In the planning and design phase of modern athletic fields and stadiums, owners may find themselves extensively weighing the value of selecting either a natural grass surface or synthetic turf system. The arguments of cost, quality, maintenance and safety are seemingly endless and the decision will be heavily influenced by the intended use of the playing field and the expected usable life of the surface.
With the proliferation of newer, safer, and more affordable options in artificial turf, what was once considered reserved for high-profile sports venues is now becoming quite a popular choice in playing fields of all shapes, sizes and uses. The experienced field and stadium designers of Eckles Architecture & Engineering have prepared a brief primer introducing the basic characteristics of artificial turf systems.
The most popular artificial turf products utilize a collection of monofilament fibers arrayed in one or more layers of backing. Each blade of artificial “grass” is a single length (monofilament) of extruded polyethylene that is formed to resemble a blade of grass. The blades are then tufted through a backing material to create a grass-like carpet. Depending on the manufacturer, this carpet typically has a uniform pile height between 2” and 2 ½”.
The playing area must be prepared with a significant base of crushed gravel that will provide stability and drainage. The gravel base can be leveled or sloped according to the intended use of the playing area, the drainage needs and the manufacturer’s installation specifications. Synthetic surface carpet is typically supplied in rolls that are 15 feet wide which are rolled out and stitched together to cover the playing surface.
The strength and durability of the finished surface is directly related to the construction and materials used in the backing layers of the surface. Each manufacturer has its own method layering the backing material such that the most effective tensile strength and dimensional stability are realized. At a minimum the product must have two specific layers. The primary layer arranges the tufted “grass” fibers and the secondary layer of heat activated urethane permanently holds the fibers in place. Some manufacturers include a number of additional layers of mesh or woven material to improve durability and to provide stitching points during installation.
A common method used to evaluate the strength of a turf product is the fabric grab tensile strength test. For best results, playing field surfaces should be have a fabric grab strength rating of not less than 200 lbs. with ratings up to 385 lbs. or more recommended for maximum durability. Of course, the frequency and duration of use of the playing surface will dictate the actual grab strength rating required.
In addition to construction of the turf product, a playing fields lifespan can be affected by environmental factors. For example, filaments and backing material should be UV rated to reduce degradation from sunlight exposure over time. Backings must also be evaluated for drainage potential as appropriate for the application. The porosity and permeability of each layer as well as the base fill over which the surface is applied must be considered together in determining the drainage capability of the finished system.
Each manufacturer will provide a specification for approved infill material which reduces slippage and provides impact absorption to reduce injuries. This layer of infill is spread uniformly across the turf surface with the most common mixture consisting of sand and rubber crumb. Specifically, the sand component is made up of uniform silica granules that have been rounded and polished to eliminate dust and prevent the granules from sticking to clothing or skin. The rubber component is typically made up of a polymer that is more formally known as Styrene-Butadiene Rubber (SBR). Many manufacturers use recycled tires to produce the granular SBR used as infill for artificial turf. While many recycling and preparation techniques are used, one method involves cryogenically freezing and shattering recycled rubber to create clean, uniform crumbs.
One of the most valuable qualities of an artificial turf surface is its impact attenuation potential. Impact attenuation is a ratio of the rate of deceleration during impact to the rate of deceleration due to normal gravity. A common way to measure impact attenuation is the g-max valuation. In testing synthetic turf, the lower the g-max value, the better the impact absorption by the surface. A value of 200 is considered the maximum safe rating by ASTM International standards. Products will have the best g-max values at time of installation. Impact attenuation performance will degrade over time so it is important to have the surface regularly tested and repaired as necessary.
Impact attenuation must be weighed against athletic performance benefits of the surface. For example, harder surfaces have a reduced impact absorption capability but softer surfaces may quickly increase player fatigue due to a quicksand-like effect.
These are just a few elements to consider when evaluating a new playing surface. Eckles Architecture & Engineering, Inc. has extensive experience designing indoor and outdoor playing fields for a variety of sports and activities. If your facility has a stadium or playing field project on the horizon, contact us today and let our designers be your trusted expert in guiding you through the process.