Dry Over Night
Special Water-Repellent Silanes Protect
the Concrete Ceiling
of the Gotthard Road Tunnel
Under a vast massif of gneiss and granite, the flow of traffic in the Gotthard Tunnel seldom abates. Every year, millions of trucks and cars pass through the 16.9-kilometer road tunnel – the third longest in the world. In winter, they carry some undesired freight into the structure: salt water, which gets deposited on the roof and walls of the tunnel. Over the years, the intrinsic porosity of the concrete enables the chlorides to eat their way further and further inside the concrete. Once salt-laden moisture makes contact with the steel bars – or reinforcing iron – in the interior of the concrete, a dangerous corrosion process is set into motion. The concrete begins to crumble, and must subsequently be renovated at great expense.
At precisely 8 p.m., both tunnel entrances were closed for repair work. The tunnel had to be reopened for traffic by 5 a.m.
At precisely 8 p.m., both tunnel entrances were closed for repair work. The tunnel had to be reopened for traffic by 5 a.m.
The Gotthard Tunnel’s operator, the Swiss Federal Roads Authority (ASTRA), was looking for a way of prophylactically protecting the tunnel entrances, which were the most at risk from the ingress of salt water. The road construction experts then hit upon WACKER’s special water-repellent silanes.
The silane cream was applied to the roof under high pressure by robot.
The silane cream was applied to the roof under high pressure by robot.
Building Material Stays Breathable
When the concrete is impregnated with SILRES®BS Creme C, the active ingredient in the product covers the pores of the concrete and makes them water-repellent – while at the same time keeping the concrete permeable. The building material stays breathable. The silane actives are designed to penetrate to a depth of about six millimeters. There they form a network that lines the concrete and keeps saline water at bay.
7,000 m² of roof had to be treated with a fine coating of silane in a single night.
7,000 m² of roof had to be treated with a fine coating of silane in a single night.
Repairs to heavily used road infrastructure are a race against time, for the Gotthard Tunnel can only be closed for a short period due to traffic logistics. 7,000 m² of roof surface had to be treated in a single night. Thanks to deep hydrophobization with SILRES®BS Creme C, this was not a problem. “In contrast to conventional liquid products, our cream is applied in a single step,” explains WACKER materials expert Dr. Johannes Ihringer. “The active ingredient only takes a short time to penetrate the substrate, depending on its porosity.” That saves time and costs – protracted lane closures are a thing of the past.
At both entrances, painters and concrete repair specialists covered 750 m of roadway with sheeting.
At both entrances, painters and concrete repair specialists covered 750 m of roadway with sheeting.
Martin Schneider, head of sales at Mapei, the company responsible for the hydrophobization of the north side of the tunnel, is convinced of the superior quality of SILRES® BS Creme C: “The cream’s pasty consistency allows it to stick to the surface better, and that enables more of it to penetrate into the concrete.”
The Fascination of Chemistry – WACKER’s Audio Magazine
