Adhesive Properties of Tall Oil Pitch Modified Bitumen

ABSTRACT Various researchers have shown that tall oil pitch (TOP) can improve the adhesion between bitumen and aggregates in asphalt concrete mixes. However, TOP contains carboxylic acids, which have been implicated in increasing the susceptibility of asphalt mixes to moisture damage. The compatibility of TOP with alkyl amine adhesion agents that are commonly used in chip sealing has also been questioned. The objective of the research was to explore the adhesive properties of TOP modified bitumen and relate these to a fundamental property such as interfacial tension (IFT). The findings of previous researchers were confirmed in that TOP reduced the susceptibility of asphalt mixes to moisture damage. However, TOP modified bitumen also reduced the effectiveness of alkyl amine adhesion agents as determined using the Vialit test. The observed improvement in adhesion in asphalt mixes can be explained by examining the interfacial tension of the TOP modified bitumen. TOP caused a small increase in the IFT between bitumen and air and a minor reduction in the IFT between bitumen and water. But more significantly, TOP reduced the contact angle that bitumen made with microscope slides in the presence of water, which increased the energy required for water to strip the bitumen from the slide.