The British Columbia Institute of Technology (BCIT) trains workers in aircraft and airport maintenance, engineering, and flight operations. When the institute in Burnaby, B.C., opened a new hangar recently, it had a much more down-to-earth dilemma to tackle.
R-Four Contractors Ltd., of Langley, B.C., performed the concrete work on the 80,000-square-foot hangar, including tilt-up and cast-in-place concrete.
The first 20,000-square-foot pour of the 12-inch-thick concrete floor contained 28% fly ash which resulted in de-lamination of one-half the surface area. R-Four immediately adjusted the concrete composition to solve the problem, and the remaining 60,000 square feet of floor was poured without incident.
The next step for project manager Charlie Salji to address was the delamination problem with his concrete supplier and a manufacturer of concrete repair products.
Jack-hammering the damaged area had many drawbacks: It would have taken months of time, ruined the piping buried in the concrete, and substantially increased construction costs.
Patching the 10,000 square feet of delaminated concrete was a better option, but this also posed several challenges. Salji needed to place a surface that was as thin as possible while still remaining structurally sound. A vapor also appeared to be percolating through the thick slab, causing hollow spots. Finally, the patch needed to be power-trowelled to match the surface of the surrounding concrete.
With a compressive strength of 3000 psi in four hours and 5000 psi in 24 hours, Mapecem 102, a fast-setting mortar by MAPEI, was selected for the power troweling. By combining the mortar with a suitable bonding agent, R-Four Contractors could alleviate the costs and environmental impact of the removal process while saving a significant amount of time.
Finding a bond
Different combinations of bonding agents were tested on 1200-square-foot test patches. Selecting an adequate bonding agent was paramount in this case because the power troweling of the Mapecem 102 caused strong reverberations through the ¼-inch screed. MAPEI's Planibond EBA epoxy bonding agent met all requirements.
The test patch and the power troweling were completed within four and a half hours. When the Mapecem 102 was burnished by the power troweling to match the surrounding cement, it became so densified that repeated pounding with a hammer did not affect the surface.
“I believe this is the first power-trowelled patch we have ever made,” said Glenn Best of Richform Construction Supply. “We believe we have come up with a unique solution for patching such a large heavy-wear surface.
Salji's team patched the few small, 2- to 3-inch hollow spots in the thick slab by injecting a very fluid epoxy through two holes that were drilled into each of these spaces. In a separate area, a crew used MAPEI's Planigrout 750 construction grout under the tilt-up panels (walls) after they were all erected and the roof was put on.
Workers placed the panels onto shims when they were first erected so that they could be positioned perfectly level and plumb. As a standard practice, the gap under the panels that is created because of the shims is filled with construction grout.
The teamwork exhibited by the contractor and material supplier allowed the BCIT Aerospace Technology Campus building to open on schedule.
For more on the product manufacturer in this story, visit www.mapei.com.