ABSTRACT:The effect of ethylene, ethylene acrylate and glycidyl methacrylate (EA) terpolymer, and ethylene butyl acrylate (EBA) copolymer on asphalt modification was investigated at 4, 6 and 8% polymer concentrations. Both melt state rheology and asphalt concrete mix (ACM) were investigated. In the melt state analysis, dynamic shear rheology, storage stability, artificial ageing, and performance grading (PG) were studied. The PG grading of polymer modified asphalt (PMA) is correlated to the elastic properties of the polymers. Both resins improved the rheological properties, reduced the temperature susceptibility, showed better storage stability, and increase the upper grading (performance) temperature of the base asphalt. The two polymers showed similar ageing characteristics with little influence on flow activation energy. In asphalt concrete mix analysis, Marshall stability, stripping (durability), resilient modulus, and permanent deformation tests were performed. Polymer-modified asphalt concrete mix (PMACM) has increased percent retained stability and the resilient modulus when compared with ACM. The elastic modulus of PMA and the resilient modulus of their ACM followed the same trend. Weak influence on water sensitivity was observed, but excellent rutting resistance was obtained for PMACM over ACM. EA (much cheaper than EBA) produced satisfactory properties of PMA and superior ACM properties when blended with the high asphaltenes Arabian asphalt.
The dynamic behaviors of the process variables of a twin screw extruder (TSE) have inherent nonlinearity and time delay. Thus, it is important to develop a process model and furthermore to design controllers based on that model for stable operation. A new approach is explained in this work to develop dynamic gray box models to predict the responses of the process output variables due to change in the screw speed (N) for a plasticating TSE. This approach comprises the selection of controlled variables and the development of gray box models relating the selected controlled variables and N. The selection of variables was based on both the steady-state correlation analysis with final product properties and the dynamic considerations. High-density polyethylenes with different melt indices were extruded in a co-rotating TSE in this work. A predesigned random binary sequence type excitation in N was imposed for the dynamic study. Gray box models were developed between two output variables, melt temperature (T melt ) at die and melt pressure (P melt ) at die, with N, by incorporating both first principles knowledge of the process and the measured process data using the classical system identification technique. A second-order ARMAX (autoregressive moving average with exogenous input) model was found to be sufficient to capture the dynamic behaviors of T melt when N was changed. However, the dynamic behavior of P melt was modeled by a third-order ARMAX structure. Both models are in agreement with the a priori process information of the TSE.
Two low‐density polyethylene (LDPE) resins and two ethyl vinyl acetate (EVA) polymers were used to modify asphalt binder, and then mixed with asphalt concrete according to Marshall Method of mix design (ASTM D 1559). Effect of weight average molecular weight (Mw) of LDPE and vinyl acetate (VA) content of EVA was studied by performing Marshall Stability, moisture susceptibility (AASHTO T 283‐89), resilient modulus (MR) and permanent deformation (rutting) tests. EVA with low VA content showed lower stability loss in Marshall Stability test and improved resistance in moisture susceptibility test in comparison to hot mix asphalt concrete mix (HMA) and other polymer modified asphalt concrete mixes (PMAMs). Higher MR and better rutting resistance were observed for PMAMs than that of HMA. This elastic behaviour of modified asphalt correlates very well with the MR and rutting resistance properties of PMAM.
A corotating plasticating twin screw extruder (TSE) was excited by changing feed rate according to predesigned random binary sequence (RBS) and stair type excitation. A high density polyethylene was used as processing material in this study. Empirical models were developed relating two output variables, melt pressure at die (Pm), and melt temperature at die (Tm), with feed rate (F). Classical linear system identification technique was used to develop models. Models were developed using a data set obtained from RBS excitation. Stair type excitation data were used to validate the developed models. The structure of the obtained models was autoregressive moving average with exogenous input (ARMAX). Models with ARMAX structure and order of 2 were found to be sufficient to capture the dynamic behaviors of Pm and Tm when F was changed. A delay‐gain model was proposed for Pm and was found to capture the response quite satisfactorily. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers
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