On many remote projects requiring large-diameter concrete pipe, plant-produced units are just too heavy to haul economically. The disadvantage of current precast piping systems is in the overall cost of transporting short, heavy sections of pipe to the location, preparing a proper bed for all the joint locations, and joining the short lengths to one another.
To overcome these problems, Anton Majnaric of Copley, Ohio, and William Bjerke of Hudson, Ohio, have developed an in situ concrete pipe system that allows much longer lengths. Aside from the obvious cost reductions in transporting and handling large pipe sections, the great functional advantage is the reduction in the number of joints in a network.
The pipe has an inner and outer sleeve separated by a spacer ring, which creates a void between the sleeves. Concrete placed in the void creates the pipe structure. The spacer ring has a number of interlocking ring forms with nesting members to allow for interconnection.
In another version, interlocking forms shape both the inner and outer surface of the pipe. Concrete fills in the conduits and between the void of the inner and outer surfaces to solidify the pipe.
Both pipe styles may be joined with cast-in-place concrete collars and sealing rings, or by banded gaskets, such that the pipe may be free to change length and pivot in the joint. Alternatively, an elbow form may be used.
The reinforcing element may be reinforcing rods, cable, wire, or rebar. The patent does not suggest or recommend a maximum feasible length. Therefore, any length up to what is feasible to pour concrete is probably possible.