Deep impregnation of bridges: The water-repellent is sprayed directly onto the bridge pier.
Silanes help build stronger bridges
Silanes offer effective long-term protection against moisture and corrosive salts, which can cause extensive damage to bridges, says WACKER Silicones.
01 February 2006
At the Germany-based Wacker Group, scientists from the Karlsruhe Research Center and Karlsruhe University have presented the results of a pioneering pilot project on the bulk impregnation of highway bridges with specialty silanes, which can substantially reduce costly maintenance and repairs.
The results of the project show that deep impregnation with water-repellent specialty silanes protects reinforced-concrete bridges against damage by moisture and aggressive salts for 15 to 20 years, if not longer.
“The costs of deep impregnation are one-tenth of those of repairs,” says Dr Andreas Gerdes, professor of construction chemicals at the University of Karlsruhe. “Effective, long-lasting water-repellency renders repairs avoidable and has less environmental impact than polymeric protective coatings.”
The project, whose participants included the Highway Inspectors of Southern Bavaria (Kempten office), the Konstruktionsgruppe Bauen (Kempten) as well as Sto, Aqua Stahl and Wacker Chemie, targeted the weathering and environmental damage that especially affects highway bridges made of reinforced concrete in Bavaria. The extent of the damage has now reached economically significant proportions. A study by Dekra shows that 14,000 of the 120,000 bridges in Germany are at grave risk. A further 20,000 bridges require extensive repairs.
Damages from salts
Most damage, especially in and around bridge piers, stems from the impact of deicing salt. The salt is in the water, which is splashed onto the piers by passing vehicles. Once on the surface, it penetrates further and further into the concrete with the passage of time. If it reaches the steel reinforcement, it triggers corrosion and that causes the concrete above it to spall. From this moment on, the bridge’s load-bearing capacity is at risk and repairs are needed.
Such repairs are technically complicated and not always entirely successful. When the old layer of concrete has been removed, fresh concrete has to be applied and the pier re-profiled. An interface is thereby created between the old and the new concrete, with the result that damage can occur again after a few years.
These repairs are exorbitantly expensive. Studies show that it can cost more to repair a bridge pier than to make a new one.
“Additionally, the building site has to be cordoned off and the traffic diverted – without these measures, repairs simply cannot go ahead.
The Pilot project
The goal of the pilot project was to establish, if deep impregnation would avoid deicing salt damage and hence lower repair costs. The first step taken by the scientists from the Research Center and University in Karlsruhe was to study the condition of 16 Bavarian highway bridges. They found high levels of chloride on both old and new bridge structures, which meant they would eventually require repairs.
The second step was to impregnate the bridge piers by spraying them with a special silane gel. Sto developed this formulation from raw materials supplied by Wacker Silicones, which was sprayed onto the piers by Aqua Stahl. A coat 0.45 to 0.65 mm thick ensured that the silanes penetrated into the building material within a few hours to cover the piers with a water-repellent silicone resin network. The network impregnates the porous building material, preventing water and salts dissolved therein from penetrating any further into the pier.
The work was coordinated by the Konstruktionsgruppe Bauen in Kempten and monitored by scientists from the Karlsruhe Research Center. Samples taken by the scientists after the formulation had been applied revealed that the water-repellent agent had effectively penetrated to a depth of 6 to 7 mm. This is deep enough to suppress chloride entry to the extent that maintenance only becomes necessary at a much later juncture, if at all.
The overall cost of the deep impregnation measure varies with the size of the structure between 5,000 and 15,000 euros – one-tenth the usual cost of repairs.
Deep impregnation with silanes thus offers scope for protecting bridges for many years against aggressive deicing salts and to substantially lower maintenance costs of new and damaged bridges.
Silanes & silicones
Silanes are highly versatile products that are derived from silicon and find application in many industrial areas, for example, as raw materials for protecting inorganic substrates (such as concrete, bricks, natural stone) and for surface-treating glass and ceramics, and as primers for coatings, among other applications. Silanes are starter materials for silicone fluids, silicone resins and silicone elastomers.
Silicones are the basis of materials with highly diverse product properties for virtually unlimited applications and are used in a broad variety of industries ranging from the automotive, chemicals and construction sectors through consumer care, cosmetics, metal processing and mechanical engineering to paper, pulp and textiles.
One of the world’s four leading producers of silicones, Wacker Silicones offers one-stop solutions for products, services and strategies in the silicones field. The company acts as co-driver for customers’ innovations and helps them penetrate global markets, optimise business processes, reduce overall costs and boost productivity. Wacker Silicones operates 10 production sites and maintains sales offices and subsidiaries in 26 countries.
