Influence of start temperature on tensile stress testing of restrained asphalt concrete specimens

U ovom se radu prikazuju rezultati ispitivanja vlačnog naprezanja pridržanih uzoraka obavljenog na uzorcima asfaltbetona AC 8 s bitumenom 50/70, pri čemu su korištene dvije početne temperature +10 °C i +20 °C. Analiza rezultata pokazuje da je razlika između tih dviju početnih temperatura beznačajna te da su rezultati u okviru standardnih zahtjeva točnosti. S druge strane, uočena je razlika između rezultata ispitivanja dobivenih u dva laboratorija: TU Beč i ZAG Ljubljana, gdje su ispitivanja obavljena u skladu s EN 12697-46 pri početnoj temperaturi od +20 °C.This paper presents the result of the Tensile Stress Restrained Specimen Tests on specimens of asphalt concrete AC 8 with bitumen 50/70 depending on two starting temperatures of +10 °C and +20 °C. The analysis of the results shows that there is only a non significant difference between these two start temperatures and the results are within the limit of standard precision. On the other hand, there is a difference between the results of two laboratory TU Wien and ZAG Ljubljana, who carried out the tests in accordance with EN 12697-46 at start temperature +20 °C

Bituminous mixtures with low percentage of natural aggregates and rubber modified bitumen with wax

The three mixtures included in the Spanish specifications (asphalt concrete, porous asphalt and very thin asphalt concrete) were designed replacing more than 80% of the natural aggregates by black slag of electric arc furnace and recycled asphalt pavement. Besides, a rubber modified bitumen was used as binder, analyzing the performance of a fatty acid amide wax as additive to decrease its viscosity at mixing temperature, and avoid the higher manufacturing temperature of this type of bitumen. Three stages were carried out to design the mixtures: first, the viscosity analysis of the rubber modified bitumen when the wax is added. Second, the experimental design of the mixtures with the alternative aggregates at conventional temperature, using the rubber modified bitumen without wax. Finally, the study of the behaviour of the three mixes with the same dosage of the previous phase, but manufactured at reduced temperature, that is including the fatty acid amide wax to the binder. The tests of the Spanish specifications have been performed to design the mixtures and compare their performance in both conditions (with and without wax): void characteristics, water sensitivity test, wheel tracking test, and Cantabro loss particle test in dry and wet conditions. The results have shown that it is feasible to design mixtures in which practically the whole mineral skeleton comes from black slag and recycled asphalt, manufacturing them with a rubber modified bitumen but at the same range of temperatures than conventional 50/70 penetration grade binder, and fulfilling the standards for any climatic zone and heavy traffic level

Characterisation of bitumen through multiple ageing-rejuvenation cycles

The multiple recycling of bitumen offers the possibility of reusing it for repeated lifecycles and achieve a higher degree of circularity of materials used in pavement construction. Aiming to identify the prospect, this study aged bitumen in a laboratory setting and then rejuvenated it using a bio-based rejuvenator for four ageing cycles. The low temperature and fatigue performance of the bitumen in each cycle was comprehensively characterised using dynamic shear rheometer (DSR) based rheological measurements. The results illustrated that although rejuvenation cannot recover all properties of the aged bitumen to the level of virgin bitumen, using rejuvenators can largely improve most properties negatively affected by ageing. The optimal dosage of rejuvenators should be determined based on the balance of the properties. The use of rejuvenation indexes, such as the one employed in this study, can assure that the low-temperature and intermediate temperature performance can be met through multiple ageing-rejuvenation cycles. In terms of chemical changes, although ageing reduces the chemical or colloidal stability of bitumen, rejuvenation can recover this property to its initial level. Overall, the results obtained in the study suggest that using appropriate rejuvenators, bitumen can potentially be recycled through multiple lifecycles

First-year asphalt mixture results from a European in situ Ageing Consortium (EurIAC)

Ageing of asphalt pavements is an inevitable phenomenon that reduces the overall lifespan of the road net-work. Typically, this process is simulated in the lab, however several climatic factors are often overlooked in such simulations. To evaluate the ageing effects more realistically, a network of universities in six West-ern-European countries was established in the summer of 2023. This paper reports the first-year results of in situ climatic conditioning and its effect on a reference asphalt mixture. Asphalt slabs were assessed for their mechanical performance via indirect tensile strength and resilient modulus. The findings depict slight differences between the participating labs concerning these properties, with the majority of them pointing to slightly increased modulus values ascribed to ageing. The extent of mix properties changes, yet in the early stages of long-term ageing, is still insignificant. Finally, a moderate positive correlation was found between the two asphalt mixture properties which can collectively explain the regional differences across Europe in the near future. Correlations with the changes at the binder level will also be considered as well as the link-age to the climatic history, as additional results will become available over extended time intervals

Rheological, physicochemical, and microstructural properties of asphalt binder modified by fumed silica nanoparticles

Warm mix asphalt (WMA) is gaining increased attention in the asphalt paving industry as an eco-friendly and sustainable technology. WMA technologies are favorable in producing asphalt mixtures at temperatures 20–60 °C lower in comparison to conventional hot mix asphalt. This saves non-renewable fossil fuels, reduces energy consumption, and minimizes vapors and greenhouse gas emissions in the production, placement and conservation processes of asphalt mixtures. At the same time, this temperature reduction must not reduce the performance of asphalt pavements in-field. Low aging resistance, high moisture susceptibility, and low durability are generally seen as substantial drawbacks of WMA, which can lead to inferior pavement performance, and increased maintenance costs. This is partly due to the fact that low production temperature may increase the amount of water molecules trapped in the asphalt mixture. As a potential remedy, here we use fumed silica nanoparticles (FSN) have shown excellent potential in enhancing moisture and aging susceptibility of asphalt binders. In this study, asphalt binder modification by means of FSN was investigated, considering the effects of short-term and long-term aging on the rheological, thermal, and microstructural binder properties. This research paves the way for optimizing WMA by nanoparticles to present enhanced green asphalt technology