Evaluating the Effect of Mixing Process on Nano-Clay Modified Binders Using the Pull-Off Test Method

Bonding strength of bitumen is one of the most important properties in need of independent evaluation. Conducting a pull-off test to determine the bonding strength of bitumen can be done using the Universal Test Machine (UTM). In this work, the UTM was used to investigate the effect of adding an additive to with a 60/70 penetration grade bitumen; the additive used was nano-clay at a percentage of 2% and 4%. A designed mold was fabricated and used with granite and stainless steel substrates. The investigation covered the influence of variation in the mixing process (mixing duration and power of rotation during mix) on the bonding strength of the samples. X-ray diffraction (XRD) was used to discover the nano-clay exfoliation within the binder structure. Also, empirical tests - penetration and softening point tests - were conducted. The results varied according to variation in percentage of additive, substrates used and the mixing process. The bonding strength and softening point results were able to identify the effect of the additive, and were able to detect changes caused by the adding condition; both were very well correlated, unlike the penetration test result which had a weaker correlation with bonding strength.