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Masonry Around the Nation

Masonry Around the Nation

   
Masonry Around the Nation
The Consigli Crew
When Bowdoin College called on Consigli Construction to help determine whether to demolish and rebuild or completely restore the college's historic Romanesque-style campus chapel, the answer became clear very quickly: do both. Thus began a two-and-a-half-year odyssey during which the tops of the twin-towered landmark were completely rebuilt from belfry to spire and the entire granite façade of the building was carefully removed, restored and replaced one stone at a time — all thanks to a combination of old-fashioned meticulous handwork and 21st century tracking tools.

Technology Facilitates Pre-construction

Masonry Around the Nation
3D Computer Model
One of the first challenges facing the Consigli team in the pre-construction phase was the existence of scaffolding the owner had already erected around the lower portion of the chapel. Using 3D computer models, Consigli determined that if the scaffolding continued to be built as planned, it would run right into the overhang of the belfry. The models also revealed that the number and position of the posts, bars and braces used would prevent work from proceeding efficiently and on schedule. Thanks to this technology, Consigli was able to propose that the existing scaffolding come down and that it be replaced with a mast climbing platform. Thanks to these 3D modeling tools, Consigli was able to demonstrate visually both the problems presented by the scaffolding and the added value the mast climbing system would bring to the job, which made it easy for the owner to readily agree to the change.

Rebuild, Stabilize, Restore
   
Masonry Around the Nation
Remote Controlled
Self-erecting Tower Crane

The structures of both towers between belfry and spire were so deteriorated they had to be completely demolished and rebuilt, and the remote-controlled self-erecting tower crane Consigli had placed on-site began to prove its usefulness right away.

First, the façade stones were carefully removed, catalogued and placed in massive storage bins, as they would later be replaced over the newly reframed spires. Since the crane is controlled from the actual site of the work being done instead of from the ground, the operator knows exactly what's needed where. He was able to remove stones and place new materials at the work site with the utmost precision and flexibility. Once the façade stones were removed and the top sections of the towers demolished, a second, hydraulic crane was brought in to pick the massive precast concrete units, which formed the new framing of the towers from the belfry up. With the use of the Manitowoc crane, the disassembly of the north tower went much more quickly than anticipated, so the Consigli team was able to start disassembly of the south tower well in advance of the scheduled date.


Masonry Around the Nation
Consigli's Project Engineer Documenting Stone
Fortunately, the rest of the building was in better shape than the tower tops, although 150 years of freeze-thaw cycles had caused considerable spreading and bulging of the façade. The Consigli team set about a key part of the restoration effort — permanently stabilizing the towers with Cintec anchors. Initial attempts at dry-coring through the stone to place the anchors accomplished little more than the destruction of one drill bit after another because ice lenses within the wall had melted and clogged the dry core bits.

The decision to move to wet-coring proved the right one, although when the temperature fell into the single digits — not an unusual occurrence during a Maine winter — the project team faced the added challenge of having to temporarily heat the scaffolding so the water used for the drill wouldn't freeze.

Back to the Quarry
Although the majority of stones removed from the façade were restored and put back in place, Consigli had to solve the problem of how to fabricate roughly 1,400 new pieces and how to match them to the older granite. The solution was obvious: re-open Grant's Quarry in Brunswick, Maine, the source of the original stone.

While obvious, the solution was not necessarily simple and, anticipating the long lead times needed to request and receive approval to re-open an abandoned quarry, the Consigli team began the process during pre-construction — nearly a full year in advance of when the finished pieces would be needed. In addition, extracting the rock in Brunswick, getting the finished shop drawings, fabricating the new pieces at a granite fabricator in Marlboro, Mass., and shipping them back to the Maine job site was a complex process.

Masons are the Stars of the Show
Nowhere are the artisanship and talents of Consigli masons more apparent than in the meticulous repairs made on some of the chapel's decorative corner stones. At least half of these pieces required epoxy-pin and patching repairs, but in the aim for authenticity, visible repair cracks would have been unacceptable.

Since the patching material only came in uniform colors, the engineer completed a petrographic analysis of the existing stone to determine its primary component (e.g., Hornblende or Magnetite), and then mixed ground-up particles of the appropriate element into the patching material to achieve a color-correct area that left no visible line on the stone.

Valuable Learning for Future Projects
The entire project team's insistence on meticulous labeling and documentation of each and every piece — even before it was removed — along with continuous updating of CAD drawings that helped the masons to know exactly which stone went where, were the key to managing 4,700 historically significant pieces of granite and ensuring that everything got put back where it belonged.

   
Masonry Around the Nation
Masons Reconstructing
the Spire of the North Tower

Another critical contributor to the success of the project was the involvement of the masons early on to analyze the existing structure, brainstorm the best ways for removal and restoration of the stones, and to build detailed mock-ups to test real-world tolerances and determine possible points of failure. Shown above is a mason working on a mock-up that includes a window, an arch top and structural back-up (flashing to be installed) — a detailed replication of the complexities of the actual job that helped to satisfy the various members of the project team that all potential points of failure had been anticipated and planned for.

   
Masonry Around the Nation
Detailed Mock-up
The Consigli project managers also note that on a job such as this, it's impossible to overestimate the lead times necessary to extract stone from a quarry and fabricate the pieces. The schedule must have generous tolerances for unexpected delays — tolerances for which the project team was grateful when they ultimately had to extract twice as much stone from the quarry as originally planned because so much of it had unacceptable imperfections.

The level of collaboration between the college's facilities management staff, the structural engineers, the fabricators, the masons and Consigli's own management team was "textbook." This, more than any other single factor, was the key contributor to the successful restoration of this historically significant structure.






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