Note: Descriptions are shown in the official language in which they were submitted.
CA 02038790 2000-07-25
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FIELD OF THE INVENTION
The present invention relates to a combination of a
flat metal plate and a four-layer paving composition which
covers the metal plate. The combination is resistant to
delamination between the paving and the metal plate, when
placed under a load.
This invention may be suitably utilized in a wide
variety of applications, including flooring material (such
as the floor of an automobile parking garage) and/or bridge
decking.
BACKGROUND OF THE INVENTION
The use of asphalt as a corrosion resistant paint (or
coating) for metal pipes/plates is known.
However, in contrast, asphalt pavement is generally not
suitable as a "paving" material when used on top of a load
bearing metal plate. In particular, asphalt pavement which
is paved onto a metal plate is liable to crack and/or
delaminate from the plate when placed under a load (such as
the load caused by automotive traffic).
It has been proposed to alleviate the above described
cracking/delamination problems associated with asphalt
paving/metal plate compositions through the use of an
epoxy-modified asphalt, as disclosed in Czechoslovakian
patents 200,873 (1980); 207,877 (1981); 207,876 (1981); and
200,874 (1980). However, epoxy-modified asphalt is
comparatively expensive, and the techniques of the above
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CA 02038790 1998-06-10
Czechoslovakian patents have not enjoyed widespread
commercial success.
SUMMARY OF THE INVENTION
The present invention provides a combination of a metal
plate and a four-layer paving system, said four layer paving
system consisting of:
(a) a first layer which is applied to the top surface of
said metal plate, said first layer having sufficient
tack to adhere to said metal plate and comprising a
first elastomer-modified asphalt composition containing
from 6 to 25 weight percent first elastomer and 94 to
80 weight percent first asphalt, wherein said first
elastomer-modified asphalt composition is:
(i) prepared with a first asphalt having a penetration
value of from 15 to 800,
(ii) applied in the form of a first emulsion, in an
amount sufficient to provide from 400 g to 1800 g
of said first elastomer-modified asphalt
composition per square meter,
(b) a second layer consisting of aggregate particles having
a maximum size of 15 mm, said second layer being
applied over said first layer in an amount of from 5 to
15 kg per square meter,
(c) a third layer which is applied over said second layer,
said third layer comprising of a second
elastomer-modified asphalt composition consisting of 3
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CA 02038790 1998-06-10
to 20 weight percent second elastomer and 97 to 8~
weight percent second asphalt, wherein said second
elastomer-modified composition is:
(i) prepared with a second asphalt having a
penetration value of from 15 to 800,
(ii) applied in the form of a second emulsion, in an
amount sufficient to provide from 100 g to 1200 g
of said second elastomer-modified composition per
square meter, and
(d) a fourth layer consisting of asphalt pavement, said
fourth layer having a minimum thickness of 10 mm.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a sectional view of the combination of the
present invention.
DETAILED DESCRIPTION
Referring to Figure 1, the top surface la of a
generally flat metal plate 1 is coated with first primer
layer 2. A layer of aggregate 3 is coated on the top of
first primer layer 2. The aggregate layer 3 is coated with
second primer layer 4. A layer of asphalt pavement 5 is
paved on top of the second primer layer 4.
The metal plate 1, the first primer layer 2, the
aggregate layer 3, the second primer layer 4 and the asphalt
pavement 5 are described in detail below.
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Metal Plate
The metal plate 1 is a conventional metal plate of the
type which is used for example, in metal flooring
applications. The dimensions of the plate 1 are not
critical to the success of the present invention, and it is
desirable to use commercially available plates for
convenience. Such plates generally have maximum dimensions
of less than 10 m x 2 m (for ease of handling). The top
surface la may be treated (e. g. plated for corrosion
resistance) by the plate manufacturer. It is preferred to
utilize a plate having a thickness from 0.5 to 4 cm (for
cost consideration), and a zinc-containing plating on the
top surface.
A plurality of the plates may be attached together to
form a large surface. This large surface may then be
covered by the four layer paving system which is described
in detail below. Alternatively, but less preferably, the
plates may be individually covered with the four layer
paving system, then installed in a plate-by-plate manner.
Either of the above alternatives may be used to prepare a
surface which can be subjected to the load of automotive
traffic, such as the floor of an automotive parking garage.
First Layer (or "First Primer Layer")
Referring again to Figure 1, the first primer layer 2
is applied to the top surface la of the metal plate 1.
The first primer layer generally consists of
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elastomer-modified asphalt having sufficient tack to adhere
to the metal plate.
The term asphalt is meant to refer to its conventional
meaning, namely a dark coloured cementitious material that
contains high molecular weight hydrocarbons which are
commonly referred to as asphaltenes. Asphalt may be
directly obtained from natural sources (i.e. native asphalt
including "Trinidad Asphalt", rock asphalt or lake asphalt)
or from the refining of petroleum (i.e. "petroleum"
asphalt). The source of asphalt is not critical to the
success of this invention, although petroleum asphalt is
preferred because it is readily available. The term
petroleum asphalt is meant to include primary asphalt (i.e.
a product of the vacuum distillation of hydrocarbon oil),
oxidized asphalt (including those asphalts known by the
terms "blown asphalt" and/or "semi-blown asphalt"), cracking
asphalt (i.e. asphalt obtained from cracking operations) and
solvent extracted asphalt (such as propane-extracted
asphalt).
Primary asphalt and oxidized asphalt are particularly
preferred for use in this invention. Further detailed
description of asphalt may be obtained from the open
literature (including volume 3 of the third edition of the
"Encyclopedia of Chemical Technology", Kirk-Othmer Editors,
ISBN 0-471-0239-7). Asphalt is commonly characterized
according to "penetration value" (or "pen value"), which is
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determined by the standard test method ASTM D5. Pen value
is expressed in units of dmm (although reference to these
units is often not explicitly given). The ASTM test
procedures were completed at a temperature of 25°C, using a
100 g needle for a period of 5 seconds. Asphalt having a
penetration value of from 15 to 800 dmm is suitable for use
in the present invention and a pen value between 200 and
600 dmm is preferred.
The elastomer-modified asphalt composition of the first
layer contains from 6 to 25 weight percent elastomer and
preferably contains from 8 to 13 weight percent elastomer.
The type of elastomer is not critical to the success of the
present invention. Examples of suitable elastomers include
natural rubber, emulsion polymerized styrene-butadiene
rubber, styrene-dime thermoplastic block rubber,
ethylene-propylene copolymer rubber, isobutylene-isoprene
copolymer rubber, polyisobutylene rubber, polybutadiene
rubber, butadiene-acrylonitrile copolymer rubber, ethylene-
vinyl acetate rubber and mixtures thereof.
The preferred elastomer is a styrene-dime
thermoplastic block rubber, such as styrene-butadiene
diblock (or "SB") rubber, styrene-butadiene-styrene (or
"SBS") rubber. This type of elastomer is well known and is
described in the open literature (particularly in volume 8
of the aforesaid "Kirk-Othmer" Encyclopedia (ISBN
0-471-02044-3). For the purpose of the present invention,
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CA 02038790 1998-06-10
an SBS rubber, having a bound styrene content of from 20 to
40 weight percent, is especially suitable. More than one
elastomer may be used in the preparation of the elastomer
modified asphalt. The use of more than one elastomer may,
for example, improve the ease of preparing the
elastomer-modified asphalt composition.
As noted above, it is essential that the first primer
layer has sufficient tack to adhere to the metal. While
certain elastomer-modified asphalt compositions do
inherently have the required tack, it is highly preferred to
incorporate a minor amount of tackifier (from 0.1 to 2
weight percent) to ensure good adhesion to the metal plate.
Terpene-resin type tackifiers are preferred.
The first primer layer may also include other
ingredients which are conventionally utilized in
elastomer-modified asphalt compositions, including extenders
such as oil, sulfur and antioxidants.
The use of a small amount of oil (from 5 to 20 weight
percent of the elastomer-modified asphalt) is a desirable
way to enhance the flexibility of the first primer layer at
a comparatively low cost, while the use of a very small
amount of sulfur (from 0.07 to 2.0 weight percent) can
increase elastomer/asphalt compatibility.
The ingredients of the first primer layer are mixed
together using conventional mixing techniques, preferably in
a high shear mixer. The resulting "first primer layer"
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composition is viscous and is difficult to apply to the
metal plate. Accordingly, the composition is emulsified in
order to improve the ease of application. The emulsion is
prepared by intensively mixing at elevated temperatures the
elastomer-modified asphalt with water and an emulsifier
(e. g. a soap or detergent) so as to produce a finely
"emulsified dispersion" of the elastomer-modified asphalt in
the water. Conventional techniques for the preparation of
asphalt emulsions are well known to those skilled in the art
and are suitable for use in the present invention. A
detailed description of such techniques is given in volume 3
of the aforesaid "Kirk-Othmer" reference.
The type of emulsifier used to prepare the emulsion is
not critical, but soaps prepared with "tall oil" (i.e. a
mixed fatty/rosin acid material, derived from coniferous
trees) have been used with favourable results. A soap
prepared by the saponification of tall oil with NaOH is
particularly preferred for reasons of cost and convenience.
This soap is commonly referred to as the sodium salt of tall
oil.
The emulsion can be characterized according to the
amount of elastomer-modified asphalt it contains (i.e. the
"solids content"). The term "solids content" is defined by
the formula:
solids content (weight $) = weiaht of elastomer modified asphalt x 100$
total weight of emulsion
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The emulsion is applied to the top surface of the metal
plate in an amount sufficient to provide from 400 to 1800 g
(preferably from 500 g to 900 g) of elastomer-modified
asphalt per m2 (i.e. square meter). Amounts less than
400 g/m2 do not provide satisfactory results, while amounts
greater than 900 g/mz would represent an over-use of the
comparatively expensive first primer layer.
By way of example, the application of 1 kg of emulsion
having a solids content of 60~ to one square meter of plate
would provide a coating of 600 g of the elastomer-modified
asphalt per m2.
Second Layer (or "Aqctregate Layer")
p
The second layer (layer 3 in Figure 1) consists o~
aggregate which is applied on top of the first primer layer
(i.e, on top of layer 2, as shown in Figure 1). The
aggregate particles should have a maximum particle size of
less than 15 mm (i.e. the particles will pass through a
screen having a screen size of 15 mm), and preferably will
have a maximum particle size of less than 10 mm, so that the
aggregate is well wetted by the first primer layer. Highly
preferred aggregate consists of gravel or stones having a
particle size distribution which is further characterized by
containing less than 20 weight percent of fines (i.e.
"fines" are particles that will pass through a sieve of 75
microns).
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The aggregate is applied on top of the first primer
layer in a manner that provides a thin layer of fairly
uniform thickness. When using a conventional stone
aggregate having the above described highly preferred size
distribution, the amount of aggregate employed is from 8 to
15 kg per m2 of surface area.
The aggregate may be rolled into the first primer layer
to enhance contact between the two. It is desirable to
allow the aggregate layer to sit for at least eight hours
before the next layer is applied.
Third Layer (or "Second Primer Layer")
The third layer, also referred to herein on occasion as
the second primer layer, is located in the position
indicated by reference numeral 4 in Figure 1.
The third layer generally consists of an
elastomer-modified asphalt composition which contains from 3
to 20 weight percent elastomer (preferably from 5 to 9
weight percent elastomer).
The composition of this layer (which may be referred to
as the second elastomer-modified asphalt composition, so as
to distinguish it from the composition of the first layer)
preferably contains less elastomer than that of the first
layer for reasons of economy, but in other respects, th.e
(
compositions of the first and third layers are similar.
In particular, the elastomer(s), asphalt and additives
used in the first layer composition may also be used in the
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third layer. The third layer is applied as an emulsion
(preferably having a solids content of from 40 to 70 weight
percent) in an amount sufficient to provide from 100 to
1200 g (preferably 200 g to 400 g) of the second
elastomer-modified asphalt composition per mZ.
It is preferable to "roll" the third layer (so as to
provide good contact with the aggregate layer) and to allow
the so-rolled layer to sit for at least 8 hours before
applying the fourth layer.
The above described first layer, second layer and third
layer have been found to provide, in combination, a
"foundation" on which asphalt pavement (the fourth layer)
may suitably be applied. While not wishing to be bound by
any particular theory, it is believed that the combination
of the flexible primer layers (i.e. the first and third
layers) with the aggregate layer serves to mitigate cracking
and delamination problems which might otherwise result from
the localized stresses caused by deflection of the metal
plate.
Fourth Layer
The fourth layer (reference numeral 5 in Figure 1)
consists of asphalt pavement. The term asphalt pavement is
meant to include all asphalt-containing paving materials
which may be used to construct roads.
Asphalt pavement typically consists of a minor amount
of "asphalt binder" (from 4 to 12 weight percent) and a
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major amount of mineral aggregate (from 95 to 88 weight.
percent). Asphalts having a wide range of penetration
values are known to be suitable for preparing pavement,
although pen values of from 15 to 800 (especially 65 to 600)
are preferred.
The fourth layer has a thickness of at least 1 cm as a
thinner layer typically does not have sufficient durability.
A thickness between 2 and 10 cm is preferred. Although it
is not intended to limit this invention to the use of any
particular asphalt pavement, it is highly preferred to
employ elastomer-modified asphalt in the preparation of the
pavement. In particular, the elastomer-modified asphalt
compositions which are used in the third layer, may suitably
be utilized as the asphalt binder component of the fourth
layer asphalt pavement.
As a note of clarification, it will be apparent that
the amount of elastomer in such preferred pavement
compositions is quite small, as the elastomer is present as
a minor constituent of the asphalt, and the asphalt is
itself only a minor constituent of the pavement.
The use of any particular type of mineral aggregate is
not critical to this invention. The term "mineral
aggregate" is meant to have broad meaning (and is used, in
the context of the present invention primarily to
distinguish it from the more narrowly defined term
"aggregate" as employed in the description of the aggregate
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CA 02038790 2000-07-25
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layer). The size of mineral aggregate commonly used in the
paving industry to prepare roads and the like is suitable
for use in the asphalt pavement of this invention.
EXAMPLES
The invention is illustrated in further detail by the
following non-limiting examples in which all references to
percentage are by weight, unless otherwise indicated.
Example 1
This example illustrates the preparation of a preferred
first primer layer.
The ingredients shown in Table 1 were mixed for 90
minutes in a conventional, laboratory-size high shear mixer.
The mixer was obtained from the Charles Ross and Son
Company of Hauppauge, N.Y., and is referred to as a "Ross 100
LX"* mixer. The mixer has a 1 horsepower motor, a drive which
operates at 3600 rpm and a mixing assembly which was
designed to accommodate a standard 5 U.S. gallon pail (i.e.
a pail having a capacity of about 19 1).
The resulting elastomer-modified asphalt composition
v
was then emulsified using the sodium salt of tall oil as
emulsifier.
* Trademark
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The final emulsion had a solids content of about 55%.
TABLE 1
Ingredient Amount (weight %)
S-B-S Elastomer - 1 ~e~ 5
S-B-S Elastomer - S ~b~ 6
Oil g
Antioxidant ~'~ 0.5
Tackif ier ~d? 0 . 5
Asphalt ~e~ 80
Notes:
(a) S-B-S block thermoplastic elastomer having a reported
bound styrene content of about 30 weight percent (sold
by Fina Oil and Chemical Company ("Fina~~) under the
trademark "Finaprene 411").
(b) S-B-S block thermoplastic elastomer having a reported
bound styrene content of about 25 weight percent (sold
by Fina under the trademark "Finaprene 1205").
(c) Antioxidant composition, believed to be tri (mixed mono
and dinonylphenyl phosphite) sold under the trademark
"Polygard HR" by Uniroyal Chemical Company).
(d Proprietary composition, believed to be based on
terpene resin, sold under the tradename SP-553 by
Schenectady Chemicals, Inc.).
(e) having a pen value of 300 to 400 (ASTM D5, at 25°C).
Example 2
This example illustrates the preparation of a preferred
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third layer composition.
The ingredients shown in Table 2 were mixed for 120
minutes in the "Ross 100-LX"* mixer described in Example 1.
The resulting second elastomer-modified asphalt
composition was then emulsified using the sodium salt of
tall oil as emulsifier.
The emulsion had a solids content of about 60 weight
percent.
TABLE 2
Ingredient . Amount (weight %)
S-B-S Elastomer - 3 ~a~ 7.00
Sulfur 0.12
Asphalt ~b~ 92.88
Notes:
(a) S-B-S block thermoplastic elastomer having a reported
bound styrene amount of about 30 weight percent (sold
by Fina under the trademark "Finaprene 416").
(b) pen value of 300 - 400 (ASTM D5, at 25°C).
Example 3
This example illustrates the preparation of an asphalt
pavement composition.
Elastomer-modified asphalt having the composition shown
in Table 2 of Example 2 was used as the "asphalt binder".
An asphalt pavement was then prepared by hot-mixing 8
weight percent of the elastomer-modified asphalt composition
* Trademark
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CA 02038790 2000-07-25
of Table 2, together with 92 weight percent of graded mineral
aggregate. In general, the mineral aggregate can be described
as a mixture of equal parts of coarse sand and a finer sand.
Example 4
This example illustrates the preparation of three separate
"metal plate/four layer paving" combinations according to the
present invention (designated as Plates A, B and C in Table
3) .
Table 3
Layer Description Application Rate
First Layer 0.9 litres / m2 @ 70°C
# 1535 emulsion tack coat
Third Layer 0.5 litres / m2 @ 70°C
# 1536 emulsion tack coat
Note Application rates apply to Plates A, B, C
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The metal plates had dimensions of about 30 cm x 90 cm
(width x length) and a thickness of about 0.8 cm.
The procedures used to prepare each of the combinations
are described below.
1. Initially, a first layer (having the composition
described in Example 1) was applied to the plates as an
emulsion in the amounts indicated in Table 3.
2. An aggregate layer was then applied on top of the first
layer. The aggregate was applied in an amount of 1 kg/mz at a
temperature of 70°C.
3. The aggregate was then rolled (i.e. with a roller, to
embed the aggregate into the first layer).
4. After 24 hours, the third layer (having the composition
described in Example 2) was applied as an emulsion in the
amounts indicated in Table 3. The third layer was applied at
a temperature of about 70°C.
After a further 24 hours, asphalt pavement (having the
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composition described in Example 3) as applied over top of
the third layer. The asphalt pavement was then rolled with
a steel roller at a temperature estimated to be between 110
and 130°C. The thickness of the asphalt pavement layer was
2 cm.
After another 24 hour period, Plate C was subjected to
simulated vehicle traffic at 15°C.
Plate C was placed under the front-left wheel of a van
(i.e. a light truck), then, while the van was stationary,
the front wheels were turned (i.e. a dry steering test, to
cause a shear force on the plate).
In another test, Plate C was elevated by placing a wood
strip, having a thickness of about 4 cm, under the opposite
(lengthwise) ends. The van was then driven over the plate,
resulting in a deflection of the plate.
At a later date, Plate C was subjected to the above
described simulated vehicle traffic test at an ambient
temperature of -20°C.
None of the tests described above produced visible
cracks in the pavement or visible delamination of the paving
layers from the metal plate.
In a final series of tests, Plate C was heated in an
oven at a temperature of 50°C, then immediately taken
outside and subjected in sequence to the above described dry
steering and deflection tests. One test observer believed
that the asphalt moved slightly on the metal plate during
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the dry steering test. However, at the completion of the
two tests, there was no visible delamination of the paving
layers from the metal plate, and the pavement was not
visibly cracked.
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