Hydrodemolition: A Unique Concrete Removal and Surface Preparation Technique

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Hydrodemolition, also known as hydroblasting or hydromilling, is a demolition technique used to remove concrete and other materials using high pressure or ultra high-pressure water jet. Compared to conventional demolition tools, hydrodemolition is an effective method to cut down concrete without affecting the substructure and other parts.

The hydrodemolition process does not involve vibrations, unlike other techniques. Hence, this method is accurate and has less impact on the surrounding materials. It is safe and reduces the risk of workplace injuries.

This article explores the historical background, essential features, and advantages of hydrodemolition in the construction industry.

History of Hydrodemolition

Researchers, McCurrich and Browne (1972) made the first serious attempt to use water jets for concrete hydrodemolition. They found that cutting of concrete using water jet consumes less energy. From the initial studies, they inferred the following results:

1. The aggregates in concrete were impossible to cut.
2. A practical site cutting tool will require pressure with a minimum value of 380 MN/m².

It then took them ten more years to overcome the abovementioned flaws and develop a commercial hydrodemolition unit. Contradictory to the above information, modern hydrodemolition systems work at operating pressures of about 100 MPa. It is 30% of the threshold suggested by McCurrisch and Browne (1972).

At present, hydrodemolition is widely used to clean, remove, drill, profile, and demolish concrete substrates and reinforced concrete structures. Hydrodemolition is  a state-of-the-art technique in concrete technology and structural rehabilitation.

Features of Hydrodemolition

Hydrodemolition, in general, can be called as a selective demolition method that involves removing damaged or low-strength concrete while keeping intact the healthy concrete. It is an efficient, cost-effective, and precise method that employs high-pressure water to remove deteriorated concrete. 

Hydrodemolition is a safe and controlled solution for the removal of concrete. It has no risks of microcracks of the existing substrate compared with other traditional methods. It is widely used to prepare bridges before placing the deck overlay to achieve high bonding.

The process is much gentler to the environment. It involves pressure jetting, which is silent compared to heavy-duty equipment. This hence helps to reduce acoustic impact on the surrounding area. The water jet systems used in hydrodemolition are a zero-dust activity that reduce air pollution to negligible levels.

Working of Hydrodemolition

Hydrodemolition is performed using hydrodemolition machines that use either high-pressure or ultra-high pressure (UHP) water jets. This can be accomplished by three methods:

1. Hydroscarification
2. Partial depth removal
3. Full-depth removal

Ultra-high pressure water jets are used in hydroscarification, which involves the removal of the top layer of concrete. The depth generally falls between 1/4 to 3/4 inches.

Partial depth removal involves selective removal of concrete that has a depth greater than 3/4 inches.

Full-depth removal involves the demolition of the entire deteriorated concrete.

The high-pressure water jetting has a pressure of around 15,000 to 25000 psi, and UHP possesses pressures in the range of 25,000 to 55,000 psi.

The equipment used for hydrodemolition is automatic such as a robotic cutting tractor. These robots are programmed to control the water jets to facilitate uniform removal of concrete. Along with these robots, trailors and water pumps are used to collect and transport water.

Applications of Hydrodemolition

The major fields for application of hydrodemolition are:

1. Bridge and parking deck repair
2. Decommissioning
3. Decontamination
4. Construction joint cleaning
5. Road maintenance
6. Tunnel rehabilitation

Benefits of Hydrodemolition

The essential benefits of hydrodemolition are:

1. Reduced dust and noise pollution
2. Water collected can be treated and reused
3. Cost and time-effective method
4. No issues of microfractures after hydrodemolition
5. High-quality bonding surface
6. The selective demolition of R.C.C structures without affecting rebars
7. Reduced risks to the operators
8. Works great in confined spaces
9. Best suitable for industrial applications

Drawbacks of Hydrodemolition

Major drawbacks of hydrodemolition are:

1. High runoff issue is faced if the water is not collected and controlled correctly.
2. Hydrodemolition demands water and sewage requirements.
3. Increased risk assessment is necessary while performing hydrodemolition for vertical and overhead works.

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