Predicting the degradation of slip resistance in paving materials

Slip resistance is an important feature of paving materials. It is essentially a measure of the coefficient of friction between the pavement and pedestrian footwear and thus describes the safety of the paving material as regards slips and falls. Slip resistance tends to decrease over time as a result of wear, but currently there is no accepted method for predicting this degradation in performance. To address this problem we developed equipment which carries out accelerated wear testing by surface abrasion. We tested seven different paving materials, subjecting them to up to 2000 cycles of abrasion. We found that slip resistance, as measured using the British Pendulum Test, declined in a non-linear way which could be represented by a power law relationship. The rate of decline varied significantly from one material to another; some materials which had initially high slip resistance degraded relatively rapidly. In some cases, reduction in slip resistance correlated to significant decreases in surface roughness. We compared the performance of materials in the accelerated wear test with their actual performance in urban locations, finding some correlations but also some complicating factors. This work is a contribution towards the design and characterisation of sustainable slip-resistant surfaces.