Types of defects

At the top level of the proposed classification system of RC railway slab span defects there are six basic defect types:

• Contamination – Dirtiness or not designed plant vegetation;

• Deformation – Geometry changes incompatible with the project, with changes of mutual distances of structure element points;

• Deterioration – Physical and/or chemical changes of structural features against designed values;

• Discontinuity – Inconsistent with a project break of material continuity;

• Displacement – Change (or restriction) of location of a structure or its part incompatible with the project but without its deformation;

• Loss of material – Decrease of designed amount of structure material.

3.3.1 Contamination

In case of concrete and protection the contamination is distinguished into the inorganic (aggressive and neutral) and the organic (penetrating and superficial) defect classes. An example of leaching effect is presented in Fig. 3-2. Products of this degradation can be observed also on the supports. Contamination classes are distinguishable at the chemical analysis level.

Fig. 3-2 Example of contamination of concrete (photographed by the Author)

Another example of contamination defect is presented in Fig. 3-3. The neutral steel corrosion products (the rust) are flowing down making the concrete slab surface stained.

Fig. 3-3 Example of neutral contamination of concrete (photographed by the Author)

Contaminations in terms of the load capacity assessment play the secondary role as an indicator of possible internal defects or material destruction for a further testing. For example the stained concrete surface indicates the corrosion of rebars which may mean some loss of

material. Many bridges, especially closely situated to the places where people live, are

“decorated” with various “paintings”, commonly called “graffiti”. This defect, considered as a neutral inorganic contamination of concrete, does not influence the load capacity, but the aesthetics of the bridge is affected. It is very difficult to struggle with this phenomenon, especially when these defects occur at night. Fig. 3-4 presents an example of a reinforced concrete railway span with this type of defect. To control this phenomenon some local authorities allows young people to paint some part of bridges, i.e. supports.

Fig. 3-4 Example of neutral inorganic contamination (photograph courtesy of Jerzy Cząstkiewicz, PKP)

3.3.2 Deformation

This defect type is prescribed for the concrete and the protection components of RC concrete and is distinguished into the following categories: deflection (caused by bending forces), slip (caused by shearing forces) and swell (related to the spatial increase of the volume).

Fig. 3-5 Example of deformation: deflection (photograph courtesy of Zygmunt Kubiak, PKP) f

In Fig. 3-5 an example of deformation (with exposed span deflection f) of railway slab span is presented. Probably this defect occurred as a consequence of construction errors. The considered span structures and their high rigidities as well as relatively short span lengths make this defect only theoretical case. Even if deformation has occurred, it is usually caused by construction errors. For this reason this defect has been excluded from the further research.

3.3.3 Deterioration

This defect type has been distinguished regarding the reinforced concrete components.

Fig. 3-6 Example of concrete deterioration: permeability increase (photographed by the Author)

For the concrete and protection (kind) several class defects have been attributed and distinguished by the categories (modification of chemical and physical features). Defect classes of reinforcement are considered as a single (modification of physical features) category. In Fig. 3-6 an example of concrete deterioration (permeability increase) is presented.

Fig. 3-7 Example of concrete deterioration (permeability increase) with coexisting with contamination and discontinuity defects (photographed by the Author)

A common situation during bridge service-life is the coexistence of various defects. In Fig.

3-7 an example of concrete permeability increase accompanied by cracks and contamination is presented. The proposed uniform multi-level defect classification system allows describing

any defect combinations. This defect type has a special meaning in terms of the load capacity assessment. The strength parameters of concrete and reinforcing steel such as strength as well as elastic modulus reduction are the most important features regarding the deterioration. Other classes of this defect can be considered as indicator of other property modifications.

For instance calcium hydroxide reduction of concrete can be translated to the strength reduction. The pH factor reduction in concrete is a suitable indicator of corrosion likelihood.

3.3.4 Discontinuity

Discontinuity has been divided into the following defect categories: crack (discontinuity of material perpendicular to the element surface covering a part of the cross-section), fracture (discontinuity of material perpendicular to the element surface occurred at the whole cross- section, dividing it into separate parts) and delamination (discontinuity of material parallel to the element surface). This defect type has been attributed to concrete (crack and delamination only), protection and reinforcement (crack and fracture only). Discontinuity is distinguished by relation to the main force direction in structure element: irregular, longitudinal, perpendicular and skew. An example of the longitudinal crack is presented in Fig. 3-8.

Concerning the considered span structures bending is the main internal interaction.

Perpendicular cracks in concrete occur in the tensile zone. For this reason this defect is important regarding the corrosion risk only. In case of the irregular cracks such as crazing, it can be translated into the concrete strength reduction. Delamination of concrete can be considered as loss of material.

Fig. 3-8 Example of discontinuity: longitudinal crack in concrete (photographed by the Author)

Fracture of concrete has been considered as a theoretical case only. This discontinuity category occurred to concrete slab spans was not observed by the Author and no comment on this defect category was found in the available literature as well. Sometimes discontinuities

occur in reinforcement. In case of fracture this defect can be interpreted as loss of material of 100% intensity. In Fig. 3-9 an example of the fracture of stirrup is presented.

Fig. 3-9 Example of discontinuity: fracture of the stirrup (photograph courtesy of Jerzy Cząstkiewicz, PKP)

3.3.5 Displacement

This defect type (Fig. 3-10 and Fig. 3-11) is prescribed for concrete component only. At the deeper level displacement is distinguished into the following categories: excessive and limited.

In both cases the rotation and translation has been considered.

Fig. 3-10 Example of limited displacement: translation (photograph courtesy of Jerzy Cząstkiewicz, PKP)

Both defects are accompanied by other defects like loss of concrete and stirrups (Fig. 3-10) and penetrating organic contamination (Fig. 3-11). Coexistence of various defects is a typical situation during bridge service life.

No space between the spans

Fig. 3-11 Example of limited displacement (translation) defects coexisting with contaminations – penetrating organic and neutral inorganic (photographed by the Author)

3.3.6 Loss of material

Loss of material has been prescribed for all of the RC components (concrete, protection and reinforcement). At the lower level (category of defect) of this system only concrete and reinforcement are divided into the more detailed defect categories like honeycomb, spalling and split (concrete) and also superficial and pitting loss of reinforcement. Fig. 3-12 presents a common situation during the bridge service life. At the same place the following defects occurred: loss of concrete, loss of reinforcement, deterioration of concrete and even superficial organic contamination of concrete.

Fig. 3-12 Example of loss of concrete and protection (photograph courtesy of Jerzy Cząstkiewicz, PKP)

The developed defect classification allows a precise identification. In Fig. 3-13 another example of loss of concrete with symptoms of reinforcement corrosion is presented.

No space between the span and

abutment

Fig. 3-13 Example of loss of concrete (photographed by the Author)