SAPEX is a line of protective coatings for the concrete and metal structures of wastewater plants, sewage pumping stations, tanks and process vessels. The coating forms a functional barrier between the structure and the aggressive environment rather than a decorative layer on the surface.
The concrete and metal structures of a wastewater plant work in an environment that ordinary construction does not know: constant humidity, contact with sewage, hydrogen sulphide, biogenic corrosion, swings of pH, salts, reagents and abrasive particles. The damage starts at the surface and looks like ordinary wear for a long while, and after that come cracks, the loss of strength in the surface layer of the concrete, exposed and corroding reinforcement, leaks and a plant stopped for repair.
The task of the coating is not a decorative layer but a functional barrier between the structure and the environment. What is asked of the barrier is to reduce the contact of the surface with the aggressive medium, to limit the access of moisture and chemical compounds into the depth of the material and to lower the rate of the corrosion processes. What the coating is worth shows not on the day the work ends but in how soon the structure calls for repair again, and in whether that repair stays a repair rather than a major reconstruction.
Hydrogen sulphide forms in sewerage structures, and in the gas zone of tanks and manholes it oxidises into acid compounds that gradually destroy the concrete surface. The zones of variable water level are vulnerable here as well as the gas zones above the sewage, and the phenomenon itself is known at wastewater plants, sewage pumping stations, collectors and inlet chambers.
Metal at the same sites carries a load of another kind: moisture, salts, aggressive gases, condensate, reagents and mechanical wear accelerate corrosion. Unprotected metal passes from a surface problem into an operating risk quickly, and ordinary paint or a standard construction coating does not always give that result. What is asked of the material here is an account of the water and sewerage environment, not of general building conditions.
Concrete needs protection from moisture, acid attack, biogenic corrosion, the ingress of aggressive substances and the breakdown of the surface layer. Metal needs protection from electrochemical corrosion, moisture, salts, aggressive gases, condensate and mechanical wear. Hence the split of the platform into two lines: SAPEX Concrete for concrete and reinforced concrete surfaces, SAPEX Metal for metal structures and equipment. The split was made for applicability, not for the sake of a product range.
The vulnerable places are known in advance. In concrete these are inlet chambers, sewer manholes, pumping stations, aeration tanks, clarifiers, sewage tanks, launders and channels, where the surface layer loses strength and roughness, friability, cracks and exposed reinforcement appear. In metal these are tanks, service stairs and platforms, pipelines, supports and brackets, covers and hatches, equipment frames and embedded parts in zones of high humidity.
The result of a protective coating depends on more than the material. Before application the type of surface is assessed, along with the degree of damage to the concrete, the presence of cracks and exposed reinforcement, the level of moisture, the degree of corrosion of the metal, the presence of old coatings, the chemical load and the temperature conditions. In a number of cases mechanical cleaning, concrete repair, removal of the friable layer, treatment of corroded areas or degreasing is needed before the protective layer.
The same assessment covers the possibility of stopping a section for the duration of the work and the regime of further operation: they decide what preparation is feasible on a working structure. Applying the protective layer remains an engineering procedure tied to the state of the particular structure rather than a finishing operation, and an error in the protection returns as a repeated repair within a short time.
In the reconstruction of a wastewater plant the attention usually goes to the equipment: pumps, compressors, aerators, control cabinets and pipework. The state of the civil structures is left aside, although new automation and new equipment do not answer for the durability of a damaged tank, a spoiled concrete surface, corroding metal elements and an unprotected gas zone.
The coating fits into such work at its own steps: after the cleaning and preparation of the surface, after the repair of damaged areas of concrete, in the protection of the gas zone of tanks and of metal elements, in the restoration of old pumping stations and in the building of new structures. When the pumps and the control cabinet are being replaced at a site, the state of the inlet tank, of the metal elements and of the gas zone belongs to the same scope of work.
Protective coatings for concrete and metal are SOLVIA's own technological development for water treatment, wastewater treatment and engineering infrastructure sites. Solutions for concrete and for metal surfaces have been developed along both lines, and the development is advancing as a practical instrument for protecting structures in an aggressive environment and extending their service life. The technical solutions are protected within the developer's patent strategy. The compositions, the ratios of components, the process parameters and the particulars of preparing the materials are not disclosed in open materials.
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