Experimental and Statistical Analysis of Bitumen’s Field Ageing in Asphalt Pavements

Field ageing gradients of bitumen samples recovered from 14 asphalt road sections were investigated via rheological and chemical characterizations and statistical analysis. The effects of air voids and environmental factors on the ageing gradient were evaluated using the field ageing and climate data. The effectiveness of the pressure ageing vessel (PAV) test was assessed in accelerating the bitumen’s long-term ageing by comparing with the field ageing data. Critical factors for field ageing were identified using statistical methods. A statistical model for the Glover-Rowe (G-R) parameter was formulated and verified by incorporating the screened key factors. Results indicate that a threshold air void content (around 6%) exists in differentiating the field ageing gradient patterns in the asphalt pavements. An increasing tendency is observed between the ageing gradient and annual days below 0°C. The chemical indices, stiffness-related indices, and G-R parameter can quantify the field ageing gradient of asphalt pavements. The PAV test can condition the bottom slices’ bitumen to the same ageing level as that in a pavement depth of 0.5–2 cm after 8 years’ field service. Pavement service life, binder content, minimum temperature, days above 32°C, and days below 0°C are the critical material and environmental factors that significantly affect bitumen’s complex shear modulus, crossover frequency, G-R parameter, and Δ Tc. The statistical model is verified with an acceptable mean absolute error of 28.1% and a R2 value of 0.95

Laboratory investigation of bitumen based on round robin DSC and AFM tests

In the past years a wide discussion has been held among asphalt researchers regarding the existence and interpretation of observed microstructures on bitumen surfaces. To investigate this, the RILEM technical committee on nano bituminous materials 231-NBM has conducted a round robin study combining differential scanning calorimetry (DSC) and Atomic Force Microscopy (AFM). From this, methods for performing DSC and AFM tests on bitumen samples and determination of the influence of wax on the observed phases, taking into account thermal history, sample preparation and annealing procedure, are presented and critically discussed. DSC is used to measure various properties and phenomena that indicate physical changes such as glass transition temperature (T g) and phase transition such as melting and crystallization. In the case of existence of wax, either natural or synthetic, it can further indicate the melting point of wax, that could be used to determine wax content. The results from seven laboratories show that T g temperatures obtained from the heating scans are more repeatable and easier to obtain in comparison to the cooling scans. No significant difference was noted for T g's obtained from the first and second heating scans. AFM is an imaging tool used to characterize the microstructures on a bituminous surface. Using AFM three phases in the materials with wax could be distinguished. The changes in the phases observed with AFM for increases in temperature were correlated with the DSC curve, and it could be established that the so called "Bee” structure disappeared around the melting peak in the DSC curve. Thus, this research has confirmed the relation between the microstructures on a bitumen surface and the wax content

Mimesis and connections: the Relations Between Architecture, Anthropology and Designerly Research

Uitgave ter gelegenheid van de lancering van de nieuwe faculteit architectuur (15 november 2012).status: publishe

Oplossingsgedrag van ataktisch polystyreen in cyclohexanol

KULeuven Campusbibliotheek Exacte Wetenschappen / UCL - Université Catholique de LouvainSIGLEBEBelgiu

Aging of bituminous binders in asphalt pavements and laboratory tests

Aging of bituminous binders is one of the key factors affecting the performance and durability of asphalt pavements. To simulate binder aging in laboratory, a number of methods are available. In this paper, RTFOT (Rolling Thin-Film Oven Test), PAV (Pressure Aging Vessel) and RCAT (Rotating Cylinder Aging Test) using different aging times and temperatures were employed to age two straight-run bitumens and a styrene-butadiene-butadiene (SBS) polymer modified binder. For field aging, a number of asphalt pavements of different years in service were investigated. The binders (virgin, laboratory aged, and extracted from asphalt pavements) were evaluated by penetration and softening point tests, rheological measurements with a Dynamic Shear Rheometer (DSR), as well as chemical analyses using Fourier Transform Infrared Spectroscopy (FTIR) and Gel Permeation Chromatography (GPC). It was confirmed that the rheological changes upon laboratory aging and the formation of chemical functionalities were strongly temperature dependent. Great differences were found between the unmodified and SBS polymer modified binders in the rheological response upon aging. For the modified bitumen, different chemical reactions of the two components (bitumen and polymer) may compensate each other in some ways, making the binder less age-hardening and more durable. Apparently, the standardized PAV and RCAT simulate about 10 years of field aging for the unmodified bitumens when used in a dense asphalt surface layer, but for open graded mixes a longer PAV or RCAT aging time is necessary. However, for polymer modified bitumen the relationship between laboratory and field ageing when studying both mechanical and chemical compositional changes is less trivial.Peer reviewe

Oxidation of bitumen : molecular characterization and influence on rheological properties

Rheological properties such as stiffness, elasticity, and viscosity are crucial parameters for the use of bitumen as a construction material. In bitumen oxidation studies, the increased viscosity has often been related to an increase in polar interactions from oxygen-containing compounds, like carbonyl groups. In this study, bitumen was subjected to two oxidation processes, aging and air blowing. Aging was performed using the rolling thin film oven test (RTFOT) and the pressure aging vessel (PAV), whereas air blowing was conducted in a laboratory unit. This investigation gives more insights in the changes observed during oxidation and highlights the differences between aging and air blowing. Moreover, the oxidation tests provide bitumen samples of increasing viscosity, which are used to evaluate relations between molecular and viscoelastic characteristics. As a comparison, the changes observed in harder bitumen samples prepared by a continued distillation are also included. As expected, the evolution of rheological properties with oxidation time is very similar in the PAV and in the air-blowing unit, although the timescales are very different. Fourier transform infrared spectroscopy (FT-IR) and acidity measurements reveal clear differences in the formation of oxygen-containing functional groups depending on the oxidation process. UV–visible spectroscopy shows that during aging as well as during air blowing, larger conjugated aromatic compounds are formed. These findings suggest that the formation of polyaromatic compounds may be the main contributor to the increase in elasticity and viscosity during oxidation.</p