Features Agronomy
Crumb rubber and natural turf work well together: researcher

In the world of sports turf management, when one thinks of crumb
rubber, it’s usually as an infill for synthetic fields, which gives the
playing surface some resiliency as a means to minimize athlete injuries.

But crumb rubber isn’t necessarily confined to only synthetic turf
fields. Research has found the product to equally enhance natural turf
surfaces.

Dr. Tim Vanini of Buffalo, N.Y.-based New Dimensions Turf spoke at February’s Ontario Turfgrass Symposium in Guelph about the attributes of crumb rubber on natural sports fields.

Having studied the relationship between crumb rubber and natural turf since the mid-1990s, he said great things are being discovered, including the mitigation of soil compaction.

“When dealing with crumb rubber in natural turf, you do have to re-establish, you do have to take care of it no differently, however, you’re improving the wear tolerance, you’re improving the playability and you’re mitigating soil compaction,” he said.

Like its function with synthetic turf, crumb rubber helps to give natural fields an extra measure of resiliency through its ability to mitigate soil compaction.

It’s important to look at the interaction between the player and the surface since surface hardness is a major issue with sports fields. Surface hardness is measured by using a Clegg hammer to determine Gmax, or the peak acceleration point of an object contacting the surface.

“How can we manipulate that surface so that it’s more consistent?”

Aerating and irrigating the field will help, Vanini said, but the effort is only temporary. By putting crumb rubber down, the surface can be softened and stabilized.

“Originally, when we were doing the research, we were looking at tilling it in, but what we found where it was tilled in it took too long to get any results or where we were able to see any results, period.”

It was found that in the U.K. sports fields topdressed with crumb rubber to fill aeration holes improved drainage and made for a more consistent playing surface.

Sports turf managers must not be content with merely green grass alone, he said.

“You’re managing four inches—two inches at the soil line and two inches of turf.”

The most important area of management for the two inches of turf is the crown tissue.

“The more impact that crown takes, the quicker it’s going to die, and you need that turf there.”

The need to protect the crown was where the concept of crumb rubber’s inclusion on natural turf began, Vanini said.

Various sizes of crumb rubber particles were studied in earlier research, but a finer, powder-like size is now being used. The cost of the powdery crumb rubber is about 30 cents a pound, or about $ 25,000 to do an entire field of 80,000 square feet. Many sports turf managers, however, are looking only at using the rubber for their high traffic areas such as goal mouths which would reduce the cost substantially.

Research into surface hardness was done by simulating typical game traffic, trying to get as close as possible to athletes running across the surface.

Surface hardness had become a hot topic of discussion in the mid-1990s, Vanini said. Retired NFL players had been complaining about chronic pain from playing so many games over several years on synthetic turf surfaces. At the time, no one was able to come up with any science-based answers to explain their lingering pain, and that’s what precipitated research into the issue.

Using a Clegg hammer to measure surface hardness on both synthetic and natural turf fields, data showed virtually the same Gmax results, even though the retired football players claimed the synthetic turf surfaces were harder. Although the Gmax numbers were the same, what was statistically significant was the duration of the impact, the time to peak and the rebound ratio.

Even two milliseconds in time of impact makes a big difference, Vanini said.

While at Michigan State University in 2003-04, he wanted to study crumb rubber from a management perspective, looking at its relationship with fertility, water, aerification, overseeding and other cultural practices.

Trials involved plots with no crumb rubber with no extra water (other than rain) and no extra fertility as well as plots with crumb rubber yet no extra water or fertility, and crumb rubber with extra water and extra fertility.

The higher the soil moisture, the softer the surface, with or without rubber.

“By manipulating the surface with crumb rubber, it would stabilize more over time vs. trying to manipulate the aerification or irrigation.”

It was found the crumb rubber was stabilizing the surface and helping the plant continue to grow, even with traffic above.

Vanini said it is not good enough that the plant is green. It must function and be able to withstand traffic and recover.

He speculated that over the next five to 10 years, there will be much more research being done with regard to biomechanics and the relationship between the athlete and the surface.

Last summer at a non-irrigated baseball diamond in the Pittsburgh area, crumb rubber was put down on a June day when the temperature had soared to 95 degrees Fahrenheit. Crumb rubber was put down on the first base side of the diamond while none was added to the third base side. By July 25, the day before a major baseball tournament, the first base side looked good.

Within four days, 3.5 inches of rain fell. The first base side, with the crumb rubber added, showed some wear, but the turf was gone on the third base side where no crumb rubber was added.

Crumb rubber in synthetic turf will show differing temperatures from crumb rubber on natural fields.
Temperatures in excess of 140 degrees Fahrenheit are not uncommon on synthetic turf fields, although it is the blades of synthetic fibres which largely account for the heat buildup. On natural turf, with the exact same air temperature, the surface temperature may increase about 10 degrees with crumb rubber added, but will never come close to approaching the same 140 degrees, Vanini said.

“If it did, it would kill the grass.”

In his research, Vanini learned that temperature was not that large of an issue. The rubber getting to the surface due to wear was not going to kill the grass.

The key to crumb rubber’s success on natural turf was its complementary relationship with aerification.
“By aerifying, we can drag that crumb rubber into these holes and we can keep the integrity of these holes.”
He showed photographs depicting healthy, white roots within the aeration holes.

With crumb rubber in the holes, the integrity of the aerification can be maintained. Crumb rubber’s particle density is less than that of sand and it has elastic properties.

Light and frequent topdressing has always been the recommended practice, with a quarter-inch of sand suggested for sports fields.

“What we found is you can go the opposite way with crumb rubber,” Vanini said. “With crumb rubber, what we’re suggesting is that you can put it down in one application at half an inch.”

He said sports turf managers may instead choose to put a quarter-inch down one day and follow up with another quarter-inch a couple of weeks later and achieve good results.

Turf density is “huge” when crumb rubber is applied, Vanini said, adding it is imperative there is 100 per cent turf coverage before starting. If a field has only 50 per cent turf coverage and crumb rubber is put down, it won’t bring back the lost turf nor will it be as effective on the field.

He said to achieve 100 per cent coverage, it might require having to take the field out of play for a number of weeks to restore its desired density before adding crumb rubber.

Mowing height also plays a vital role in the effectiveness of crumb rubber. If a field is mowed at three inches and only a half-inch of rubber is put down, only 16 per cent of the plant will be covered, leaving its crown tissue vulnerable.

In his research, Vanini said he got best results from mowing at 1.5 inches and putting down three-quarters of an inch of crumb rubber, with 50 per cent of the plant covered. During his PhD work, the mowing height was two inches and enough crumb rubber was put down to cover 25 per cent of the plant.

“That was huge and it made a big difference.”

A grounds manager for a Triple-A baseball team told Vanini that he has been incorporating crumb rubber into his natural turf field since 2011, saying it has saved him considerable work in resodding the area between the pitcher’s mound and home plate. Previously, the amount of wear the area would incur resulted in having to resod it about five times in a season. With crumb rubber, he resodded the area only twice in 2012. The amount of time and labour saved was worth the investment of crumb rubber, he said.

Vanini added a golf superintendent told him he planned to use crumb rubber at the end of his cart paths, figuring he would have to resod those areas only once a year instead of twice.