While the durability of concrete structures is greatly influenced by many factors, previous studies typically considered only a single durability deterioration factor. In addition, these studies mostly conducted their experiments inside the laboratory, and it is extremely hard to find any case in which data were obtained from field inspection. Accordingly, this study proposed an Adaptive Neurofuzzy Inference System (ANFIS) algorithm that can estimate the carbonation depth of a reinforced concrete member, in which combined deterioration has been reflected based on the data obtained from field inspections of 9 buildings. The proposed ANFIS algorithm closely estimated the carbonation depths, and it is considered that, with further inspection data, a higher accuracy would be achieved. Thus, it is expected to be used very effectively for durability estimation of a building of which the inspection is performed periodically.
In reinforced concrete (RC) structures, the carbonation depth is a key deterioration factor to determine the durability of concrete structures [
Although the intended service life of an RC structure differs depending on its use, size, and so forth, it is often set to approximately 65 years in many international standards [
As previously mentioned, while the deterioration of an RC structure is influenced by various factors, it is practically impossible to consider all the factors. In this study, field inspections were performed to get the data such as the crack width, concrete compressive strength, chloride ion diffusion coefficient, and surface chloride ion concentration, and these were then considered as the input parameters of ANFIS.
Chloride attack is an important factor contributing to the deterioration of concrete durability. It accelerates the deterioration through a combined action with carbonation and has a particularly significant impact on the durability of structures exposed to a marine environment. The chloride ion concentration that can lead to corrosion of steel bars is called the critical chloride ion concentration. The chloride ion concentration (
The concrete compressive strength of an existing concrete structure is typically measured by the Schmidt hammer test [
Structural cracks in reinforced concrete structures have a significant impact not only on structural performance, but also on durability reduction. In addition, nonstructural cracks including surface finishing cracks accelerate the durability reduction of concrete as they facilitate the penetration of the carbon dioxide and chlorine ion from the concrete surface exposed to the outside air. Therefore, both structural cracks and nonstructural cracks can be considered as the factors contributing to durability reduction. Song et al. [
The aim of this study was to estimate the carbonation depth of a reinforced concrete member in which combined deterioration is reflected. In this study, therefore, detailed safety inspection on a total of 9 buildings has been performed to get the field data that are required for the estimation of the carbonation depth. Table
Field investigation data (Building 9, construction completion year: 1976).
Measurement point | Member type | Concrete compressive strength (MPa) | Concrete carbonation depth (mm) | Cover depth (mm) | Crack width (mm) |
---|---|---|---|---|---|
B9P1 | Column | 21.1 | 20.13 | 45 | — |
B9P2 | Column | 26.1 | 23.45 | 40 | Surface finishing crack |
B9P3 | Slab | 22.2 | 19.12 | 65 | — |
B9P4 | Beam | 20.7 | 32.73 | 60 | — |
B9P5 | Wall | 20.9 | 20.19 | 45 | — |
B9P6 | Wall | 21.3 | 30.61 | 25 | Surface finishing crack |
B9P7 | Slab | 25.6 | 22.46 | 25 | 0.1 |
B9P8 | Beam | 20.9 | 49.87 | 70 | — |
B9P9 | Beam | 23.0 | 14.62 | 70 | — |
B9P10 | Slab | 22.8 | 16.49 | 20 | — |
B9P11 | Beam | 21.3 | 30.80 | 65 | — |
B9P12 | Slab | 24.7 | 23.92 | 20 | — |
B9P13 | Beam | 19.9 | 23.99 | 60 | — |
B9P14 | Slab | 21.5 | 23.06 | 30 | — |
B9P15 | Beam | 21.5 | 26.46 | 30 | 0.1 |
B9P16 | Slab | 27.3 | 19.06 | 35 | Surface finishing crack |
B9P17 | Slab | 22.9 | 26.47 | 30 | — |
B9P18 | Beam | 20.5 | 40.20 | 75 | — |
B9P19 | Wall | 22.2 | 25.54 | 45 | Surface finishing crack |
B9P20 | Wall | 31.9 | 26.24 | 55 | — |
B9P21 | Wall | 29.7 | 22.71 | 25 | Surface finishing crack |
B9P22 | Wall | 28.3 | 29.94 | 45 | Surface finishing crack |
Measurement of chloride concentration (Building 9).
Location | Chloride ion concentration |
Chloride ion diffusion coefficient |
---|---|---|
Inside |
|
|
Surface to 10 mm | 0.22 | |
Outside | ||
Surface to 10 mm | 0.27 | |
10 to 20 mm | 0.24 | |
20 to 30 mm | 0.18 |
Field investigation data (Building 1, construction completion year: 1981).
Measurement point | Member type | Concrete compressive strength (MPa) | Concrete carbonation depth (mm) | Cover depth (mm) | Crack width (mm) |
---|---|---|---|---|---|
B1P1 | Beam | 18.6 | 24.18 | 86 | — |
B1P2 | Slab | 22.4 | 17.07 | 67 | — |
B1P3 | Wall | 32.6 | 9.44 | 50 | Finishing crack on surface |
B1P4 | Slab | 20.6 | 19.75 | 52 | — |
B1P5 | Beam | 17.7 | 8.87 | 67 | — |
B1P6 | Column | 29.5 | 14.33 | 67 | — |
B1P7 | Wall | 26.1 | 5.81 | 49 | — |
B1P8 | Column | 24.7 | 15.61 | 39 | — |
B1P9 | Slab | 23.8 | 9.98 | 57 | — |
B1P10 | Beam | 28.4 | 9.95 | 51 | — |
B1P11 | Slab | 28.6 | 5.62 | 32 | — |
B1P12 | Beam | 35.3 | 10.73 | 77 | — |
B1P13 | Wall | 36.6 | 5.06 | 58 | — |
B1P14 | Wall | 30.2 | 5.04 | 33 | 0.1 |
B1P15 | Wall | 37.7 | 5.39 | 26 | — |
B1P16 | Wall | 25.9 | 29.95 | 42 | 0.1 |
B1P17 | Slab | 26.1 | 10.10 | 49 | Finishing crack on surface |
B1P18 | Beam | 34.1 | 10.14 | 78 | Finishing crack on surface |
B1P19 | Slab | 37.4 | 10.85 | 55 | Finishing crack on surface |
B1P20 | Beam | 36.5 | 18.66 | 65 | Finishing crack on surface |
Field investigation data (Building 2, construction completion year: 1981).
Measurement point | Member type | Concrete compressive strength (MPa) | Concrete carbonation depth (mm) | Cover depth (mm) | Crack width (mm) |
---|---|---|---|---|---|
B2P1 | Slab | 27.1 | 7.04 | 43 | — |
B2P2 | Slab | 32.9 | 4.55 | 40 | — |
B2P3 | Beam | 24.4 | 8.73 | 65 | — |
B2P4 | Slab | 23.1 | 8.95 | 40 | — |
B2P5 | Wall | 31.2 | 10.50 | 75 | — |
B2P6 | Wall | 33.2 | 12.88 | 55 | — |
B2P7 | Column | 23.2 | 11.52 | 40 | Surface finishing crack |
B2P8 | Column | 22.9 | 9.58 | 60 | — |
B2P9 | Beam | 26.0 | 8.93 | 85 | — |
B2P10 | Slab | 20.7 | 7.59 | 35 | — |
B2P11 | Beam | 26.8 | 9.50 | 60 | Surface finishing crack |
B2P12 | Slab | 28.2 | 18.89 | 35 | — |
B2P13 | Beam | 27.1 | 10.87 | 67 | Surface finishing crack |
B2P14 | Slab | 28.0 | 18.55 | 40 | Surface finishing crack |
B2P15 | Beam | 24.7 | 6.33 | 45 | Surface finishing crack |
B2P16 | Slab | 24.8 | 8.79 | 45 | — |
B2P17 | Wall | 21.3 | 4.91 | 100 | — |
B2P18 | Wall | 33.0 | 7.71 | 45 | — |
B2P19 | Wall | 24.3 | 7.62 | 25 | — |
B2P20 | Wall | 31.4 | 10.96 | 40 | 0.1 |
Field investigation data (Building 3, construction completion year: 1981).
Measurement point | Member type | Concrete compressive strength (MPa) | Concrete carbonation depth (mm) | Cover depth (mm) | Crack width (mm) |
---|---|---|---|---|---|
B3P1 | Beam | 31.3 | 41.08 | 30 | — |
B3P2 | Slab | 29.9 | 34.74 | 25 | — |
B3P3 | Beam | 24.4 | 19.91 | 75 | — |
B3P4 | Beam | 24.5 | 41.3 | 55 | — |
B3P5 | Wall | 19.3 | 42.18 | 40 | — |
B3P6 | Wall | 26 | 29.49 | 40 | — |
B3P7 | Beam | 26 | 28.49 | 45 | Surface finishing crack |
B3P8 | Slab | 30.5 | 29.96 | 30 | — |
B3P9 | Slab | 29.3 | 9.62 | 40 | — |
B3P10 | Beam | 32.8 | 7.06 | 70 | — |
B3P11 | Slab | 25.6 | 11.26 | 30 | — |
B3P12 | Beam | 19.4 | 34.83 | 45 | — |
B3P13 | Wall | 22.5 | 38.34 | 30 | — |
B3P14 | Wall | 29.3 | 26.48 | 65 | — |
B3P15 | Wall | 20.2 | 32.06 | 75 | — |
B3P16 | Wall | 27.8 | 14.72 | 35 | Surface finishing crack |
B3P17 | Beam | 25.4 | 55.9 | 30 | — |
B3P18 | Beam | 25.5 | 51.41 | 40 | — |
B3P19 | Slab | 18.9 | 49.74 | 20 | — |
B3P20 | Slab | 25.2 | 44.05 | 30 | — |
Field investigation data (Building 4, construction completion year: 1984).
Measurement point | Member type | Concrete compressive strength (MPa) | Concrete carbonation depth (mm) | Cover depth (mm) | Crack width (mm) |
---|---|---|---|---|---|
B4P1 | Column | 32.2 | 20.35 | 35 | — |
B4P2 | Column | 29.7 | 23.56 | 35 | — |
B4P3 | Beam | 29 | 17.9 | 20 | — |
B4P4 | Beam | 26.9 | 21.35 | 60 | — |
B4P5 | Beam | 31.7 | 12.89 | 70 | — |
B4P6 | Beam | 29.4 | 18.18 | 30 | — |
B4P7 | Slab | 26.5 | 71.06 | 44 | 0.2 |
B4P8 | Slab | 29.8 | 16.69 | 35 | — |
B4P9 | Beam | 26.6 | 45.91 | 60 | 0.5 |
B4P10 | Slab | 31.2 | 26.82 | 50 | — |
B4P11 | Beam | 26.5 | 28.49 | 20 | — |
B4P12 | Slab | 27.1 | 26.29 | 40 | — |
B4P13 | Beam | 24.8 | 22.74 | 30 | Surface finishing crack |
B4P14 | Beam | 30.9 | 19.09 | 35 | Surface finishing crack |
B4P15 | Slab | 20.5 | 25.74 | 35 | Surface finishing crack |
B4P16 | Slab | 18.6 | 46.42 | 20 | Surface finishing crack |
B4P17 | Wall | 34.3 | 15.9 | 90 | — |
B4P18 | Wall | 28.9 | 14.6 | 55 | — |
B4P19 | Wall | 32 | 11.21 | 50 | — |
B4P20 | Wall | 34.4 | 15.22 | 50 | — |
Field investigation data (Building 5, construction completion year: 1983).
Measurement point | Member type | Concrete compressive strength (MPa) | Concrete carbonation depth (mm) | Cover depth (mm) | Crack width (mm) |
---|---|---|---|---|---|
B5P1 | Wall | 25.7 | 14.47 | 100 | — |
B5P2 | Wall | 30.9 | 18.39 | 60 | — |
B5P3 | Beam | 27.9 | 12.74 | 55 | — |
B5P4 | Column | 30.7 | 15.37 | 40 | — |
B5P5 | Slab | 34.0 | 8.77 | 25 | — |
B5P6 | Beam | 30.7 | 20.91 | 70 | — |
B5P7 | Column | 25.8 | 9.76 | 50 | — |
B5P8 | Slab | 34.0 | 21.46 | 35 | — |
B5P9 | Beam | 31.4 | 10.17 | 45 | — |
B5P10 | Column | 28.4 | 15.57 | 45 | — |
B5P11 | Slab | 25.4 | 20.04 | 25 | — |
B5P12 | Beam | 30.6 | 17.82 | 45 | — |
B5P13 | Beam | 27.7 | 40.23 | 50 | — |
B5P14 | Slab | 23.2 | 37.25 | 30 | — |
B5P15 | Column | 31.5 | 17.92 | 60 | — |
B5P16 | Beam | 29.2 | 12.85 | 55 | — |
B5P17 | Column | 25.9 | 14.65 | 50 | Surface finishing crack |
B5P18 | Column | 32.8 | 52.01 | 70 | Surface finishing crack |
B5P19 | Column | 27.3 | 77.60 | 80 | — |
B5P20 | Beam | 33.9 | 10.17 | 75 | — |
B5P21 | Beam | 27.6 | 18.01 | 50 | — |
Field investigation data (Building 6, construction completion year: 1981).
Measurement point | Member type | Concrete compressive strength (MPa) | Concrete carbonation depth (mm) | Cover depth (mm) | Crack width (mm) |
---|---|---|---|---|---|
B6P1 | Wall | 22.1 | 25.82 | 60 | — |
B6P2 | Wall | 20.2 | 22.68 | 45 | — |
B6P3 | Slab | 25.0 | 17.20 | 55 | Surface finishing crack |
B6P4 | Beam | 27.9 | 13.72 | 45 | Surface finishing crack |
B6P5 | Beam | 30.3 | 17.24 | 60 | 0.1 |
B6P6 | Slab | 28.7 | 18.43 | 40 | 0.1 |
B6P7 | Slab | 22.4 | 11.70 | 35 | — |
B6P8 | Beam | 29.9 | 11.08 | 70 | — |
B6P9 | Beam | 28.4 | 15.87 | 50 | — |
B6P10 | Slab | 26.8 | 11.73 | 40 | — |
B6P11 | Column | 25.9 | 18.03 | 75 | — |
B6P12 | Column | 25.1 | 19.52 | 40 | — |
B6P13 | Slab | 22.9 | 12.98 | 40 | Surface finishing crack |
B6P14 | Beam | 28.6 | 12.50 | 70 | — |
B6P15 | Beam | 26.2 | 18.17 | 50 | Surface finishing crack |
B6P16 | Slab | 23.9 | 13.07 | 45 | Surface finishing crack |
B6P17 | Beam | 25.9 | 25.77 | 80 | — |
B6P18 | Beam | 26.5 | 21.92 | 90 | Surface finishing crack |
B6P19 | Slab | 23.1 | 19.53 | 45 | — |
B6P20 | Slab | 20.8 | 15.53 | 20 | — |
B6P21 | Wall | 20.6 | 13.58 | 50 | — |
B6P22 | Wall | 31.1 | 12.67 | 80 | — |
B6P23 | Wall | 27.8 | 13.26 | 95 | — |
B6P24 | Wall | 22.6 | 12.96 | 85 | — |
Field investigation data (Building 7, construction completion year: 1983).
Measurement point | Member type | Concrete compressive strength (MPa) | Concrete carbonation depth (mm) | Cover depth (mm) | Crack width (mm) |
---|---|---|---|---|---|
B7P1 | Slab | 25.2 | 7.69 | 35 | — |
B7P2 | Beam | 18.6 | 10.35 | 70 | — |
B7P3 | Slab | 25.5 | 11.78 | 40 | — |
B7P4 | Beam | 26.4 | 7.35 | 45 | — |
B7P5 | Beam | 31.4 | 11.36 | 55 | 0.1 |
B7P6 | Slab | 32.1 | 7.85 | 35 | — |
B7P7 | Column | 25.9 | 12.90 | 30 | — |
B7P8 | Column | 26.3 | 8.77 | 25 | — |
B7P9 | Beam | 25.1 | 11.98 | 55 | — |
B7P10 | Slab | 25.2 | 13.37 | 35 | — |
B7P11 | Beam | 26.0 | 7.82 | 35 | — |
B7P12 | Slab | 22.0 | 9.87 | 30 | — |
B7P13 | Slab | 20.0 | 12.31 | 25 | 0.1 |
B7P14 | Beam | 27.5 | 11.03 | 40 | — |
B7P15 | Slab | 19.9 | 8.02 | 35 | — |
B7P16 | Beam | 24.5 | 13.34 | 60 | — |
B7P17 | Wall | 19.7 | 17.89 | 45 | — |
B7P18 | Wall | 20.5 | 20.35 | 40 | 0.1 |
B7P19 | Wall | 24.4 | 18.41 | 30 | — |
B7P20 | Wall | 21.6 | 23.06 | 40 | 0.1 |
Field investigation data (Building 8, construction completion year: 1982).
Measurement point | Member type | Concrete compressive strength (MPa) | Concrete carbonation depth (mm) | Cover depth (mm) | Crack width (mm) |
---|---|---|---|---|---|
B8P1 | Column | 23.3 | 20.79 | 40 | — |
B8P2 | Column | 20.8 | 57.84 | 45 | — |
B8P3 | Beam | 20.8 | 41.53 | 40 | — |
B8P4 | Slab | 16.0 | 26.89 | 30 | — |
B8P5 | Wall | 33.5 | 11.36 | 85 | — |
B8P6 | Wall | 29.0 | 11.63 | 40 | — |
B8P7 | Slab | 29.0 | 22.84 | 25 | — |
B8P8 | Beam | 26.1 | 29.72 | 75 | — |
B8P9 | Beam | 22.4 | 16.29 | 20 | — |
B8P10 | Slab | 25.3 | 22.88 | 25 | 0.1 |
B8P11 | Beam | 23.1 | 43.93 | 40 | — |
B8P12 | Slab | 26.6 | 45.86 | 20 | — |
B8P13 | Beam | 27.4 | 16.62 | 60 | 0.1 |
B8P14 | Slab | 25.9 | 35.64 | 30 | — |
B8P15 | Beam | 31.4 | 13.83 | 40 | 0.2 |
B8P16 | Slab | 24.6 | 9.18 | 20 | Surface finishing crack |
B8P17 | Beam | 30.8 | 11.98 | 40 | 0.2 |
B8P18 | Slab | 26.8 | 21.00 | 20 | 0.1 |
B8P19 | Wall | 29.3 | 32.27 | 45 | — |
B8P20 | Wall | 25.6 | 69.13 | 70 | — |
B8P21 | Wall | 30.0 | 47.35 | 45 | — |
B8P22 | Wall | 28.4 | 38.69 | 55 | — |
Measurement of chloride concentration (Buildings 1–4).
Building 1 | ||
---|---|---|
Location | Chloride ion concentration |
Chloride ion diffusion coefficient |
|
||
Inside |
|
|
Surface to 10 mm | 0.27 | |
Outside | ||
Surface to 10 mm | 0.63 | |
10 to 20 mm | 0.15 | |
20 to 30 mm | 0.11 | |
|
||
Building 2 | ||
|
||
Location | Chloride ion concentration |
Chloride ion diffusion coefficient |
|
||
Inside |
|
|
Surface to 10 mm | 0.15 | |
Outside | ||
Surface to 10 mm | 0.18 | |
10 to 20 mm | 0.13 | |
20 to 30 mm | 0.13 | |
|
||
Building 3 | ||
|
||
Location | Chloride ion concentration |
Chloride ion diffusion coefficient |
|
||
Inside |
|
|
Surface to 10 mm | 0.47 | |
Outside | ||
Surface to 10 mm | 0.47 | |
10 to 20 mm | 0.38 | |
20 to 30 mm | 0.22 | |
|
||
Building 4 | ||
|
||
Location | Chloride ion concentration |
Chloride ion diffusion coefficient |
|
||
Inside |
|
|
Surface to 10 mm | 0.40 | |
Outside | ||
Surface to 10 mm | 0.63 | |
10 to 20 mm | 0.61 | |
20 to 30 mm | 0.49 |
Measurement of chloride concentration (Buildings 5–8).
Building 5 | ||
---|---|---|
Location | Chloride ion concentration |
Chloride ion diffusion coefficient |
|
||
Inside |
|
|
Surface to 10 mm | 0.24 | |
Outside | ||
Surface to 10 mm | 0.42 | |
10 to 20 mm | 0.33 | |
20 to 30 mm | 0.18 | |
|
||
Building 6 | ||
|
||
Location | Chloride ion concentration |
Chloride ion diffusion coefficient |
|
||
Inside |
|
|
Surface to 10 mm | 0.13 | |
Outside | ||
Surface to 10 mm | 0.38 | |
10 to 20 mm | 0.29 | |
20 to 30 mm | 0.27 | |
|
||
Building 7 | ||
|
||
Location | Chloride ion concentration |
Chloride ion diffusion coefficient |
|
||
Inside |
|
|
Surface to 10 mm | 1.38 | |
Outside | ||
Surface to 10 mm | 1.58 | |
10 to 20 mm | 0.72 | |
20 to 30 mm | 0.70 | |
|
||
Building 8 | ||
|
||
Location | Chloride ion concentration |
Chloride ion diffusion coefficient |
|
||
Inside |
|
|
Surface to 10 mm | 0.15 | |
Outside | ||
Surface to 10 mm | 0.22 | |
10 to 20 mm | 0.15 | |
20 to 30 mm | 0.11 |
In the design phase, KCI [
Comparison between measured and estimated carbonation depths.
ANFIS is a technique used for optimizing premise parameters and consequent parameters by introducing a training algorithm into Sugeno fuzzy inference system [
ANFIS structure.
In Figure
Bell-shaped fuzzy set.
Fuzzy sets of input parameters.
Initial carbonation velocity coefficient
Surface chloride ion content
Chloride ion diffusion coefficient
Concrete compressive strength
Crack width
Time
In Figure
In Figure
In Figure
In Figure
The coefficient that affects the shape of the fuzzy set, the premise parameter defined in Layer 1, was determined by referring to the inspection criteria presented by the Korea Infrastructure Safety & Technology Corporation [
Fuzzy sets of input parameters after training.
Initial carbonation velocity coefficient
Surface chloride ion content
Chloride ion diffusion coefficient
Concrete compressive strength
Crack width
Time
As shown in Figure
Location of target buildings in South Korea.
ANFIS results for trained data.
Building 1 (construction completion year: 1981)
Building 2 (construction completion year: 1981)
Building 3 (construction completion year: 1981)
Building 4 (construction completion year: 1984)
Building 5 (construction completion year: 1983)
Building 6 (construction completion year: 1981)
Building 7 (construction completion year: 1983)
Building 8 (construction completion year: 1982)
ANFIS results with respect to input parameters.
Concrete compressive strength
Crack width
Surface chloride content
Chloride ion diffusion coefficient
Among the 9 buildings investigated in this study, Building 9 was not used in training and was used to verify the accuracy of the ANFIS algorithm in estimating the carbonation depths at which the combined deterioration is reflected. As shown in Table
ANFIS result for Building 9 (construction completion year: 1976).
In this study, detailed safety inspection on a total of 189 spots of 9 buildings has been performed to get the field data that are required for the estimation of the carbonation depth. The ANFIS algorithm was proposed to estimate the carbonation depths of the buildings exposed to the actual environment, in which combined deterioration is reflected. From this study, the following conclusions were drawn: Although a variety of factors affect the concrete carbonation, it is practically impossible to consider all factors in this study. Therefore, the carbonation velocity coefficient, surface chloride ion concentration, chloride ion diffusion coefficient, concrete compressive strength, and crack width were used as the input parameters of the ANFIS algorithm. The optimized ANFIS rules were derived by training the inspection data of 8 of the 9 buildings. With the optimized ANFIS algorithm, the carbonation depths of these 8 buildings were reevaluated, and the result showed that the proposed model well reflected the combined effects of the surface chloride ion concentration, chloride ion diffusion coefficient, concrete compressive strength, and crack width. The analysis results also indicate that the finishing status of concrete surface shall be considered as an influencing factor for the estimation of the carbonation depths. In addition, the inspection data of Building 9 which were not used in training were used to verify the accuracy of the ANFIS algorithm, and the verification results showed that the proposed model provided relatively good accuracy compared to the carbonation depth estimation method presented by the Korea Concrete Institute and the Japan Society of Civil Engineers. The accuracy of the proposed ANFIS algorithm in this study for estimating carbonation depth is due to consideration on the combined deterioration, and as more inspection data are obtained, it is expected to be used very effectively in a building of which the inspection is performed periodically.
See Tables
The authors declare that they have no competing interests.
This work was supported by a Research Project, “Development of Remaining Service Life Evaluation Model for Substation Buildings Considering Combined Deterioration,” funded by Korea Electric Power Research Institute (KEPRI).