CAN 'RUBBLE ASPHALT' RID US OF OUR RUBBLE MOUNTAINS?

In order to assess the possibility of using demolition rubble as aggregate for bituminous mixtures in road construction test sections were laid in which rubble asphalt was used for the roadbase instead of gravel asphaltic concrete. The Marshall stability of rubble asphalt with 6 to 9% of 45/60 grade bitumen was approx 10 kn and the Marshall flow approx 2 mm. Mixtures with 5 or 6% bitumen had a poor workability and were hard to compact. The bitumen content had therefore to be raised to 8%. On bored cores creep tests were carried out and on prismatic specimens taken from compacted rubble asphalt fatigue tests were executed. The modulus of stiffness was determined at temperatures between -10 and +30 deg C and at frequencies between 5 and 100 hz. For the fatigue tests the 'controlled strain' method was used. The strain varied between 0.00008 and 0.0003; the test temperature was +20 deg C. It appeared that the resistance to plastic flow of rubble asphalt with 8% bitumen is higher and the resistance to fatigue is lower than the respective properties of the commonly used gravel asphaltic concrete. It is recommended that the layer thickness of roadbases should be increased by a factor of 1.5 when rubble asphalt is used instead of gravel asphaltic concrete. /TRRL/