Artificial Turf

 
Artificial turf was not a result of efforts to achieve a uniform playing surface for competitive sports but was originally developed as a playground surface for city children.
 
During the 1950s, the Ford Foundation attempted to find ways to improve the physical fitness of young people.
 
In comparing all aspects of physical examination records of young man inducted into the armed forces from all parts of the USA, it was determined that young man from small towns and rural areas were more fit than those from the cities.
 
In the early 1960s, the Ford foundation's Education Facilities Laboratory was working with Chemstrand, a subsidiary of Monsanto Corp., on the use of synthetic fibers for carpeting in school buildings.
 
Being aware of the fitness studies of the Foundation, Dr. Herald Gores, President of the Educational Facilities Laboratory, requested Chemstrand to develop a suitable playing surface for city children which would withstand heavy play, be easy to maintain, and would retain its playing characteristics year round for a number of years.
 
In 1964, under the Ford foundation sponsorship, a synthetic grass surface called Chemgrass was installed in the Fieldhouse of Moses Brown school in Providence, Rhode Island.
 
In 1965, the Houston Astrodome (thought of at the time as the eighth wonder of the world) was completed.
 
This indoor sports facility was to have a natural turf as a playing surface but it was soon discovered that baseball outfielders were unable to track fly balls because of the glare from the sunlight through the translucent panels in the roof of the dome.
 
To solve this problem the panels were painted to eliminate the glare, but as a consequence the grass would not grow properly under the low artificial light and heavy use.
 
Astrodome operator, Judge Roy Hoafheinz, approached Monsanto and ask if it's Chemgrass could be used as a synthetic surface for the dome.
 
By April 1966 Monsanto had manufactured and installed AstroTurf on the baseball infield and in midsummer the outfielder of the dome was covered with synthetic turf.
 
Early that fall the artificial turf field for football was completed. The addition of more than 4.9 km (3 mi.) of zippers made it possible remove the turf and its underpad which was installed directly over the earth floor.
 
Removing the turf and underpad allowed rodeos, circuses, midget auto races, and cattle shows on the floor of the dome.
 
Early turf systems-the three original turfs
 
The first outdoor AstroTurf fields were installed in Memorial Stadium in Seattle, Washington and at Indiana State University in Terre Haute, Indiana in 1967.
 
In 1968, the 3M Co. of St. Paul, Minnesota introduced Tartan Turf as a complement to tartan track surfaces which were initially installed in 1961.
 
Shortly after that the American Built-Rite Co. of Boston began installing Poly-Turf.
 
 
The substructure is a permanent or heavy-duty athletic fields consist of stable compacted earth over which a layer of crushed stone is placed and covered by a layer of asphalt graded to provide good drainage.
 
The asphalt was sealed to pervent water infiltration and any subsequent frost upheaval.
 
The shock-absorbing underpad system of AstroTurf is glued to the asphalt.
 
This underpad is a closed-cell, synthetic elastomeric foam made by incorporating a chemical blowing agent into the foam latex or plastisol. The blades of synthetic grass are made of 500 denier nylon 6-6 ribbon mated into a high-strength polyester backing.
 
The fabric panels of turf, 3.6 to 4.5 m (12-15 feet) wide, are bonded together by gluing on a reinforcing tape, sewing, or some other technique.
 
The underpad of the Tartan Turf consisted of a polyurethane foam base, 16-millimeters (5/8 inch) thick, laid over a special urethane-formulated adhesive that provided a bond to the asphalt subbase.
 
Another coat of urethane adhesive was then spread over the foam base and the 13 mm (0.5 in.) carpet-like nylon surface was then layed down.
 
The Tartan Turf had rounded, crimped, thread-like nylon 6 pile fiber in contrast to the more flat grass-like blades used in AstroTurf and many of the other synthetic surfaces.
 
Poly-Turf's construction was a three component system.
 
  1. The base layer was a shock-absorbing underpad of closed-cell foam material similar to that used for Astroturf.
  2. The middle layer designed to spread forces of impact over greater area consists of solid virgin vinyl.
  3. The top layer was composed of blades of poly-propylene fibers that were longer than either of the AstroTurf or Tartan fibers.
 
In the USA, Tartan turf and Poly-Turf were manufactured within a few years after the original installation of AstroTurf in Houston, however, by 1976 both 3M and American Built-Rite had discontinued marketing synthetic turf fields.
 
There are few fields, if any, of these two turf systems still in use.
 
Other turf systems
 
Although the three types of turf previously described first appeared in the USA , European companies are also developing synthetic fields, which used somewhat different types of installations.
 
The bonded turf-pad system was commonly used, which was laid on top of permeable asphalt without gluing.
 
The special porous backing material allows water to percolate through the turf and drain away laterally through the aggregate subbase.
 
The Poligrass division of J. F. Adolff in Germany has use this type of installation combined with a special geotextile pad quite successfully for several years in outdoor installations for soccer and field hockey.
 
This special geotextile pad keeps dust and small particles of soil from working their way up through the turf to the surface.
 
The current permeable installations of poly-grass are fixed at the sides to curbing using metal concrete nails.
 
They also may include a golf-green type sprinkling system installed at the sides to wet down the surface, which is frequently done for field hockey competitions, and a side drainage system that readily handles run-off of excess water on the surface.
 
Sand-filled turf systems were invented by an American, Frederick T. Hass, Jr., in 1976.
 
The concept was first applied and developed in England but since 1983 sand-filled fields have been installed in the USA.
 
In general, the system consists of some type of a shock-absorbing underpad that is loosely laid on the asphalt subbase, the carpet surfaces laid over the underpad.
 
The major difference in the surface is that the synthetic blades of grass are longer than on nonsand-filled systems and that the spaces between the blades are filled with a silica sand to within 6 mm (0.25 in.) of the top of the fibers, thus keeping the synthetic fiber blades of grass upright.
 
Omniturf, one of the more widely known Sand-filled surfaces, uses 25 mm (1 in.) long 100 000 denier polypropylene fibers tufted into a polypropylene backing.
 
Because of the weight of the sand, it is not necessary to bond the fiber to the underpad in these sand-filled installations.
 

Turf characteristics
knitted vs tufted turfs

 
In general, most grasslike surfaces are either knitted or tufted, although a few are woven.
 
These are procedures that are routinely used in the carpet industry, and therefore, artificial turf companies that have been more successful and have the greatest tenure in artificial turf are those that have been closely aligned with the carpet manufacturing industry.
 
In the tufted surface, the fibers are inserted into the backing by a series of needles each of which forms the loop or tuft as the fiber penetrates the backing.
 
The looped turfs formed as a result of this process are then cut to provide the individual blades of the grass-like surface.
 
In contrast to the tufting process, the kniting process is somewhat more complex.
 
The fibers in this technique are fed through knitting needles of a knitting machine and each individual fiber is knotted into the backing fabric.
 
This provides a surface of high strength and firmer bonding of the fibers to the backing.
 
Because the knitting process is more complex, the knitted artificial turf's are more expensive than the tufted artificial turf and in general are more durable.
 
Backing and durability
 
Both knitted and tufted surfaces use a backing that is a fiber-forming polymer of considerable strength usually a polyester or a polypropylene.
 
Although not visible in the finished product, the backing material is an essential component of the surface since it is responsible for holding the fibers together.
 
This backing provides mechanical strength and dimensional stability of the surface and provides the life of the surface.
 
A typical artificial surface should have a service life of at least five years.
 
Many installations have been used for 8 to 10 years or longer without requiring replacement.
 
Underpadding
 
The underpad material is primarily designed for shock absorption. In case of athletic field use for football, this padding is usually a closed-cell foam.
 
These types of materials, usually polyvinyl chloride or polyethylenes, provide good energy absorption and the cost is reasonable.
 
This underpad must be resistant to water absorption otherwise the foam padding would deteriorate in a couple of years, particularly in climates with freezing temperatures.
 
The underpad must not only absorb shock but must also possess proper rebound characteristics for the ball and should not be so soft the players leg muscles fatigue quickly when running on the surface.
 
For the athletic fields in which shock-absorbency was a prime consideration, the earlier surfaces were usually nonpermeable, and therefore, runoff drainage for outdoor services was provided by the field camber or slope.
 
In sports such as baseball, soccer, and field hockey, the attenuation of shock is not so important.
 
In fields designed specifically for these sports, a light underpad, which is permanently bonded to the carpet is often used.
 
Many of the outdoor fields now installed for these three field sports are permeable surfaces that allow water to drain through the artificial turf system into a special drainage system installed under the surface.
 
Sometimes these permeable fields may also include a supplementary drainage system at the edges to accommodate excessive water.
 
Permeable systems may include a close-cell foam underpad with small holes punched through it after manufacturing thus allowing the water to float vertically downward through the system.
 
In other instances, a geotextile fabric laid down under the turf allows water to easily drain through it in a vertical direction.
 
The Poligrass Division of Adolff Company of Germany has recently been successful in laying their surfaces with a geotextile fabric underpad directly over a gravel substructure.
 
This gravel structure must be carefully leveled and prepared to ensure that the carpet surface will be uniformly level.
 
Substructure
 
In general, the substructure under the shock-absorbing padding material consists of a fine finished layer of asphalt that provides a smoothing consistent base for the surface.
 
Concrete could be used but this is unusual because the concrete is cost prohibitive.
 
In climates where the artificial surface will be subjected to freezing and thawing a coarse layer of asphalt, 102 to 152 mm (4-6 inches) thick, is put down before the final layer of finished asphalt.
 
This coarse layer will prevent the surface from heaving and the asphalt from cracking under adverse weather conditions.
 
A bottom base of crushed stone may also be recommended when the earth is not thoroughly compacted or solid.
 
Maintenance
 
Although artificial turf fields generally require much less maintenance than natural grass fields, it is a fallacy to expect that no maintenance is necessary.
 

Astroturf industries have outlined three simple rules for their surfaces:

  1. keep it clean
  2. do not abuse it with vehicular traffic, heavy static loads, fireworks or open flames
  3. make all repairs promptly
 
Routine cleaning
 
To maintain a clean artificial turf field, it is important remove all litter left behind by users and spectators.
 
Accesses to the field should be designed so that a minimum of mud and soil particles are brought onto the field.
 
Loose soil should be picked up as soon as possible before it begins to accumulate and work its way down between the fibers of the surface.
 
Electrically powered vacuum sweepers may be used to remove dust and light traffic from the surface of a field, to maintain a field in optimum condition and should be washed periodically with a generous amount of clean water.
 
A fire hose using maximum pressure and a full flow will flush away loose dust and blast away dirt particles embedded in the carpet.
 
For hosing down a nonpermeable field, AstroTurf industries recommends starting at the crown and directing the water flow towards the sides the field while working first down one side and then up the other side of the field.
 
Vacuum-type cleaning machines may also be employed to remove loose trash, small cups of paper, dirt, dust, and other debris from a synthetic surface.
 
A combination vacuum-brush type of machine is highly recommended for cleaning the surfaces.
 
The sweepers should have synthetic fiber bristles of at least 50 to 65 mm long (2-2 1/2 inches) with a maximum bristle diameter of 0.75 mm.
 
There should be no metal fibers in the brush to prevent damage to the turf.
 
The best results will be attained if the brush is set so that it just touches the top of the surface.
 
The brush will then agitate the fibers to loosen and dislodge dirt so that it is readily picked up by the suction of the machine.
 
Generally a thorough wet cleaning once or twice a year is sufficient. Excessive brushing with heavy-duty equipment may damage the synthetic surface and the under padding.
 
Soiled turf
 
Low-sudsing household detergents with plenty of hot water will remove most of the soil that occur on artificial turf.
 
The surface should be thoroughly rinsed with generous amounts of clean water after scrubbing or mopping.
 
More stubborn stains such as those from motor oil or grease, asphalt, chewing gum, lipstick, shoe polish, suntan oil, can usually be removed with dry-cleaning fluid.
 
In general, most cleaners that are suitable for cleaning household or commercial carpets a be used on artificial turf.
 
Field markings
 
If desired, permanent in-laid markings may be placed on the field when it is installed.
 
Since most synthetic fields are multipurpose, the maintenance personnel will probably be responsible for marking a field at various times.
 
Very temporary markings may be achieved by applying the same white chalk dust as use on natural grass fields.
 
A wet application may be used by making a slurry as a result of mixing the dust with water.
 
This may be picked up by shoes and can easily be washed away or spread by water.
 
The only advantage of dry markings on fields is that they are inexpensive.
 
More permanent markings are put down with paints.
 
A top-quality water-based acrylic latex exterior paint such as Sherman Williams A-100 SuperWhite paint will provide satisfactory results.
 
These markings were made visible with relatively hard used for reasonable length of time, possibly up to a full season.
 
The semipermanent paints are quite readily removed by brushing the striped area with a solution of mild detergent followed by a soil flushing with high-pressure water hose.
 
In applying markings, three precaution should be noted.
  1. Do not apply paints to a surface when it is wet.
  2. Do not apply paint to heavily.
  3. Be sure to give the paint time to dry thoroughly before using the field.
 
Minor repairs
 
Minor repair may become a major problem if not repaired soon after it is discovered.
 
Regluing or resewing of seams that have become loose may be easily accomplish by user's maintenance staff if simple directions provided by the turf manufacturer are followed.
 
Even small tears in the surface of 6 in. or less may be readily repaired by competent maintenance workers.
 
Protection against damage from static loading
 
Synthetic surfaces are not designed to accommodate long-term static loads.
 
Such loads usually exist when playing fields are used for commencement exercises, assemblies, convocations, rock concerts, and even circuses.
 
Long-term static load should not exceed 1.2 to 1.4 kPa to ensure that the turf is not damage as a result of special events.
 
Sheets of plywood (3/4 inch) thick are recommended for use as loads spreaders.
 
Although most synthetic surfaces are difficult to ignite and do not burned openly, open flames can easily cause major damage the surface.
 
For this reason, smoking by spectators or participants should not be allowed when they are on the surface of the synthetic field.
 
Turf related injuries
 
One of the ongoing controversies associate with artificial turf fields since they were first installed was the effect of the surface on the incidence of injuries, particularly knee and ankle injuries in football.
 
Although coaches, administrators, players, and researchers were concerned about injuries long before the introduction of synthetic turfs, they seem to be prone to injuries as inevitable.
 
A three-year study of injuries sustained by all 26 teams in the National Football League was conducted by Stanford research Institute.
 
To analyze the effects of turf on the injuries in professional football, the investigators differentiated injuries in terms of severity or gradients rather than frequency alone.
 
Gradient 1 included the incidence of both major and minor injuries.
 
Gradient 2 the incidence of reinjury,
gradient 3 injuries causing 2 or more missed games,
gradient 4 injuries requiring hospitalization, and
gradient 5 injuries requiring surgery.
 
The analysis of data for gradient 1, both major and minor injuries, indicated that a number of injuries per game was 2.0 on natural turf and 2.7 on synthetic turf.
 
This difference was statistically significant indicating a lower injury on natural grass.
 
For the other for gradients, however, there was no statistical significant difference between injuries per game on natural and artificial turf.
 
 
Factors to consider in the choice of a playing surface
 
The decision to install an artificial or natural surface playing field is usually quite difficult for most institution or communities.
 
Too frequently the final decision is based primarily on hearsay, limited experience, and the biased opinion of some outspoken individual in the decision-making group.
 
One of the primary factors to be considered is the amount or cost of available land.
 
If suitable land area is lacking and an extensive varied program of sports or other ancillary programs must use the facility, then the maximum must be anticipated.
 
If this situation exists, perhaps on artificial surface will better satisfy the needs than natural grass fields.
 
 
New Designs
 
FieldTurf
 
FieldTurf is a patented permeable artificial turf sold by Field Turf Inc.
 
FieldTurf is generally backfilled with pure sand and has fiber characteristics that closely mimic a 1.5 in. tall fescue turf.
 
 
AstroPlay
 
AstroPlay is also a patented permeable artificial turf sold by SRI Sports Inc.
 
AstroPlay was originally designed for soccer fields.
 
It has very similar characteristics to Field turf, but is often only backfilled with crumb rubber.
 
 
 
 
Both systems are being widely installed in practice fields, baseball fields, football fields, and soccer fields.
 
At this point in time it appears to be a reasonable compromise between natural turf and the old carpet systems.