Laboratory Evaluation of Constructibility Issues with Surface Treatment Binder Page: 33
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Chapter 3. Laboratory Evaluation of Binder Curing
3.1 Introduction and Background
Asphalt products for road construction include asphalt cements, cutback asphalts, and
emulsified asphalts. The basic purpose of producing emulsified or cutback asphalt is to
reduce the temperature at which it can be applied. From an environmental perspective,
reduced temperatures and the omission of volatile fractions other than water are
beneficial.
An asphalt emulsion is composed of three ingredients- asphalt cement, water, and an
emulsifying agent. Asphalt emulsions that include an anionic surfactant base are
categorized as anionic emulsions, while those with a cationic surfactant base are
classified as cationic emulsions. Anionic emulsifiers are commonly fatty acid derivatives
that are saponified with sodium or potassium hydroxide. Similarly, cationic emulsifiers
are derived through salification of fatty amines. Special emulsion grades like "High
Float" emulsions use higher quantities of emulsifiers, which gives a gel character to the
residual binder after the emulsion breaks down.
The use of polymers to produce modified asphalt binders has created a whole new family
of asphalt emulsions types. Letters P (Polymer-modified) or L (Latex-modified) are
suffixed to the name of base emulsion to designate emulsions that utilize polymer
modified binders. Some agencies have an additional cationic sand-mixing grade (CMS-
2S) that contains more solvent than usual (Asphalt Institute, 2008). The suitability of an
emulsion for a particular project is dependent on factors such as climate, type of job and
type of aggregates, among many others.
Emulsion breaking signifies the phenomena in which a great majority of the droplets of
the emulsion undergo an irreversible process that results in the formation of a continuous
macroscopic bituminous phase (SFERB, 2008). The emulsions are formulated to have a
sufficient level of potential repulsion between the adjacent particles to prevent premature
coagulation. The particles coalesce only if modification occurs, at least locally within the
surfactant films (SFERB, 2008). This can be due to a variety of reasons including:
* A change in the hydrophilic and lipophilic balance of the emulsifier
* A change in acidity or basicity (pH)
* An increase in the ionic force of the medium
* Adsorption of the surfactant by the mineral aggregates
Emulsion curing signifies the combination of phenomena which result in the removal of
the water from the bituminous material, after the breaking phase is completed or is at
least sufficiently initiated. This improves the mechanical properties of the product
prepared with the emulsion (SFERB, 2008). The statement above therefore implies that
the development of stiffness as well as its ability to hold the aggregates back will be
governed by the rate of moisture removal from the system. Early placement of aggregates
can lead to tire pickup by rollers while delayed placement of stones will require more33
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Senadheera, Sanjaya Priyantha, 1959-; Prozzi, Jorge Alberto; Smit, Andre; Bannerjee, Ambarish; Tubb, Andrew & Niu, Lei. Laboratory Evaluation of Constructibility Issues with Surface Treatment Binder, report, October 2011; Lubbock, Texas. (https://texashistory.unt.edu/ark:/67531/metapth326616/m1/49/: accessed May 2, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.