Asphalt Mix Compliance Testing Flashcards

According to CCIL procedures for Asphalt Mix Compliance (Type B Certification), which of the following is a primary reason for determining the bulk specific gravity (Gmb) of a compacted asphalt specimen?

Answer: To calculate the percent air voids and degree of compaction.

The bulk specific gravity (Gmb) of a compacted specimen is a critical value used in conjunction with the theoretical maximum specific gravity (Gmm) to calculate the percent air voids in the mix. Additionally, it is compared to the lab-compacted density to determine the in-place degree of compaction on the roadway.

A technician is performing a Marshall Stability and Flow test (ASTM D6927) for a municipal road project. The flow value represents which characteristic of the asphalt mix?

Answer: The plastic deformation of the specimen at the point of maximum load.

In the Marshall test, 'Flow' is the measure of the vertical plastic deformation of the specimen from the start of loading until the maximum load (Stability) is reached. It is measured in units of 0.25 mm and indicates the mix's flexibility and potential for plastic movement.

During the determination of theoretical maximum specific gravity (Gmm) using the Rice test (LS-264 / AASHTO T209), a technician notices that not all air bubbles have been removed from the loose asphalt sample under vacuum. What is the most likely consequence of this error?

Answer: The calculated Gmm will be erroneously high, leading to a lower calculated air void content.

The Gmm test relies on measuring the volume of the sample by water displacement after all air has been evacuated. If air bubbles remain, they occupy volume, making the measured volume of the sample larger than it actually is. This leads to a lower calculated density (Gmm). However, the question asks for the consequence if not all air is removed, which means the measured volume of the asphalt-coated particles will be understated (as the volume of the entrapped air is not accounted for), leading to an erroneously high calculated Gmm value. This, in turn, results in a lower-than-actual calculated air void percentage (Va = 100 * (1 - Gmb/Gmm)). A higher Gmm in the denominator will result in a lower calculated Va.

A CCIL certified technician is testing a compacted asphalt core sample and finds that it absorbs more than 2.0% water by volume when tested according to AASHTO T 166 / ASTM D2726. Which of the following procedures should be used to determine the bulk specific gravity?

Answer: Use the paraffin-coated specimen method (AASHTO T 275) or a vacuum sealing method.

Standard test methods like AASHTO T 166 and ASTM D2726 for bulk specific gravity are not suitable for samples that absorb more than 2.0% water because the water that infiltrates the interconnected voids is not accounted for properly. For such high-absorption specimens, methods like coating the sample in paraffin (AASHTO T 275) or using an automatic vacuum sealing device are required to get an accurate volume measurement.

A scenario-based question: A compliance test on a plant-produced Superpave mix shows that the Voids in Mineral Aggregate (VMA) is below the minimum specification limit. Which of the following is the MOST likely cause?

Answer: The aggregate gradation is too fine, lacking sufficient space in the particle structure.

VMA represents the volume of intergranular void space between the aggregate particles of a compacted paving mixture. A primary cause of low VMA is an aggregate gradation that is too fine or has a particle shape and texture that allows for excessive packing, reducing the available space for asphalt binder and air voids. While other factors can influence VMA, the aggregate structure is the fundamental contributor.

Which CCIL certification type is specifically required for a laboratory performing routine quality control tests on asphalt mixes, such as asphalt content, gradation, and compaction, to ensure they meet project specifications?

Answer: Type B - Mix Compliance

CCIL designates Type B certification for laboratories involved in Marshall and/or Superpave Mix Compliance testing. This includes the routine tests performed to check if a plant-produced asphalt mix complies with the established job mix formula and project specifications.