Method of forming the primary core of a prestressed concrete pipe

Abstract

The present invention relates to a method of forming the primary core of a concrete pipe. A steel cylinder is disposed vertically on the base of the pipe forming machine. A conventional rotary packerhead having a diameter less than the inner diameter of the steel cylinder is lowered concentrically to the bottom thereof. Concrete is then introduced within the steel cylinder through the upper end thereof. The packerhead is rotated to force the concrete into the annular gap between the packerhead and the steel cylinder. As the primary core is formed, the packerhead is raised and rotated while concrete is introduced within the steel cylinder, thereby forming a primary core consisting of a steel cylinder having an inner lining of concrete. In an alternative embodiment, the steel cylinder is completely embedded within the concrete.

What is claimed is: 
     
       1. A method of forming .[.an adherent concrete lining on the inside surface of a cylindrical metal pipe and an adherent concrete casing about the outside surface of the metal sleeve.]. .Iadd.the primary core of a prestressed concrete pipe .Iaddend.comprising the steps of: (a) positioning a cylindrical metal sleeve having .Iadd.a substantially fluid impervious side wall and .Iaddend.a predetermined height in substantially vertical and coaxial relationship within a cylindrical mold having substantially the same height as the metal sleeve such that the outer surface of the metal sleeve is spaced from the inner surface of the mold;   (b) supplying concrete to the space between the outer surface of the metal sleeve and the inner surface of the mold while vibrating the mold to compress the concrete therebetween to form an adherent concrete casing about the outer surface of the metal sleeve;   (c) simultaneously with step (b), supplying .Iadd.a zero slump .Iaddend.concrete to the interior of the metal sleeve;   (d) simultaneously with step (b), radially compressing the concrete in the metal sleeve against the inner surface thereof to form a concrete lining along the length of the inner surface of the metal sleeve; and   (e) removing the metal sleeve having the inner concrete lining and the outer concrete casing from the mold. .Iadd.2. The method according to claim 1 including the step of forming the zero slump concrete supplied in step (c) of a mixture of approximately 72 parts cement, 146 parts aggregate, 208 parts sand, and one part water by weight. .Iaddend.   
     
     
        .Iadd.    The method according to claim 1 and further including the steps of: (f) prestressing the primary core produced in step (e) by wrapping the core with a wire in helical form at a predetermined spacing and tension for substantially the full length of the core;   (g) subsequent to step (f), applying a protective coating to the exterior surface of the primary core to cover the prestressed wire. .Iaddend.   
     
     
        .Iadd..  A method of producing a prestressed concrete pipe comprising the steps of: (a) positioning a cylindrical metal sleeve having a substantially fluid impervious side wall in a substantially vertical orientation on a base of a rotary packerhead assembly;   (b) lowering the packerhead of the packerhead assembly within the metal sleeve to the base of the packerhead assembly;   (c) supplying a zero slump concrete to the interior of the metal sleeve;   (d) simultaneously rotating and raising the packerhead to radially compress the concrete over the inside surface of the metal sleeve to form an adherent concrete lining in the sleeve;   (e) curing the concrete lining on the inside surface of the metal sleeve to form a primary core consisting of the metal sleeve having the inner concrete lining thereon;   (f) prestressing the primary core of step (e) by wrapping the core with a wire in helical form at a predetermined spacing and tension for substantially the full length of the core;   (g) subsequent to step (f), applying a protective coating to the exterior surface of the primary core to cover the prestressed wire. .Iaddend. .Iadd.5. The method according to claim 4 including the step of forming the zero slump concrete supplied in step (c) of a mixture of approximately 72 parts cement, 146 parts aggregate, 208 parts sand, and one part water by   
     
     
        weight. .Iaddend. .Iadd.6.  The method according to claim 4 and further including, prior to step (f), the steps of: (h) positioning a cylindrical mold in a substantially vertical position about the metal sleeve such that the outer surface of the metal sleeve is spaced from the inner surface of the mold to form a uniform gap therebetween;   (i) supplying concrete to the space between the outer surface of the metal sleeve and the inner surface of the mold to form an adherent concrete casing about the outer surface of the metal sleeve; and   (j) removing the metal sleeve having the inner concrete lining and the outer concrete casing from the mold to form the primary core consisting of the metal sleeve having the inner concrete lining and the outer concrete casing thereon. .Iaddend. .Iadd.7. The method according to claim 6 wherein step (i) further includes the step of vibrating the mold to form the concrete casing about the outer surface of the metal sleeve. .Iaddend. .Iadd.8. The method according to claim 6 wherein step (i) is performed simultaneously with step (d). .Iaddend. .Iadd.9. The method according to claim 1 including the step of forming one cubic yard of the zero slump concrete supplied in step (c) of a mixture of 1875 pounds of sand, 1312 pounds of five-eighths inch diameter crushed stone, 650 pounds of Portland Type Two cement, and approximately nine gallons of water. .Iaddend.   
     
     
        .Iadd. 0.  The method according to claim 4 including the step of forming one cubic yard of the zero slump concrete supplied in step (b) of a mixture of 1875 pounds of sand, 1312 pounds of five-eighths inch diameter crushed stone, 650 pounds of Portland Type Two cement, and approximately nine gallons of water. .Iaddend.