Composite shape forming structure for sealing and reinforcing concrete and method for making same

A multiple ply composite structure used to reinforce, seal and shape concrete structures has a first ply formed of unidirected continuous filament reinforcements which are bonded together by a thermosetting polymeric resin matrix. A second ply comprises a plurality of separately spaced protuberances, each of which is individually coated with a hardenable thermosetting polymeric resin. The hardenable thermosetting polymeric resin of the second ply bonds the first ply to the second ply by forming a concave resin meniscus which anchors each of the protuberances of the second ply to the first ply.

BACKGROUND OF THE INVENTION 
This invention relates to integral tensile-strength reinforcing materials 
applied to concrete structures. 
The tensile strength of concrete is approximately one tenth that of its 
compression strength. For this reason, concrete structures subjected to 
bending or deflection, such as beams, roofs, columns, piling, and buried 
pipe must be reinforced by a material that increases its tensile strength. 
The material most commonly used previously to reinforce concrete is carbon 
steel. Among the advantages of using carbon steel as a concrete 
reinforcement material are its low cost, its ready availability, its 
predictable physical properties and its long history of use and approval 
by building code committees. 
However, in many applications serious problems have been encountered with 
the use of these carbon steel reinforcements. Corrosion of carbon steel 
reinforcing members has caused the deterioration of concrete bridge decks, 
concrete pipe and other concrete structures. For example, a primary cause 
of bridge deck deterioration is the cyclic freeze-thaw exposures and the 
reinforcing steel corrosion caused by the extensive use of de-icing salts. 
Practical realities of the concrete formation process can exacerbate steel 
corrosion problems. For example, due to the shortage of fresh salt-free 
water in certain regions of the world, steel-reinforced concrete 
structures have frequently used saltwater in the concrete mix. When sea 
water was utilized in the concrete mix used to build reinforced concrete 
structures in Saudi Arabia, the resulting high internal chloride level of 
the concrete produced extensive corrosion of the steel reinforcement 
within the concrete as well as cracking, delamination and spalling of the 
concrete. 
The steel bar and wire materials used to form and reinforce concrete are 
generally placed inside rather than outside the concrete structure, for 
several reasons. First, it is difficult and expensive to bond or otherwise 
attach steel reinforcement members to the exterior of concrete structures 
subjected to beam loads. Second, encasing the carbon steel reinforcement 
members within the alkaline concrete material protects the steel from 
corrosion due to acidic water. 
However, the placement of steel reinforcements within the concrete 
structures they reinforce presents numerous drawbacks. In a typical 
concrete beam, its bottom exterior surface bears the greatest tensile 
load. Accordingly, placement of the steel reinforcement within the 
concrete beam fails to support the beam at its weakest point. Internally 
placed steel reinforcements do not enclose the outer surface of the 
concrete, and thus provide no protection for the outer surface from water 
intrusion or leaking. Similarly, internally placed steel reinforcements do 
not prevent concrete from spalling or breaking loose in crisis conditions 
such as an earthquake. Furthermore, steel reinforcements placed within a 
reinforced concrete structure are hidden from view and are thus difficult 
and expensive to inspect. 
In order to avoid problems with corrosion, makers of concrete structures 
have turned to nonmetallic materials as alternatives to carbon steel 
reinforcements. For example, steel reinforcing bars can be replaced by 
pultruded bars of fiber-reinforced plastic ("FRP") or filament-wound FRP 
tubular structures, or steel mesh can be replaced by FRP grating or 
screens. These materials, however, are used as internal reinforcements. 
Thus, their use does not alleviate the problems described above found with 
all internally placed reinforcements. 
Corrosion-resistant stainless steel fibers or alkaline-resistant fiberglass 
fibers may be intermixed or otherwise placed within concrete before it 
hardens in order to increase the tensile strength of the concrete. 
However, this method fails to protect the outer surfaces of the concrete 
structures it reinforces, and further requires high cost and complex 
mixing procedures in order to provide uniform dispersion of the 
reinforcing fibers within the concrete. 
Certain externally-mounted structures have also been explored as 
alternative means to reinforce concrete. For example, paper-thin polymeric 
composite laminates, made in the form of sheets, can be bonded to the 
exterior surface of a dry concrete structure. Such composite laminates, 
made from continuous carbon fibers and a prepreg epoxy resin, have been 
used to reinforce or repair concrete bridge decks and concrete walls. In 
California, polymeric composite materials containing continuous filament 
reinforcements have been used after earthquakes to reinforce fully cured 
concrete column structures that support automotive highways. These 
composite sheet reinforcements are usually bonded to a dry concrete 
surface with a thin layer of epoxy resin adhesive. 
These external surface concrete reinforcements are expensive to make and 
apply and their reinforcing strength depends upon the bond strength 
between the composite laminate and the concrete surface material. Because 
the composite laminates are not bonded to the concrete until after the 
concrete has already been cured, no truly intimate bond between the 
laminate and the concrete can be made. Furthermore, the bond strength 
which can be established between the laminates and the concrete is 
vulnerable to the low peel strength characterizing epoxy adhesives. Long 
term exposure to weathering and severe temperature changes can also cause 
the thin composite sheet to delaminate from the concrete structure. 
Beyond reinforcements, external structures used in the creation of concrete 
structures include shaping forms into which wet concrete can be poured and 
maintained in a desired shape until it dries. If external conditions are 
such that ice forms in the concrete while it dries, the concrete can lose 
nearly half its potential design strength, even though cement hydration 
can be reestablished upon re-warming the frozen concrete. Keeping concrete 
warm or using accelerators to reduce the curing time increases the cost of 
the concreting job. Thus, to control the temperature of the concrete as it 
dries, these forms have been made of thermally insulative materials. 
However, these forms have not also served to reinforce the completed 
concrete structure or permanently seal its outer surface. 
Shaping forms are used in the formation of centrifugally cast concrete 
pipes. One characteristic of these pipes has been that, due to unavoidable 
variations in the quantity of concrete placed within the rotating form, 
the pipe cannot be made to possess identical internal diameters. 
Conventional concrete pipe liners, such as those cast within the concrete, 
are usually made of flexible sheets of thermoplastic materials that do not 
increase the structural strength of the pipe. The interior of conventional 
concrete sewer pipe is commonly protected from the corrosive effects of 
the sulfuric acid produced by hydrogen sulfide in sewer gas, by 
cast-in-place pipe liners made of poly vinyl chloride. These pipe liners 
sometimes have protrusions which are pushed into the wet concrete in order 
to anchor the liner to the concrete. However, these protrusions are not 
formed to be integral structural constituents of the concrete pipe. 
One particular method used to attach pipe liners to concrete pipes has been 
to extend circumferentially spaced extruded tee shapes longitudinally 
within the pipe wall. A downside of this method is that the concrete is 
weakened in direct proportion to the depth of the plastic anchor tee. Such 
"tee locks" provide longitudinal grooves that serve as built-in 
stress-risers that can produce fractures in the concrete pipe structure 
when the pipe is shifted during earthquake or other soil motion events. 
One attempt to create a concrete liner having protrusions which can be made 
internal structural constituents of the concrete is known. To create this 
liner, a laminate surface was coated with a bonding resin, and rock 
aggregate particles were sprinkled upon the resin. The rock aggregate 
particles were then embedded in fresh concrete. However, it was found that 
the resulting bond strength for the liner was limited to the tensile 
strength of the hardened resin present between the bottom of the rock 
particle and the laminate surface with which it was in contact. This 
particle bond strength was found to be less than the tensile strength of 
either the rock particles or the concrete. For this reason, such aggregate 
covered laminates were deemed not suitable as concrete reinforcement 
constituents. 
SUMMARY OF THE INVENTION 
A multiple ply composite structure is provided for reinforcing, sealing, 
and shaping concrete. A first ply of the inventive composite structure is 
formed of unidirected continuous filament reinforcements which are bonded 
together by a thermosetting polymeric resin matrix. A second ply of the 
inventive composite structure comprises a plurality of separately spaced 
protuberances, each of which is individually coated with a hardenable 
thermosetting polymeric resin. The hardenable thermosetting polymeric 
resin of the second ply bonds the first ply to the second ply by forming a 
concave resin meniscus which anchors each of the protuberances of the 
second ply to the first ply. 
A primary object of the current invention is to provide a fiberglass 
composite laminate for shaping, sealing and structurally reinforcing a 
wide variety of concrete structures, including beams, bridge decks, roofs, 
floors and tilt-up building panels. 
Another object of the current invention is to provide a fiberglass laminate 
structure bonded to individual rock particles such that the bond strength 
between the rock particles and the fiberglass laminate at least equals the 
tensile strength of the rock particles. 
A further object of the invention is to provide a corrosion-resistant 
replacement for the steel wire and reinforcing bars currently used to 
increase the tensile strength and fracture-resistance of concrete 
structures. 
Yet another object of the invention is to provide an impermeable exterior 
surface for a concrete structure, such as a bridge deck, building wall or 
concrete pipe, that is able to resist the effects of weathering or 
continuous exposure to corrosive liquids. 
A still further object of the invention is to provide a thermally 
insulative non-removable shape-forming structure for forming concrete that 
inhibits the loss of exothermic heat to the surrounding atmosphere and 
prevents loss of water from the concrete as it cures. 
Yet another object of the invention is to provide a permanent external 
concrete reinforcement that does not delaminate or separate from the 
concrete as a result of low peel strength, earthquake shock, explosive 
pressures, or dimensional changes resulting from extremes in surface 
temperature. 
A still further object of the invention is to provide a corrosion-resistant 
concrete pipe liner that enables a concrete pipe having a given wall 
thickness to increase its resistance to stresses produced by internal 
pressure and bending moments resulting from such events as earthquake, 
faulty handling and improper pipe installation. 
Yet another object of the present invention is to provide a concrete 
cylinder, such as pipe, poles, piling and tanks with an exterior as well 
as interior laminate reinforcement. 
A still further object of the present invention is to provide a method of 
folding and installing an aggregate-covered composite pipe liner in a 
centrifugally-cast concrete pipe to make a centrifugally-cast concrete 
pipe having identical internal diameters.

DESCRIPTION OF A PREFERRED EMBODIMENT 
The present invention provides a composite laminate structure which may be 
bonded to a concrete member with a bond strength at least equal to the 
bond strength of the concrete. This was made possible by the discovery 
that when clean dry rock aggregate particles are completely coated with a 
thermosetting resin prior to being placed on a dry composite laminate 
surface, and there remain stationary until the bonding resin hardens, the 
resulting bond strength of the rock aggregate particles to the laminate 
will exceed the tensile strength of any concrete material that 
subsequently may be cast to enclose the rock aggregate particles. This 
high particle-to-laminate bond strength is primarily due to the complete 
enclosure of each rock aggregate particle with a resin shell and the 
anchoring strength of a concave meniscus of resin formed when the resin 
flows toward the panel structure. 
Referring to FIG. 1 of the drawings, there is illustrated a preferred 
aggregate-covered composite laminate panel 1 of the present invention. 
Aggregate-covered composite laminate panel 1 comprises a single ply 
thickness of appropriately spaced resin-coated rock aggregate 
protuberances 2 bonded to one side 10 of a unidirected composite laminate 
panel structure 3. Unidirected composite laminate panel structure 3 
contains at least one ply of parallel strands of continuous filament 
reinforcements 4 which are impregnated and bonded together with an 
impermeable thickness of a thermosetting polymeric resin 5. A single ply 
thickness of resin coated rock protuberances 2 comprises a plurality of 
rock aggregate particles 6. Preferably rock aggregate particles 6 are 
spaced 1 millimeter to 20 millimeters apart. While rock aggregate 
particles 6 will typically have an irregular shape, each rock aggregate 
particle 6 preferably is shaped such that any cross section through what 
is roughly the center of the particle has a width in the range of from 3 
millimeters to 20 millimeters. Referring now to FIG. 2, each rock 
aggregate protuberance 2 is individually covered with a hardenable 
thermosetting polymeric resin 7. The application of a force, such as 
gravity or centrifugal force, causes hardenable resin 7, while still wet, 
to flow to the base 8 of each rock aggregate protuberance 2, and to harden 
to form a concave meniscus anchor 9 that connects and bonds each rock 
aggregate protuberance 2 to side 10 of unidirected composite laminate 
panel structure 3. 
FIG. 2 depicts an enlarged cross section view of a concrete structure 15 
reinforced by aggregate-covered composite laminate panel 1. This 
enlargement shows how each individual rock aggregate protuberance 2 is 
bonded to the exterior surface of the composite laminate 10 by the 
hardened shell of resin 7 and the hardened concave resin meniscus anchor 9 
formed between the rock 2 and the interior composite laminate surface 10 
to provide a composite laminate anchor structure. The concrete of concrete 
structure 15 encloses each rock aggregate protuberance 2 such that 
aggregate-covered composite laminate panel 1 becomes a structural 
constituent of concrete structure 15. 
A composite laminate reinforced concrete structure such as concrete 
structure 15 can be constructed by applying wet concrete to the 
aggregate-covered side 10 of unidirected composite laminate panel 
structure 3, or alternatively, by embedding the ply of resin-coated rock 
aggregate protuberances 2 into a wet concrete surface. Preferably the 
parallel strands of continuous filament reinforcements 4 and thermosetting 
polymeric resin 5 are composed of substances which form a waterproof, 
insulating surface for the concrete structure. Aggregate-covered composite 
laminate panel 1 will then, in addition to providing structural 
reinforcement, inhibit deterioration of the reinforced concrete caused by 
acidic water and reduce water evaporation to prevent the concrete from 
losing design strength as it cures. 
FIG. 3 illustrates a preferred embodiment of the invention in which 
aggregate-covered composite laminate panel 1 is used as a tensile strength 
reinforcement 11 for a concrete wall structure 12. Aggregate-covered 
composite laminate panel 1 is bonded to the exterior unreinforced portion 
of the concrete structure 12. 
Another preferred embodiment of the invention utilizing aggregate-covered 
composite laminate panel 1 is illustrated in FIGS. 4 and 5. A simply 
supported concrete beam 13 employs the aggregate-covered composite 
laminate panel 1 as an external bottom structural reinforcement that 
resists the external surface tensile stress that results when the concrete 
beam 13 is loaded. 
FIGS. 6 and 7 depict another preferred embodiment in which 
aggregate-covered composite laminate panel 1 is used to reinforce a 
cantilever concrete beam 14 which is set into a concrete wall 16. In this 
embodiment, aggregate-covered composite laminate panel 1 acts as an 
external upper structural constituent of concrete beam 14. It should be 
noted that such a cantilever concrete beam 14 could be further reinforced 
by a second aggregate-covered composite panel acting as an external lower 
structural constituent. 
To determine the effectiveness of the present invention to increase the 
tensile strength of a concrete beam, the 20 ton compression machine shown 
in FIG. 8 was used to test the load resistance of four concrete beams. 
FIG. 8 schematically illustrates the arrangement of the two beam loading 
noses 17 and the concrete beam specimen 18. The beam testing apparatus was 
equipped with a movable anvil 19 that moved vertically at a rate of 2.5 
millimeters per minute to impart a load to the specimen. An electric 
displacement sensor 20 measured the beam deflection. Each concrete beam 
specimen 18 measured 100 millimeters in width and 400 millimeters in 
length. A first 30 millimeter thick concrete beam specimen was cast 
without any bottom reinforcement and served as a reference. FIG. 9 shows 
the actual plot of load versus deflection 21 when the plain unreinforced 
concrete beam specimen was tested. Without any reinforcement, the specimen 
quickly broke in two after resisting a load of only 0.068 metric tons (68 
kg). 
A second 30 millimeter thick concrete beam specimen was reinforced with a 
thin 1 millimeter thick sheet of aluminum glued to the bottom of the 
concrete beam. As can be seen from the plot of load vs. deflection 21a in 
FIG. 10 this reinforcement enabled the concrete beam to resist a slightly 
greater load before breaking. However, due to the aluminum reinforcement 
sheet glued to the bottom of the specimen, the fractured concrete beam 
remained together while undergoing a bending deflection of 16 millimeters 
at which time the aluminum sheet delaminated from the concrete. This test 
demonstrated that the bonding resin peel-strength is more important than 
the bonding resin tensile or shear strength when bonding a thin sheet 
reinforcement to the surface of cured concrete. 
A third 30 millimeter thick concrete beam specimen was reinforced by an 
aggregate-covered composite laminate panel constructed according to the 
present invention and was also tested by the apparatus shown in FIG. 8. To 
construct the third beam specimen, a wet concrete mixture was poured upon 
a flat aggregate-covered composite laminate panel similar to that 
illustrated in FIG. 1, and was smoothed and allowed to dry. 
FIG. 11 shows the load vs. displacement plot 21b when the third beam 
specimen was tested with the 20 ton compression machine. The test showed 
that the composite reinforced concrete beam was able to deflect 
approximately 10 times the distance of a conventional concrete beam before 
it fractures. This indicates a substantial increase in the ability of the 
concrete structure to withstand earthquakes. The plot 21b shown in FIG. 11 
also illustrates that before the concrete beam fractured it was able to 
resist a load more than six times greater than an unreinforced 
conventional concrete beam. This means that load-bearing concrete 
structures such as building floors, streets and sidewalks can be produced 
at a much lowered cost. Plot 21b also indicates that following the 
concrete beam fracture, the concrete beam member did not come apart, but 
remained intact and continued to resist a load while its displacement 
distance continued to increase. This greatly reduces the hazard that 
concrete pieces will break off and fall when concrete structures are 
subjected to earthquake or explosion. 
The fourth beam specimen which was tested by the 20 ton compression machine 
of FIG. 8 was a composite-reinforced beam having identical characteristics 
to the third beam specimen except having half the beam thickness: 15 
millimeters. FIG. 12 shows the load vs. displacement plot 21c for the test 
of the fourth beam specimen. Despite the substantial reduction in beam 
thickness, plot 21c indicates that when a concrete beam is reinforced with 
the inventive aggregate-covered composite laminate panel the beam strength 
is 2.5 times greater than an unreinforced concrete beam twice as thick. 
Accordingly, the present invention can be used safely and economically to 
provide strong concrete structures using substantially less concrete 
material than is presently used in concrete construction. If a high rise 
structure can reduce its weight of concrete it is not only less expensive 
to build, but is also safer when subjected to earthquake. 
A preferred method of manufacture of the inventive composite laminate 
structure is described as follows. The process of making this composite 
laminate structure can be divided into two main steps. 
The first step is to manufacture the unidirected composite laminate panel 
structure 3. A flat and smooth panel forming surface is chosen having the 
same shape as the desired panel. In the preferred embodiments described 
above and pictured in FIGS. 1 to 7, the panels have a rectangular shape; 
however, a panel can have any contour appropriate to reinforce a 
particular concrete structure. The panel forming surface is coated with a 
resin release agent, and then is covered with a first layer of a liquid 
hardenable thermosetting resin. In practice, such a panel is made using a 
thermosetting isophthalic polyester resin matrix, having a weight of 0.121 
pounds per square foot (0.60 kilograms per square meter). An acceptable 
polyester resin is Aropol No. 7240 from Ashland Chemical that has a 
viscosity of 350 centipoise. This resin is promoted with 0.5% of cobalt 
naphthenate by weight and catalyzed with 1.5% MEK peroxide. The resin is 
then cured until it is firm. 
Next, either one or two layers of a dry fiberglass cloth should be placed 
upon the partially-cured resin. In practice, where only one layer of 
fiberglass cloth has been used, the fabric is 0.5 millimeter thick, has a 
weight of 0.81 pounds per square yard (0.44 kilograms per square meter), 
and is made from strands containing continuous filaments of E glass. The E 
glass filaments preferably have a filament diameter of 25 microns, a 
roving yield of 450 yards per pound (905 meters per kilogram), and a 
strand spacing of 9 per inch. Such a fiberglass cloth may be obtained from 
Composite Materials Incorporated as KNYTEX A 130 or from Fiber Glass 
Industries as Fortesil 1300. Where two layers of fabric have been used, a 
second preferred fiberglass fabric was used in addition to the first. This 
second preferred fiberglass fabric is 0.25 millimeter thick and has a dry 
weight of 6 ounces per square yard (0.21 kilograms per square meter). Such 
a fabric may be obtained from Mutual Industries, Inc. as Style 7628 woven 
fiberglass cloth. 
Where two layers of fabric are used, the second fiberglass fabric 
preferably is first placed on the partially-cured resin. It is then coated 
with a second layer of resin. The second layer of resin may use the same 
type of resin used for the first resin layer. The fiberglass cloth layer 
composed of E glass filaments is then placed on top of the second resin 
layer. 
At this point, either the first or second layer of fabric constitutes the 
top layer of the forming composite laminate surface. The fabric of this 
first or second layer should also be covered with a third layer of resin. 
Again, the third layer of resin may use the same type of resin used to 
make the first resin layer. This new resin covering should be smoothed 
across the surface of the top resin layer to coat uniformly the parallel 
filaments of the fiberglass cloth. Such smoothing may be done with a 
squeegee. At this point, the resin layers should be cured until they are 
non-liquid, forming the completed unidirected composite laminate panel 
structure 3. When made from the materials described above, unidirected 
composite laminate panel structure 3 will be about 1 millimeter thick and 
have a tensile strength in the direction of the fiberglass strands in 
excess of 281 kilograms per centimeter (1400 pounds per inch). 
The second step for making the inventive aggregate-covered composite 
laminate panel is to form the second ply of resin-coated rock aggregate 
protuberances 2 upon the unidirected composite laminate panel structure 3. 
In forming this second ply, another liquid hardenable thermosetting 
polyester resin is used, preferably having a viscosity in the range of 350 
to 1000 centipoise. The Ashland Chemical Co. resin Aropol No. 7240, 
promoted with cobalt naphtenate and catalyzed with MEK peroxide as above 
is well-suited for this purpose. Also used is crushed rock aggregate, 
clean and dry, with each particle preferably having every cross-sectional 
width through its center in the range of from 0.5 cm to 1 cm. The rock 
aggregate particles should be placed into a container filled with the 
resin and removed when coated with a resin coat from 0.1 to 0.5 
millimeters thick. The aggregate particles are then placed upon 
unidirected composite laminate panel structure 3 as rock aggregate 
protuberances 2 such that they are separated from each other by a distance 
ranging from 1 millimeter to 20 millimeters. 
A protuberance spacing apparatus (not shown) may be used to properly space 
out the aggregate protuberances 2 on the unidirected composite laminate 
panel structure. A preferred embodiment of a protuberance spacing 
apparatus comprises a metal or plastic sheet upon which the resin-coated 
aggregate protuberances are manually spaced out. The aggregate-covered 
side of the sheet may be pressed against the composite laminate panel 
structure before the resin hardens and the sheet may be removed, leaving 
the aggregate protuberances properly spaced across the laminate surface. 
It should be understood that other protuberance spacing apparatus could be 
employed. 
The resin coating the aggregate protuberances is then subjected to a force 
normal to the upper surface of the unidirected composite laminate panel 
structure. This force can simply be gravity, in which case the panel 
should simply be placed aggregate-side up. However, other forces can be 
used. For example, with a cylindrical composite laminate form, as used in 
concrete pipe liners, centrifugal force may be applied by rotation of the 
composite laminate. 
The application of the force should be continued until the resin 7 has 
flowed to the base 8 of each aggregate protuberance 2 to form the concave 
resin meniscus anchors 9 bonding each aggregate protuberance 2 to the 
composite laminate panel. The resin should then be fully cured. At this 
point the reinforcing aggregate-covered composite laminate panel is 
completed. 
The present invention may also be utilized to provide an aggregate-covered 
composite concrete pipe liner. FIG. 13 illustrates a preferred concrete 
pipe liner embodiment 22 which is prepared for insertion into a wet 
concrete pipe. Liner embodiment 22 comprises a folded cylindrical 
composite laminate 23 covered with a ply of resin-coated rock aggregate 
protuberances 2. FIG. 14 shows a cross section of the unfolded 
configuration 25 of the pipe liner 22. FIG. 15, which shows an exploded 
view of the surface of pipe liner 22, depicts that these resin-coated rock 
aggregate protuberances 2 are, as in composite laminate panel 1, anchored 
to the cylindrical composite laminate 23 by a concave resin meniscus 9 
formed when a layer of hardenable thermosetting polymeric resin 7 coating 
the rock aggregate protuberances 2 flows to the base 8 of each rock 
aggregate protuberance 2. 
Liner embodiment 22 can be used as a liner for a centrifugally cast 
concrete pipe 24 (see FIG. 24). As before, the bond between the liner 
embodiment 22 and the centrifugally cast concrete pipe 24 has a tensile 
and shear strength at least equal to the tensile and shear strength of 
rock aggregate protuberances 2. 
A preferred method of manufacture of a concrete pipe using the inventive 
liner embodiment 22 is described as follows. The preferred liner 
embodiment 22 constructed as described below had a 600 millimeters (24 
inch) diameter and a wall thickness of approximately 1.5 millimeters (0.06 
in), and was able to resist a pressure of 856 Kpa (125 psi) and an end 
load greater than 37 tons. The process of making the concrete pipe using 
liner embodiment 22 can be divided into three main steps: making the 
cylindrical composite laminate structure, applying the resin-coated 
aggregate particles to the cylindrical composite laminate structure, and 
making the aggregate-coated cylindrical composite laminate structure a 
structural constituent of a concrete pipe. 
To make the cylindrical composite laminate structure, a cylindrical mandrel 
is used having a mandrel forming surface with the same length and diameter 
desired for the liner embodiment 22. The cylindrical mandrel is mounted 
into a filament winding machine and the mandrel forming surface is coated 
with a resin release agent. The mandrel forming surface is then covered 
with a first layer of a liquid hardenable thermosetting resin. In 
practice, the resin used in the preferred liner embodiment was again the 
thermosetting isophthalic polyester resin matrix Aropol No. 7240 from 
Ashland Chemical, with a weight of 0.15 pounds per square foot and a 
viscosity of 350 centipoise. The resin was promoted with 0.5% of cobalt 
naphthenate by weight and catalyzed with 1.5% MEK peroxide. However, it 
should be understood that other resins could be used. This first layer of 
liquid hardenable thermosetting resin should then be partially cured until 
it is firm. 
Next, a 0.1 millimeter thick piece of dry woven fiberglass fabric is placed 
upon the partially-cured first layer of liquid hardenable thermosetting 
resin. A preferred fabric to use is a 0.1 millimeter layer of Style 7628 
fiberglass cloth impregnated with Derakane 470-36 epoxy vinyl ester resin, 
available from Dow Chemical Co. This dry woven fiberglass fabric piece 
should have a dry weight of approximately 6 ounces per square yard. A 
second layer of liquid hardenable thermosetting resin is then applied to 
cover the piece of dry woven fiberglass fabric and allowed to impregnate 
the fabric piece. Preferably, this resin is the same Aropol No. 7628 used 
for the first resin layer. This second layer of resin should be 
approximately 0.25 millimeter thick. 
Next, a 0.5 millimeter thick piece of dry unidirected fiberglass fabric is 
placed upon the second layer of resin. This fabric preferably has a weight 
of 0.44 kilograms per square meter (0.81 pounds per square yard) and is 
made from strands containing parallel, continuous filaments of the 
borosilicate glass referred to as E glass. These continuous filaments 
preferably have a filament diameter of 25 microns, a roving yield of 450 
yards per pound (905 meters per kilogram), and a strand spacing of 9 per 
inch. Such fabric is available from Composite Materials Inc (CMI) as 
KNYTEX A 130 or from Fiber Glass Industries, (FGI) as Fortesil 1300. The 
fabric should be oriented so that the parallel filaments parallel the 
longitudinal axis of the cylindrical mandrel and remain in that 
orientation until they absorb resin from the second layer of resin by 
capillarity. 
Next, a 0.75 millimeter thick filament winding ribbon should be prepared 
from parallel, continuous strands of E glass fiberglass roving. The 
preferred filament winding ribbon has a filament diameter of 25 microns, a 
roving yield of 450 yards per pound (905 meters per kilogram), and a 
strand spacing of 9 per inch. Such a filament winding ribbon is available 
from Owens Corning Fiberglass, Certainteed Corp., PPG, or FGI. The 
filament winding ribbon is dipped into a third liquid hardenable 
thermosetting resin, which again may be the same resin used for the first 
and second layers of resin. The resin-wet filament winding ribbon is then 
filament wound upon the piece of dry unidirected fiberglass fabric. In 
this process, the piece of dry unidirected fiberglass fabric will become 
impregnated with the third liquid hardenable thermosetting resin as well. 
At this point, the layers of resin should be fully cured, finishing the 
first step and forming a completed cylindrical composite laminate 
structure. 
In the second step, applying the resin-coated aggregate particles to the 
cylindrical composite laminate structure, the cylindrical composite 
laminate structure is first removed from the mandrel and placed on top of 
a horizontal surface. The cylindrical composite laminate structure is then 
flattened so that its upper hemispherical surface becomes roughly planar 
and the upper and lower surfaces of the composite laminate structure are 
brought closely together. The flattened upper surface should form a first 
aggregate-applying surface which extends along the entire length of the 
cylinder and has a width equal to approximately one third of the 
circumference of the cylinder. The aggregate-applying surface should be 
sufficiently planar such that resin-wet aggregate can be placed on the 
aggregate-applying surface and remain stationary. On either side of this 
aggregate-applying surface, this flattening leaves curved sides which bend 
around to the lower surface of the composite aggregate structure. Then, at 
both ends 34 of the composite laminate structure, the upper surface and 
lower surface of the composite laminate structure should be clamped 
together at the juncture point between the edge of the aggregate-applying 
surface and the curved sides of the flattened composite laminate 
structure. This will hold the planar aggregate-applying surface in place. 
The curved edges should be covered from exposure by plastic. 
At this point, rock aggregate particles should be dipped into a fourth 
hardenable thermosetting resin, which again may be the same resin used for 
the first three resin layers. The preferred rock aggregate particles used 
for the liner embodiment have a maximum dimension ranging in size from 6 
millimeter to 12 millimeter. One third of the total rock aggregate 
particles which are to cover the entire surface of the liner embodiment 22 
should be removed from the fourth hardenable thermosetting resin once they 
are coated with a resin coat which is between 0.1 and 0.25 millimeters 
thick. 
These rock aggregate particles are then placed upon the aggregate-applying 
surface. The rock aggregate particles should then be allowed to remain 
stationary until the fourth hardenable thermosetting resin flows to the 
bottom of each rock aggregate particle and forms the concave resin 
meniscus used to anchor the rock aggregate particles to the composite 
laminate structure. At this point, the fourth hardenable thermosetting 
resin should be heated until it hardens, thus completing the bond between 
the rock aggregate particles and the composite laminate structure. 
A principal discovery disclosed in the present invention relates to the 
density distribution or spacing of the rock aggregate protuberances 2 
bonded to the cylindrical composite laminate structure. Since the 
aggregate coated liner embodiment 22 is folded as shown in FIG. 16 before 
being inserted into a rotating pipe mandrel 26 (FIG. 19) whose inner 
surface is coated with a layer of wet concrete mix 27, liner embodiment 22 
unfolds in the sequence shown first by FIG. 17 and subsequently by FIG. 18 
before retaking its completely cylindrical form, shown in FIG. 14. 
However, because the liner embodiment 22 is flexible, the portion of the 
rotating pipe liner having the greatest mass 28 will be most quickly 
pressed against the wet concrete mix by the centrifugal force set up by 
the rotating mandrel, and thus will be the first portion of the liner 
embodiment to contact the wet concrete. This can be used to alleviate a 
common problem in centrifugally cast concrete pipe construction, which is 
that the most liquid and sandy parts of the concrete mix tend to collect 
in the center portion of the pipe, weakening the center of the pipe. If 
the mass of the rock aggregate protuberances bonded to the pipe liner 
laminate is greatest in the middle portion of the liner embodiment, then 
this middle portion will be first part of the liner embodiment to contact 
the liquid concrete mixture and will force the adjacent liquid concrete 
mixture to move toward the rotating mandrel ends. If the density of the 
spacing of the rock aggregate protuberances gradually tapers toward the 
ends of the liner embodiment, the remaining portions of the liner 
embodiment will continue to force the liquid cement until each gradually 
come in contact with the liquid cement until it is forced to the ends, 
where it can be trimmed away. This activity additionally will force the 
concrete to completely enclose each aggregate protuberance 2. 
Accordingly, as shown in FIG. 13, the rock aggregate protuberances 2 should 
be placed such that their density, and thus their mass, is greatest in the 
middle 28 and least at the end portions of the liner embodiment. Note that 
here the middle and ends of the liner embodiment are defined according to 
the longitudinal axis of the liner embodiment. 
After the first one-third of the rock aggregate particles are bonded to the 
flattened composite laminate structure, the plastic covering the curved 
edges should be removed, the clamps should be removed, and the cylindrical 
composite laminate structure should be rotated by 120 degrees. Then, the 
process used to bond the first one-third of the rock aggregate particles 
to the composite laminate structure is repeated on the second 120 degree 
arc of the cylindrical composite laminate structure. The composite 
laminate structure is flattened and clamped so that a second 
aggregate-applying planar surface is formed having one edge abutting the 
first, aggregate-covered aggregate-applying surface, and the two new 
curved edges are covered with plastic. The second third of resin-covered 
rock aggregate particles are applied to the composite laminate structure 
with the same concentrated center density gradually tapering toward the 
ends. The second third of rock particles are again allowed to stand until 
the resin meniscus structures form, and then are heated so that the fourth 
hardenable thermosetting resin will bond the rock aggregate particles to 
the composite laminate structure. Finally, the plastic is again removed 
from the curved edges of the composite laminate structure, the clamps are 
removed, and the composite laminate is again rotated by 120 degrees, and 
the process is repeated a last time to covering the last one-third of the 
surface of the cylindrical composite laminate structure with the last 
one-third of the rock aggregate particles. At this point, the second step 
of making the preferred liner embodiment 22 is completed. 
The third and final step in the process of making a concrete pipe using 
liner embodiment 22 is to make the aggregate-coated cylindrical composite 
laminate structure a structural constituent of the concrete pipe. The 
recommended sequence of operations used to insert liner embodiment 22 into 
the concrete pipe is illustrated in FIGS. 19, 20, 21, 22, 23 and FIG. 24. 
FIG. 19 is a schematic end view of the cylindrical rotating pipe mandrel 
26 used to form the centrifugally cast concrete pipe. The mandrel 26 is 
supported on motorized rotating drive wheels 30 that control the 
rotational speed of the mandrel, and thereby the centrifugal force imposed 
on the concrete mixture 27 and on the folded concrete pipe liner 23 placed 
within the rotating mandrel. The mandrel should first be rotated at a 
speed sufficient to press wet concrete mix inserted into the rotating 
mandrel against the inner surface of the mandrel to form a pipe structure 
of approximately equal thickness along the full length of the mandrel. 
Speeds in the range of 30 to 120 rpm are appropriate; a preferred speed is 
60 rpm. Second, wet concrete mix should be so inserted into the rotating 
mandrel and allowed to make the described pipe structure. FIG. 20 is a 
schematic end view of the mandrel 26 that shows the liquid concrete 
mixture 27 after it has been placed within the rotating pipe mandrel 26 
and allowed to form a pipe structure. 
Next, the aggregate-covered liner embodiment 22 should be inserted into the 
rotating pipe mandrel. A preferred method of carrying out the insertion is 
to insert a metal laminate support pole 31 through the center of the 
cylindrical composite laminate structure and to fold the composite 
laminate structure with a longitudinal crease directly beneath the metal 
laminate support pole, creating two hanging folded portions 33 of the 
composite laminate structure, as shown in FIGS. 16 and 21. The metal 
laminate support pole 31 should have a length greater than the length of 
the rotating pipe mandrel so that the pole can be fully extended through 
the pipe mandrel with accessible portions at either end of the pipe 
mandrel. The two abutting, innermost edges of the two hanging folded 
portions of the composite laminate structure should then be clamped 
together with removable clips 32 at each end 34 of the composite laminate 
structure to hold the composite laminate structure in this position. The 
metal laminate support pole 31, supporting the composite laminate 
structure 23, should then be inserted in this folded position into the 
rotating mandrel 26. FIG. 21 shows the position of the folded composite 
laminate structure 23 as it is inserted in the rotating pipe mandrel while 
supported by metal laminate support pole 31 and held at each end by 
removable clips 32. Clips 32 should each be attached to a clip-retrieval 
cord which can be pulled to release the clips and thereby allow the 
composite laminate structure to unfold. 
A preferred method of suspending metal support pole 31 within the rotating 
pipe mandrel is described as follows. A pole support cable (not shown) 
having a length at least twice the length of the concrete pipe mandrel is 
inserted through the concrete pipe mandrel and secured to hang below the 
upper surface of the concrete pipe mandrel by a distance approximately 
equal to twice the intended concrete pipe wall thickness. Movable cable 
trolleys are then affixed to the pole support cable, and the laminate 
support pole is hung from the pole support cable by the cable trolleys. 
The laminate support pole may then be moved into the concrete pipe mandrel 
such that the folded composite laminate structure is completely inside the 
concrete pipe mandrel by moving the cable trolleys along the pole support 
cable. 
Once the composite laminate structure, suspended from the metal laminate 
support pole 31, is completely inserted into the rotating concrete pipe 
mandrel 26, the removable clips 32 should be retrieved by pulling upon 
their respective clip retrieval cords. At this point, the speed of 
rotation of the pipe mandrel 26 should be set such that sufficient 
centrifugal force is created to press the aggregate-covered composite 23 
laminate structure firmly against the wet concrete 27. Again, speeds in 
the range of 30 to 120 rpm are appropriate, and a preferred rotation speed 
is 60 rpm. FIGS. 22, 23, and 24 show how the composite laminate structure 
unfolds once the clips 32 are removed and embeds itself into the wet 
concrete 27 to become an integral structural constituent of the completed 
concrete pipe 24. Note that the metal laminate support pole 31 is 
preferably suspended near the upper portion of the concrete pipe mandrel 
so that the uppermost portion of the composite laminate structure is 
quickly pressed into the wet concrete mix against the force of gravity, 
while the lower portions of the composite laminate structure will 
naturally fall to the bottom of the concrete pipe mandrel due to both 
gravity and centrifugal force. 
It may also be noted that, since the larger stone and gravel constituents 
of the concrete mix are the first to be pressed against the inner surface 
of rotating pipe mandrel 26, due to centrifugal force, the inner-most 
portion of the pipe concrete mix contacting the rock aggregate 
protuberances 2 of the composite laminate structure 23 is more fluid and 
has a higher proportion of sand and cement. For this reason, larger-sized 
rock aggregate in the gravel portion of the concrete mix will not impede 
the enclosure of the rock aggregate protuberances bonded to the composite 
laminate structure by the rotating concrete mix. 
Once the cylindrical composite laminate structure is embedded in the wet 
concrete mix, the pipe mandrel 26 should be maintained at the same speed 
of rotation until the wet cement dries. At this point, the composite 
laminate structure 23 has become a structural constituent of the concrete 
pipe 24 formed by the wet concrete mix 27, and a completed reinforced 
concrete pipe is formed. The completed reinforced concrete pipe can then 
be trimmed and removed from the pipe mandrel. 
An alternative preferred cylindrical embodiment of the inventive concrete 
reinforcement structure in which aggregate protuberances are bonded to the 
inner surface of the cylindrical structure utilizes the completed 
aggregate-covered cylindrical concrete reinforcement structure finished 
after step two. The cylindrical composite laminate structure itself may be 
rotated upon rotating support rollers to generate an internal centrifugal 
force. Rock aggregate protuberances coated with resin as for the 
cylindrical liner embodiment above are inserted into the rotating 
cylindrical composite laminate structure and spread across the inner 
surface of the composite laminate structure will then be pressed against 
that inner surface by the centrifugal force. An appropriate range of 
rotation speeds again is from 30 to 120 rpm. The cylindrical composite 
laminate structure is then continued in rotation until the resin coating 
the rock aggregate flows to the base of the rock aggregate protuberances 
to form a concave resin meniscus between each rock aggregate protuberance 
and the inner surface of the rotating composite laminate structure, and 
until the resin coating the rock aggregate protuberances and forming the 
concave resin menisci hardens. At this point the cylindrical composite 
laminate structure can be removed from the rotating support rollers and 
used as a cylindrical pipe mandrel for making a concrete pipe, where the 
cylindrical pipe mandrel would form the outer surface of the concrete 
pipe. Alternatively, if the cylindrical composite laminate structure is to 
be used as the outer surface for a concrete column, concrete should be 
poured into the rotating cylindrical composite laminate structure and 
allowed to harden while the structure rotates. 
Although the foregoing invention has been described in some detail by way 
of illustration for purposes of clarity of understanding, it will be 
readily apparent to those of ordinary skill in the art in light of the 
teachings of this invention that certain changes and modifications may be 
made thereto without departing from the spirit or scope of the appended 
claims.