A set of extruded panels is provided which can be assembled on site to create a permanent form-work for concrete. The set includes inside and outsi de extruded side wall panels which are arranged to be connected edge to edge to form inside and outside walls. Longitudinally spaced connecting wall panels span between the inside and outside walls at spaced positions across the width of the walls to hold the walls apart and define a hollow interior therebetween including a plurality of interconnected cells with a plurality of holes for communicatio n of concrete and reinforcing bars between each cell and the next. Each connectin g wall panel has T-shaped connectors at each edge for attachment to corresponding C -- shaped receptacles on the side wall panels. Rigid foam insulation is inserted at th e outside wall. The inside wall panels are arranged to support without bowing cast concrete poured into the interior within each cell and a support wall identical to the connector walls spans between the inside and outside walls to hold the panel s against bowing.
