Apparatus and method for forming cavities of complex configuration within concrete

A tubular form for creating smooth-walled tubular cavities within concrete structures, said form comprising:

• a plurality of interconnected rigid section members, each said section member comprising a lightweight, flexible mold skeleton member and a polymer-aggregate concrete panel member bonded to said mold skeleton member, the combination of said interconnected section members defining a smooth tubular exterior surface;
• wherein said mold skeleton members each comprises an interior tubular wall portion, annular flanges and longitudinal flanges;
• said annular flanges and longitudinal flanges extending internally and externally to said interior tubular wall portion to define flange internal portions and flange external portions;
• wherein said polymer-aggregate concrete panel member completely fills the area between said externally extending flange external portions;
• and
• wherein said section members are interconnected by joining said flange internal portions of adjacent said section members.

A tubular form comprising a plurality of interconnected rigid section members having a smooth-walled exterior surface for forming a curvilinear, tubular, smooth-walled cavity within a concrete structure, said tubular form produced by:

• providing a plurality of section members each comprising a flexible mold skeleton member comprising a tubular wall portion, a pair of annular flanges and a pair of longitudinal flanges, with said annular flanges and said longitudinal flanges extending internally and externally to said tubular wall portion;
• inserting spacer members between said annular flanges and said longitudinal flanges of adjoining said section members, said spacer members extending externally beyond said annular flanges and said longitudinal flanges;
• joining said section members to each other to create a three-dimensional tubular form;
• applying polymer-aggregate concrete onto the exterior of said section members to completely fill the space between said annular flanges, said longitudinal flanges and said spacer members, planing said sprayed polymer-aggregate concrete using said spacer members as planing guides to produce a smooth-walled, curvilinear exterior surface on said three-dimensional tubular form, and allowing said polymer-aggregate concrete to cure to rigidify said section members.