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JOURNAL OF IRON A N D STEEL RESEARCH, INTERNATIONAL. 2012, 19(12)·. 48-52

Comprehensive Properties of 400 MPa Grade Corrosion-Resistant Rebar

C H E N Ying, Y A N G Zhong-min, W A N G Hui-min (China Iron and Steel Research Institute Group , Beijing 1 0 0 0 8 1 , China)

Abstract; T h e corrosion resistance of the developed 400 MPa grade rebar w a s evaluated by a series of exper iments ,

including cycles of corrosion-accelerating tes t s in the simulated concrete pore solution and reinforced concrete cube

corrosion-accelerating tes ts and in-situ exposure experiments in chloride ions condition. In addition, the tensile and

bending properties and the connection adaptability of the developed rebar were investigated. T h e results verify that

the comprehensive properties of the corrosion-resistant rebar are excellent. T h e tensile and bending properties of the

rebar are up to the standard of GB1499-2007 . T h e c o m m o n welding method and the mechanical connection technology of

knob-cut rolled parallel thread splicing are suitable for the rebar.

Key w o r d s : corrosion-resistant rebar; chloride ion; comprehensive property

T h e corrosion of rebar is the primary cause of reducing concrete s t ructure service-life 1- 1 - 5- 1. Espe­cially tha t the rebar exposed to the high chloride lev­el condition will lead to the severe s t ructure deterio­ration or even collapse. There fore , preventing rebar from chloride induced corrosion is still a concern th roughout the w o r l d C 6 _ l o ; l .

Early in the 1930s, low alloyed atmospheric corrosion resistance steel was studied in America. And the patent named Cor-Ten steel was developed, which has been commonly used. Since the 1960s, corrosion-resistant steel sheet has been widely used in the bridge and s t ructure technology in Japan and European countries. But the yield s t rength of the steel such as Corten-A steel is about 345 MPa. T h e corrosion-resistant rebar with 400 MPa grade used in s t ructure is as yet blank space.

With the increasing large scale infrastructural project and the high-rise long span s t ruc tu re , the 400 MPa grade corrosion-resistant rebar will be widely used in China , which can save a lot of the cost of maintenance and improve the durability of new construction near the seashore.

Since 2006, the Iron and Steel Research Inst i tu­te has developed the low alloyed 400 MPa grade cor­rosion-resistant rebar. The comprehensive proper­

ties of the developed corrosion-resistant rebar , in­cluding its tensile and bending properties, weldability, mechanical connections and corrosion resistance in the environment of chloride, were investigated.

1 Mechanical Properties of Corrosion-Resist­ant Rebar

For comparison, three different series microal-loyed corrosion-resistant r eba r s , respectively with the C u - P , Cu-Cr and the Cu-Cr-Ni , have been devel­oped. T h e steels were smelted in the medium fre­quency furnace. The billets were controlled rolled to rebars with 16 mm in diameter. Table 1 presents the chemical compositions of the developed rebar ob­tained by spectroscopic analysis.

1.1 Properties of corrosion-resistant rebar at ambi­ent temperature

Three standard samples were taken from each corrosion-resistant rebar. The tensile properties of the specimens at ambient temperature are presented in Table 2.

Table 2 provides that the tensile properties of the different series corrosion-resistant rebar all reach the standard of GB1499—2007. And the yield ratios of the specimens are less than 0. 8 , which accord with

Foundation I temjtem Sponsored by National High-Tech Research and Development Program of China (2006AA03Z518); National Key Technology Research and Development Program in 11th Five-Year Plan of China (2007BAE30B05)

Biography:CHEN Ying(1973—), Female, Master, Senior Engineer; E-mail: ym-cy@163.com; Received Date ; August 3 , 2011

Issue 12 Comprehensive Properties of 400 MPa Grade Corrosion-Resistant Rebar 49

T a b l e ! Chemical composition of corrosion-resistant rebar ( m a s s percent , % )

Sample number C Si Mn Ρ S Cr Ni Cu Nb V

No. 1 0. 21 0. 55 1. 58 0. 035 0. 011 < 2 . 00 < 1 . 50 < 1 . 00 < 0 . 03 < 0 . 05

No. 3 0. 22 0. 58 1. 56 0. 032 0. 010 < 2 . 00 < 1 . 50 < 1 . 00 < 0 . 03 < 0 . 05

No. 4 0. 20 0. 56 1. 55 0. 089 0. 010 < 2 . 00 < 1 . 50 < 1 . 0 0 < 0 . 03 < 0 . 05

No. 6 0. 23 0. 58 1. 59 0. 033 0. 010 < 2 . 00 < 1 . 50 < 1 . 00 < 0 . 03 < 0 . 05

No. 0 0. 23 0. 36 0. 74 0. 035 0. 042 0. 020 0. 015 0. 043 < 0 . 005 < 0 . 005

Note : The steel No. 0 is the plain carbon steel; Steels No. 1 » No. 3 , No. 4 , and No. 6 are the developed corrosion-resistant rebar.

Table 2 Tensile properties of corrosion-resistant rebar

Sampling number Tensile strengh/MPa Yield strength/MPa Elongation/ % Yield ratio

No. 1 745 789 425 427 16. 5 0. 57

No. 3 580 576 325 295 20. 0 0. 56

No. 4 630 659 415 377 25. 5 0. 66

No. 6 785 784 455 350 18.0 0. 58

No. 0 590 603 475 478 20. 0 0. 81

the seismic resistance requirement.

1. 2 Bending properties of corrosion-resistant rebar T h e bending tes ts of the corrosion-resistant re­

bar were carried out in accordance with the Chinese

standard of GB232—1999. T w o samples were taken from each corrosion-resistant rebar for cold bending tests . One sample was taken from each corrosion-re­sistant rebar for reverse bending tests. The test results given in Table 3 meet the bending propert ies require-

Table 3 Bending properties of corrosion-resistant rebar

Sampling number Diameter of rebar Recurvating

Sampling number Diameter of rebar Bending (d=5 a; a = 90°) Reverse bending (a = 20°)

No. 1 16 mm 5 pieces qualified, 1 piece has microcrack

No. 4 16 mm 6 pieces tested are qualified

No. 6 16 mm 6 pieces tested are qualified

ments of the Chinese standard GB1499—2007.

2 Corrosion-Resistance of Rebar

2 . 1 Corrosion-resistance of rebar in simulated con­crete pole fluid containing chlorine ion

T h e rebars were machined into corrosion test samples with 12 mm in diameter and 50 mm in height. The accelerating corrosion tes ts were carried out in the simulated concrete pole fluid. T h e concentration of chloride ion, the p H value and the accelerating

corrosion time were adjusted in order to establish a reliable evaluation method. After several round t e s t s , the p H value is confirmed to be 7 , the concen­trat ion of chloride ion is 2 % and the cycle time per test is 72 h. T h e degree of corrosion was measured as gravimetric loss in mass of the tested rebar. T h e re­sults are given in Table 4. Fig. 1 (a ) and ( b ) show that the corrosion order of the steels is No. 0 > N o . 4 > No. 3 > N o . l > N o . 6. The relative corrosion rate of steel No. 6 is 5 6 % of carbon steel.

Table 4 Result of corrosion test of rebar

Tested rebar '-No. 0 No. 1 No. 3 No. 4 No. 6

Average corrosion rate/(g · m z · r T 1 ) 8.118 5.42 6.328 6.449 4.528

Relative corrosion rate 1 0. 667 0. 779 0. 794 0. 558

2. 2 Corrosion-resistance of rebar embedded in con­crete cube

In order to make the experimental condition closer to the in-situ service condition, environment simulation

technique was adopted in the study. The mixed salt concrete cubes were prepared according to A S T M G109. Sodium chloride solution with different concen­trations was respectively sprayed to the concrete cube.

50 Journal of Iron and Steel Research , International Vol . 19

No.O No.l No.3 No.4 No.6 No.O No.l No.3 No.4 No.6 Tested rebar number

Fig. 1 Average corrosion rate of tested rebar ( a ) and relative corrosion rate of tested rebar (b )

T h e degree of corrosion was measured as gravimetric loss in mass of the tested rebar and crack width of concrete cube. T h e resul ts are shown in Fig. 2 ( a ) and ( b ) .

T h e resul ts shown in Fig. 2 (a) and (b ) indicate that there is no obvious difference in mass loss of re­bar and crack width of cube for the cube without the

mixed salt. But with the increasing mixed sa l t , the mass loss of the tested rebar is increasing. T h e mass loss of carbon steel is the most serious. The sequence of mass loss of the samples is No. l > N o . 4 > N o . 6. And the sequence of the crack width of concrete cube is No. 1 > No. 4 > No. 6. It shows the same trend between the above mentioned results .

Tested rebar number Mixed salt percent of concrete cube/%

Fig. 2 Mass loss rate of different rebar ( a ) and crevice width of different concrete cubes ( b )

2 . 3 Corrosion-resistance of rebar exposure near seashore The naked rebar samples were respectively placed

in typical coastal areas of China, such as Bo Sea Area ( Q i n g d a o ) , Changjiang River Delta (Zhoushan) and Pearl River Delta (Wanning). The exposure time is re­spectively 0. 5 , 1 , 2 and 4 years so as to verify the re­liability of the labora tory ' s research. T h e resul ts of 0. 5 and 1 year presented in Fig. 3 ( a ) and ( b ) indi­cate that the corrosion-resistance of the developed rebar prefers to that of carbon steel rebar.

In addit ion, Fig. 3 (a) and (b ) provide informa­tion that there is the same t rend as the resul ts ob­tained from the laboratory study. The corrosion re­sistance of No. 1, No. 3 , No. 4 , and No. 6 steel is higher than that of carbon steel. Comparing the av­erage corrosion rate in Zhoushan and Wann ing , the

test in Wanning is similar to the accelerated corro­sion test because of its high chloride ion level. The re­sults show that the corrosion resistance degree of the tested samples is No. 6 > N o . 4 > N o . l > N o . 3 , which is the same as the result of the laboratories evaluation. Table 5 provides additional information that the rel­ative corrosion rates of No. 1 , No. 4 , and No. 6 steel are less than 5 0 % of the carbon steel.

T h e resul ts of the concrete cube mixed wi th salt exposure in Qingdao experiment station for 0. 5 years are listed in Table 6 and shown in Fig. 4.

Fig. 4 (a) shows that the sequence of the corrosion resistance of the rebar is as follows: No. 6 > No. 4 > No. l > N o . 0. Fig. 4 ( b ) shows the crack width of concrete cube comparison between the developed steel and the carbon steel in the marine environment con-

Issue 12 Comprehensive Properties of 400 M P a Grade Corrosion-Resistant Rebar 51

No.l No.3 No.4 No.6 Tested rebar number

No.O No.l No.3 No.4 No.6 Test steel number

No.O

Fig. 3 Average corrosion rate of samples exposure in Zhoushan ( a ) and in Wanning ( b )

Table 5 Relative corrosion rate of tested steel

exposure of 1 year in Wanning

Sample number No. 1 No. 3 No. 4 No. 6 No. 0

Relative corrosion rate 0. 443 0. 571 0. 425 0.355 1

taining salt of 2. 5%. T h e data both in the simulated marine environment and the actual marine environ­ment have good correlation. It indicates that envi­ronment simulation technique is reliable.

In the three kinds of tes ts mentioned above, the

Table 6 Results of concrete test piece mixed with salt

No. 0 No. 1 No. 4 No. 6

Crack width/mm (near seashore) 0. 177 0. 076 0. 019 0. 024

Crack width/mm (in simulated environment) 0. 165 0. 072 0. 037 0. 061

Corrosion area of rebar/ % 60 36. 67 30 11. 67

Q 10

No.O No.l No.4 No.6 No.O Tested rebar number

A Near seashore • In simulated environment

No.l No.4 No.6

Fig. 4 Corrosion area percentage of rebar near seashore ( a ) and comparison of crack width of

concrete cube near seashore and in simulated marine environment ( b )

corrosion resistance degree of the rebar shows the same trend. The corrosion resistance of the developed re­bar is be t te r than that of the carbon steel rebar. T h e r e are some changes about the corrosion resist­ance sequence of No. 4 steel. T h e different speeds of phospha te film formation in the solution and in the concrete cube would be the influence factor.

3 Weldability of Corrosion-Resistant Rebar

Nine kinds of welding methods were used for test ing the weldabil i ty of the corrosion-resistant re­bar in China Nat ional Construct ion Steel Quality Su­pervision and T e s t Center . Welding pat tern tes ts in­

clude flash but t welding, lap welding, groove weld­ing , weld slot for lap welding, narrow interval welding, electroslag pressure welding, gas pressure welding and submerged arc welding. The resul ts are all qualified.

4 Mechanical Connection of Corrosion-Resist­ant Rebar

Mechanical connection of rebar is widely used in construction. In order to check the performance of the corrosion-resistant rebar , the joint connection tes ts were carried out according to the rules of the industrial s tandard " general technical specification

52 · Journal of Iron and Steel Research , International Vol . 19

for mechanical splicing of b a r s " —JGJ 107 2003. T h e dimension of the tested rebar is 20 mm. Rolled str ip rib s t raight thread connection is used in the t e s t , which is the main connection method at work­place in China. Joint ing is produced in China Acade­my of Building Research. By tes t ing , the connec­t ions are all qualified. It indicates that the ordinary rolled strip rib straight thread connection can be used in the corrosion-resistant rebar connection.

5 Conclusions 1) Developed 400 MPa grade corrosion-resistant

rebar has comprehensively excellent performance. The tensile and bending propert ies completely satisfy GB1499—2007 requirements .

2) In the different simulation conditions with chloride ion , 400 MPa grade corrosion-resistant re­bar has bet ter corrosion resistant performance than that of the carbon steel. T h e corrosion resistance of steel containing Cu-Ni-Cr element is 2 t imes of that of the carbon steel.

3) T h r o u g h 9 kinds of welding methods t e s t , the weldability of 400 MPa grade corrosion-resistant rebar is good.

4) T h r o u g h the rolling str ip rib s t raight screw joint t e s t , 400 MPa grade corrosion-resistant rebar has good applicability for the mechanical connection which can meet the construction requirements .

The authors hope to express gratitude to Mr. Sun Wei , Mr. Wan Weiguo of Maanshan Iron and Steel Co Ltd and Mr. Zhu Jianguo , Mrs. Chen

Jie of MCC building research institute and Mr. Wang Xiaofeng of China Academy of Building Research.

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