PIPES

When concrete pipes are to be internally lined with AKS, the following methods and equipment will be required.

The best results are achieved through the vertically cast method. Other techniques have been used, but they require more care and may not achieve the same pull off resistance between the liner and the concrete.

The vertical cast method normally employs a collapsible inner mould, which can be inserted into the prefabricated tube of AKS and removed once the pipes has been cast.

Alternative and very successful systems involving a hinged outer mould are also available.

Pipes may be lined to 360 degrees or less than 360 degrees of their internal surfaces.

Each design must be individually assessed to ensure that backpressure from ground water is correctly dealt with. There is also a need to differentiate between large pipes (greater than 800mm diameter) and small pipes (less than 800mm diameter) as this may affect jointing details.

The following procedure for casting AKS into the concrete pipe is recommended:

> AKS tubes are pre-manufactured to the exact internal diameter of the pipe.

> These tubes are constructed with a male and female side. The male side will have a 50mm wide tapered projection which, when laid on site, will fit into the female side, which is fitted with a 50mm wide collar - like a spigot and socket joint.

> The pre-fabricated tubes are fitted onto the collapsible inner mould.

> The reinforcing cage is positioned around the AKS lined inner mould with spacers installed where necessary to position reinforcement correctly.

> Care must be taken not to damage or puncture the liner during this process.

> Once the reinforcing is in place, the outer formwork is positioned and the concrete poured.

> After the concrete has set, the formwork can be removed.

> When laying or installing the pipe, care must be taken not to damage the 50mm long "male" projecting portion of the joint.

> This projection will slip into the female collar to give a complete AKS lined pipeline.

> It is not always necessary to weld these joints in a sewer pipe system as any degradation of the concrete at the joint will require Oxygen. Once the limited Oxygen has been consumed by the bacteria present (causing minimal attack to the concrete), no further degradation will take place.

> For an aggressive industrial effluent application, it will be necessary to extrusion weld these joints to ensure that no effluent comes in contact with the concrete pipe.

It is not considered practical for "in situ" welding to be carried out in pipes of less than 800mm internal diameter due to difficulty in man access.