Anti-stripping agents

The use of anti-stripping agents applies both to surface dressings (Cawsey and Gourlet 1989 Woodside and Macoal 1989), where excellent and permanent adhesion is required, and to hot or cold bituminous mixtures (Anderson et al. 1982 Christensen and Anderson 1985). In both cases, the bitumen-aggregate adhesion is improved and the mixture resistance to the disastrous impact of water is increased, in case hydrophilic aggregates are used. 

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Generally, bituminous binders adhere well to limestones and are resistant to stripping [8.1]. Section 26.5 describes the use of hydrated lime as an anti-stripping agent. 

Bitumen, bituminous binders and anti-stripping agents... 

Apart from the above three basic ingredients, a bitumen emulsion may contain, in minute amounts, one or more of the following stabilisers, break control agents, acidity regulators, coating improvers or anti-stripping agents. 

Anti-stripping agents are chemical substances that have a similar composition to emulsifiers and are divided into (a) anionic type, such as organic acids (creosote) and fatty acids (oleic acid, stearic acid, pine pitch, etc.), and (b) cationic type, such as amines (simple amines, diamines, tertiary amines, polyamines and imidazolines) and salts of quaternary ammonium. 

Usage of anti-stripping agents 3.7.2./ Anti-stripping agents in surface dressings... 

As it was mentioned, the anti-stripping agents are used in surface dressings. They may be incorporated using one of the following ways ... 

Anti-stripping agents are also used in the production of hot or warm asphalts (bituminous mixtures) in order to improve the adhesion between bitumen and hydrophilic aggregates in the presence of water. The addition of anti-stripping agent not only preserves the cohesion, stability and stiffness of the asphalts when wet but also prevents ravelling. 

Asphalts treated with anti-stripping agent, apart from increasing their retained stability, showed better behaviour in bitumen ageing (Anderson et al. 1982 Christensen and Anderson 1985). Furthermore, some anti-stripping agents decrease the susceptibility of the bitumen to temperature variations (Anderson et al. 1982). 

The determination of susceptibility to stripping in the presence of water or affinity between aggregate and bitumen and thus the necessity of anti-stripping agent usage is carried out by various laboratory tests. In fact, by carrying out these tests, the hydrophilia of the aggregate... 

The ratio of indirect tensile strength should be higher than the value determined by the contractual requirements. If the ratio is lower than the required value, the use of a suitable anti-stripping agent is required and the test is repeated. 

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