When it comes to rehabilitation in traffic route construction, speed is one of the most important factors: the shorter a road is closed to traffic, the better it is for the infrastructure of the affected area, because additional congestion, environmental pollution and nuisance on alternative routes are otherwise inevitable.
What is true for all types of roads is even more true for bridges. Because if a bridge is closed to traffic, then alternative routes in the immediate vicinity are rare and traffic collapse is therefore almost inevitable.
With the help of the HANV system, however, it is possible to significantly reduce bridge closure times during roadway rehabilitation.
Usually, the pavement is removed down to the base layer – steel or concrete – during rehabilitation, this base layer is then prepared and the pavement is resurfaced layer by layer – in Germany, in accordance with ZTV-BEL-B. The first step is to apply a primer layer based on epoxy resin, which is then sprinkled directly with quartz sand. After drying, a sealing layer – also made of epoxy resin – is applied, which then also has to be sprinkled with quartz sand again: This creates the so-called bridge seal, which in turn also has to dry again. The third layer is a bituminous welded membrane, which, after drying, is followed by a layer of protective asphalt and finally the surface course, i.e. the roadway.
In addition to the long time required for the numerous drying and curing phases, this approach has the further major disadvantage that it is highly dependent on the weather. While the application on matt damp substrates is usually still tolerated according to ZTV-BEL-B, rain and snow completely prevent the application: The bridge must inevitably remain closed to traffic for even longer. In addition, the necessary epoxy resin work is also not technically possible anyway at outside temperatures of less than 5°C.
The “Notes for the production of waterproofing systems from asphalt load-bearing scaffolds with void-rich backfill for concrete engineering structures (HANV – 2015 edition)” describe a construction method for the waterproofing of concrete bridges that permits greatly reduced construction times compared with standard construction methods. After preparation of the bridge base course, an open-pored asphalt substructure with a high void ratio is applied directly in place of the epoxy resin primer in a thickness of approx. 25 mm, which is then immediately rolled off.
The HANV resin is then applied to the rolled asphalt, which is still warm at around 100°C – either directly from buckets or by pump. The resin is spread with rubber pushers until all accessible voids of the cavity-rich asphalt supporting structure are completely filled; the reactive resin is then sharply drawn off over the tops of the asphalt. Due to the high residual temperature of the asphalt, the HANV reactive resin can still react without any problems even at low outside temperatures of less than 5°C.
No welding membrane is required, as the low viscosity of the HANV resin allows it to penetrate through the voids of the entire asphalt supporting structure to the concrete or steel base, creating a robust waterproofing layer by bonding.
To improve adhesion, the still warm HANV resin is first sprinkled with special thermal pellets made of melting granules.
During the directly subsequent final operation, asphalting of the pavement, the pellets melt due to their low melting point, creating a waterproof bond and very high adhesion between the layers.
After the final marking work, the bridge can then be reopened to traffic – saving additional time-consuming work steps.
Ideally, therefore, HANV systems can be used to rehabilitate the carriageway of a bridge quickly, effectively and durably in the shortest possible time – over a single weekend, for example.
Damaged roadway and substructure require rehabilitation
Removal of the old road surface down to the substructure
Application and rolling of a cavity-rich asphalt layer
Application of the special HANV resin which, due to its low viscosity, penetrates the cavity-rich asphalt down to the substructure
Spreading and stripping of the HANV resin
Application of melting pellets
Asphalting the road surface
After curing and cooling, finished robust waterproofing layer – bridge rehabilitation completed within a few hours