|July 16th, 2016, 01:16 AM||#1|
Joined: Jul 2016
what is the bitumen emulsions?!!
Bitumen Emulsions. bitumen normally needs to be used or processed as liquid. There are basically three ways to make bitumen liquid:
Dissolve it in solvents. This has been done from the earliest times using Naptha. Principle uses of liquid bitumen produced with Naptha included mummification (Egypt) and waterproofing (Hanging Gardens of Babylon)
Emulsify it. At the beginning of the 1920’s, two English chemists, Hugh Alan Mackay and George Samuel Hay discovered and patented the first bitumen emulsion for use in road construction. This development allowed cold spraying. Since that time, the uses of bitumen emulsions have expanded, so that today, globally, more than 10 million tones of bitumen emulsions are now produced and applied.
The use of bitumen emulsions began in the early part of the 20th century. Today 5% to 10% of paving-grade bitumen is used in emulsified form, but the extent of emulsion usage varies widely between countries. More than 8 million tons of emulsions are produced worldwide and the United States is the world’s largest producer among the significant producers of bitumen emulsion: France, Mexico, and Brazil.
Advantages of Emulsion. With viscosities in the range 0.5–10 Poise at 60°C, bitumen emulsion is of considerably lower viscosity than bitumen itself (100–4,000 Poise), allowing it to be used at lower temperature. Low-temperature techniques for construction and maintenance reduce emissions, reduce energy consumption, avoid oxidation of the bitumen, and are less hazardous than techniques using hot bitumen. They are also more economical and environmentally friendly than cold techniques using cut back bitumen. The environmental benefit of bitumen emulsion is particularly positive when used for in-place or on-site techniques which avoid the energy usage and emissions associated with heating, drying, and haulage of aggregate. The construction of a roadway with cold techniques has been calculated to consume approximately half the energy of one of similar bearing capacity made with hot-mix bitumen. An environmental impact analysis (EIA) technique called “eco-efficiency” has been applied to emulsion maintenance techniques (micro surfacing and chip seal) and it was concluded that the emulsion system had less environmental impact than a thin hot-mix overlay.
Emulsions are water-based and in many cases can be diluted further with water for applications such as dust control and priming. They are also compatible with hydraulic binders like cement and lime as well as water-based polymer dispersions like natural and synthetic latex.
When mixtures of cement, latex, and bitumen emulsion cure, a composite binder is produced with a structure that cannot be duplicated with hot bitumen and with significantly improved properties compared to pure bitumen.
The choice of emulsion type mainly depends on the type of aggregate to be used in the road construction. For example, aggregates may be of an acidic type, with surfaces that tend to be negatively charged. Acidic type aggregates include those with high silica content, such as Quartzite and Granite. Negatively charged aggregate would be used with a positively charged cationic bitumen emulsion, on the basis that unlike charges attract. Conversely, positively charged limestone aggregate would be used with a negatively charged anionic emulsion. 90% of the emulsions produced globally for road construction are Cationic.
A successfully produced emulsion should “break” after contact with aggregate in the road base. “Breaking” is the separation of the water from the bitumen, in the emulsion. After breaking, the residual bitumen retains all of the properties of adhesion, durability and water resistance of the bitumen from which the emulsion was originally produced. The speed at which a cationic bitumen emulsion breaks is classified in EN 13808 on a scale of 1 (fastest) to 7 (slowest).
Variables Affecting Emulsion Quality. There are many factors that affect the production, storage, and performance of a bitumen emulsion. It would be hard to single out any one as being the most significant. Variable having a significant effect include:
Chemical properties of the base bitumen cement
Hardness and quantity of the base bitumen cement
Bitumen particle size in emulsion
Type and concentration of the emulsifying agent
Manufacturing conditions such as temperature, pressure , and shear
Ionic charge on the emulsion particles
Order of addition of the ingredients
Type of equipment used in manufacturing, storage
Properties of the emulsifying agent
Addition of chemical modifiers or polymers
Water quality (hardness)
These factors can be varied to suit the available aggregates or construction conditions. It is always advisable to consult the emulsion supplier with respect to a particular bitumen-aggregate combination, as there are few rules that apply under all conditions.
Testing Bitumen Emulsion. Proper sample handling is important to achieve the valid test results. Follow the test method. Care should be taken to adjust the temperature of the emulsion sample in accordance with the test method. Samples should be stirred, not shaken, to ensure homogeneity. Here are some tests applied to bitumen emulsion and the test run on the bitumen emulsion residue after the water distillation or evaporation:
Particle charge test (ASTM D 244)
Viscosity (ASTM D 244)
Demulsibility (ASTM D 244, D 6936)
Cement mixing test (ASTM D 244, D 6935)
Classification of cationic rapid-setting emulsions (ASTM D 244)
Classification of cationic slow-setting emulsions (ASTM D 244)
Settlement and storage stability (ASTM D 244, D 6930)
Oversized particles (sieve) (ASTM D 244, D 6933)
Coating ability and water resistance (ASTM D 244)
Density (ASTM D 244, D 6937)
Residue and oil distillate by distillation (ASTM D 244, D 6997)
Residue by evaporation (ASTM D 244, D 6934)
Breaking index (no ASTM or AASHTO standards)
Tests on residue:
Penetration (ASTM D 5, AASHTO T 49)
Ductility (ASTM D 113 and AASHTO T 51)
Float test (ASTM D 139 and AASHTO T 50)
Elastic recovery (ASTM D 6084, AASHTO T 301)
Force ductility (AASHTO T 300)
Torsional recovery (California test 332)
Toughness and tenacity
Ring-and-ball softening point (ASTM D 36 and AASHTO T 53)
Solubility (ASTM D 2042, AASHTO T 44)
Absolute viscosity (ASTM D4957 and AASHTO T 202)
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