This is one of a series of 46 pictures, which compares two bridges. The first bridge, (pictures 1 – 45) is part of the Canadian freeway QEW (Queen Elizabeth Way), crossing the Welland river and “Oakwood Drive” in Niagara Falls, Ontario, Canada. The second bridge (picture 46) crosses a canal inside the City of Amsterdam, Netherlands. The structural steel and concrete of the Canadian bridge are in a state of corrosion. The bridge is rotting. The Dutch bridge is unharmed. The Canadian bridge has already had restoration work done on it. However, the restoration work has apparently not eliminated the causes of the corrosion. Because the causes of the corrosion have not been eliminated, the corrosion and disintegration of the steel and the concrete continue unhindered. The upper steel beams of the Canadian bridge are coated with a covalent paint to prevent rust formation. This does not resolve the rust formation issue because it appears that the steel beams are directly supporting concrete elements above, which then crush/destroy the coating, so it can no longer protect the steel against rust. The concrete is porous, thus letting rain water together with chlorides (road salt) in and out. The now vulnerable and unprotected steel then rusts due to the water, salt and air contact. Once rust has set in, it then goes underneath the coating on the rest of the steel, popping off more of the coating as it goes along, just like it does on a rusting car. Even if that steel were sandblasted and re-coated, the contact point between the top of the steel beams and the concrete above would remain unprotected. It does not appear as though there is any room or barrier between the steel and the concrete. Even if there were something there, it does not appear to have protected the rust paint enough to remain intact under the weight of the concrete. Because of this apparent dynamic, it cannot be expected that further restoration work of this type (sandblasting and recoating that does not reach the contact points that are the root cause) will be successful. The concrete is of poor quality for this application because it lets the water and diluted road salt in, which then attacks the reinforcing steel bars. A small coating of rust on the rebars normally is not cause for concern because it allows the alkaline concrete to adhere better. However, in this case it appears that a cheap concrete was chosen, with a cement that cannot withstand outdoor weather and salt influence. Because of this, the rebar is corroding vigorously. The added rust causes the volume of the rebar to expand, until the outer concrete pops off, which reduces the strength of the bridge and imperils the population. Because the root causes of the rot were not removed, it is apparent that concrete repair patches are but a temporary measure as the existing and new cracks carry on right into the repair patches, which dooms the patches to pop off along with the rest of the concrete right from the start. The Dutch bridge on the other hand transfers its load through purpose-made covalent rubber pads to the columns below in such a manner that no corrosion is created. The concrete has received a covalent paint such as to protect it against the influence of outdoor weather and road salt. It would be possible to protect the steel in the Canadian bridge by conducting a small electrical current through it. The physical and chemical error sources that have led to the rot in the Canadian bridge were known and were the subject of teaching engineers in technical universities internationally during the time of the construction of the Canadian bridge.
<a href="//commons.wikimedia.org/wiki/User:Achim_Hering" title="User:Achim Hering">Achim Hering</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>