Comparison of degradation effects for three types of crumb rubber used on a sport surface

Crumb rubber (CR) that had been used in an outdoor football stadium in the U.S.A. for over 10 years was sampled, analysed and compared to samples taken from an on-site, covered excess CR stockpile and from fresh CR that could be used to replace the used CR. These tests were accomplished to determine if the original CR properties had changed significantly, from new/un-used CR, which could have safety and performance implications if continued use of this CR was planned. A series of analytical and mechanical tests were performed to determine degradation effects over time that included Fourier-transform infrared spectroscopy (FTIR), solvent swell tests, differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), X-ray emission spectroscopy (XES), vertical impact, hardness and bulk density. Results inferred compositional differences and mechanical property changes between all three CR samples, with indications that the older CR was demonstrating concurrent increased crosslinking and molecular scissioning, with subsequent loss in resilience. The FTIR results indicated various polymer types present that originated from recycled automobile tyres as well as evidence of oxidation in the used CR. The DSC exhibited lower thermal enthalpy and higher glass transition temperatures confirming compositional changes in older samples. Both vertical impact and hardness tests showed a significant increase in hardness and lower resilience in the used CR. A significant decrease in average size in the used CR was revealed through sieving and microscopy, which indicated mechanical wear. Bulk density measurements of un-sieved used and stockpile CR showed a substantial increase in bulk density for the used samples. The fresh, new potential replacement CR appears to originate from a different supplier than the CR originally used on the sports surface (and accompanying stockpile CR) and possessed much higher resilience than the used CR.