Terhi Pellinen

USE OF STIFFNESS OF HOT-MIX ASPHALT AS A SIMPLE PERFORMANCE TEST

The objective was to determine whether the stiffness of a mix could be used as a simple performance test (SPT) parameter to complement the Superpave® volumetric mix design. This was investigated by a statistical analysis of the strength of the correlation between different mixture stiffness parameters and field performance (rutting, thermal, and fatigue cracking). A total of 30 mixtures were tested with laboratory-fabricated specimens. The studied stiffness parameters were compressive dynamic (complex) modulus |E*|, simple shear tester (SST) shear (complex) modulus |G*|, and dynamic elastic modulus Ed, obtained from ultrasonic wave propagation. Also, computed stiffness factors |E*|/sin ϕ and |G*|/sin ϕ for rutting and |E*|sin ϕ for cracking were studied as analogous to the Superpave binder specification. Research indicated that the correlation to rutting varied based on test temperature and frequency; it peaked at 54.4°C and 5 Hz. At peak conditions, |E*|/sin ϕ had better statistical correlation to rutting than |E*|, but correlations reversed at lower frequencies. Although |E*| and |G*| had similar correlation to rutting, analysis of test data indicated that the SST shear testing gave lower stiffness values and higher phase-angle values than the compressive dynamic modulus testing, even when Poisson’s ratio effects were considered. This was especially true at high temperatures. Because of these and other reasons, the dynamic modulus |E*| was recommended as the SPT parameter for rutting as well as for fatigue cracking. None of the studied parameters turned out to be adequate performance indicators for thermal cracking.

Asphalt Mix Master Curve Construction Using Sigmoidal Fitting Function with Non-Linear Least Squares Optimization

This paper presents a new simplified method of constructing a master curve of asphalt mix using test data covering a large range of temperatures from –18°C to 55°C. It utilizes sigmoidal fitting function and compressive cyclic (complex) modulus test data obtained at matrix combination of different frequencies and test temperatures. In the master curve construction, the time temperature superposition was modeled two different ways. First, using known time-temperature superposition equations, and second, shilling test data experimentally, i.e., not assuming any functional form for the time-temperature relationship. The master curve construction was done using an Excel spreadsheet with the solver function, which is a tool for performing optimization with non-linear least squares regression technique. The analysis of over sixty mixtures indicated that the experimental approach agreed the best with the Arrhenius shifting equation, correlation coefficient R 2 being 0.922. Also, the experimental shifting was most flexible, producing the best fit among the studied shifting equations due to the fact that it has the most degree of freedom.

Macro- and micro-texture evolution of road pavements and correlation with friction

This article features a field experiment conducted on existing road pavements to characterise macro- and micro-texture variations at actual road conditions and to substantiate links to friction values. Three-dimensional inspections of the wearing course surface of three asphalt mixes were performed during a short period of 9 months. Several statistical texture indicators, spectral analysis and photo-simulated images of surface height maps were employed to analyse macro/micro-texture evolution and to study the physical phenomena behind it. Fractal and non-fractal parameters, with a focus on Hurst exponent (H), were used in associating texture with friction. The results of texture evolution clearly state that changes in macro/micro-scales occur within full surface profile and not solely from the polishing phenomena of a small percentage of top surface topographies. It was demonstrated that H, as an indicator of full surface profile specification, could not be employed for road texture–friction studies at actual road conditions.

The multiple stress creep-recovery test: a detailed analysis of repeatability and reproducibility

The multiple stress creep-recovery (MSCR) test was recently introduced to evaluate bituminous binders at high service temperatures, in particular to evaluate the stress or loading resistance. This test allows classifying binders at the high-performance graded temperature, according to the traffic loading, starting from standard, to heavy, very heavy and extreme traffic loading. It is the intention that this test includes nonlinear binder properties. In this study, five laboratories have participated in a round robin test to evaluate the repeatability and reproducibility of the parameters derived from the MSCR test. Nine different binders were evaluated, including unmodified, slightly and highly modified binders. The MSCR tests were conducted at 50°C, and each laboratory performed testing five times under repeatability conditions. The test results were analysed according to ISO 5725 and observations and reasons for deviating test results are discussed in detail.

Fatigue-Transfer Functions: How Do They Compare?

The primary objective of this work was to investigate which of several fatigue-transfer functions predict the failure of mixtures and expected fatigue life most accurately. A second objective was to study existing fatigue models and how they relate to mixture volumetrics. This work was done by employing layered elastic analysis to obtain stresses and strains in the pavement under monthly temperature variations. The calculated tensile strains were then used in the fatigue-transfer functions to predict the fatigue life of the pavement. The mix and distress data were obtained from the WesTrack project. In general, all fatigue-model predictions were poor to fair; even the locally calibrated models (WesTrack) yielded at best 57% accuracy in predicting failing or surviving mixtures. The Strategic Highway Research Program (SHRP) model predicted failures with 72% accuracy; the Asphalt Institute model, 39%; Medani and Molenaars model, 31%; and the Shell models, 28% accuracy. The SHRP and Asphalt Institute models used suggested field shift factors (FSFs). The fatigue models studied were originally developed for predicting crack initiation in the laboratory. In using these models to predict fatigue life in actual pavements, crack propagation is usually addressed through an empirically determined FSF. An attempt was made to calibrate and recalibrate the fatigue-transfer models using the WesTrack data. This analysis indicates that there is a trade-off in predicting failing or surviving mixtures correctly and the accuracy of the predicting fatigue life compared with the applied traffic loading. Because the nonfailed mixtures were trafficked with only 5 million traffic repetitions, the error associated with the fatigue-life predictions was unknown. Therefore, the overall improvement of the model accuracy through this calibration process cannot be assessed. For several reasons, this study recommends using the Asphalt Institute fatigue-transfer equation in layered elastic analysis to evaluate the fatigue-cracking potential of asphalt mixtures.

Physicochemical properties of bitumens modified with bioflux

Five laboratory-produced cut-back bitumens with same target viscosity of 600 mm2/s at 60°C were investigated to determine the effect of chemical composition on the rheological properties. Studied cut-back bitumens comprised four bioflux-modified bitumens and one traditional slow-curing cut-back bitumen as a reference. The generic fractions (saturates, aromatics, resins and asphaltenes) of base bitumens (viscosities of about 1500, 3000, 6000 and 37,000 mm2/s at 60°C) were quantified by thin-layer chromatographic method with flame-ionisation detection (IATROSCAN MK-6s) and the rheological properties of the base bitumens and cut-back bitumens were studied with a Physica 301 rheometer. The soft base bitumens (viscosity≤6000 mm2/s at 60°C) and their biofluxed solutions proved to be rheologically complex, which was witnessed by wax crystallisation and melting phenomena observed at temperatures between 10 and 30°C. The harder base bitumens with higher asphaltene content did not exhibit noticeable crystallisation. The low polarity and low molecular weight of the bioflux solvent reduced the stiffnesses of cut-back bitumens remarkably under 30°C. Thus, the composition of cut-back bitumens had a significant effect on the rheology of blends, although the target viscosities at 60°C were the same.

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.

Investigation of pavement light reflection characteristics

ABSTRACT Current road lighting standards and recommendations are based on luminance levels and luminance distributions on the road surface. The luminance of the road surface depends on the amount of light falling on it and the reflection properties of the road surface. Using light aggregate for road surface pavements, significant energy savings in road lighting could be achieved due to significantly higher reflectance properties of the surface. In this study several experimental pavement samples with light surface characteristics were manufactured and their reflection properties were measured. The results indicate that lighter pavement materials result in higher average road surface luminance values and lower average lighting energy usage costs per kilometer.

The use of accelerometers in the pavement performance monitoring and analysis

This study investigated the use of sensor technology to enhance the management of highway infrastructure. With the help of monitoring data, it is possible to assess the current analytical pavement analysis method, which is based on multi-layered elastic analysis, and, thus enhance the pavement design practices in use. Pavement response was measured using different sensors, installed at various depths. Most promising sensors for the continuous monitoring purposes were the accelerometers. The drawback of these sensors is that the measured quantity is acceleration, which must be converted to the deflection via mathematical integration. In this paper some issues related to the manipulation of accelerometer data is presented and discussed, in addition of the discussion of the calculated and measured pavement response.

A New Microwave Asphalt Radar Rover for Thin Surface Civil Engineering Applications

Abstract This paper presents a beyond state-of-the-art, sweeping microwave asphalt radar mounted on a small radio controlled four-wheel-drive rover. The quasi-monostatic, remote-controllable radar operates at Ku-band and has an output power of +10 dBm. Detection follows the zero intermediate frequency principle. The sweep width allows for a depth resolution better than 10 mm. With its four microprocessors and laptop computer processing, the radar system can provide pavement permittivity data with an uncertainty close to 0.1. This is a considerable advancement when applying electromagnetic measurement techniques for applications where near surface or thin surface layer measurements are needed.