Innovative manufacturing process for added-value car tyre re-use into safer surfaces

Final Report Summary - IMPACT-USS (Innovative manufacturing process for added-value car tyre re-use into safer surfaces)

The overall industrial objective of the project IMPACT-USS was to develop a prototype manufacturing system for producing a pre-mixed, one part safety surfacing material in a format that can be sold to and used by general contractors and the DIY market.

The technological objectives of the work were to develop a protective surface that:
- achieves OSHA friction value greater than 0.6 giving it a 'very safe' status for pedestrian surfaces;
- achieves a product cost of EUR 20 per square metre for a thickness of 25 mm which is less than half the cost of incumbent products;
- maintains OSHA friction performance between -10 and +40 degrees Celsius;
- achieves impact performance corresponding to critical fall height and maintains this between -10 and +40 degrees Celsius;
- impact surface conforms to EN1177 standard;
- contains less than 15 % PU binder to maximise the use tyre recyclate which is the lowest cost most abundant component;
- can be applied without the need for pre mixing and cures within 24 hours of application;
- withstands weathering for at least ten years;
- has a shelf life of at least six months.

The material in old tyres has for some time been used to produce impact absorbing surfaces in sports and playground applications, but the traditional wet pour systems require accurate mixing of hazardous chemicals on site and can this lead to variability of the final surface. This, and the fact that the chemicals typically cost 10 times as much as the recycled material, has meant that the work is only carried out by a minority of specialist contractors, effectively excluding the larger community of smaller building contractors.

The project was structured into four Work packages, as follows:

Work Package 1 - Enabling knowledge of polyurethane chemistry, rubber crumb geometry and polyurethane / rubber crumb interactions
The first stage in the development of the IMPACT-USS technology was to review the field of polyurethane chemistry and characterise commercially available isocyanates, polyols and polyurethane prepolymers which would give the required properties to the premix and the final cured system. Prepolymers have reduced diisocyanate vapour pressure, thus lowering inhalation hazards, and have higher viscosities compared to diisocyanate monomers thus allowing better mixing efficiency and minimising settling. Methylene diphenyl diisocyanate (MDI) based prepolymers have the advantage of much improved freeze protection and reduced toxicity compared to Toluene diisocyanate (TDI) systems. The second stage was to investigate whether any particular tyre crumb particle size, size distribution, or bulk density provided optimum impact resistance properties.

Work Package 2 - Chemistry development of stable pre-mix
Throughout the project the consortium continued to explore alternative chemistries which would provide increased stability. The use of water-borne Polyurethane dispersions (PUDs) were thought to provide an interesting alternative to the isocyanate based prepolymer traditionally used in the fabrication of rubber crumb surfaces. These water based dispersions have no isocyanate content and are generally very low hazard. Furthermore, these polymers cure by evaporation as opposed to moisture cure meaning that special packaging conditions were not needed and pre-drying of the rubber crumb was also not required. Excellent tensile and impact absorption performance were achieved with the PUDs, but the longer curing and drying of such binders compared to prepolymers made them impractical.

Work Package 3 - Development of binder and crumb manufacturing process
The next stage in the development of the IMPACT-USS technology was to design and build a prototype manufacturing system capable of producing a minimum of 100 kg of premix. The individual stages of the prototype system were considered and the technologies available were reviewed and selected by the consortium.

Work Package 4 - Technology validation
The consortium demonstrated the ease of sub-surface preparation and application of the IMPACT-USS product through field trials. Overnight curing occurred for even a 100 mm thick section.

Test beds were analysed at a FIFA accredited laboratory. Tested in accordance with BS EN 1177 'Impact Absorbing Playground Surfacing - Safety Requirements and Test Methods:1998' a 50 mm thick product gave a critical fall height of 1.25 m, comparable to existing two-layer wet-pour systems. Slip resistance was measured in accordance with BS 7188:1998 'Impact absorbing playground surfacing - Performance requirements and test methods'. This is more appropriate to safety surfaces than the Occupational Aafety and Health Administration (OSHA) static coefficient of friction recommendations.

To assess whether any deterioration of the impact absorption properties occurred with time, the product was subjected to UV ageing for 1000 hours. Little change in the performance was observed. A successful field trial carried out at Pera Innovation Limited was monitored for wear resistance. No deterioration of the surface laid in a pedestrian walkway was observed over a five month period. Application specifications have been included within a technical data sheet and a material safety data sheet has been produced for the purpose of the COSHH regulations. Finally, the consortium has produced a cost analysis and are currently completing a business case. Based on the present analysis, a product cost of EUR 20 per square metre for a thickness of 25 mm is achievable.

In conclusion, the project has met the objectives to develop a prototype manufacturing system for producing a pre-mixed, one part safety surfacing material in a format that can be sold to and used by general contractors and the DIY market.

Final Report Summary - IMPACT-USS (Innovative manufacturing process for added-value car tyre re-use into safer surfaces)

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