Use of recycled plastics for structural building forms

A planar modular plastic structural composite comprising at least one pair of a grooved side and an integrally molded tongue-forming side positioned parallel opposing to each other, defining therebetween a width or length dimension of the composite, wherein said width dimension is between about two and about ten times the size of the height (thickness) dimension of the composite, each side perpendicular to the plane of the composite, in which the composite is formed from a co-continuous immiscible polymer blend consisting essentially of a high-density polyolefin and a thermoplastic polymer-coated fiber material or a thermoplastic polymer having fiber material embedded therein, wherein the grooved side defines a groove comprising a top surface, a side surface, and a bottom surface and the tongue-forming side is dimensioned to possess a tongue-shaped member comprising a top surface, a side surface, and a bottom surface that interlockingly engage a groove having the dimensions of the groove defined by the grooved side, and the grooved side and tongue-forming side are dimensioned so that the top surface, the side surface, and the bottom surface of the tongue-shaped member directly contact each corresponding top surface, side surface, and bottom surface of the groove and a plurality of the essentially planar modular plastic structural composites may be interlockingly assembled to distribute a load received by one assembly member among other assembly members.