Analysis of viscosity and composition properties for crumb rubber modified asphalt

Abstract

The preparation of crumb rubber modified asphalt (RA) shall effectively recycle waste rubber and abate environmental contamination. To ascertain the composition and the factors affecting the viscosity of RA, some samples were prepared in the case of different conditions of mixing temperature and processing time for different rubber dosage and rubber size. Brookfield viscosity tests were conducted on RA samples, and the impact exerted by these factors on viscosity of RA was anatomized. The visco-flow activation energy (Eη) of RA was acquired through adopting Arrhenius equation in line with the viscosity values of asphalt in the case of different temperatures. The changing regularity of Eη was anatomized. The viscosity of rubber asphalt can be split into three parts: the contribution of base asphalt (BE), rubber and asphalt interaction effect (IE) and crumb rubber particle effect (PE), and additionally the viscosity definition is proposed as ηRA=η0(1+IE+PE). To isolate the PE, the sieving test was designed. Rotary viscosity tests were conducted on RA samples and asphalt samples separated from crumb rubber through adopting Brookfield viscosity meter. The impact exerted by these factors on the viscosity composition parameters IE and PE of rubber asphalt was anatomized. In line with the viscosity definition, the viscosity prediction model of rubber asphalt was established. It is indicated from the results and analysis that the viscosity values of RA increase by the exponential growth model continuously with the increase of rubber content. There is a certain equivalence for rubber asphalt viscosity between raising mixing temperature and extending the processing time. But too high temperature or excessive time may result in excessive degradation of rubber molecules, which shall cause the decrease of RA viscosity. With the rising of the dosage of crumb rubber, Eη of RA for origin or aged samples both goes up first and thereupon drops down. And peak Eη exists in the range of rubber content from 10% to 15%. The Eη value of aged RA outstrips that of original sample for the same rubber dosage. For the rubber asphalt samples prepared through adopting the same type and size crumb rubber, the IE values show linear relation with the dosage of crumb rubber, while PE values increase by the exponential growth model continuously with the dosage of crumb rubber. Within a certain temperature range, IE and PE values both show linear relation with the mixing temperature, and show parabola relationship with the processing time. The proposed prediction model can manifest the viscosity composition of rubber asphalt and has an expected fitting precision.