To restore two sumps used to treat boiler water in a powerhouse, many construction methods had to be adapted to this hard-to-access project. Built in 1955, the reinforced concrete walls of the sumps had been attacked by chemicals used to change the pH of the water in the sumps. Getting to the walls was a challenge. The sumps could only be entered through a 2 1/2-foot square opening. This created problems with getting equipment and workers into the sumps and ensuring adequate air flow and light. Workers constructed a working platform, supported by four cables and winches inside the sump. They also installed adjustable flood lights. Flexible hoses ran through the access opening, supplied fresh air, and vented dust and chemical fumes.


Workers first waterblasted to remove any chemicals, oils, and greases embedded in the concrete pores. Sandblasting followed the waterblasting. Next workers lowered precut sections of wire mesh through the access hole. Then they applied a dry-mix shotcrete.


The dry-mix shotcrete used silica fume and Type II cement. Its advantages include a high early and final compressive strength. The shotcrete also has a very low permeability, making it resistant to penetration by chlorides, nitrates, sulfates, and other chemicals.


To ensure the concrete won't deteriorate again, the newly shotcreted walls were sprayed with a silica-filled epoxy.