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Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR
Construction and Building Materials xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR Takao Ueda a,⇑, Junji Kushida a, Masayuki Tsukagoshi a, Akira Nanasawa b a b
Department of Civil Engineering, The University of Tokushima, Tokushima, Japan Omi Plant, Denki Kagaku Kogyo Co., Ltd., Niigata, Japan
h i g h l i g h t s Complex deterioration of chloride attack and ASR was affected by temperature. Rise in electrolyte temperature from 30 to 40 °C improved penetration of lithium. 40 °C electrolyte of LiNO3 was most effective to suppress expansion due to ASR.
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Complex deterioration Chloride attack ASR Lithium salts Electrochemical method
a b s t r a c t Complex deterioration mechanism due to both chloride attack and ASR are greatly affected by environmental temperature. In this study, the influence of environmental temperature on concrete expansion and steel corrosion was experimentally investigated. As a result, some protection effect against steel corrosion was found in the cases of storage at 30 °C or 40 °C, although ASR expansion was promoted. This would be caused by the formation of alkali silica gel around the steel. As a remedial measure against such a complex deterioration, electrochemical penetration of lithium from the electrolyte solution was also investigated. It was clarified that electrolyte temperature greatly affected the extent of lithium penetration and the treatment at 40 °C remarkably accelerated lithium penetration into concrete compared with the case of 30 °C. Regarding the kind of lithium salt, LiNO3 solution was most effective among a number of different kinds of lithium salt. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Both chloride attack and ASR are serious deterioration mechanisms of concrete structures which play an important role as infrastructure [1]. Moreover, in such cases as the marine environment and areas with a cold climate, complex deterioration of these mechanisms can be observed because of the supply of sea water or de-icing salts. A complex deterioration mechanism due to both chloride attack and ASR has not yet been clarified. Obviously, it would be greatly affected by environmental temperature. Moreover, past research suggests that alkali silica gel formed around steel in concrete due to ASR may have a protection effect against steel corrosion [2]. In this study, the influence of environmental temperature on concrete expansion and steel corrosion was experimentally investigated in order to make an adequate decision on the strategy of remedial measures considering the environmental situations of structures. Using reinforced concrete specimens, ⇑ Corresponding author. Address: 2-1 Minami-josanjima cho, Tokushima 770-8506, Japan. Tel.: +81 88 656 2153; fax: +81 88 656 7351. E-mail address: [email protected] (T. Ueda).
concrete expansion and electrochemical steel corrosion indexes, namely, half-cell potential, polarization resistance and electric resistivity of concrete were measured regularly during the saving period in each temperature condition. As a remedial measure against such complex deterioration, in this study we tried electrochemical penetration of lithium from electrolyte solution. It has been confirmed by many researchers that lithium salts act to suppress ASR-induced expansion of concrete [3,4]. Assuming the application of the lithium salts as a repair additive for concrete structures deteriorated by ASR, sufficient amounts of Li+ must be driven into the ASR-affected concrete [5]. Past researches have shown that Li/Na molar ratio should be around 1.0 or more in order to suppress concrete expansion [6,7]. Thus, an electrochemical technique to accelerate the penetration of the lithium ions (Li+) in a lithium-based electrolyte solution into concrete has been employed for the purpose of suppressing ASR-induced expansion due to Li+ [8]. However, from the results of past research works, the penetration area of Li+ is limited around the concrete surface and it is difficult to make Li+ penetrate into the deeper into concrete [9,10]. In this study, the complex deterioration mechanism by the combination of ASR and chloride attack, in particular the influence
0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
2
T. Ueda et al. / Construction and Building Materials xxx (2013) xxx–xxx
of environmental temperature, was experimentally investigated. As a remedial measure, electrochemical treatment was also conducted aiming to grasp the influence of different kinds of lithium salts and temperature of the electrolyte solution on migration properties of ions in concrete and ASR-induced expansion of concrete. 2. Experimental program
Fig. 1. Outline of an RC specimen.
2.1. Materials Mixture proportions of concrete used in this study are shown in Table 1. Water to cement ratio (W/C) of concrete was 0.55 for all mixture proportions. Concrete named NCl is assumed to be deteriorated by chloride attack solely. This concrete contained only non-reactive aggregate and sodium chloride (NaCl) was added to adjust the amount of alkali. Concrete named RCl is assumed to be damaged by the complex deterioration. This concrete contained reactive aggregate and NaCl was added as the source of alkali. Concrete named ROH is assumed to be damaged by ASR solely. This concrete contained reactive aggregate and NaOH was mixed to adjust the amount of alkali in the concrete. In order to adjust the total alkali contents as R2O = 10.0 kg/m3 for acceleration of deterioration, a corresponding amount of NaCl or NaOH was dissolved in the mixing water. All specimens subjected to electrochemical treatment were made of RCl concrete. Ordinary portland cement (density: 3.16 g/cm3, specific surface area: 3280 cm2/g, R2O: 0.56%) was used. As the fine aggregate, non-reactive fine aggregate (S1, density: 2.56 g/cm3) and reactive aggregate (S2, density: 2.60 g/cm3) were mixed at a pessimum weight ratio of 3:7, so as to maximize expansion of concrete. As the coarse aggregate, non-reactive aggregate (G1, density: 2.55 g/cm3, Gmax: 15 mm) and reactive aggregate (G2, density: 2.68 g/cm3, Gmax: 15 mm) were also mixed at a pessimum weight ratio of 3:7. 2.2. Preparation of specimens and electrochemical treatment Specimens prepared in this study were 100 100 300 mm reinforced concrete prisms with a steel bar u13 SR235 (JIS number) at the center of the square section as shown in Fig. 1. All specimens were cured in a wet (100% RH) and 20 °C condition. The number of specimens for each factor was three. In the case of specimens used for investigation of complex deterioration mechanism, brass chips were attached to concrete surfaces for the measurement of concrete expansion after curing of 14 days. These specimens were kept in a moist condition and temperature levels were 20, 30 or 40 °C. In the case of specimens to be subjected to electrochemical treatment, brass chips were attached after curing of 28 days, as shown in Fig. 1, and five concrete faces of each specimen were insulated with epoxy resin coating, leaving one exposed surface. Epoxy resin was spread on the concrete surface twice with a brush. After the epoxy coating, each specimen was immersed into electrolyte liquid in a plastic container, and direct electric current was supplied between rectangular shaped titanium mesh as the anode and the steel bar in concrete as the cathode. A current density, of 1.0 A/m2 to the exposed concrete area was adopted. The treatment period was 8 weeks. Different kinds of electrolyte liquid and their temperature conditions are shown in Table 2. The standard temperature level of electrolyte liquid was 30 °C so as to accelerate the lithium penetration except for the case of 40 °C of LiNO3 solution. 2.3. Tests of specimens Specimens used for investigating complex deterioration mechanism were kept at a wet and constant temperature (20, 30 or 40 °C) environment and expansion rate of concrete was measured regularly by means of a contact gauge. While measuring concrete expansion, half-cell potential, polarization resistance of steel in specimens and resistivity of concrete were also measured regularly using the electrochemical monitoring system for steel corrosion in concrete. As a reference electrode for this electrochemical monitoring, saturated silver chloride (Ag/AgCl) was used. Polarization resistance was measured by the rectangular wave electric current polarization method, as the difference of impedances at 800 Hz and 0.1 Hz of electric current frequency. Resistivity was obtained as the impedance at 800 Hz of electric current frequency.
Table 2 List of electrolyte. Name of salt
Content of salt (%)
content of Li (%)
Temperature (°C)
LiOH Li2CO3 Li2SiO4 LiNO3
10 1.2 23 30
3.0 0.22 2.9 3.0
Ca(OH)2
0.2
0
30 30 30 30 40 30
After completion of electrochemical treatment, distribution profiles of ion content (Cl, Na+, K+, Li+) in the concrete specimens were measured using powder samples grinded from samples cut out as seven concrete plates in a specimen, as shown in Fig. 2. The Na+, K+ and Li+ contents were measured by means of atomic absorption spectrometry using a crashed fine powder sample dissolved in HNO3 solution. Cl content was measured according to JIS A 1154 applying potentiometric titration with AgNO3. Variation of concrete expansion rate with time after the treatment was also measured regularly by means of a contact gauge.
3. Results and discussion 3.1. Observation of concrete cracks after storage for about one year Typical examples of concrete cracks observed after storage for about one year under a constant temperature are shown in Figs. 3–8. Each photo shows a zoom of the concrete part between brass chips for measuring concrete expansion rate. Here, it can be seen that NCl specimens showed no cracking regardless of storage temperature. Since the cover depth of concrete is relatively high, sole chloride-induced corrosion would not cause concrete cracking during storage for about one year. On the other hand, all specimens containing reactive aggregates show concrete cracks as shown in Figs. 3–8. Cracking shape is much affected by the kind of alkali. ROH specimens cause mapshaped cracking, while RCl specimens show mainly longitudinal cracks along the steel bar. These longitudinal cracks may be caused by the influence of steel corrosion combined with the cracks due to ASR. In the case of 20 °C storage, the RCl specimen is stained by steel rust with fine cracks, while the ROH specimen has relatively bold net shaped cracks. In the case of 30 °C storage, crack width appears to be widest compared with cases of 20 and 40 °C storage. The condition of 40 °C storage would most intensively accelerate the ASR expansion and steel corrosion but this storage condition (moist and high temperature) also accelerates cement hydration, which could result in refilling of concrete cracks during long term storage [11,12].
Table 1 Mixture proportions of concrete. Name
W/C (%)
s/a (%)
NCl RCl ROH
55 55 55
48 48 48
Content (kg/m3) C
W
S1
S2
G1
G2
NaCl
NaOH
338 338 338
186 186 186
832 250 250
– 591 591
871 261 261
– 641 641
15.1 15.1 –
– – 10.3
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
T. Ueda et al. / Construction and Building Materials xxx (2013) xxx–xxx
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Fig. 6. Concrete cracking observed in ROH specimen stored at 20 °C.
Fig. 2. Cutting way of a specimen for chemical analysis.
Fig. 7. Concrete cracking observed in ROH specimen stored at 30 °C.
Fig. 3. Concrete cracking observed in RCl specimen stored at 20 °C.
Fig. 8. Concrete cracking observed in ROH specimen stored at 40 °C.
Fig. 4. Concrete cracking observed in RCl specimen stored at 30 °C.
concrete followed by the environmental temperature. From this figure, ROH40 shows the earliest initiation of concrete expansion because of higher alkalinity in the pore solution [13] by dosage of NaOH and a higher temperature. The next initiation of concrete expansion occurs with specimens of RCl40 and ROH30. RCl30 shows about 100 days delay of initiation from other early expansion specimens. However, when one year passed from the
Fig. 5. Concrete cracking observed in RCl specimen stored at 40 °C.
3.2. Variation of expansion rate of concrete Regarding specimens kept at 20, 30 or 40 °C after curing, variation curves of concrete expansion rate with time are shown in Fig. 9. The horizontal axis of this figure expresses the period after the end of curing. Legends used in this figure show the name of
Fig. 9. Variation of concrete expansion rate after curing.
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
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beginning of storage, RCl30 shows the largest expansion rate with the widest concrete cracking along the steel bar as shown in Fig. 4. From these results, it is evident that slow concrete expansion cases could result in long term progressing of expansion and larger expansion rate. 3.3. Monitoring of steel corrosion in concrete Variation curves of half-cell potential and polarization resistance of steel in specimens during the storage period for each temperature condition are shown in Figs. 10 and 11 respectively. Standard lines used to judge steel corrosion probability as specified in ASTM C876-91 are also indicated in Fig. 10. Moreover, variation curves of electric resistivity of cover concrete in concrete specimens are shown in Fig. 12. According to Fig. 10, NCl and RCl specimens generally show base values of half-cell potential with a high dosage of NaCl into the concrete. These specimens initially contained Cl of 9.1 kg/m3 which is much higher than the threshold Cl content necessary to initiate steel corrosion. On the other hand, ROH specimens keep relatively nobler potential values because they did not contain the pre-mixed NaCl. Especially, when the storage temperature is 30 or 40 °C, the half-cell potential values of ROH specimens gradually increase with time regardless of growing concrete expansion due to ASR as shown in Fig. 3. This result may be due to the possibility that there is a closing of concrete cracks due to the self-mitigation mechanism caused by cement hydration [11,12] or by steel protection due to the formation of alkali silica gel around the steel bar [2]. In the case of 20 °C storage, the half-cell potential values tend to decrease gradually with progress of ASR. As shown Fig. 11, in the cases of NCl and RCl specimens, values of polarization resistance remain small during the entire period of storage because of the high dosage of NaCl in the concrete. Such a
Fig. 10. Variation of half-cell potential.
Fig. 11. Variation of polarization resistance.
Fig. 12. Variation of concrete resistance.
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
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Fig. 14. Distributions of chloride content in concrete after treatment. Fig. 13. Relationship between polarization resistance and concrete expansion rate.
small polarization resistance means a high rate of steel corrosion. Although RCl specimens stored at 30 °C show larger values of polarization resistance compared with the cases at 20 or 40 °C until about 160 days from the beginning of storage, a drop of polarization resistance is observed after this point. On the other hand, the value of RCl stored at 40 °C becomes larger than those of NCl specimens. In the cases of ROH specimens, the variation tendency of polarization resistance depends on storage temperature. The relationship between polarization resistance and concrete expansion rate is shown in Fig. 13. From this figure, it can be seen that polarization resistance increases in accordance with concrete expansion growing due to ASR until the expansion rate reaches about 0.1%. This tendency suggests that the formation of alkali silica gel due to ASR may suppress the corrosion rate of steel in concrete. In both 20 and 30 °C cases, the drop of polarization caused by the growing of concrete cracks can be observed in Fig. 13. However, when the storage temperature is 40 °C, the protection effect against steel corrosion may be maintained by cracks closing due to self-mitigation of concrete. According to Fig. 12, generally speaking, the concrete resistivity values become large with concrete expansion continuing due to ASR. These specimens do not show a reduction of concrete resistivity even when a drop of polarization resistance is observed. This may shows that the damage of cover concrete due to ASR is not so significant. 3.4. Migration of ions in concrete due to applying electrochemical treatment Distributions of Cl content in specimens just after completing treatment are shown in Fig. 14. The steel bar is located at the center (50 mm from the exposed surface) of each specimen. Although this technique is not intended for extracting Cl from concrete, Cl content around the steel bar is decreased by the electrochemical treatment compared with the non-treated case (N), because this technique is based on the same principle as that of desalination [14,15]. Since such a side effect is expected, this technique could be applied with positive effect on concrete structures deteriorated by the complex mechanism of chloride attack and ASR. There appears to be no significant difference between the chloride removal effect among some kinds of lithium salts but the rise in electrolyte temperature from 30 to 40 °C improves the desalination effect in the case of LiNO3. Distributions of R2O content in concrete specimens immediately after completing treatment are shown in Fig. 15. Amount of R2O was calculated by the following formula.
R2 O ¼ Na2 O þ 0:658K2 O ðkg=m3 Þ
ð1Þ
According to this formula, in the case of specimens treated with the electrolyte at 20 °C, a large amount of R2O accumulates around the steel bar in the concrete. It is considered that such an accumulation of alkali is caused by the electrophoresis of cations (Na+, K+) contained in the concrete toward the steel bar acting as the cathode. As with the case of Cl distribution, the rise in electrolyte temperature from 30 to 40 °C probably accelerates electrophoresis of Na+ and K+. Thus, it can be expected that the rise in temperature would result in a larger amount of R2O accumulation around the steel bar. However, in Fig. 15, the accumulated amount of R2O is reduced with a rise in the electrolyte temperature from 30 to 40 °C. Such a moderation of the alkali accumulation at the steel bar may be caused by a decrease of transference numbers of Na+ and K+ in concrete with migration of Li+ and lithium-based electrolyte solution. Transference number is defined as the percentage of electric charge carried by a certain kind of ion. When the total amount of electric charges is fixed, increase of electric charges carried by Li+ and lithium-based electrolyte solution means there is a decrease of electric charges carried by Na+ and K+. The authors reported similar results in a past paper [16]. Reduction of concentrated alkali at the steel bar would, in turn, mean a reduction of risk of ASR or ASRinduced expansion of concrete around the steel bar. Distributions of Li+ content in the concrete immediately after treatment are shown in Fig. 16. In this figure, it can be seen that Li+ content around the concrete surface increases with the electrochemical treatment. However, when the temperature of electrolyte is 30 °C, penetration depth of lithium is about 25 mm regardless of the kind of lithium salt. The authors already reported that it was difficult to drive a sufficient amount of Li+ into the concrete at the depth of the steel bar by the electrochemical treatment with the LiOH electrolyte solution at room temperature [9,10]. On the other hand, Fig. 16 shows that at 40C electrolyte of LiNO3 increases the amount and depth of lithium penetration compared with the
Fig. 15. Distributions of R2O content in concrete after treatment.
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
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Fig. 16. Distributions of lithium content in concrete after treatment.
case of 30 °C. The authors reported similar results from the experiment using Li2CO3 solution as the electrolyte. Further investigation is necessary to clarify the adequate conditions of the electrochemical treatment considering concrete expansion behavior after the treatment. 3.5. Concrete expansion after electrochemical treatment Variation curves of concrete expansion rate with time, which were measured in the longitudinal and the vertical direction in each concrete specimen (refer to Fig. 1), are shown in Fig. 17. Each curve is the average of measured data from three specimens treated under the same conditions. The horizontal axis of this figure expresses the total period after the end of curing. N is a non-treated case, whilst the others are treated cases with different kinds of electrolyte liquid. Non-treated specimens were moved to the natural environment for accelerating ASR immediately at the end of the curing period of 28 days and values of concrete expansion rate were measured regularly. Treated specimens were subjected to conditions for ASR acceleration after completion of electrochemical treatment, at which time expansion measurements started. Original lengths were measured before treatment began. In Fig. 17, it can be seen that although non-treated specimens, kept in the environment for ASR acceleration, show relatively large
expansion, all treated specimens show smaller expansion rates after treatment. Such a suppression of concrete expansion would be achieved by a large amount of Li+ contained in the concrete around the concrete’s surface, as shown in Fig. 16. When the electrolyte temperature is 40 °C with LiNO3, concrete expansion after treatment is less than the other treated cases using electrolyte at 30 °C. It can be considered that high temperature treatment increases the risk of accelerating concrete expansion during treatment, but it also has the effect of promoting lithium penetration that may serve to suppress concrete expansion after the treatment. As can be seen in Fig. 15, a large amount of alkali accumulated around the steel bar due to electrochemical treatment and such alkali could accelerate ASR-induced expansion of concrete. However, according to Fig. 17, concrete expansion rates are not promoted by the electrochemical treatment, compared with non-treated cases. It has been reported that excessive supply of electricity, exceeding the pessimum value, does not accelerate ASR-induced expansion of concrete [17]. In this study, amount of accumulated alkali around the steel bar due to treatment may exceed the pessimum value, and this may have resulted in relatively small ASR-induced expansion. From Fig. 17 (the lower one), expansion rates in the vertical direction are larger than those in the horizontal direction because concrete expansion in the vertical direction is not confined by the embedded steel bar. However, even in this case, Li2CO3 and LiNO3 show effective suppression of concrete expansion rate. From these results, the 40 °C electrolyte of LiNO3 would be most effective to use for the electrochemical method against ASR damage of concrete. 4. Conclusions This study conducted experimental investigations in order to grasp the complex deterioration mechanism due to chloride attack and ASR, and to confirm the effect of electrochemical remedial measures against it. The results obtained from this study can be summarized as follows. (1) Storage of specimens at 30 °C or 40 °C promoted concrete expansion due to ASR, while a protection effect against steel corrosion was observed. Possible reasons for this are closing of concrete cracks or formation of alkali silica gel around the steel. (2) Polarization resistance and concrete electric resistivity increased with progress of ASR until concrete cracks became dominant. (3) Rise in temperature of electrolyte solution from 30 to 40 °C remarkably accelerated the migration of Cl and Li+ in concrete due to applying electrochemical treatment. Regarding the kind of lithium salt, LiNO3 solution was most effective among some kinds of lithium salt contained in electrolyte solution from the viewpoint of lithium penetration. (4) Rise in temperature of electrolyte solution from 30 to 40 °C did not promote accumulation of Na+ and K+ around the steel bar in concrete. (5) Regardless of conditions of electrochemical treatment, concrete expansion rate after treatment was suppressed when compared with that of the non-treated cases. It was evident that the 40 °C electrolyte of LiNO3 would be more effective than other electrolytes used in this study to suppress the ASR expansion of concrete. References
Fig. 17. Variation of concrete expansion rate after treatment.
[1] Ueda T, Miyagawa T. Deterioration of concrete structures and some relevant issues. Corros Eng 2010;59:111–6.
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
T. Ueda et al. / Construction and Building Materials xxx (2013) xxx–xxx [2] Japan Society of Civil Engineers. Standard specifications for concrete structures. Maintenance 2007. [3] MacCoy WJ, Caldwell AG. New approach to inhibiting alkali–aggregate expansion. J ACI 1951;22:693–706. [4] Kawamura M, Ichise M. Characteristics of alkali–silica reaction in the presence of sodium and calcium chloride. Cem Concr Res 1990;20:757–66. [5] Diamond S, Ong S. The mechanism of lithium effects on ASR. In: Proceedings of the 9th international conference on alkali-aggregate reaction, 1992. p.269– 78. [6] Mo Xiangyin, Yu Chenjie, Xu Zhongzi. Long-term effectiveness and mechanism of LiOH in inhibiting alkali–silica reaction. Cem Concr Res 2003;33:115–9. [7] Collins CL, Ideker JH, Willis GS, Kurtis KE. Examination of the effects of LiOH, LiCl, and LiNO3 on alkali–silica reaction. Cem Concr Res 2004;34:1403–15. [8] Whitemore D, Abbott S. Use of an applied electric field to drive lithium ions into alkali-silica reactive structures. In: Proceedings of 11th international conference on alkali-aggregate reaction, 2000. p.1089–98. [9] Ueda T, Yoshida Y, Yamaguchi K, Ashida M. Effect of electrochemical penetration of lithium ions on ASR expansion of concrete. In: Proceedings of the 3rd international conference on engineering materials, 2005. [CD-ROM].
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[10] Ueda T, Yoshida Y, Yamaguchi K, Ashida M. Electrochemical migration of lithium ions into hardened concrete and ASR expansion after treatment. In: Proceedings of structural faults and repair, 2006. [CD-ROM]. [11] Sangadji S, Schlangen E. Self-healing of concrete structures–novel approach using porous network concrete. J Adv Concr Technol 2012;10:185–94. [12] Reinhardt HW, Jooss M. Permeability and self-healing of cracked concrete as a function of temperature and crack width. Cem Concr Res 2003;33:981–5. [13] Böhm M, Baetzner S. The effect of the alkalinity of the pore solution on ASR. In: Proceedings of the 13th international conference on alkali-aggregate reaction, 2013. [CD-ROM]. [14] Page CL. Application of electrochemical techniques for maintenance of corroding reinforced concrete structures. In: Proceedings of the 1st fib congress, 2002. p.147–58. [15] Hondel AJ, Polder RB. Electrochemical Realkalisation and chloride removal of concrete. Constr Repair 1992:19–24. [16] Ueda T, Baba Y, Nanasawa A. Effect of electrochemical penetration of lithium ions on concrete expansion due to ASR. J Adv Concr Technol 2011;9:31–9. [17] Page CL, Yu SW. Potential effects of electrochemical desalination of concrete on alkali–silica reaction. Mag Concr Res 1995;47:23–31.
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR Takao Ueda a,⇑, Junji Kushida a, Masayuki Tsukagoshi a, Akira Nanasawa b a b
Department of Civil Engineering, The University of Tokushima, Tokushima, Japan Omi Plant, Denki Kagaku Kogyo Co., Ltd., Niigata, Japan
h i g h l i g h t s Complex deterioration of chloride attack and ASR was affected by temperature. Rise in electrolyte temperature from 30 to 40 °C improved penetration of lithium. 40 °C electrolyte of LiNO3 was most effective to suppress expansion due to ASR.
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Complex deterioration Chloride attack ASR Lithium salts Electrochemical method
a b s t r a c t Complex deterioration mechanism due to both chloride attack and ASR are greatly affected by environmental temperature. In this study, the influence of environmental temperature on concrete expansion and steel corrosion was experimentally investigated. As a result, some protection effect against steel corrosion was found in the cases of storage at 30 °C or 40 °C, although ASR expansion was promoted. This would be caused by the formation of alkali silica gel around the steel. As a remedial measure against such a complex deterioration, electrochemical penetration of lithium from the electrolyte solution was also investigated. It was clarified that electrolyte temperature greatly affected the extent of lithium penetration and the treatment at 40 °C remarkably accelerated lithium penetration into concrete compared with the case of 30 °C. Regarding the kind of lithium salt, LiNO3 solution was most effective among a number of different kinds of lithium salt. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Both chloride attack and ASR are serious deterioration mechanisms of concrete structures which play an important role as infrastructure [1]. Moreover, in such cases as the marine environment and areas with a cold climate, complex deterioration of these mechanisms can be observed because of the supply of sea water or de-icing salts. A complex deterioration mechanism due to both chloride attack and ASR has not yet been clarified. Obviously, it would be greatly affected by environmental temperature. Moreover, past research suggests that alkali silica gel formed around steel in concrete due to ASR may have a protection effect against steel corrosion [2]. In this study, the influence of environmental temperature on concrete expansion and steel corrosion was experimentally investigated in order to make an adequate decision on the strategy of remedial measures considering the environmental situations of structures. Using reinforced concrete specimens, ⇑ Corresponding author. Address: 2-1 Minami-josanjima cho, Tokushima 770-8506, Japan. Tel.: +81 88 656 2153; fax: +81 88 656 7351. E-mail address: [email protected] (T. Ueda).
concrete expansion and electrochemical steel corrosion indexes, namely, half-cell potential, polarization resistance and electric resistivity of concrete were measured regularly during the saving period in each temperature condition. As a remedial measure against such complex deterioration, in this study we tried electrochemical penetration of lithium from electrolyte solution. It has been confirmed by many researchers that lithium salts act to suppress ASR-induced expansion of concrete [3,4]. Assuming the application of the lithium salts as a repair additive for concrete structures deteriorated by ASR, sufficient amounts of Li+ must be driven into the ASR-affected concrete [5]. Past researches have shown that Li/Na molar ratio should be around 1.0 or more in order to suppress concrete expansion [6,7]. Thus, an electrochemical technique to accelerate the penetration of the lithium ions (Li+) in a lithium-based electrolyte solution into concrete has been employed for the purpose of suppressing ASR-induced expansion due to Li+ [8]. However, from the results of past research works, the penetration area of Li+ is limited around the concrete surface and it is difficult to make Li+ penetrate into the deeper into concrete [9,10]. In this study, the complex deterioration mechanism by the combination of ASR and chloride attack, in particular the influence
0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
2
T. Ueda et al. / Construction and Building Materials xxx (2013) xxx–xxx
of environmental temperature, was experimentally investigated. As a remedial measure, electrochemical treatment was also conducted aiming to grasp the influence of different kinds of lithium salts and temperature of the electrolyte solution on migration properties of ions in concrete and ASR-induced expansion of concrete. 2. Experimental program
Fig. 1. Outline of an RC specimen.
2.1. Materials Mixture proportions of concrete used in this study are shown in Table 1. Water to cement ratio (W/C) of concrete was 0.55 for all mixture proportions. Concrete named NCl is assumed to be deteriorated by chloride attack solely. This concrete contained only non-reactive aggregate and sodium chloride (NaCl) was added to adjust the amount of alkali. Concrete named RCl is assumed to be damaged by the complex deterioration. This concrete contained reactive aggregate and NaCl was added as the source of alkali. Concrete named ROH is assumed to be damaged by ASR solely. This concrete contained reactive aggregate and NaOH was mixed to adjust the amount of alkali in the concrete. In order to adjust the total alkali contents as R2O = 10.0 kg/m3 for acceleration of deterioration, a corresponding amount of NaCl or NaOH was dissolved in the mixing water. All specimens subjected to electrochemical treatment were made of RCl concrete. Ordinary portland cement (density: 3.16 g/cm3, specific surface area: 3280 cm2/g, R2O: 0.56%) was used. As the fine aggregate, non-reactive fine aggregate (S1, density: 2.56 g/cm3) and reactive aggregate (S2, density: 2.60 g/cm3) were mixed at a pessimum weight ratio of 3:7, so as to maximize expansion of concrete. As the coarse aggregate, non-reactive aggregate (G1, density: 2.55 g/cm3, Gmax: 15 mm) and reactive aggregate (G2, density: 2.68 g/cm3, Gmax: 15 mm) were also mixed at a pessimum weight ratio of 3:7. 2.2. Preparation of specimens and electrochemical treatment Specimens prepared in this study were 100 100 300 mm reinforced concrete prisms with a steel bar u13 SR235 (JIS number) at the center of the square section as shown in Fig. 1. All specimens were cured in a wet (100% RH) and 20 °C condition. The number of specimens for each factor was three. In the case of specimens used for investigation of complex deterioration mechanism, brass chips were attached to concrete surfaces for the measurement of concrete expansion after curing of 14 days. These specimens were kept in a moist condition and temperature levels were 20, 30 or 40 °C. In the case of specimens to be subjected to electrochemical treatment, brass chips were attached after curing of 28 days, as shown in Fig. 1, and five concrete faces of each specimen were insulated with epoxy resin coating, leaving one exposed surface. Epoxy resin was spread on the concrete surface twice with a brush. After the epoxy coating, each specimen was immersed into electrolyte liquid in a plastic container, and direct electric current was supplied between rectangular shaped titanium mesh as the anode and the steel bar in concrete as the cathode. A current density, of 1.0 A/m2 to the exposed concrete area was adopted. The treatment period was 8 weeks. Different kinds of electrolyte liquid and their temperature conditions are shown in Table 2. The standard temperature level of electrolyte liquid was 30 °C so as to accelerate the lithium penetration except for the case of 40 °C of LiNO3 solution. 2.3. Tests of specimens Specimens used for investigating complex deterioration mechanism were kept at a wet and constant temperature (20, 30 or 40 °C) environment and expansion rate of concrete was measured regularly by means of a contact gauge. While measuring concrete expansion, half-cell potential, polarization resistance of steel in specimens and resistivity of concrete were also measured regularly using the electrochemical monitoring system for steel corrosion in concrete. As a reference electrode for this electrochemical monitoring, saturated silver chloride (Ag/AgCl) was used. Polarization resistance was measured by the rectangular wave electric current polarization method, as the difference of impedances at 800 Hz and 0.1 Hz of electric current frequency. Resistivity was obtained as the impedance at 800 Hz of electric current frequency.
Table 2 List of electrolyte. Name of salt
Content of salt (%)
content of Li (%)
Temperature (°C)
LiOH Li2CO3 Li2SiO4 LiNO3
10 1.2 23 30
3.0 0.22 2.9 3.0
Ca(OH)2
0.2
0
30 30 30 30 40 30
After completion of electrochemical treatment, distribution profiles of ion content (Cl, Na+, K+, Li+) in the concrete specimens were measured using powder samples grinded from samples cut out as seven concrete plates in a specimen, as shown in Fig. 2. The Na+, K+ and Li+ contents were measured by means of atomic absorption spectrometry using a crashed fine powder sample dissolved in HNO3 solution. Cl content was measured according to JIS A 1154 applying potentiometric titration with AgNO3. Variation of concrete expansion rate with time after the treatment was also measured regularly by means of a contact gauge.
3. Results and discussion 3.1. Observation of concrete cracks after storage for about one year Typical examples of concrete cracks observed after storage for about one year under a constant temperature are shown in Figs. 3–8. Each photo shows a zoom of the concrete part between brass chips for measuring concrete expansion rate. Here, it can be seen that NCl specimens showed no cracking regardless of storage temperature. Since the cover depth of concrete is relatively high, sole chloride-induced corrosion would not cause concrete cracking during storage for about one year. On the other hand, all specimens containing reactive aggregates show concrete cracks as shown in Figs. 3–8. Cracking shape is much affected by the kind of alkali. ROH specimens cause mapshaped cracking, while RCl specimens show mainly longitudinal cracks along the steel bar. These longitudinal cracks may be caused by the influence of steel corrosion combined with the cracks due to ASR. In the case of 20 °C storage, the RCl specimen is stained by steel rust with fine cracks, while the ROH specimen has relatively bold net shaped cracks. In the case of 30 °C storage, crack width appears to be widest compared with cases of 20 and 40 °C storage. The condition of 40 °C storage would most intensively accelerate the ASR expansion and steel corrosion but this storage condition (moist and high temperature) also accelerates cement hydration, which could result in refilling of concrete cracks during long term storage [11,12].
Table 1 Mixture proportions of concrete. Name
W/C (%)
s/a (%)
NCl RCl ROH
55 55 55
48 48 48
Content (kg/m3) C
W
S1
S2
G1
G2
NaCl
NaOH
338 338 338
186 186 186
832 250 250
– 591 591
871 261 261
– 641 641
15.1 15.1 –
– – 10.3
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
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Fig. 6. Concrete cracking observed in ROH specimen stored at 20 °C.
Fig. 2. Cutting way of a specimen for chemical analysis.
Fig. 7. Concrete cracking observed in ROH specimen stored at 30 °C.
Fig. 3. Concrete cracking observed in RCl specimen stored at 20 °C.
Fig. 8. Concrete cracking observed in ROH specimen stored at 40 °C.
Fig. 4. Concrete cracking observed in RCl specimen stored at 30 °C.
concrete followed by the environmental temperature. From this figure, ROH40 shows the earliest initiation of concrete expansion because of higher alkalinity in the pore solution [13] by dosage of NaOH and a higher temperature. The next initiation of concrete expansion occurs with specimens of RCl40 and ROH30. RCl30 shows about 100 days delay of initiation from other early expansion specimens. However, when one year passed from the
Fig. 5. Concrete cracking observed in RCl specimen stored at 40 °C.
3.2. Variation of expansion rate of concrete Regarding specimens kept at 20, 30 or 40 °C after curing, variation curves of concrete expansion rate with time are shown in Fig. 9. The horizontal axis of this figure expresses the period after the end of curing. Legends used in this figure show the name of
Fig. 9. Variation of concrete expansion rate after curing.
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
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T. Ueda et al. / Construction and Building Materials xxx (2013) xxx–xxx
beginning of storage, RCl30 shows the largest expansion rate with the widest concrete cracking along the steel bar as shown in Fig. 4. From these results, it is evident that slow concrete expansion cases could result in long term progressing of expansion and larger expansion rate. 3.3. Monitoring of steel corrosion in concrete Variation curves of half-cell potential and polarization resistance of steel in specimens during the storage period for each temperature condition are shown in Figs. 10 and 11 respectively. Standard lines used to judge steel corrosion probability as specified in ASTM C876-91 are also indicated in Fig. 10. Moreover, variation curves of electric resistivity of cover concrete in concrete specimens are shown in Fig. 12. According to Fig. 10, NCl and RCl specimens generally show base values of half-cell potential with a high dosage of NaCl into the concrete. These specimens initially contained Cl of 9.1 kg/m3 which is much higher than the threshold Cl content necessary to initiate steel corrosion. On the other hand, ROH specimens keep relatively nobler potential values because they did not contain the pre-mixed NaCl. Especially, when the storage temperature is 30 or 40 °C, the half-cell potential values of ROH specimens gradually increase with time regardless of growing concrete expansion due to ASR as shown in Fig. 3. This result may be due to the possibility that there is a closing of concrete cracks due to the self-mitigation mechanism caused by cement hydration [11,12] or by steel protection due to the formation of alkali silica gel around the steel bar [2]. In the case of 20 °C storage, the half-cell potential values tend to decrease gradually with progress of ASR. As shown Fig. 11, in the cases of NCl and RCl specimens, values of polarization resistance remain small during the entire period of storage because of the high dosage of NaCl in the concrete. Such a
Fig. 10. Variation of half-cell potential.
Fig. 11. Variation of polarization resistance.
Fig. 12. Variation of concrete resistance.
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
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Fig. 14. Distributions of chloride content in concrete after treatment. Fig. 13. Relationship between polarization resistance and concrete expansion rate.
small polarization resistance means a high rate of steel corrosion. Although RCl specimens stored at 30 °C show larger values of polarization resistance compared with the cases at 20 or 40 °C until about 160 days from the beginning of storage, a drop of polarization resistance is observed after this point. On the other hand, the value of RCl stored at 40 °C becomes larger than those of NCl specimens. In the cases of ROH specimens, the variation tendency of polarization resistance depends on storage temperature. The relationship between polarization resistance and concrete expansion rate is shown in Fig. 13. From this figure, it can be seen that polarization resistance increases in accordance with concrete expansion growing due to ASR until the expansion rate reaches about 0.1%. This tendency suggests that the formation of alkali silica gel due to ASR may suppress the corrosion rate of steel in concrete. In both 20 and 30 °C cases, the drop of polarization caused by the growing of concrete cracks can be observed in Fig. 13. However, when the storage temperature is 40 °C, the protection effect against steel corrosion may be maintained by cracks closing due to self-mitigation of concrete. According to Fig. 12, generally speaking, the concrete resistivity values become large with concrete expansion continuing due to ASR. These specimens do not show a reduction of concrete resistivity even when a drop of polarization resistance is observed. This may shows that the damage of cover concrete due to ASR is not so significant. 3.4. Migration of ions in concrete due to applying electrochemical treatment Distributions of Cl content in specimens just after completing treatment are shown in Fig. 14. The steel bar is located at the center (50 mm from the exposed surface) of each specimen. Although this technique is not intended for extracting Cl from concrete, Cl content around the steel bar is decreased by the electrochemical treatment compared with the non-treated case (N), because this technique is based on the same principle as that of desalination [14,15]. Since such a side effect is expected, this technique could be applied with positive effect on concrete structures deteriorated by the complex mechanism of chloride attack and ASR. There appears to be no significant difference between the chloride removal effect among some kinds of lithium salts but the rise in electrolyte temperature from 30 to 40 °C improves the desalination effect in the case of LiNO3. Distributions of R2O content in concrete specimens immediately after completing treatment are shown in Fig. 15. Amount of R2O was calculated by the following formula.
R2 O ¼ Na2 O þ 0:658K2 O ðkg=m3 Þ
ð1Þ
According to this formula, in the case of specimens treated with the electrolyte at 20 °C, a large amount of R2O accumulates around the steel bar in the concrete. It is considered that such an accumulation of alkali is caused by the electrophoresis of cations (Na+, K+) contained in the concrete toward the steel bar acting as the cathode. As with the case of Cl distribution, the rise in electrolyte temperature from 30 to 40 °C probably accelerates electrophoresis of Na+ and K+. Thus, it can be expected that the rise in temperature would result in a larger amount of R2O accumulation around the steel bar. However, in Fig. 15, the accumulated amount of R2O is reduced with a rise in the electrolyte temperature from 30 to 40 °C. Such a moderation of the alkali accumulation at the steel bar may be caused by a decrease of transference numbers of Na+ and K+ in concrete with migration of Li+ and lithium-based electrolyte solution. Transference number is defined as the percentage of electric charge carried by a certain kind of ion. When the total amount of electric charges is fixed, increase of electric charges carried by Li+ and lithium-based electrolyte solution means there is a decrease of electric charges carried by Na+ and K+. The authors reported similar results in a past paper [16]. Reduction of concentrated alkali at the steel bar would, in turn, mean a reduction of risk of ASR or ASRinduced expansion of concrete around the steel bar. Distributions of Li+ content in the concrete immediately after treatment are shown in Fig. 16. In this figure, it can be seen that Li+ content around the concrete surface increases with the electrochemical treatment. However, when the temperature of electrolyte is 30 °C, penetration depth of lithium is about 25 mm regardless of the kind of lithium salt. The authors already reported that it was difficult to drive a sufficient amount of Li+ into the concrete at the depth of the steel bar by the electrochemical treatment with the LiOH electrolyte solution at room temperature [9,10]. On the other hand, Fig. 16 shows that at 40C electrolyte of LiNO3 increases the amount and depth of lithium penetration compared with the
Fig. 15. Distributions of R2O content in concrete after treatment.
Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020
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Fig. 16. Distributions of lithium content in concrete after treatment.
case of 30 °C. The authors reported similar results from the experiment using Li2CO3 solution as the electrolyte. Further investigation is necessary to clarify the adequate conditions of the electrochemical treatment considering concrete expansion behavior after the treatment. 3.5. Concrete expansion after electrochemical treatment Variation curves of concrete expansion rate with time, which were measured in the longitudinal and the vertical direction in each concrete specimen (refer to Fig. 1), are shown in Fig. 17. Each curve is the average of measured data from three specimens treated under the same conditions. The horizontal axis of this figure expresses the total period after the end of curing. N is a non-treated case, whilst the others are treated cases with different kinds of electrolyte liquid. Non-treated specimens were moved to the natural environment for accelerating ASR immediately at the end of the curing period of 28 days and values of concrete expansion rate were measured regularly. Treated specimens were subjected to conditions for ASR acceleration after completion of electrochemical treatment, at which time expansion measurements started. Original lengths were measured before treatment began. In Fig. 17, it can be seen that although non-treated specimens, kept in the environment for ASR acceleration, show relatively large
expansion, all treated specimens show smaller expansion rates after treatment. Such a suppression of concrete expansion would be achieved by a large amount of Li+ contained in the concrete around the concrete’s surface, as shown in Fig. 16. When the electrolyte temperature is 40 °C with LiNO3, concrete expansion after treatment is less than the other treated cases using electrolyte at 30 °C. It can be considered that high temperature treatment increases the risk of accelerating concrete expansion during treatment, but it also has the effect of promoting lithium penetration that may serve to suppress concrete expansion after the treatment. As can be seen in Fig. 15, a large amount of alkali accumulated around the steel bar due to electrochemical treatment and such alkali could accelerate ASR-induced expansion of concrete. However, according to Fig. 17, concrete expansion rates are not promoted by the electrochemical treatment, compared with non-treated cases. It has been reported that excessive supply of electricity, exceeding the pessimum value, does not accelerate ASR-induced expansion of concrete [17]. In this study, amount of accumulated alkali around the steel bar due to treatment may exceed the pessimum value, and this may have resulted in relatively small ASR-induced expansion. From Fig. 17 (the lower one), expansion rates in the vertical direction are larger than those in the horizontal direction because concrete expansion in the vertical direction is not confined by the embedded steel bar. However, even in this case, Li2CO3 and LiNO3 show effective suppression of concrete expansion rate. From these results, the 40 °C electrolyte of LiNO3 would be most effective to use for the electrochemical method against ASR damage of concrete. 4. Conclusions This study conducted experimental investigations in order to grasp the complex deterioration mechanism due to chloride attack and ASR, and to confirm the effect of electrochemical remedial measures against it. The results obtained from this study can be summarized as follows. (1) Storage of specimens at 30 °C or 40 °C promoted concrete expansion due to ASR, while a protection effect against steel corrosion was observed. Possible reasons for this are closing of concrete cracks or formation of alkali silica gel around the steel. (2) Polarization resistance and concrete electric resistivity increased with progress of ASR until concrete cracks became dominant. (3) Rise in temperature of electrolyte solution from 30 to 40 °C remarkably accelerated the migration of Cl and Li+ in concrete due to applying electrochemical treatment. Regarding the kind of lithium salt, LiNO3 solution was most effective among some kinds of lithium salt contained in electrolyte solution from the viewpoint of lithium penetration. (4) Rise in temperature of electrolyte solution from 30 to 40 °C did not promote accumulation of Na+ and K+ around the steel bar in concrete. (5) Regardless of conditions of electrochemical treatment, concrete expansion rate after treatment was suppressed when compared with that of the non-treated cases. It was evident that the 40 °C electrolyte of LiNO3 would be more effective than other electrolytes used in this study to suppress the ASR expansion of concrete. References
Fig. 17. Variation of concrete expansion rate after treatment.
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Please cite this article in press as: Ueda T et al. Influence of temperature on electrochemical remedial measures and complex deterioration due to chloride attack and ASR. Constr Build Mater (2013), http://dx.doi.org/10.1016/j.conbuildmat.2013.10.020