Road Aggregate Choice Based on Silicate Quality and Bitumen Adhesion

Abstract

An adsorption mechanism of bitumen onto the silicate surface is presented. Amines are capable of acting as adhesion agents on siliceous surfaces and the carboxylic acids on carbonate stones. An acid adsorbate, tall‐oil pitch is shown to be a very durable adsorbate also on the silicate surface. The pitch is mixed with bitumen of 10–20% by weight. Surface energy and the polar and dispersive components of 34 Finnish silicates are measured. The oxides of Si, Al, Na, K, Ca, Mg, and Fe in silicates are tested with an X‐ray fluorescence spectrophotometer. The adhesion of the silicates to bitumen is estimated. The correlations between the polarity of the silicates and the adhesion are calculated. The increase in the silica dioxide content causes an increase in the polarity of the stone surface and the adhesion is decreased. When the surface is enriched in Mg, the surface is less polar and the adhesion is improved. Silicates containing a lot of Na, K, Si, and Al were poorer in their adhesion onto bitumen.