Composition Optimisation of Selected Waste Polymer-Modified Bitumen

Abstract

Waste plastomer disposal is currently a major challenge facing modern economies. This article reports on a study and analysis regarding the implementation of plastomers into bitumen, with a special focus on the influence of mixing process factors. Two plastomers were selected for analysis, PP and PET, and two bitumen types, 20/30 and 70/100, were modified. Determination of the basic characteristics, such as penetration, softening temperature, cohesion energy, and Fraass temperature, was complemented with advanced multiple-stress creep recovery (MSCR) rheological testing. The entire experimental process followed the Plackett−Burman design. Rheological effects of modified bitumen were evaluated using the generalized Maxwell model. Microstructural analysis with epi-fluorescence microscopy showed the ability of plastomer-modified bitumen to obtain a fine-grained structure with a particle size of <10 μm. In addition, creep susceptibility (Jnr) was found to be statistically significantly dependent on the polymer type and particle size, rotational speed, and bitumen type. In turn, the particle dispersion structure in the bitumen matrix significantly depended on the rotational speed, plastomer particle size, and mixing temperature. Ultimately, the process of bitumen 70/100 modification was optimized. It was demonstrated, following the experimental design, that by using fine-grained PP for a temperature of 160 °C, rotational speed of about 6300 rpm and time of 105 min, it is possible to obtain modified bitumen with rheological properties very similar to those of modified bitumen PmB 45/80-55.

Keywords: Plackett–Burman experimental design; composition optimisation; modified bitumen; rheology; waste plastomer.

Figure 1

Samples of used plastomers: (a) PET (b) PP.

Figure 2

System for bitumen modification with plastomer.

Figure 3

Execution principle of MSCR test; (a) one cycle scheme; (b) scheme of full test for 10 cycles; (c) Discovery Hybrid Rheometer HR-1 setup.

Figure 4

Designated penetration index values.

Figure 5

Microstructures of polymer-modified bitumen: (a) 2 s (b) 4 s (c) 6 s (d) 8 s (e) PMB 45/80-55 (f) PMB 45/80-65.

Figure 6

Quantitative analysis of the dispersion of plastomer particles in bitumen: (a) particle surface; (b) roundness coefficient; (c) largest particle size (Major diagonal).

Figure 7

Quantitative analysis of the dispersion of plastomer particles in bitumen: (a) particle surface area; (b) roundness coefficient; (c) major diagonal.

Figure 8

Plot of creep compliance Jnr for shear stress: (a) 100 Pa (Jnr₁₀₀); (b) 3200 Pa (Jnr₃₂₀₀).

Figure 9

Plot of elastic recovery R for shear stress: (a) 100 Pa (R₁₀₀); (b) 3200 Pa (R₃₂₀₀).

Figure 9

Plot of elastic recovery R for shear stress: (a) 100 Pa (R₁₀₀); (b) 3200 Pa (R₃₂₀₀).

Figure 10

Creep compliance vs recovery.

Figure 11

Pareto plot of standardised effects: (a) J_nr3200, (b) R₃₂₀₀.

Figure 12

Comparison of the match between the generalised Maxwell model and the experimental results of cyclic strain at 100 Pa and 3200 Pa acc. to the MSCR [55]: (a) PmB 45/80-55; (b) case 8 s.

Figure 13

Results of the search for the optimal bitumen and plastomer mixing solution.