ABSTRACT
This paper reports the degradation of concrete structures in Gunkan island in Japan. Visual inspections were performed and measurements of chloride ion, moisture content and relative humidity of concrete were measured. The chloride-ion content in concrete was detected by the EPMA.
It can be seen that the content of inherent chloride decrease with the age of construction (Fig. 1). Chloride content and years of construction (left). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig222_1.tif"/>
Fig. 2 shows the year of construction for each structure and the salt content regulations of JASS5 (Japanese Architectural Standard Specification 5). Year of construction structures and of salt content regulations of JASS5 (right). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig222_2.tif"/>
The average deterioration grades of Buildings No. 16–20 and No. 30, which were constructed before the enforcement of the salt content regulations in 1932, were very significant.
Table 1 shows the results of steel corrosion. It would be interesting that in spite of extreme content of chloride, some steel bars exhibited “Slight corrosion” and it can be seen that moisture content of concrete increase with the increase of relative humidity of cover concrete and its trend is along with the curvature of moisture sorption isotherm as shown in Fig. 3. The steel corrosion will be affected not only by chloride content but also moisture content and cover thickness of concrete. Appearance of Gunkan-Island. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/pho_1.jpg"/> Results of steel corrosion.
Research Point
Cover thickness (mm)
Average CI content (kg/m3)
CI content at steet bar (kg/m3)
R.H. in Concrete (%)
Moisture content in concrete (%)
Total volume by MIP*1 (mm3/g)
Condition of steel bar
30_O_1F_N1
40
10.8
16.08
86.0
-
84.0
Extreme corrosion
16_O_1F_N1
60
5.2
3.19
84.0
4.57
117.2
Slight corrosion
16_I_3F_N1
30
4.1
3.55
82.2
2.83
45.1
Slight corrosion
16_I_3F_M1
70
3.7
2.48
77.9
3.12
129.1
Sliglit corrosion
16_I_5F_N1
40
0.5
0.35
-
-
113.8
Sligtit corrosion
50_O_1F_T1
70
2.2
2.01
117.2
-
76.9
Slight corrosion
25_O_1F_M1
70
4.2
3.21
104.9
6.09
78.9
Sligiit corrosion
57_O_1F_M1
50
1.1
1.44
-
-
113.5
Slight corrosion
65N_O_1F_M1
40
14.1
10.23
98.9
7.62
135.1
Extreme corrosion
65N_O_1F_M2
90
3.1
3.05
96.7
8.90
129.6
Slight corrosion
65E_I_1F_M1
110
0.5
0.29
-
-
100.6
Slight corrosion
67_O_1F_M1
80
5.7
0.38
89.6
5.63
72.6
Slight corrosion
65S_I_1F_M
100
0.4
0.25
-
-
94.4
Slight corrosion
69_I_1F_T
90
0.3
0.21
-
-
130.5
Slight corosion
3_I_1F_M1
120
0.2
3.74
93.3
5.54
108.6
Slight corrosion
Relationships among the concrete interior relative humidity, mass water content and adsorption isotherms. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig222_3.tif"/>Following findings were obtained throughout researches:
The concrete of Gunkan Island has inherent chloride ion amounts exceeding critical level.
In spite of extreme chloride ion contents, some re-bars were sound.
The concretes in Gunkan Island created moisture sorption isotherm as the basic information which governed physical properties of concrete.
