Impact of Chemical Composition on Foaming Characteristics of Asphalt Binder

Abstract

During the foamed bitumen production process, cold water is injected into hot bitumen within a closed chamber. Due to mixing of these fluids and transfer of heat energy, steam is generated. The dispersion of steam within bitumen results in production of foamed bitumen. Owing to close interaction between the water and bitumen, the physical and chemical properties of bitumen affect foaming characteristics [i.e., expansion ratio (ER) and half life (HL)] significantly. The present work evaluates the effect of physical and chemical constituents of bitumen on foamed bitumen characteristics. For this purpose, six distinct asphalt binders were characterized for their physical properties and chemical composition. The foaming characteristics of these asphalt binders were measured at various bitumen temperatures and foaming water content. Other parameters being held constant, an increase in the viscosity grade of bitumen resulted in decreased ER and increased HL. At a particular temperature, increasing ER and decreasing HL were observed with an increase in foaming water content. A strong negative correlation was found between ER and all saturate, aromatic, resin, and asphaltene (SARA) fractions (except aromatics), sulfoxide, and carbonyl indexes. Further, a strong positive correlation was found between HL and the parameters mentioned previously. The observations were made when the Gaestel index was used as an indicator of chemical composition. Statistical analysis indicated that generalized exponential function could describe the variation of foaming characteristics as a function of SARA fractions, sulfoxide index, and carbonyl index. Further, a logarithmic relationship can describe the variation of ER with the aliphatic index. The same was confirmed through computed coefficient of determination values. The regression equations developed in this work can be used for predicting foaming characteristics before actual evaluation of foaming characteristics is initiated.