Laboratory Assessment of Temperature Effects on the Strength of Recycled Asphalt Concrete Mixture

Crushed asphalt is made by recycling of asphalt pavements (by crushing or milling the old materials). This material may be used in making new asphalt mixes. Using crushed asphalt in making new asphalt, reduces the consumption of new materials and thus results some savings in capital as well as natural resources. The main objective of heating the crushed asphalt in the process of hot mix recycling is to change the hard state of asphalt to soft and liquid state and thus making the possibility of segregation of the aggregates in the asphalt mix. Not to mention that too much heating may also result corrosion or burning of the bitumen. Meanwhile heating the asphalt less than the required time, may result incomplete mixing of crushed asphalt components with aggregates and new bitumen materials. In this paper the effect of temperature changes and heating periods of crushed asphalt on some parameters like real gravity, Marshall Stability and indirect tensile strength of recycled crushed asphalt have been evaluated. Also the Marshall Stability and indirect tensile strength of recycled asphalt mix have been compared to similar amounts in the ordinary asphalt mixes. The obtained results are as follows:1-Heating time and heating temperature of crushed asphalt influence the real gravity, Marshall Stability and indirect tensile strength of the asphalt mix. These influences are meaningful, by other words; the occurred changes in the mentioned parameters are not accidental, but affected by the developed changes in time and temperature of heating process.2-Taking into account the Marshall Stability diagrams and indirect tensile strength of asphalt mixes on the basis of heating time and temperature parameters of crushed asphalt, it is considered that the average amounts of both parameters, at the heating time of four hours and heating temperature of 160◦ have reached their maximum level. By other words, those parameters that are indicative of hardness and strength of asphalt mix, at the mentioned time and temperature have reached their maximum level.3-Results show that the recycled asphalt mix has had considerable Marshall Stability and tensile strength. For instance the Marshall Stability of the recycled asphalt mix at 4-hour heating time and 175◦ heating temperature has approximately reached 3700 Kg. Also the indirect tensile strength of the asphalt mix at 4-hour heating time and 160◦ temperature has approximately reached 26 Kg/cm2. Comparison of the mentioned amounts with the same amounts in ordinary mix asphalt (without crushed asphalt) it can be resulted that making use of crushed asphalt in asphalt mix increases the strength and hardness of the asphalt mix to a considerable extent. 4- Relatively intensive slump of real gravity, Marshall Stability and indirect tensile strength diagrams at the point of 8-hour heating time and 175◦ temperature shows that at the mentioned point the properties of asphalt mix have considerably changed. The reason for these changes is developing considerable changes in the properties of crushed asphalt, due to the high temperature and long period of heating.