Investigating the Efficacy and Variability of the Bar Linear Shrinkage Test for Aggregates

About the project

Aggregate is a widely used construction material in the Virginia Department of Transportation (VDOT) construction projects. Its quality is governed by many properties, including gradation, soundness, and Atterberg limits. Specifically, VDOT sets specification requirements for both the plasticity index (PI) and liquid limit (LL). These limits are determined by Atterberg limit tests. The requirements for PI and LL aim to limit or eliminate contaminants like active clay in aggregate, which negatively impact performance.

The fines in aggregates are typically non-plastic (NP) or marginally plastic, which creates challenges when determining PI and LL using conventional test methods—for example, materials may slide on the Casagrande cup or may not roll into 1/8-inch threads. A bar linear shrinkage (BLS) test, which measures the shrinkage limit of fine materials, is proposed as a surrogate test for these properties. The BLS test is simple, repeatable, and sensitive to the presence of active clay particles.

Materials with a range of properties will be tested in the laboratory to evaluate the effectiveness of the BLS test in distinguishing low-PI materials across the acceptance range for aggregate materials and to standardize the test method for VDOT use. The study will also include an interlaboratory evaluation to quantify repeatability and reproducibility, ensuring the BLS test can be reliably incorporated into routine VDOT quality‑assurance operations.

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