Why does concrete deteriorate in biogas plants?
Biogenic sulphuric acid formed from hydrogen sulphide can attack concrete, particularly on wet surfaces in the gas zone.
From H₂S to acid
Hydrogen sulphide is produced during anaerobic processes and enters the gas space of the tank. Where moisture and oxygen are present, sulphur-oxidising microorganisms can transform sulphur compounds into sulphuric acid.
Attack on the cement matrix
Acid dissolves calcium compounds in the cement matrix. Sulphate reactions may also produce expansion, cracks and deterioration of the surface.
Influencing conditions
Condensation, temperature, oxygen availability and the composition of the biogas affect the location and progression of corrosion.
Can the damage extend below the visible concrete surface?
Yes. An apparently firm surface may conceal chemical attack and reaction products below it.
Near-surface zone
Practical field observations have found affected zones within approximately the first 1–3 cm of otherwise apparently sound concrete. This is an observed range, not a universal damage depth.
Why it matters
The actual extent varies with exposure and concrete properties and must be assessed before selecting a rehabilitation method or setting anchorage requirements.
Why is substrate preparation so important for liquid-applied coatings?
The protective layer must develop and retain adequate adhesion to sound, correctly prepared concrete.
Typical preparation
Depending on the system, work may involve removing loose and chemically affected concrete, washing, blasting, establishing sufficient substrate strength, drying and controlling temperature and humidity.
Operational effect
Moisture, condensation and changing conditions may influence adhesion and curing. These requirements can add stages or waiting periods before the tank returns to operation.
The chemical resistance of many epoxy and polyurethane products can be excellent. The requirement for a suitable bonding surface is a separate consideration.
Which methods can protect an existing concrete tank?
Several material families can be appropriate; they differ in chemical resistance, flexibility, adhesion and installation requirements.
Mineral systems
Can be relatively straightforward where the substrate and exposure are suitable.
Epoxy, polyurethane and polyurea
Can provide high chemical resistance and, depending on formulation, low permeability, flexibility and crack bridging.
Rubber and fibre-reinforced linings
Can offer elasticity or continuous protective layers, including for more complex geometries.
Thermoplastic sheet linings
A mechanically fixed plate lining forms a separate protective layer without requiring a full-area adhesive bond. Its fixings, joints and penetrations are part of the system design.
How does a mechanically fixed thermoplastic lining work?
The concrete remains the load-bearing structure; a separate thermoplastic layer protects it from the stored medium.
Load transfer
The lining is fixed at defined locations. Where the near-surface concrete is chemically affected, anchorage must pass beyond that zone and achieve adequate capacity in competent concrete.
System details
Joints, fasteners, transitions and pipe penetrations must be designed together. In TP·VAS, PP-H fixing strips and rings also help limit possible paths behind the lining; FPP bands cover the fasteners on the medium-facing side.
Read the TP·VAS technical system description
How do temperature and structural movement affect tank linings?
A coating fully bonded to concrete follows its surface movement. A mechanically fixed lining is not rigidly coupled to every point of the wall.
Temperature gradients
Direct sun, moving shade, daily heating and night cooling can create differential movement across concrete walls.
Own expansion of the lining
PP-H also expands and contracts with temperature. Panel arrangement, mechanical fixing, flexible connecting components and joint details must accommodate this behaviour.
Mechanical separation reduces full-area strain transfer; it does not eliminate the need for structural detailing.
What installation conditions affect downtime?
Liquid coating systems may need drying and curing stages; mechanical PP-H plate installation generally does not require a dry, prepared bonding surface across the whole tank.
Weather and handling
Limited rain and wet concrete can be tolerated for plate positioning under suitable conditions. Snow does not create full-area coating-curing requirements for the plates. Strong wind is often a practical problem when handling large sheets.
Handling and access
Individual PP-H panels can normally be brought in without crane handling of large membrane rolls. Access, safety, welding and any local sealing layer still impose project-specific requirements.
Restart
Shorter preparation and the absence of full-area curing stages can reduce the overall rehabilitation period; no fixed downtime is promised without a project assessment.
What determines the service life of a lining?
The entire system matters: material compatibility, fixing, thermal movement, welded joints, corrosion protection, inspection and repair.
Metal fasteners
In the completed TP·VAS system, all metallic fixing components are covered on the medium-facing side with welded FPP bands. They are not intended to be directly exposed to the aggressive tank medium.
Possible pathways and maintenance
Fixing strips and rings can limit possible pathways behind the lining. Selected areas may be opened for inspection and subsequently welded closed. Local thermoplastic repairs are often possible.
There is no universal service-life claim independent of the actual medium, temperature, workmanship and maintenance.
How does POLY·VAS prepare a rehabilitation project?
By examining the existing structure and operating conditions before deciding whether a proposed method is suitable.
Technical preparation
Depending on the work, this may include review of chemical and physical exposure, material selection, construction details, quantities and supply requirements.
Execution
Technical preparation and coordination may involve qualified independent installation companies selected for the particular project. There is no exclusive execution partner.
First information
Please provide tank dimensions, construction, medium, temperatures, known damage, drawings, photographs, location and an intended rehabilitation period.
Contact: info@poly-vas.com
