土木工程外文文献及翻译Word文档下载推荐.docx

1、Rebecca Gravina 3（1 School of the Built En viro nment, Heriot Watt Uni versity,） Edi nburgh, EH14 4AS, UK（2 VicRoads, Melbourne, VIC,） Australia（3 School of Civil, Environmental and Chemical Engineering, RMIT） Un iversity, Melbourne, VIC, 3000, AustraliaDavid W. LawEmail:D.W 丄awhw.ac.ukReceived: 14

2、Ja nuary 2010 Accepted:AbstractThis paper reports the results of a research project compari ng the effect of surface crack width and degree of corrosi on on the bond strength of confined and unconfined deformed 12 and 16 mnmild steel rei nforci ng bars. The corrosi on was in duced by chloride con ta

3、m in ati on of the con crete and an applied DC curre nt. The prin cipal parameters inv estigated were confin eme nt of the rein forceme nt, the cover depth, bar diameter, degree of corrosi on and the surface crack width. The results in dicated that pote ntial relatio nship betwee n the crack width a

4、nd the bond stre ngth. The results also showed an in crease in bond stre ngth at the point where in itial surface crack ing was observed for bars with confining stirrups. No such in crease was observed with unconfined specime ns. Keywords: bond ;corrosi on ; rebar ; cover ; crack1IntroductionThe cor

5、rosion of steel reinforcement is a major cause of the deterioration of reinforced concrete structures throughout the world. In uncorroded structures the bond between the steel reinforcement and the concrete ensures that reinforced concrete acts in a composite manner. However, when corrosion of the s

6、teel occurs this composite performance is adversely affected. This is due to the formation of corrosion products on the steel surface, which affect the bond between the steel and the concrete.The deterioration of reinforced concrete is characterized by a general or localized loss of section on the r

7、einforcing bars and the formation of expansive corrosion products. This deterioration can affect structures in a number of ways; the production of expansive products creates tensile stresses within the concrete, which can result in cracking and spalling of the concrete cover. This cracking can lead

8、to accelerated ingress of the aggressive agents causing further corrosion. It can also result in a loss of strength and stiffness of the concrete cover. The corrosion products can also affect the bond strength between the concrete and the reinforcing steel. Finally the corrosion reduces the cross se

9、ction of the reinforcing steel, which can affect the ductility of the steel and the load bearing capacity, which can ultimately impact upon the serviceability of the structure and the structural capacity 12, 25.Previous research has investigated the impact of corrosion onbond 2 5, 7, 12, 20, 23 25,

10、27, 29, with a number of models being proposed 4, 6, 9, 10, 18, 19, 24, 29. The majority of this research has focused on the relationship between the level of corrosion （mass loss of steel） or the current density degree （corrosion current applied in accelerated testing） and crack width, or on the re

11、lationship between bond strength and level of corrosion. Other research has investigated the mechanical behaviour of corroded steel 1, 11 and the friction characteristics 13. However, little research has focused on the relationship between crack width and bond 23, 26, 28, a parameter that can be mea

12、sured with relative ease on actual structures.The corrosion of the reinforcing steel results in the formation of iron oxides which occupy a larger volume than that of the parent metal. This expansion creates tensile stresses within the surrounding concrete, eventually leading to cracking of the cove

13、r concrete. Once cracking occurs there is a loss of confining force from the concrete. This suggests that the loss of bond capacity could be related to the longitudinal crack width 12. However, the use of confinement within the concrete can counteract this loss of bond capacity to a certain degree.

14、Research to date has primarily involved specimens with confinement. This paper reports a study comparing the loss of bond of specimens with and without confinement.2Experimental investigation2.1SpecimensBeam end specimens 28 were selected for this study. This type of eccentric pull out or beam end t

15、ype specimen uses a bonded length representative of the anchorage zone of a typical simply supported beam. Specimens of rectangular cross section were cast with a longitudinal reinforcing bar in each corner, Fig. 1. An 80 mmplastic tube was provided at the bar underneath the transverse reaction to e

16、nsure that the bond strength was not enhanced due to a （transverse） compressive force acting on the bar over this length.mndiameter with cover of three timesbar diameter were inv estigated. Duplicate sets of confined and unconfined specime ns were tested. The confined specime ns had three sets of 6

17、mm sta ini ess steel stirrups equally spaced from the plastic tube, at 75 mm cen tres.This represe nts four groups of specime ns with a comb in ati on of differe nt bar diameter and with/without confin eme nt. The specime ns were selected in order to in vestigate the in flue nce of bar size, confin

18、eme nt and crack width on bond stre ngth.2.2MaterialsThe mix desig n is show n. Table 1. The ceme nt was Type I Portia nd ceme nt, the aggregate was basalt with specific gravity 2.99. The coarse and fine aggregate were prepared in accorda nee with AS 1141-2000. Mixing was undertaken in accordanee wi

19、th AS 1012.2-1994.Specimens were cured for 28 days under wet hessian before testing.Table 1 Con crete mix desig nMateri alCeme ntw/cSand10 mm washed aggrega te7 mm washed aggrega teSaltSlumpQua nti381 kg0.4517kg463 kg18.84k140 25ty/m39/m3 Jg/m3mmIn order to compare bond stre ngth for the differe nt

20、con cretecompressive strengths, Eq. 1 is used to normalize bond strength fornon-corroded specime ns as has bee n used by other researcher 8.（1）where is the bond strength for grade 40 concrete, t exptl is the experime ntal bond stre ngth and f c is the experime ntal compressive stre ngth.The tensile

21、strength of the 12 and 16 mm steel bars wasnomin ally 500 MPa, which equates to a failure load of 56.5 and100.5 kN, respectively.2.3Experime nt methodologyAccelerated corrosi on has bee n used by a nu mber of authors to replicate the corrosion of the reinforcing steel happening in the natural en vir

22、o nmen t 2, 3, 5, 6, 10, 18, 20, 24, 27, 28, 30. Thesehave involved experiments using impressed currents or artificial weathering with wet/dry cycles and elevated temperatures to reduce the time until corrosion, while maintaining deterioration mechanisms representative of natural exposure. Studies u

23、sing impressed currents have used curre nt den sities betwee n 100 卩 A/cm2 and 500 mA/cm220. Research has suggested that current densities up to200 卩 A/cm2 result in similar stresses duri ng the early stages of corrosion when compared to 100 卩 A/cm2 21. As such an applied curre nt den sity of 200 卩

24、A/cm2 was selected for thisstudy representative of the lower end of the spectrum of such current densities adopted in previous research. However, caution should be applied when accelerating the corrosion using impressed current as the acceleration process does not exactly replicate the mechanisms in

25、volved in actual structures. In accelerated tests the pits are not allowed to progress naturally, and there may be a more uniform corrosion on the surface. Also the rate of corrosion may impact on the corrosion products, such that different oxidation state products may be formed, which could impact

26、on bond.The steel bars served as the anode and four mild steel metal plates were fixed on the surface to serve as cathodes. Sponges （sprayed with salt water） were placed between the metal plates and concrete to provide an adequate contact, Fig. 2.Fig. 2 Accelerated corrosi on systemWherithe required

27、 crack width was achieved for a particular bar, the impressed curre nt was disc ontinued for that bar. The specime n was removed for pullout testi ng whe n all four locati ons exhibited the target crack width. Average surface crack widths of 0.05, 0.5, 1 and 1.5 mm were adopted as the target crack w

28、idths. The surface crack width was measured at 20 mmintervals along the length of thebar, beg inning 20 mmfrom the end of the （plastic tube） bond breaker using an optical microscope. The level of accuracy in the measurements was 0.02 mm.Measurements of crack width were taken on the surface no rmal t

29、o the bar direct ion regardless of the actual crack orientation at that location.Bond stre ngth tests were con ducted by means of a hand operated hydraulic jack and a custom-built test rig as show n in Fig. 3. Theloadi ng scheme is illustrated in Fig. 4. A plastic tube of len gth80 mm was provided a

30、t the end of the con crete sect ion undern eath the tran sverse reacti on to en sure that the bond stre ngth was not enhan ced by the reactive （compressive） force （acti ng no rmal to thebar）. The specimen was positioned so that an axial force was applied to the bar being tested. The restraints were

31、sufficiently rigid toensure minimal rotation or twisting of the specimen during loading.3Experimental results and discussion3.1 Visual inspectionFollowing the accelerated corrosion phase each specimen was visually inspected for the location of cracks, mean crack width and maximum crack width （Sect. 2.3）.While each specimen had a mean target crack width for each bar, variations in this crack width were observed prior to pull out testing. This is due to corrosion and cracking being a dynamic process with cracks propagating at different rates. Thus, while individual bars w