Issue 58

K. Nabil et alii, Frattura ed Integrità Strutturale, 58 (2021) 65-76; DOI: 10.3221/IGF-ESIS.58.05

Viscosity at 135 °C Dynamic viscosity (cP) Torsion ratio (%)

Pure bitumen BMP 5.0 BMP 7.5

1500 0.30 0.42

4500 0.90 1.26

9500 1.90 2.66

Shear Stress (Pa)

Table 4: Rheological properties of pure and BMP.

According to Tab. 4, the dynamic viscosity of the bitumen is multiplied by 3 and 6 for the bitumen modified by 5.0 and 7.5% of the polymer, respectively. This increase is accompanied by an increase in the rate of torsion and the shear stress, which means that the modified bitumens require more stress to their mixing. Dynamic mechanical analysis Dynamic mechanical analysis (DMA) is a measurement where sinusoidal stress or strain is given as the input, and the strain or stress, respectively, is measured as the output (Fig. 5). Because of damping, the strain in a viscoelastic material is observed with a phase delay φ from the stress. The stress and strain can be thus expressed as : The results of the DMA test are presented in Fig.s 9 and 10. The test measured the stiffness modulus ||E*||, the shear modulus ||G*|| was obtained by the following formula. ||E*|| = 3 ||G*|| (2) 10x20mm cylindrical specimens were tested in traction-compression mode under 30ºC at the frequencies: 1, 1.58, 2.51, 3.98, 6.31, and 10Hz. In Fig. 9, the values of the stiffness modulus E of the modified bitumen PMB7.5 are shown compared to the control bitumen, moreover, Fig. 10 represents the evolution of the shear modulus G.

20000

Neat bit.

BMP 7.5

16000

12000

8000

E (kPa)

4000

0

1

1,58

2,51

3,98

6,31

10

Frequency (Hz)

Figure 9: Effect of SBS polymer on stiffness modulus for different frequencies.

Figure 10: Effect of SBS polymer on shear modulus for different frequencies.

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