Emulsified asphalt is an emulsion formed by asphalt dispersed in water. The water in it is only a temporary medium in the asphalt. After the emulsified asphalt is sprayed or mixed, it breaks the emulsion and the water in the emulsified asphalt evaporates. The ratio of water to asphalt in emulsified asphalt not only affects the production and transportation costs of emulsified asphalt, but also has a significant impact on the storage stability, viscosity and other indicators of emulsified asphalt. Therefore, it is necessary to test the asphalt content in emulsified asphalt.
In order to detect the asphalt content in emulsified asphalt, the emulsified asphalt needs to be dehydrated. However, different countries and organizations have different methods for dehydrating emulsified asphalt. In summary, there are four main methods: distillation, oven evaporation, direct heating evaporation and natural drying.

1. Distillation method
The more representative distillation methods are the distillation method of ASTM in the United States, the low-temperature vacuum distillation method of ASTM, and the distillation methods with different distillation temperatures and distillation times used in many states in the United States.
(1) ASTM distillation method. The United States ASTM D244-00 stipulates three methods for extracting emulsified asphalt residue: Residue and oil distillate by distillation, Residue by evaporation, and low-temperature (135°C) vacuum distillation. The ASTM distillation method is to pour 200g of modified emulsified asphalt into a special aluminum alloy container and distill it at 260°C for 15 minutes to separate the water and asphalt in the emulsified asphalt. The residue obtained by this method can also be used to test the properties of residual asphalt.
(2) ASTM low-temperature vacuum distillation method. Considering that some emulsified asphalts, especially modified emulsified asphalts, are distilled at high temperatures, the properties of the residual asphalt obtained will be greatly affected and cannot truly reflect the actual state of the emulsified asphalt during use. Therefore, the low-temperature pressure distillation method was added to the 2000 edition of ASTM D244. This method uses a distillation instrument and distills at 135°C for 60 minutes.
(3) Distillation methods with different distillation temperatures and distillation times used in many states in the United States. Many states in the United States use distillation to obtain emulsified asphalt residues, but the specific methods are not the same: Illinois and Pennsylvania use a method of distilling at 177°C for 15 minutes, Kansas uses a method of distilling at 177°C for 20 minutes, Oklahoma uses a method of distilling at 204°C for 15 minutes, and so on.
2. Oven evaporation method
The more representative ones are the ASTM evaporation method and the method of California, USA.
The ASTM evaporation method is to take four beakers with a capacity of 1000mL, pour 50g ± 0.1g of the stirred emulsion into each beaker, and then put them into an oven with a temperature of 163°C ± 2.8°C for heating for 2h, take them out and stir them thoroughly, then put them into the oven for heating for 1h and take them out to measure the index of the residue.
The method in California, USA is to take 40g ± 0.1g of emulsified asphalt, keep it at 118℃ for 30min, then heat it to 138℃, keep it at 138℃ for 1.5h, stir it, and keep it at 138℃ for 1h. The obtained residue is made into relevant test specimens to measure the index.
3. Direct heating evaporation method
Both Japan and my country use this method. The test for the evaporation residue of emulsified asphalt in my country is to heat and stir 300g of emulsion on an electric furnace for 20-30min, confirm that the water has completely evaporated, and then keep it at 163℃ ± 3℃ for 1min, and then measure the index of the residue after filling the mold. This test method is formulated with reference to Japanese standards.
In addition, in order to obtain the ratio of asphalt to water in emulsified asphalt, it can be obtained not only by detecting the asphalt content in the emulsified asphalt, but also by detecting the water content in the emulsified asphalt. ASTM D244-00 also has a test method for the water content in emulsified asphalt.
The residue content and properties obtained by different methods of obtaining residual asphalt are different.
Experimental research has found that the method of drying in an oven for a period of time often results in incomplete evaporation of water; the ASTM distillation test results are stable, but due to the relatively complex test equipment, it is currently difficult to promote in my country. Although my country's method of directly heating to 163°C to obtain residues will be affected by human factors, the method is simple, the test results are credible, and it is basically feasible.