foundation system of burj al arab

Hydrodemolition for concrete removal

We know optimum removal of concrete that are deteriorated or damaged is necessary to establish economy of repair work. Here water jetting is used to remove concrete. Very high pressure is obviously required to remove concrete but while choosing this method, objective is to preserve reinforcement.


Reinforcement is relatively costly material in reinforced concrete construction. Removal with water jetting leaves a clean surface of steel reinforcement that can be reused if not deteriorated itself. This method produced least damage to sound concrete. The total method is called hydrodemolition.


Concrete is disintegrated under high pressure water jets and produce small pieces; size ranging from sand to gravel and perform better on deteriorated and unsound concrete. Hydrodemolition produced a rough profile after removal.


The pressure of water jets may vary from 70 Mpa (10 Ksi) to 240 Mpa (35 Ksi). The capability of removal depends on pressure. The equipment should be chosen depending on water demand. As huge amount of water is required, contamination and disposal as well after/during operation is an important consideration in planning removal work.


It should keep in mind that thin slabs/decks should not be punched by water jets if selected repair area contains unsound concrete throughout its full depth. So important information about hydrodemolition are:

a. Water jets of 70 Mpa (10 Ksi) have water demand (130~150) liter/min

b. Water jets of 100-140 Mpa have water demand (75~150) liter/min

c. Water jets of 170 -240Mpa pressure can be called ultra-high pressure. In this pressure water jets have milling capacity. It can remove 1/8” to several inches.

d. Water jet having pressure of 70-140 Mpa have water demand of (75~150) liter/min and very useful to remove concrete from area where large equipment cannot be reached.

e. Usually capable up to depth of less than equal 150 mm depth. Common example are parking decks, bridge surface etc.


Advantage:

1. Does not damage sound concrete

2. Steel reinforcements remain undamaged can be reused and left clean after operation.

3. The debris produced can be handled easily (size of aggregate).


Disadvantage:

1. Large amount potable water is required for water jet.

2. Disposal of waste water have to be controlled; if waste water enter in to waterway, environmental impact assessment (EIA) is required.

3. Flying debris produce hazard.

4. Hearing protection is required due to production of high level noise.

5. Removal profile follows depth of deterioration.

6. Removal rate reduced when sound concrete have to be removed.

7. Additional safety is required as these systems produce high pressure.

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