PSI - Issue 13

Myroslava Hredil / Procedia Structural Integrity 13 (2018) 1657–1662 Author name / Structural Integrity Procedia 00 (2018) 000–000

1660

4

only concrete pores (defects) in the near-surface layer. Evidently, for low corrosion rates, corrosion products have much time to penetrate into concrete. Hence, the critical pressure required for the crack formation is attained if the amount of products is large. In addition, the influence of the creep in concrete should not be neglected, since it depends on time and promotes the relaxation of stresses in concrete. Under the real operating conditions, the corrosion rate of reinforcement is not high comparing to the laboratory tests. Thus, the tests carried out under moderate polarization regimes give, most likely, more adequate description of the processes running in reinforced concrete.

10

3

2

i , mA

1

1

0,1

0,01

0,1

1

10

100

 , hours

Fig. 3. Time dependencies of the anodic current at the voltage of 10 ( 1 ), 20 ( 2 ) and 40 V ( 3 ) in the accelerated corrosion tests.

Table 1. The results of the accelerated corrosion tests for the specimens R1.

Specimen number

U , V

t , h 864 241

q , C 659 604 497

m (Fe), g

1 2 3

10 20 40

0.191 0.175 0.144

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a d Fig. 4. The example of the specimen R1 after the accelerated corrosion test: a – concrete cover cracking; b – macrocrack in concrete cover filled with corrosion products; c – transversal fracture surface; d – specimen’s cross-section. Depth of corrosion products penetration into concrete matrix usually does not exceed several mm. However in the present study a deep penetration was revealed (Fig. 4 c ). Rust seems to be distributed not only in pores and other concrete defects but also in unbroken concrete matrix (Fig. 4 d ). Wong et al. (2010) explained this effect as following. The process of corrosion involves soluble species that can dissolve in the concrete pore solution and subsequently migrate or diffuse through the cement paste matrix away from the corroding steel. In the presence of chloride ions, the dissolution of iron is increased by formation of intermediary chlorocomplexes, i.e. ‘green-rusts’ described by Sagoe-Crentsil et al. (1993). These soluble complexes migrate away from the anodic sites, and subsequently break down in oxygen-rich areas, releasing the chlorides to transport more ferrous ions from the corroding steel. The mobility of these soluble species and subsequent precipitation in oxygen-rich areas results in the corrosion products being distributed within the porous cement paste. However the question remains open whether rust, present in significant amounts in concrete matrix, can create internal stresses which could influence the stress state in RC installations on the whole and facilitate their deterioration. b c