Effect of NMH and DA Additives and Bitumen Aging on Cohesion and Adhesion Failures Using Surface Free Energy and Pull-Off Methods

Abstract

Moisture damage is closely related to bitumen cohesion and bitumen-aggregate adhesion. Aging is among the factors affecting the occurrence of adhesion and cohesion failure by changing the adhesion and cohesion characteristics of bitumen and affecting its moisture sensitivity. Various methods exist for assessing moisture damage, one of the most efficient of which is combining mechanical tests with thermodynamic methods. This study investigated the effect of nano-magnesium hydroxide (NMH) and dodecylamine (DA) additives and bitumen aging on cohesion and adhesion failures, which are important moisture damage mechanisms, by adopting the pull-off and surface free energy (SFE) methods. In the basic state (without aging), DA and NMH resulted in a slight increase in the free energy of adhesion. Similarly, the free energy of cohesion also experienced a slight rise with the use of these materials. During short-term aging (STA), the free energy of adhesion showed a moderate increase with DA and NMH. Additionally, the cohesion free energy demonstrated a considerable rise in this aging condition. In long-term aging (LTA), DA and NMH led to a slight increase in the free energy of adhesion. Furthermore, the cohesion free energy showed a moderate increase with the use of these materials in this aging condition. Both NMH and DA additives contributed to the enhancement of pull-off cohesion and adhesion strength. Therefore, the use of these additives in asphalt mixtures improves moisture resistance and diminishes the stripping phenomenon. By increasing the total SFE of bitumen, aging improved the bitumen’s resistance against cohesion failure. It raised the cohesion free energy, decreased the adhesion free energy, raised the pull-off cohesion strength, and reduced the pull-off adhesion strength.