Analysis of use of natural fibers and asphalt rubber binder in discontinuous asphalt mixtures

The growth of traffic requires more pavements with high durability and security to users. One of the solutions adopted in developed countries is a mixture with discontinuous graduation of type SMA (stone matrix asphalt), which requires a higher content of protecting the asphalt pavement of damage by forming a thicker film around the aggregate, which holds up oxidation, dampness penetration and cracking and separation of aggregates. Due to the higher content of asphalt it is necessary to add fiber to avoid drain down the binder. Bahia was the first state in northeastern Brazil to build an urban stretch with SMA, but without fibers. Despite not meeting the technical recommendations, the pavement did not show any defect in terms of the absence of fiber. The mixture was produced with asphalt–rubber binder which, because of its viscosity, allowed the use of a higher content of asphalt, even without fiber. The objective of this paper is analysis the use of natural fibers in mixture of type SMA. The fiber standard (for example, DER-SP) and usually recommended for using in SMA are imported and expensive, resulting in a higher final cost. To reduce the cost and meet standards we intend to use residues available in the region (coconut and sisal), since Bahia is one of the largest producers of coconut and sisal in Brazil and, consequently, of coconut shells and sisal fibers. In this work, there was produced asphalt mixtures with four fibers: coconut, sisal, cellulose and polyester. The results of mechanical tests (tensile strength and modulus of resilience) demonstrate that blends with natural fibers showed high resistance, while preventing the asphalt to drain down.

► SMA (stone matrix asphalt) mixtures requires a higher binder content to protect the asphalt pavement of damage.
► We analyze the use of sisal fibers and coconut in SMA.
► All the asphalt mixtures showed high tensile strength, accompanied by a high value of modulus of resilience.
► These show also that the type of fiber has little influence on mechanical parameters.
► The results of drain down test showed that the asphalt mixtures with natural fibers present excellent performance.