Determination of Acid Number of Asphalt by Improved Color-Indicator Titration Method

Abstract

Acidic substances contained in asphalt have varying effects upon emulsifiability of asphalt and its adhesion with aggregates, and therefore, determination of acidity of asphalt is of importance. However, there has not been established a method of precisely determining the acidity of asphalt. This paper reports on an improved color-indicator titration method, by which the acid number of asphalt is determined.
By treating benzene solution of asphalt with alcohol, acidic constituents were selectively extracted into alcohol solution, while asphaltic matters precipitated. A color-indicator titration method then was applied to the resultant faint-colored solution. The change of color at the end point was clearly observed, and the results were obtained with good reproducibility and checked well with the results by the I.P. 177/64 method. Alcohols having not more than three carbon atoms have been found suitable for extraction.