Fig. 1. Thermal dependency of dynamic flexing strength
for sand based asphalt concrete:
1 – • – thin bitumen; 2 – О – original bitumen;
3 –´ – polymerized + 2% polymer; 4 – ¦ – polymerized + 5% polymer.
Fig. 2. Thermal dependencies of equilibrium modulus
type G asphalt concrete:
1 – thin bitumen; 2 – polymerized with 2.5% polymer.
Fig. 3. Thermal dependencies of modulus of deformation
of polymer asphalt concrete and asphalt concrete:
1 and 2 – thin
bitumen; 3 and 4 – Polymer modified bitumen 2,5.
Figures 2 and 3 show that the obtained data confirms higher deformability of asphalt concrete with polymer modified bitumen at sub-zero temperatures (as compared with using thick or thin bitumen), as well as higher elasticity at positive temperatures, lower thermal sensitivity and higher dynamic stability.
Aging of asphalt concrete with polymer modified bitumen was evaluated by acoustic parameters after heating.
Aging indication is considered the ratio of sonic wave attenuation in test beams (α) before and after heating to 120°C for 40 hours.
It is safe to assume that polymer macromolecules adsorb part of the light hydrocarbons from the bitumen dispersion media, therefore slowing the transition of oil to tar and formation of asphaltenes.
Besides, smaller amount of open pores should restrict oxygen access to the binding material. In combination, these two factors ensure higher aging stability of asphalt concrete with polymer modified bitumen (table 2).
Since in the recent years the optimal plasticizing agent for polymer modified bitumen is considered to be industrial oil, certain concerns arose regarding shear strength of polymer asphalt concrete.
This issue caused heated debate during reconstruction of Moscow Beltway. Due to this, considering that the top layer was designed to be type A 90/130 polymer modified asphalt concrete, the asphalt binding material was tested with equal content of mineral powder and powder/binder ratio of 2:1 (tables 3 and 4).