VERY HIGH-PERFORMANCE, WET SPRAYED CONCRETE FOR THE REHABILITATION OF MANDAL CITY BRIDGE

摘要

Mandal City Bridge is located close to the city center of Mandal on the very southern part of the Norwegian coast line. The bridge was built in 1956. After 37 years in service the bridge needed rather comprehensive rehabilitation. The 42 prestressed concrete beams carrying the 130 m concrete roadway over seven spans were severely corroded due to weather action and unsatisfactory concrete quality. Because of the limited load bearing capacity of the bridge, the weight of the repairing materials was focused - and very high-performance concrete was evaluated aiming at minimizing the amount (thickness) of the repairing materials. As part of this evaluation, a small part of the bridge was test-rehabilitated in 1993 using a 100 MPa shotcrete with layer thickness of 10-20 mm. To evaluate this material compared to more traditional shotcrete materials a test area was selected and a normal-performance and a high-performance concrete were sprayed together with the very high-performance concrete. From this test area cores were drilled out and tested. Results from the test program - including water permeability, capillary absorption, chloride diffusion and frost action - are given. After evaluation of the test program the very high-performance wet-sprayed concrete was selected for the rehabilitation job which was performed in 1994. The very high-performance shotcrete was used for filling the corroded, highly reinforced areas and to give the lower 50% of the prestressed concrete beams a 10 mm new "skin". The total sprayed area of more than 1000 m~2 was tested with regard to bond strength - and has been evaluated over a two-years period. The repairing material and performance method is described and the experience data are included in the report.