Hollow, composite rebar structure, associated fabrication methodology, and apparatus

Abstract

A rebar structure for concrete reinforcement may include an elongate tubular central wall portion having an inside surface and an outside surface. The central wall portion may be formed circumferentially around a core axis and may include glass or carbon fibers mostly being oriented longitudinally parallel to the core axis. The rebar structure may include an inner wall portion bonded to the inside surface of the central wall portion. The inner wall portion may include glass or carbon fibers and may have a higher percentage of fibers oriented non-parallel to the core axis as compared to the central wall portion.

We claim: 
     
         1 . A method of making rebar, comprising:
 forming an uncured inner layer of a hollow tubular rebar structure around an internal support structure and a core axis, along a processing path, upstream from a pultrusion die, the inner layer comprising resin and fibers comprising at least one of glass, carbon, and basalt,   forming an uncured central layer of the hollow tubular rebar structure around the uncured inner layer, upstream from the pultrusion die, the central layer comprising resin and fibers comprising at least one of glass, carbon, and basalt, the fibers oriented mostly parallel to the core axis, the inner layer having a higher percentage of fibers oriented non-parallel to the core axis as compared to the central layer.   
     
     
         2 . The method of  claim 1 , further comprising
 forming an uncured outer layer of the hollow tubular rebar structure around the uncured central layer, upstream from the pultrusion die, the outer layer comprising resin and fibers comprising at least one of glass, carbon, and basalt, the outer layer having a higher percentage of fibers oriented non-parallel to the core axis as compared to the central layer.   
     
     
         3 . The method of  claim 1 , further comprising
 forming a purchase-enhancing structure on the exterior of the rebar.   
     
     
         4 . The method of  claim 1 , wherein the step of forming a purchase-enhancing structure includes wrapping a textured material around an external surface of the uncured rebar structure upstream of the pultrusion die and removing the textured material downstream of the pultrusion die, thereby leaving a permanent granular external texture to the rebar after curing. 
     
     
         5 . The method of  claim 1 , wherein the inner layer comprises a mat material. 
     
     
         6 . The method of  claim 1 , wherein the inner layer comprises texturized rovings. 
     
     
         7 . The method of  claim 4 , wherein the hollow rebar structure is partially cured in the pultrusion die and fully cured in an oven disposed downstream of removing the textured material. 
     
     
         8 . The method of  claim 4 , wherein the internal support structure is an elongate mandrel. 
     
     
         9 . An apparatus for making an elongate, composite-material rebar structure, said apparatus having a rebar-formation axis and upstream and downstream regions disposed at spaced locations along said axis, said apparatus comprising:
 an internal support structure having a long axis which is substantially coincident with said rebar-formation axis, extending from said upstream region toward said downstream region;   a guide configured to form an uncured inner layer around the internal support structure and an uncured central layer around the uncured inner layer, the inner and central layers comprising resin and fibers, the fibers comprising at least one of glass, carbon, and basalt, the central layer having fibers oriented mostly parallel to the rebar-formation axis and the inner layer having a higher percentage of fibers oriented non-parallel to the core axis as compared to the central layer;   a pultrusion die having a long axis which is substantially coincident with the rebar-formation axis, circumsurrounding the internal support structure, configured to form an elongate, composite, hollow rebar structure including the inner layer and the central layer, disposed downstream of the guide.   
     
     
         10 . The apparatus of  claim 9 , further comprising
 a peel/ply application assembly disposed upstream of the pultrusion die and configured to wrap a textured material over the uncured central layer.   
     
     
         11 . The apparatus of  claim 10 , further comprising
 a peel/ply removal assembly disposed downstream of the pultrusion die and configured to remove the textured material from the hollow rebar structure.   
     
     
         12 . The apparatus of  claim 11 , wherein the pultrusion die is configured to cure the hollow rebar structure to a less-than 100% cured state and further comprising
 an oven disposed downstream of the peel-ply removal assembly, the oven configured to cure the hollow rebar structure to a fully cured state.   
     
     
         13 . The apparatus of  claim 10 , wherein the guide is further configured to form an uncured outer layer around the uncured central layer comprising resin and fibers, the fibers comprising at least one of glass, carbon, and basalt, the outer layer having a higher percentage of fibers oriented non-parallel to the core axis as compared to the central layer. 
     
     
         14 . The apparatus of  claim 10 , wherein the internal support structure is an elongate mandrel.