Question

Grouting of suspension bridge cables.

Answer 1

The oldest and most common protection against corrosion is the use of grout. Cables are fitted in ducts that will be filled with grout (therefore isolating the cables from the external environment).

The main disadvantages of this method:

* Difficulty to fill the duct uniformly with grout "

Since the ducts are holding the grout, they should well protected against corrosion and external factors

* The heavy weight of the grout will reduce the effective tension that a cable can provide

* Due to its low tensile strength, the stiff grout (usually cement grout), not being able to follow the deformation of the cables will crack. The uncovered areas of the cable will lead to weakness points (by being exposed to the atmosphere)

These are done by pumping and vaccum injection method

Usually, cement grout is injected after the cable is under dead Ioad stresses because cement grout is the cheapest filling material and also has good corrosion protection characteristics.

Pumping:

The standard method for placing grout in a tendon duct is by pumping. The pumps used for grouting are typically screw or auger type pumps. The mixed grout is discharged into a hopper, which feeds the pump directly. The pump is connected to the duct inlet pipe with a hose and valve. The air and water are pushed out of the duct as the grout displaces it.

Vacuum injection

it is the specified technique for filling voids after initial grouting. It can also be used for the initial grouting but the sealing of an entire tendon is more problematic than sealing a small void. The vacuum injection method requires the duct system to be sealed. The air is drawn out of the void by a vacuum pump. A calibrated meter then measures the volume of air drawn back into the void as the vacuum is released. The final step is to re-establish the vacuum and inject the measured volume of grout into the evacuated void.