Vacuum dryers(such as CoreDry)are designed to quickly remove internal moisture from asphalt mixture specimens at near room temperature.Their core function is to dry specimens efficiently and non-destructively for subsequent testing of key indicators such as mass and density,and they comply with standards such as ASTM D7227 and AASHTO PP75.

I.Working Principle:

A vacuum pump creates a vacuum(up to approximately 6 mmHg),significantly lowering the boiling point of water and causing the moisture inside the specimen to evaporate rapidly at low temperatures.The equipment's built-in intelligent heating and airflow circulation system effectively compensates for the heat required for moisture evaporation,ensuring stable specimen temperature and preventing changes in its microstructure and physical properties due to thermal expansion and contraction or asphalt aging.

II.Core Advantages:

◦High Speed:On-site core samples can usually be dried in<15 minutes;for saturated specimens with high moisture content(water content>30g),the drying time is only about 30 minutes,much faster than the traditional oven drying method(several hours).

◦High fidelity:The room temperature drying process avoids the potential impact of high temperatures on asphalt binder properties(such as oxidation and changes in softening point)and microcracks caused by thermal stress in the specimens,ensuring the authenticity of the specimens'void structure,density,porosity,and other indicators.

◦Wide range of applications:It can process specimens of various shapes and sizes,including cylindrical pavement core samples with diameters of 100–150 mm,cubic specimens,as well as loose mixtures and aggregate particles.

III.Main Applications:

◦Compaction Degree Testing:This is one of its core applications.Road surface core samples taken from the construction site can be immediately placed in a vacuum dryer for rapid drying and weighing,thereby quickly calculating the on-site compaction density.This enables real-time monitoring and feedback of the compaction quality during construction,allowing for timely adjustments to the compaction process.

1.Density Test Preparation:

▪Provide accurate calibration and compensation data for rapid on-site density testing equipment such as nuclear density meters or non-nuclear density meters.

▪Quickly obtain the dry weight of the specimens before conducting indoor tests such as Marshall stability and indirect tensile strength to improve testing efficiency.

2.Quality Control and Scientific Research:

▪Used for rapid monitoring of the moisture content of asphalt mixtures in asphalt mixing plants,especially during the rainy season or in the production of materials sensitive to moisture content(such as recycled RAP).

▪Used in materials research and performance studies to compare the effects of different gradations,different asphalt dosages,or different additives on the water absorption characteristics of mixtures.

3.Selection and Usage Guidelines

•Define the test objective:If the core requirement is to remove moisture from the specimen quickly and without damage,a professional vacuum dryer(such as CoreDry)should be selected,rather than a device that only has a simple vacuuming function.

IV.Focus on Key Performance Indicators:

◦Vacuum Level:It should be able to reach and remain stable at the low vacuum level required by the standard(e.g.,approximately 6 mmHg or below the corresponding absolute pressure of 97.3 kPa,depending on the standard).

◦Temperature control capability:The vacuum dryer should have a good temperature control or compensation mechanism to ensure that the specimen temperature is maintained at near room temperature during the drying process,avoiding overheating.

◦Automation level:Equipment with automatic vacuuming,timing,completion prompts,and even data recording functions can significantly improve experimental efficiency and operational consistency,and reduce human error.

•Follow standard procedures:Strictly follow the procedures specified in ASTM D7227,AASHTO PP75 or relevant domestic equivalent standards(if any),including the placement of specimens,vacuum holding time,and determination of drying endpoint,to ensure the accuracy and comparability of test results.