polymer cement concrete or polymer concrete is introduced into the conduit within the beam shell by pumping it through the injection port 39 located in the side of the conduit the vent ports 40 are used to ensure that no air is trapped within the conduit 38 during the placement of the compression reinforcement 31 the compression reinforcement as seen in fig6 has a rectangular cross section that is 15 5 34 wide and 14 7 34 tall but could be manufactured to larger or smaller dimensions the profile 50 of the compression reinforcement as shown in fig3 follows a path which starts at approximately 7 34 off of the bottom of the beam at the beam ends and varies parabolically with the highest point on the profile located at the center of the beam such that the conduit 38 is tangent to the top flange 33 the profile 50 of the compression reinforcement is designed to resist the compression and shear forces resulting from vertical loads applied to the beam in much the same manner as an arch structure as is known in the art the profile 50 of the compression reinforcement 31 could be constructed along a different geometric path and to different dimensions from those indicated while the embodiment presented assumes introduction of the compression reinforcement after the beam shell has been erected it could also be introduced during fabrication of the beam shell the thrust induced into the compression reinforcement resulting from externally applied loads on the composite beam is equilibrated by the tension reinforcement 32 of the composite beam 11 the tension reinforcement 32 consists of layers of unidirectional carbon reinforcing.