Note: Descriptions are shown in the official language in which they were submitted.
1 2 3 ~0~
-1- 22-21(1261)A
ARTIFICIAL TURF PLAYING FIELDS
This invention pertains to artificial turf
playing fields installed over a layer of
water-conducting asphaltic concrete which is capable
of allowing horizontal drainage of rainfall. This
invention also permits conversion of non-permeable
artiicial turf playing fields to fields with a
sub-surace layer capable of accumulating and draining
rain water under a substantially dry artificial turf
playing surface.
A variety o designs for playing fields have
been proposed to extend recreation time into periods
of rain and to provide a quality playing surace after
periods of rain. Among basic yield designs are the
sloped impermeable playing field which allows rain
water to run off and the permeable playing field which
allows rain water to drain through.
Sloped playing fields may be provided with
interceptors as disclosed in U.S. Patent 3,611,729
which discloses vertical slots extending through the
top layer of a natural field and U.S. Patent 3,625,011
which discloses covered trenches for installation in
an artificial turf field. In many cases fields of
artificial turf comprise an impervious layer requiring
slopes, for instance of a 1-1~ percent grade on
America football fields, to provide water run off.
In other cases where a flat field is reguired, for
instance in baseball outfields, water can be removed
mechanically by blowers or vacuum cleaners.
To assist in water removal from flat playing
surfaces permeable fields have been proposed in a wide
variety of constructions. US. Patent 2,837,984
discloses a guick drying tennis court comprising
layexs of granular limestone over a clay base. U.S.
Patent 1,763,78~ discloses a playing field of fibrous
mats inverted in a drained cement basin. U.S. Patent
2 8~
-2 22-21(1261~A
1,906,494 discloses a pl yi~y surface comprising a
layer o felt, a layer of peI~ious concrete and a
b dding of coarse stone or broken stone.
Grass-like artifici.al turf systems have been
proposed as an alternative to high maintenance
surfaces such as golf putting greens which, although
not necessarily flat, have been required to by highly
permeable. See, for i.nstance, U.S. Patents ~,515,847;
3,740,303; and 4,007,307; and Canadian Patent 886,152
which disclose artificial turf over permeable layers
of sand, gravel, stone, rubber, plastic chips and the
like. While such playing fields appear to provide
some degree of permeability they do not appear to have
a base with sufficient stability to maintain a smooth
playing surface even with only occasional traffic of
maintenance vehicles.
In recent years flat playing fields have
been designed with both advantageous permeability and
strong, stable base by overlying artificial turf on
a base of permeable concrete. Permeable concrete
bases were proposed as early as 1930 in U.S. Patent
1,906,494 which relates to playing surfaces comprising
a layer of felt, a layer of pervious concrete and a
bedding of coarse stone or broken stone. In one
embodiment the porous concrete is said to bP
compounded of a mixture containing about eight parts
by volume of coarse crushed stone having mean
diameter of three-quartPrs of an inch about 19
millimeters) and a shape actor of about 1.5, one part
by volume of Portland cement and water. Permeable
concrete which may be usefuly for supporting
artificial turf is also disclosed in U.S. Patents
4,333,765 and 4,376,595.
Peremable asphaltic concrete has been
utilized in the construction of special air strips,
p2rking lots, road surfaces and other areas where
~318~
-3- 2~-Z1(1261)~
vertical draining for removal of rain water to prevent
ice formation and to prevent hydroplaning of vehicle
tires was desired. Critical to the performance of
permeable asphaltic concrete is the requirement for an
open-graded aggregate mix to provide void space to
facilitate vertical drainage of water Other critical
factors include resistance to stripping of asphaltic
cement from the aggregate, and temperature control of
the mix to prevent the asphaltic mix from flowing down
off of the aggregate.
At least three automobile parking lots haze
been constructed from pexme~ble asphaltic concrete at
the University of Delaware during the period 1972
through 1974. As of 1983 these parking lots appear to
be in excellent condition with the permeable asphaltic
concrete exhibiting acceptable load-bearing
properties. A parking lot has also been installed in
1981 in Tallahassee, Florida utilizing a 4 inch (10
centimeters) layer of permeable asphaltic concrete
over a 36 inch (about 90 centimeters) deep rock base.
Permeable asphaltic concrete has been
applied with some success to highways to provide a
friction course to minimize the pos6ibility of
hydroplaning on accumulated rain water. See, for
instance, U.S. Patent 3,690,227 which discloses a
frictional, self-draining paving surface useful for
runways and roadways comprising a porous layer of
aggregate particles of greater size Han 1/16 inch
(about 1.6 millimeters mesh bonded with a resinous
binder.
Permeable asphaltic concrete has also been
utilized as a base layer for highways. Within the
last several years a 56-mile (about 90 kilometers
section of highway was constructed near Sao Paulo,
Brazil where permeable asphaltic concrete was covered
with a dense gxaded impervious asphalt. The permeable
2 8
~4- 22-21(1261)A
asphal~ic concrete was used to carry away surface
water which might otherwise have undermined the road
base.
Permeable asphaltic concrete has also been
utilized in the construction of athletic fields of
artificial turf. Within the last five yeaxs at least
16 athletic fields have been installed in Europe and
Australia with artificial turf overlaid on a base of
permeable asphaltic concrete. Athletic fields in
Europe comprising artificial turf installed over
permeable asphaltic concrete often comply with -
Deut che Normen (DIN) 18 035, Part 6 on Permeable
Asphalt, April 1978, which specifies that the
permeable concrete is installed in two lifts (a lift
being a separate layer of concrete). The aggregate
for the separate upper and lower lifts is speciied
according to gradation diagrams from which the
gradation data listed in Table l has been extracted.
2 3 1
-I- 2~-21~1~61)~
TABLE 1
Ag~re~ate Gradation For Two Lifts of Permeably Concrete
Fxtracted From Gradation Dia~ms in
Deutsche Norme~ ODIN) 18 035 (April, 1978~
Aggregate Weight Percent of Aggregate
Sieve Size Pas~i~g Thy sieve
(Millimeters) Lower Lift Upper Lift
13 90-100
11 4~-100
9.5 35-75
8 ~30-62 90-lnO
21-41 41-100
4 30-80
3 20-55
2 10-25 15-30
1.2 6-19 . 9~22
0.25 5-14 S-~6
0~9 3-6 4-7
A disadvantage of such specification for
permeable asphaltic concrete is of course that the
asphaltic concrete be applied in two lifts, that is
two separate layers. A more signif.icant disad~an~age
is that the upper lift comprises aggregate of a
substantially smaller particle size than an aggregate
of a lower lift
A preferred method of installing artificial
tuxf is to glue the artificial turf assembly to the
upper layer of asphaltic concrete to avoid migration
of line markers vn a playing field. However, in such
30 installations it is almost always required that the
artificial turf be laid loosely on top of the upper
lift of permeable asphaltic concrete. Gluing of
artificial turf to the upper surface of the asphaltic
concrete is generally precluded because the adhesive
tends to occlude the smaller-size pores in the upper
2 2
-6- 22-21~1261)A
surface of such asphaltic concrete which comprises
aggregate of smaller particle sizes.
This same deficiency is inherent in most
specifications for permeable asphaltic concrete. For
instance permeable asphaltic concrete designed for use
in paving surfaces such as parking lots and highways
generally comprise an aggregate of a small particle
size to provide the necessary strength to suppoxt
vehicle traffic. This requirement to provide
structural strength requires significant sacrifice in
the permeability qualities of the permeable asphaltic
concrete.
To avoid such disadvantages a preferred
permeable asphaltic concrete composition for use in
toe construction of artificial turf playing fields is
disclosed in copending patent application Serial No.
466,544, filed October 29, 1984, (Canada).
It would be desirable to convert existing
non-permeable artificial turf playing fields to
permeable artificial turf playing fields. A
considerable number of such non-permeable artificial
turf playing fields are installed with the layer of
artificial turf playing surface an optional polymeric
foam cushion over a substantial non-permeable base,
for instance, af asphaltic concrete or Portland cement
concrete. However the cost of removing such a
non-permeable concrete base to install a permeable
base and water conduit piping may be excessive and
economically prohibitive.
Accordingly when resurfacing with new
artificial turf is required on existing non-permeable
playing field, a conversion to a permeable artificial
turf playlng field often cannot be justified.
SUMMAXY OF TOE INVENTION
This invention provides an artificial turf
playing field having an interlayer of water conducting
l~lao2
asphaltic concrete composition having a porosity sufficient to
accumulate a moderately high level of rainfall and allow hori-
zontal drainage of accumulated water. The interlayer of water-
conducting asphaltic concrete comprises a gradated rnixture of
S aggregate rock of particle sizes much larger than those pre-
viously used in asphaltic concrete designs.
In accordance with one embodiment of the present
invention, there is provided an artificial turf playing field
comprising a layer of artificial turf, a resilient shock-
absorbing cushion, an in~erlayer of water-conducting a~sphaltic
concrete and a substantially impervious base, wherein said
interlayer of water-conducting asphaltic concre-te comprises a
gradated mixture of aggregate rock having a size distribution
such that -the percent by weight oE aggregate rock passing a
15 sieve with square openings of
(a3 38~1 millimeters is 100 percent,
(b) 25.4 millimeters is 95-100 percent,
(c) 19.0 millimeters is 75-95 percent,
(d) 12.7 millimeters is 40-60 percent,
(e) 9.52 millimeters is 30-40 percent,
(f) 4.75 millimeters is 20-30 percent,
(g) 2.36 millimeters is 15-25 percent,
and
(h) Q.075 millimeters is 0-3 percent; and wherein
said interlayer of water-conducting asphaltic concrete has a
minimum thickness of 1-1/2 to 2 times the largest sieve size oE
said aggregate rock.
~3
-7a-
~RlEF DESCRIPTION OF THE DRAWING
-
Figure 1 is a gradation diagram which illustrates the
particle size ranges for a gradated mixture oE aggregate rock
useful in the asphaltic concrete composition oE this invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
By this invention applicants have provided an artifi-
cial turf playing field which can be advantageously and economi-
cally incorporated into the design of existing non-permeable
artificial turf playing fields to convert such existing fields
to an artificial turf playing field capable of accommodating
moderate rainfall while retaining a substantially dry artifi-
cial turf playing surface.
The artificial turf playing field of this invention
comprises a layer of artificial turf, an optional shock-
absorbing cushion, an interlayer of water-conducting asphaltic
concrete and a substantially impervious base. In a preferred
aspect of this invention the interlayer of water-conducting
asphaltic concrete comprises a gradated mixture of aggregate
rock having a size distribution such that the percent by weight
of aggregate rock passing a sieve with square openings is with-
in the limits expressed in Table 2.
1 3 1 8~
~8- 22-21(1261)A
TABLE 2
Aggregate Gradation For_Permeable Asphaltic
Concrete According To this Invention
Apgregate Weight Percent of
Sieve Square Sieve OpeningAggregate Passing
Designation(Millimeters) (Inches) the Sieve
lo 38.l l.5 lO0
l 25.4 1.0 9S-100
3/4 19.0 0.75 75-95
112 12.7 0.5 40-6~
3/8 ~.52 0.375 30-40
No. 4 4.75 0.187 20-30
ho. 8 2.36 0.094 15-25
No. 200 0.075 0.003 0-3
The gradation of the aggregate rock can also
be determined by reference to Figure 1 which
graphically illustrates the gradation speciied in
Table 2. Figure 1 provides a gradation diagram which
is a semi-logarithmic plot of the percent by weight of
aggrPgate smaller than the size indicated (that is,
the percent by weight passing a designated sieve
versus the particle size of the aggregate rock as
determined by sieve designation. With reference to
Figure 1 a gradated mixture of aggregate rock useful
in the layer of water-conducting permeable asphaltic
concrete of the artificial turf playing field of this
invention it reguired to have a size distri~u~ion
substantially within the area identified as
a-b-c-d-e-f-a.
This gradated mixture comprises a very high
percent by weight of aggregate rock above the 3/8
sieve size. About 60 to 70 percent hy weight of the
aggregate rock is above 3/8 sieve size. A minor
amount by weight, for instance in the range of about
15 percent by weight, of the aggregate rock is in the
range of No. 8 to 3/8 sieve size. A somewhat larger
2 3 8 02
-9- 22-21(1261)A
but still minor amount by weight of the aggregate rock
is in the range of No. 200 to No. 8 sieve size.
Essentially none of the aggregate rock is of a size
smaller than No. 200 sieve size. Because of the
specification the gradation profile is bimodal with
points of inflection near the ends of the particle
size distribution bracket by the No. 8 and the 3/8
sieve size. Such a gradation profile is referred to
as "skip-graded" or ~'gap-graded". In this regard the
large percentage of aggregate rock above 3/8 sieve
size provides exceptional porosity, enhanced
permeability, to the asphaltic concrete. The minor
amount by weight of asgregate rock in the No. 8 to 3/8
sieve bracket provides considerable stability to the
aggregate within the concrete without unduly impairing
permeability.
The shape of the aggregate rock is important
to enable the permeable asphaltic concrete to perform most
effectively. The three dimensions of the individual
particles of the aggregate rock should be of the same
order of magnitude. Such particles are described as
being bulky in shape. Many of these bulky particles
of aggregate rock are approximately spherical. In
this regard it is undesireable that anything but a
minor amount by weight of the aggregate rock be of
plate-liXe shape or rod-like shape.
The aggregate rock may comprise any of a
variety of compositions, for instance crushed quarry
stone of granite or washed gravel or any other stable
mineral composition which can be graded to the
required specifications.
In preparing the water-conducting asphaltic
concrete it is desireable that the aggregate rock be
substantially free of moisture to promote the adhesion
of the asphaltic cement to the aggregate. In thi5
regard it is often desireable that an anti-stripping
~318~2
-10- 22-21(1261)A
agent bP added to the dry mix of the aggregate rock
prior to the intxoduction of asphaltic cement. Such
anti-stripping agents axe intended to remove residual
moisture, provide better contact and promote adhesion
between the asphaltic cement and the aggregate rock.
A useful anti-stripping agent comprises hydrated lime
which can be added at a rate of about 1 percent by
weight based on the dry weight of the aggregate rock.
The anti-strlpping agent such as hydrated lime should
he adequately mixed wit the aggregate rock to
sufficiently coat the dry aggregate rock at a point in
the mixing process so as not to become unduly air
entrained in the exhaust air system of the mixing
plant.
hlternatively, promotion of adhesion of
asphaltic cement to aggregate is sometimes achieved by
adding surface active agents to asphal.tic cement.
Preferred surface active agents include those derived
from lignin. Such surface active agents should be used
in minor amounts, say at a level of about 0.5 percent by
weight of the liquid asphaltic cement. At high levels
of surface active agent the viscosity of the asphaltic
cement can be significantly reduced which may promote
separation of the cement from the aggregate and
~5 puddling of cement at the bottom of the layer of
concrete. Moreover at high levels of surface active
agent the concrete may tend to be susceptible to
stripping by water.
The layer of w~ter-conducting asphaltic
concrete useful in this invention also comprises an
asphaltic cement which is present at a level of about
4.5 percent by weight of the asphaltic concrete.
Suitable asphaltic concretes include whose designated
as AC 5, AC-10, AC-20 or AC-30, or their equivalents,
the selection of which depends on geographical
1 i 8~
22-21(1261)A
considerations, such as weather and climate, and
material availability.
The Mix Design Methods For Asphalt Concrete
published by the Asphalt Institut2 as Manual Series
No. 2 (MS-2~, Fourth Edition, March 1974, is
particularly useful in defining terms and methods
relating to this invention, especially in Chapter III,
which relates to the r~.arshall ~leth~d of fix ~esi~n.
The Marshall Method of Mix Design provides
procedures useful in specifying certain parameters for
preparing the hot mix of the asphaltic concrete of
this invention. Among the more critical criteria of
the Marshall Method are what is known as "flow",
"stability" and "voids". The Marshall Method of Mix
Design test procedures have been standarized by the
American Society for Testing and Materials (ASTM) as
Test Method D-1559, entitled a Standard Test Method
for "RESISTANCE TO PLASTIC FLOW OF BITUMINOUS MIXTURES
USING MARSHALL APPARATUS".
TAe Marshall Method of Mix Design is
generally applicable only to hot-mix asphalt paving
mixtures containing aggregates with maximum sizes of 1
inch (25.4 millimeters) or lessO However, for
purposes of defining and practicing this invention the
Marshall Method of Mix Design will he modified where
necessary. For instance, the method will be extended
to apply to mixtures containing aggregate up to a
maximum size of l inch (38 millimeters3.
This Marshall Method of Mix Design is
generally modified in conducting stability and flow
tests of water-conducting asphaltic concrete such that
these tests are conducted at room temperature, that
is, at 25C, rather than at the generally solid
test temperature of 140F (60C~. This is necessary
I 2 3 ~02
-12~ 72-21(1261)A
because wa~er-conduc~ing asphaltic concretes art
generally intrinsically extremlely weak and often
degrade at the generally speciied test temperature of
140F (60C). At best prPviously known
S water-conducting asphaltic concrete compositions have
disintegrated at loads of about 200 lbf (890 newtons)
when tested at 140F ~60C~.
Surprisingly the water-conducting asphaltic
concxete of this invention is remarkably stable at the
specified test temperature of 140F (60C) and have
exhibited "stabilityl' at loads in the range of 700 to
900 lbf (3100 to 4000 newtons). In this regard the
water-conducting asphaltic concrete compositions of
this invention will preferably exhibit stability of at
least about 400 lbf (1780 newtons) and more preferably
at least about 500 lbf (2225 newtons) at the specified
test temperature of 140F (60C).
In this regard the constituents of the
water-conducting asphaltic concrete should be
proportioned to produce water-conducting asphaltic
concrete having a "Marshall" flow at 25C in the range
of about 8 to 20 10 2 inches (I to 5 millimeters,
"Marshall" a stability at 60C of at least 400 lbf
(2780 newtons). Moreover it is generally desireable
that the water-conducting asphaltic concrete be
compacted to have voids at a level of at least lO
percent by volume and preferably .in the rangP of 12 to
22 percent by volume.
In preparing the hot mix of the
water-conducting asphaltic concrete of this invention
care should also be taken to control the temperature
of the asphaltic concrete hot mix so as to minimize
asphaltic concrete separation from the aggregate rock.
When using asphaltic cement having a viscosity
designation AC-10 satisfactoxy results have been
23 8~2
-13- 22~21(1261~A
obtained by maintaining hot mix in the temperature
range of from 116C to 127C.
The water-conductir,g asphaltic concrete is
particularly useful as an interlayer between
artificial turf and a supportlng base, for instance of
impervious asphaltic concrete.
In this regard athletic field are often
prepared with a sub base of stable fill material, for
instance gravel or rock. The sub base supports an
impervious slab of concreke, such as asphaltic
concrete or asphaltic concrete. The impervious slab
of concrete may be 6 inches (about 15 centimeters or
more in thickness. In the construction of sloped
playiny fields a practice his been to install the
artificial turf, including the optimal resilient
polymeric foam cushion, over a sloped surface of an
impervious slob of concrete. For instance an American
football field may have surfaces sloping from a
crowned center of the field at a grade of l percent
say in the range of about 1 to 2 percent. Baseball
outfields are generally constructed with slopes of 1
percent.
Such sloped plying fields of artificial
turf can be improved by this invention by providing an
interlayer of water-conducting asphaltic concrete over
the impervious concrete slab. The interlayex
comprise the gradated mixture of aggregate rock
described above and has a minimum thickness of 1.5
times the sieve size of the largest aggregate rock
present in toe gradated mixture. The interlayer may
have larger thickness, for instance up to about 6
inches (15 centimeters) or more to accommodate higher
~ua~tities of rainfall. Asphaltic concrete is not
generally applied in layers thicker than about 1 inch
(2.5 centimeters) or so in a single lift because of
compactisn instability in installing such a layer.
-14- 2~-21(12613A
however, interlayers of water-conduGting asphaltic
concrete of larger thickness are achievable with a
gradated mixture of aggregate :cock of large particle
size as specified above because of the inherent
stability ox such a gradated mixture. The interl~yer
should be of uniform thickness with an upper surface
generally conforming to the upper surface o the slab
of impervious concrete. In some cases however it may
be desireable to provide the interlayer with a
substantially horizontal upper surface to provide a
flat playing field.
To provide superior adhesion of the
interlayer to the impervious slab it is often
desireable to apply a tack coat to the upper surface
of the impervlous slabO The tack coat can comprise
low viscosity alaphatic cement or a water emulsion of
~sphaltic cement and can be applied at a rate of about
0.15 gallons per squarP yard ~O.68 livers per square
meter).
An interlayer prepared acrording to this
invention is substantially porous and will accumulate
rainfall quickly, however because of the underlying
impervious slab the accumulated rainfall is required
to drain laterally across the field.
In this regard a 2 inch thick (5
centimeters) interlayer of water-conducting asphaltic
concrete was prepared according to this invention with
a 13 percent void volume and applied over an
impervious concrete slab having a 1.5 percent grade.
Such interlayer of water-conducting concrete has an
initial capacity to store about 0.3 inches ~7.6
millimeters) of rainfall which of course must drain
laterally down the slope. When such an interlayer is
applied over a large field, say a field of 200 foot x
300 foot (60 meters x 90 meter) with a 1.5 percent
1 2 8~
15- 22-21(1261~A
slope, it could take about 30 clays for complete
drainage, neglecting evaporation.
The drainage is so relatively slow, because
of the long distances for drainage, for instance about
lO0 feet (30 meters. Moreover such an interlayer
exhibits a steady-state rainfall-handling capacity of
about 0.0025 inches per hour (O.064 millimeters per
hour).
It is often desireable to improve the
rainfall-handling capacity of such an interlayer of
water-conducting asphaltic concrete. This can be
accomplished by providing water-conducting channels
intermediate the periphery and center o the sloped
playing field. Such water-conducting channels can be
cut into the impervious slab of concrete for instance
with a trenching saw. The channels can be run at
various angles to the slope of the field to optimize
water dx~inage. The channel should not be
excessively wide such that the interlayer of
water-conducting asphal~ic concxete can collapse and
occlude the channel. In thi5 regard channels of about
1-inch wide may be satisfactory.
The interlayer is overlaid with an
artificial turf which may optionally compri-~e a layer
of resilient polymeric foam cushion. It is generally
desirable that the artificial turf be glued to the
optional cushion layer and that the artlficial turf or
cushion layer be glued to the interlayer. For
instance a suitable adhesive is used to glue the
artificial turf Jo the underlying layer of resilient
polymeric foam cushion. Similarly, the artificial
turf is desirably glued to the interlayer of
water-conducting asphaltic concrete. Sufficient
adhesive is required to provide a good bond between
the layers. However, the adhesive should not be
applied in such exces6ive amounts as to occlude pores
I 1 8~2
-16- 22~21~1261~A
in the top surface of the interlayer of
wa~er-conducting asphal~ic concrete. In this regard
the interlayex of waxer conduc1ing asphaltic concrete
of this invention is advantageous in that it utilizes
aggregate rock of a sufficiently large size that the
possibility of pore occlusion by the adhesive is
minimized.
In order to provide an athletic field
comprising artificial turf which is
vertically-draining to the water-conducting interlayer
it is necessary that the layer or layers of artificial
turf be permeable. Axtificial turf can generally be
provided in a permeable configuration. For instance,
artificial turf of knitted or woven construction is
generally permeable. Artificial turf of tufted
construction is generally not permeable unless holes
or perforations are provided after the turf is
fabricated. The optional resilient polymeric foam
cushion can be made permeable by either utilizing an
open-celled polymeric foam or, when a close-celled
polymeric foam is utilized a cushion can be made
permeable by punching or drilling a sufficient number
of holes in the polymeric foam cushion. Sufficient
holes should ye provided so as to provide suitable
permeability without adversely affectiny the resilient
properties of the cushion.
While specific embodiments of the invention
have been described, it should ye apparent to those
skilled in the axt that variol~s modifications thereof
may be made without departing from the true spirit and
scope of the invention. Accordingly it is intended
that the scope of the following claims cover all such
modifications which fall within the full inventive
conceptO
