Moving from Stone to Concrete
The ‘Hole-in-the-Wall Bridge’ over Canal Lake pioneered a novel new concrete reinforcement system in the early part of the 20th century.
By Sarah B. Hood
It is not one of Ontario’s most famous bridges, but the Canal Lake Concrete Arch Bridge holds a special place in the history of this country’s concrete structures. Located on the Trent-Severn waterway system between Balsam Lake and Lake Simcoe, it’s affectionately known to summer visitors in the area as the ‘Hole-in-the-Wall Bridge’ because of its appearance: a single arch braced by abutments on either shore.
It may seem like a fairly modest and out-of-theway structure, but this rather simple arch bridge is nationally recognized for its historic significance. Its construction marked the first time a bridge was built of reinforced concrete in Canada using the Melan System of reinforcement, which had been pioneered in Europe. The 62-metre-long bridge was built by the Canadian Department of Rivers and Canals between 1904 and 1905, and its completion date of 1905 is cast into the centre of the arch.
The early 20th century saw quite a bit of experimentation with bridge construction techniques, and there are few surviving examples of the Melan System in existence. Patented by its inventor, Joseph Melan, in 1893, this construction method essentially entails building an arched steel-beam armature that follows the general shape of the bridge, then building the forms around it and encasing the structure in concrete.
In 1905, however, the Canadian builders were not completely familiar with the properties of reinforced concrete, so the Canal Lake Bridge arch ring and abutments were significantly overbuilt, probably in an excess of caution. The structure has been modified over the years. In particular, it was rehabilitated in 1987. The deck was widened slightly beyond the original archway, and the original railings were replaced by solid concrete parapets with inset rectangular panels on the outside.
In 1988, the bridge was designated a National Historic Site of Canada. The official plaque marking the site states that “this structure illustrates the transition from stone to concrete, with massive abutments and surface markings imitative of its masonry predecessors.”
Parks Canada describes this distinctive feature in more detail, noting that at the time of its construction, the surface of the bridge “was enhanced by markings on the concrete surface, which simulate the voussoir stones of masonry arches and the coursed stonework of stone masonry bridge abutments.”
These faux-stonework markings would have made the bridge seem more familiar to members of the public at a time when poured concrete was still something of a novelty, and perhaps even increased the confidence of people driving over it. Not long afterwards, however, concrete almost entirely replaced stone as the favoured material for bridges, and surface treatments like these were no longer used.
RECENT REHABILITATION
Over the 30 years following its rehabilitation and historical designation, the Canal Lake Bridge deteriorated further, and in 2018, GMP Contracting Ltd. was hired by the City of Kawartha Lakes to carry out further rehabilitation work to extend its lifespan without sacrificing its historical integrity. The project entailed the construction of a cofferdam, excavating existing fill to expose the bridge arch, repairing damage and deterioration to the concrete, and backfilling using new granular fill at the interior face of the arch itself and the spandrel walls.
In addition, the existing concrete curb and barrier wall were removed to facilitate the construction of a new concrete deck slab, new concrete curbs and new parapet walls. The surface of the concrete arch soffit and exterior bridge walls were completely refaced, and a new guide-rail system was installed. The project was completed in March 2019.
“The surface of the concrete was in poor condition,” says David Bonsall, manager of structural engineering for D.M. Wills Associates Limited, which worked on the project. He says that the rate of deterioration might be slower than you would see in modern bridges, but attributes this to the structure’s location on a roadway that receives a relatively low volume of traffic and fewer applications of road salt in winter than a typically busier urban road. “It’s a unique location in that it’s been protected from heavy uses over the years,” he notes.
Bonsall says that preserving the original look of the etched lines in the concrete that were meant to simulate the look of stonework was “really the most important part of the rehabilitation that we did. We measured all those lines and had the contractor put those back exactly the way they were. Now the concrete is newer looking, but the [appearance] is exactly the same. Give it a few years, and it will probably look the way it did in its midyears. It was a good job by the contractor [GMP Contracting Ltd].”
“We also unearthed the arch, so it’s backfilled, and that’s what gives you the flat driving surface,” Bonsall adds. “We took all that off and waterproofed the top, so now it’s protected from water coming down from above.”
The concrete used in the rehabilitation was, of course, modern, and sourced from nearby Beaverton, which has a long history of concrete supply. The source of the original bridge construction materials is unknown, but its builders would not have had to travel very far even in those days, because Canal Lake lies on the edge of the Carden Plain.
This is a notable expanse of land characterized by very shallow limestone bedrock made by the compressed shells of millions of prehistoric sea creatures. They would have drifted and collected on the bottom of Algonquin Lake, formed by the melting of the gigantic Wisconsin Glacier some 13,000 years ago. Over the course of several millennia, the glacier withdrew southwards, scouring the land in its wake and creating a landscape that is quite distinct from the Canadian Shield.
Ian Burney, president of the local Kirkfield District Historical Society and Museum, speculates that the concrete might have been supplied by the Raven Lake Portland Cement Company, which was founded in 1902. The company used the then-new Toronto and Nipissing Railway line to bring down marl from Raven Lake to Beaverton. Operating until 1914, the company could produce as many as 700 barrels of cement per day. It even built its own hydroelectric plant at Elliott Falls to supply the energy needs of four huge kilns.
Both the cement company and its electrical power plant have long since vanished, but the bridge remains, a sturdy monument to a time of change and innovation in Ontario’s construction history.
THE INVENTOR OF THE MELAN SYSTEM
Joseph Melan was born in Austria in 1854 and lived until 1941. During his lifetime, he was regarded as a leading authority on bridge construction. He studied civil engineering at the Technical University of Vienna from 1869 to 1874 and went on to pursue a career in railway engineering and bridge-building.
In 1893, Melan published his highly regarded work on concrete-andiron arches. His Melan System – quicker and cheaper than other methods – was first adopted in Europe, but soon moved to North America and other parts of the world. In 1900 he was awarded a gold medal at the World Exposition in Paris, and by 1924, some 5,000 bridges in the U.S. alone employed the Melan System or a closely similar method of construction.