Alan Carter

Impact of different ageing levels on binder rheology

This paper evaluates the variability of binder rheology for different ageing levels and the influence of ageing at different testing temperatures. Three different ageing levels were applied on a single type of bitumen with a penetration grade of 70/100.The artificial ageing of the binder was performed using the rolling thin-film oven test and the pressure ageing vessel. The rheological behaviour was investigated at low temperatures with the bending beam rheometer (BBR) and at medium and high temperatures with the dynamic shear rheometer (DSR). Several experiments were conducted to determine the range of stiffness and complex modulus results, the type of distribution comparing real and theoretical models, and the effects of ageing on the variability of the rheological behaviour. It was shown that not only the mean results from BBR and DSR tests change with ageing, but also the variability of the results changes with ageing. This would have an impact on mechanistic-empirical pavement design because it would influence the calculated stresses and strains as well as the calculated reliability.

New conceptual model for filler stiffening effect on asphalt mastic of microsurfacing

AbstractThis research focused on the stiffening effect of the filler on the asphalt mastic of microsurfacing. One challenge that researchers are faced with in the field of bituminous materials is the interaction between the filler and binder. In this study, a new conceptual model for filler stiffening of the mastic was developed that allows the asphalt mix designer to establish the minimum and maximum filler concentration to incorporate in the asphalt mixture. The proposed model has only one parameter that can be determined using the filler and asphalt emulsion selective properties, such as D10 and pH of the filler and the asphaltene content of the emulsion. A new mechanism for the stiffening effect of filler on mastic was developed based on the physicochemical interaction between filler and bitumen. Based on the model, the increase in mastic stiffness (G*) as a function of the increase in filler concentration can be divided into three regions: diluted region, optimum concentration region, and concentrate...

Comparison of Some Pavement Design Methods from a Fatigue Point of View: Effect of Fatigue Properties of Asphalt Materials

ABSTRACT The paper presents a comparison between the principle international flexible pavement design methods based on fatigue material properties. Four methods were studied for the design of two pavement sections. Laboratory tests showed an enormous difference between the fatigue and the complex modulus results for the two asphalt mixes used in the base course (Stone Matrix Asphalt: SMA, and EB14: reference mix). The required thickness of the base course changes depending on the pavement design method used. Despite the laboratory results, certain methods showed no difference in thickness of the base course for the two asphalt base mixes while others showed an important difference and proves the benefit of the materials fatigue performance. Discussions underlined that the complex modulus of an asphalt material should not be used as a performance indicator to predict the fatigue life of that material.

Quantification of emission potential from asphalt binders using mass loss and opacity measurements

A total of 23 asphalt binders were obtained from around the country. Contractors that reported emission complaints from neighbors were asked to supply samples from problem binders as well as a sample of asphalt binders, when used, generated either fewer or no complaints. The percent mass loss and opacity measurements were used to determine if a simple means of identifying asphalt binders with emission potential could be identified for use as a screening or process control test for the contractors. Results indicate that a maximum mass loss of 0.5% as measured with the rolling thin film oven test or 0.7% as measured with a prototype emissions oven will minimize emission potential. The prototype oven was fitted with an opacity meter; a percent mass loss of 0.7% or lower corresponds with visible emissions of 1.2% or less. Most of the asphalt binders rated with high emissions problems by the contractor are identified by using these limits.

In-situ permeability of the outermost layer of asphalt and cement concrete road materials water permeability evaluated with gas flow

ABSTRACT A permeability cell was developed by applying Carman and Klinkenberg principles to measure the permeability of a porous medium to gas. The method applied concentrates gas flow on a better well-defined area on the surface of the material tested. Both the cell and the calculations used are explained in detail in this paper. The permeability was measured on three hot-mix asphalt mixes (HMA), which were compacted into 125x400x600 mm3 slabs in order to allow the simulation of in-situ conditions. The permeability cell test results show a higher variability in the permeability values of HMA as compared to those obtained from cement concrete measurements. The permeability to gas, when transformed to water permeability, found in this research is comparable to the results found in the literature.

Laboratory evaluation of complex modulus and fatigue resistance of asphalt mixtures with RAP

The evaluation of the performance of recycled asphalt mixtures is a priority for the asphalt materials community. The results of the investigation dealing with the linear viscoelastic properties and fatigue resistance on RAP mixtures are presented. Complex modulus and fatigue properties of recycled asphalt mixtures are investigated on tension–compression tests (T-C). Four asphalt mixtures including four RAP contents (0, 15, 25, 40 %), one virgin aggregate, and one asphalt binder (PG 64-28) were investigated in this study. In general, the results of this study indicate that: 1) the asphalt mixtures containing RAP have higher or similar stiffness with the control mixture containing no RAP, 2) the asphalt mixtures containing 25 % RAP have the highest stiffness at lower temperatures or high frequencies, and 3) no general trend was found between the amount of RAP and the number of cycles to reach fatigue failure. In addition, high fatigue resistance was observed in mixtures containing 40 % RAP.

EVALUATION OF TEST METHODS AND SELECTION OF AGGREGATE GRADING FOR TYPE III APPLICATION OF MICRO-SURFACING

ABSTRACT Micro-Surfacing is a polymer modified, binder emulsion based, dense graded, cold mixed, and quick setting, asphalt resurfacing material. Type III application of microsurfacing is used as the rut fill materials for highly trafficked roads. As of now, International Slurry Surfacing Association (ISSA) mix design guideline is the widely used standard to design micro-surfacing mixtures. The research described in this paper intended to suggest modifications to the actual ISSA mix design procedure to accurately select aggregate grading for type III micro-surfacing mixtures. To do this, a sensitivity analysis was performed in order to study the effect of aggregate gradation, and binder emulsion residue on five micro-surfacing mixture design tests, including Loaded wheel test (ISSA TB 109), Wet track abrasion test (ISSA TB 100), modified cohesion test (ISSA TB 139), vertical displacement test (ISS TB 109, Method-A), and Mixing time test (ISSA TB 113). The second part of study consisted mainly of establishing a limit for the aggregate gradation used in type III application of micro-surfacing, which gives higher resistance to rutting as it is the main property of type III micro-surfacing. In order to do this, the resistant of different micro-surfacing mixtures against rutting was evaluated, and modified specifications were suggested to select aggregate grading for type III microsurfacing.

Initial Ride Quality of Hot-Mix Asphalt Pavements

Ride quality assessed with an inertial profiler on flexible pavement was used to provide initial information on the following key issues: repeatability associated with international roughness index (IRI) values for a wide range of hot-mix asphalt (HMA) material variables, timing of acceptance testing for initial ride quality, IRI changes with type of roadway, influence of stops and starts in the paving operation on ride quality, identification of “bump,” and effect of grinding on IRI. IRI was calculated for 25-ft intervals instead of the standard 0.1 mi (528 ft) for all testing to highlight local anomalies such as bumps due to paving stoppages. Results indicate that the standard deviation of three replicate passes with an inertial profiler is 5 in./mi (includes 46 HMA mixes on the Auburn University National Center for Asphalt Technology test track). IRI measurements with time suggest that initial acceptance testing can be conducted within 7 days, which allows more flexibility in scheduling by the agency. Limited traffic also slightly reduces the IRI values, which is to the contractors advantage. IRI values are suggested for two-lane county roads and medium- to high-traffic facilities. Separate IRI ranges are indicated for each of these categories on the basis of the type of HMA construction: new, repair and overlay, and mill and overlay. These ranges are set for best and good practices (continuous paving, no stoppages; consistent supply of trucks, very short stops). IRI values greater than 125 in./mi in any given 25-ft interval indicate a bump; bumps can be ground so that these areas have IRI values of less than 100 in./mi.

Effect of Artificial Ageing on Two Different Bitumen of Different Origin but Same Performance Grade

Performance grade system for bitumen characterization is used to ensure that the selected bitumen has the required properties for the environmental conditions found in-situ. However, it has been shown that within a given PG grade, the properties can differ thru time. In this study the rheological characteristics evaluated with a DSR and a BBR are compared with the chemical composition of two different bitumen produced from different crude oil but with the same PG grade. The results have shown that even if both bitumens performs similarly with the usual ageing, RTFO and PAV, their characteristics get more different with intensive artificial laboratory ageing. The chemical characteristics of the bitumens were measured with infrared spectroscopy. It was shown that the change of their chemical composition with ageing is different. The links between their rheological properties and their chemical characteristics measured with FTIR that have been found is different for both bitumens.

Performance evaluation and behavior of microsurfacing with recycled materials

Road networks play a vital role in the development of country’s economy. It is necessary to develop new technologies to improve the performance and safety of the roads. Added to that, it is necessary to enhance the evolution of the roadways over time in terms of maintaining its surface while respecting the challenges of sustainable development. Microsurfacing is one of the techniques used to satisfy these challenges. However, there is very little information on the evolution and behavior of the product on short and long term, and there is no information on the use of recycled materials in the latter. In this context, this study aims to study and improve the performance of mixtures of microsurfacing with recycled materials. After the development of an adapted accelerated aging method on Microsurfacing, materials were prepared in lab with reclaimed asphalt pavement (RAP) and with recycled asphalt shingles. It was shown that it’s possible to prepare microsurfacing with 100% RAP while respecting all International Slurry Surfacing Association (ISSA) standards. The results have shown that the filler’s characteristics have a big impact on the rutting resistance of those mixes. Procedures were developed during this project to measure the water sensitivity of the mixtures and their behavior over time.