This study investigated experimental bearing capacity of corroded reinforced concrete beams. Six testing beams were made of concrete having compressive strength of 25 MPa, with the dimensions of 80 × 120 × 1200 mm. They were divided into two groups depending of tension reinforcement ratio.
Journal of Science and Technology in Civil Engineering NUCE 2019 13 (1): 1–11 AN EXPERIMENTAL STUDY ON FLEXURAL BEHAVIOR OF CORRODED REINFORCED CONCRETE BEAMS USING ELECTROCHEMICAL ACCELERATED CORROSION METHOD Nguyen Ngoc Tana,∗, Nguyen Dang Nguyena a Faculty of Building and Industrial Construction, National University of Civil Engineering, 55 Giai Phong road, Hai Ba Trung district, Hanoi, Vietnam Article history: Received 08 January 2019, Revised 16 January 2019, Accepted 17 January 2019 Abstract This study investigated experimental bearing capacity of corroded reinforced concrete beams Six testing beams were made of concrete having compressive strength of 25 MPa, with the dimensions of 80 × 120 × 1200 mm They were divided into two groups depending of tension reinforcement ratio Of which, two beams were used as the controls, whereas the other fours ones having tension reinforcement were subjected to corrosion by the electrochemical accelerated corrosion method After accelerated corrosion, the beams were tested under monotonic loading to investigate their performance All the tested beams were failed in flexural failure mode corresponding to spalling of cover concrete Test results showed that as corrosion rate in tension reinforcement increased, the lower cracking load and the displacement at the cracking load were observed As the corrosion rate of tension reinforcement ranging from 7.5% to 8.3%, it had little effect on the peak load As the corrosion rate increased further, approximately 10.8% and 14.1% in this study, the peak load decreased significantly The higher the corrosion rate, the lower the displacement of corroded beams Moreover, as corrosion rate of tension reinforcement increased the number of concrete cracks and their spacing reduced, and the width of cracks was generally larger Keywords: reinforced concrete beam; electrochemical accelerated corrosion; corrosion rate; load-carrying capacity; displacement; concrete cracking https://doi.org/10.31814/stce.nuce2019-13(1)-01 c 2019 National University of Civil Engineering Introduction The reinforced concrete was used more than a century ago because it is a flexible, economic, and sustainable structure In the process of exploitation and use of the work, reinforcement corrosion is one of the major cause which deteriorate behavior of RC structures Corrosion attack can be classified into two sources which are carbonation of concrete or chloride penetration The former typically induces uniform corrosion, whereas the latter causes non-uniform corrosion refers to as pitting corrosion Uniform corrosion can be evaluated simply by reducing cross-sectional area and using the corresponding properties for uncorroded bar [1, 2] Meanwhile, pitting corrosion localizing stress at pitting locations reduces strength and ductility of the reinforcing steel [1–4] Furthermore, expansion of corrosion products, which is about 2-6 times the volume of virgin steel [5], exerts tensile stress to the surrounding concrete and ultimately causing cracking even spalling of cover concrete [6, 7] In ∗ Corresponding author E-mail address: tannn@nuce.edu.vn (Tan, N N.) Tan, N N., Nguyen, N D / Journal of Science and Technology in Civil Engineering addition, the corrosion of steel bars can also cause weakening of the bond and anchorage between concrete and reinforcement [8–11] Consequently, the stiffness, strength and deformation capacities of RC members are reduced and the safety and serviceability of the structure are impaired [12–15] In fact, two main causes of corrosion in reinforced concrete structures are: (i) Carbonation of concrete due to the infiltration of CO2 ; (ii) attack of chloride ions [16, 17] In the first case, the carbon dioxide in the air penetrates the cover concrete through a network of voids and cracks With the presence of a liquid phase in concrete and hydrocarbon products of cement, especially Ca(OH)2 , the carbonation reaction occurs to form CaCO3 (limestone) The pH of the cementitious media is decreased from about 12.5 to 13.5 to approximately 9.0, resulting in the disruption of the passive protective membrane to the reinforcement In the second case, due to the liquid phase, chloride ions penetrate into the structure, change the condition of the concrete’s protection environment to the reinforcement This phenomenon results in morphological changes of the passive membrane, and thereby accelerating the corrosion process in the structure The data collected shows that the frequency and the cost of work repair for damage and degradation caused by corrosion has been increasing [17] In Japan, a study indicated that 90% of existing RC structures have been exposed to the marine environment with protection concrete layer been not large enough and only 10-year-old works damaged are accounted for a large proportion In the United States, based on the track of 586000 highway bridges, 15% of them have damaged structures, primarily due to aggressive corrosion Vietnam has a very long coastline and major cities are not far away from the coastline In our country, many coastal RC structures built from the 1960s to now have been applied building codes with little attention to the requirements for protection against corrosion under TCVN 9346:2012 [18] In Vietnam, the effects of corrosion are more apparent than in other countries Journal ofofScience and Technology in Civil Engineering NUCE2018 2018 Journalconditions, Science and Technology in Civil Engineering NUCE in the world, due to climatic temperatures, high humidity, large wet periods, high chloride ion concentration Many works are severely affected by the corrosion process after a short time of use Fig illustrates the severe corrosion situation of some existing RC structures in Vietnam [19] (a) Corroded RC beam atbeam a distance of distance km from the (b) Corroded Corroded RC RC beam at a distance of 20 km from the Corroded RC (b) at (a)(a) Corroded RC atatprovince a adistance ofof11 (b) Corroded RCinbeam beam ataprovince adistance distanceofof2020 coastline in beam Hai Phong coastline Thanh Hoa km from the coastline in Hai Phong km from the coastline in Thanh Hoa km from the coastline in Hai Phong km from the coastline in Thanh Hoa province province Figure Reinforcement corrosion in existing corroded structures [19] province province Figure Reinforcement corrosion in existing corroded structures [19] Figure Reinforcement corrosion in existing corroded structures [19] Corrosion of steel reinforcement for sure is an important issue which has attracted more attention of steel reinforcement for sure is an important issue and which has fromCorrosion theCorrosion Vietnamese recently [20, 21] studies on corrosion problems its effects of researchers steel reinforcement forLocal sure is an important issue which has attracted attention from time the isVietnamese recently 21] Local have limited more as the actual corrosion measured in researchers units of year This study[20, was conducted to attracted more attention from the Vietnamese researchers recently [20, 21] Local give an experimental procedure that allows for the creation of reinforced concrete structure in various studies on corrosion problems and its effects have limited as the actual corrosion time studies on corrosion problems and its effects have limited as the actual corrosion time is measured in units of year This study was conducted to give an experimental is procedure measured that in units of year This study conducted to give an experimental allows for the creation of was reinforced concrete structure in various procedure that allows for the creation of reinforced concrete structure in various corrosion levels in the laboratory for a resonable time by using electrochemical corrosion levels in themethod laboratory for a beam resonable time are by used usingBeam electrochemical accelerated corrosion Small-scale specimens specimens Tan, N N., Nguyen, N D / Journal of Science and Technology in Civil Engineering corrosion levels in the laboratory for a reasonable time by using electrochemical accelerated corrosion method Small-scale beam specimens are used Beam specimens were tested under monotonic loading to investigate their behavior This research is significant in that it advances the understanding of behavior of corroded reinforced concrete beams, which lays the foundation for further study on effect of reinforcement corrosion on reinforced concrete structures and assessing the durability of Vietnam maritime RC structures Experimental program 2.1 Materials used The testing samples in this study were conducted at the Laboratory of Construction Testing and Inspection - National University of Civil Engineering They were made of the concrete with B20 grade Table shows the aggregate component of concrete used The compressive strength of concrete was determined by compression test on standard cubic samples with the dimensions of 150×150×150 mm in accordance with TCVN 3118:1993 [22] The compressive strength of concrete was the average value of a sample group of three pellets The axial compressive strength of concrete manufactured in 28-days is R28 = 25 MPa (see Table 1) The longitudinal reinforcements are the deformed bars with nominal diameters of mm and 10 mm having the steel grade of CB300-V (under TCVN 1651-2:2008 [23]) Stirrup is a plain bar with nominal diameter of mm having the steel grade of CB240-T For each type of reinforcement diameter, a group of three steel bars was tested according to TCVN 1971:2014 [24] to determine the actual tensile strength The average results of tension test of the sample groups are shown in Table Table Concrete mix and compressive strength at 28 days Grade Cement PCB40 (kg) Sand (kg) Gravel (kg) Water (liter) R28 (MPa) B20 325 680 1240 195 25.0 Table Mechanical properties of steel bars Type of steel D6 plain bar D8 deformed bar D10 deformed bar Area (mm2 ) Yield strength fy (MPa) Ultimate strength fu (MPa) Ultimate strain ε su (%) 28.3 50.3 78.5 288.6 334.0 337.3 419.3 437.4 437.4 29.3 25.7 23.7 2.2 Design of testing beams There are six testing beams were divided into two groups that were cast with the details shown in Fig These beams were made has cross section of 80 × 120 mm (width × length); the concrete protective layer is 15 mm and the beam length is 1200 mm There was 2D6 steel bars on the top side for hanging purpose The rectangular stirrups No in the section 1-1 were D4a150 along 400 mm segment at two ends and D4a300 at the mid-span segment The stirrup was plain bar The difference between the two groups was the two longitudinal reinforcing bars at the bottom (No 1), which were 2D8 deformed bars and 2D10 deformed bars for Groups and 2, respectively stirrups No.3 in the section 1-1 were D4a150 along 400mm segment at two ends and D4a300 at the mid-span segment The stirrup was plain bar The difference between the two groups was the two longitudinal reinforcing bars at the bottom (No.1), which were 2D8 deformed bars and 2D10 deformed bars for Groups and 2, respectively Tan, N N., Nguyen, N D / Journal of Science and Technology in Civil Engineering Journal of Science and Technology in Civil Engineering NUCE 2018 3.1 Diagram ofFigure corrosion experiments Dimensions andD10 D10 testing beams Figure Dimensionsof of D8 D8 and testing beams After curing the experiment samples for at least 28 days, the reinforcement was induced corrosion by electrochemical accelerated corrosion methods The two beam Electrochemical accelerated corrosion method samples in each sample group are corroded, named D8-2, D8-3, D10-2, and D10-3 3.1 Diagram of corrosion experiments Two remaining beams (named D8-1 and D10-1) are not corroded and will be used as After curing the experiment samplesthe forelectrochemical at least 28 days, the reinforcement was induced corrosion control beams Fig illustrates accelerated corrosion method The by electrochemical accelerated corrosion methods The two beam samples in each sample group are longitudinal rebars (D8 or D10) of the testing samples were connected to the anode of corroded, named D8-2, D8-3, D10-2, and D10-3 Two remaining beams (named D8-1 and D10-1) a DC powerand supply cathode of the DC Fig supply power was connected to a accelerated copper are not corroded will beThe used as control beams illustrates the electrochemical bar placed in The NaCllongitudinal solution ofrebars 3.5%(D8 concentration (35g NaClsamples in liter of water) With corrosion method or D10) of the testing were connected to the anode of NaCl a DC content, power supply The cathode the DC supply power wasofconnected copper bar this salt water has the of salinity equivalent to that seawater to in aVietnam placed in NaCl solution of 3.5% concentration (35g NaCl in liter of water) With this NaCl and in the world, and in the experiment, it served as the electrolyte solution Thecontent, DC salt water has the salinity equivalent to that of seawater in Vietnam and in the world, and in the power supply allows converting alternating current into direct current In this experiment, it served as the electrolyte solution The DC power supply allows converting alternating experiment, a voltage U = 5V was maintained stability during the implementation of current into direct current In this experiment, a voltage U = V was maintained stability during electrochemical The corrosion maximumThe period of electrochemical corrosion testing the implementation of corrosion electrochemical maximum period of electrochemical corrosion was 1414 days D10-3beams beams testing was days(336 (336hours) hours)for for D8-3 D8-3 and D10-3 Electrochemical accelerated corrosion method Figure3.3.Accelerated Accelerated corrosion setup Figure corrosion setup 3.2 Testing setup and measuring instruments 3.2 Testing setup and measuring instruments After electrochemical accelerated corrosion of corroded beams and after curing for at least 28 days with non-corroded beams, the testing samples were subjected to monotonic loading to investigate their performance In the test, the 1200 mm-length specimen was singly supported over a span of 1100 mm and was subjected to two symmetrical concentrated loads at points P1 and P2 which were both at a distance of 400 mm from the supports R1 and R2 The loads were generated by means of a (a) Diagram of 4-point bending test (b) Photo of testing beam Figure Loading experiment diagram electrochemical corrosion TheThe maximum period of of electrochemical corrosion testing electrochemical corrosion maximum period electrochemical corrosion testing waswas 14 days (336 hours) for D8-3 and D10-3 beams 14 days (336 hours) for D8-3 and D10-3 beams Tan, N N., Nguyen, N D / Journal of Science and Technology in Civil Engineering hydraulic jack and an oil pump by hand A load cell was used to measure the load applied during the test Three Linear Variable Deformation Transducers (LVDTs) were installed to measure the vertical displacement of each tested beam The sets of displacement transducers (I1 and I3) were used to measure the displacement at the supports (R1 and R3), respectively The I2 displacement transducer was used to measure the displacement at mid-span of the beam All displacement transducers were connected to a TDS-530 data-logger and a computer to collect automatically measurement data in Figure Accelerated corrosion setup order to establish the relationship between applied load and displacement Figure Accelerated corrosion setup Fig 4(a) shows the loading diagram and arrangement of the measuring instruments 3.2.3.2 Testing setup andand measuring instruments Testing setup measuring instruments (a) Diagram of 4-point bending test (a) Diagram of 4-point bending testtest (a) Diagram of 4-point bending (b) Photo of testing beam (b)(b) Photo of of testing beam Photo testing beam Figure Loading Loadingexperiment experiment diagram Figure experiment diagram Figure Loading diagram After electrochemical accelerated of corroded beams after curing electrochemical accelerated of beam corroded beams andand after curing Fig.After 4(b) shows a photo of the bending testcorrosion oncorrosion a typical During the experiment, the applied atcontinuously least with non-corroded beams, testing samples were subjected to load wasleast increased until the beam failed At the same time, were each testing beamtowas for for at 28 28 daysdays with non-corroded beams, thethe testing samples subjected observed carefully to detect the appearance of the first concrete cracking The development of concrete monotonic loading to investigate their peformance test, 1200 mm-length monotonic loading to investigate their peformance In In thethe test, thethe 1200 mm-length cracks was highlighted on the testing beam surface After the end of the experiment, the distance specimen singly supported over a span 1100 was subjected two specimen waswas singly supported over a span of of 1100 mmmm andand was subjected to to two between the concrete crackings was measured for the tested beams 5 Experimental results and discussion 4.1 Corrosion rate of reinforcements The reinforcement corrosion rate of beam tested was calculated based on the mass of the lost metal for the bearing principal bars The steel bars were weighed to determine the mass before making the corrosion experiments (m0 ) After the corroded beams were subjected to monotonic loading, they were demolished and the corroded reinforcement was extracted for corrosion measurement The reinforcement was firstly cleaned by a bristle brush to remove concrete adhering to the surface The reinforcement is then immersed in 5% HCl solution with 3.5 g hexamethylenetetramine for day and then cleaned to remove corrosion products The cleaning procedure was also applied to a control steel bar without corrosion It was found the procedure resulted in insignificant loss of the steel of the control, uncorroded bar Then, the bars were weighed to determine the remaining mass (m) The corrosion rate of the reinforcement, c (%) are defined by Eq (1) c (%) = m0 − m ∆m × 100 = × 100 m0 m0 (1) where m0 (g) being the stell mass before corrosion, m (g) being the stell mass after corrosion, and ∆m (g) being the steel mass lost by corrosion 55 66 Group Group2 D10-2 D10-2 554.5 554.5 508.5 508.5 46.0 46.0 8.3% 8.3% 71.98 71.98 D10-3 D10-3 554.5 554.5 476.0 476.0 78.5 78.5 14.1% 14.1% 67.43 67.43 Tan, N N., Nguyen, N D / Journal of Science and Technology in Civil Engineering Fig Fig.5 5shows showsthe thereinforcement reinforcementphotos photosafter aftercorrosion corrosionofofthe thetesting testingbeams beams.ItItcan can Table shows the results of the determination of reinforcement corrosion rate for all testing bebeobserved observedthat thatallallrebars rebarsare arealong alongthe theupper upperlayer, layer,the thelower lowerlayer, layer,and andthe thestirrups stirrups beams For each corroded beam, the corrosion rate is the average value of the two corroded bars were werealso alsocorroded corroded.The Thepitting pittingcorrosion corrosionwas wasalso alsoobserved observedfor forboth boththe thelongitudinal longitudinal at the bottom layer (D8 or D10 steel bars) bar barand andthe thestirrup stirrup.Especially, Especially,ininthe thecorners cornersofofthe thestirrup, stirrup,it itisisshown shownatatthe thedegree degreeofof Table Determination of corrosion rates of D8 and D10 steel bars localized localizedcorrosion corrosionisishigher higher(pitting (pittingcorrosion) corrosion)than thanatatthe theother otherpositions positionsofofthe the stirrup, stirrup, can can bebeseen seeninBeam inFigs Figs.6(a) 6(a) 6(b).m This This was∆m also also observed observed ininexperiments experiments No asas Test group mand (g)6(b) (g) was (g) c (%) A s (mm2 )onon and the the corrosionmade madebyby [14, [14,15, 15, 25] 25].Four Four corroded- specimens specimens didnot not display display corrosion D8-1 390.0 - corroded - did 50.30 Group cracks D8-2According 390.0 totoUomoto 360.8 and 29.3 7.5% 46.53been significant significant visible visible cracks According Uomoto and Misra Misra[26] [26] cases caseshave have been D8-3 390.0 348.0 42.3 10.8% 44.88 reported reportedininwhich whichnonovisible visiblecracks cracksappear appearononthe theconcrete concretesurface surfacedespite despitesevere severe D10-1 especially 554.5 when - the - barsisisless 78.50 corrosion corrosion ofofthe thereinforcement, reinforcement, especially when thediameter diameter ofofthe thebars less than than1616 Group D10-2 554.5 508.5 46.0 8.3% 71.98 mm mm InInthis thisstudy, study,maximum maximum diameter diameter ofofreinforcements reinforcements has hasa 14.1% adiameter diameterofof only only1010 D10-3 554.5 476.0 78.5 67.43 mm, mm,explaining explainingwhy whynonovisible visiblecracks crackswere werefound foundfor forD8-2, D8-2,D8-3, D8-3,D10-2, D10-2,and andD10-3 D10-3 tested testedbeams beams (a)(a)Group of D8 D8 beams beams (a)Group Group111 ofof D8 beams (b) (b)Group Group 1of D10beams beams beams (b) Group 1of ofD10 D10 Figure Figure5.5.Overview Overview of ofnon-corroded non-corroded beam beamand and reinforcements reinforcements corrosion corrosion rate rateofof Journal ofof Science and Technology in in Civil Engineering 2018 Journal Science and Technology Civil Engineering 2018 Figure Overview of non-corroded beam and reinforcements corrosion rate NUCE of NUCE corroded beams corroded corrodedbeams beams 77 (a) Corroded steel steel bars in bars D8-2 beam with c beam = 7.5% (a)(a) Corroded ininD8-2 Corroded steel bars D8-2 beam Corroded steel bars in D10-3 with beam c =beam 14.1% (b)(b) Corroded steel bars inbeam D10-3 (b) Corroded steel bars in D10-3 with c= 14.1% with c= 14.1% with withc = c =7.5% 7.5% Figure Close view on corroded steel bars Figure corroded steel bars Figure6.6.Close Closeview viewonon corroded steel bars Fig shows the reinforcement photos after corrosion of the testing beams It can be observed that 4.2 capacity ofof thethe testing beams 4.2.Effect Effectofofreinforcement reinforcementcorrosion corrosionononthethebearing bearing capacity testing beams Figs Figs.7(a) 7(a)and and7(b) 7(b)show showthetheresponse responseforfortesting testinggroups groupsofofD8D8and andD10 D10beams, beams, respectively respectively.The Thecontrol controlbeams beamsand andcorroded corrodedbeams beamsexhibited exhibiteda atypical typicalflexural flexural failure failure failuremode, mode,asasevidenced evidencedbybythetheclear clearsoftening softeningofofhysteretic hystereticbehavior behaviorbefore before failure Tan, N N., Nguyen, N D / Journal of Science and Technology in Civil Engineering all rebars are along the upper layer, the lower layer, and the stirrups were also corroded The pitting corrosion was also observed for both the longitudinal bar and the stirrup Especially, in the corners of the stirrup, it is shown at the degree of localized corrosion is higher (pitting corrosion) than at the other positions of the stirrup, as can be seen in Figs 6(a) and 6(b) This was also observed in experiments on(a) theCorroded corrosion steel made by [14, 25].beam Four corroded specimens steel did not display significant visible (a) Corroded steel bars bars in 15, D8-2 beam (b)Corroded Corroded steel bars D10-3 beam in D8-2 (b) bars ininD10-3 beam cracks According to Uomoto and Misra [26] cases have been reported in which no visible cracks with cc = = 7.5% 7.5% withcc==14.1% 14.1% with with appear on the concrete surface despite severe corrosion of the reinforcement, especially when the Figure Close view oncorroded corroded steel bars of reinforcements has a Figure steel bars diameter of the bars is less than 16Close mm Inview this on study, maximum diameter diameter of of only 10 mm, explaining why noon visible cracks were found for D8-2, D8-3, beams D10-2, and 4.2 Effect reinforcement corrosion the bearing bearing capacity the testing 4.2 Effect of reinforcement corrosion on the capacity ofofthe testing beams D10-3 tested beams 7(b) show show the the response response for for testing testing groups groups of ofD8 D8and andD10 D10beams, beams, Figs 7(a) and 7(b) respectively The control control beams beams and and corroded corroded beams beams exhibited exhibited aa typical typical flexural flexural Figs 7(a) and 7(b) show the response for testing groups of D8 and D10 beams, respectively The failure mode, as evidenced evidenced by by the the clear clear softening softening of of hysteretic hystereticbehavior behaviorbefore beforefailure failure control beams and corroded beams exhibited a typical flexural failure mode, as evidenced by the inclined cracksbefore and/or fracture ofsignificant stirrupswere wereobserved observed the tests and significant inclined cracks and/or fracture of stirrups ininthe tests clearno softening of hysteretic behavior failure and no inclined cracks and/or fracture The flexural developed first onflexural the bottom bottom face ofthe thefirst specimen andpropagated propagated of stirrups werecracks observed in the tests The cracksface developed on the bottom face of the developed first on the of specimen and specimen deep the section asincreased the displacement Whenspalled, the concrete section as as theinto displacement increased Whenincreased the concrete concrete spalled, the deep intoand thepropagated section the displacement When the the spalled, the flexural strength dropped drastically and hence the test was terminated dropped drastically drastically and and hence hencethe thetest testwas wasterminated terminated flexural strength dropped 4.2 Effect of reinforcement corrosion on the bearing capacity of the testing beams (a) Results of D8 beams (b) Results of D10 beams (a) Results Results of of D8 D8 beams beams (b) (b)Results Resultsof ofD10 D10beams beams Load versus displacement for testing testing groups of D8 and D10 beams beams Figure 7.Figure Load Load versus versus displacement displacement for for testinggroups groupsof ofD8 D8and andD10 D10 beams performance indicators indicators the cracking load (Pcr ), cracking ( fcr ), and peak TheThe performance include the load (P cracking indicatorsinclude include the cracking cracking load (Pcrcr),),displacement cracking displacement displacement load (P ), ultimate displacement ( f ) The cracking load (P ) is considered as the applied )load peak u (fcr displacement load (P (Ppeak ), ultimate ultimate displacement (f(fucru).) The The cracking cracking load load (P (Pcrcr) isis cr), and peak load peak), corresponding to the first concrete crack observed The cracking displacement ( fcr ) is the measured considered applied load corresponding to first concrete crack observed The considered as thecracking appliedload loadThe corresponding to)the the first concrete crack observed The displacementas at the the peak load (P peak is the maximum applied load on each tested cracking displacement (f ) is the measured displacement at the cracking load The beam The displacement ultimate displacement ) is defined as the displacement atthe time of terminating cracking (fcrcr) is( futhe measured displacement theright cracking load The the test when the concrete spalled and the flexural strength dropped significantly Table summarizes peak peak load load (P (Ppeak is the the maximum maximum applied applied load load on on each each tested tested beam beam The The ultimate ultimate peak)) is the performance indicators for the beam specimens It can be observed that corroded beams in the two groups (D8-2 and D8-3 beams in Group 1; D10-2 and D10-3 beams in Group 2) showed similar phenomenon on the cracking load and the dis88 Tan, N N., Nguyen, N D / Journal of Science and Technology in Civil Engineering Table Test results of D8 and D10 beam specimens No Test group Group Group Beam Pcr (kN) fcr (mm) P peak (kN) fu (mm) D8-1 D8-2 D8-3 D10-1 D10-2 D10-3 7.80 5.80 5.30 13.70 7.80 6.30 0.28 0.15 0.15 0.91 0.29 0.18 27.59 29.49 24.79 36.39 36.59 29.19 18.11 12.94 14.07 13.44 13.01 6.60 placement at the cracking load The higher the reinforcement corrosion rate, the lower the cracking load and the displacement at the cracking load This is because corrosion induced expansion of the reinforcement, subsequently causing tensile stress in the cover concrete, and ultimately decreasing the cracking load Table reveals that the peak load decreased when the reinforcement corrosion rate reach to a sufficient level In this study, the percentage difference in the peak load of D8-2 corroded beam is compared to D8-1 non-corroded beam about 6.8% (29.49 versus 27.59 kN), and of D10-2 corroded beam is compared to D10-1 non-corroded beam about 0.5% (36.59 versus 36.39 kN), which are insignificant considering several factors such as material variation, size effect, and insufficient corrosion rates (about c = 7.5 – 8.3%) that could also produce such a difference amount The peak load in the remaining tested beams (D8-3 and D10-3) significantly decreased with an increasing amount of reinforcement corrosion, about 10.1% to 19.8% in compared with the non-corroded beams This can be explained by the reduction of cross-sectional area of tension steel bars due to sufficient corrosion rates (c = 10.8% for D8-3 beam, and c = 14.1% for D10-3 beam) and the reduction of the bond between steel bars and concrete The ultimate displacement of the tested beams decreased clearly when increasing the corrosion rates For the D8 beams group, the displacement reduced approximately of 28.5% ( fu = 18.11 versus 12.94 mm) between the non-corroded and corroded beams For the D10 beams group, this reduced approximately of 50.9% ( fu = 13.44 mm versus 6.60 mm) between the non-corroded and corroded beams It is may be due to the fact that top reinforcements were also corroded, the expansion of corrosion product generated from top reinforcements induced tensile stress to the top cover concrete, which was consequently decreasing the compressive capacity of the concrete to balance the tensile force of the reinforcements Thus, as corrosion rate increases the corroded beam may be failed earlier 4.3 Effect of reinforcement corrosion on concrete cracking distribution At the end of bending test, the length and spacing among the concrete cracks were measured and highlighted in Figs and It is found that the number of concrete cracks on the non-corroded beams is more than that of corroded beams Furthermore, crack spacings on the non-corroded beams are smaller than that of corroded beams, and the width of cracks on the corroded beams are generally larger than that of non-corroded beams That is because reduction of bond reduces the ability of the section to mobilize the strain in the steel bars The section must rotate more to yield the longitudinal reinforcement Concrete capability to share tension from reinforcement (tension stiffening) is decreased due to bond reduction, subsequently decreasing the number of crack appeared in the beam and enlarging the width of the crack on the corroded beams mobilize the strain in the steel bars The section must rotate more to yield the longitudinal reinforcement Concrete Concrete capability capability toto share share tension tensionfrom fromreinforcement reinforcement longitudinal reinforcement (tension stiffening) is is decreased decreased due due to to bond bond reduction, reduction, subsequently subsequentlydecreasing decreasingthe the (tension stiffening) number of crack crack appeared appeared in in the the beam beam and and enlarging enlarging the thewidth widthofofthe thecrack crackononthe the number of corroded beams Tan, N N., Nguyen, N D / Journal of Science and Technology in Civil Engineering corroded beams 0.5P 0.5P 0.5P 0.5P D8-1 D8-1 (a) Cracks distribution on on beam (a) Cracks Cracks distribution onthe theD8-1 D8-1 beam (a) distribution the D8-1 beam 0.5P 0.5P 0.5P 0.5P D8-2 D8-2 (b) Cracks distribution on on beam (b) Cracks Cracks distribution onthe theD8-2 D8-2 beam (b) distribution the D8-2 beam Journal of Science and Technology in Civil Civil Engineering Engineering NUCE NUCE 2018 2018 FigureFigure Comparison of distribution cracks testing beams Comparison of the thethe distribution ofconcrete concretecracks cracks on D8 testing beams Comparison of distributionof concrete onon D8D8 testing beams 0.5P 0.5P 0.5P D10-1 D10-1 1010 (a) Cracks distribution on beam (a) Cracks distribution onthe theD10-1 D10-1 beam D10-1 beam 0.5P 0.5P 0.5P D10-2 D10-2 (b) Cracks distribution on beam (b) Cracks distribution onthe theD10-2 D10-2 beam D10-2 beam Figure Comparison ofofthe ofcracks cracks D10 testing beams Figure Comparison thedistribution distribution of onon D10 testing beams cracks on D10 testing beams Conclusion In this this study, study, six In six reinforced reinforced concrete concrete beams beams were were fabricated fabricated and and corrosion corrosion was was induced to steel bars using the electrochemical accelerated corrosion method The induced to steel bars using the electrochemical accelerated corrosion method The tested beams were subjected to four-point bending tested beams were subjected to four-point bending under under monotonic monotonic loading loading to to investigate their flexural behavior Some main conclusions can be drawn as follows: investigate their flexural behavior Some main conclusions can be drawn as follows: • Corrosion of transverse and longitudinal reinforcements was non-uniform Larger Tan, N N., Nguyen, N D / Journal of Science and Technology in Civil Engineering Conclusions In this study, six reinforced concrete beams were fabricated and corrosion was induced to steel bars using the electrochemical accelerated corrosion method The tested beams were subjected to fourpoint bending under monotonic loading to investigate their flexural behavior Some main conclusions can be drawn as follows: - Corrosion of transverse and longitudinal reinforcements was non-uniform Larger corrosion pit depths were observed, particularly at the corners of the transverse steel hoops - The higher the reinforcement corrosion rate, the lower the cracking load and the displacement at the cracking load - As corrosion rate of tension reinforcement ranges from 7.5% to 8.3%, the peak load had not much apprarently difference with those of the non-corroded beams As the corrosion rate being greater (about 10.8% to 14.1% in this study), the peak load of these tested beams significantly decreased about 10.1% to 19.8% in compared with that of the non-corroded beams - As corrosion rate increased the ultimate displacement of the corroded beams considerably decreased - The number of concrete cracks on the non-corroded beams was more than that of corroded beams Furthermore, the higher the corrosion rates, the smaller of cracks spacing and generally the larger of crack width References [1] Du, Y G., Clark, L A., Chan, A H C (2005) Effect of corrosion on ductility of reinforcing bars Magazine of Concrete Research, 57(7):407–419 [2] Du, Y G., Clark, L A., Chan, A H C (2005) Residual capacity of corroded reinforcing bars Magazine of Concrete Research, 57(3):135–147 [3] Kashani, M M., Crewe, A J., Alexander, N A (2013) Nonlinear stress–strain behaviour of corrosiondamaged reinforcing bars including inelastic buckling Engineering Structures, 48:417–429 [4] Kashani, M M., Crewe, A J., Alexander, N A (2013) Use of a 3D optical measurement technique for stochastic corrosion pattern analysis of 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Comparison of distribution cracks testing beams Comparison of the thethe distribution ofconcrete concretecracks cracks on D8 testing beams Comparison of distributionof concrete onon D8D8 testing beams. .. reinforced reinforced concrete concrete beams beams were were fabricated fabricated and and corrosion corrosion was was induced to steel bars using the electrochemical accelerated corrosion method. .. groups of ofD8 D8and andD10 D1 0beams, beams, Figs 7(a) and 7(b) respectively The control control beams beams and and corroded corroded beams beams exhibited exhibited aa typical typical flexural flexural