in the control beams. It is proposed that calcareous aggregates, which have less density and a much higher water absorption capacity compared to siliceous aggregates, as indicated in Table V, may improve the performance of the thermally sprayed zinc SACP. An additional advantage is that CP will not promote secondary effects on the concrete such as the alkali-silica reaction.

Andrade, C., Alonso, C. and Castro, P. (2000), “Corrosioń y proteccioń de armaduras de hormigoń”, Proceedings 3er Curso Internacional sobre Corrosioń en Puentes y Estructuras Concreto Metal, Veracruz, Me´xico, p. 99. ASTM C876 (1995), Standard Test Method for Half-Cell Potentials of Uncoated Reinforcing Steel in Concrete, ASTM International, West Conshohocken, PA. Baeckmann, W., Schwenk, W. and Prinz, W. (1997), Cathodic Corrosion Protection, Theory and Practice of Electrochemical Protection Processes, 3rd ed., Gulf Professional Publishing, Houston, TX. Berkeley, K.G. and Pathmanaban, S. (1990), Cathodic Protection of Reinforcement Steel in Concrete, Butterworths, London, pp. 60-68, 140-145. Bermu´dez, C.M., Aguirre, L.O., Va´squez, C. and Castillo, H. (1996) Paper No. LA 96006, paper presented at 2nd Latin American Region Corrosion Congress. Brousseau, R., Baldock, B., Pye, G. and Gu, P. (1997), “Sacrificial cathodic protection of a concrete overpass using metallized zinc: last update”, Paper No. 239, paper presented at NACE Corrosion Congress ’97. Chess, P.M., Gronvold, F. and Karnov, A.S. (1998), Cathodic Protection of Steel in Concrete, Routledge, London, pp. 37-41. Covino, B.S., Holcomb, G.R., Bullard, S.J., Russell, J.H., Cramer, S.D., Bennett, J.E. and Laylor, H.M. (1999), “Electrochemical aging of humectant: treated thermalsprayed zinc anodes for cathodic protection”, Paper No. 548, paper presented at NACE Corrosion Congress ’99. Funahashi, M., Daily, S.F. and Young, W.T. (1997), “Performance of newly developed sprayed anode cathodic protection system”, Paper No. 254, paper presented at NACE Corrosion Congress ’97. Hartt, W.H. (1997), “Analytical evaluation of sacrificial anode cathodic protection systems for steel in concrete”, Paper No. 252, paper presented at NACE Corrosion Congress ’97. Hartt, W.H. (2002), “Analytical evaluation of galvanic anode cathodic protection systems for steel in concrete”, Corrosion, Vol. 58 No. 6, p. 513. Holcomb, R.G. and Cryer, C.B. (1998), “Cost of impressed current cathodic protection for coastal Oregon bridges”, Materials Performance, Vol. 37 No. 9, pp. 22-6. Kessler, R.J. and Powers, R.G. (1991), “Cathodic protection using scrap and recycled materials”, paper presented at Corrosion/91, Paper No. 555, NACE, Houston, TX. Kessler, R.J. and Powers, R.G. (1993), “Update on cathodic protection of reinforcing steel in concrete marine substructures”, Paper No. 326, paper presented at Corrosion/93, NACE, Houston, TX. Kessler, R.J., Powers, R.G. and Lasa, I.R. (1990), “Zinc metallizing for galvanic cathodic protection of steelreinforced concrete in a marine environment”, Paper No. 324, paper presented at Corrosion/90, NACE International, Houston, TX. Kessler, R.J., Powers, R.G. and Lasa, I.R. (1997), “Cathodic protection using zinc sheet anodes and an ion conductive gel adhesive”, Paper No. 234, paper presented at NACE Corrosion Congress ’97. Manual de Inspeccioń (1998), “Evaluacioń y Diagno´stico de Corrosioń en Estructuras de Hormigoń Armado”, 2a.

Conclusions The SACP system worked satisfactorily when applied to steel reinforced concrete structures in contact with a tropicalhumid marine environment such as are found in the South East of the Gulf of Mexico. The high relative humidity prevalent during the year (RH . 70 per cent) in the Yucatan Peninsula, and the properties of the calcareous aggregates, ensure the formation of the galvanic cell between the thermal sprayed zinc and the steel rebar. However, the system needed a potentiostatic activation to induce a current flow through the concrete in order to complete the protection circuit. Even though the application of the SACP method did not polarise the steel-concrete inter-phase to protection potential levels, it was observed to produce galvanic currents that were sufficiently high that they would protect the steel rebar. The ICCP method kept the steel rebar at protection potential levels (2 950 mV vs Ag/AgCl) regardless the exposure conditions of the concrete beams, i.e. both when exposed to the atmosphere or when partially immersed in natural seawater. Table V Aggregates properties Type of aggregate Calcareous Siliceous

Density (kg/m3)

Absorption (per cent)

2,250 2,650a

1.52 0.6a

Source: aPe´rez (2000)

109




Volume 54 · Number 2 · 2007 · 103 –110

Edicioń, Programa Iberoamericano de Ciencia y Tecnologıá para el Desarrollo, Red Tema´tica XV.B DURAR, Julio. NMX C-414-ONNCCE (2003), “Industry of the construction, hydraulic cements, specifications and methods of test”. Pe´rez, T. (2000), “Kinetics study of the concrete steel embedded reinforcement subject to different exposure conditions at marine environment”, PhD thesis, UNAM, Me´xico (in Spanish). Powers, R.G., Saguë´s, A.A. and Murase, T. (1992), “Sprayed-zinc galvanic anodes for the cathodic protection of reinforcing steel in concrete”, in White, T.D. (Ed.), Proc. Materials Engineering Cong., Paper No. 732, American Society of Civil Engineers, New York, NY. Rincoń, O., Sańchez, M.A. and Contreras, D. (1991), “A study of practical cases of steel corrosion in reinforced

concrete, causes and solutions”, Materials Performance, No. 8, p. 42. Torres, A.A., Martıńez, M., Backhoff, M. and Nuń˜ez, G. (2000), “Application of a geo-statistical software to evaluate the effect of environmental corrosive agents on the degradation of the bridge’s infrastructure of Mexico”, paper presented at International Workshop ALCOMPAT 2000. Whiting, D.A., Nagi, M.A. and Broomfield, J.P. (1996), “Laboratory evaluation of sacrificial anode materials for cathodic protection of reinforced concrete bridges”, Corrosion, Vol. 52 No. 6, pp. 472-9.

Corresponding author J. Gonza´lez-Sańchez can be contacted at: [email protected]

To purchase reprints of this article please e-mail: [email protected] Or visit our web site for further details: www.emeraldinsight.com/reprints

110