安藤ハザマ研究年報 Vol.8 2020
報 告Relationship between crack width and rebar corrosion
volume in the electro galvanic corrosion experiment andin the actual structure
電食試験と実構造物の鉄筋腐食量とひび割れ幅の関係
峰沢ジョージヴゥルペ George Vulpe MINESAWA *1
室山拓生 Takuo MUROYAMA *1・ 三反畑勇 Isamu SANDANBATA *1

研究の目的
Technologies for deterioration assessment of RC structures corrosion degradation are being developed, but
the difficulty of sampling corrosion data and the variability associated with RC degradation had hampered
the progress. In the study, the detailed survey of surface crack and corrosion surveys of the RC slab samples
extracted from the deck of a marine piers and the results of electro galvanic corrosion experiments on RCmembers were compared. At first the specimen surfaces cracking condition was visually evaluated and thenthe degree of internal corrosion of the reinforcement was quantitatively assessed.

研究の概要
RC specimens with a single rebar were used for the RC member electro galvanic accelerated corrosion test.
Two types of reinforcing bars (D16 / D25) and two concrete cover thicknesses (30 mm and 40 mm) were usedfor comparison and identification of the parameter’s effect. In the experiment, the cracking occurrence timeand galvanic current values were monitored while the crack width distribution was measured every 10 mmalong the surface crack. After the crack inspection, the RC blocks were cut into blocks 100 mm in length andthe amount of rebar corrosion was determined for each block. The experimental maximum crack width wasunder 0.55 mm, while large variability is recorded along the crack and even between the specimens under
the same conditions. The relationship between the crack width and the amount of corrosion shows large
variability, blocks with large corrosion show tendency to develop larger cracks.
Investigation and survey of the actual RC marine pier deck structure was conducted for the deck’s slab,
the underside rebar cover of the slab almost collapsed due to wave erosion and corrosion while upper surface
shows only minor cracking. The survey was conducted on the upper surface rebars of the deck slab. Onsite
crack measurement was conducted followed by the extraction of two sample RC blocks. Measurement ofchloride concentration distribution in concrete indicates the exceedance of NaCl threshold for corrosion
initialization including at deck’s upper surface bars location, therefore there is the possibility of cracks becaused by corrosion of the rebars. The top layer of the reinforcing bars just below the crack was extracted anda quantitative survey was conducted for the corrosion volume. As the result of investigation, the maximum
crack width was below 0.08 mm, which is very small value compared to the crack width on the underside
surface of the same deck. Since the crack developed along the upper reinforcing bar of the deck slab, it wasjudged that most of the confirmed cracks were related to corrosion of the rebars. The rebar cover thicknessof the samples ranged from 50 to 60 mm. The corrosion mass loss for the rebars below the crack was low,
between 0 to 0.54%, (0 to 0.17 mg/mm2), which is confirming the upper rebar corrosion onset.

結論

The results of the crack width and the amount ofreinforcing bar corrosion obtained by the galvanic
corrosion test and from the actual structure survey,
were compared with data reported in five previous
studies in relation to the crack width and thecorresponding rebar corrosion. Although only a limited
number of data were collected, the survey of the actual
structure’s samples were showing a similar tendency
between corrosion and cracking, and slightly lower
corrosion compared to previous studies. Corrosion
survey provides essential data for assessing structuraldegradation status.
*1 土木研究部

Fig.1 Relation between crack width and corrosion