CONCRETE LIBRARY OF JSCE NO. 36, DECEMBER 2000 AN EXPERIMENTAL STUDY ON IMPROVEMENT AND REPAIR EFFECTS USING ELECTROCHEMICAL (Translation from Proceedings of JSCE, No.641/V-4§ OF CONCRETE METHODS february 2000 ) ^à"\ "à"f Yukio II KITAGO, Masanobu ASHIDA, Norihiro KIKUTA, Toyoaki MIYAGAWA An experimental study was carried out to find the threshold value of the chloride ionto hydroxy ion ratio ([Cf]/ [OH]: mol ratio) fortheonset of reinforcing steel corrosion in concrete. After application of an electrochemical concrete improvement method (desalination and realkalizaton) to specimens, a five-year follow-up survey was made to check the effectiveness of the rehabilitation method. The results of tests showed that reinforcing steel did not corrode when pH value was 12 or higher and Cl'/OH" ratio was 1 or lower. Rehabilitation using the desalination and realkalizatiou method increased pH value to between 12.6 and 13.2 and reduced water-soluble chloride content to 0.47 to 0.56 kg/m around reinforcing bars in concrete of existing structures. Almost no rediffusion of chloride ions into concrete around reinforcing bars was detected in the five-year follow-up survey, and the presence of clear shadow spots behind the reinforcement was not noted. Key Words: desalination, corrosion realkalization of reinforcing steel, Yukio Kitago is a director of Civil Engineering design research interests relate to the technology of rehabilitating JSCE. threshold of [Cl]/[OH], repair, in the JR West Japan Consultants Company. His concrete structures. He is a member of the JCI and Masanobu Ashida is a manager in the technical division of the Special Cement Additives Department at Denki Kagaku Kogyo Kabushiki Kaisha Co., Ltd., Japan. He received his doctorate in engineering from Kyoto University in 2000. His research interests relate to the technology of rehabilitating concrete structures. He is a memberof the JSMS, JCI and JSCE. Norihiro Kikuta is a manager in the department of structual maintenance at the West Japan Railway Company. He inspects concrete structures of SANYO SHINKANSEN in Hiroshima district. He is a member of the JCI and JSCE. Toyo Miyagawa is a professor in the Department of Civil Engineering, Kyoto University, Kyoto, Japan. He received his doctorate in engineering from Kyoto University in 1985. He is the author of a number of papers dealing with the durability, maintenance and repair of reinforced concrete structures. He is a member of the ACI, RILEM, CEB, JSMS, JCI and JSCE. -227- 1. INTRODUCTION Concrete is known as a material of excellent durability. Not a few concrete structures have been in service for long periods and even now remain in satisfactory functional condition. However, it is also a fact that certain structures have deteriorated for various reasons, and concrete, which had been thought of as a maintenance-free material, was found actually not to be so.In fact, durability cannot be attained unless proper maintenance is carried out, and in a sense, what should have been obvious is only now beginning to be recognized. Many of the changes seen in railway structures, of which rigid-frame viaducts are representative, are caused by corrosion of reinforcing steel. Where such deteriorated structures are located in normal environments, they are often treated by the " lining method", which entails giving a surface coating to the concrete. Results of previous investigationsC |) C 3 suggest that the causes of reinforcing bar corrosion are chlorides and carbonation due to inadequate chloride removal from fine aggregate, particularly the latter. The actual situation is that, in application of the lining method, there were many places where the chloride content of concrete had not been measured, and that when chloride content was high, repairs by lining and similar methods were not necessarily done after having removed the chloride. Recognizing that there are limits to the durability of lining materials themselves, a method that improves the quality of concrete itself through realkalization (after desalination) by an electrochemical method has been tried in recent years as a radical alternative to the lining method. In this case, it is necessary-to clearly determine the chloride content and the alkaline environment after desalination and realkalizaton, which will ensure that subsequent reinforcing bar corrosion will not occur. However, it has not necessarily been made clear what influences chlorides and carbonation, respectively, have on reinforcing bar corrosion. In this possibility hydroxy quality desalination follow-up study, an attempt is made at the laboratory level to quantify the reinforcing bar corrosion in concrete with the chloride ion to ion ratio ([C1"J/[OH"]) as a parameter. The way in which the of concrete in an actual structure was improved through and realkalizaton are also discussed. The results of a survey made over aperiod offive yearsare reported. of 2. INFLUENCE ON REINFORCING OF CHLORIDE ION-HYDROXY STEEL CORROSION The results of a previous surveyC3) normal environment, when carbonation far as reinforcing steel, noprominentcorrosion in agreement with the thinking that, ions (Cl~), the presence of hydroxy ions accelerates the formation of a passive thus repairing any passive film, which words, whether or not reinforcing steel influenced by the [C1"]/[OH"] ratio hydroxy ion concentration in the steel's should exist. The results of past studiesare ION RATIO (rcn/fOH'1) suggest that, with a structure in a of concrete has not progressed as of the steel is seen. This is even though there may be chloride (OH) above certain concentration film on the reinforcing bar surface, may have been broken. In other corrosion occurs should be greatly of chloride ion concentration to environment. Also threshold value given in Table 1. 225 Table 1 Threshold pH values E x p e rim e n ta l c o n d itio n s H au sm am i l l .6 1 2 .4 1 3 .2 0 .5 0 .6 1 0 .8 3 S t e e l in a lk a li n e s o lu tio n G ou d a & D iam o n d l l .8 12 .1 1 2 .6 1 3 .0 1 3 .3 0 .5 7 0 .4 8 0 .2 9 0 .2 7 0 .3 0 S te e l in a lk a lin e s o lu tio n P ag e 1 3 .9 1 0 .5 4 S te e l in c em 62 cS ot ne te a li n i ni ng HP aagv ed a&h l Y o ii e z a w a , V .A s h w o rt h ,R .P .M . P ro c te r S .E . H u s s a i n et al. (l)Threshold [C1']/[OH'] [c r /O H ] Value L 1 M 1 for ess 3 .3 o re 3 .3 th a n th a n was considered as being measurement. Hausmann's of [CT]/[OH'] with pH increase, it is approximately 3 0c %e m s ei lni ct a fp u am s et e 5 S te e l in c e m e n t m o rta r 1 .1 2 .0 1 .2 8 1 .8 6 S t e e l in c e m e n t m o r ta r Reinforcing Hausmann's value of [C1"]/[OH"] for reinforcing steel corrosion that when pHvalueswere ll.6, [C1"]/[OH'] values were 0.5, e n t p a st e Steel Corrosion 0 0.6CO is in an alkaline 12.4,and 13.2, 0.61, and 0.83, in Alkaline well known solution. corrosionwould respectively. Solution as the threshold Hausmann found not occurif The 0.83 value of poor reliability because of difficulties met in conclusion was that although the threshold value in the range of ll.6 to 12.4 shows a trend of 0.6. Gouda studied alkaline solutions with pH values from ll.75 to more than 135 C5}. Diamond modified Gouda's results using the activity coefficient of NaOH to estimate hydroxy ion concentration from pH value. A check of the results reveals that the threshold [C1"]/[OH] value decreases as pH value increases. In a range of pH ll.8 to 12.1, there is good agreement with Hausmann's value of 0.60. Further, HausmannC0 holds that these values are influenced by the amount of oxygen supply. He reports that, consequently, the threshold value increases if the concrete is fully saturated with water. (2) Threshold Value for Reinforcing Steel Corrosion in Cement Paste Page et al.C7} C8} , in tests using reinforcing bars embedded in cement paste, foundthatwhenthepHvalue of pore waterand [Cl]/[OH] are 13.91 and 0.54, respectively,the steel is inactive. Thisvalue of0.54 at a pHof 13.91 is more than double the [C1"]/[OK] = 0.23,the value estimated from Gouda' s results. Therefore, in case of steel embedded in cement paste, [C1"]/[OH~] as the threshold value is thought to be a value far higher than that in an alkaline solution. Page et al.CS} found that steel embedded in hardened cementpasteisinactiveup to a [CI]/[OH] valueof62. (3) In Threshold cement Value mortar, for the Reinforcing conditions Steel are -229- still Corrosion more in lenient, Cement and Mortar YonezawaC 9 et al. obtained a threshold on the characteristics of adherence between steelbar steel a) Filter paper embedded b) bar Steel Yonezawa steel bars compared of separating embedded [CT]/[OH"]i bar corrosion and mortar, a) directly in found that the threshold embedded in cement withthat in an alkaline steel approx. for and b) bar 5. They two different as defined also reported states of below. and mortar mortar value mortar solution. of [CI]/[OH] under both was far adherence higher for conditions The reportby S.E. Hussaineta1.C10) concerns corrosion of steel inmortar with a water-cement ratio of 0.55. Although hydroxy ion concentrations were varied in the comparatively narrow range of pH 13.26 to 13.36, the threshold value of [C1"]/[OH"] decreased with increasing hydroxy ion concentration. For example, at hydroxy ion concentrations of pH 13.30 and under, the threshold values of [CT]/[OH] were in a range of 1.7 to 2.0, while at hydroxy ion concentrations above pH 13.30,the threshold values of [Cr]/[OH'] were in arange of1.28to 1.86. (4) Threshold Value for Reinforcing Steel Corrosion in Concrete With regard to the above reports, Glass and BuenfeldC11} studied the proposed [C1"]/[OH'] threshold value and chloride threshold value based on published data. The objects of examination were reinforced concrete structures; concrete specimens exposed to an outdoor environment; concrete, mortar, and cement paste specimens in a laboratory environment; and simulatedpore water. The study also included parts of(1) to (3) above. A summary of the examination results follows. à" Regarding the method of defining threshold value as the ratio chloride content or water-soluble chloride content to hydroxy concentration, the effectiveness of such a definition cannot be verified the data available. à" Initial oxidation at the anode increases local activity of chlorides accelerate the release of bound chlorides. à" Even though chlorides are bound, there exists a risk of corrosion occurring. à" The most important corrosion-prevention property of cement is that restrictingpHvalue from declining locally to below 12.6. à"Regarding the threshold value for steel corrosion in concrete, it is best to indicate the total chloride content byweight of cement. The maximum and minimum compiled in Table 2. Threshold by weight of cement. Table 2 Threshold values threshold values for values for are given concrete as total of steel in concrete corrosion T h r e s h o l d v a lu e s o f t o t a l c h lo r id e io n s f o r st e e l c o r r o s i o n ( C l 'w t % C e m ) C o n c re te s tru c tu re 0 .1 7 2 .2 (4 ) C o n c r e te s p e c im e n (o u t d o o r e x p o s u re ) 0 .3 2 - 1 .9 (4 ) ( lCa ob on rc ar te ot er y )s p e c i m e n 0 .5 ( l aM b o r at at or r y s)p e c i m e n 0 .2 5 ^ Figures in ( ) indicate -230- 2 .5 1 .6 numbers (4 ) (2 ) of references and chloride of by to of mortar are content and mortar 3. EXPERIMENTS REINFORCING STEEL ON THRESHOLD CORROSION IN Experiments were conducted steel in cement mortar. (1) Experimental [Cr]/[OH'] CEMENT MORTAR on threshold [Cl]/[OH a) Materials Reinforcing steel: steel form polished bars (0 results oftension tests 0.14%, ] values for Si = bars for reinforcement 13 mm x 100mm). of the original bars 0.18%, Mn = 0.49%, P =0.017%, and of [Cl]/[OH] reinforcing S were of the [C1']/[OH"], kinds two Table was JIS proportions indicated ofeachkindbeing 3 Varieties pH 1 2 .0 [c iy o JT ] 0 2 .0 standard percubic 1 2 .5 0 .1 3 .0 = 0.011%, 1 3 .5 1 .0 7 .5 yieldpoint= = 29% strength of forpH 10 3, with made. molecularweight ofmortaris 251 can be determined 10cm, with of cover 19 using epoxy was zero. 1. 4 levels of pH ratio ofO.50.The and le v e l s a water-cement given in Table 4. of mortar 5 0 2 k g /m 1 5 0 7 k g /m 3 2 5 1 k g /m J = 13.0 and [C1']/[OH'] 1.0 from pH = 13.0, = 1.0, [CT] of chlorine), and since the kg, the quantity of chloride by the followingequation: water ions = as 3.16 The pH values were set up by adjusting the amount water. However, apH of12.0 was considered to mean solution, and noadjustment with NaOH was node. Forexample, and [Cr]/[OHT] cement" 4 l e v e ls 1 .5 10 mortar with meter are Table 4 Mixture proportions W a te r Table to and of specimens 1 3 .0 0 .5 5 .0 O rd in a ry p o rtla n d c e m e n t S ta n d a rd sa n d in placed in the were shaved composition b) Specimens Cylindrical mortar specimens of diameter 5 cm, height reinforcing bars embedded at centers were made with thickness mm. The bars were bonded to the bottom surfaces of molds resin before casting the mortar. Cover at the ends of specimens The appearance and dimensionsofaspecimen are shownin Fig. Mortar mixture reinforcing values, bars (JIS G 3112) The chemical are as follows: 330 N/mm2, tensile strength = 472 N/mrn , elongation Sand: standard sand ("standard sand for testing specified in JIS R 5201), specific gravity: 2.64 Cement: ordinary portland cement, specific gravity: Alkali: sodium hydroxide Chloride: commercial table salt, NaCl: 99% Specimens 10 levelsof FOR Method Mortar specimens were made withvarying pH in a desiccator, and whether or not corrosion specimens had occurred was investigated. C= VALUES since =0.1mol/l of NaOH a saturated [OH'] content ofa used in the = in = 0.1 3.55g/l mixing calcium mol/1 (V cubic meter experiments 231 3.55(g/1) The X 251 (1/m3)=891 (g/m') amounts of chloride ionsused in the experiments are given in Table Table 5 [Cl-]/[OH-] when placing mortar, total chlorides in mortar [g/m3], and percentage of total chlorides by weight ofcement [wt%] 5 pH C l 7o H 13 .5 1 3 .0 1 2 .5 1 2 .0 0 0 (0 ) 0 (0 ) 0 (0 ) 0 (0 ) 0 .1 2 8 5 .1 (0 .0 5 7 ) 8 9 .1 (0 .0 1 8 ) 2 6 .7 (0 .0 0 5 ) 8 .9 (0 .0 0 2 ) 0 .5 1 4 2 5 .7 (0 .2 8 4 ) 4 4 5 .5 (0 .0 8 9 ) 1 3 3 .7 (0 .0 2 7 ) 4 4 .5 (0 .0 0 9 ) 1 2 8 5 1 .4 (0 .5 6 8 ) 8 9 1 .0 [0 .1 7 7 ) 2 6 7 .3 (0 .0 5 3 ) 8 9 .0 (0 .0 1 8 ) 1 .5 4 2 .8 (0 7;: 4 0 1 .0 (0 .0 8 0 ) 1 3 3 .5 (0 .0 2 7 ) 2 5 7 0 2 .8 (1 .1 3 6 ) 1 7 8 2 .0 (0 .3 5 5 ) 5 3 4 .6 (0 . 1 0 6 ) 3 8 5 5 4 .2 (1 .7 0 4 ) 2 6 7 3 .0 (0 .5 3 2 ) 8 0 1 .9 (0 .1 6 0 ) 5 7 .5 10 'ォサ サ I II II m m Figures in ( ) indicate percentages of total chlorides Shaded portions indicate corroded parts. c) Environmental The experimental Figs. 2.1 to 2.3. Conditions apparatus for by weight of cement (wt%). accelerating G a s m ix tu re corrosion of steel is shown in L a b o r ato ry N28oVJ0xiia i%ty UgrllA oe ngU Ue Cn S tpep alym su I^ I o f B ud bi sbt il lle i n gc I r > ォ ^ :ォ ォ ^ . W jM H U U M j w ate r D is ti ll e d w a t e r h e a t e d w it h chw o antttearia nnireo rt f(inrho omct o an irtoa uca t) tns di d ed i's tgillle a si D e s ic c a to r (sp e c im e n ) ftn ^a Bm H a I L^ 0 ::: J .- .T S F ig . 2 .1 O u t l in e 232 Gas m ixture lind f I " ¥ I 0 I'wDbgai.sbttbe!irliniegd Gas exhaust 0«siccator Fig.2,2 Schematic of experimental apparatus spediman In order to'prevent progress of carbonation, a gas mixture of 20% oxygen and 80% nitrogen (free of c a r b o n dioxide) was passed through distilled water and conducted into the desiccator in which specimens w e r e r e s t i n g . The specimens in the desiccator w e r e in a moist but not dripping condition. Temperature and humidity were measured using an automatic temperature-humidity recorder. Testing w a s performed up to the age of 115 d a y s . H o w e v e r , b e c a u s e o f t h e possibility that corrosion of steel would not o c c u r e v e n o v e r this length of time, parts of the experimental environment w e r e changed. To elaborate, the conditions between 4days and 33days of age were temperatures f r o m 20 to 3 0 ° C and relativehumidities from 80 to 9 0 % . T h e n , later, the conditions were changed to temperatures from 20 to 3 0 ° C a n d relativehumidities from 80 to 90%upto 90days of age, withthe bottom 2cm ofmortarspecimens immersed in an aqueous solution. Also, it w a s decided t o w a r m t h e distilled water used for bubbling. Thereafter, the ambient temperature w a s m a d e 6 0 ° C u p to llSdays of age. The rates of absorption in mortar portions of specimens w e r e m e a s u r e d after completion of the experiments. Absorption was measured by following -233- JIS A 1110 and the procedure below was used. Absorption by mortar specimens was allowed to proceed for 24 hours in water at a temperature of20± 2°c . Upon removal from thewater, surface water was wiped off with an absorbent cloth to obtain a saturated surface-dry condition, after which the mass (m) was immediately measured. Upon determination 100-110°C and, measured. The absorption of after of mass cooling specimens Q = ms - mo where, (m), to was / me Q: absorption (%) ms: mass of sample me: mass of sample X specimens were room temperature, calculated by the dried the for 24 hours mass (m>) following at was equation: 100 in saturated after drying surface-dry (g) (2) Experimental Results The temperatures and humidities in the dessicator set up. Reinforcing bars were taken out at the degrees of corrosion were investigated. The results state (g) satisfied the conditions age of 115days and are shown in Photo. the 1. The results of determining whether or not corrosion had occurred are given in Table 5. The shaded portions of the table indicate specimens, which had corroded. Since cover at ends of specimens was zero, there were some specimens in which corrosion appeared to have progressed from the ends. Here, the effects of cracking and inadequate cover frequently seen in actual structures were taken into consideration, and these specimens were included among cases of corrosion to be on the conservative side. The absorption of mortar portions of specimens was indicated as 7.6 wt% as a result of measurements. The unit mass of mortar was 2050 kg/m. Portions of cement paste which had been in direct contact with reinforcing bar surfaces, where specimens had been split and bars removed, were sampled and X-ray diffraction was performed. Distinct peaks of Friedel's salt-were not seen in the results. Given the [C1~]/[OH"] experiments, [Cl'J/fOIT] results of the experiments, conditions initially set up pH values of mortar valuesof 0.1, 1.5, and since it was expected that would change during the course of in the specimens were measured the the for and2.0. The method of measurement was as follows: © Drymortarfor7daysinadryerat60°C. 0) Coarsely grind the dried mortar followed by fine pulverization mortar andpestleto 88JLL m andunder. d) Add40 gofdistilledwaterto 100gofthefinelypulverizedmortarand storeinadesiccaator(filledwithN* gas)at 20°C for7days. (D Using the suction filtering method, separate moisture finely-divided mortar to which distilled water had been added. 0) Measure the separated moisture by pH electrode. (D [OH']/40g x1000g=[OH']mol 0) [OH"] mol x moisture content of mortar The results are given in Table 6. It may solution had changed because temperature during the testing period. For example, considered a saturated calcium solution and -234- be considered conditions the solution adjustment with from that had of with a the pH of the been altered pH 12.0 was NaOH was not pH=13.5 pH=12.0 pH=12.5 pH=13.0 à".o ot-yoM-^a 0.1 à"12.0 C1'/OH-»0.» 0.5 r>H-13:S C1 /OH-0,S o o r 1.0 3.0 .8 C» /OM I8,0 "3-0 C1 /OHn}.0 5.0 7.5 35>ptioli.i. 0" /3H «T.» 10.0 Corroded bar ( Legend) Photo 1 Corroded -255- conditions of reinforcing bars made. Since thepH at 20°C was 12.6, and at 60°C itwas ll.4, pH during the experiments varied in a range of ll.4 to 12.6. However, the differences between pH values at completion of the experiments and the originally set pH valuewere 0.07to 0.1, close tothevalue initially targeted. Table 6 Values of pH after completion of tests pH [c kr ] ] [o 1 3 .5 1 3 .0 1 2 .5 1 2 .0 1 .0 1 3 .0 7 (13 .5 8 ) 1 2 .4 6 (1 2 .9 7 ) 1 2 .0 7 (1 2 .5 8 ) l l .5 6 (1 2 .0 7 ) 1 .5 12 .5 6 ( 13 .0 7 ) 1 2 .2 7 (1 2 .7 8 ) l l .9 6 (1 2 .4 7 ) l l .5 7 (1 2 .0 8 ) 2 .0 13 .1 0 (1 3 .6 1 ) 1 2 .4 1 (1 2 .9 2 ) 1 2 .1 8 (1 2 .6 9 ) l l .5 9 ( 1 2 .1 0 ) Upper tier: measured Lower tier: calculated Even when NaOH had been added, solution varied depending on between pH values at completion ranged from 0.03 to 0.43, indicating (3) Discussion The testing and it may solution. environment be assumed that it may be considered temperature conditions. of experiments and considerable scatter. ensured that specimens all pores (=voids) were in were close that The initial the pH of the differences pH values a saturated to full with state pore Though pore solution is consumed by the hydratiou reaction, since the testing environment ensured an adequate moisture supply, it was assumed that Cl" and OH" in the pore solutionwould not become concentrated.Also, although pH varied because of changing temperature, and pH values at completion showed considerable scatter, it is assumed here that the [C1']/[OH'] ratio did not vary and that the initially set pH value remained unchanged. As already noted the shaded portions of table 5 indicate specimens in which corrosion was recognized. Although comparatively on the conservative side, these results indicate that if pH is 12.0 or higher and [CI]/[OH] is 1.0 or lower, steel does not corrode. Further, although judged as corroded in case pH was 13.5 or higher and [C1"]/[OH'] was 1.5, and in case pH was 13.0 and [C1']/[OH] was 1.5, it is possible from the conditions of adjacent specimens that the results had been of special nature, and it is considered that further studies are still required to be made. This result is considerably different from the threshold value in an alkaline solution. That is, thethreshold value in mortar, at pHof12.0 to 13.0, is higher than in an alkaline solution, while at pH of 13.5 they are approximately equal. The value is small compared with the results obtained by Yonezawa et a1, and this is thought to have been because of the lack of cover at the specimens ends and the considerable influence of differences in oxygen supply conditions. So far as can be judged pH, and it appears that express the threshold total chloride content from Table 5, corrosion of steel is influenced what Glass and Buenfeld have said that it is bestto value for corrosion of steel in concrete in terms by weight of cement is notnecessarily true. -236 - by of Further, the limit value of [C1']/[OH'J was studied using polished reinforcing bars. It is known that limit values of [C1]/[OH] differ for polished bars and bars with mill scale on their surface.The experiments in this case were carried out strictly with the aim of gaining basic knowledge, andthe influence of mill scale is amatterforfuture study. The absorption at the mortar portion of measured and was found to be 7.6 wt%. measured and it was 2,050 kg/m3. Therefore, 2,050kg/m3 and the pores On the concrete provided to the Therefore, evaluation x7.6wt%=155.8kg/m' involved in absorption were approximately 15.6 other hand, absorption of concrete cores structures (number of samples.-38) indicated that the unit mass of concrete assumed to absorption of the mortar specimens used it is considered that the results obtained of actual structures. In measuring pore structure not carbonated. of is moisture altered 4. IMPROVEMENT ELECTRO-CHEMICAL by contents of carbonation, OF CONCRETE TECHNIQUES Improvement of way concrete in realkalizalion will be described, survey carried out over a period was also done on adjacent structures of this treatment and the results described. (1) Structures Treated The structures tested rigid-frame viaducts, These chlorides due to a specimen after testing The unit mass of mortar the absorption in mortarwas as were shown vol%. sampled from actual 7 wt% (= 16.1vo1%, be 2,300 kg/rn ), close in these experiments. here can be used in actual structures, sampling was IN was was ACTUAL done since it is said from portions STRUCTURES BY an actual structure by desalination and along with the results of a follow-up of five years after treatment. Treatment using realkalization only. The effects of a one-year follow-up survey are single-line, in Fig.3. single-column beam-and-slab viaducts were constructed at a time when regulations concerning in concrete were not clear-cut, and the chloride content was high the use of marine sand. Asaresult, carbonation had progressed. The mixture proportions givenin Table 7. Whether Table 7 Estimated s(k D tgre f/c esnimggt)hn M a x . siz e S(cmlu )m p c o amrs)e a g g , (m 24 0 25 of the concrete at the time admixtures had beenused specified A ir (% ) 1 2 ア 2 4 .5 ア 1 were as mix of concrete w )/ c (% U n it c o n te n t (k g /m ) W a te r 53 157 C em en t 2 97 Admixture: Test treatments were applied to Prior to treatment, the structures investigation, and the results, are of construction is not known. columns, were described 257 beams, examined, below. - F in e ag g . C o a rs e a g g . 699 115 8 AE water-reducing agent and cantilevered slabs. detail and methods of f e vv r~B DesaIinatIon + reafkal1rat1en ,treatment $ection R6 re»Ikailzation treatment section r-A. Star t po in't st $outh sid No r t h s i de IOOE d« NJLSJUS. .CantiIever tIab South s i de Nor th s i de We s t face jSBJsH PoI4riza11on curve core sampling l.R..9..?J.l?_G // //. a)Visual Inspection 3, Structure numeraI:Msaturernent l-ocation CoIumn Fig, 0ireIed Unit:mm tested of Appearance Visual inspections of overall appearance ware carried out, but no prominent cracking was recognized. Cores sampled from columns and beams were split in half longitudinally,and the fractured surfaces were visually inspected, but no cracks or leaching of gel-like substances were noted from either columns or beams. Not did coarse aggregate particles show signs cracking or reaction rings. b) Measurement Carbonation Concrete reinforcing same time, of Reinforcing cover was bars judged measurements Bar Corrosion, Cover, removed by chipping and the according to the grading given were made of cover and carbonation Table 8 Corrosion C orro sio n deg ree 0 and corroded in Table depth. degrees V isu ally o bserv ed state I C o n d ition at tim e of co n stru ctio n m ain tain ed , w ith n su bsequ en t c o rro sio n n o ticeab le C o rro sion in p arts seen L ig ht co rrosio n II cG ro reate ss se r pction art o fb ro su ke rface n off c orro in pd arts ed Ill C ro ss se ction b rok en o ff ov er entire c ircu m ferenc e o re inforcin g b ar IV C ross sectio n o f reinfo rcin g b ar ab ou t 1/6 to 1/3 m issin g -238- Depth state 8. At of of the The method of measuring carbonation depth is as described below. After chipping, any powdered concrete on the surface was removed by means of a blower or similar apparatus, anda 1% phenolphthalein solution was sprayed on the chipped surface. The distance from the concrete surface to the portion turned red was measured using calipers. Measurements were made at roughly 20 equidistant points around the circumference of the chipped portion and the average was taken as the carbonation depth. The resultsaregiven inTable 9. Table 9 Reinforcement corrosion degree, cover, and carbonation depth investigation results P ar t R e in fo rc e B ar C o rro s io n d ia m e te r d e g re e m e u t ty p e 0 C o lu m n M a in re in fo rc e m e n D 32 ( wc e e)ョsA fa 0 9 II H o o p re in fo r ce m e n t 0 B e a m M a in re iu fo rc e m e n D 32 c(ae ron tu en r d) 6 13 II S tirru p The results given in of carbonation Table 10. Table 10 Core P art cB ee na tme r) ( a r o u n d carbonation Chloride Content Table ll carried out on sampled cores are tests 23 28 26 28 2 6 .8 22 19 20 23 25 2 1.8 B e a m of Test of total chloride contents of the analysis results were determined meter of concrete was 2,300 kg. JCI-SC4, "Method of Analysis Chloride quantity n days cores sampled are on the hypothesis Chloride analysis for Chlorides conerete(kg/m) f r o m 0 15 3 0 4 5 60 75 15 30 45 60 75 90 1 .0 0 2 .5 1 3 .3 0 2 .8 5 1 .9 0 2 .0 6 1 .0 6 2 .5 1 4 .5 3 4 .0 0 3 .0 1 2 .5 4 Treatment treatment consisted and realkalization realkalization only The desalination current for 60 in Ds u e rp f ta hc e o (fm ms )a m p l i n g C o l u m The test desalination after which 2 2 .1 19 Analysis P a r t Details 52 44 29 The results of analyses given in Table ll. The that the mass per cubic was performed following Contained in Concrete." (2) tests 62 C a rb o n atio n d e p th (m m ) 3 3 .6 C a r b o n a t i o n A v . c a r b o n a ti o n d e p t h (m m ) d e p th (m m ) ゥ ョ (D <D ゥ sC iod elu/ wm ens t f( ae ca es )t c) depth C o v e r(m m ) + realkalization for desalination, firstly of (= desalination wasperformed procedure then -239- carrying out + realkalization), on an adjacent consisted carrying out a process of four years viaduct. of applying realkalization electric for a further 15 days. The anode for the desalination + realkalization procedure consisted of pneumatically applying fibers of cellulose nature together with the specified electrolytic solution (saturated calcium hydroxide solution) to the concrete surface, fixing a titanium mesh over this, and then applying one more layer of fibers and electrolytic solution. Maintaining the anode in a moist condition, reinforcing steel embedded in the structure was made the cathode, and direct current was applied for 60 days to achieve desalination. The current density was 1 A per square meter of concrete surface. Realkalization was by a method called electroendosmosis in which a lithium-based alkali metal salt (lithium carbonate) is introduced from the concrete surface to the vicinity of reinforcing steel aim of restoring the alkalinity of the carbonated concrete. More specifically, alkalization was achieved by maintaining the anode used in desalination in a moist condition with a solution containing a combination sodium carbonate plus lithium carbonate solution (Li/Na mol ratio = 0.1). After applying electric current for desalination, the electric current was applied for 15 days for realkalization. In cases applied where for 15 realkalization days; however, only that was carried in this case out, steel current mesh was similarly was used as the treatment, + realkalization at 3, 6, anode. (3) Confirmation of Effect survey, out In the locations follow-up were carried 12, 24, and 18, 36, 60 investigations a total of of desalination times after eight Where realkalization only was implemented, out three times, at 3, 6, and 12 months. made against the state before application completing treatment. a) Chloride Analysis Concrete cores sampled before of electric current were used and thereby ascertain the effects 3.5 "E 3 s 2.5 -+t01-> 02 c 1.5 n l -o0> o 4 Total treatment and periodically to measure the chloride of desalination. ¥ V X m application of concrete -Before treatment 一* treatment 2 days after 3 months aft er 一*- 6 months aft er -9 months aft er BIT looitfcn / / after content X :.> a - 0 -- 1 2 m o n t h s af te r ".-- 1 8 m o n t h s a ft e r W .i 0 .5 0 Fig. follow-up surveys were carried In both cases, comparisons were of electric current two days after of Concrete o 9, months. in T^サ chloride o n m) m *t oJ o (o u*s m r^ o} o 0 > in¥ o c*4 i-i o in t? o m i-? o -rCMI o *f CMI o t CMI o Q CO I i- W n - tO I^ - ォO O CM O IO O cO TO - TO J- O r- ^ T- i- CM CM CM content (desalination -240- - 2 4 m o n t h s a ft e r 3 6 m o n t h s a ft e r 6 0 m o n t h s a ft e r + realkalization)coliimn(D With regard to changes with time in chloride subjected to the desalination + realkalization contents are shownin Fig. 4 andsolublechloride 1.8 Bir [octtlcci ^ y 1.6 T ¥ V.E 1.1.42 / ¥ ¥x 3ce 1 / S o.8 / x T I) 0.6 T ^ 2 i8S 0. ^ s ^ / <O p r go 0-4 1 0.2 0 contents of procedure, contentsinFig.5. .'/ .' ^! Fig. 5 Soluble c *j I ** I to J r ^ o cN I ^ - co -a- CD r- o chloride in I oo I ^ I ^ J r^ I o I oc j <D e pt h (m m ) ion i- oc o - o*一 cs o* * CM or- ォ es content Chloride Chloride Ion Selective Contained seen iu both while hardly months after total chloride any increase treatment. " サ 0 .8 0 .7 o .6 ¥ 0 .5 "<V N X :i o .4 l_ E 0 .3 0 .2 0 .1 w O + realkalization) column® centers and measurements were contents. Chloride content was Difference Titration Using in JCI-SC4, "Method of Analysis for Concrete." Significant reductions were soluble chloride contents after treatment, seen in chloride content even at 60 and was indicate reinforcing bar ions into the surrounding shadow spots behind locations concrete reinforcing where took bars ¥ ¥ /* / / / vt m TI O - 3 6 m o nt h s af te r column chloride of Potential The broken lines in the figures almost no rediffusion of chloride place, while it appears prominent were not recognizable. -o o -C0 I - Before treatment -2 days aft er treatment . 3 m onths after it.- -6 m onths after -JK- -9 m onths after -12 m onths after 一?- 18 m onths after -24 m onths after to Electrode" Hardened in portions chloride 6 0 m o n t h s a f te r (desalination At 36 months, coring was done made of total chloride and soluble measured according to "Method column total I I o co I in I m ** I O CO I o co I m Tf I 10 rI O o as I tr> - Before treatm ent -2 days aft er treatm ent -3 m onths after -6 m onths after - OK- 9 m onths aft er 一 - 12 m onths after - 18 m onths aft er 24 m onths after - 36 m onths after 一-<>- 60 m onths after Depth(mm) Fig. 6 Percentage of soluble chlorides (desalination + realkalization) The ratios of soluble to total chloride contents are shown in Fig.6. Immediately after treatment, the ratio at a point 15 mm from the surface was zero, and this was due to both total and soluble chloride contents being practically zero. To around 30 mm from the surface, portions with -241 - high soluble chloride that had been carbonated. portions that had been Below 30 50% even The soluble is thought totalchloride content ratios Apparently, carbonated. more or chlorides with areas form in mm, where carbonatioii had not occurred, the ratio was around after 60 months had elapsed, and no great variation was seen. chloride content was reduced by desalination treatment, but it fixed chloride became soluble so the ratio of soluble chloride to didnotvary to any greatextent. Regarding changes with lime in chloride contents had been implemented, total chloride contents soluble chloride contents in Fig. 8. Compared treatment, there was little change in eithertotal chloride content. J 2 .5 ・c m / * ^ where realkalization are shown in Fig. with the situation chloride content or 3 . 2 ォ *s ^ W 0 c 1 .5 o o -a<D l 1_ -2 0 .5 o 0 Fig. treatment -*-2 days after ^ 7 treatme nt m T? o c s I if ) ォ!* I o co I to r I o 0 1 I O ID T- O co LO ** O co IO r- Total chlorides I.D 1 .4 1 .2 (realkalization ^ " 0 .6 0 .4 0 .2 0 Measurement 8 of pH, Concrete cores were split, in concrete were soaked and alkali blue (pH test alkalinity was maintained ¥¥ ¥ ¥ 0 ^ *S SSi= Z w ¥ / -x-12 months after -*Before treatment -«2 days afte r tre atment ---*-3 months afte r m i-I o Fig. -&-3months afte r only) / A <o 3+ォ8O3> ^fr-^E 0 -81 o only 7 and before soluble -+~ Before 5 Depth(mm) b) less overlapped existed in soluble o COI 10 Y- Soluble m o I I o in CO TtD e p th (m m ) chlorides Confirmation to I o CO o I m f (realkalization ofAlkalinity and the concrete surface with alizarin yellow (pH paper, pH ll.0-13.6) to after realkalizaton; -242- -x12 months afte r only) Maintenance sides and Reinforcement testpaper, pH 10.0-12.0) judge how well concrete note, however, that this method using pH test paper only allowedjudgments in terms of ranges such as iO.2 to 0.4. It must also be noted that even a single split surface exhibited scatter, such as for example pH = 12.8-13.6. Therefore, it was decided to express results as average pH values obtained by adding together maximum and minimum values and dividing by two. The average pH values of cores before treatment, two days after completion of treatment, and 6, 12, 24, 36, and 60 months after treatment, are shown in Fig. 9. 14 - D esalin atio n -frea lkalization co lum n^ s urf "" "^ "" " D e salin atio n + rea lkalization co lum n (5 rein for O U n tre ate d s ection c olum n(6)su rfa ce 13 12 ll > K V/ c- & - y - X X o o 10 X- X - X O Q ゥ - X - U ntreate d se ction c olum n(D reinfo rce m e nt 9 8 - R e alka liz ation se ction co lu m n ョ surfac e ^^ V,/ o^f><^<o * /o^^ 9 .^ /o^^< l^ /0<> >?rJ^NV /o^^^ ^o^^j f o^ / /^ /o^^ , X R ea lka liz atlon se ction co lu m n ョ re in forc e m en t ^ &6^^ jr Fig. 9 At locations where desalination period between treatment and so it For parts reinforcement treatment. at concrete isclearthat that 60 + realkalization months after surfaces and 12.8-13.6 there were stable alkaline underwent in treated parts realkalization had pH in was treatment, implemented, pH values vicinities zones. of only, the of 13.0-13.6,12 values x-s 30 J25 £20 <D T3 c 15 o 2 10 o ll.2-12.0 bars, AveragepHofcores ^ Fig.10 Results of carbonation -243 T^ CJ depth measurements - in the were reinforcing surroundings months of after Carbonation depths were measured spraying 1% phenolphthalein solution on concrete cores. The results of these measurements are shown in Fig. 10. Immediately after treatment, the carbonation depth became 0 mm, while even at 60 months after treatment, it remained0 mm. c) Measurement Measurements below. Copper Sections Measured Examples of Spontaneous Potential of spontaneous sulfate electrodes potentials were used were made as reference treated with desalination + realkalization: 0) cantilever slab, undersurface (north side) 0) cantilever slab, undersurface (south side) (D beam, undersurface 0) column, side surface Untreated sections of the same viaduct ("untreated 0) beam, undersurface 0) column, side surface sections of adjacent viaduct ("outside treated CD slab, undersurface (south side) 0) beam, undersurface 0) column, side surface of spontaneous potential sections,inFig.llfor(D,inFig. measurement B efore treatment 2 days after treatment 3 mont 6 mont 9 mont 12 18 24 36 60 months months months months months Fig. m m ® -200>E^-350mv Spontaneous measurement ll nO listed span"): are shown 13for® . 1 00% >0 ?:* VO lim iiim"^m m Sn riSK」m ! aftei aftei aftei aftei aftei 0 E^-200mV 80% 40% the parts electrodes. locations"): results 12ford),andinFig. 20% at !V 4H ^ H H ^ H 40% H M ^ B H e ;il H -350mV>E potential (beam results/(desalination 20% H 60% undersurface(S) ) + realkalization) 80% 1 00% Before treatment (j 2 days after treatment 3 mont 6 mont 9 mont 12 18 24 36 60 months months months months months aftei aftei aftei aftei aftei 0 E^-200mV Fig. 12 H -200>E^-350mv Spontaneous measurement H -350mV>E potential (beam results/untreated -244- undersurface(5) part ) for beam 20% 40% B efore treatment 2 days after treatment 3 mont 6 mont 9 mont 12 months after 18 months after 24 months after 36 months after 60 months after !s ^ ^ = s s^ ^ ^ ^ a f D E ^ - 20 0m V m - 200 > E ^ - 350 m v Fig. 13 100% 60% Spontaneous measurement potential results/outside - 3 50m V > E (beam undersurface® treated span ) For desalination + realkalization sections, months after treatment was little different treatment, but the potential distributions shifted in the noble direction. the potential compared with at 24, 36, and Meanwhile, at untreated shift in the noble direction, were recognized. treated spans, there was some no large changes in potential Variations in potential in Fig. 14. The effectwas which were comparatively initially to the base direction. parts and but outside as a whole, at parts treated with that ofrealkalization on the noble side. side after treatment 20% 40% realkalization only havingbeendone It can be seen that shifted later in 18 after had are shown onparts, what went the noble 1 00% 60% m Before treatme nt distribution 12 months 60 months ;!:9P m 2 days after tre atment 5| 3 mont 61 12 months after d E^-200mV Fig. Spontaneous ASTM are 14 potentials giveninTable il H -200>E^-350mv Spontaneous measurement B -350mV>E potential (column results/realkalization and corrosion l2. probability member^ only assessments according to Looking at Fig.13, on comparing the results of spontaneous potential measurements on the undersurfaces of beams before treatment and 60 months after desalination + realkalization treatment following ASTM C 876-87, what were 0% of Rank I in corrosion activity (E > -200 mV) or "90% or higher probability of no corrosion" were 97% 60 months after -245- treatment. "indeterminate," What Table 12 were were, 56% reduced Spontaneous of to potential C o r r o s io n S p o n t a n e o u s c t i v i t y vp so ctes En t i a l (m V ) ra n k I E > -20 0 90 % corrosion In d e te r m in a t e Ill -35 0 ^ E > -50 0 9 0 % -50 0 > E were 44% or higher of be seen that, after treatment. as III a whole, Similar results were obtained (north side), slab undersurface it may be thought permissible stable spontaneous potential reinforcing bars in concrete. In contrast, and side potential there of Anode ap p ro x im ate ly shift was to o ne 60 the h alf (-350mV^ months noble Polarization of beams outside changes were seen Curve of of E), after side at other treated parts, "slab undersurface (south side), side surface of column," to consider that a shift had been made zone where a passive film was formed with regard to undersurfaces surfaces of columns, hardly any measurement results. d) Measurement (Laboratory) mV), probability IV ill corrosion activity corrosion," were 0% and of -350 o r h i g h e r p ro b a b il it y o f c o r ro s io n C r a c k in g in s p e c im e n s Ranks probability > o r h i g h e r p r o b a b il it y o f n o c o r ro s i o n -20 0 ^ E > -3 50 It can months Anode concrete between potential, formed and mV ^ E after treatment. C o r r o s io n p r o b a b i lit y II IV What "90% treatment. Rank II (-200 3% 60 months 60 and to a on treated spans in spontaneous Reinforcing Steel polarization curves of reinforcing bars were measured using cores with hoop reinforcement. The maximum current density Imax +200 mV and +600 mV was determined from the spontaneous and it was attempted to judge whether or not passive films are on reinforcing bars in concrete. Core samples obtained from "column® " of the column portion of the desalination + realkalization section and "column © " of the column portion of the untreated section for comparison were used, and polarization curves of reinforcing bars were measured. The cores were collected in a form that ensured parts of hoop reinforcement would be included. Values realkalizatiou section At 18 indicated A/cm2. Evaluation of are Imax up section plottedinFig. to 60 months after and Imax up to 12 15. treatment months in in the the desalination realkalization months after treatment the desalination + realkalization a slight increase to 17 JUL A/cm, but by 60 months It is considered that apassive state had been reproduced. criteria for anode polarization -246 curves - are given it in Table + only section was 5jU. 13. IUU 90 80 70 60 50 40 30 20 10 0 "E o ^ y / ./ ォ A ¥ ¥ ^ 1 H t_. . ^ " ---. ..一 - " ...f x g - ** ***^ c^ ,^ォ ー & "> N, ^J- * ;&. s* */&jf /^ f^> ^0<^0* < Fig. 15 Desalination + realkalizat lumnョ / /J ^ /-<^ /-o^ /-<^ ^J ? /& Results of anode Untreated section ilum nゥ 0? - Realkalizatio n section colum nョ polarization! tests (Imax) Imax where desalination + realkalization had been performed was 29jU. A/cm' and in the zone of Grade 1, "Incomplete but some amount of passivity" before treatment. Contractedly, at 60 months after treatment, it was5 0A/cm2 andhadshiftedto aGrade2or3 zone, inthedirectionof forming passive films on bar surfaces. Table 13 Evaluation criteria G ra d e for anode E v a lu a tio n polarization c r it e r i o n 0 (C c u o r mr ep nl et t e dl ye n n s oi t py a s es ix v c iet ey d) s 1 aC mu or rue nn tt o d f e pn as si ts yi v il tO y ) 1 0 0 jU . A /c m 2 iC n u c rlru e d n et d d ie n n sG i rt ya d ee xs c Oe ,e d1 s o lr O 3o 3 C u rr e n t d e n s it y 4 iC n u c r lru e dn et d d i.en ii Gs i rt ay d ee sx cO e , e 1d ,s 2 I, jU o. rA /c3 m 5 C u r r e n t d e n s it y p a s s iv it y ) At sections of realkalization 14 JUL A/cm2 was indicated same as for locations performed l curvesC13} 1 00 /Z A /c m (t h o u g h A /c m a t le a s t o n c e i n c o m p le t e ,s o m a t le a s t o n c e , b u t n o 1 0 fJ. A /c m d o e s n o t only, current 12 months after where desalination e x c ee d a t le a s t o n c e , b u t I jU A /c m (v e ry density became 90jU treatment, a value + realkalization n o g o o A/cm roughly had , but the been The maximum current density in the anode polarization curve for untreated sections, which was 31JLL A/cm2 before treatment, was 38JLL A/cm 60 months after treatment, indicating hardly any change. If remained in the zone of Grade 1, "Incomplete but some amounts of passivity." Anode concrete resistance potential passive values gradient polarization curves of reinforcing bars were measured using cores taken to include hoop reinforcement, and polarization from the anode polarization curve gradient at a spontaneous plus 50 mV. From this, it was attempted to judge whether or not films would be formed on reinforcing steel in the concrete. The of polarization resistance obtained from the polarization curve before treatment and 60 months after treatment are shown in Fig. -247- 16. Criteria for corrosion evaluation from polarization resistance are given in 14. <fO 40 35 30 25 20 15 10 5 0 o Table ci j* >Xo .4 J^ ^ / O ir x^ i tr 1 K / A . * ¥ / - D esalination + realkalizat colum nョ v - -S&- " U ntreated section )lum n(D ? ^-F^c> </F^^ ><>F <^^S </^^ i <<>,fVb^^-/<b^</"F^->^<^O<^NV </o ^NS> -R ealkalization section colum nョ JsO<J<t> & & Fig. Table 14 Criteria 16 for Polarization corrosion resistance evaluation by polarization resistanceC 10*) P o la ri z a t io n C o r r o s i o n e v a lu a t io n re s is t a n c e L e s s t h a n 4 k cZ oo rnr oe s ioo fn g w r ie tah t or ce ci un fr ro er nc ce em e on ft !) -c m c ra c k in e Z o n e o f m e d iu m re in f o r c e m e n 4 8k (! -c m c o r ro s i o n Z o n e o f m e d iu m re in f o rc e m e n t 8 12 k fi -c m c o r ro s i o n M o r e Z o n e o f n o r e in f o r c e m e n t c o r ro s io i t h a n 12 k Q c m o r z o n e o f m i n u t e c o r ro s io n R an k I n Ill IV The polarization resistance of a part where desalination +realkalization was performed, 16.7 kQà"cm2 before treatment, became 35.7 kQà" cni 24 months after treatment but by 60 months it had declined slightly. However, it was of Rank IV, "Zone of no reinforcement corrosion or zone of minute corrosion" (12.kQà"cm2 or higher), and it may be considered that polarization resistance is increased by desalination +à"realkalization and there is a shift toward passive film formation. At the realkalization only section, a value slightly lower than where desalination + realkalization had been carried out was indicated immediately after treatment, but 12 months after treatment it was 20 kQ à" cm2, roughly the same as where desalination -f realkalizatiou had been done. Polarization resistance outside the treated span, which was 14.7 kQ à" cm before treatment, became 7.7 kQ à" cm.2 60 months after treatment, RankII, "Medium reinforcingsteelcorrosion zone" (4-8 kQ à" cm). (4) Summary The following realkalization summarized and realkalizatiou a) of Application Desalination the effects only of test treatments application on actual of desalination structures: + + Realkalization 248- 1) Evaluations of spontaneous potential, resistance, indicate passive films tendedto corrosion activity of anode polarization that, for the period up be formed on reinforcing 2) The alkalinity of the concrete paper and 1% phenolphthalein months after treatment. 3) The chloride distribution there was no rediffusion of even 60 months after treatment. 4) The ratio parts extremely major changes in the chloride of soluble chlorides near the surface, were noted. 5) Noclearshadow b) Application spots could of test reinforcing of13.0-13.6 and realkalization results and to as measured found to be after the treatment vicinity behind after usingpH test stable even 60 of Table desalination 1.28 and 15 indicated reinforcement reinforcing polarization to bars were cases resistance where in treated indicated. TEST were measurements ChangesinpH + realkalization parts RESULTS evaluated on actual and pH [C1"]/[OH"] 12 months desalination 12 months T o t a l c(k hg l /ir o f r )i d e s 6 0 m o n t h s a fte r through structures. S o l u b l e c h (kl go /n r i )d e s application [ c l-] C o H -] 45 60 1 0 .4 1 0 .8 2 .8 5 (0 .9 6 ) 1 .4 4 (0 .4 8 ) 7 9 0 .8 1 9 8 8 .0 60 - 75 1 0 .4 1 0 .8 1 .9 0 (0 . 6 4 ) 0 .8 0 (0 .2 7 ) 5 2 6 .1 1 3 2 2 .7 45 60 1 2 .6 1 3 .2 1 .2 5 (0 .4 2 ) 0 .5 6 (0 .1 9 ) 1 .3 8 5 .4 9 60 75 1 2 .6 1 3 .2 1 .1 6 (0 .3 9 ) 0 .4 7 (0 .1 6 ) 1 .2 8 5 .1 0 -249- after + after AND MEASUREMENTS dueto (m m ) B e fo re tre atm e n t at no bars, a comparison of realkalization be identified application of reinforcement while soluble pores in would be 5.49. D e p th that remained except 60 months, and Changes in pH and Cl'/OH" after application of desalination + are summarized in Table 15. Specific values of pH could not because of problems with measurement techniques, but the desalination + realkalization resulted in pH values around being improved to 12.6-13.2 60 months after treatment, chlorides were also reduced to 0.47-0.56kg/rn . Considering concrete as amounting to 16.1vo1% of total volume, [Cl]/[OH] between on Only 5.COMPARISON OF LABORATORY ON ACTUAL STRUCTURES Desalination laboratory concrete ions be seen polarization curves and were roughly equivalent was applied. vicinities pHvalues treatment, was to total chlorides around 50% even of Realkalization 1) Anode treatment realkalization 2) In treatment after solution, reinforcing steel based curves, and polar-ization to 60 months after treatment, steel. of Note) pH values for reinforcement parts in treated portion @ Calculation of [C1]/[OH] performed for total chlorides withquantity pores inconcrete taken as 16.1 vol% of total volume. Figures in ()ratios (%)of chloride ion quantity to unitcementcontent The conclusion treatment tests mortar used in structures were pHis 12orhigherand be applied without pH, but not with drawn from laboratory on structures based tests and laboratory tests approximately equal [C1']/[OH~]is modification, regard to [C1"]/[OH"]. it tests carried out in tandem with on the fact that moisture contents of concrete cores collected from actual was that steel does not corrode when 1.0orunder. would Changes in pH and [C1']/[OH"] after application summarizedin Table 16. Through application the vicinity of reinforcement was improved [Crj/[OH'] wasbetween 0.76 and 3.41. Table 16 ChangesinpHand realkalization [C1']/[OH"] Ifthisconditionwereto satisfactory with be of to dueto regard to of realkalization only are realkalization only, pH in a range of 13.0-13.6, while applicationof only D e p th (m m ) 12 m o n th s 45 a f t e r t re a t m e n t 60 Note) of pH values forreinforcement Calculation of [C1"]/[OH"] pores in concrete taken Figures in ()ratios (%) pH [ c r] / [ o H ] T o t a l S o l u b le c h lo r i d e s c h l o r id e s (k g A n ') (k g A n ) 6 0 1 3 .0 1 3 .6 1 .9 5 (0 .6 6 ) 0 .6 0 (0 .2 0 ) 0 .8 6 3 .4 1 7 5 1 3 .0 1 3 .6 1 .7 4 (0 .5 9 ) 0 .5 3 (0 .1 8 ) 0 .7 6 3 .0 4 parts in treated portion ® performed for total chlorides with as 16.1 vol% oftotalvolume. of chloride ion quantity to unitcementcontent. In this case, to pH, while not more than strong alkali logarithmic, the conditions with regard to 1.0. Thereduction direction) both the contribution for preventing steel [C1']/[OH"] also, in chloride contribute to the due to risein pH The relationship 1.0 and 1.3 between pH and total chloride and with pH in the range 12.6-13.6 corrosion are satisfied there is a possibility ions andtheincrease fall in [Cl]/[OH], is claminant. content for as obtained quantity of with respect that it will be in pH (shift in but since pH is [Cl]/[OH] in treatment values of is shown 25 ill Fig. 17. With the threshold value of reinforcing t steel corrosion I 3 .5 ^ A 3 E 2 .5 *s :i C c i- ] / [ O H - ] = 1 .0 A *o A - L l .5 o 1 - - - A - - - [ OC l-H -] ]/ = 1 .3 A ' 0 .5 0 12 Fig. [C1']/[OH"] ^ 1.0, below the solid "not corroded." as line Considering that film after application ^ 1.3 is allowed line in the figure an The past value of notedby of1.7-2.0, 18, based relationship 17 12.5ph|3 13.5 Corrosion obtained in the from figure threshold the is actual structure of desalination onthethreshold from isthe range,whichmay value resultsoflaboratory the range which may tests, be the part considered shift toward formation of a passive + realkalization if up to [Cl]/[OH] Table 14, the part below the broken be considered "not corroded." research summarized in Chapter 2 indicates that the threshold [C1"]/[OH"] for corrosion of reinforcing steel in cement mortar S.E.Hussainetal.C10) atapHoflessthan13.30isinarange while for pH greater than 13.30, the range is 1.28-1.86. In Fig. on these values, and with a pore volume of 16.1 vol%, the with total chloride is shown, further superimposing Fig. 17. Fig. It can be seen value is obtained. that 18 even Corrosion threshold S.E. Hussain et a1. with [C1"]/[OHT]i values according and accordingto 1.3, a relatively to thisstudy conservative 6. CONCLUSIONS This investigation (1) Experiments [C1"]/[OH"] is judged by the leads to the with mortar 1.0 or less, steel results of these following conclusions: indicate that if pH is 12 or higher reinforcement will not corrode. So experiments, whether corrosion occurs -257 - far or and as not steel is greatly influenced by pH. From the results of experiments actual structures, it isconcludedthat steel will not corrode if [Cl]/[OH] 1.3 orunder. This result isin conformity with results of past research. (2) By carrying out desalination + realkalizalion, pH values on is around reinforcing steel in structures were improved to 12.6-13.2 60 months after treatment, while soluble chlorides were reduced to 0.47-0.56 kg/m . Even 60 months after treatment, practically no changes were noted in the alkalinity and chloride content of the concrete, while there was hardly any rediffusion of chloride ions around reinforcing bars. No prominent shadow spots were seen behind reinforcing bars either. (3) The ratio of soluble chlorides about 50% after the elapse of surface, and no large variations to total 60 months, were seen. chlorides except was extremely (4) Where realkalization only was carried out as treatment, pH values around reinforcement in structures had improved months later, while [C1']/[OH"] values were between 0.76 there is a possibility that the threshold [C1']/[OH] value through application ofrealkalization only. estimated close to be the to after treatment, to 13.0-13.6,12 and 3.41. 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