New insight on the restructuring and breakage of particles during uniaxial confined compression tests on aggregates of petroleum coke

•The solid skeleton manages most of the deformation.•The particle damages are the main cause of the curvature in the densification rate.•The particles with a lower roundness undergo a higher level of breakage.•The paste recipes having a higher level of binder reach a higher densification.•The acoustic emission system has recorded the energy from the particle interactions.

With the aim of modelling the mechanical behaviour of carbon anode paste, compression tests within a rigid mould were performed on different recipes of carbon paste containing 32 to 44 wt.% binder. The compression was performed by applying a series of loading/unloading cycles. The maximum load was incrementally increased at each cycle. Test results showed that a softening behaviour occurs after the hardening of the anode paste during compaction cycles. This paper attempts to explain the mechanism of this peculiar behaviour. For comparison, two cokes with different shape factors were used to prepare the paste recipes. It was observed that round particles result in less resistance to local shear stress than do the angular ones. Binder, which consists of coal tar pitch and fine coke particles, acts as a lubricant enhancing the compaction of the paste. The breakage and slippage of particles during loading were monitored using an acoustic measurement system. A creep test, performed on a carbon paste and dry aggregates, corroborates that the time-dependency, or creep, of the paste is mainly governed by the solid skeleton.

Graphical abstractThis is a loading/unloading compaction test performed on a sponge coke bed without binder. The test was performed at room temperature using a rigid mould. The initial aggregate sizes were ranging from − 8 to + 14 US Mesh (1.41 to 2.38 mm). The loading profile is presented in the middle of the graph with a serrated shape and is associated to the green axis (on the right).The relative densities of the sponge and shot coke are presented on the top part of the figure according to the blue axis (on the left). The coloured line represents the relative density of the sponge coke and the shot coke relative density is also presented in the same figure (black curve) for comparison.An acoustic recording system was installed on the mould wall, at a third of its height, to record the acoustic emission (AE) coming from the particle–particle interaction. The acoustic emission energy is presented at the bottom of the graph according to the red axis (on the right).The curves of the relative density, loading and acoustic energy are linked together through the colour of the points. These colours reflect the energy level.Figure optionsDownload full-size imageDownload as PowerPoint slide