Analysis - Asphalt

Asphalt Analysis

Asphalt Analysis primarily involves the determination of asphalt binder content in asphalt mixtures and pavement specimens. Quantitative determination of the asphalt binder content of HMA mixtures and pavement samples is necessary for many reasons, including: quality control, specification acceptance, and mixture evaluation studies. HMA that has too much asphalt binder can experience problems such as bleeding, lowered skid resistance, and lowered resistance to permanent deformation (rutting and shoving). HMA that has too little asphalt binder can have lowered fatigue resistance and problems with raveling and stripping.

There are primarily two methods for asphalt analysis: the ignition method and solvent extraction. Each method offers a way to determine asphalt content. Both methods are based around determining the binder content of an asphalt mix. Asphalt binder content affects HMA mixture performance in the areas of stiffness, strength, durability, fatigue life, raveling, rutting and moisture damage. Therefore, it is important in HMA quality assurance, pavement forensic investigations and HMA research.

Ignition Method
The ignition method of determining asphalt binder content allows for the asphalt binder in an HMA sample to be burned off in an oven at temperatures above the flame point of the binder. Asphalt binder content is then calculated by subtracting the mass of the aggregate remaining after the asphalt binder is burned off from the initial mass of the test sample. This method eliminates the need for the chlorinated solvents used in solvent extraction methods.

The ignition test is the most common method used to determine HMA asphalt binder content. In the ignition method the HMA is heated in an oven sufficiently to burn the asphalt binder within the mixture. The difference in weight before and after burning in the ignition oven gives a measure of asphalt binder content. .

The asphalt content furnace (NCAT Oven) automatically determines the asphalt content of paving mixtures. Developed by NCAT, the National Center for Asphalt Technology, this furnace is an environmentally-friendly and cost-effective method for the accurate determination of asphalt content. It eliminates the cost and safety concerns of using solvent and solvent disposal plagued by other methods.

This ignition method reduces testing time compared to solvent testing methods and features an internal electronic balance automatically monitors sample weight throughout the ignition process and determines endpoint, saving valuable technician time and increasing productivity.

Solvent Extraction Methods
Solvent extraction methods (described in AASHTO T 164 and ASTM D 2172) use a solvent to remove asphalt binder from aggregate in an HMA mixture. Asphalt binder content is then calculated by subtracting the mass of the aggregate remaining after the asphalt binder is removed from the initial mass of the test sample. These methods have been used reliably for many years but their use of chlorinated solvents create disposal problems.

Solvent extraction uses a chemical solvent (trichloroethylene, 1,1,1-trichloroethane or methylene chloride) to remove the asphalt binder from the aggregate. Typically, a loose HMA sample is weighed and then a solvent is added to disintegrate the sample. The asphalt binder/solvent and aggregate are then separated using a centrifuge (see Figures 7 and 8) and the aggregate is weighed. The initial and final weights are compared and the difference is assumed to be the asphalt binder weight. Using this weight and the weight of the original sample a percent asphalt binder by weight can be calculated. A gradation test can then be run on the aggregate to determine gradation.

Centrifuge Extractors
Centrifuge Extractors are used to separate the liquids in the field of gravity inside the rotor and uses the rotation of the rotor inside a centrifuge to mix two immiscible liquids outside the rotor. It is designed for efficient and reliable quantitative determinations (weight and grade) of bitumen content in hot-mix asphalt specimens to determine constituent proportions. This method supports the following standards: AASHTO T164 (METHOD E).

Vacuum Extractors
Vacuum Extractors are designed to determine the bitumen content of a hot paving mixture by separating the aggregate and/or mineral matter from the mixture by means of a vacuum. The aggregate remaining after extraction of the bitumen may be used for sieve analysis. These extractors are primarily meant to be used for field quality control work on freshly-mixed hot paving mixtures, but they can be adapted for other uses. This method supports the following standards: AASHTO T164 (METHOD E).

Reflux Extractors
Reflux Extractors are used to determine the percentage of bitumen in a paving mixture using hot solvent extraction. These units support the following standards: ASTM D2172, AASHTO T164 METHOD B. They typically come in two sample sizes: 1000g and 2000g.

Asphalt Solvent Recycling
The Asphalt Solvent Recycler is designed to recycle the solvents used in asphalt extraction tests. It successfully extracts pure solvent from the oil and wastes generated from the extraction process and generates clean solvent ready for reuse in a new test. The unit reduces the need for new solvent and eliminates problems with solvent disposal.

If you have questions or need help selecting equipment, please call us at 1.800.544.7220 or use our Ask Humboldt form.content.