Cold recycled mixes (CRM) at a very young age are similar to an unbound granular material and will then become a cohesive material when cured. This initial aspect is due to the presence of water in the mix at a young age, for handling purposes. For this reason, conventional asphalt mix characterisation tests are not suitable. However, it is important to know how CRM behaves at a very young age, after compaction, as the pavement quickly reopens to traffic. A nondestructive technique based on shear waves velocity, the Piezoelectric Ring Actuator Technique (P-RAT), is used. This frequency analysis technique determines the propagation velocity of the shear wave (Vs). It has been used successfully in soils and concretes and in a dissertation project to characterise CRMs at a young age.
The present PhD project continues this work and aims to determine the relevance of the Vs parameter for characterising CRMs during curing. It is also important to assess the limitations of P-RAT in terms of the materials tested and the test conditions. Finally, P-RAT will be used to determine the anisotropic behaviour of CRMs.
Initial tests on CRM plates show the evolution of the Vs parameters, water loss and signal amplitude from 90 minutes after compaction to 30 days of curing in open air. Vs and water loss evolve rapidly at young age and then reach an asymptote. A link between Vs and water loss exists, but the lack of measurements at a very young age means that their evolution cannot be modeled correctly.
Subsequently, Vs measurements were carried out on CRM cylinders compacted to different void contents (10.7 to 17.5 %) using a shear gyratory compactor (SGC). Improvements to the experimental set-up allow tests to begin 10 minutes after compaction, and surface temperature and water loss are measured in parallel. The latter was found to be influenced by surface temperature and curing conditions (free air or oven), and by specimen geometry. The Michaelis-Menten model is used to successfully model the evolution of Vs and water loss as a function of curing time. The preponderance of bituminous bond creation compared to water loss is highlighted. Vs evolves linearly with compaction, increasing from 253 to 330 m.s-1 and from 370 to 610 m.s-1 for initial and final values, respectively. The Vs results obtained are consistent with literature data.
Finally, the anisotropy in CRMs is evaluated based on Vs. Measurements in three directions differ from 0.6 to 11.5 % and a symmetrical trend appears in the CRM plates tested. Vp measurements via a temporal method show the same phenomenon. In addition, computed tomography scans (CT-Scan) reveal a preferential alignment of aggregates in the direction of the compacting wheel.
| Date | 14 Apr 2025 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Yannic A. Éthier (Supervisor) & Alan Carter (Co-supervisor) |
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Lecuru, Q. (Author),
Éthier (Supervisor) &
Carter (Co-supervisor),
14 Apr 2025Student thesis: Doctoral thesis › Doctorate in Engineering: Engineering