Title: Repair of High-Strength Concrete Walls Using Low-Pressure Spray-Up Techniques
Author(s): G. C. Hoff
Publication: Symposium Paper
Appears on pages(s): 417-440
Keywords: bond strength; concrete; high-strength concrete; repair; shotcrete; silica fume; slipform
This paper describes the repair of a high-strength silica fume concrete structure using a high-strength repair material that also contains silica fume. The repair represented the largest single application of this material and the largest single use of low-pressure spraying of the repair material. Information is provided on the repair procedures, proficiency of the nozzlemen, acceptance criteria applied to this type of operation. Because of the lack of actual in-situ bond and compressive strength data in the literature for high strength concrete repair materials, preliminary trials were conducted for material acceptance and to establish acceptance criteria for the actual repair. Approximately 1,300 m3 of the repair material was used to repair 24,000 m2 of concrete surface damaged during a slipform operation. The damaged concrete had compressive strengths in the range of 78 to 82 MPa. The repair material had a target compressive strength of 80 MPa and an in-situ bond strength requirement (minimum) of 1.5 MPa. Using low-pressure spraying techniques because of confined working areas, the repairs were successfully completed over a 24-week period. Compressive strengths of cores from sprayed production test panels averaged 85 MPa at 28-days. The in-situ bond strength of the repairs did not appear to increase with age and averaged 1.87 MPa for all ages evaluated.