Masonry sewers with cement-bound joint mortar can show several defect types due to different causes. These types of defect include the partial or total loss of the joint mortar; bricks that are damaged, displaced or have fallen out of the bond; the breakdown of individual arch elements or the entire demolition of the constructional system (collapse).

In EN 13508-2, this spectrum of defect types is not covered completely. There is only a distinction …

According to [EN13508-2:2011], defective masonry is defined as follows: “Individual bricks or masonry units from the fabric of a brick or masonry drain or sewer have moved from their original position”.

Within the scope of the corresponding characterisation this narrow definition is broadened and, subject to the extent of the “displacement”, there is a distinction among:

• displaced (code specification A) – bricks or masonry units still present but …

The above-mentioned characterisations C (dropped invert) and D (collapse) do not apply for individual bricks, but for the brickwork bond. If, in the case of a missing brick, the additional characterisation cannot be done using the additional code specification A, the additional code specification B should be used. For specifications with regard to leak-tightness, the code for infiltration (BBF) or exfiltration (BBG) applies [DWAM149-2:2013].

(Table: …

Possible consequences of defective brickwork or masonry are:

• infiltration (BBF) / exfiltration (BBG) (leakage)
• reduction of the structural load-bearing capacity and leak-tightness
• deformation (BAA)
• increased operating expenditure
• break / collapse (BCA)
• blockage as a consequence of the collapse

(Image: Deformation of a cracked masonry sewer due to soil infiltration caused by leaks) (Image: Deformation of a cracked, masonry sewer due to soil infiltration …

(Image: Defective mortar - joint corrosion)

Concerning brickwork or masonry sewers, the defect classified as “missing mortar” is important and must be payed attention to. In EN 13508-2, that type of defect is defined as “all or part of the mortar from brickwork or masonry is missing”. A detailed characterisation inclusive of additional code specifications cannot be found in EN 13508-2.

Examples of the defect "missing mortar" are shown below.

The quantification of this defect is conducted by indicating the depth between the masonry surface and the mortar surface in mm (in). The location of the defect should be indicated [EN13508-2:2011].

In Germany, “missing mortar” shall not be recorded up to a depth of 5 mm. The client will decide on deviating tolerances” [DWAM149-2:2013].

(Table: Missing mortar – Partly missing)

(Table: Missing mortar – …

According to [DWAM149-2:2013], the following combinations of the type of surface damage and the cause of damage are not permitted:

• BAFJA - corrosion phenomena on the surface, cause of damage: mechanical
• BAFBB - spalling, cause of damage: chemical - general
• BAFBC - spalling, cause of damage: chemical - damage in the upper part of the pipe
• BAFBD - spalling, cause of damage: chemical - damage in the lower part of the pipe

In the following, descriptions of defects under consideration of their cause will be introduced in accordance with DIN EN 13508-2.

(Table: Surface damage in a concrete sewer – …

The same applies to the reinforcement, for which there are also three separate characterisations:

• Reinforcement visible (F)
• Reinforcement protruding (G)
• Reinforcement corroded (H) (picture)

It is recommended that the code specification H may only be used in the case of corrosion-related loss of fabric of the reinforcement.

(Table: Surface damage in a sewer made of reinforced concrete – Reinforcement visible and corroded)

(Image: Corrosion of the reinforcement in a large profile made of reinforced concrete)

The description of surface damage classified as “missing wall” (I) includes types of defect where entire pipe wall segments are missing due to chemical attacks. The chemical attack is the criterion according to which this description of damage is not classified into “missing parts” and the main code break / collapse.

The characterisation “corrosion products at the …

According to [EN13508-2:2011], there are two main causes of surface damage:

• Mechanical stress
• Chemical attack (corrosion)

The pipe materials used in sewer systems up to now are not all equally susceptible to corrosion. Vitrified clay pipes are generally corrosion-resistant, except for hydrofluoric acid. Particularly at risk are:

• cement-bound materials (concrete, reinforced concrete, asbestos cement, fibre cement, mortar) as well as
• metallic materials (…

Wear is defined as the progressing material abrasion from the surface of a solid body caused by tribological stresses in the form of contact- and relative movements of a solid, liquid, or gaseous counter body [Czich2010].

An overview of possible tribological stresses (types of wear) that can occur during the service life of drains and sewers is illustrated in the table.

(Table: Overview on possible tribological stresses (types of wear) in sewer systems …