Abstract
The use of tire crumb rubber in road engineering as a modifier of bituminous mixes constitutes one of the revalorization techniques for this waste. The main objective of this research consists of analysing the possible fatigue cracking improvements in the performance of bituminous mixtures containing crumb rubber in comparison to bituminous mixtures manufactured with conventional bitumen and bitumen modified with SBS polymers. For this purpose, four different types of mixes with the same mineral skeleton but different bitumens were studied. The test used to evaluate their behaviour was the UGR-FACT with an additional system for taking pictures, which allows controlling the propagation of the cracks at every moment. The results show that the addition of crumb rubber retards the appearance of cracks; however, once it begins, the damage propagation is faster. Therefore, the fatigue cracking life of mixes with crumb rubber seems considerably longer than the fatigue cracking life of those with conventional bitumens. Moreover, in the mixes with crumb rubber added by the dry process, cracks are thinner and less ramified than in the other ones.
Highlights
In the last years, waste valorisation has become an important issue due to the policies of environmental sustainability
It can be observed that the fatigue life of all the modified bitumens is very similar, independently of the modification applied to the bitumen (SBS polymer, high-viscosity rubber or 1.5% of crumb rubber added by the dry process)
These results demonstrate that the use of crumb rubber in the production of bituminous mixtures can enlarge their fatigue life and improve their behaviour in the long term, having a similar behaviour to highperformance mixtures made with SBS polymers
Summary
Waste valorisation has become an important issue due to the policies of environmental sustainability. Civil engineering has an important effect on the consumption of natural resources; the application of new techniques is crucial to contribute with these policies. In this sense, the reuse of scrap tires as a modifier of the mechanical properties of materials has become increasingly useful in recent years. The use of crumb rubber from scrap tires in road engineering as a modifier of bituminous mixes is becoming a common practice. When crumb rubber interacts with the bitumen, it modifies the rheological properties of the resulting mix (lower susceptibility to temperature and better elastic performance) and increases its viscosity (Ruiz 2010). The processes used to incorporate crumb rubber in asphalt paving mixes are the Wet process (in which the crumb rubber is directly added to the bitumen, prior to mixing it with the aggregates; it is added to the mix as modified binder) and the Dry process (in which the crumb rubber is added to the aggregate as another ingredient in the mix, prior to the addition of the bitumen, and the bitumen is modified when it comes in contact with the rubber)
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