Buried concrete elements are intended to have a long service life. The chemical properties of the fluid and the surrounding environment, together with abrasion conditions, may determine the need for surface protection. The concrete composition and protective applications are selected by assessing these effects together.
Why Is a Protective Coating Important?
Concrete is an alkaline material; in acidic and chemically aggressive environments, its surface dissolves over time. Two important mechanisms of attack are explained below.
Coming from Outside: Chemical Waste
Today, even domestic wastewater lines have a chemical content that is far from negligible; discharges from many sources, from cleaning products to small-scale businesses, mix into the line. The effect increases markedly, however, in industrial infrastructure: in the waste lines of production facilities, the composition is both more concentrated and more variable.
Acidic waste can dissolve the binder in concrete. Sulphate attack can lead to expansion and deterioration of the binder, while chlorides are assessed separately with regard to reinforcement corrosion. Not all chemical attack develops through the same mechanism.
Produced by the Line Itself: Acid Formed from Gas
One of the mechanisms that may be encountered in domestic wastewater lines is biogenic sulphuric acid attack:
- By its nature, wastewater carries compounds containing sulphur.
- In oxygen-free zones where the flow slows down and sludge accumulates, bacteria convert these compounds into hydrogen sulphide gas; this gas is the source of the rotten-egg smell noticed in manholes.
- The gas separates from the liquid, rises into the space at the top of the line and dissolves in the film of water on the moist surface.
- Under suitable oxygen and moisture conditions, the action of microorganisms can lead to the formation of sulphuric acid; the acid damages the concrete surface.
Damage caused by this mechanism can be seen particularly on moist surfaces above the water level. Abrasion and direct chemical attack can also develop at the invert. The risk is assessed taking into account temperature, flow, retention time and ventilation conditions. The role of a protective coating is to extend the service life of the line by placing a barrier between the aggressive environment and the concrete.
Which Protection Is Used for Which Product?
- Pipes and jacking pipes: internal surface protection is most often considered in this group; for lines that are difficult to maintain, the decision is made at the start of the project.
- Inspection manhole and property connection chamber elements: turbulence and ventilation conditions can affect the release of gas and the risk of corrosion; the need for protection is assessed on a project-specific basis.
- Box culvert and U-channel elements: protection is assessed for lines carrying industrial discharge and aggressive fluids.
HDPE-lined products are not a project-specific application; they are included in our standard product catalogue. This page covers applications carried out on request.
Epoxy Coating on Request
An epoxy-based surface coating contributes to the protection of the concrete when it is selected to suit the chemicals it will come into contact with and the conditions of use. It is not part of our standard product range; it is considered on request for a specific project.
Surface preparation, application thickness and curing conditions are checked in accordance with the technical instructions for the selected system. Factory application can make it easier to carry out these checks consistently.
Deciding on Protection Together
The concrete composition and surface protection are assessed together, taking into account the effects to which the product will be exposed. To select a suitable system, the characteristics of the environment, the product geometry and the application conditions are determined.
The information we need to carry out this assessment is as follows:
- The nature of the fluid the line will carry (domestic wastewater, industrial discharge, storm water).
- The gradient of the line and its ventilation conditions.
- Any deterioration observed in existing lines in the same area.
- The target service life.
- Where available, wastewater analysis and information on pH, temperature, chemical content and abrasive solids.
With this information, we determine together whether protection is needed and, if so, which method should be used and in which part of the cross-section it should be applied.