Composite filled hollow structure having roughened outer surface portion for use as a piling

A filled structure characterized by the combination of high compressive and tensile strength to allow a high bending load includes a fiber reinforced resinous hollow structure having a tensile strength of at least 30,000 psi. The hollow structure has first and second ends, an inside surface forming a boundary which encloses a space, and an outside surface. At least a portion of the outside surface of one of the ends has a roughened portion sufficient to provide frictional resistance with the ground when the one end is driven into the ground. A hard core is disposed within the space enclosed by the hollow structure. The hard core has a density of at least 35 pounds per cubic foot and a compressive strength of at least 1500 psi. The hard core is formed from a mixture of particulate cementitious material and liquid.

BACKGROUND OF THE INVENTION 
This invention deals generally with stock material, and more specifically 
with filled hollow structures such as light poles, fence posts and pilings 
constructed of plastic or fiberglass. 
The benefits of plastic and fiberglass for articles which are used where 
they are subject to corrosion are generally well recognized. Structures 
using such materials are light weight, strong and attractive. They can be 
made with color integrated into the material so that they do not need 
frequent painting during. their use, and possibly their greatest asset is 
the inherent chemical resistance of the material. A fiberglass or plastic 
structure such as a fence post can be expected to last as long as anyone 
wants it to, even in the most severe environment, with no sign of 
deterioration, and it will not require any maintenance. 
Unfortunately, the major limitation on the availability of such pole type 
fiberglass or plastic structures has been the cost and difficulty involved 
in their manufacture. One typical method of fiberglass construction is the 
forming of the fiberglass into a specific shape by wrapping multiple 
layers of fiberglass fabric on the outside of a core and impregnating the 
fabric with resin or epoxy, however such manufacturing methods are very 
expensive because they involve a great deal of hand labor. 
Another approach, particularly to the construction of cylindrical 
structures, is to use preformed fiberglass or plastic pipe. However, such 
pole structures are not strong enough for most applications unless the 
pipe is very thick or the structure includes wood or metal reinforcing, 
and both of these approaches raise the cost of fiberglass and plastic 
poles so that they are not competitive with conventional metal poles. 
One approach to reinforcing fiberglass or plastic pipe so it can be used as 
a structural member has been the use of fillers which are poured into the 
inside of the pipe, and then harden into a core. Fillers have been 
suggested which include wood with an adhesive binder (U.S. Pat. No. 
4,602,765 by Loper) and rigid foam or concrete (U.S. Pat. No. 3,957,250 by 
Murphy), but these approaches do not furnish strength comparable to metal 
poles. 
Accordingly, there is a need to provide a fiber reinforced pole filled with 
a cementitious material to provide a piling having strengths similar to 
that of a steel piling and having surface features which create skin 
friction as the piling is driven into the ground, to increase bearing load 
capability of the pole. 
SUMMARY OF THE INVENTION 
An object of the invention is to fulfill the need referred to above. In 
accordance with the principles of the present invention, this object is 
attained by providing a filled structure characterized by the combination 
of high compressive and tensile strength to allow a high bending load. The 
filled structure includes a fiber reinforced resinous hollow structure 
having a tensile strength of at least 30,000 psi. The hollow structure has 
first and second ends, an inside surface forming a boundary which encloses 
a space, and an outside surface. At least a portion of the outside surface 
of one of the ends has a roughened portion sufficient to provide increased 
frictional resistance with the ground when the one end is driven into the 
ground. A hard core is disposed within the space enclosed by the hollow 
structure. The hard core has a density of at least 35 pounds per cubic 
foot and a compressive strength of at least 1500 psi. The hard core is 
formed from a mixture of particulate cementitious material and liquid. 
Other objects, features and characteristics of the present invention, as 
well as the methods of operation and functional of the related elements of 
the structure, the combination of parts and economies of manufacture, will 
become more apparent upon consideration of the following detailed 
description and appended claims with reference to the accompanying 
drawings, all of which form a part of the specification.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows an end view across the axis of pole 10 of an embodiment of the 
invention. Pole 10 is preferably formed of four distinct materials, one of 
which, core 12, takes on a particular significance because of the manner 
in which it is formed. Core 12 is encased within pipe 14 which is covered 
by veil 16, on top of which is placed protective surface coating 18. Each 
of the four parts of composite pole structure 10 adds a particular 
characteristic to the pole structure, and together they furnish a pole of 
superior strength and durability which can be produced economically. In 
the broadest aspect of the invention, the veil 16 and coating 18 need not 
be provided. 
The construction of pole 10 is essentially based upon the filling of pipe 
14 with core 12, but core 12 has unique properties which produce a 
non-metallic pole with strength equivalent to that of steel poles. Core 12 
is a Portland cement based product with admixtures which enables the 
mixture to expand as it hardens, or at least limit shrinkage of the 
mixture as it hardens. 
In one embodiment of the invention, it is important that the core material 
normally expand in order that it have a permanent positive stress and 
produce a force fit with exterior pipe 14. It is also vital that the 
hardened core have significant strength, which is best indicated by a 
compressive strength rating of at least 1500 psi, so that it adds 
significant strength to the structure and does not act to merely fill the 
interior space of the pipe. The load/force developed as the core 12 
hardens must, however, be less than the structural strength of pipe 14 in 
order to prevent the forces produced by the attempted expansion during 
hardening of core 12 from distorting and/or substantially weakening pipe 
14 as it restrains the expansion of core 12. 
In a preferred embodiment, cylindrical pipe 14 has a two inch outer 
diameter with 0.030 inch wall thickness up to a ninety-six inch diameter 
with at least 0.500 inch wall thickness. The pipe 14 is constructed with a 
standard polyester, epoxy or vinyl ester resin base, reinforced with 
fibrous roving, chop, or woven mat throughout its entire thickness. Such a 
material has a tensile strength of at least 30,000 psi. Added bending 
strength can be attained if the significant portion of the fibrous roving 
are oriented to be at an angle of at least 45 degrees to the axis of the 
pole or oriented generally along the axis of the pole. The fibrous rovings 
in the illustrated embodiment is fiberglass. It can be appreciated that 
other fibrous rovings such as carbon, etc. may be used. 
As with all fiberglass and resin structures, color pigments may be added 
during manufacture of pipe 14 to produce consistent color throughout the 
entire pipe. 
It is also advantageous to produce veil 16 on the exterior surface of pipe 
14 when it is being manufactured. Veil 16 is a layer of polyester or other 
material cloth impregnated with resin. The production of such a veil is 
well understood by those skilled in the art of fiberglass construction. 
Veil 16 protects the fiberglass against ultraviolet radiation, provides a 
moisture barrier, protects against blooming of the surface fibers of the 
fiberglass and also adds strength to pole 10. 
The core 12 is composed primarily of a mixture of stone, sand, water, and 
Portland-type cement. In one embodiment of the invention, the specific 
material used is Type I Portland-type cement as manufactured by the Lehigh 
Cement Co. The stone component could be solid limestone, as commonly found 
at may local quarries, or lightweight type aggregate as produced, for 
example, by Solite Corp. The sand component is clean washed and 
specifically graded round silica material as is available from many local 
sand quarries. Normal potable water is used and other cementitious 
products may be employed to promote expansion or at least limit shrinkage 
of the core upon hardening. For example, expansion additives such as 
INTRAPLAST N manufactured by Sika (plastic state expansion), or CONEX, as 
manufactured by IM Cement Co. (early hardened state expansion) may be used 
in the core. Alternatively, a standard expansion agent such as alumina 
hydrate may be employed in the core, or the core may comprise Type K 
cement. 
When hardened this formula yields a compressive strength of 1500-15,000 
psi. Moreover, one particular formula normally expands about 0.1-10 
percent upon hardening, except that it is restrained by the hollow tube 14 
and therefore provides an exceptionally strong force fit with hollow tube 
or pipe 14. The density of such a core is at least 35 pounds per cubic 
foot. Instead of expanding, the mixture may be formulated such that 
shrinkage is limited or made to be generally negligible, unlike shrinkage 
which may occur 
Protective coating 18 may also be added to pole 10, for the purpose of 
enhancing ultraviolet protection and corrosion resistance and to produce a 
smooth surface. The coating 18 is applied during the manufacture of the 
pipe and is at least 0.001 inch thick. Protective coating 18 is clear, can 
be made with or without pigments, and includes specific ultraviolet 
absorbers and/or shields. An example of such a coating could be 
"Amerishield" as manufactured by Ameron Corp. or "Tufcote" as manufactured 
by DuPont. 
The composite pole of the present invention can furnish bending strength 
equal to or greater than Schedule 40 steel pipe (ASTM F-1083) of the same 
diameter, and its inherent corrosion resistance is far superior to that of 
steel. Moreover, the present invention actually furnishes a pole which 
will flex more than twice as far as steel and return to its original shape 
without failure. 
FIG. 2 shows another embodiment of a composite pole structure 100 of the 
invention. As shown, the inner surface 110 of the pipe 140 is roughened to 
form a regular or irregular pattern therein. In the illustrated 
embodiment, the inner surface 100 includes an irregular pattern defining a 
plurality of recesses 112 which increases the surface area contact between 
the core 120 and the pipe 140 when the core 120 hardens within in the pipe 
140. Thus, a portion of the core 120 is disposed in the recesses 112 
defining a mechanical lock between the core 120 and the pipe 140. The core 
120, pipe 140, veil 160 and coating 180 are otherwise identical to the 
embodiment of FIG. 1. Alternatively, as shown in FIGS. 4a and 4b, instead 
of the recesses, ridges 112' or 112 can be molded or otherwise formed into 
the inner surface 110 of the pipe 140'. The ridges may be concave 112' 
(FIG. 4a) or convex 112' FIG. 4b) and may be in a regular or an irregular 
pattern. It can be appreciated, however, that the core 120 need not be of 
the type which expands its volume when it hardens to provide a force fit 
with the pipe 140, since the mechanical lock provides the desired locking 
of the core 120 to the pipe 140. Thus, a conventional type cement material 
may be employed as the core material in this embodiment of the invention. 
It can also be appreciated that the core material may be of the type 
discussed above, in which shrinkage is limited during hardening thereof 
FIG. 3 shows yet another embodiment of a composite pole structure 200 of 
the invention. As shown, an adhesive 250 is coated on the inner surface 
212 of the tube 240 such that when the core 220 hardens it is chemically 
locked with respect to the pipe via the adhesive 250. The adhesive 250 is 
preferably SIKADUR 32 .RTM. manufacture by Sika. However, any type of 
adhesive suitable for securing the resin pipe 240 to the hardened core may 
be employed. The core 220, pipe 240, veil 260 and coating 180 are 
identical to the embodiment of FIG. 1. It can be appreciated, however, 
that the core 220 need not be of the type which expands its volume when it 
hardens to provide a force fit with the pipe 240, since the chemical lock 
provides the desired locking of the core 220 to the pipe 240. Thus, a 
conventional type of cement material may be used as the core material in 
this embodiment of the invention. It can also be appreciated that the core 
may be of the type discussed above, in which shrinkage is limited during 
hardening thereof 
Tests were performed to determine the push-out strength or frictional 
resistance of the core material to the inner wall of the composite pole 
structure. The total load in pounds required to dislodge the core from the 
hollow tube was measured and divided over the unit area and represented in 
units of psi. The average frictional resistance of the core made in 
accordance with the embodiment of FIG. 1, (no mechanical or chemical 
locking of the core) was measured to be on average 25 psi over the entire 
inner wall surface of the pipe. With the addition of an adhesive 250 
bonding the core 220 to the pipe 240 (FIG. 3) the average frictional 
resistance of the core was determined to be approximately 90 psi. Thus, 
there is a corresponding minimum increase in bending strength of 
approximately 30% as a result of a better bond between the core and the 
pipe which provides for a better transfer of shear between the structural 
component parts. With both expansion of the core 220 and the use of the 
adhesive 250 (FIG. 3), failure of the composite structure is often in the 
cohesive strength of the core 220 itself. Namely, the cohesive strength of 
the bond between the core and pipe can be stronger than the cohesive 
strength of the core 220. 
Additives 20 may be included in the core of the invention to improve the 
composite pole structure. For example, silica fume, an extremely fine 
aggregate that fills tiny voids in the core may be added to the core to 
improve the compressive thus, making he composite pole structure even 
stronger. Steel, glass or polymer fibers additives mixed into the core 
could also be employed. The fibers deter cracking which cause premature 
failures, provide higher stiffness, provide higher compressive strength 
and provide higher bending strength, all of which enhance the performance 
of the composite pole structure. 
FIGS. 5a and 5b show other embodiments of the invention, each having a 
roughened portion on at least a portion of an outside surface of at least 
one of the ends of the filled structure. It can be appreciated that the 
poles or filled structures of FIGS. 5a and 5b may be configured as 
disclosed in any of the embodiments of FIGS. 1-4b, but also include a 
roughened portion on an outside surface thereof, as explained below. 
As shown in FIG. 5a, the fiber reinforced pipe 140 of pole 300 has an outer 
surface 310. In the illustrated embodiment, the outside surface 310 
includes an abrasive adhesive 320 coated on at least one end of the pole 
300. The abrasive adhesive 320 includes an abrasive such as a grit 
material, e.g., sand, in an epoxy, and defines a roughened portion on the 
outside surface 310. When the pole 300 is driven into the ground, the 
roughened portion creates skin friction with the ground which increases 
the bearing load capabilities of the pole 300 as compared to that of a 
smooth pole. Thus, the pole 300 may be relatively shorter than traditional 
material pole (smooth steel and/or concrete poles) since it does not have 
to be driven as deep as the traditional poles to achieve the same load 
bearing. The abrasive adhesive defining the roughened surface works well 
in mounting the pole 300 in sandy ground, particularly when the size of 
the grits of the abrasive closely match the size of the grits of sand in 
the ground. 
FIG. 5b shows a pole 400 having a plurality of fiber rovings 412 wrapped 
about a lower portion of the fiber reinforced pipe 140 so as to extend 
from outside surface 410 thereof. Each of the fiber rovings 412 may be a 
singular fiber roving strand or may comprise a group of smaller roving 
strands. Thus, during manufacture of the fiber reinforced pipe 140, the 
fiber rovings 412 may be wrapped to extend from the outside surface 410 
and cured to be integral with the pipe 140. In the illustrated embodiment, 
the fiber rovings 412 are disposed in spaced relation thereby defining a 
roughened portion on the outside surface 310. The fiber rovings 412 may be 
evenly or unevenly spaced. Further, the fiber rovings 412 are arranged so 
as to be generally perpendicular to the longitudinal axis 420 of the pole 
400 so as to create more driving friction than would be created if the 
rovings 412 were more vertically oriented with respect to the longitudinal 
axis 420. The fiber rovings 412 create increased skin friction when driven 
into the ground, resulting in the advantages noted above, with reference 
to the embodiment of FIG. 5a. The fiber rovings 412 have been found to 
provide a pole having good load bearing capabilities in muddy soil or 
clay. 
In the illustrated embodiments, only a portion of poles 300 and 400 near an 
end thereof is roughened since one end portion is typically driven into 
the ground when the pole is used as a piling. In piling applications under 
water, the portion of the pole exposed to water is preferably smooth to 
prevent biological attack from mollusks, barnacles and the like, which 
have a more difficult time attaching to a smooth surface. 
Although two examples of surface roughening have been described above, it 
can be appreciated that the pole of the invention may be roughened any 
amount to produce increased skin friction with the ground. 
It is to be understood that the form of this invention as shown is merely a 
preferred embodiment. Various changes may be made in the function and 
arrangement of parts; equivalent means may be substituted for those 
illustrated and described; and certain features may be used independently 
from others without departing from the spirit and scope of the invention 
as defined in the following claims. 
For instance, structures may be produced without either veil 14 or 
protective coating 16 when the application does not require ultraviolet 
protection. Moreover, the diameter and cross sectional configuration of 
the external member may, of course vary, and the particular formula of the 
core could be changed as long as the requirements of the claims are 
retained. Further, although a generally round cross-sectioned pipe is 
disclosed, the composite structure may be in any shape or closed section, 
such as, for example a square, rectangular, oval etc, cross-section.