Performance analysis of non-conventional Stone Mastic asphalt (SMA) elaborated with crumb rubber bitumen or by mean of glass macrofibers addition

Abstract

Stone Mastic Asphalt (SMA) are high performance mixes that are widely used throughout the world. Originally designed in Germany, they are identified as mixtures with high percentages of coarse aggregates, lower quantities of fine materials, high filler content and higher bitumen contents than a conventional asphalt. To achieve these higher bitumen percentages, it is necessary to incorporate fibres, generally cellulose fibres, to prevent binder draindown during mixing, transport and compaction. There are currently studies, at research level, to eliminate or reduce the dosage of fibres using high-viscosity bitumen's. One way to achieve this kind of bitumen is through high rates of Crumb rubber (CR) from end-of-life tyres. This allows the use of high bitumen percentages without draindown and dispense with the use of fibres. Another alternative is to replace cellulose fibres with synthetic or glass macrofibre's, these latter being considered structural. The macrofibre acts improving rutting and cracking resistance, providing performance improvements, especially in extreme weather conditions. This work focuses on the study of a 19 mm maximum size SMA analysing its performance to rutting, cracking, dynamic modulus, and moisture damage. Alternatives to the traditional SMA with cellulose fibres were studied here; one through the addition of glass macrofibres maintaining the commercial polymer modified asphalt and other alternative was a fibreless SMA elaborated with a high-viscosity modified asphalt with Crumb rubber (CR) from end-of-life tyres. It was found it is possible to produce SMA with high viscosity crumb rubber bitumen binder without fibres (SMA CR) and met all the volumetric characteristics specified for SMAs, specifically the draindown. The SMA CR and Glass addition in SMA showed improvements in dynamic modulus behaviour. The addition of glass macrofibres provide improvements with higher cracking resistance at low temperatures.