SmartRock-Based Research on Gyratory Locking Point for Stone Mastic Asphalt Mixture

Zhiqiang Cheng,Pawel Andrzej Polaczyk,Tao Wang,De Zhang,Shengjia Xie

doi:10.3390/buildings12020097

Abstract

For gyratory compaction, the concept of the locking point was initially developed to identify the compactability of asphalt mixes and to alleviate potential aggregate crushing in the mold. Most previous studies on the locking point were based on specimens’ height change. Recent studies have indicated that the gyratory locking point of cold mix asphalt mixtures could be determined by the rotation angle range indicator using SmartRock. However, height or rotation angle change ultimately reflects a change in volume. Additionally, there is no clear physical and mechanical connection between the volume change and the gyratory locking point. In this paper, a stone mastic asphalt mixture (SMA 13) was selected for gyratory compaction applying various compaction temperatures. The compaction data were recorded by a SmartRock embedded in different positions. Collected data included stress, rotation angle, and acceleration. The major findings are as follows: (1) the specimen’s locking point could be determined based on a representative stress value when the SmartRock was embedded in the specimen’s center, and the results are close to the traditional evaluation results (LP3 or LP2-2-3); (2) the representative rotation angle value reached a plateau earlier than the representative stress value; (3) the representative acceleration value is not suitable for characterizing the interlocking process during gyratory compaction.

Highlights

Compaction is a crucial factor in the construction of asphalt pavement, directly related to the pavement’s quality and durability
Air voids [1,2] and various indicators based on gyratory compaction densification curves, such as the initial number of compactions, the slope of the curve at the initial number of compactions [3], the compaction energy index (CEI), the traffic densification index (TDI) [4], the ratio of compaction times when the air void reaches 2% and 5% [5], the locking point [4], and the densification slope [6], are employed to describe an asphalt mixture’s compactability
Positions axis is the representative triaxial stress were (X-axis, Y-axis,inand values (RS ) for each indicating the relative stress change range. and Figure 8,compaction, the horizontal axis represents the number of gyrations, vertical were in various positions collect original dataZ-axis) duringvalues gyratory axis is embedded the representative triaxial stressto(X-axis, Y-axis, and

Summary

Introduction

Compaction is a crucial factor in the construction of asphalt pavement, directly related to the pavement’s quality and durability. Air voids [1,2] and various indicators based on gyratory compaction densification curves, such as the initial number of compactions, the slope of the curve at the initial number of compactions [3], the compaction energy index (CEI), the traffic densification index (TDI) [4], the ratio of compaction times when the air void reaches 2% and 5% [5], the locking point [4], and the densification slope [6], are employed to describe an asphalt mixture’s compactability. A consensus has been reached: there is a critical state that forms the internal skeleton structure of the asphalt mixture during the compaction process. Before this state, the compaction effort can increase the compaction density; beyond this state, the external input compaction effort cannot effectively increase the asphalt mixture’s density. The concept of the locking point, which is defined as the critical point beyond which the asphalt mixture will obviously become arduous to compact [7], is consistent with researchers’ consensus

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Conclusion