Compaction studies on open-graded aggregate materials: Moving towards deflection-based compaction control

Abstract

Compaction quality control of unbound aggregate layers in pavements has been typically based on target density values, which are defined in reference to the highest densities that can be achieved in the lab using standardized compaction tests. For Open-Graded Aggregate (OGA) base/subbase layers, however, density-based compaction control becomes difficult due to the presence of excessive voids. Due to the absence of specific compaction control protocols, a recipe-based approach is often used during compaction of these layers. This study focused on studying the compaction behavior of two different OGA materials conforming to ASTM #4 and ASTM #57 gradations, using Portable Impulse Plate Load Testing Devices such as the Light Weight Deflectometer (LWD). Deflection-based compaction control protocols can provide not only an idea about the level of compaction achieved in the field, but also a direct mechanistic design input parameter such as stiffness/modulus.

In this study, an integrated approach involving laboratory and full-scale field testing was undertaken to accomplish the research objectives. Laboratory testing included testing of the aggregates in a custom-made steel mold as well as in a large wooden box. The aggregates were compacted to different levels using different methods: Jackhammer, Vibratory Shake Table, and Vibratory Plate Compactor. LWD testing was performed on the aggregate material after different levels of compaction to measure the corresponding surface deflections. LWDs from two different manufacturers were used to ensure the developed protocol was device-agnostic. Finally, full-scale pavement test sections, comprising multiple test cells, were constructed using a combination of ASTM #4 and ASTM #57 aggregates in the subbase and base layers, respectively. Surface deflections were tracked with the LWDs after different number of vibratory steel-drum roller passes. Detailed findings from this study are discussed in this thesis and a foundation is laid for developing deflection-based compaction control protocols for OGA base/subbase layers.