Exploring artificial turf from the ground up
In this article, Robbie Craven, Head of Research and Development at TigerTurf UK, provides an insight into the considerations that need to be made when it comes to the use of artificial turf, and stresses the need to view it as a complete system rather than a mere natural grass replacement
As an industry, the market for artificial turf can still be considered as one which is still in the infant stage of its development. Despite the early synthetic grass systems having only been brought to the UK market some thirty years ago, the evolution of the products on offer within this market has been rapid. The result of this is that we now have an extremely competitive market here in the UK, which boasts a remarkable number of different artificial turf systems to meet a vast range of end user requirements.
Whilst the rapid evolution of the artificial turf industry is exciting and has increased the appeal of artificial grass, consequently, assessments relating to which systems are most suitable for which requirements have become more complex.
The material with which the end-users have the most interaction is the yarn used to form the artificial grass itself. Here, we generally see four different types of yarn used to offer different aesthetics, not to mention a range of performative features.
The different types of yarn
- Fibrillated yarns - in this instance, a wide tape yarn is perforated to create a strong lattice structure which, during usage, splits into individual blades to produce a multi-fibre appearance at the exposed surface but maintains the lattice structure within the infill.
- Monofilament yarns - are individually created filaments which are twisted or wrapped together during yarn manufacturing to form a multiple filament yarn. The manufacturing process enables different profiles and thicknesses to be offered, which has the potential to increase durability, resilience and improve aesthetic effect.
- Texturised yarns - this is a straight yarn that has been heat set to produce a tight, curly appearance. The benefit of this is its allowance for a non-directional surface which prevents ball roll and bounce deviation for hockey and tennis, whilst it can also be thatched in layers for landscaping.
- Profiled yarns - a profiled yarn is shaped during the extrusion process in order to offer various performance qualities. Two dimensional shaped profiled yarns offer the capability to encapsulate a sand or rubber infill, whilst three dimensional shaped yarns are designed to spring back upright after wear, which ensures its ball/surface and aesthetic characteristics remain intact.
It is important to remember that behind each type of yarn construction is a material that boasts its own list of performance benefits. The polyethylene used to manufacture fibrillated and monofilament yarns brings about a soft and supple, non-abrasive surface with a waxy texture, whilst polypropylene tends to be more abrasive, rougher, drier and more brittle. Again, it is the end-user requirements and budgetary constraints that will determine the most appropriate yarn material for use.
Wider system components
One of the most common oversights, when it comes to the specification and installation of artificial turf, is the failure to look beyond the structure of the yarn, and the tufts it is used to create. Of equal significance is the primary backing fabric that supports the turf structure. The quality of the primary backing fabric will play a big part in the way the quality of surface installation, and the way in which it will perform once in place.
The primary backing fabric is critical because of the manner in which it forms the backbone of the turf construction. This fabric must ensure the turf is dimensionally stable in all extreme environmental conditions and provides the correct platform for strong, durable jointing seams.
It is vital to control the application and placement of the latex compound, and that its quality is engineered to give maximum performance whilst controlling the application weights. It is often regarded that quality of latex is preferable to quantity; highly filled latex compounds add unnecessary weight and cost to the overall system whilst offering no improved long-term performance. The key is to target the latex compound where it is needed the most, which is in and directly around the grass fibre tufts and inside the primary backing structure.
Generally speaking, there are four main types of system than can apply to artificial turf products, which can be categorised as follows:
- Fully synthetic - these systems tend to comprise straight and/or texturised yarns tufted into short, dense pile constructions and installed with a shock pad. These are non-infilled systems, and most systems utilise water within the turf structure for play performance and stabilisation. The most common use of these systems is for elite level hockey
- Sand dressed - this type of system tends to be adopted by education and community sectors due to its resilience, non-directional ball playing characteristics and the ability to play multiple sports codes on the surface. The turf construction tends to be a slightly less dense version of the fully synthetic turf constructions; however, a light dressing of sand is infilled into the pile in order to assist the surfaces stability.
- Sand-filled - this type of system generally utilises less yarn in favour of additional infill, which creates an affordable system which can be used for a multitude of uses. With a medium density and pile height, these systems are filled with sand leaving only a very small amount of grass fibre exposed.
- 3G - the latest generation of artificial turf comprises a long pile and open construction of turf which utilises the advanced monofilament and fibrillated straight yarns. A combination of sand and rubber infills provide stability for the turf structure and the additional improvement of player/surface and ball/surface interaction.
Most artificial turf systems contain sand, which is used to keep the surface stable without adding too much additional cost for the investor. The sand is used to weigh the surface down to ensure it remains stable throughout its lifespan.
With a number of the more modern 3G surfaces however, a rubber infill tends to be added to the system to enhance ball/surface and player/surface interaction - particularly when it comes to football and contact sports pitches. As an example, under FIFA requirements, a product test is required to determine the vertical bounce of the ball which must meet a certain height in order to pass. As a further example, under IRB regulation 22, the system must have and maintain a critical fall height value, which ensures safety for rugby players.
These are two of the performance characteristics which can be affected, not only by the choice of yarn, primary backing, latex compound and application weights, but also the infill and shock pads. In other words, the whole turf system, engineered together deliver the desired performance results
When it comes to comparing the different systems available and assessing their costs, the pile weight is absolutely key. More yarn generally means a thicker, denser surface, which is likely to last longer, and offer better performance. Use of quality primary backings and latex compounds provide the backbone to the turf construction.
The use of shock pads varies depending on the function of the system but, in certain sports, such as rugby, hockey and cross-code surfaces, it can be vital to the play performance and the safety of the surface. This is true, not only for the durability of the system, but also the long-term consistency of the ball/surface and player/surface interactions.
There are many shock pad options available on the market and the addition of a shock pad will increase the project's cost but, as long as the quality of the shock pad selected is considered, the pad will be re-useable if and when the turf playing surface is replaced.
The quality and consistency of the infill material is, again, a vital element to ensure the system performs to its potential during its lifetime. Poor quality infills can pose risks to the surface, players and the environment.
Laying the foundations for premium performance
As with the installation of any outdoor surface, the base construction is a vital component of a successful project.
Base constructions sit underneath the shock pad (if one is being used) and effectively form the system foundations. There are two types of base construction used in artificial turf system construction - dynamic and engineered.
The most popular base construction profiles we see in the UK are engineered bases. These consist of a predetermined unbound, compacted and porous stone layer. This layer is then capped with porous asphalt. It goes without saying that the average rainfall in the UK tends to exceed that of our European counterparts, so it is imperative that a porous base is used, to ensure drainage is as effective as possible.
The other factor which plays an important part in UK construction work is the number of standards and regulations we are required to meet. With this in mind, we need to ensure we engineer stable base constructions in order to maintain a level of surface consistency during and after the installation. In applications such as hockey and tennis, the tolerances of the finished base is vital and the surface must be smooth and consist; use of porous asphalt allows the pitch builder to achieve these vital conditions.
Dynamic base constructions again use a predetermined unbound, compacted and porous stone layer. However, a porous asphalt capping layer is not applied. This arrangement can often prove cheaper than the engineered equivalent but, in most cases, this system proves more challenging to achieve the desired surface tolerances and smoothness required in sports such as tennis and hockey. The use of dynamic base constructions is often only applied to long pile surfaces for football and rugby.
Like any surface used in a sports and leisure environment, the performance of an artificial turf system is a fundamental consideration, and a number of associated considerations need to be made when it comes to selecting the right system for a given purpose. It is vital for the customer to recognise what the surface will be used for and how many playing hours will be required of that facility.
It is vital for the customer to understand the maintenance requirements in order for the surface to realise its potential. From this understanding, manufacturers can design, produce, and install systems which meet and exceed the customer's expectations.
By working closely with a manufacturer however, these considerations needn't be too challenging, and will ultimately lead to the creation of an environment that can maintain a premium level of performance for years to come.