Development and Verification of Sample Reduction Method for Rubberized Asphalt Mixtures

Abstract

The research evaluated a newly developed sample reduction method—the direct reduction procedure—aiming to minimize the variability of the reduced rubberized hot mix asphalt-gap graded (RHMA-G) mixture sample. The impact of the newly developed method was analyzed against the mechanical splitting method and the quartering method recommended in American Association of State Highway and Transportation Officials (AASHTO) R 47, Standard Practice for Reducing Samples of Asphalt Mixtures to Testing Size. The variability of three measured properties were compared between the three methods: maximum theoretical specific gravity, asphalt binder content, and aggregate gradation. The standard method of hot mix asphalt (HMA) sample reduction is not applicable to RHMA-G because RHMA-G mixes are fundamentally different than HMA. RHMA-G is gap graded and has high binder content, and RHMA-G binder is highly tacky. In addition, RHMA-G materials adhere to sample reduction tools, leading to the variability of material properties. To support this, an interlaboratory study with nine participating laboratories was conducted using a single source ¾ in. RHMA-G mixture. Participating laboratories were provided with random loose RHMA-G samples and requested to reduce samples through the three methods, and to test four replicates for each of the three mixture properties on the samples. The data was used to develop the repeatability and reproducibility limits for each of the three measured properties. As a result, data analyses indicated that the newly developed sample reduction method introduced the least variability on the three measured properties. The study led to the development of California Test 306, as the standard for sample reduction method of RHMA-G mixtures.