This research compares the rheological behavior of different cold-recycled mixtures (CRMs) produced in-place through full-depth reclamation. Reclaimed asphalt pavement (RAP) obtained from the milling of the old asphalt layers was blended with reclaimed unbound aggregate from the existing subgrade. Asphalt emulsion, foamed asphalt, and portland cement were employed as stabilizing agents. The complex modulus was measured on cylindrical cores, applying a sinusoidal strain with an amplitude of 30 microstrain at testing temperatures ranging from 0°C to 50°C and frequencies ranging from 0.1 to 20 Hz. The Huet-Sayegh (HS) rheological model was applied to simulate the experimental data. The results showed that the behavior of CRM is thermo- and frequency-dependent and that the time-temperature superposition principle can be applied. The HS model provides an excellent fitting of the dynamic modulus data, whereas fitting of the loss angle data was improved, introducing a temperature- and frequency-independent correction. The RAP influences the rheological behavior, but viscous dissipation is mainly due to the asphalt-stabilizing agents (emulsion residue or foamed asphalt).
Cold bitumen emulsion mixtures are ecofriendly materials for road pavement construction. Portland cement and other supplementary cementitious materials are added to the mixtures to improve their performance. In bitumen emulsion-cement (BEC) mixtures, the two binders affect the mechanical behaviour and the curing process. In this research, BEC mixtures are considered as multiphase composite materials consisting of a mortar matrix and coarse aggregate inclusions. The main objectives are to identify the composition of BEC mortar phase and to compare mixtures and mortars throughout the curing process. Starting from two BEC mixtures containing 80% reclaimed asphalt, eighteen mortars were manufactured by changing their water and air voids content. Then, two design composition were selected to analyse the curing process by monitoring indirect tensile strength (ITS), indirect tensile stiffness modulus (ITSM) and moisture loss. Results showed that the short-term ITS of mortars (1 day of curing) increased by reducing their water and their air voids content. During curing (from 1 to 28 days), the mechanical properties (ITS and ITSM) of mixtures and mortars increased in a similar way. Unique relationships were identified between mortar and mixture properties, regardless of bitumen to cement (B/C) ratio, curing time and curing condition. In terms of predictive behaviour, the design composition slightly underestimated mixture stiffness and overestimated mixture strength. Keywords Cold paving technologies Á Bitumen emulsion Á Cement Á Mortar Á Curing The original version of this article was revised due to a retrospective Open Access order.
The cold recycling of reclaimed asphalt (RA) for the rehabilitation of end-of-life pavements is becoming very common. Cold recycled asphalt mixtures (CRAMs) are characterised by a curing time, required to reach the material design mechanical performance. Since the laboratory simulation of the long-term field curing is not yet a standardised procedure, a CRAM was laid as binder course in a full-scale trial section that was monitored for more than two years. The comparison between field curing and oven-curing in laboratory at 40 °C was performed by carrying out indirect tensile stiffness modulus (ITSM), indirect tensile strength (ITS) and complex modulus tests, as well as measurements of the air voids content. The evolution of the ITSM as a function of the curing time (field/oven-curing) was obtained for both gyratory specimens and cores taken from the trial section at different time periods. Results showed that the material stiffness development can be accelerated with a small effect on its long-term value if oven-curing is applied a few days/weeks after compaction. A linear relationship was found between the ITS measured on the cores and their air voids content. Finally, the complex modulus tests confirmed that CRAMs provide an intermediate behaviour between asphalt concrete mixtures and cement-bound mixtures.
Nowadays, one of the main challenges to a wider application of cold recycling techniques is the lack of reliable information on the mechanical behavior of cold recycled materials (CRM). In this context, measurement and modelling of the complex modulus of CRM mixtures may give an important contribution to the design and analysis of pavements including cold recycled layers. In this study, we analyzed the rheological behavior of CRM mixtures produced using bitumen emulsion and cement through the study of their fine aggregate matrix (FAM). Starting from a fixed CRM mixture composition, we compared different FAM mortars, focusing on the effect of water and air content. Then, we selected a composition as representative of the FAM in the mixture and investigated the evolution of both materials during a fixed curing period. Next, we measured the complex modulus of the CRM mixture and FAM at two curing stages and applied a rheological model to simulate and compare their behavior. Results showed that the properties of CRM mixtures are comparable to those of FAM mortars produced using all the binding agents (bitumen emulsion and cement) and a fraction of the voids contained in the mixture. Despite the huge difference in volumetric compositions, the FAM mortar controlled the curing and the thermo-rheological behavior of the CRM mixture, while the coarse reclaimed asphalt aggregate fraction and the voids mainly affected the asymptotic properties (equilibrium and glassy moduli) and the non-viscous dissipation component.
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