RepairQ We are rehabilitating a limestone-brick masonry storm sewer by lining it with shotcrete. The sewer is approximately 7 ft (2.1 m) tall with an arch ceiling and walls that are 8 ft (2.4 m) apart. The limestone surface is fairly rough, but the brick portions are not. While the existing structure shows no signs of needing to be reinforced for structural support, we are reinforcing to prolong the service life of the culvert. Is there a recommended minimum shotcrete thickness and reinforcement?
Shotcrete has been used to successfully rehabilitate sewers for over 50 years.
The thickness to be used is an engineering issue and beyond the scope of our association. We would recommend a 2 in. (50 mm) minimum thickness reinforced with either polypropylene fibers or a light-gauge welded wire reinforcement. The surfaces must be cleaned thoroughly to remove grease, oils, and other substances deleterious to good bond. Bonding to brick is not a problem.
Finish is another consideration. The added liner thickness will reduce the size of the culvert. If capacity is not an issue, it is recommended to leave the new shotcrete lining with a nozzle finish. If capacity might be a problem, then a float or trowel-smooth finish may be necessary.
