Note: Descriptions are shown in the official language in which they were submitted.
21 7q~ 4 ~3
FORMULATION AND METHOD FOR
PRODUCING RUBBER VEHICULAR IMPACT BARRIERS
FIELD OF THE INVENTION
The invention relates to a novel formulation for the
manufacture of rubber vehicular impact barriers, for use as
continuous highway medians for example, which for the first
time allows on-site manufacture of rubber impact barriers.
BACKGROUND OF THE INVENTION
Highways and motor speedways are often constructed with
temporary or permanent barriers to contain and direct
vehicles that have lost control. Conventionally, the
barriers are massive concrete walls which are either formed
in situ or are prefabricated in interlocking modules. The
modules may be prefabricated in a concrete manufacturing
facility and transported to the erection site to be lifted
into place with cranes or forklift trucks.
Modular barriers are typically used on a temporary basis
to protect workers and equipment during highway construction,
whereas permanent barriers to be used as highway medians are
preferably continuous and therefore must be produced on-site.
U.S. Patent No. 5,336,016 to Baatz, the disclosure of
which is incorporated herein by reference, teaches a rubber
vehicular impact barrier comprising 80 to 90 percent by
weight particles of recycled waste rubber and 10 to 20
percent by weight virgin rubber. Rubber impact barriers
having this composition provide a number of advantages over
conventional concrete barriers, as discussed at length in the
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above patent.
However, at least partly due to the use of virgin rubber
in the formulation, heavy equipment is needed for mixing,
extrusion and curing of barriers having the composition
disclosed in the above patent. Specifically, the formulation
of the above patent tends to be very viscous, requiring heavy
mixing equipment and high pumping pressures. Also, the
presence of virgin rubber requires that such barriers must be
cured at high temperature and pressure for relatively long
periods of time. The patent requires curing temperatures
between 250 and 400~C at a pressure of from 500 to 1000 psi
(pounds per square inch) for a period of time from 1.5 to
7.5 hours.
Because of the long curing time and heavy equipment
required to manufacture barriers according to the above
patent, such barriers must be manufactured in an off-site
facility and subsequently transported to the erection site.
Therefore, the process of the above patent is limited to the
production of barrier modules which are primarily used on a
temporary basis and is impractical for use in on-site molding
of continuous, permanent barriers.
On-site molding of impact barriers requires the use of
simple equipment and requires that the barriers be molded and
cured at temperatures and pressures as close as possible to
ambient conditions. Furthermore, continuous molding of
barriers requires that the curing time be relatively short,
for example about 60 minutes or less, to allow the barrier to
be produced at an acceptable rate.
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The disadvantage exists that no formulations or
processes are presently known which are acceptable for on-
site molding of rubber vehicular impact barriers.
SUMMARY OF THE INVENTION
The invention overcomes the disadvantages of the prior
art in a novel manner by providing a formulation which
permits on-site molding of rubber vehicular impact barriers,
and further provides a process for on-site manufacture of
such barriers.
Impact barriers according to the present invention may
be manufactured using simple equipment similar to that used
for on-site manufacture of concrete barriers, without the
application of external heat and at low pressure.
Furthermore, the formulation of the present invention has a
shorter curing time than the prior art formulation taught in
the above-discussed patent, which permits continuous
production of barriers on-site at an acceptable rate.
The formulation of the present invention produces a
barrier having impact strength, hardness and other properties
desired in impact barriers as good or better than those of
the prior art formulation discussed above.
In one aspect, the present invention provides a
homogeneous molded solid rubber vehicular barrier,
comprising: 55-75% by weight particles of rubber crumb; 5-12%
by weight liquid polyurethane prepolymer; 10-15% by weight of
a diol or polyol cross-linking agent; 10-20% by weight
filler; and 3-8~ by weight fibrous material.
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In another aspect, the present invention provides a
homogeneous molded solid rubber vehicular barrier,
comprising: about 60% by weight particles of rubber crumb
having a size of 20 to 30 mesh; about 7.5% by weight of a
liquid polyurethane prepolymer comprising a polyether based,
methylene diisocyanate or methylene bis-(phenyl isocyanate)
terminated polyurethane prepolymer having a percent
isocyanate of from about 6 % to about 15%; about 12.5% by
weight of polypropylene glycol having a molecular weight of
about 6,000; about 15% by weight ground coal; and about 5% by
weight chopped fiberglass having a fiber length of about 1/4
to 3/8 inches, said liquid polyurethane prepolymer and said
polypropylene glycol forming a matrix in which said rubber,
ground coal and chopped fiberglass are dispersed, wherein
said barrier is a continuous highway median.
In yet another aspect, the present invention provides a
method of manufacturing a homogeneous, solid rubber vehicular
barrier, comprising the steps of: blending 55-75% by weight
rubber crumb and 10-20% by weight filler; adding 10-15% by
weight polyol or glycol cross-linking agent; adding 5-12%
polyurethane prepolymer; and adding 3-8% fibrous material;
forming the mixture in a mold to a selected barrier
configuration; curing the mixture within the mold without
application of external heat for a period of time from 45-
60 minutes; and removing the cured barrier from the mold.
The impact barriers of the present invention utilizeinexpensive, readily available materials, most of which are
available as recycled materials.
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Further aspects of the invention will become apparent
upon review of the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be readily understood,
a preferred embodiment of the invention will be described by
way of example with reference to the accompanying drawings in
which:
Figure 1 is a sectional, perspective view of a portion
of a continuous, permanent impact barrier which may be
produced according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 illustrates a portion of a preferred impact
barrier 10 which may be produced using the formulation and
the method of the present invention. Barrier 10 is a
continuous highway median having a similar shape and size as
a conventional concrete highway barrier, having two opposite,
inclined side surfaces 12 and an outwardly flaring base
portion 14.
Although barrier 10 is shown as a continuous highway
median, it is to be understood that the formulation and
method of the present invention may be used to produce impact
barriers having any suitable configuration, either continuous
or modular, and may for example have the shape and size of
the barrier shown in Figures 1 and 2 of the above-discussed
patent.
Barrier 10 is preferably produced on-site in long,
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continuous lengths as will be described below.
Barrier 10 is shown in Figure 1 as having a pedestal 16
to be embedded in the roadway to provide increased resistance
to vehicular impact loads. Alternatively, pedestal 16 may be
eliminated and the barrier 10 may be simply placed on its
base 14 upon the roadway surface. If pedestal 16 is
eliminated, it is preferable to increase the overall
dimensions of the barrier 10 in order to provide a larger
inertial mass to resist vehicular impact loads.
The formulation of the present invention preferably
comprises rubber crumb as the main ingredient, a low
viscosity binder which sets quickly at low temperatures and
pressure, a filler and a fibrous material.
Rubber crumb, the primary ingredient in the formulation,
is preferably obtained as a recycled product derived from
discarded automobile tires. The rubber crumb preferably
comprises from about 55 to about 75 percent by weight of the
formulation, and more preferably about 60 percent by weight
of the formulation. The rubber crumb preferably comprises
fine particles having a size of about 20 to 30 mesh.
The rubber crumb used in the formulation preferably does
not contain significant amounts of steel. However, it is to
be appreciated that in some cases it may be desirable that
the barrier contains a minor amount of steel to improve
impact strength of the barrier. In such cases, rubber crumb
may be used which contains a small amount of steel derived
from the metal wire reinforcement in the waste automobile
tires. Although small amounts of steel in the formulation
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may improve the impact strength of the barrier, barriers
according to the present invention having acceptable impact
strength and other properties may be manufactured with rubber
crumb containing no steel.
The low viscosity binder preferably comprises a two part
liquid polymer, comprising a polyurethane prepolymer and a
liquid cross-linking agent. The inventor has found that the
use of such a low viscosity binder permits low shear mixing
of the formulation using relatively simple equipment, such as
conventional "Ready Mix" cement mixing trucks. Also, the low
viscosity of the binder permits the formulation to be pumped
after mixing and compressed in the mold under low pressure.
Another important characteristic of the binder is that it may
be cured without the application of an external heat source
and is preferably cured at atmospheric pressure. Even under
such mild conditions, the binder sets in about 30 to 60
minutes, which is significantly faster than the formulation
of the above-discussed patent.
The preferred polyurethane prepolymers for use in the
low viscosity binder are polyether based polyurethanes.
Particularly preferred polyurethane prepolymers are polyether
based, methylene diisocyanate (MDI) or methylene bis-(phenyl
isocyanate) terminated polyurethane prepolymers having a
percent NC0 ranging from about 6% to about 15%, such as those
sold under the trade marks Vibrathane RB871~ and Vibrathane
RB873~ by Uniroyal Chemical.
Vibrathane RB871~ is the most preferred polyurethane
prepolymer because of its low cost and ready availability.
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However, it is to be understood that other types of
polyurethane prepolymers may be equally suitable. The
polyurethane prepolymer component of the binder preferably
comprises from about 5 to about 12 percent by weight of the
formulation, more preferably about 7.5 percent by weight of
the formulation.
In preferred binders according to the present invention,
a cross-linking agent (also referred to as a "chain
extender") is reacted with the polyurethane prepolymer to
form a matrix in which the other ingredients of the
formulation are dispersed. The cross-linking agent is a
hydroxyl group containing compound preferably selected from
one or more members of the group comprising water, diols and
polyols. Polyols are defined herein as polyhydric alcohols
having three or more hydroxyl groups per molecule. A
particularly preferred diol is ethylene glycol, and a
particularly preferred polyol is polypropylene glycol. The
most preferred polyol is polypropylene glycol having a
molecular weight of about 6000 and a hydroxyl number of 29,
such as that sold under the trade mark Polyol G~. The cross-
linking agent preferably comprises from about 10 to about 15
percent by weight percent of the formulation, most preferably
about 12.5 percent by weight.
It is to be understood that atmospheric water and water
present in the ingredients of the formulation will form at
least some of the cross-links in the polyurethane prepolymer.
However, it is preferred that water is not added to the
formulation as one of the ingredients.
21791~5
The filler is preferably an inexpensive material which
is compatible with the other ingredients and has a hardening
effect on the formulation. The most preferred filler is
ground coal which, like the rubber crumb, may be a reclaimed
material. The ground coal is the preferred filler because it
is inexpensive, enhances the hardness and stiffness of the
final product, and helps to blend the formulation by
providing an interface between the polar urethane and the
non-polar rubber crumb.
It is also possible in some formulations to use other
conventional fillers, for example calcium carbonate, although
this produces less advantageous results than ground coal.
It has been found that in the absence of a filler such
as ground coal, the molded product has a hardness of only 60
to 70 Shore A and may have a poor bending modulus. The
addition of a filler such as ground coal makes the molded
product harder and stiffer, raising the Shore A hardness to
about 80 to 90 and improving the bending modulus.
The filler is preferably contained in the formulation in
an amount of from about 10 to about 20 percent by weight, and
more preferably about 15 percent by weight, the most
preferred filler being ground coal known as "Austin Black".
The fibrous material is preferably added to the
formulation to provide the molded product with improved
impact resistance and tear strength. The fibrous material is
preferably selected from one or more members of the group
comprising chopped fiberglass, nylon fibers, polyester
fibers, aromatic polyamide fibers such as Kevlar~, chopped
2 1 7~ 1 4 j
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steel, and steel strands. It is to be understood that when
chopped steel or steel strands are included in the
formulation, it may be present in the rubber crumb, added as
a separate ingredient, or a combination of both.
The most preferred fibrous material is chopped
fiberglass fibers having a length of from about one-quarter
to about one-half inch, preferably, about one-quarter to
about three-eighths inches. The use of longer fiberglass
fibers may result in tangling in the mixing equipment.
Instead of fiberglass, steel strands having a length of
about one-quarter inch to about one and one-half inches may
be used as the fibrous material. The use of longer steel
strands is not preferred since they tend to stick out from
the molded product. Also, steel is less preferred than
fiberglass because of abrasion of the steel strands against
metal parts in the process machinery, which may cause
excessive wear of the machinery, and against metal parts of
vehicles impacting the barrier, which may cause sparks.
The fibrous agent is preferably a reclaimed material,
with polyester, nylon, aromatic polyamide and steel strands
being preferably recovered from discarded tires. The fibrous
material is preferably contained in the formulation in an
amount of from about 3 to about 8 percent by weight, and more
preferably about 5 percent by weight.
One or more optional ingredients may also be added to
the formulation, if desired, without departing from the scope
of the present invention. These additives may be added to
enhance properties other than those related to the strength
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and hardness of the barrier.
For example, a catalyst may be added to the formulation
to accelerate the curing of the binder, preferred catalysts
being tin or amine catalysts. The most preferred catalysts
for use with the polyurethane prepolymer and glycol or polyol
cross-linking agent are Stannous Octoate (Stannous-2-
ethylhexoate), such as that produced by Air Products DMDI,
and DABCO 33LE~, produced by Texaco, which is a
triethylenediamine catalyst. Amounts of catalysts added are
preferably kept to a minimum since they reduce the pot life
of the formulation after mixing and its ability to be poured
into a mold.
Other optional ingredients include ground glass,
reflective paint, fire retardants such as borates,
antioxidants and W absorbers to prevent weathering of the
highway impact barrier caused by exposure to W radiation and
ozone, and coloring pigments such as zinc oxide or titanium
oxide which may give the barrier a gray color similar to that
of concrete.
The following is the most preferred formulation for a
rubber impact barrier according to the present invention:
Rubber crumb, 30 mesh60.0 wt.%
Vibrathane RB871 7.5 wt.%
Polyol G (PPG 6000: 85-29) 12.5 wt.%
Ground Coal (Austin Black) 15.0 wt.%
Chopped Fiberglass (1/4") 5.0 wt.%
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A preferred process for the production of an impact
barrier according to the present invention is now discussed
below.
The formulation is preferably mixed in a large mixer,
S such as a conventional cement mixer truck, an industrial
concrete mixture or a full scale "Hobart" mixer, in the
following preferred sequence of steps:
1. The filler is blended with the rubber crumb (typically
requiring about 3 min.);
2. The cross-linking agent is added to the mixture of
rubber crumb and filler and mixed until the mixture is
completely wetted (typically requiring about 3 mins.);
3. The polyurethane prepolymer is then added and mixed
until it is completely dispersed throughout the mixture
(typically requiring about 5-10 mins.);
4. The fibrous agent is added to the mixture and mixing is
continued until all ingredients are blended homogeneously
together; and
5. If desired, a suitable catalyst is added to the mixture
for faster curing.
The mixing of the ingredients typically requires from
about 10 to about 30 minutes, more typically from about 15
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to about 20 minutes. However, these mixing times are
approximate only and may vary according to the type of
equipment being used and the amount of material being mixed.
Furthermore, it is to be appreciated that the above
sequence of steps is merely a preferred sequence, and not
essential. The sequence to be used in any given case is at
least partially dependent on the particular ingredients used.
However, since rubber crumb is the primary ingredient, the
other ingredients are preferably added into the rubber crumb.
Also, the catalyst is preferably the last ingredient added to
prevent premature setting of the mixture.
The mixing may preferably be performed in a conventional
cement mixing truck, such as a "Ready Mix" mixer, which may
be driven to the molding site while at least some of the
components of the formulation are being mixed by the truck.
It is preferred when using a cement mixing truck to load the
mixer with at least the dry ingredients, i.e. rubber crumb,
filler and fibrous material, and add at least some of the
liquid ingredients on-site. However, the ingredients may be
added in any order as long as the formulation does not begin
to set before it is released from the mixer. Therefore, it
is preferred to add at least one component of the binder and
the catalyst, if required, to the mixture, after the cement
mixer has reached the molding site.
Once the formulation is completely mixed, it is pumped
under minimal pressure into a mold. The pressure required is
only that necessary to pump the material and compact it into
the mold, typically about 40 psi. Preferably, during the
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mixing and mold filling operations, the formulation has a
consistency similar to that of concrete and can be mixed and
pumped into a mold using the same or similar equipment as
would be used to form conventional concrete highway barriers.
As discussed above, it is preferred that the mold is not
pressurized and that no external heat is applied during the
molding operation, in contrast to the prior art process
described in the above-mentioned patent. Therefore, the mold
is preferably unheated. However, the reaction of the
polyurethane prepolymer with the cross-linking agent is
typically exothermic and therefore the temperature of the
mixture rises above ambient temperatures as the mixture sets,
with the temperature inside the mold typically reaching about
100 to 120~C during setting. However, when using some
formulations according to the present invention, it may be
desirable to pre-heat the mold to about 80-90~C.
While the mixture is in the mold and before it has set,
it may be advantageous to vibrate the mixture by known means
to remove air bubbles therefrom, in the same manner as in
setting concrete. When molding smaller amounts of material,
as when manufacturing barrier modules in a manufacturing
facility, it may be possible to vibrate the mold to remove
air bubbles. However, in on-site casting of permanent,
continuous barriers, it is preferred to vibrate the mixture
with a vibrating pipe or the like inserted in the mold as
when pouring large amounts of concrete.
The mixture typically sets within a period of about 30
to about 60 minutes without addition of a catalyst, more
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typically about 45 to about 60 minutes. After the mixture
has set, it is removed from the mold and allowed to cure for
a period of about 24 hours.
For on-site molding of continuous impact barriers, for
use as highway medians for example, the molding process is
preferably continuous, and is analogous to an extrusion. In
a continuous molding process, liquid mixture comprising the
formulation of the present invention is pumped or poured
under gravity from a mixer and compacted into a mold or form
at a first end thereof. As the mixture sets, it is gradually
pushed from the first end of the mold to a second end of the
mold, as for example by a piston, so that freshly mixed
mixture can be pumped or poured into the first end of the
mold and solidified mixture can be forced, or extruded, from
the second end of the mold. The rate at which the mixture is
forced through the mold is preferably such that the mixture
has sufficient time to set into a solid mass and retain its
shape. Preferably, the set mixture is ejected from the mold
directly onto the roadway in its desired position, where it
cures under ambient temperature and atmospheric pressure.
It is to be appreciated that large amounts of the
mixture must be mixed and added to the molding equipment to
form a continuous impact barrier. For example, one meter of
highway median of conventional size molded from the
formulation of the present invention requires about
500 liters of ingredients. On the other hand, the capacity
of a "Ready-mix" cement mixing truck is about 30 yards to
about 80 yards. Therefore, with a set time of about 45 to
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about 60 minutes, the limiting step in the production of
barriers according to the present invention is more likely to
be the delivery of materials to the molding apparatus rather
than the set time of the mixture.
The following is an estimate of the amount of materials
needed to make one kilometer of highway barrier from a
formulation according to the present invention:
Rubber crumb (20-30 mesh)324,000 kg
Vibrathane RB873 40,500 kg
Ethylene Glycol 67,500 kg
Ground Coal 81,000 kg
Chopped Fiberglass (%")27,000 kg
Total 540,000 kg
It is to be understood that this formulation is not the
most preferred formulation of the present invention and is
used only to illustrate the amount of materials necessary to
produce one kilometer of highway barrier.
The formulation according to the present invention is
designed to provide a highway barrier having physical
properties which meet the standards specified by government
agencies for such barriers. The Standards for Highway Safety
Barriers specified by the U.S. National Transportation
Research Board have been adopted by many government agencies
worldwide, such as the Ministry of Transportation of Ontario,
and are now considered the worldwide standards for highway
safety barriers. Although these specifications are geared
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towards barriers made from concrete, rubber impact barriers
according to the present invention have been produced having
the following properties, which meet the above-mentioned
safety standards:
Hardness, Shore A 80-90
Tensile Strength, psi 1200 (minimum)
Tear Strength, pli (Die C) 150 (minimum)
Tear Strength, pli (D4701) 50
Bahshore Rebound 15-25 percent
Impact Resistance at -40~C,
G.M.9300P, Gardner-Denver
Impact Test No Failure.
Although this disclosure has described and illustrated
certain preferred embodiments of the invention, it is to be
understood that the invention is not restricted to these
particular embodiments. Rather, the invention includes all
embodiments which are functional or mechanical equivalents of
the specific embodiments and features that have been
described herein.
