Effect of Stirring Speed in Hot Mixing Process of Modified Asphalt with SBS Copolymer on Polymeric Distribution and its
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Effect of Stirring Speed in Hot Mixing Process of Modified Asphalt with SBS Copolymer on Polymeric Distribution and its Rheological Properties Esteban Alberto González García1, Rafael Herrera Nájera1. 1 Facultad de Química, UNAM, Av. Universidad #3000, Ciudad México, Distrito Federal, 04510, México.
ABSTRACT The current work reports the effect of particle size on the rheological behavior of polymer modified asphalt PMA. The modified asphalt was generated with AC-20 asphalt precursor provided by Pemex Salamanca and Solprene® 416 provided by Dynasol Mexico. Solprene® 416 is a SBS star-type copolymer with 4 poly(b-styrene-b-butadiene) arms and Mw = 2.36X105 g/gmole. Modified asphalt samples were prepared with 3 wt % of SBS via hot mix process. Mixing time and temperature were kept constant at 4h and 180 °C. This study also varied the agitation in the mixing process: 500, 1000 and 1500 rpm. All PMAs shown sphere-shaped polymer particles as observed via fluorescent microscopy using a Carl Zeiss KS-300 system. Base asphalt and PMAs were also characterized through rheological measurements using a TA Instruments AR-G2 rheometer. Shear viscosity (η) and tan δ data shown that the flow resistance of the PMA increases as the size its polymer particles decreases. Since the size of the polymer particles decreases with the increase of the stirring speed, it is concluded that the stirring speed of the process determines the size of the polymer particles and so the mechanical resistance of the PMA.
INTRODUCTION Modified asphalt is a composite material generated by the addition of base asphalt and different composite materials. The mixture is expected to enhance the mechanical and thermal properties of base asphalt [1,2]. Asphalt is a complex mixture of hydrocarbon molecules that can be grouped into maltenes and asphaltenes, only maltenes are soluble in n-heptane. Maltenes are low molecular weight hydrocarbon species (200-5000 g/mole), and they are classified as saturated, unsaturated, and resins. Asphaltenes are higher molecular weight species (1000-100000 g/mol), and they are assembled forming planar structures [3]. The ratio of the maltenes and asphaltenes is a key factor in determining the viscoelastic behavior of the base asphalt. Maltenes are responsible for the viscous behavior, an asphaltenes for the elastic behavior. The importance of the maltenes/asphaltenes ratio is also related to the spatial arrangement of the asphaltenes in the mixture. Resins are the stabilizing agents in base asphalt, so determining the assemblage of micelles of asphaltenes and its distribution inside the maltenes-rich matrix [4, 5]. Maltenes/asphaltenes ratio is also an important parameter during the production of modified asphalt via styrene and butadiene processing. The poly(b-butadiene) absorbs maltenes, developing a polymer-rich phase that can be up to nine-time actual volume of the neat polymer [6-11]. On the contrary, the polystyrene blocks are incompatible with the asphalt and this allows the formation of a two-phase system: a polymer-rich p
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