Lily D. Poulikakos

Construction and Maintenance Practices for Permeable Friction Courses

This report recommends design, construction, and maintenance guidelines for permeable friction courses (PFCs). It presents recommended practices for (1) design and construction of PFCs and (2) PFC maintenance and rehabilitation. The report will be of immediate interest to public and private sector engineers with responsibility for the specification, construction, and maintenance of PFCs.

Fatigue Evaluation of Porous Asphalt Composites with Carbon Fiber Reinforcement Polymer Grids

Porous asphalt (PA) has been widely used in many countries because of its positive benefits, such as efficient water drainage, improved safety in wet weather conditions, and noise reduction. However, the attractive features of PA do not last long because of clogging, stripping, and accelerated aging. Application of fiber reinforcement materials can be a possible solution to the structural weakness in PA pavements. Fatigue of fiber-reinforced PA composite systems was investigated with a model mobile load simulator (MMLS). Carbon fiber reinforcement polymer (FRP) grids were used to strengthen the fatigue resistance of PA. FRP grids were placed between two asphalt layers as a reinforcement interlayer. The dynamic fatigue traffic loadings were applied on the top surface of reinforced specimens to investigate the performance improvement by reinforcement materials. These fatigue tests were conducted under four different conditions: absence and presence of reinforcement at dry conditions and wet conditions. The stiffness difference between unaged and aged specimens was 25% at minimum and 55% at maximum. The surface deflection of PA was successfully reduced by 23% at dry and by 48% at wet conditions by using interlaid carbon FRP grids. In addition, the reinforcement layer could increase the fatigue life by 23% at dry and by 27% at wet conditions based on MMLS test results.

Time resolved analysis of water drainage in porous asphalt concrete using neutron radiography

Porous asphalt as a road surface layer controls aquaplaning as rain water can drain through its highly porous structure. The process of water drainage through this permeable layer is studied using neutron radiography. Time-resolved water configuration and distribution within the porous structure are reported. It is shown that radiography depicts the process of liquid water transport within the complex geometry of porous asphalt, capturing water films, filled dead end pores and water islands.

Challenges While Performing AFM on Bitumen

Using modern microscopic techniques such as atomic force microscopy (AFM) has added significant knowledge on the microstructure of bitumen. The advantages of AFM are that it requires relatively simple sample preparation and operates under ambient conditions. As the use of AFM is becoming more widespread and useful the RILEM technical committee (TC) on nano bituminous materials NBM 231 has conducted a round robin study on this method, the results with respect to reproducibility, repeatability or accuracy limits are presented elsewhere. However, the execution of good quality AFM experiments especially on bitumen is still a challenging task. Sample extraction and preparation are very crucial and attention should be paid to obtain homogenous samples with a sufficient thickness and no surface contamination. The preparation should include a high temperature treatment to provide a smooth homogenous surface. Annealing/resting of the sample has to be sufficiently long, at least 24 h under ambient temperatures to ensure the formation of a (meta)stable micro-structure. Imaging should be done using non-contact (Tapping) mode with stiff cantilevers (resonance frequency ~300 kHz) with a minimum amount of damping as possible.

EVALUATION OF IMPROVED POROUS ASPHALT BY VARIOUS TEST METHODS

In this study, test procedures are compared and discussed with respect to their suitability for porous asphalt optimization and for development of improved mix design. Several industry standard tests, namely wheel tracking, indirect tensile, interlayer shear strength, Cantabro and water permeability weer carried out to compare performance related properties of both theoretically and empirically designed porous asphalt specimens. The specimens were produced using an improved theoretical mix design approach for porous asphalt. It is based on a new packing theory for aggregate grading optimization, reducing the post compaction effects on the pavement under traffic. In this international co-operative research project between JHRI and EMPA, porous asphalt specimens produced by the new mix design method were compared to both Swiss and Japanese Standard mixes from conventional empirical mix designs. Different tests concerning both durability and functional properties of porous asphalt were carried out. The results of this ongoing research indicate that the new method leads, in many cases, to porous asphalt mixes with superior quality as compared to traditional standard mixes. In addition it is shown that the different test methods applied in this study generally lead to comparable results. For the covering abstract see ITRD E117423.

Effect of short-term ageing temperature on bitumen properties

Properties of asphalt mixtures after ageing are fundamental parameters in determining long-term performance (e.g. durability) of these materials. With increasing popularity of reduced temperature mixtures, such as warm-mix asphalt, WMA, the question remains how a reduction in short-term ageing affects the properties after long-term ageing of bituminous materials. This paper aims to improve our understanding of the effect of asphalt manufacturing temperature on ageing and the resulting mechanical properties of bituminous binder by studying the effect of short- and long-term ageing of different bitumen samples as a function of short-term ageing temperatures. For this purpose, round robin experiments were conducted within the RILEM technical committee (TC) 252 chemo-mechanical characterisation of bituminous materials by 10 laboratories from 5 countries using four binders of the same grade (70/100 pen) from different crude sources. The short-term ageing was carried out using the standard procedure for rolling thin film oven test (RTFOT), but varying the temperatures. Long-term ageing was carried out using the standard procedure for pressure aging vessel (PAV) in addition to RTFOT. For the mechanical characterisation, rheological data were determined by using the dynamic shear rheometer (DSR) and conventional tests, with needle penetration and softening point using the ring and ball method. The results show that although different short-term ageing temperatures showed a significant difference in the mechanical properties of the binders, these differences vanished after long-term ageing with PAV.

Investigation of Water Uptake in Porous Asphalt Concrete Using Neutron Radiography

Porous asphalt (PA), a highly porous hydrophobic composite material, is subjected to water uptake and the process is documented with neutron radiography (NR). While the un-aged laboratory-prepared PA specimens do not show any water uptake, we observe uptake in aged PA even though the bitumen binder is a hydrophobic material. The moisture content distribution plots derived from the NR images clearly identify regions in the aged specimens where water uptake is active. Two-dimensional degree of saturation (DoS) distribution images, which are obtained by combining micro-computer tomography and NR images, identify those pores where saturated flow is certainly active. However, to clearly distinguish between saturated and unsaturated flows in the remaining wet pores, the DoS distribution images are read together with the three-dimensional PA microstructure obtained by micro-CT. It is observed that uptake begins mainly as unsaturated film/corner flow at large well-defined pores. As this uptaken water travels further into the material, the flow transforms into a combination of saturated flow and unsaturated film/corner flow. Saturated flow is seen to be mostly active in the small pores within the mastic. From the observed succession of unsaturated and saturated flows in an aged PA specimen, it can be concluded that years of environmental and mechanical loading has resulted in the stripping of binder from the aggregate surfaces and has consequently exposed patches of hydrophilic aggregate to water, which enables the capillary uptake of water. We also simulate an absolute permeability experiment and observe that relatively less tortuous and more connected paths play an important role in determining the preferential path of the uptaken water.

Differential Scanning Calorimetry Applied to Bitumen: Results of the RILEM NBM TG1 Round Robin Test

The application of Differential Scanning Calorimetry (DSC) has been proven useful in characterizing bituminous binders, distillates and crude oils. In this paper, results of the round robin test, organized by the Rilem TC 231 Nanotechnology-based Bituminous Materials (NBM) TG1 group are reported. The purpose is to investigate the repeatability and reproducibility of standard DSC measurements when applied to bituminous binders. In the full test program of the Rilem NBM group, DSC measurements are further compared to observations made in atomic force microscopy (AFM), AFM measurements are reported in a separate paper. Seven laboratories have participated in this round robin test. Four bituminous binders were investigated, containing various amounts of natural or added wax. The test program consisted of a well-defined isothermal annealing procedure, followed by a first heating and cooling scan, and afterwards followed by a second heating scan. At this stage, the data, as they were reported by the different participants, were compared. For the glass transition (Tg), mid temperatures, can be defined with a reasonable reproducibility, which improves if natural wax is not present. Regarding melting and crystallization, the shape of the melting curve is highly dependent on the thermal history of the samples. Peak temperatures of melting and crystallization phenomena were reported with a good reproducibility, while the reproducibility of melting enthalpies (or surface area’s under the melting and crystallization signals) was not satisfactory. Different reasons for this and recommendations for improving the results are discussed in the paper.

Coaxial Shear Test and Wheel Tracking Tests for Determining Porous Asphalt Mechanical Properties

ABSTRACT Performance oriented test procedures are compared and discussed with respect to their suitability for porous asphalt optimization and for development of improved mix design. Coaxial shear tests and wheel tracking tests were carried out in order to compare the properties of both theoretically and empirically designed porous asphalt specimens. The specimens were produced using an improved theoretical mix design approach for porous asphalt. This method is based on a packing theory for aggregate grading optimization, reducing the post compaction effects on the pavement under traffic. The problems with porous asphalt arise from premature aging and therefore laboratory aging of the mix was used for the simulation of in-situ condition. As presented in this paper the test results vary significantly with aging as seen in the rutting behavior and shear modulus. The packing theory leads, in many cases, to porous asphalt mixes with superior quality as compared to traditional standard mixes provided that the influence of the binder is considered accordingly.

Multiscale imaging and characterization of the effect of mixing temperature on asphalt concrete containing recycled components

When producing asphalt concrete mixture with high amounts of reclaimed asphalt pavement (RAP), the mixing temperature plays a significant role in the resulting spatial distribution of the components as well as on the quality of the resulting mixture, in terms of workability during mixing and compaction as well as in service mechanical properties. Asphalt concrete containing 50% RAP was investigated at mixing temperatures of 140, 160 and 180°C, using a multiscale approach. At the microscale, using energy dispersive X‐ray spectroscopy the RAP binder film thickness was visualized and measured. It was shown that at higher mixing temperatures this film thickness was reduced. The reduction in film thickness can be attributed to the loss of volatiles as well as the mixing of RAP binder with virgin binder at higher temperatures. X‐ray computer tomography was used to characterize statistically the distribution of the RAP and virgin aggregates geometric features: volume, width and shape anisotropy. In addition using X‐ray computer tomography, the packing and spatial distribution of the RAP and virgin aggregates was characterized using the nearest neighbour metric. It was shown that mixing temperature may have a positive effect on the spatial distribution of the aggregates but did not affect the packing. The study shows a tendency for the RAP aggregates to be more likely distributed in clusters at lower mixing temperatures. At higher temperatures, they were more homogeneously distributed. This indicates a higher degree of blending both at microscale (binder film) and macroscale (spatial distribution) between RAP and virgin aggregates as a result of increasing mixing temperatures and the ability to quantify this using various imaging techniques.