Concretum

Initial situation

As part of the expansion of the Zurich Northern Bypass, the ARGE Nordring is upgrading the national highway N01, including the section at the Birchstrasse underpass near the traffic roundabout. The load-bearing capacity of the bridge deck is to be increased, specifically with regard to torsional strength and shear resistance. A fully enclosed formwork was installed. Due to the challenging geometry and limited accessibility, the concrete had to be self-compacting and pumpable. Rapid hardening was also essential to ensure that the setting process could proceed vibration-free during the bridge closure window between 23:00 and 04:30. During this time, night traffic was rerouted via the Seebach exit, through the roundabout, and back onto the access ramp.

Solution and evaluation

A self-compacting, pumpable, rapid-hardening special concrete from Concretum was used. Concretum^® Q-FLASH 5/20 SCC reached a compressive strength of 20 N/mm² just five hours after production.

Concreting was carried out in night-time stages. The SCC high-performance concrete was produced at the Rümlang batching plant and delivered with an open time of 2 hours and a slump flow of 72 cm. The Concretum rapid-hardening concrete was pumped into the column formwork through dedicated pump openings prior to the bridge closure. Two hours after production, shortly after the closure at 23:00, the setting process of the SCC rapid-hardening concrete began. Despite the large cross-section thickness of 50 cm, the heat of hydration remained low at only 45°C. One hour before reopening to traffic, a compressive strength of 20 N/mm² was achieved.

Compared to conventional self-compacting concrete, the bridge could be reopened after just 5.5 hours of closure. This Concretum^® Q-FLASH 5/20 SCC rapid-hardening concrete is characterized by excellent flowability and fast strength development, delivering reliable results even under complex geometric and construction conditions.