Adhesion between bitumen and aggregate: implementation of spectroscopic ellipsometry characterisation and estimation of
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ORIGINAL ARTICLE
Adhesion between bitumen and aggregate: implementation of spectroscopic ellipsometry characterisation and estimation of Hamaker’s constant ˚ sa Laurell Lyne • Olga Krivosheeva A Bjo¨rn Birgisson
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Received: 13 December 2011 / Accepted: 21 December 2012 Ó RILEM 2013
Abstract Refractive indices of seven bitumen samples and three aggregates (typical components in flexible asphalt pavement) were determined by ellipsometry in order to predict dispersive bitumen–aggregate adhesion and dispersive bitumen–bitumen cohesion using Hamaker’s constant. Hamaker’s constant according to Lifshitz was introduced to the asphalt field by two of the authors to describe and estimate van der Waal’s interaction and bitumen–aggregate adhesion. Lifshitz used the refractive index to estimate the dispersive nonpolar van der Waal’s interaction component of adhesion, the predominant component in adhesion between minerals and bituminous binder. The impact of an intervening thin medium such as air or water on the adhesion can be estimated using Hamaker’s coefficient, which in turn can be related to stripping potential. The bitumen binders studied were delivered as a paving grade 70/100 according to EN 12591:2009 and came
˚ . L. Lyne (&) B. Birgisson A Highway and Railway Engineering, Architecture and the Built Environment, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden e-mail: [email protected] B. Birgisson e-mail: [email protected] O. Krivosheeva Surface and Corrosion Science, Chemical Science and Engineering, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden e-mail: [email protected]
from different bitumen suppliers. The three aggregates studied were two types of granite and one diabase. It is concluded from the measurement of refractive indices and calculations of the dispersive component of Hamaker’s constant that there was a larger spread in refractive index among the three aggregate samples studied than among the seven bitumen samples. Keywords Bitumen Mineral Aggregate Hamaker Adhesion Moisture damage Refractive index
1 Introduction Many kilometers of highways worldwide have been replaced too early due to water related damage. Deterioration and damage of asphalt pavements typically occur when water penetrates into pores, cavities and hollows, and stays there for some time. Deterioration and damage originates during different types of climate conditions and seasons, and during very low and high traffic loading. In order for asphalt pavement to be durable, it is crucial that the asphalt pavement resists moisture damage. Moisture damage in asphalt pavements can manifest itself as a loss of cohesion within the bitumen itself or the loss of adhesion between the bitumen and the aggregates resulting in stripping. This latter phenomenon is the displacement of bitumen films from aggregate surfaces when the aggregate has a
Materials and Structures
greater affinity for water than for bitumen. Loss of cohesion and loss of adhesion typically coexist. The main components of asphalt pavements are aggreg
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