Bridges are an important part of infrastructure – an enabler for urbanization and efficient movement of people in daily life. Bridges are by default very exposed to weather and wind thanks to their surrounding environment. Hydrodemolition is the right method to get the concrete bridge repair job done most effectively – here we tell you why!
The history of bridges started in ancient times, and ever since then architects and engineers have improved them to the point they are today – mighty structures that span mountains, lakes and oceans. The Romans revolutionized the building technique by introducing arches, resulting in a structure that was very rigid and strong. The Turkish Karamagara Bridge that was built in the 5th or 6th century represents the oldest surviving Roman bridge that features pointed arch.
Many historical battles have been fought over the control of these bridges, making them a symbol of control of the flow of people and goods across rivers and canyons. Today, bridges are an important part of infrastructure – an enabler for urbanization and efficient movement of people in daily life.
No one really knows how many bridges there are on planet earth, but the fact that there were over 600,000 bridges in the US alone in 2016 tells us something about the great number.
Out of these, 4 out of 10 – or 240,000 – are older than 50 years. It is estimated that 188 million trips annually are done over bridges that are structurally deficient, and recent estimates puts the investment needed for bridge rehabilitation in the US alone to a $123 billion.
In Europe, the situation is the same. In Italy, 300 bridges are at risk for failure and in Sweden, 800 out of a total 21,000 bridges are being investigated for needs of repair. Out of France’s 12,000 bridges one-third are in urgent need of repair and in Germany 1 out of 10 of the country’s 39,000 bridges are in bad condition.
AGEING AND OTHER CHALLENGES WHEN RESTORING A BRIDGE
Bridges are by default very exposed to weather and wind thanks to their surrounding environment. Additional causes of aging over time are in general:
- Chloride penetration. Chloride (salt) is often spread on roads and bridges in order to prevent ice from being created on road surfaces. On structures close to water, the salt is brought by wind or permeated in through cracks directly from the ocean. Once inside, the chloride causes corrosion at the rebars. The rebars expand when they corrode and, consequently, crack the surrounding concrete. These damages lead to an increased penetration of water and chloride, which speed up the aging procedure.
- Freeze-thaw cycles. A similar cracking procedure of the concrete occurrs when water and moist inside the concrete freezes and thereby expands. The concrete can only withstand a specific amount of freezing cycles. This means that a concrete structure e.g. a bridge in an area where the temperature fluctuates around the freezing point will age a lot faster than one in a less seasonal climate.
- Concrete is naturally basic but in contact with the air a chemical reaction caused by the carbon dioxide (Co2) decreases the pH value. When it gets too low (pH < 9) the corrosion of the reinforcement will accelerate (compared to the chloride penetration mentioned above). When this phenomenon occurs the carbonated concrete must be replaced.
Other challenges when restoring a bridge:
- Abutment walls can be located on cliff faces and inaccessible to some equipment.
- Beams can be at great heights above the ground or over water with nowhere to station a robot underneath.
- Bearing foundations have limited access for a conventional hydrodemolition robot.
- Decks with today’s high volumes of traffic the schedules are tighter than ever before.
- Piers (Pillars): being the foundation of the bridge they can be of great height and are sometimes located partially under water or in the medians of other roadways or shipping channels.
- Parapet walls: located along the edges of the bridge these are most exposed to the elements but are vulnerable to impact and even fire damage caused by vehicle accidents.
The keys to a sustainable, long-lasting result when restoring a bridge are:
- Create a surface that is ideal for bonding new concrete.
- Ensure that no micro-cracks are created in the process of removing damaged and/or old concrete.
- Ensure that no damage is caused to the re-bars when removing the damaged and/or old concrete.
- Use a methodology allowing the choice of selective (removal of the concrete down to a specific quality/strength) or non-selective removal (removal of x, y or z metrics of concrete, no matter the quality.
The aging of concrete is not linear, so hydrodemolition is the right method to get the bridge repair job done most effectively. The ACR™ robots have been developed to allow both selective and non-selective removal, leaving no micro-cracks or damage to the re-bars in the structure and a surface ideal for bonding.
THIS IS HOW ACR™ AND HYDRODEMOLITION HELPS:
- Abutment walls: If the robot arm does not allow you to reach the removal area a tower attachment or a frame system are available.
- Beams: the integrated arm of the robot allows you to remove the slab with the robot positioned on a solid area.
- Bearing foundations: if there is not enough room for the robot, a frame system can get the job done.
- Decks: with today’s high volumes of traffic the schedules are tighter than ever before. The arc robot with One control allows for ease of operation and less downtime, helping you keep on schedule.
- Piers (Pillars): A frame system can be setup on the pier, and you can accomplish the removals either in stages or with a larger frame to cover the entire area in one setup.
- Parapet walls: not only can you extend the tracks but also slide the body of the robot for extra stability, when reaching over the wall. All without any additional attachments.