Michalina Makowska

Curing and ageing of biofluxed bitumen: a physicochemical approach

Bitumen solutions, comprising of four bioflux-modified bitumens and one traditional slow-curing cut-back bitumen as a reference, were stabilised with two-phased process consisting of recovery and stabilisation parts. The oxidative long-term ageing (LTA) of the stabilised bitumen solutions was performed by a pressure ageing vessel (PAV). The generic fractions of the base bitumens were determined after LTA by thin-layer chromatographic method with flame-ionisation detector (IATROSCAN MK-6s). Complex shear moduli and phase angles of both base bitumens and bitumen solutions were examined with Physica 301 rheometer in oscillatory mode. The curing and ageing behaviour of the biofluxed bitumens differed notably from the traditional cut-back bitumen. Based on PAV and rheometer testing, the effects of ageing on the rheological properties of biofluxed binders may be solely bound to the evaporation of bioflux. Sigmoidal functions were introduced as an option for evaporation models with limited evaporation. However, interpretation of chemical composition of cut-back bitumens as analysed by thin layer chromatography-flame ionisation detector leaves a reasonable doubt for this method to give ultimate composition result.

Analytical Methodology to Determine the Composition of Filler Used in Hot-Mix Asphalt: Case Study

For more understanding about asphalt pavement deterioration in Finland, a premature failure of major arterial Ring Road II surface layers was investigated. Documentation of mix design (MD), construction, and material quality analysis, before and after construction, was reviewed and compared with samples collected from the road. The traditional quality assessment of the pavement by means of binder content and aggregate gradation analysis, air void content, and indirect tensile stiffness and strength, as well as binder tests (penetration, ring and ball softening point, and dynamic shear rheometer), did not provide information on the possible reasons for failure. A discrepancy was then found in the filler composition; the discovery was made by applying the standard analytical procedure of hydrochloric acid solubility, coupled with material composition simulations. This finding (and forensic technique) was positively verified by means of thermogravimetral analysis and X-ray diffraction. Scanning electron microscopy, supported by the BET-adsorption (Brunauer–Emmet–Teller) surface area measurements, suggested that, between the stage of MD and construction, the limestone filler was substituted with a mixture of limestone and fly ash. The filler blends were reconstructed on the basis of the MD report and established forensic laboratory findings. The comparative analysis of reconstructed fillers, by means of Fourier transform infrared spectrom-etry, verified that an almost ideal match was obtained with the latter. Alteration of construction material is suggested as the main reason for discrepancies between the MD and actual properties of the analyzed performance of the wearing course.

Exploring the Observed Rheological Behaviour of In-Situ Aged and Fresh Bitumen Employing the Colloidal Model Proposed for Bitumen

This paper compares in-situ (field) aged road bitumen and fresh paving grade bitumen by presenting various rheological measurements conducted with Dynamic Shear Rheometer (DSR). Performed tests included strain sweeps, frequency sweeps and shear rate sweeps in the linear and nonlinear viscoelastic region of response at temperatures ranging from 2 to 120°C. Some fundamental rheological concepts were utilised to explain the origins of observations employing colloidal model describing bitumen structure. However, additional testing, including chemical analysis techniques like GPC and IR, is needed to validate and maximise output from this single equipment analysis. Testing suggests that Lissajous figures from strain sweep tests could be used to characterise cracking propensity of binders; research revealed ductile like behaviour for aged bitumen in the nonlinear region, which is postulated here to originate from the formation of crazes (microcracks) capable of load transfer.

The rheological transformation of bitumen during the recycling of repetitively aged asphalt pavement

This article explores changes in bitumen during the recycling of asphalt pavement and what consequences the observed rheology has on pavement performance in the short and long term in the Nordic environment. As the existing environment dictates the state of performance, this research focuses on the intermediate and cold temperature performance and requirements, especially transformation from ductile to brittle behaviour. An asphalt pavement, originally constructed by using conventional paving grade bitumen 70/100 and 50/70, was rehabilitated by hot in-place recycling (HIR) for the first, second and third time. The HIR yields the pavement surface consisting of more than 70% of the in situ recycled asphalt. Samples were taken prior to, during construction and in the service. The rheological evaluation of ageing and rejuvenation of bitumen was conducted to investigate the effect of repetitive recycling on bitumen properties. Contractors used soft bitumen 650/900 as a rejuvenator and admixture with the virgin penetration grade 70/100 bitumen. Extracted binders were analysed by means of Penetration, Fraass breaking point and Dynamic Shear Rheometer. The typical rheological analysis was extended by comparing the Glover–Rowe parameter with the Damage Zone, and a good correlation between field performance and material properties was found. Such field sample analysis was complimented by the laboratory simulation of repetitive ageing and rejuvenation of penetration grade 70/100 bitumen. Although the stiffness of the binder could be restored by using the fresh admixture and rejuvenator, the treatment could not recover the original balance between the viscous and elastic response of the bitumen. The criterion given by this Damage Zone was evaluated. A second provisional zone (Insufficient Binder Ductility Zone), now providing the means to evaluate binder properties capable of withstanding the cold Nordic climate conditions, is proposed.

Qualitative detection of the presence of Gilsonite in the bituminous blends based on thin layer chromatography

The natural asphalts, of which Gilsonite is a representative, are modifiers used to increase the stiffness modulus of the asphalt concrete. For quality control purpose, recognizing if such material is present in the final blend is of an interest. The thin layer chromatography using a flame photometric detector (FPD), in addition to the typical flame ionization detector, was demonstrated hereby as a viable analytical tool for this problem. Gilsonite also contains the material soluble in solvent used in the development of the fraction referred to as aromatics. However, for straight run bitumen and Gilsonite the color of that fraction is different as well as their mobility. Due to the lower mobility of Gilsonite molecules on the stationary phase, the elution stops at different position than for fresh bitumen, convoluting the signal in the chromatogram region typically assigned for resins. The presence of Gilsonite is identifiable visually after the second development bath, but also with FPD from the final chromatogram.

Incorporating the transverse profile of the wearing course into the control of the hot in-place recycling of asphalt concrete

The hot in-place recycling (HIR) of asphalt concrete (AC) is one of the least CO2 emissive reuse techniques. It allows for 100% reuse of material in-situ in the same application, at a reduced need for the material transport to and back from the construction site, as well as the reduced price in comparison with the fresh wearing course overlay. Finland uses the technique predominantly to fill wheel path ruts caused by the studded tire abrasion, to retain structural capacity and prevent hydroplaning. During the HIR process, the aged AC material is heated up in-situ, milled to the approximate depth of 40 mm, blended with fresh AC admixture and rejuvenator. However, the amount of the aged material and the amount of the aged bitumen that undergoes rejuvenation depends on the pavement transverse profile. The rut depth, width and shape determine the minimum volume of admixture necessary for refill during the process in order to retain the structural capacity, as well as the amount of the aged binder requiring rejuvenation. In favor of achieving homogenous rheological properties in the final product, the proportion between the aged binder and the fresh binder should be controlled, as it influences the required amount of rejuvenator. Therefore, the rut cross-sectional area and furthermore, the rut volume is one of the previously unrecognized or ignored major variables of the hot in-place recycling process in Finland that should be incorporated to the HIR process control. This article demonstrates the methodology of incorporating the transverse road profile measurements by 17 vehicle-mounted laser sensors into the calculation of required rejuvenator amounts. This can be done during the procurement preparation phase or during the paving work as a continuous in-situ process control. In the rheological optimization the apparent Newtonian viscosity concept and the rotational viscosity are utilized in the viscosity based blending equation, which then allows the use of oily rejuvenators. The method reduces the need for aged pavement sampling compared with the determination of the calibration curve between rejuvenator concentration and the rheological response. Additionally, the apparent Newtonian viscosity corrects the complex viscosity by the phase angle derived correction factor, opening a previously unexplored opportunity of targeting desired viscoelastic characteristics. The approach is less sensitive to the frequencies and temperatures at which the shear measurements are conducted. This makes proposed calculative method of the desired proportioning of the aged binder, the fresh binder and the rejuvenator a promising tool for the industry. The combined algorithm presented allows for: the discrimination of sites where HIR type maintenance of pavement in question would result in a substandard product; the choice of the most promising material combination of the admixture and rejuvenator, as well as for the adjustment of the admixture and rejuvenator amount in-place.

The "false positive" on the antiaging properties of asphalt fines investigated by RTFO laboratory aging of mastics

Asphalt concrete has the advantageous ability to heal autonomously, however the mechanisms behind this are not fully understood. To increase insight in the healing mecha-nism, the healing model used in polymer science is adopted. It interprets healing as the sum of wetting and intrinsic healing. The presented work introduces a new test set-up, which is de-signed to investigate the relative contribution of wetting and intrinsic healing by measuring the strength gain when two pieces of binder are brought into contact. Results obtained show that for a soft, pure binder, wetting is the dominant process. This can be concluded from the fact that at least 50% of the observed healing can be attributed to wetting. Wetting is highly de-pendent on both the load level and the duration of load application. Consequently, it is shown that the level of healing observed in asphalt concrete is very dependent on the boundary condi-tions.